structural shielding design for fff linacs (ncrp-151) · from a flattening filter free clinical...

STRUCTURAL SHIELDING DESIGN FOR

FFF LINACS (NCRP-151)

David Sánchez Artuñedo

30/11/2017

Index

1. Introduction

2. Workload, Use factor, Occupancy factors

3. Calculation methods (primary and secondary barriers)

4. FFF vault shielding

5. Examples

6. Conclusions

Basic principles:

Distance

Time

Shielding

Shielding design goal:

Controlled Areas 100 µSv/week (5 mSv/year)

Uncontrolled Areas 20 µSv/week ( 1mSv/year)

HUVH: CA 20 µSv/week; UCA 10 µSv/week

Conservative assumptions

1.Introduction

Time integral of the absorbed-dose rate

determined at the depth of the maximum

absorbed dose.

NCRP 151

2.Workload (W)

W=1000 Gy/week E10 MV

2.Workload (W) IMRT, VMAT

2.Use factors

2.Occupancy factors

3. Primary barriers

3. Secondary barriers (patient scattered)

3. Secondary barriers (leakeage)

3. Doors and Mazes (Low-Energy linacs)

LTPSLSS HHHH

3. Doors and Mazes (Low-Energy linacs)

ncgLTPSLSS HHHHHH

KRY, Stephen F., et al. Treatment vault shielding

for a flattening filter-free medical linear

accelerator. Physics in medicine and biology, 2009,

54.5: 1265.

4. FFF vault shielding

PDD (6MV FFF) ≈ PDD(4MV)

BEAMnrc

6, 10, 18 MV

FF and FFF scaled to match FF NCRP data

4. FFF Primary beam

4. FFF Patient scattered radiation

4. FFF Head-leackage

VASSILIEV, Oleg N., et al. Dosimetric properties of photon beams

from a flattening filter free clinical accelerator. Physics in medicine

and biology, 2006, 51.7: 1907.

5 NCRP

Prostate, lung, spineliver

and head and neck plans

“The same TVL for head leakage was used with and without the flattening filter because the flattening filter produces or interacts with only a portion of head leakage.”

4. FFF Head-leackage

5

1.11 6MV

1.40 18MV

4. FFF Neutron production

KRY, Stephen F., et al. Energy spectra, sources, and shielding

considerations for neutrons generated by a flattening filter‐free Clinac. Medical physics, 2008, 35.5: 1906-1911.

•Clinac 21EX 18 MV 5000 MU

•Gold foild activation in Bonner spheres

•MCNPX V2.5

FF FFF

Fluence

(isocenter)(n/cm2/MU)

1.06 e05 7.47e04

(Fluence 18 MV FFF)= Fluence 18 MV FF/3.7

5. Example 2:HUVH Single Energy (SE)

Muelle de carga

Pasillo RT

Pa

sillo

R

T

Ascensores

Hormigón 2.3 g/cm3

6m

1.45m

1.5m

1.45m

1.51m

1m

4.7

2m

2.36

m

2.3

6m

3.5m 0.62m

0.32m

1.2m

1m

5.68m

1m

6.05m

0.35m

1m

1.94m

1

2

4 5

6

7 8

9

11

10

W=1000 Gy/week 6 MV

WL=3000 Gy/week 6 MV

5. Example 2:HUVH SE-Primary

Location 1

corridor

Location 2 drop

off area

Location 3 roof

P(µSv/week) 20 µSv/sem 10 µSv/sem 10 µSv/sem

Concrete

thickness (cm)

190 180 220

80% FF 20% FFF -3cm concrete

50% FF 50% FFF -9 cm concrete

100% FFF - 30 cm concrete

nTVL≈ 5-6

5. Example 2:HUVH SE-Primary

Location 1 corridor

W

(1000 Gy/week)

0% FFF 20%FFF 50%FFF 100% FFF

H(µSv/week) 12.176 9.866 6.401 0.625

5. Example 2:HUVH SE-Secondary

Location 4

corridor

Location 6

control room

Location 5

elevator

P (µSv/week) 20 µSv/week 20 µSv/week 20 µSv/week

Concrete

thickness (cm)

100 110 110

80% FFF 20% FF 1 cm concrete


100% FFF 7 cm concrete

nTVL≈ 3-4


0% FFF 20%FFF 50%FFF 100%FFF

W (Gy/week)

6

1000 800 500 0

WL(Gy/week)

6

3000 2400 1500 0

W (Gy/week)

6 FFF

0 200 500 1000

WL(Gy/week)

6 FFF

0 340 850 1700



100% FFF 7 cm concrete


Location 4 corridor

W 0% FFF 20%FFF 50%FFF 100% FFF

H(µSv/week) 8.78 8.019 6.877 4.974

5. Example 3:HUVH Dual Energy (DE)-

Primary

W=1000 Gy/week 6 MV

WL=3000 Gy/week 6 MV

W=500 Gy/week 18 MV

WL=500 Gy/week 18 MV*

5. Example 3:HUVH DE-Primary

0% FFF 80%FF

20%FFF

50%FF

50% FFF

100% FFF

Concrete

thickness (cm)

(11.2 µSv/week)

(cm)

245 242 237 223

0% FFF 80%FF

20%FFF

50%FF

50% FFF

100% FFF

H (µSv/week)(245

cm concrete)

11.247 9.683 5.572 3.425

5. Example 3:HUVH DE-Primary

0% FFF 100% FFF

Concrete

thickness (cm)

(11.2 µSv/week)

(cm)

245 223

0% FFF 100% FFF

H (µSv/week)(245

cm concrete)

11.247 3.425

5. Example 3:HUVH DE-secondary

5. Example 3:HUVH -Secondary

0% FFF 80%FF

20%FFF

50%FFF

50% FFF

100% FFF

Concrete

thickness (cm)

(12.854 µSv/week)

(cm)

110 109 108 105

0% FFF 80%FF

20%FFF

50%FFF

50% FFF

100% FFF

H (µSv/week)(135

cm concrete)

12.854 12.091 10.995 9.042

5. Example 3:HUVH DE-maze-door

W=1000 Gy/week 6 MV T=1/8

WL=3000 Gy/week 6 MV P=20 µSv/week

W=500 Gy/week 18 MV

WL=500 Gy/week 18 MV*

5. Example 3:HUVH CF3-Primary

0% FFF 80%FF

20%FFF

50%FFF

50% FFF

100% FFF

Paraffin (mm)

(16.71 µSv/week)

80 75 75 65

Lead (mm)

(16.71µSv/week) 35 35 25 15

0% FFF 80%FF

20%FFF

50%FFF

50% FFF

100% FFF

H (µSv/week)

( paraffin 80mm&

35mm lead)

16.71 14.90 12.18 7.66

FF shielding > FFF shielding

FFF new vault designs

Conservative assumption FF

6. Conclusions

structural shielding design for fff linacs (ncrp-151) · from a flattening filter free clinical...

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