i

MC LC

Danh mc cc k hiu, cc ch vit tt ................................................................. iii

Danh mc cc bng ................................................................................................. iv

Danh mc cc hnh v, th ................................................................................... v

CHNG 1: UNG TH V CC PHNG PHP IU TR ............................. 3

1.1. Tng quan v ung th ....................................................................................... 3

1.2. Cc phng php iu tr ung th ..................................................................... 3

1.3. C s x tr ung th ........................................................................................... 4

1.3.1. C s sinh hc ............................................................................................ 4

1.3.2. C s vt l ................................................................................................ 6

1.3.2.1. Tng tc ca bc x ion ho ln t chc sinh hc ............................ 6

1.3.2.2. C ch tc dng sinh hc ca bc x ion ho ...................................... 7

1.4. Cc loi hnh iu tr bng bc x .................................................................... 9

1.4.1. iu tr bng ngun xa ............................................................................... 9

1.4.2. iu tr p st ........................................................................................... 10

CHNG 2: MY GIA TC TUYN TNH V K THUT X TR 3D-CRT

TRONG IU TR UNG TH .......................................................... 12

2.1. Nhng hn ch ca my x tr cobalt trong iu tr ........................................ 12

2.2. Tng quan v my gia tc tuyn tnh .............................................................. 14

2.2.1. Cu to my gia tc tuyn tnh ................................................................. 15

2.2.2. Nguyn l hot ng ................................................................................ 16

2.3. K thut x tr 3D-CRT................................................................................... 17

2.3.1. H thng lp k hoch iu tr TPS ......................................................... 18

2.3.2. Quy trnh thc hnh lm sng k thut x tr 3D-CRT ............................ 18

2.3.2.1. nh gi bnh nhn v quyt nh x tr ........................................... 19

2.3.2.2. C nh t th bnh nhn ................................................................... 19

2.3.2.3. M phng ........................................................................................... 20

2.3.2.4. Ghi nhn v x l hnh nh bnh nhn .............................................. 21

2.3.2.5. Khoanh vng iu tr v vng bo v ................................................ 22

ii

2.3.2.6. Thit lp trng chiu v s dng cc thit b h tr ........................ 25

2.3.2.7. Tnh ton liu lng v phn b liu ................................................. 25

2.3.2.8. nh gi k hoch .............................................................................. 26

CHNG 3: K THUT X TR IU BIN CNG JO-IMRT .............. 29

3.1. Nguyn l ca k thut x tr iu bin cng IMRT ............................... 30

3.2. Bi ton lp k hoch ngc trong k thut x tr IMRT ............................... 33

3.2.1. Bi ton lp k hoch xui v lp k hoch ngc .................................. 33

3.2.2. Quy trnh v cc m hnh ti u ha trong k thut IMRT ..................... 37

3.3. M hnh ti u ha theo liu ........................................................................... 41

3.3.1. Hm mc tiu ........................................................................................... 42

3.3.1.1. Cng thc ton hc ............................................................................ 42

3.3.1.2. C s xy dng hm mc tiu............................................................ 44

3.3.2. Mc tiu v liu lng ............................................................................. 45

3.3.3. Mc tiu liu lng-th tch ..................................................................... 47

3.3.4. Mc tiu v EUD ..................................................................................... 48

3.3.5. H s quan trng ...................................................................................... 50

3.4. Thut ton ti u ha trc tip m (DAO) ................................................ 50

CHNG 4: NG DNG K THUT X TR JO-IMRT V KT QU O

THC NGHIM TI BNH VIN A KHOA NG NAI .......... 55

4.1. Trang thit b cn thit trin khai k thut x tr JO-IMRT ....................... 55

4.2. Quy trnh k thut x tr iu bin cng (JO-IMRT) ............................... 55

4.2.1. Lp k hoch x tr JO-IMRT vi phn mm Prowess panther ............... 56

4.2.2. Quy trnh o liu kim tra cht lng (QA) cho JO-IMRT ..................... 60

4.3. Kt qu lp k hoch x tr JO-IMRT v kt qu QA .................................... 64

4.4. Kt lun ........................................................................................................... 70

KT LUN ............................................................................................................... 71

KIN NGH .............................................................................................................. 72

TI LIU THAM KHO ......................................................................................... 73

PH LC .................................................................................................................. 75

iii

DANH MC CC K HIU, CC CH VIT TT

3D-CRT: Three dimensional conformal radiotherapy

AFC: Automatic frequency control

CT: Computed comography

CT SIM: Computed tomography simulation

CTV: Clinical target volume

DAO: Direct aperture optimazation

DICOM: Digital imaging and communications in medicine

DNA: Deoxyribo nucleic acid

DVH: Dose volume histogram

EUD: Equivalent uniform dose

GTV: Gross tumor volume

IAEA: International atomic energy agency

ICRU: International commission on radiation units

IGRT: Image guided radiation therapy

IMRT: Intensity modulated radiation therapy

MLC: Multileaf collimator

MRI: Magnetic resonance imaging

NTCP: Normal tissue complication probability

OAR: Organs at risk

PET: Position emission tomography

PTV: Planning target volume

RNA: Ribonucleic acid

SAD: Source axis distance

SPECT: Single photon emission computed tomography

SSD: Source surface distance

TCP: Tumor control probability

JO-IMRT: Jaw only Intensity modulated radiation therapy

iv

DANH MC CC BNG

Bng 4.1: Kt qu so snh liu hp th gia 2 k hoch JO-IMRT v 3D-CRT ............ 66

Bng 4.2: Sai s gia liu tnh v liu o ca bnh nhn Nguyn Th M, ung th

vm ti bnh vin a khoa ng Nai ...................................................... 67

Bng 4.3: Sai s gia liu tnh v liu o ca bnh nhn ung th vm ti bnh vin

K-H Ni ................................................................................................. 67

Bng 4.4: Sai s gia liu tnh v liu o ti bnh vin Bch Mai-H Ni ............. 68

Bng 4.5: Sai s gia liu tnh v liu o ca bnh nhn Trn Vn H, ung th vm

ti bnh vin a khoa ng Nai .............................................................. 70

v

DANH MC CC HNH V, TH

Hnh 1.1: Chu k t bo ............................................................................................. 5

Hnh 2.1: My gia tc tuyn tnh ti bnh vin a khoa ng Nai ......................... 14

Hnh 2.2: Cu to my gia tc tuyn tnh ................................................................. 15

Hnh 2.3: K thut x tr thng thng 2D (a) v k thut x tr 3D-CRT (b) ........ 17

Hnh 2.4: Quy trnh lp k hoch x tr .................................................................... 19

Hnh 2.5: H thng my CT m phng ti bnh vin a khoa ng Nai ................ 20

Hnh 2.6: Cc vng th tch khc nhau cn xc nh theo ICRU ............................ 23

Hnh 3.1: So snh phn b liu lng gia k hoch 3D (tri) v IMRT (phi) ..... 30

Hnh 3.2: Phn b liu ca k thut x tr 3D-CRT v IMRT ................................. 31

Hnh 3.3: Hnh dng chm tia c to ra bi MLC (tri) v Jaw (phi) ................ 32

Hnh 3.4: Bn liu lng phc hp ..................................................................... 32

Hnh 3.5: Bi ton k hoch xui ............................................................................. 33

Hnh 3.6: Bi ton lp k hoch ngc .................................................................... 34

Hnh 3.7: Ngun c chia thnh nhiu chm tia n v ........................................ 36

Hnh 3.8: Quy trnh ti u ha trong k thut IMRT ............................................... 38

Hnh 3.9: Chm tia v c th bnh nhn c chia thnh nhiu phn nh .............. 43

Hnh 3.10: t iu kin cho bi ton ngc ........................................................... 46

Hnh 3.11: th mc tiu liu-th tch ................................................................... 48

Hnh 3.12: Quy trnh thut ton DAO ...................................................................... 51

Hnh 3.13: Bc u tin trong qu trnh ti u ...................................................... 52

Hnh 3.14: Cc tiu a phng v cc tiu ton cc .............................................. 53

Hnh 3.15: Cc phn on trng chiu (segment) v bn cng ................. 54

Hnh 4.1: Quy trnh k thut x tr JO-IMRT .......................................................... 56

Hnh 4.2: Cc trng chiu: 720, 1000, 1550, 1800, 2100, 2650, 3000 ....................... 57

Hnh 4.3: Biu din cc hm mc tiu trong phn mm Prowess panther ............... 58

Hnh 4.4: ng DVH thay i khi iu chnh trng s ca PTV .......................... 59

Hnh 4.5: ng DVH ca k hoch cui cng ...................................................... 59

Hnh 4.7: Thit b o liu Dose 1 ............................................................................. 61

vi

Hnh 4.8: S h o kim tra cht lng............................................................... 62

Hnh 4.9: V tr cc im o liu trong k hoch QA JO-IMRT .............................. 62

Hnh 4.10: Thit lp plastic phantom o h s hiu chnh my ............................... 63

Hnh 4.11: Liu tnh ton v liu o c ti im kho st. .................................. 64

Hnh 4.12: Hnh nh lt ct CT c xc nh GTV, CTV ................................ 65

Hnh 4.13: So snh k hoch x tr JO-IMRT v 3D-CRT ...................................... 65

Hnh 4.14: So snh 2 DVH: JO-IMRT (nt t) v 3D-CRT (nt lin) .......................... 66

Hnh 4.15: ng isodose k hoch JO-IMRT bao st khi u hn 3D-CRT .......... 69

Hnh 4.16: So snh 2 DVH: JO-IMRT (nt lin) v 3D-CRT (nt t) ......................... 69

1

M U

Nh vo s pht trin ca khoa hc v cng ngh, thi gian qua c rt

nhiu k thut hin i gip iu tr ung th t hiu qu cao v cu sng c rt

nhiu bnh nhn. Hin nay, chng ta c nhiu phng php iu tr cho bnh

nhn ung th nh phu thut, ha cht, x tr,... Tuy nhin, x tr vn l mt trong

nhng phng php ph bin i vi hu ht cc loi ung th.

C th ni, x tr l mt trong nhng ngnh ng dng k thut ht nhn vo y

hc mnh m nht. Cc k thut x tr hin ti c nhng tin b vt bc v gip

cho s phn b liu ti u ti th tch bia (khi u), ng thi gim n mc ti thiu

s nguy hi cho cc t chc lnh lin quan. T k thut phn b hai chiu (2-D); ba

chiu theo hnh dng khi u (3D-CRT) n x tr iu bin cng (IMRT); x tr

di s hng dn ca hnh nh (IGRT); x tr ct lp (tomotherapy) v x tr bng

ht nng (heavy ion),... v ang c ng dng rng ri ti nhiu nc trn Th

Gii.

K thut x tr ba chiu theo hnh dng khi u (3D-CRT) l mt k thut c

s dng ph bin hin nay ti cc trung tm x tr trong c nc. Tuy nhin, k

thut ny c mt vi hn ch nht nh trong vic xc nh s phn b liu, nht l

vi nhng trng hp khi u c hnh dng phc tp v p st cc vng c quan lnh

cn bo v. Trong ti ny chng ti trnh by k thut x tr iu bin cng

(IMRT). K thut ny c tha nhn v ng dng rng ri trong lm sng vi

h thng my c ng chun trc a l (MLC). Nhng i vi mt s h thng my

gia tc khng c MLC vn c th thc hin k thut IMRT ch vi bn l ngm

(jaw only). K thut ny l k thut JO-IMRT c tch hp trong phn mm lp k

hoch x tr Prowess panther v c p dng ti Trung tm ung bu-bnh vin

Bch Mai t nm 2008 n nay. Mc ch ca lun vn l nghin cu nhm ng

dng, trin khai k thut x tr JO-IMRT ti bnh vin a khoa ng Nai.

2

Ni dung ca lun vn ny gm 4 chng

Chng 1: Ung th v cc phng php iu tr. Trong chng ny trnh by

v c s ca x tr cng nh c s dit t bo ung th bng bc x ion ha.

Chng 2: My gia tc tuyn tnh v k thut x tr 3D-CRT trong iu tr ung

th: Trnh by s lc v cu to, nguyn l ca my gia tc tuyn tnh s dng

trong x tr, v nhng hn ch ca k thut x tr 3D-CRT.

Chng 3: K thut x tr iu bin cng JO-IMRT: Trong chng ny

chng ti trnh by tng quan v k thut x tr iu bin cng (IMRT), cc m

hnh ti u ha trong k thut x tr IMRT, thut ton ti u ha.

Chng 4: ng dng k thut x tr JO-IMRT v kt qu o thc nghim ti

bnh vin a khoa ng Nai: Trnh by v vic lp k hoch, o kim tra trn thc

t nh gi chnh xc, tin cy ca k thut x tr iu bin cng JO-IMRT,

so snh kt qu o ti bnh vin a khoa ng Nai vi kt qu o ti bnh vin

Bch Mai v bnh vin K.

3

CHNG 1

UNG TH V CC PHNG PHP IU TR

1.1. Tng quan v ung th

Ung th l mt trong nhng nguyn nhn hng u gy t vong cho con ngi

trn ton cu. Hin nay, vic phng chng ung th i vo ba hng chnh: Phng

bnh, pht hin sm v ng dng khoa hc cng ngh hin i vo iu tr ung th.

Vic iu tr ung th cn c vo nhiu yu t nh c quan, v tr b ung th, th gii

phu bnh l, giai on bnh, cng nh tnh trng chung ca bnh nhn. Pht hin

sm cng nh chn on ng giai on bnh c ngha tin quyt trong vic quyt

nh phng php iu tr em li hiu qu cao cho ngi bnh.

Trn Th Gii, theo s liu ca T chc Ung th M cng b th nm 2007 c

khong 7,6 triu ngi cht do bnh ung th. Ngoi ra cn c 12 triu ngi mang

trong ngi cn bnh ung th trn ton Th Gii. Cn theo T chc kim sot ung

th Th Gii th trong nm 2005, t l ngi cht do bnh ung th l 13% trong

tng s 58 triu ngi cht trn Th Gii. Trong khong hn 70% s ngi cht

v bnh ung th xy ra cc nc c thu nhp thp v trung bnh. Theo c tnh th

s ngi cht v ung th s tip tc tng khong 9 triu ngi vo nm 2015 v 11,4

triu ngi trong nm 2030 [4].

Ti Vit Nam, theo nghin cu ca GS.Nguyn B c th ung th vn l

nguyn nhn gy t vong hng u, mi nm c khong 150.000 ngi mc bnh

ung th mi v khong 75.000 ngi t vong v bnh ny. Theo c tnh n nm

2010 s ngi mc bnh l 200.000 v t vong l 100.000 ngi [4].

1.2. Cc phng php iu tr ung th

Hin nay c 3 phng php iu tr ung th: Phu thut, x tr, ha tr. Ngoi

ra c th iu tr kt hp cc phng php t c hiu qu mong mun.

Phu thut: L phng php iu tr ung th c in nht. Khi phu thut, cc

t bo ung th c ly i cng nhiu cng tt. i khi nhng t bo ln cn xung

quanh khi u cng c ct b m bo chc chn t bo ung th c loi b

hon ton. Phng php ny hiu qu cho nhng khi u cn khu tr, cha di cn.

4

X tr: L phng php s dng bc x ion ha tiu dit khi u. V c bn,

x tr c chia ra lm 2 loi: X tr ngoi v x tr trong.

Ha tr: L phng php s dng ha cht iu tr ung th. N c dng

khi ung th lan ra ngoi v tr ban u, di cn nhiu ni, hoc khi u qu ln.

1.3. C s x tr ung th

1.3.1. C s sinh hc

T bo l n v cn bn ca c th. Nhiu t bo hp li thnh m: M si,

m m, m c, m lin kt, m xng, m sn, m thn kinh, nhiu m hp

thnh c quan: Tim, phi, mt, mi, tay, chn, rut, gan, cc c quan to thnh c

th sng. Do nhu cu hot ng ca cc c quan, nht l b p cho cc t bo

gi ci cht i, cc t bo phi sinh sn thm bng cch phn chia thnh 2 t bo

con. Qu trnh phn chia t bo gi l chu k t bo [1].

Chu k t bo l chui cc s kin lin quan n s sao chp DNA (deoxyribo

nucleic acid) v s phn b cn bng ca n i vi cc th h t bo con chu c

sinh ra do s phn chia. S phn chia t bo c din tin qua mt s giai on

(cn gi l pha). Tt c cc t bo, k c c tnh v khng c tnh trong qu trnh

u tri qua 5 pha ca chu k t bo l G0, G1, S, G2 v M (hnh 1.1).

Pha G0 (pha ngh sau phn bo). Pha G0 l giai on trong chu k khi m cc

t bo c kh nng thay mi bnh thng v khng tng sinh. Trong pha ny, cc t

bo hnh thnh mi chc nng, ngoi tr nhng chc nng lin quan ti tng sinh.

Pha ny gm c cc t bo ang phn chia ln cc t bo ang trong trng thi ngh.

Cc t bo bnh thng trong pha G0 c hot ho ch bng mt kch thc no

i vo chu k ti sinh sn ngha l s cht ca t bo cng loi.

Pha G1 l pha pht trin hoc giai on sau phn bo/tin tng hp. Pha G1

din ra trong khong t 12-14 gi, ko di t khi hon thin s phn chia t bo

trc cho ti thi im bt u sao chp nhim sc th. Cc t bo mang theo

cc chc nng sinh l c phn cng ca chng v tng hp cc protein v axit

ribonucleic (RNA). Pha G1 l s khi u, sn sng cho cc t bo chun b bc

vo giai on tng hp - pha S.

5

Pha S (tng hp). Trong pha tng hp, ko di khong t 7-20 gi, RNA c

tng hp v l c s cho s tng hp nn DNA. S tng hp DNA ch c thc

hin pha ny. Cc t bo d b tn thng nht trong pha S ny.

Hnh 1.1: Chu k t bo

Pha G2 (pha tin phn bo). Pha G2 ko di t 1- 4 gi, nm trong nhng giai

on hot ng tng i yu v cc t bo ch i i vo pha phn bo, pha ny

bao gm khong thi gian t khi kt thc s tng hp DNA cho n khi bt u s

phn chia t bo. i khi tng hp protein b sung c th xy ra trong pha G2 ny,

nhng ch yu pha ny tng hp nn cc cu trc protein ch khng phi thnh cc

enzym. Mt vi tng hp RNA b sung c th xy ra trong pha ny.

Pha M (s phn bo). Trong pha M, t 40 pht n 2 gi, din ra s phn bo

v phn chia cc t bo. S sao chp DNA phi c hon thin trc khi cc t

bo i vo chu k phn bo. Sau phn bo, cc t bo con hoc s quay v pha

G0 v ngng phn chia, hoc nu c kch thch s phn chia th chng s i vo pha

G1 v tip tc chu k sinh sn mi.

Cc t bo ung th c kh nng kt thc chu k t bo nhanh hn bng cch

gim khong thi gian trong pha G1. Chng rt t khi i vo hoc li pha G0 ca

chu k t bo hn cc t bo lnh; bi th m chng phn chia mt cch lin tc [5].

c im ca t bo ung th l nhy cm vi cc tia bc x hn cc t bo khe

mnh bnh thng. iu ny c ngha l cc t bo ung th rt yu trong c ch sa

cha nhng sai hng trn DNA so vi cc t bo bnh thng. Khi c chiu x

6

mt liu thch hp th s tiu dit c cc t bo ung th ny nhng vn m bo

kh nng phc hi ca cc t bo lnh. Vic ny c thc hin bng cch chia qu

trnh iu tr thnh nhiu phn on chiu.

1.3.2. C s vt l

1.3.2.1. Tng tc ca bc x ion ho ln t chc sinh hc

Bc x ion ho khi gp vt cht s gy nn hin tng kch thch hoc ion ha

cc nguyn t v phn t cu to. Nh vy nng lng ca bc x b hao ht, mt

tia b suy gim v ng i c th b thay i. Kt qu l cng b suy gim

v hng i ca chm tia b thay i. S thay i ph thuc nhiu vo bn cht

tia, nng lng tia v c im ca vt cht m n i qua. Ti khi vt cht m tia

i qua do b hp thu nng lng nn xy ra nhng bin i trong . S bin i

tu thuc rt nhiu vo hin tng kch thch v ion ho. D c ch c khc nhau

ty loi tia nhng kt qu ca s tng tc ph thuc trc ht vo s lng cp ion

c to ra trong vt cht trn n v ng i [7].

a. Liu hp th

Liu hp th l nng lng b hp th trn n v khi lng ca i tng b

chiu x. Theo nh ngha ta c:

ht

ED

m

(1.1)

Trong h SI n v ca liu hp th l J/kg hoc erg/g. n v ngoi h l rad:

1rad = 100erg/g. Ngy nay ngi ta thng dng n v Gray (Gy) 1Gy=100rad.

b. Liu chiu

Liu chiu ca tia X hoc tia gama l phn nng lng ca n mt i bin

i thnh ng nng ca ht mang in trong mt n v khi lng khng kh, kh

quyn iu kin tiu chun. K hiu chD .

ch

QD

m

(1.2)

Trong h SI n v liu chiu l Coulomb trn kilgam (C/kg). n v ngoi

h l Rnghen (R). Gia R v C/kg c mi lin h sau.

7

1 R = 2,57976. 10-4

C/kg hay 1 C/kg 3876 R

Rnghen l liu chiu ca chm photon khi chiu vo 1 cm3 khng kh (tc

1,293 mg) iu kin tiu chun s to ra mt s ion m in tch tng cng cc ion

cng du l mt n v in tch (tc l khong 2,09 x 109 cp ion). Rnghen(R) l

n v trc y hay dng trong y hc phng x v phng x sinh hc. Ngi ta

cn gi liu chiu l liu biu kin.

c. Liu tng ng

Trong thc nghim cho thy hiu ng sinh hc gy bi bc x khng ch ph

thuc vo liu hp th m cn ph thuc vo loi bc x. Mt i lng c dng

l liu tng ng. Liu tng ng l liu hp th trung bnh trong m hoc c

quan T do bc x r, nhn vi h s trng s phng x tng ng Wr ca bc x

Liu tng ng = Liu hp th x Wr (1.3)

n v ca liu tng ng l J/Kg, rem hoc sievert (Sv) vi 1Sv=100rem.

d. Liu hiu dng

Cc m khc nhau nhn cng mt liu tng ng nh nhau li c tn

thng sinh hc khc nhau. l do nhy cm phng x ca cc m khc nhau,

c trng cho tnh cht ny ngi ta a ra khi nim trng s ca m WT. Liu

hiu dng c tnh.

Liu hiu dng = Liu tng ng x WT (1.4)

1.3.2.2 . C ch tc dng sinh hc ca bc x ion ho [1]

cc phn trn chng ta kho st bn cht cc hin tng vt l trong qu

trnh tng tc gia bc x v vt cht. Tuy nhin qu trnh truyn nng lng ca

bc x ln t chc sinh hc v gy tc dng c nhng c ch phc tp hn.

Hin nay ngi ta vn cho rng c hai c ch tc dng ca bc x ion ha ln t

chc sinh hc:

- C ch tc dng trc tip

Nng lng ca bc x trc tip chuyn giao cho cc phn t cu to nn t

chc sinh hc m ch yu l cc i phn t hu c, nng lng gy nn cc qu

trnh kch thch v ion ha cc nguyn t, phn t. Tip theo l cc phn ng ha

8

hc xy ra gia cc phn t mi to thnh sau khi b kch thch hoc ion ha. Hai

giai on ny xy ra rt nhanh. Cc phn t hu c quan trng b tn thng gy

nn cc tc dng sinh hc tip theo nh tn thng chc nng hot ng, gy t

bin gen, hy dit t bo, v.v...

Cc qu trnh kch thch v ion ha cc nguyn t, phn t, cc phn ng ha

hc xy ra gia cc phn t trc ht gy nn cc tn thng ti v sau c th

lan truyn ra cc phn t khc xung quanh.

- C ch tc dng gin tip

Tuy nhin vi l thuyt c ch tc dng trc tip ngi ta khng gii thch

c mt s kt qu thc nghim v quan st thc t. Ta bit nc chim mt t l

rt cao (70% n 90%) trong cc t chc sinh hc. V vy c th xem t chc sinh

hc nh mt mi trng bao gm cc phn t hu c v nc. Do vy c th ngh

rng bn cnh c ch tc dng trc tip cn c mt c ch khc khng km phn

quan trng vi vai tr to ln ca cc phn t nc lm trung gian. l c ch tc

dng gin tip. C ch gin tip ca bc x ion ha ln t chc sinh hc l bc x

ion ha tc dng ln cc phn t nc, gy nn nhng bin i to ra cc sn

phm ha hc mi l cc ion dng hoc m (H2O-, H2O

+, H

+, OH

-) v cc phn t

trng thi kch thch (H2O*, H

*, OH

*, HO2

*, v.v...). Cc phn t trng thi kch

thch H*, OH

* rt d kt hp vi nhau to ra cc sn phm ha hc mi:

* * *

2

* * *

2

* *

2 2

H H H

OH H H O

OH OH H O

H2O2 l mt hp cht rt c i vi cc phn t hu c v l mt cht oxy

ha rt mnh. Trn thc t lng H2O2 c sn sinh ra nhiu hn v c cc phn

ng sau y nu trong t chc c nhiu O2.

Hoc:

* *

2 2 2

*

2 2

2 2 2 2 2

H O O OH HO

H O HO

HO HO H O O

9

Nu hm lng oxy trong mi trng cng nhiu th lng H2O2 c sn

sinh cng ln. Nu trong nc c cc cht ha tan th (HO2)*

s thu electron ca

cht v bin thnh (HO2)- ri sau tng tc vi H+ cng thnh peroxyd.

*

2 2 2 2HO e HO H H O

Phn ln cc phn t hu c (RH) trong t chc b ph hy bi cc phn t

H2O2. Ngoi ra cc gc t do (phn t, nguyn t trng thi kch thch) H*, OH

*

cng d phn ng vi cc phn t hu c gy nn nhng bin i v to ra thm

nhng gc kch thch R* v RO2* theo c ch sau y.

* *

2RH H R H v * *

2RH OH R H O

Cc gc R* b kch thch cng d gy ra cc phn ng ha hc mi lm cho s

lng cc phn t hu c b tn thng tng ln rt nhiu v cc phn ng dy

chuyn sau y.

* *

2 2

*

2

R O RO

RO RH ROOH+R

Da vo l thuyt ny ngi ta hiu c tc dng lan truyn ra xa, tc dng

ko di sau khi chiu x, tc dng ca hm lng nc, oxy trong mi trng chiu

v nhiu hin tng khc trong phng x sinh hc.

Trong c ch tc dng ca bc x ion ha ln t chc sinh hc, hai c ch tc

dng trc tip v tc dng gin tip u c gi tr quan trng ca n. Ty thuc mi

trng v iu kin m c lc c ch ny c vai tr v v tr ln hn c ch kia. Hai

c ch h tr cho nhau v gip chng ta hiu c su sc hn bn cht ca cc

qu trnh phng x sinh hc, chng ta tin hnh p dng bc x ion ha c hiu

qu hn trong cng tc thc tin.

1.4. Cc loi hnh iu tr bng bc x

1.4.1. iu tr bng ngun xa

Khi nim x tr chiu ngoi l trong phng thc ny tn ti mt khong

cch nht nh gia ngun x v i tng b chiu. Do trn thc t thng s

dng cc photon trong iu tr chiu ngoi. l tia X v tia gamma [1].

10

Khi s dng cc tia ny iu tr cn lu cc c im sau:

- Photon c nng lng cng cao th kh nng m xuyn cng ln v hiu qu

sinh hc cng cao. V vy ngi ta tm cch to ra cc thit b pht ngun photon c

nng lng ngy cng cao. Thc nghim cho thy su 10 cm di mt da liu

hp th tng dn theo nng lng tia v t hiu qu cao nht (gn 80% liu ti a)

vi cc photon c nng lng trung bnh l: 8 MeV (t 3 10 MeV).

- Tia m xuyn c nng lng cng ln khi vo c th bnh nhn cng to

nn sut liu iu tr trong su tt hn, ng thi liu gy hi cho cc m lnh trn

ng xuyn qua cng t hn.

- Nng lng tia cng ln th t l liu hp th khi u trn tng liu cng tng.

- S tn x (khuch tn) ra m lnh xung quanh u cng t hn khi nng lng

chm photon cng ln.

- Chm tia c cng cng mnh cng to ra mt phng ng liu (isodose)

trong m bnh tt hn.

1.4.2. iu tr p st (brachytherapy)

1.4.2.1. iu tr p st c in

Trong iu tr p st thng dng cc ng v phng x (VPX) pht ra beta

cng hoc gamma mm, c th dng ngun phng x kn hoc h. in hnh ca k

thut iu tr p st l s dng cc kim, ch, ht,...bng ngun radium hoc cobalt.

Cng vic ny thng c kt hp vi phu thut n gin hoc phc tp vng

cn iu tr p st. V vy to thnh cc phn khoa c th cho iu tr p st vng

u c, kh ph qun, ng tiu ho...

Radium-226 (266

Ra) ln u tin c dng vo mc ch iu tr vo nm

1917. Ngi ta s dng nng lng tia gamma pht ra t cc ngun radium tiu

dit cc t bo ung th cc hc t nhin nh t cung, bng quang, i trc trng,

hc ming ... Tuy 266Ra c chu k bn r (T1/2) l 1580 nm, dng c lu nhng

kh c c ngun ln. Cc c s iu tr thng ch c c cc ngun di dng

cc kim nh c 2 -10 g m thi. Vic sn xut n tn km, gi thnh t v phi tinh

lc t cc qung uran.

11

n nm 1951 ng v phng x nhn to 60Co mi c s dng vo iu tr

v n ngy cng c thay th rng ri cho 266Ra v ngi ta c th sn xut c

cc ngun 60Co c phng x ln hn 266Ra nhiu ln v r hn hng ngn ln.

1.4.2.2. iu tr p st np ngun sau (afterloading Brachytherapy)

Phng php iu tr p st c in i hi ngi thy thuc phi thao tc lu

v trc tip vi cc ngun x. V vy cc nc tin tin khng cn p dng na.

Gn y vi tin b ca tin hc, k thut in t ngi ta c th xc nh v tr, liu

lng ngun x v to ra ng dn trc, sau mi np ngun x theo ng

dn . Bng cch ny gim c liu chiu cho nhn vin iu tr v c gi l

k thut iu tr p st np ngun sau.

1.4.2.3. iu tr chiu trong bng ngun h

Khc vi 2 phng thc iu tr k trn, iu tr chiu trong l phng php

a cc ngun phng x h vo tn t bo, m bnh da theo cc hot ng sinh l

chc nng hoc ri lon bnh l ca c quan, c th. Dc cht phng x c th ch

l cht v c hoc hp cht hu c c gn cc VPX thch hp. C th a chng

vo c th bng ng ung, tim hoc truyn. Mc ch ch yu vn l km hm

s hot ng cng nng ca m, tuyn hoc tiu dit cc t bo bnh.

12

CHNG 2

MY GIA TC TUYN TNH V K THUT X TR 3D-CRT

TRONG IU TR UNG TH

Vic ng dng ca tia X vo iu tr ung th nng ngy cng phong ph.

Trong l cc my pht tia-X 150 kV v 300 kV c s dng rt hiu qu ln

lt cho iu tr ung th da v cho s lm gim bt cc triu trng tm thi. Tuy

nhin tnh cht vt l ca tia ny khng p ng c cc yu cu iu tr cc khi

u su bn trong. Vic nghin cu chm bc x vi mc nng lng cao hn, ng

ngha vi kh nng m xuyn ln hn, dn n s pht trin ca my x tr

cobalt-60. Ph chm tia gamma pht ra t ngun cobalt-60 c 2 nh nng lng ti

1,17 MeV v 1,33 MeV, cho nng lng photon trung bnh khong 1,25 MeV,

chm bc x ny c th c dng iu tr tt nhng khi u nm gn b mt da.

Tuy nhin tnh cht vt l ca chm tia gamma ny vn cn c mt s mt hn ch

vic iu tr cc khi u su bn trong nh: Liu b mt tng i ln v iu tr

km hiu qu vi cc khi u nm su trong da. V vy ngi ta phi s dng my

gia tc trong x tr ung th v s ra i my gia tc to ra bc ngot ln trong

iu tr ung th. Trong chng ny chng ti trnh by nhng li th ca my gia

tc so vi my cobalt dn ti s ra i ca my gia tc, sau i tm hiu nguyn

l cu to chung ca my gia tc. Cui cng l trnh by v k thut x tr thch ng

ba chiu (3D-CRT).

2.1. Nhng hn ch ca my x tr cobalt trong iu tr

My x tr cobalt l loi my s dng chm bc x gamma pht ra do s phn

r ca ng v phng x 60Co iu tr. Ngun 60Co c sn xut c dng ng

xu (ng knh 2cm) c ghp li thnh hnh tr. Hot ban u 6500 Ci. Thi

gian s dng khong 5 - 7 nm. Ngun 60Co pht bc x gamma () vi hai mc nng

lng l 1,17 MeV v 1,33 MeV, nng lng trung bnh l 1,25 MeV, c thi gian

bn r 5,27 nm. Cc mc nng lng ca 60Co c nh lm cho vic iu tr tr nn

km linh hot trong vic iu tr ung th vi cc v tr khi u khc nhau. i vi

13

nhng khi u rt nng, nm rt gn b mt da, khi iu tr bng my cobalt, liu hp

th cc i nm su su hn v tr ca khi u.

Nh vy, khi iu tr cc khi u nng bng my cobalt th liu khng tp trung

vo khi u, v nh hng ln n nhng vng m lnh nm su trong da. khc

phc iu ny, nu iu tr bng my cobalt th ngi ta phi s dng thm mt

dng c, gi l dng c b tr. Dng c b tr c tc dng a vng liu hp th

cc i v gn b mt da hn, nh vy s tp trung c liu vo nhng khi u nm

rt gn b mt da. Tuy nhin, vic s dng dng c b tr ny cng tng i bt

tin. khc phc hon ton nhng nhc im ny, khi iu tr nhng khi u

nng, ngi ta s dng chm bc x electron. Bi v cc chm tia electron mt

nng lng gn b mt da v cng chm tia suy gim nhanh chng v s mt

hn su 5 cm. iu ny khin nhng vng lnh t b tn thng hn.

Khng ch khng ph hp cho nhng khi u rt nng, my Co-60 cng khng

th p ng c vi nhng khi u nm su trong c th. V d : Mt khi u nm

gia phi, cch b mt da trung bnh 8 cm, liu x ca my cobalt khi vo n y

li qu thp bi. gip cho vic iu tr trong trng hp ny t hiu qu tt hn,

cn phi c chm bc x photon c mc nng lng cao, a vng liu cc i

su hn vo c th.

Nh vy, iu tr ung th linh hot vi nhng khi u nhng v tr khc

nhau trong c th i phi c nhng chm bc x khc nhau nh electron v photon,

ng thi vi iu l vi mi loi bc x phi c nhiu mc nng lng. S a

dng v linh ng ny gip cho ta c th iu tr c tt c cc khi u bt c v

tr no. My gia tc ra i hon ton c th p ng c nhng i hi ny. Ngoi

ra, s dng my gia tc trong x tr cn c nhng li th ni tri: My gia tc an

ton hn nhiu v n ngng pht tia khi tt my, cn my cobalt th ng v phng

x vn phn r lin tc v pht tia khi khng cn cn n. My Co-60 i hi phi

thay ngun nh k do phn r phng x. Ngun c b ra cn x l m bo an

ton bc x khng gy nhim mi trng. c bit sut liu bc x ca my

gia tc cao hn ngun cobalt (thng gp 2-3 ln).

14

2.2. Tng quan v my gia tc tuyn tnh

My gia tc c ng dng trong lm sng t u nhng nm 1950, hoc bng

cc chm electron hoc cc chm tia X v tr thnh thit b ch yu ti nhiu

trung tm x tr. V nguyn tc, khng c gii hn trong cng ngh ch to my gia

tc vi nng lng ca electron, ngoi tr bn thn cu trc chiu di tng tc ca

thit b. Gii hn nng lng chm electron hiu dng t c trong thc t lm

sng nm trong phm vi t 4-40 MeV.

Hnh 2.1: My gia tc tuyn tnh ti bnh vin a khoa ng Nai

Vi mc ch ng dng trong lm sng, cc loi my gia tc cn thit k sao

cho tha mn mt s nhng tiu chun, yu cu ch yu nh sau [2]:

- Chm tia bc x phi xc nh c r nng lng v thay i c v cc kch

thc chm tia.

- Liu lng bc x phi ng u bn trong chm tia.

- Liu lng ca thit b pht ra phi n nh khng ch trong giai on iu tr m

phi n nh sut trong qu trnh s dng.

15

- Liu lng bc x phn b trn bnh nhn phi c o c mt cch chnh xc.

- Chm tia bc x phi iu chnh v thay i c hng v v tr bt k trn bnh

nhn.

- An ton v n nh v c kh cng l mt thng s ht sc quan trng.

2.2.1. Cu to my gia tc tuyn tnh

Cc b phn chnh l sng in t, ngun pht sng cao tng klystron, ng gia

tc, h thng un chm tia, b phn kim sot liu lng v bia pht tia X.

Hnh 2.2: Cu to my gia tc tuyn tnh

- Cn my ng (gantry stand): c thit k chu ti, mt khc c th cha:

My pht sng, sng in t, v ng dn sng gia tc.

- My pht sng: Gm hai thnh phn chnh: Ngun pht sng (klystron hoc

magnetron) v b iu ch xung. Magnetron v klystron: L cc ngun pht vi

sng hot ng di dng xung ngn c mt vi s. C hai c lp thm b iu

chnh tn s t ng AFC (automatic frequency control) c th duy tr dao ng

vi tn s ti u.

- Sng in t: L thit b pht ra electron, n gm c hai loi chnh l loi hai cc

v loi ba cc. C ch cung cp nhit cho catt ca sng in t c th l trc tip

hoc gin tip tu theo nh sn xut.

16

- ng dn sng gia tc: Gm c ng dn sng v ng gia tc dng truyn n v

tng tc chm electron.

- Cn my (gantry): Cha h thng truyn ti electron, u my iu tr. Cn my

c gn vo cn my ng v c th quay c quanh trc vung gc vi n.

- H thng truyn ti electron: a electron n u my iu tr.

- u my iu tr bao gm: Bia tia - X c dng to ra chm photon x tr nh

hiu ng bc x hm khi chm electron ( c gia tc) tng tc vi bia; ng

chun trc (gm c cc loi: S cp, xc nh hnh dng chm bc x, i xng v

c lp) thng c cu to bi hai cp ngm (jaw) to dng (chun trc)

chm bc x theo hnh ch nht; cc khi che chn to hnh dng trng chiu

thch hp; cc b lc phng dng lm phng chm bc x to ra tnh ng nht;

b phn kim sot liu lng (monitor).

- Ging bnh: L ni t bnh nhn v b tr cc t th x tr. N c th quay c

quanh trc trn mt phng nm ngang v cng c th nng ln, h xung to

khong cch iu tr thch hp.

- Bng iu khin: L thit b iu khin cc hot ng ca my gia tc nh: Quay,

t v tr cho cc ngm trong ng chun trc nh v trng iu tr.

- Ngun cao p: Cung cp ngun in mt chiu cho my pht sng.

2.2.2. Nguyn l hot ng

Cc electron c sinh ra do bc x nhit t sng in t, c iu ch thnh

cc xung v phn vo ng gia tc. l cu trc dn sng m trong nng lng

dng cho electron c cung cp t ngun sng siu cao tn (vi tn s khong

3000 MHz bc sng 100 mm). Chm electron c gia tc c xu hng phn k

khi ra khi ng gia tc v c hi t theo mt qu o thng nh h thng in

trng ng trc. Sau chm electron c un theo mt gc 900 hoc 2700.. Nu

cn s dng chm tia electron th cho electron ra trc tip s dng, nhng nu s

dng tia X th cho chm electron sau khi gia tc chm vo mt bia kim loi (target).

Ti y electron b hm li v pht ra tia X (theo hiu ng bc x hm

bremstralung).

17

2.3. K thut x tr 3D-CRT

Nhng tin b trong cng ngh my tnh lm tng kh nng qu t lp

k hoch v thc thi k thut phn b liu theo 2-D cho n k thut phc tp hn,

hin i hn l phn b liu theo khng gian 3 chiu, ph hp vi hnh dng

khi u (3D-CRT).

3D-CRT l mt thut ng c s dng m t k thut phc tho v thc

hin mt k hoch x tr c da trn cc d liu t phim CT theo ba chiu cng

cc trng chiu c to theo hnh dng ring bit ph hp khi u.

Hnh 2.3: K thut x tr thng thng 2D (a) v k thut x tr 3D-CRT (b)

K thut x tr 3D-CRT l mt trong cc k thut x tr ngoi. So vi k thut

x tr thng thng 2D trc y, cc chm tia c pht ra ch c dng hnh ch

nht hoc hnh vung, th k thut 3D-CRT u vit hn rt nhiu. Vi s c mt

ca cc tm che chn ch, ng chun trc a l MLC, chm bc x pht ra c th

c iu chnh vi hnh dng bt k c th bao kht khi u theo tng hng

chiu (hnh 2.3b).

Mc ch ca x tr 3D-CRT l to c mt vng phn b liu hp th cao ti

th tch bia v do gim liu c hi cho cc t chc lnh xung quanh, qua s

lm gim thiu cc hiu ng ph hoc bin chng mun, tng xc sut kim sot

khi u v ci thin kt qu iu tr. thc hin c iu ny, bnh nhn cn phi

tri qua mt qu trnh m phng v lp k hch iu tr.

18

2.3.1. H thng lp k hoch iu tr TPS (Treatment planning system)

M phng v lp k hoch x tr thc cht l qu trnh thit k, m phng mt

ca iu tr trc khi tin hnh iu tr tht. Nh , cc bc s c th kim sot

c liu lng bc x ti khi u, ti cc t chc lnh xung quanh ca bnh nhn,

cng nh tin lng, nh gi c kh nng p ng ca bnh nhn trong qu

trnh iu tr.

Cng vi s pht trin ca tin hc, cc h thng lp k hoch x tr cng ngy

cng pht trin, lp k hoch nhanh chng v chnh xc hn. Trong cc h thng

ny, c c th bnh nhn v my iu tr cho bnh nhn u c m phng trn

phn mm lp k hoch. Thng tin bnh nhn c dng trong qu trnh m phng

chnh l tp hp d liu nh ct lp vi tnh (nh theo chun DICOM). nh ct lp vi

tnh khng nhng c s dng m t hnh dng, t th ngi bnh, xc nh v

tr khi u, cc c quan cn bo v m n cn cung cp thng tin chnh xc v mt

vt cht (c th l mt electron), gip ch cho vic tnh ton liu lng bc x

hp th. Vic m phng my iu tr trn phn mm c thc hin bng cch to

ra mt my o c cc thng s k thut ging ht vi my iu tr thc. Ph bc x

pht ra t my iu tr thc cng c m phng chnh xc trn phn mm bng

cch nhp b d liu o c thc t. Hin nay trn Th Gii c mt s h thng lp

k hoch x tr nh: Prowess, CMS, ADAC PinacleTuy cc h thng ny c

nhng im khc bit, nhng nhn chung, cc bc trong qu trnh lp k hoch u

theo mt quy trnh.

2.3.2. Quy trnh thc hnh lm sng k thut x tr 3D-CRT

Phn ny cp ni dung thc hnh lm sng ca chng trnh x tr theo 3D-

CRT. C nhiu khu k thut i hi phi thc hin trong chng trnh ny. Hnh

2.4: Gii thiu s khi bao gm cc bc c bn ca quy trnh k thut 3D-CRT.

Nhiu chi tit c th khc nhau gia cc trung tm, trong phn di y chng ti

trnh by quy trnh k thut x tr 3D-CRT ti khoa Y hc Ht nhn, bnh vin a

khoa ng Nai.

19

2.3.2.1. nh gi bnh nhn v quyt nh x tr

Bc u trong quy trnh l nh gi v quyt nh xem bnh nhn c th

c iu tr nh th no. Trong qu trnh nh gi tt c cc khu chn on, xt

nghim khc nhau c tin hnh xc nh tnh trng, cng nh giai on bnh.

Nhng yu t bao gm chn on hnh nh, cc xt nghim c bn v sinh ha

hay nhng thng tin v m bnh... gip xc nh loi bnh, giai on bnh cng

nh mc xm ln ca khi u. Sau , tiu ban chuyn mn a ra nhng quyt

nh iu tr cho bnh nhn.

Hnh 2.4: Quy trnh lp k hoch x tr

2.3.2.2. C nh t th bnh nhn

Trc khi i n quyt nh iu tr, tiu ban chuyn mn cn thng nht t

th bnh nhn c th p dng cho tng trng hp v phng php c nh t th

bnh nhn sao cho thch hp nht.

nh gi bnh nhn

C nh bnh nhn

M phng

Khoanh vng cc t

chc ch nh liu

Thit lp trng chiu

Tnh ton liu

nh gi

k hoch

iu tr

Chp nhn

Khng chp nhn

20

Vic p dng k thut 3D-CRT thng kt hp vi kh nng lm gim cc

mp ng bin ca th tch khi u. Phng php c nh hiu qu c th lm gim

thiu sai s t t th bnh nhn. Do , vic s dng phng tin c nh ph hp,

to s thoi mi cho bnh nhn v thao tc cho nhn vin k thut s l mt yu t

quan trng nh hng n ton b quy trnh v kt qu iu tr bnh nhn. Mi mt

c s x tr cn trang b y nhng phng tin, dng c c nh ph hp cho

tng v tr, tng loi bnh. Nhng dng c ny phi d dng ti to chnh xc t th

bnh nhn trong qu trnh iu tr.

2.3.2.3. M phng

Hnh 2.5: H thng my CT m phng ti bnh vin a khoa ng Nai

H thng m phng bao gm my m phng v h thng my tnh iu khin

my m phng cng nh lu tr v x l d liu m phng. Chc nng ca my m

phng l thu nhn d liu nh phc v cho qu trnh lp k hoch, ng thi n

cng c s dng m phng, kim tra vic iu tr v che chn c to ra t

h thng lp k trc khi a bnh nhn vo iu tr chnh thc trn my iu tr.

Ti khoa Y hc Ht nhn bnh vin a khoa ng Nai, h thng m phng l h

thng CT-SIM gm 2 phn chnh: My chp CT c phn gii cao cng my tnh

i km v h thng laser m phng.

21

Nh h thng m phng CT-SIM ny, vic x tr tr nn n gin v chnh

xc hn rt nhiu. H thng laser m phng c gn trong phng chp CT nh

v chnh xc v tr, t th v ta khi chp nh. Kt qu m phng c gi ti

phn mm iu khin chm laser v h thng lp k hoch o VPS (virtual planning

systems). Trong h thng VPS, bc s s xc nh v tr, kch thc khi u trong c

th ngi bnh. Sau , ta tm khi u s c truyn li v phn mm iu

khin ca h thng laser. Phn mm ny t ng tnh ra khong cch gia tm khi

u vi ta gc trn nh CT ca bnh nhn. Sau , n iu khin t ng s dch

chuyn ca ging a h laser v tm khi u ca bnh nhn (bnh nhn vn

nm c nh trn ging CT) v k thut vin s nh du v tr tm khi u trn

bnh nhn.

2.3.2.4. Ghi nhn v x l hnh nh bnh nhn

a. Chp nh CT

Vi nhiu loi v tr khi u khc nhau, nhng hnh nh chp CT s gip cho

vic xc nh chnh xc cc thng s nh kch thc cng nh v tr ca n. Nhng

hnh nh c thc hin trn CT dng cho qu trnh lp k hoch iu tr phi sao

cho cng st thc t cng tt, ngha l phi y nhng g s dng trn my iu

tr. Chng hn cc dng c c nh, gi chn tay, khung tr gip t th bnh

nhn, h thng laser nh v,... phi ging ht nhau.

b. Chp cng hng t-MRI

Trong x tr ung th, MRI c dng ch yu trong nhng trng hp cn b

xung nhng thng tin gii phu hoc kt hp vi cc phim CT ci thin s nh

gi mt cch chi tit v r rng hn tnh trng khi u, nht l nhng khi u tin lit

tuyn v khi u h thn kinh

Trong h thng VPS, d liu nh ca bnh nhn c th c x l gip cc

bc s quan st khi u cng nh vng cn bo v r hn. Nh , s v chnh xc

cc vng ny, nng cao chnh xc v kt qu ca qu trnh lp k hoch. Mt s

thao tc x l nh hay c s dng nh: iu chnh sng ti ca d liu nh,

in thm mt s thng tin c nhn khc ca bnh nhn: Tiu s bnh, nm sinh,

22

2.3.2.5. Khoanh vng iu tr v vng bo v

Qu trnh lp k hoch x tr da vo hnh nh c xc nh theo th tch

khi u v cc t chc nguy cp lin k. Cc vng th tch ny c v theo tng lt

ct da trn b d liu ca phim CT. Th tch khi u thng c v chu vi bng

th cng mc d nhng h thng phn mm hin i c kh nng phn bit cu trc

gii phu khi u. Cng vic ny c v tn thi gian nhng bc s x tr s yn tm

hn v chnh xc ca n. Khi v cc ng bin xc nh th tch khi u v cc

th tch lin quan khc, bc s x tr v k s vt l cn phi tnh n nhng x dch

c th xy ra ca bnh nhn v ca mt s t chc. Sau y l mt s hng dn chi

tit gip vic xc nh cc th tch ny.

Cn phi ht sc cn trng xc nh chnh xc cc vng th tch lin quan

bng k thut x tr 3D-CRT. Nh ni dung bn bo co s 50 v 62 ca ICRU,

hnh 2.6 m t hng dn vic xc nh v m t mt s vng th tch cng nh cc

t chc nguy cp lin quan.

a. Th tch khi u th GTV (gross tumor volume): L phm vi biu hin pht trin

ti ch ca cc t bo c tnh m qua c th nhn thy, s nn hoc thm khm

trc tip.

GTV thng c xc nh bng cc phng tin chn on hnh nh nh

CT, MRI, PET..., bng nhng thng tin t m bnh hc hay gii phu bnh do

thm khm trc tip lm sng.

b. Th tch bia lm sng CTV (clinical target volume): L th tch m m trong

bao gm th tch GTV v cc t chc c tnh biu hin mc vi th, kh pht

hin bng lm sng nhng cn phi loi b. V vy, th tch ny cng phi iu

tr mt cch y v liu lng c trong trng hp x tr triu chng hay trit

.

xc nh th tch bia lm sng, cn phi to dng mt mp ng bin

vi s tri rng vi xm ln ca cc t bo v nhng vng lin quan khc c coi

l c tnh, cn phi iu tr (ngha l nhng hch lympho dng tnh). Thng tin,

d liu ca nhng t chc ny cung cp bng xt nghim m bnh hc c ly

23

t mt s mu bnh phm ti vng c nghi ng. Vng th tch bia lm sng sau

phu thut, chng hn khi u v thng c tnh l ton b t chc nguyn pht

c ct b (GTV). Theo kinh nghim, khi xc nh ng bin CTV thng

c m rng thm 1 cm (ngha l CTV=GTV+1 cm).

Hnh 2.6: Cc vng th tch khc nhau cn xc nh theo ICRU

c. Th tch bia ni ti ITV (internal target volume): L mt khi nim mi c gii

thiu trong bn bo co s 62 ca ICRU. b tr cho nhng thay i v kch

thc, hnh dng v v tr ca CTV. Khi xc nh ITV, iu quan trng l phi

tnh n s bt i xng t nhin v s thay i ca t chc c th. Chng hn,

s thay i v hai pha bn ca tuyn tin lit s khc vi s thay i trc, sau.

S thay i bn trong nh vy l do bn cht sinh l ca c th, khng d kim

sot. khc phc nhng yu t ny, c nhiu cng trnh nghin cu p dng

k thut khng ch, kim sot nhp th hoc s cng y ca bng quang, trc

trng.

24

d. Th tch lp k hoch iu tr PTV (planning target volume): L mt khi nim

v hnh hc, c xc nh la chn s phn b cc chm tia mt cch thch

hp, trong c tnh n nh hng thc t ca nhng thay i v mt hnh hc

ln th tch CTV, m bo phn b liu lng theo ng yu cu trn .

m bo rng tt c cc m bn trong th tch bia lm sng nhn c

mt liu lng ch nh, v nguyn tc chiu x, ta phi lp k hoch chiu

x mt th tch hnh hc ln hn th tch bia lm sng. Th tch bia lp k hoch

c nh ngha l khi th tch bao gm th tch bia lm sng vi mt on mp

bao quanh th tch bia lm sng. on mp ny c xc nh da vo s di

chuyn khi u trong c th bnh nhn v nhng sai s lin quan n sai s ca

my mc. S di chuyn ca khi u trong c th bnh nhn c th k n nhng

nguyn nhn nh: S p ca tim, s th, s cha nc khng ging nhau ca

bng quang. Nhng sai s lin quan ti my mc c th l do sai s ca ging,

ca h laser Tuy nhin, xc nh c on mp t CTV ti PTV, ta khng

c php cng dn cc sai s k trn. on mp bao quanh CTV ny, bt k v

hng no, cng phi ln c th b p c nhng sai s trn. Tc l sao

cho theo bt k hng no, CTV lun lun nm gn trong PTV trong qu trnh

iu tr. Trong thc t lp k hoch, ta phi c gng lp k hoch sao cho ti

thiu 95% th tch bia lp k hoch PTV nhn 100% liu ch nh.

e. Th tch iu tr TV (treated volume): Th tch iu tr thng ln hn th tch

bia lp k hoch v ph thuc vo k thut iu tr c th. Khi lp k hoch, ta

mong mun mt th tch ng liu no n bao trn PTV. Tuy nhin, rt kh

th tch ng liu bng ng th tch PTV m n thng ln hn PTV. Ngi

ta gi th tch ng liu l th tch iu tr .

f. Th tch chiu x IV (irradiated volume): L vng th tch nhn mt lng liu

ng k (thng l 50% liu ch nh). Th tch chiu x ln hn th tch iu tr

v cng ph thuc vo k thut x tr c s dng. Vi k thut x tr 3D-CRT,

th tch chiu x gim khi s dng h thng my gia tc c ng chun trc a l

(MLC) v th tch chiu x tng khi s trng chiu tng.

25

2.3.2.6. Thit lp trng chiu v s dng cc thit b h tr

Vic thit lp trng chiu l la chn cc hng chiu v mc nng lng

ca tng chm tia. Vic ny ph thuc vo v tr, kch thc khi u trong tng

trng hp c th v theo kinh nghim ca tng ngi. S la chn mc nng

lng ca tng chm tia ph thuc vo bn cht ca chm tia bc x. Vi nhng

khi u nm trn da hoc v tr rt nng gn b mt da, ngi ta thng s dng

chm tia electron. Do liu lng do chm tia electron b li ln nht gn b mt

da v suy gim rt nhanh khi i su vo c th bnh nhn. Vi nhng khi u nm

su trong c th, ta c th s dng cc chm tia photon. Ty thuc vo mc su

ca khi u, m ta quyt nh la chn chm tia photon nng lng thp hay cao.

Vi khi u su hn th nn s dng chm photon c nng lng cao hn.

Vi tng trng hp c th, s lng chm tia v cc hng chiu chm tia

hon ton ph thuc vo v tr, kch thc khi u, cng nh kinh nghim ca ngi

lp k hoch.

Song song vi vic thit lp cc trng chiu, ta phi s dng cc thit b ph

tr to ra mt k hoch tt. s dng cc thit b ph tr mt cch hiu qu

nht, ngi lp k hoch cn phi hiu r v bn cht ca cc thit b .

2.3.2.7. Tnh ton liu lng v phn b liu

Sau khi thit lp cc trng chiu, v s dng cc thit b ph tr cn thit.

Ngi lp k hoch s tin hnh tnh ton liu. Hin nay, trong phn mm Prowess

panther, c hai phng php tnh liu cho k thut x tr 3D-CRT. l: Fast

Photon v fast photon effective.

S dng thut ton fast photon tnh ton liu lng cho nhng vng iu

tr l nhng vng tng i ng nht, h s m ca cc vng l tng ng nhau.

Trong thut ton ny khng tnh n s sai khc h s m gia cc vng iu tr.

Nhng khi vng iu tr l nhng vng khng ng nht, v d nh vng

ngc c nhiu khng kh, hay vng tiu khung c nhiu xng (v gia m mm,

khng kh v xng, h s m ca chng rt khc bit) chng ta s dng thut ton

fast photon effective.

26

2.3.2.8. nh gi k hoch

Sau khi tnh ton liu lng v xem phn b liu, ta tin hnh nh gi k

hoch. nh gi xem k hoch va thit k tt v ti u cha. Khi k hoch ny

c chp nhn th n s c a vo iu tr thc t. Vic iu tr thc t s c

thit lp ging ht nh thit k trn phn mm. Nu k hoch ny cha p ng

c cc yu cu v phn b liu lng nh bc s t ra ban u, cn phi lm t

bc thit lp trng chiu v s dng cc thit b ph tr.

Hnh 2.7: nh gi k hoc da trn lt ct

C hai tiu ch c xt n khi nh gi k hoch, l liu lng ti khi u

v liu lng ti cc t chc nguy cp cn bo v. Mt k hoch tt l k hoch

m bo cc iu kin sau:

- liu bc s ch nh ti khi u, vng nhn liu ln nht nm trong khi u

v khng vt qu 107% liu ch nh.

- Liu ti cc t chc nguy cp cn bo v nm trong gii hn liu cho php.

27

nh gi mt k hoch x tr trong phn mm Prowess panther, ta c th

quan st cc ng ng liu (isodose line) trn tng lt ct (hnh 2.7) v trn bn

liu lng-th tch DVH (dose volume histogram - hnh 2.8).

Hnh 2.8: nh gi k hoch da trn biu DVH

Da trn lt ct hnh 2.7 ta thy ng 95% liu bao ht ton b khi u

(100%), cc ng liu cao trnh c ty sng, tim, phi. Hnh 2.8 m t liu hp

th trong mt qu trnh iu tr ca khi u v cc c quan cn bo v. Da vo hnh

ny ta c nhn xt: Cc c quan cn bo v u nhn liu di mc liu gii hn

cho php, v khi u nhn c 95% liu ch nh. Vy k hoch ny t c yu

cu ca bc s a ra.

2.3.2.9. Tin hnh iu tr

Sau khi k hoch c chp nhn, cc thng s lin quan n k hoch iu

tr c chuyn sang phng my gia tc thng qua h thng mng LAN. H thng

my tnh v phn mm s iu khin my gia tc pht tia iu tr mi ngy cho

bnh nhn.

28

Nh vy, k thut x tr 3D-CRT phn b liu hp th cao ti th tch bia v

gim liu c hi cho cc t chc lnh xung quanh nh vic s dng khi che chn

ch (block) hoc ng chun trc a l (MLC). Hn na, nh c cc dng c lc nm

(wedge), cc khi b m (bolus) th phn b liu c ti u t c yu

cu ca bc s a ra.

Tuy nhin, k thut ny c mt vi hn ch nh sau:

- Gy hin tng chy da cho bnh nhn.

- Chi ph cho vic ct xp lm khun ch, c ch kh tn km v c hi,

nguyn him.

- Mt thi gian tho lp ph kin che chn cho bnh nhn vi tng trng

chiu: Khi ch che chn, lc nm.

- Vi nhng ca ung th phc tp, khi u c hnh dng phc tp v nm ngy

cnh cc c quan nguy cp cn bo v th vi k thut 3D-CRT kh c th

a ra c mt phn b liu ti u.

khc phc nhng hn ch trn, ngi ta c ra mt k thut x tr mi.

l k thut x tr iu bin cng (IMRT). Nhng chng tip theo, chng

ti s trnh by c th hn v k thut x tr iu bin cng v ng dng trong

lm sng.

29

CHNG 3

K THUT X TR IU BIN CNG JO-IMRT

Nhng tin b trong cng ngh my tnh lm tng kh nng qu t lp

k hoch phn b liu lng theo 2D cho n k thut phc tp hn, hin i hn

l phn b liu lng theo khng gian 3D, ph hp vi hnh dng khi u (3D-

CRT). Mt k thut mi, hin i ang pht trin l k thut iu bin cng

IMRT (intensity modulated radiation therapy) s lm ti u s phn b liu theo

hnh dng khi u khng u [2].

X tr iu bin cng IMRT l mt k thut hin i trong iu tr ung th,

liu x c phn b ti a theo hnh dng khi u ng thi liu c hn ch ti

thiu cc t chc lnh xung quanh. Nh vic ti u ho liu ti khi u v gim

thiu cc c quan lnh m k thut IMRT hn ch c bin chng do tia x ng

thi nng cao hiu qu iu tr. cc nc pht trin, i vi cc khi u gn cc c

quan nhy cm, khi u c hnh dng phc tp, k thut ny c thc hin mt cch

thng quy vi cc my gia tc tuyn tnh c ng chun trc a l (MLC). Vit

Nam, do iu kin kh hu nng m, vic dng my gia tc vi MLC gp rt nhiu

kh khn trong vn hnh, bo dng. Tuy nhin vi phn mm Prowess panther ca

M, k thut IMRT vn c th thc hin c vi my gia tc khng c MLC qua

h thng ng chun trc vi cc ngm (jaws) chuyn ng c lp. K thut ny

c thc hin qua vic ng thi chia cc trng chiu (beams) nhiu gc

khc nhau thnh nhiu phn on hnh ch nht (segments) vi cc trng s khc

nhau (weights) nhm ti u ho liu cao nht theo hnh dng khi u v liu cho

php gii hn t chc lnh. Nh vy, IMRT cng c th thc hin ti Vit Nam

trn my gia tc ch vi cc ngm chuyn ng c lp m khng c MLC. iu

ny c bit c ngha trong iu kin nc ta cn nhiu kh khn, vic trang b

cc my gia tc vi MLC rt tn km. Mt khc, kh hu Vit Nam nng m, vic

vn hnh v bo dng my gia tc vi MLC rt phc tp. Do vy, vic nghin cu

v ng dng trin khai k thut x tr JO-IMRT tht s c ngha c mt y t ln

kinh t.

30

3.1. Nguyn l ca k thut x tr iu bin cng IMRT

3.1.1. K thut x tr IMRT l g?

K thut x tr IMRT xut hin trong iu tr lm sng nh l kt qu ca s

pht trin k thut x tr thch ng ba chiu (3D-CRT) trong nhng nm 1980. n

nhng nm 1990, IMRT c tha nhn v ng dng ti M. V mt vt l, tnh

nng chung ca IMRT l c gng tng cng vic kim sot phn b liu ba chiu

thng qua s chng chp ca cc trng chiu nh c lp nhau trong mt hng

ca chm tia. Ni cch khc, trong k thut ny, cng chm tia chiu ra c

iu bin, khng ng nht (hnh 3.1).

Hnh 3.1: So snh phn b liu lng gia k hoch 3D (tri) v IMRT (phi)

Hnh 3.1 cho ta thy, liu bc x ti k hoch 3D phn b ng u trong khi

ti k hoch IMRT liu bc x phn b theo hnh dng v mt t bo u: Ch m,

ch nht khc nhau.

3.1.2. V sao IMRT li tt hn 3D-CRT ?

Nh cp chng 2, k thut x tr 3D-CRT gm cc hng chiu, mi

hng chiu c che chn sao cho trnh c c quan bo v v khng lm che

khut khi u. K thut x tr IMRT c pht trin t k thut 3D-CRT, k thut

ny c thm mt bc t do na l s iu bin cng chm tia lp k hoch

iu tr. Chnh v th, k thut ny to ra phn b liu tt hn (hnh 3.2).

31

Hnh 3.2 l nh CT ca bnh nhn c cc bc s xc nh th tch khi u

v cc c quan cn bo v nh ty sng, tuyn mang tai. Th tch khi u thng

c chiu x t pha trc v hai bn vo, ng ng liu bao trm khi u ng

thi bao trm c ty sng v tuyn mang tai (hnh 3.2). Do , cc c quan cn bo

v nhn mt liu tng ng vi liu m khi u nhn c. Nhng vi k thut

IMRT th vng liu cao bao kht theo hnh dng khi u v trnh c ty sng. K

thut 3D-CRT kh c th lm c iu ny.

Hnh 3.2: Phn b liu ca k thut x tr 3D-CRT v IMRT

3.1.3. Lm th no iu bin cng chm tia ?

K thut IMRT c tha nhn rng ri l c th thc hin trn nhng my

gia tc c ng chun trc a l, tuy nhin IMRT cng c kh nng thc hin vi

my gia tc c cc ngm chuyn ng c lp. Trong k thut ny, chm tia c

chia nh thnh nhiu chm tia n v, trng s ca cc chm tia n v c ti u

ha to nn bn phn b cng cho mi chm tia. T bn phn b

cng , my tnh s tnh ton thit lp chm tia thnh cc trng chiu lin

tip theo mt trnh t nht nh ca my gia tc da trn vic di chuyn v tr ca

cc l ngm. Kt qu l hng lot cc trng chiu nh c hnh dng bt k i vi

my c MLC hoc cc trng hnh vung, hnh ch nht i vi my ch s dng

jaws (hnh 3.3) c hnh thnh t mi hng ca chm tia c chng chp ln

nhau to ra cc m hnh liu lng (cng ) phc hp (hnh 3.4).

32

Hnh 3.3: Hnh dng chm tia c to ra bi MLC (tri) v Jaw (phi)

Hnh 3.4: Bn liu lng phc hp

S khc nhau gia MLC-IMRT v JO-IMRT l MLC-IMRT chia cc trng

chiu thnh cc phn on c hnh dng bt k, cn JO-IMRT chia cc trng chiu

ra cc phn on hnh ch nht hoc hnh vung, nhng vi nhiu hnh ch nht

khc nhau cng bm st c hnh dng khi u. Trong lun vn ny, chng ti

nghin cu v k thut x tr s dng cc l ngm chuyn ng c lp (jaws).

33

3.2. Bi ton lp k hoch ngc trong k thut x tr IMRT

3.2.1. Bi ton lp k hoch xui v lp k hoch ngc

3.2.1.1. Bi ton k hoch xui

Vi k thut x tr 3D-CRT, ta phi thc hin qua cc bc:

- Thit lp trng chiu.

- S dng cc thit b ph tr.

- Tnh ton liu lng.

- nh gi k hoch.

Khi tin hnh nh gi k hoch, nu k hoch p ng c cc yu cu ca

bc s a ra ban u th k hoch c chp nhn, qu trnh lp k hoch s kt

thc. Nu k hoch cha p ng c yu cu ca bc s, ngi lp k hoch s

tip tc lm li theo cc bc trn.

Hnh 3.5: Bi ton k hoch xui

V th, ta c th ni, vic lp k hoch 3D-CRT nh mt bi ton xui.

34

3.2.1.2. Bi ton k hoch ngc

a. nh ngha bi ton k hoch ngc

tng v bi ton ngc ln u tin c a ra bi Brahme nm 1988 khi

ng a ra cu hi: Bit trc phn b liu mc tiu, lm sao iu chnh cc thng

s t c phn b liu ?.

Hnh 3.6: Bi ton lp k hoch ngc

K hoch ngc s dng thut ton ti u ha trn my tnh, xc nh cc

thng s tt nht ca chm tia a ra gii php cng gn d liu ra mong mun

cng tt. V phng din ton hc, vic ti to nh, phc hi nh, x l tn hiu v

qun l danh mc c th c xem nh qu trnh gii quyt mt bi ton ngc.

Chng ta c th ni rng bi ton ngc c hiu nh mt bi ton c p n

nhng cha c li gii.

V mt l thuyt, hon ton c th to c mt k hoch iu tr sao cho

100% liu lng c chiu vo khi u v 0% liu c chiu vo phn khe mnh

k bn-tc l phn khe mnh bn cnh hon ton khng chu liu bng cch a

dn vo cc trng s cho cc trng chiu.

35

Tuy nhin, iu ny trn thc t l khng th lm c, khi chiu mt bc x

vo mt khi u, cc vng ln cn s phi chu mt liu chiu nht nh. Liu chiu

vo phn khe mnh bn cnh l t hay nhiu ph thuc vo hng chiu chm tia

cng nh cc k thut che chn m k thut vin s dng trong qu trnh lp k

hoch x tr. Nh vy vic dng bi ton ngc gii quyt bi ton a 100%

liu vo khi u v 0% liu vo phn khe mnh bn cnh l khng kh thi. Do

phng php thc hin a ra c mt phng n tt nht trong trng hp

ny chnh l mt qu trnh ti u ha m mc tiu ca n chnh l a ra c mt

k hoch iu tr gn ng nht so vi yu cu ban u ca cc k thut vin, da

trn mt s cc ty chn mang tnh tha thun v liu vo phn khi u v phn khe

mnh xung quanh. Nh vy bi ton ngc cng gn ging nh bi ton thun

trong vic s dng mt qu trnh lp i lp li nhm tm ra mt phng n l ti u

nht, tuy nhin bi ton ngc phc tp hn so vi bi ton thun, cc bc thc

hin ca bi ton ngc c thc hin mt cch t ng v c s h tr ca my

tnh nn qu trnh thc hin nhanh hn rt nhiu so vi bi ton thun.

b. Cc thng s, mc tiu qu trnh ti u ha trong bi ton ngc

Trong tng v bi ton ngc, cc thng s gm: S lng chm tia,

hng chiu chm tia, nng lng chm tia v cng chm tia cn c ti u

to c phn b liu lng nh yu cu t ra ban u. Trong bn thng s trn,

s lng chm tia, hng chiu v nng lng chm tia c a vo trc khi

thc hin bi ton. Vic la chn s lng v hng chiu, nng lng chm tia

hon ton da trn c s nhng hiu bit ca cc k s vt l x tr v cu trc sinh

hc cng nh yu cu liu lng ban u cho mi c quan. Thng s duy nht c

ti u ha trong bi ton ngc chnh l bn phn b cng ca mi chm tia

c s dng.

Vy c th ni, mc tiu ca bi ton ngc ny l ti u phn b cng

chm tia thng qua vic chng chp cc hnh dng trng chiu khc nhau trong

qu trnh di chuyn cc l ngm. Da trn mc tiu ca bi ton ngc, c th c

hai cch tip cn gii bi ton ny nh sau:

36

Cch 1: Ti u phn b cng chm tia da trn cc chm tia n

v (pencil beam hay beamlet). Chm tia n v l nhng chm tia nh

c chia ra t chm tia ban u.

Cch 2: Ti u phn b cng chm tia da trn hnh dng cc

trng chiu c chng cht ln nhau.

Phng php ti u ha da trn chm tia n v bao gm hai bc:

Bc 1: Chia nh chm tia thnh nhiu chm tia n v. Trong bc ny,

trng s ca cc chm tia n v c ti u ha to nn bn phn b cng

cho mi chm tia.

Hnh 3.7: Ngun c chia thnh nhiu chm tia n v

Bc 2: T bn phn b cng ca mi chm tia, my tnh s tnh ton

thit lp chm tia thnh cc trng chiu lin tip theo mt trnh t nht nh

ca my gia tc da trn vic di chuyn v tr ca cc l ngm.

Vi phng php ny, ta gp mt s hn ch nht nh. Th nht l t bn

phn b cng ca mi chm tia, ta s tin hnh m cc trng chiu lin tip

theo mt trnh t nht nh da trn s di chuyn ca l ngm, nhng rt kh sau

khi chng chp cc trng chiu nh ny, ta t c bn cng chm tia

ging ht nh mong mun ban u. mt chm tia c phn b cng cng

chnh xc nh trong bn cng , th s ln chiu lin tip ca hng chm tia

phi cng ln. Th hai, t bn phn b chm tia, vic m ra cc trng chiu

37

khng th trnh khi xut hin cc trng chiu c kch thc nh. Vic ny s nh

hng ti s chnh xc ca vic tnh ton trong qu trnh lp k hoch cng nh

vic o c trc khi bnh nhn iu tr, hay iu tr bnh nhn. Do , trong mt

s trng hp, mc d ta c th tnh ton c bn phn b cng rt ti u,

nhng thc t li khng th thit lp cc ln chiu sao cho t c bn phn b

cng chnh xc nh th.

Phng php ti u phn b cng chm tia da trn hnh dng cc

trng chiu c chng cht ln nhau.

Khc vi phng php trn, phng php ti u ha da trn hnh dng v

m ca cc trng chiu hay cn gi l phng php ti u ha trc tip m

(direct aperture optimazation-DAO) s tin hnh ti u ha trc tip v tr cc l

ngm v trng s ca m do l to ra trong mi mt bc.

3.2.2. Quy trnh v cc m hnh ti u ha trong k thut IMRT

3.2.2.1. Quy trnh ti u ha k thut IMRT

V c bn, qu trnh ti u ha c thc hin nh s hnh 3.8. Thng

thng, trc khi tin hnh ti u ha, s lng chm tia, hng chiu chm tia v

nng lng chm tia c chn trc, cc yu cu ca bc s ban u c s dng

cho vic tnh ton trong hm mc tiu, nhm tm ra phng n tt nht.

hiu r hn bi ton, ta gi s c k hoch IMRT dng su chm tia. Nu

mi chm tia c chia thnh 100 chm tia n v v mi chm tia n v c 10

mc cng cho php s c 106100 k hoch kh thi (nhiu hn rt nhiu so vi

k hoch 3D-CRT 6 chm tia).

i vi mt liu mong mun D0 cho, nhim v ca k hoch ngc l tm

ra mt liu D trong tp cc liu kh thi (D) ging hoc sai khc t nht so vi D0. C

nhiu cch chn liu D. Mt cch tip cn thng c s dng ti u ha k

hoch l cc tiu ha sai khc gia D v D0 theo mt hm bc 2.

Trong cc ng dng iu tr, ngi ta thng a ra mt h s quan trng r

kim sot tm quan trng tng i ca cu trc . iu ny c th hin qua

phng trnh bc 2.

38

2

c 0n

1F r D n D n

N (3.1)

Trong , r l h s quan trng hay trng s quan trng ca cu trc , D0 v

Dc ln lt l liu ch nh v liu tnh ton. Vic ti u ha hm ny v bn cht l

mt php phn tch thng k bng phng php bnh phng ti thiu. Ngoi cng

thc (3.1), nhiu hm ti u khc cng c xut.

Hnh 3.8: Quy trnh ti u ha trong k thut IMRT

Vic xy dng cc hm ti u c vai tr rt quan trng i vi s thnh cng

ca iu tr IMRT v vic la chn phng n cui cng ph thuc vo c s l

thuyt ca m hnh. Mt hm c a ra nh gi mc ti u ca k hoch

v khi ti u ho hm ny ta s thu c cc thng s ti u. Trong vic lp k

hoch iu tr thng thng, hm ny ph thuc vo trng s chm tia, gc ca lc

nm, hng chm tia. Trong khi , IMRT l mt hm ca trng s cc chm tia

n v hoc l hm ca trng s cc hnh dng trng chiu ca tng chm tia.

Thit lp hng chiu v

nng lng cc chm tia

Xc nh cc tiu ch cn

t c

Cc bin khi to

iu chnh cc bin

Hm ti u

Dng ti u

Kt thc

Khng

C

39

thun tin, ngi ta chia cc phng php ti u ho thnh bn loi:

- Ti u ha theo liu.

- Ti u ha theo nhng hiu bit lm sng.

- Ti u ha theo liu ng nht tng ng (EUD).

- Ti u ha theo xc sut kim sot khi u hoc xc sut bin chng m lnh.

S khc bit c bn gia cc m hnh ny l cc i lng dng nh gi

k hoch ti u. Thc ra, mi m hnh k hoch ngc u c nhng u v khuyt

im ring.

3.2.2.2. Cc m hnh ti u ha

a. M hnh ti u ha theo liu

M hnh ti u ho theo liu lin quan n s phn b liu chnh xc hoc cc

bn liu lng-th tch (DVH) ca cc cu trc lin quan. Hm bc 2 trong

phng trnh (3.1) l mt v d ca m hnh ny. Hin nay phng php tip cn

da trn liu l phng php c s dng rng ri nht.

b. M hnh ti ha da trn hiu bit lm sng

Ngi ta mong mun a cc bin chng lm sng vo quy trnh ti u ha k

hoch iu tr. M hnh nh gi theo liu khng thc s phn nh ng n mi

quan h phi tuyn gia liu v phn ng ca khi u cng nh cc m bnh thng.

Trong thc t, s ph thuc ca cc bin chng lm sng vo liu ca mt cu trc

c th b suy bin theo ngha l mt bin chng lm sng c th c gy ra bi

mt lot cc bng phn phi liu hoc DVH. V d cc tuyn mang tai, bin chng

lm sng l nh nhau nu 15 Gy c gi n 67% th tch, 30 Gy cho 45% th tch,

hoc nu 45 Gy cho 24% th tch. Nu m hnh ti u ha theo liu c s dng

trong trng hp ny, kt qu cho ba k hoch khc nhau s khc nhau. khc

phc iu ny, ti u ho da trn lm sng gn y c pht trin bi Yang v

Xing [10]. Ni dung chnh ca phng php l d liu lm sng c s dng vo

vic ch nh qu trnh ti u ha. Trong phng php ny, cht lng mt k

hoch iu tr c o bng mt hm c xy dng t thc nghim, hm ny

khng ch ph thuc vo cc c tnh liu lng m cn vo c tnh liu lng-th

40

tch. i vi cc tuyn mang tai, v d: Ba DVH khc nhau c cp trn s

c ghi bi cng mt hm. Vic phn liu cui cng hoc DVHs ca cc tuyn s

c xc nh bng thut ton ti u vi vic xem xt cc yu cu i vi cc cu

trc khc. Nu mt trong ba cn phi c chn, ci to c s ghi nhn tt hn

cho cc cu trc lin quan s c u tin.

c. M hnh da trn liu ng nht tng ng EUD

Ti u ha ca phn b liu cng c th da trn EUD vi vic s dng h s

sinh hc. EUD l liu tng ng sinh hc (nhng phn b liu khc nhau nhng

gy ra cng 1 hiu ng sinh hc).

1

aa

i

i

1EUD D

N

(3.2)

N l s voxels trong cu trc quan tm, aiD l liu trong voxel th i, a l tham

s c trng cho khi u hoc cc m lnh.

Hm nh gi da trn EUD nh sau:

j

j

F f (3.3)

Trong , fj c th l:

+ Cho khi u: T n0

1f

EUD1

EUD

(3.4)

+ Cho cc m lnh: T n

0

1f

EUD1

EUD

(3.5)

u im ca phng php ny l nhng cng thc rt n gin, cc cng thc

c th c p dng cho c hai t chc cn quan tm: Khi u v c quan nguy cp

(OAR), c t cc thng s hn so vi ti u da trn liu lng hoc cc h s sinh

hc. Kt qu ghi nhn cho thy vi vic ti u ha da trn EUD khi u c bao

tt hn v bo v tt hn cho c quan nguy cp.

41

d. M hnh sinh hc

M hnh ny c tnh n hiu ng sinh hc ca bc x i vi t bo. Hiu

ng sinh hc v cc thng s bc x c lin kt bi liu bc x thng qua vic s

dng hm p ng liu. Tuy nhin, mi quan h gia liu-bin chng khng n

thun l s tng quan 1-1. Cng mt bin chng sinh hc c th c to ra bi

nhiu s phn b liu, m thng s khng c ghi nhn nh nhau nu s dng

m hnh nh gi da trn liu lng. V nguyn tc, m hnh da trn c tnh

sinh hc thch hp nht cho vic nh gi mt k hoch x tr. Tuy nhin, hm p

ng liu ca cc cu trc khc nhau cha hon ton tha ng, c nhiu tranh ci

v cc m hnh cho vic tnh ton da trn ch s liu-phn ng cng nh vic s

dng chng trong ti u ha.

Mc tiu iu tr trong lp k hoch ngc da trn m hnh sinh hc thng

c xem nh l vic cc i ha xc sut kim sot khi u (TCP) trong khi gi xc

sut bin chng m lnh (NTCP) t mt mc liu chp nhn c. Nhng iu

kin vt l v liu v th tch liu thng c a ra m bo rng cc kt qu

t c ph hp vi chn on lm sng ca bc s.

3.3. M hnh ti u ha theo liu

Hm mc tiu trong m hnh ti u ha theo liu l mt cng thc ton hc,

n i din cho ch s nh gi mt k hoch a ra c gn ging vi yu cu ca

bc s hay khng, khi gi tr hm mc tiu cng nh tc l ta ang i ti mt k

hoch gn ng vi yu cu ca bc s. Trong qu trnh thc hin ti u ha, my

tnh lp li mt s ln tm ra phng n tt nht c th cho ti khi cc tiu ch

dng qu trnh lp c tha mn. Vic hiu chnh cc thng s trong qu trnh ti

u ha c t ng tnh ton da trn cc thut ton ti u ha khc nhau. iu

kin dng c xc nh khi s ln lp vt qu gii hn c ch nh ban u

hoc khng c ci tin ng k no c tm thy trong hm mc tiu. Khi qu trnh

ti u ha kt thc, k s lp k hoch nh gi k hoch ging nh trong bi ton

thun, h c th thay i mt s cc thng s ci thin cht lng ca k hoch

nu phn b liu l khng chp nhn c sau qu trnh ti u ha. Vic thay i

42

cc thng s ny bao gm iu chnh cc iu kin trong qu trnh ti u ha, v

hm mc tiu, thay i hng chiu chm tia, chnh sa li ng khoanh vng ca

khi u v vng bo v. Mt s h thng lp k hoch iu tr cho php dng qu

trnh ti u ha iu chnh cc iu kin lin quan ti hm mc tiu trong qu

trnh ti u, v khi ng li qu trnh ti u ngay lp tc bi v khi ma trn v

liu phn b cho cc chm tia n v khng phi tnh ton li. Nu thay i v

hng chiu chm tia th cn phi c mt qu trnh ti u ha mi, bi v lc ny

hng chiu thay i lm cho ma trn phn b liu ca cc chm tia n v b

thay i v phi tnh ton li. Vic hiu chnh cc thng s tip theo ph thuc

nhiu vo trnh hiu bit ca ngi lp k hoch v k thut s dng ca bi ton

ngc ny. H cn phi hiu r v mi quan h khi iu chnh cc thng s ti kt

qu phn b liu lng khi s dng bi ton ngc hiu chnh cc thng s mt

cch hp l nht.

3.3.1. Hm mc tiu

3.3.1.1. Cng thc ton hc

Bi ton ngc trong x tr chnh l mt qu trnh ti u ha tm ra mt

phn b liu tt nht cho bnh nhn trong qu trnh iu tr.

Trong m hnh bi ton ngc ti u ha theo liu, thng s ti u ha

chnh l trng s ca cc chm tia n v v bn cng bc x ca mi chm

tia. N tng ng vi vic tm gi tr nh nht ca hm s f(x) trong x l

vector trng s ca chm tia n v.

x 0

min f x

(3.6)

f(x) chnh l mt hm s i din cho cht lng ca k hoch thu c, v n

c gi l objective function hay hm mc tiu. Hm mc tiu c xy dng

da trn phn b liu lng ban u v c s dng so snh gia cc k hoch

iu tr vi nhau, nhm tm ra mt k hoch tt nht. iu kin x > 0 l v my gia

tc khng th pht ra mt liu lng m, hay ni cch khc bnh nhn khng th

nhn c mt liu lng m.

43

Trong x tr nh CT c chp khi bnh nhn ti iu tr, v c s dng

chnh hnh dung v gii phu cc c ca bnh nhn v c s dng tnh ton

liu trong qu trnh tnh ton liu phn b cho bnh nhn. Thng tin v mt

electron trn nh CT c dng tnh ton liu trong c tnh ti s khng ng

u v vt cht ca cc m. Thm vo ngi ta c th s dng kt hp nh CT

vi cc loi nh nh MRI, SPET, SPECT tng tnh chnh xc khi khoanh vng

khi u v cc b phn khe mnh khc. Tp cc ta ca bnh nhn trong qu

trnh chp nh CT c a vo h thng lp k hoch x tr (TPS) t xy dng

nn m hnh 3D ca bnh nhn. tnh ton liu lng, TPS chia nh bnh nhn

thnh nhiu hnh khi lp phng nh gi l voxel.

Hnh 3.9: Chm tia v c th bnh nhn c chia thnh nhiu phn nh

S lng cc voxel trong mt c quan c th ph thuc vo kch thc c

quan v kch thc ca voxel. Trong thut ton ny, cc voxel c nh cc ch

s i=0, 1, 2, n. Bn phn b cng ca mi chm tia c chia thnh cc

hnh ch nht hoc hnh vung nh gi l im nh (pixel) vi ch s l j=0, 1,

2, m. Cc pixel i din cho mt ct ca cc chm tia n v vi mt phng i

qua im cch trc chnh ca chm tia 100 cm v vung gc vi trc chnh ca

chm tia (isocenter plane). S lng cc pixel ph thuc vo kch thc ca cc c

quan v s lng chm tia c s dng.

44

Gi ijA l liu nhn c ca mt voxels th i t mt chm tia n v c trng

s jw . Khi tng liu nhn c ca voxels i c tnh bng tng liu lng ca

cc chm tia n v vi cc trng s tng ng chiu ti n.

m

i ij j

j 1

D A w

(3.7)

y jw chnh l h s ca bn phn b cng tng ng vi chm tia

n v th j.

Nu s dng ma trn v vector th s phn b liu cho mt vng c quan

tm c tnh: D Aw . Trong m hnh ti u theo liu, hm mc tiu l mt hm

ca phn b liu thc s D v phn b liu mong mun D0 c ngi lp k hoch

a vo da theo yu cu ca bc s.

0OF = f(D, D ) (3.8)

Khi cng thc (3.6) c vit li nh sau:

min f(Aw, D0) (3.9)

Kch thc khng gian ti u ca bi ton (3.9) ph thuc vo s lng voxel

ly ban u v s lng hoc kch thc ca chm tia n v.

3.3.1.2. C s xy dng hm mc tiu

V mt ton hc, mc tiu ca qu trnh ti u ha theo liu l tm gi tr nh

nht ca hm mc tiu. V vy, vic a ra mt cng thc ton hc dng so snh,

nh gi cc k hoch vi nhau l rt quan trng. Mt k hoch iu tr thng

c nh gi bng vic so snh ng DVH hoc ng ng liu (isodose line).

Hm mc tiu nn bao gm c hai cch trn c th so snh, nh gi cc k

hoch vi nhau mt cch chnh xc nht. Tuy nhin mt s yu cu chng hn nh

s phn b ng ng liu lin quan n cc cu trc gii phu ca bnh nhn nn

rt kh so snh mt cch nh lng. V vy ngi ta a vo cc ch tiu liu-th

tch v liu ng nht tng ng (EUD) thay th.

Vic lp hm mc tiu ph thuc vo cc tiu ch nh gi k hoch thng

c s dng. Cc tiu ch khc nhau s yu cu nhng hnh thc khc nhau ca

45

hm mc tiu. Vic xy dng hm mc tiu c th chia thnh hai loi da trn bn

cht ca cc tiu chun:

- Xy dng hm mc tiu da trn c s vt l, bao gm mc tiu v liu lng.

- Xy dng hm mc tiu da trn c s sinh hc.

Trong phn tip theo, chng ti s trnh by r hn v s khc nhau gia tiu

chun sinh hc v vt l, v hm mc tiu c xy dng da vo chng nh th

no? Trong hm mc tiu, cc tiu chun ny c th l cc iu kin hay cc mc

tiu c th. Trong thc t chng c thit lp da trn vic thit lp mc u

tin ca cc mc tiu.

3.3.2. Mc tiu v liu lng

Mt tiu chun quan trng cho mt k hoch x tr l s phn b liu cho khi

u. V d, theo khuyn co ca ICRU, liu vo khi u phi nm trong khong 95%

ti 107% tng liu ch nh. Vi cc c quan khc nhau th gii hn khong liu ny

cng khc nhau. Khi lp k hoch cho bnh nhn cn phi t c cc yu cu ny.

V vy ton b cc im bn trong th tch c chiu nhn c liu chiu

ln hn hay nh hn khong gi tr qui nh th u b a vo tnh ti cht

lng ca k hoch x tr khi dng so snh vi cc k hoch khc thng qua

cng thc sau.

TN2

T i

i 1

OF (D D)

(3.10)

Trong (Di-D)2 dng tnh ton s sai khc gia liu nhn c v liu

c yu cu ban u ti im th i trong vng quan tm. Trong thc t khng th

c c mt phn b liu m trn mi im u nhn c liu lng nh ch

nh ban u, gi tr nh nht v ln nht thng c dng thay th cho phn

b liu ca mt b phn ang c quan tm, tc l phn b liu by gi khng th

c ch ra bng ch mt gi tr m n s nm trong mt khong gi tr t gi tr nh

nht ti gi tr ln nht. Ton b cc im trong vng ang quan tm, nu gi tr

liu lng ca n nh hn gi tr Dmin s b a vo tnh ton s sai khc. Tng t

nh vy ton b cc im trong vng quan tm c liu ln hn gi tr Dmax cng b

46

a vo tnh gi tr cho s sai khc so vi gi tr ch nh ban u. Khi hm mc

tiu cho khi u c tnh ton nh sau:

TN2 2

T i min min i i max i max

i=1

1OF = u(D -D ) .H(D -D )+w(D -D ) .H(D -D )

N (3.11)

Trong : - H l hm bc nhy: 1 if x>00 if x 0H(x) - u v w l cc trng s tng ng vi trng hp liu nh hn Dmin

v liu ln hn Dmax.

- Di l liu nhn c ti voxels th i.

Hnh 3.10: t iu kin cho bi ton ngc

Hnh 3.10 l biu din hm mc tiu v liu lng trong phn mm Prowess

panther cho cc th tch cn chiu x v cc c quan cn bo v. V d, liu ch nh

l 70 Gy th mc tiu v liu lng bt buc ngi lp k hoch phi t liu ti

thiu 95% tng liu ch nh v khng vt qu 107%. Tc l khng c di

66,50 Gy v khng c vt qu 74,90 Gy.

47

Vi cc vng cu trc cn bo v, ch nhng im nm trong vng c quan

cn bo v nhn liu ln hn gii hn liu cho php DOAR c a vo tnh ton

s sai khc. Do , hm mc tiu cho cc phn cn bo v xung quanh nh sau:

OARN2

OAR i OAR i OAR

i 1OAR

1OF (D -D ) .H(D D )

N (3.12)

Trong DOAR l phn liu gii hn c ch nh cho phn th tch cn bo

v ang xt.

3.3.3. Mc tiu liu lng-th tch

Vi cc c quan ni tip nh ty sng th hm mc tiu da trn liu lng-

th tch c p dng i vi gi tr liu ti a. i vi cc c quan song song nh

gan, phi, thn, cc tiu chun v liu ti a trn n t quan trng hn so vi cc

c quan ni tip. V d 1/3 th tch phi c th nhn liu nhiu nht l 45 cGy, 2/3

th tch nhn liu nhiu nht l 30 cGy, v ton b th tch phi ch c th nhn liu

nhiu nht l 17,5 cGy. Vi mc tiu liu-th tch, ngi dng t do hn trong vic

a ra cc tiu ch ca mnh cho k hoch x tr mong mun. Cc tiu ch v liu ti

thiu v liu ti a c th d dng nh ngha bng vic s dng tiu chun liu-th

tch. V d, trong trng hp liu ti a l X Gy, ta c th nh ngha da trn mc

tiu liu th tch l: 0% th tch nhn liu X Gy. Hoc liu ti thiu l Y Gy, s

c nh ngha l 100% th tch nhn liu Y Gy. Trong thc t, tiu chun liu-th

tch chim mt s lng ln s tiu chun hu ch cho cc yu cu khi lp k hoch.

Mc tiu liu-th tch ca cc th tch cn bo v thng c nh ngha l

V(D>D1) < V1: Tc l th tch V nhn c liu D ln hn D1 phi nh hn th tch

V1. T th DVH biu din phn b liu lng theo th tch nh hnh 3.11-a bn

di ta c D2 l liu trung bnh m th tch V1 nhn c: D2= D(V1), tc l D2 l

liu lng c xc nh thng qua hm D(V1). Nu D2D1 th ton b nhng im c D2>D1 s c a vo

tnh ton s sai khc so vi yu cu v liu lng ban u. Cng thc ton hc ca

hm mc tiu cho s sai khc ny c tnh nh sau:

48

OARN2

OAR i 1 i 1 2 1

i 1OAR

1OF (D -D ) .H(D D ).H(D D )

N (3.13)

Ngc li, mc tiu liu-th tch cho phn khi u thng c nh ngha nh

sau: V(D>D1)>V1 : Tc l th tch V nhn c liu D ln hn D1 phi ln hn th

tch V1 (hnh 3.11-b). Hm mc tiu cho trng hp ny c nh ngha nh sau:

TN2

T i 1 1 i i 2

i 1T

1OF (D -D ) .H(D D ).H(D D )

N (3.14)

Hnh 3.11: th mc tiu liu-th tch

3.3.4. Mc tiu v EUD

Niemierko (1997) nh ngha liu ng nht tng ng EUD ca mt

phn b liu trong khi u l liu ng nht vo khi u cn thit tiu dit cng

mt s lng t bo trong khi u.

Hai nm sau, Niemierko (1999) m rng khi nim EUD p dng cho

cc c quan cn bo v. Mt cch tng qut, EUD l mt hm n gin ca phn b

liu vt l, c kh nng c s dng trong vic nh gi s phn b liu khng

ng nht trong x tr 3D-CRT hoc IMRT.

Ta c cng thc ca EUD nh sau:

1

aa

i

i 1

1EUD D

N

(3.15)

49

Trong , Di l liu lng ti voxels th i. N l s lng cc voxels trong vng

cu trc gii phu ang quan tm. ngha ca a l khi u hoc l m lnh bnh

thng, v n c xc nh bng thc nghim thng qua s so snh k hoch iu

tr vi kt qu lm sng. Thng thng, gi tr ca a l dng i vi cc vng m

bnh thng v cc t chc cn bo v. Gi tr ca a l m i vi khi u.

T phng trnh (3.15), ta c th thy.

- Nu a = 1, EUD tr thnh liu trung bnh.

- Nu a = , EUD tr thnh liu cc i.

- Nu a = -, EUD tr thnh liu cc tiu.

Wu (2002) v cc cng s xut cng thc hm mc tiu da trn EUD

nh sau [8].

T n

0

1OF ln

EUD1

EUD

(3.16)

OAR n

0

1OF ln

EUD1

EUD

(3.17)

Trong , EUD0 l gii hn liu mong mun nu liu a ra l khng ng

nht. Vi vng khi u, EUD phi ln hn gi tr EUD0 c xc nh trc, gi tr

ny ph thuc vo bn cht ca t bo ung th trong khi u. Do , hm mc tiu s

gn tin v gi tr 0 khi gi tr ca EUD0/ EUD nh hn 1 v mc tiu EUD l m

bo an ton. Mt k hoch vi EUD0/ EUD ln hn 1 s c a vo tnh s sai

khc theo phng trnh (3.16) v mc tiu EUD b vi phm. Ngc li, i vi

cc vng cn bo v, EUD c yu cu nh hn so vi mt gi tr EUD0 xc nh

trc ph thuc vo c quan cn bo v. Do , k hoch s a vo tnh ton s

sai khc nh phng trnh (3.17) trong trng hp EUD0 < EUD.

50

3.3.5. H s quan trng (importance factor)

Mc ch ca qu trnh ti u ha trong lp k hoch x tr l thu c s cn

i gia khi u v vng cn bo v. Do , hm mc tiu cui cng thng l s

kt hp ca cc hm mc tiu ring r cho tng c quan. Cch kt hp hm mc

tiu ph bin nht t cc c quan khc nhau l da trn h s quan trng ca c

quan , hay cn gi l trng s ca c quan .

N Mn m

n T m OAR

n=1 m=1

OF= w .OF w .OF

(3.18)

Tuy nhin, mt c quan c th c nhiu iu kin, khi , cng thc trn c

vit li nh sau:

N I M Jni mj

ni T mj OAR

n=1 i=1 m 1 j=1

OF= w .OF w .OF

(3.19)

Trong :

- n

TOF v m

OAROF l cc hm mc tiu tng ng cho khi u th n v c quan

cn bo v th m.

- niw , mjw ln lt l trng s ca yu cu th i i vi th tch khi u th n,

v yu cu th j ca th tch cn bo v th m.

Vic a ra cc trng s ny gip ngi lp k hoch c th chnh sa k

hoch ci thin cht lng t c. Nhng mc tiu no yu cu cn phi t

c ln, th trng s a ra cho mc tiu cng ln. Nhng mc tiu t quan

trng hn s c trng s thp hn. Nu k hoch khng c chp nhn sau qu

trnh ti u ha IMRT, ta c th thay i li trng s hoc cc mc tiu t c

k hoch mong mun [8].

3.4. Thut ton ti u ha trc tip m (DAO)

Trong bi ton ngc c trnh by trn, cc chm tia c chia nh

thnh nhiu chm tia n v, liu lng tng ng ca cc chm tia n v ny

c tnh ton trc khi qu trnh ti u ha din ra. Trong qu trnh ti u ha, cc

k hoch khc nhau c to ra trong qu trnh di chuyn cc l ngm, cht lng

ca tng k hoch thu c s c lu gi li da trn cc yu cu ch nh ban

51

u. Sau khi kt thc qu trnh ti u ha, da vo v tr cc l ngm di chuyn

trong qu trnh ti u ha, n to nn mt bn phn b cng chm tia. V tr

ca cc l ngm tng ng vi cc ln m trng chiu lin tip ca ngm v c

gi l tng phn on trng chiu (segment) [3].

Hnh 3.12: Quy trnh thut ton DAO

Thut ton DAO l thut ton m t chi tit cch thc di chuyn ca cc l

ngm trong sut qu trnh ti u ha. ng thi, thut ton ny s la chn kt qu

ti u nht thng qua vic nh gi hm mc tiu. K hoch no c gi tr hm mc

tiu thp nht s c chn.

Thut ton DAO c trin khai da trn cc thng s u vo ca bi ton

ngc. N yu cu ba thng s u vo: S lng chm tia, nng lng chm tia v

hng chiu cc chm tia. Ba thng s ny s c ngi lp k hoch thit lp

trc tin ph thuc vo kinh nghim v s hiu bit lm sng. Hnh 3.12 m t

tin trnh ca thut ton DAO. Ban u cc l ngm c m ra sao cho n m kht

vi hnh dng khi u, qu trnh ti u s c bt u bng vic tnh ton hm mc

tiu t v tr ban u ca cc l ngm [8].

Trng chiu

khi to

Thay i hnh dng trng chiu

khi to Tnh ton liu

Hm mc tiu

Dng qu trnh ti u

khi to

Kt thc

Khng

C

52

Hnh 3.13: Bc u tin trong qu trnh ti u

Sau thut ton s duyt qua tt c cc gi tr ca cc bin ca n, cc bin

y gm: m ca trng chiu v trng s ca m . Trng s ca mt

trng chiu y c th hiu l thi gian hay s ln m ca trng chiu .

Trong qu trnh ti u ha, cc l ngm c chn v di chuyn mt cch ngu

nhin, t to nn cc hnh dng trng chiu khc nhau. Cc l ngm c

la chn di chuyn ngu nhin theo hm phn b Gaussian, cn khong cch mi

ln di chuyn ca l ngm c la chn c xc nh theo cng thc:

step

succ 0n / T1 A 1 e

(3.20)

y, A l m ca trng chiu ti thi im bt u ti u ha, nsucc l s

ln di chuyn ngm to ra c k hoch c gi tr hm mc tiu nh hn gi tr

nh nht hin thi ca n (tc l to c ra k hoch tt hn), step

0T phn nh s cho

php di chuyn l ngm mt khong nhiu hay t, khi qu trnh ti u cng gn ti

gi tr ti u th gi tr step

0T ny cng nh. Khi nsucc th 1. trnh trng

hp cc phn on trng chiu c kch thc qu nh, ngi ta thng chn gii

53

hn ti thiu cho m ca cc phn on trng chiu trc khi tin hnh ti u

ha. Do , sau khi tnh ton c khong dch chuyn ngu nhin ca l ngm bt

k no , thut ton s tnh c kch thc ca segement sau khi dch chuyn v

so snh vi m ti thiu cho php (v d 3x3 cm2). Nu m ca phn on

trng chiu nh hn m ti thiu, th thut ton s t ng la chn ngu

nhin li mt l ngm bt k, v tnh ton dch chuyn ngu nhin cho l ngm

. Nu m ca phn on trng chiu ln hn hoc bng m ti thiu

cho php, th thut ton s chuyn sang bc tip theo l tnh gi tr hm mc tiu.

Sau khi di chuyn v tr l ngm, hm mc tiu OF c tnh ton li, v tr l

ngm va di chuyn ti c chp nhn nu nh gi tr hm mc tiu OF l gim

dn. Ngc li, nu gi tr hm mc tiu khng gim th v tr mi ca l ngm

c chp nhn vi xc sut P c tnh theo cng thc sau:

prob01/ T

succ

1P B

(n 1)

(3.21)

y B l xc sut ti thi im bt u ti u ha, nsucc v T0pro

c ngha

ging vi cng thc tnh khong di chuyn ca l ngm bn trn. Khi nsucc th

P0.

Hnh 3.14: Cc tiu a phng v cc tiu ton cc

54

Vic chp nhn v tr ca l ngm vi xc sut P nhm mc ch vt qua

c cc trng hp m hm mc tiu ang t trng thi cc tiu a phng (min

local) hi vng tm c gi tr cc tiu ton cc (min global) trong cc ln di

chuyn v tr l ngm tip theo (hnh 3.14).

Kt thc qu trnh ti u ha, chng ta thu c k hoch m gi tr hm mc

tiu l nh nht, hay ni cch khc, k hoch thu c l k hoch c biu phn

b liu lng gn ging nht so vi yu cu t ra ban u. Khi bn phn b

cng chm tia cng c ti u v n c to thnh nh vic chng chp cc

trng chiu lin tip vi m khc nhau c to ra trong qu trnh ti u ha

(hnh 3.15).

Hnh 3.15: Cc phn on trng chiu (segment) v bn cng

55

CHNG 4

NG DNG K THUT X TR JO-IMRT V KT QU O

THC NGHIM TI BNH VIN A KHOA NG NAI

Trong chng ny, chng ti tin hnh lp k hoch x tr trn phn mm

Prowess panther cho bnh nhn bng k thut x tr JO-IMRT so snh vi k

thut x tr 3D-CRT. Da trn kt qu thu c, chng ti thy rng k thut x tr

JO-IMRT cho kt qu tt hn hn so vi k thut x tr thng thng (3D-CRT).

ng thi, chng ti cng tin hnh o thc nghim ti khoa Y hc Ht nhn, bnh

vin a khoa ng Nai nh gi sai s gia liu tnh ton c da trn phn

mm Prowess panther vi liu o thc nghim thu c cho cc k hoch x tr

c thit lp bng phng php JO-IMRT. Nu kt qu thu c c sai s nh hn

5% l chp nhn c, nu kt qu sai s ln hn 5% l khng chp nhn c

(theo tiu chun ca IAEA).

4.1. Trang thit b cn thit trin khai k thut x tr JO-IMRT

c th trin khai k thut x tr iu bin cng ch bng cc ngm

chuyn ng (JO-IMRT) cn phi c cc trang thit b sau :

- My gia tc x tr vi h thng cc ngm c lp (independent jaws).

- My m phng ct lp (CT-SIM).

- H thng phn mm lp k hoch thc hin c JO-IMRT.

- H thng thit b dng kim tra cht lng k hoch iu tr (QA):

Phantom, my o liu, u d, ...

4.2. Quy trnh k thut x tr iu bin cng (JO-IMRT)

Bc u tin trong quy trnh k thut IMRT l vic s dng cc dng c

c nh bnh nhn. Vic nh v v c nh bnh nhn ngy cng quan trng v v tr

v t th ca bnh nhn lin quan n s chnh lch liu lng ngay trong th tch

khi u v gia th tch khi u vi cc t chc nguy cp lin k.

Bc tip theo l chp CT m phng vi phng tin c nh, sau chuyn

ton b hnh nh CT m phng vo my tnh lp k hoch x tr (hnh 4.1).

56

Hnh 4.1: Quy trnh k thut x tr JO-IMRT

4.2.1. Lp k hoch x tr JO-IMRT vi phn mm Prowess panther

Nm 2006, John Nguyen, nh pht minh ngi M gc Vit, a ra k

thut IMRT c th thc hin c vi my gia tc khng c MLC bng vic s

dng h thng cc ngm chuyn ng c lp, chnh l k thut JO-IMRT. Pht

minh ny c cp bng sng ch ti M vo nm 2006 [6].

Cng ging nh lp k hoch x tr thng thng, u phi qua cc bc nh:

Xc nh th tch khi u (bia): GTV, CTV, PTV, v th tch cc c quan cn c

bo v, cng vi s hiu bit r rng v liu ch nh cho khi u v liu gii hn

chu ng cho php i vi cc c quan. im khc nhau gia lp k hoch x tr

thng thng v lp k hoch IMRT th hin ch thit lp trng chiu v qu

trnh ti u ha k hoch. Tu tng v tr khi u so vi cc c quan cn c bo v,

xc nh s trng chiu vi cc gc chiu khc nhau, mi trng chiu c th t 5-

9 phn on trng chiu (segments). V d: Vi ung th vm, chng ti s dng 7

trng chiu: 720, 1000, 1550, 1800, 2100, 2650, 3000. Mi trng chiu chia lm 7

C nh bnh nhn

Chp CT m phng

Lp k hoch JO-IMRT

o liu kim tra (QA)

Tin hnh iu tr

57

phn on trng chiu. Vy tng cng c 49 phn on trng chiu trong