ionization chamber array for external beam radiotherapy

CONFIDENTIAL MATERIAL - 1 -Michele Togno - III ARDENT Annual Meeting, Schwarzenbruck - September, 30th 2014

Ionization Chamber Array for External Beam Radiotherapy

Michele Togno - III ARDENT Annual Meeting, Schwarzenbruck - September, 30th 2014


Project goal

oAbsolute dose measurement

oMachine quality assurance

oPatient quality assurance

MV X-Rays ~100÷230MeV protons

A short summary


Outline

o Experimental Activity• Characterization at IBA DosLab• Characterization at Klinikum rechts der Isar & University

of California (San Francisco)-Radiation Oncology dep.• Characterization at Proton Therapy Center Czech s.r.o.

o ARDENT project: trainings, conferences, secondments

o Ongoing activities and future work


Experimental Activity



Detector evolution

First Prototype

Second Prototype

Measurement setup

o 80 ionization chambers, 3.5mm pitch


Example: two 60Co irradiations (detector biased at 100V).

Current ~ 10pA

Characterization at IBA DosLabPrototype optimization

Main debug issue: time stability of the chamber current.

0 -20 40 60

Sig

nal

(no

rmal

ized

)

Time (s)

0 20 40 60 80 90 100 120 -0.2

0

0

.2

0.4

0

.6

0.8

1

1

.2 Sig

nal

(no

rmal

ized

)

Time (s)

0 50 100 150 200 250 300

0

.92

0.

96

1.0

0

1.0

4

Optimization of signal routing led to a better time stability of the sensor:

o Pretty good stability in time of the signal

o Prompt rise and fall time

Signal about 8pA (@2.2Gy/min)

Sensitivity 200pC/Gy

Fluctuation 0.3% (st.dev.)

60Co, 150V bias, Tint=0.8s


Charge collection efficiency

Characterization at IBA DosLabo Charge collection efficiency higher than 99% already at 150V (99.5% ± 0.3% at 250V)

0 50 100 150 200 250 300 350 400 4500.86

0.88

0.9

0.92

0.94

0.96

0.98

1

Bias voltage (V)

Effi

cien

cy

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1630

640

650

660

670

680

690

700

710

720

730

1/Bias (V-1)

Sig

nal (

pC)

Ion-chamber array data

Linear fit

Theoretical (Boag, 1950)

Measured, ion-chamber array

Elekta Agility linac10MVFFF beam quality2.67mGy/pulse220MU/min


Characterization at IBA DosLabSensitivity dependence on dose per pulse

0 0.5 1 1.5 2 2.5 30.985

0.99

0.995

1

1.005

Dose per pulse (mGy)

Sen

sitiv

ity (

norm

aliz

ed)

10MV FFF beam quality6MV beam quality

Elekta Agility linac

SDD 77cm

SDD 59cm

SDD 150cm

SDD 100cm

o ± 0.8% sensitivity change on dose per pulse in the range 0.09÷2.67mGy/pulse


Characterization at IBA DosLabTissue to phantom ratio measurement

0 50 100 150 200 250 300

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

depth (mm)

TP

R (

norm

aliz

ed to

max

imum

)

ion-chamber arrayIBA PPC05

10 20 30 400.95

0.96

0.97

0.98

0.99

1

1.01

Elekta Agility linac6MV beam quality430 MU/minSDD 100cm10x10cm2 field

o Very good agreement with PPC05 (better than 0.5%) at every depth of measurement


Characterization at IBA DosLabElekta Agility Output Factors

a:Si flat panel, a prototype optimized for dosimetry

-2.4% -3.7%

o Good agreement with reference for small fields, reduced sensitivity with large fields


Characterization at IBA DosLabBeam profiles (photons)

-100 -80 -60 -40 -20 0 20 40 60 80 1000

0.2

0.4

0.6

0.8

1

1.2

Distance from central axis (mm)

Dos

e (n

orm

aliz

ed)

a:Si flat panelIon-chamber arrayMatriXX Evolution

1x1cm2

10x10cm2

Elekta Agility linac6MV beam qualitySDD 100cm@11cm depth


Characterization at MRIMachine QA: virtual wedges, MLC QA, dose in depth (see pics)

-200 -150 -100 -50 0 50 100 150 2000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

position (mm)

pro

file

no

rm

MapCheck21D IC Prototype II

o Secondment, 22nd April - 3rd May, Klinikum rechts der Isar (Munich)

Varian Clinac DHX

MapCheck2 (SunNuclear) diode array


Characterization at MRI

-100 -50 0 50 100-0.2

0

0.2

0.4

0.6

0.8

1

1.2

position (mm)

dose

pro

file

norm

aliz

ed to

max

imum

MapCheck2EBT31D IC array

Example of patient QA

Varian Trilogy, Millennium MLC,VMAT delivery technique

50 100 150 200 250 300 350 400 450 500 550

50

100

150

200

250

300

350

400

EBT3


Characterization at UCSFClinical tests & clinical training

o Secondment, 28th July - 8th August, UCSF department of Radiation Oncology;o Detector characterization through clinical test;o Clinical training:

• Machine QA;• Introductory training to Pinnacle TPS;• Use of gafchromic films;• Joined the daily activity of medical physicists.


Characterization at UCSFExample of small field dosimetry and linac commissioning

-25 -20 -15 -10 -5 0 5 10 15 20 25

0

0.1

0.2

0.3

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0.5

0.6

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0.9

1

distance from central axis (mm)

pro

file

(n

orm

aliz

ed

)

Varian TrueBeam facility - UCSFTrueBeam,6MV, 1cmx1cm, SDD=110cm, depth of measurement=10cm

1D IC arrayEBT2a:Si flat panel

-100 -80 -60 -40 -20 0 20 40 60 80 100

0.2

0.4

0.6

0.8

1

1.2


pro

file

(n

orm

aliz

ed

)

Varian TrueBeam facility - UCSFTrueBeam,6MV, 10cmx10cm, 45°vw, SDD=110cm, depth of measurement=10cm

1D IC arraya:Si flat panelWP

1x1cm2

Virtual wedge 45°

Varian TrueBeam


Example of linac commissioning measurement

Characterization at UCSF

-100 -80 -60 -40 -20 0 20 40 60 80 1000

0.2

0.4

0.6

0.8

1

1.2


pro

file

(n

orm

aliz

ed

)

Varian TrueBeam facility - UCSFTrueBeam,6MV, 10cmx10cm, SDD=110cm, depth of measurement=10cm

-100 -80 -60 -40 -20 0 20 40 60 80 100-5

0

5

10


diff

ere

nce

(%

)

1D IC arraya:Si flat panelWater phantom

a:Si - WP1D IC array - WP

Water phantom as reference


Characterization at PTC czech s.r.o.

PBS mode only

1ms pulse duration,

10ms pulse period,

3.5mm spot at 226MeV

10-1

100

101

101

102

103

PPC05 charge (nC)

IC a

rra

y si

gn

al (

pC

)

Linear fitIC array

0.02-2MU/spot33x17 spot mapOutput norm. to 1MU/spot

-0.04%

1.7%

-0.9% 0.8%

-0.1%

-0.05%

0.01%

PPC05 signal (nC)

IC a

rra

y si

gnal

(pC

)Ref detector: PPC05

Dose linearity


Beam profiles (protons)

-80 -60 -40 -20 0 20 40 60 80

0

0.2

0.4

0.6

0.8

1

Distance from central axis (mm)

Dos

e (n

orm

aliz

ed)

Ion-chamber arrayMatriXX PTLynx

PBS mode, 226MeV, 5nA beam current@11mm depth

Characterization at PTC czech s.r.o.

Lynx: a scintillator based detector for PBS mode machine QA


Ongoing activities/Future work

o Long term stability measurements with 60Co

o Further test with PBS proton beams;

o Paper about the characterization of the 1D IC array prototype;

o Extend the technology to a 2D detector - components drawing already started, first prototype assembling foreseen for the end of the year.


Trainings, conferences, secondments…



Secondments

Klinikum rechts der Isar, Munich (22.04 - 03.05.2014)

UCSF RadOnc dep., S.Francisco (28.07 - 08.09.2014)

o Upcoming:

• B&A secondment at STMicroelectronics (Catania, July 2015 tentative)

• UCSF (early 2015 tentative)


Conferences, trainings…

o AAPM, Austin (TX), 20.07 - 25.07.2014

Poster presentation: “An Ionization Chamber Array with High Spatial Resolution for External Beam Radiotherapy”, M.Togno, D.Menichelli, J.J.Wilkens.

Upcoming: AAPM 2015, …

o Trainings:• Clinical trainings at MRI & UCSF (already mentioned);• Radiation protection training (IBA Dosimetry);• Training on SBRT radiotherapy technique (Klinikum rechts der Isar);

• ARDENT B&A training (CERN): Technology Transfer, Management, Entrepreneurship.

o PhD activities: already spent more than 2 weeks at the University to teach students at physics labs.


Thank you!


ionization chamber array for external beam radiotherapy

Documents

ardent annual meeting

ardent project

mgypulseconfidential

pitchconfidential material

time signal

iba doslabcharacterization

iba doslabtissue

signal normalizedtime