STRUCTURAL SHIELDING DESIGN FOR FFF LINACS (NCRP-151) · from a flattening filter free clinical...
Transcript of STRUCTURAL SHIELDING DESIGN FOR FFF LINACS (NCRP-151) · from a flattening filter free clinical...
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STRUCTURAL SHIELDING DESIGN FOR
FFF LINACS (NCRP-151)
David Sánchez Artuñedo
30/11/2017
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Index
1. Introduction
2. Workload, Use factor, Occupancy factors
3. Calculation methods (primary and secondary barriers)
4. FFF vault shielding
5. Examples
6. Conclusions
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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
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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
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2.Workload (W) IMRT, VMAT
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2.Use factors
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2.Occupancy factors
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3. Primary barriers
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3. Secondary barriers (patient scattered)
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3. Secondary barriers (leakeage)
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3. Doors and Mazes (Low-Energy linacs)
LTPSLSS HHHH
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3. Doors and Mazes (Low-Energy linacs)
ncgLTPSLSS HHHHHH
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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
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4. FFF Primary beam
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4. FFF Patient scattered radiation
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4. FFF Patient scattered radiation
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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.”
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4. FFF Head-leackage
5
1.11 6MV
1.40 18MV
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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
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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
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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
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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
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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
50% FFF 50% FF 3 cm concrete
100% FFF 7 cm concrete
nTVL≈ 3-4
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5. Example 2:HUVH SE-Secondary
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
80% FFF 20% FF 1 cm concrete
50% FFF 50% FF 3 cm concrete
100% FFF 7 cm concrete
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5. Example 2:HUVH SE-Secondary
Location 4 corridor
W 0% FFF 20%FFF 50%FFF 100% FFF
H(µSv/week) 8.78 8.019 6.877 4.974
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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*
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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
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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
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5. Example 3:HUVH DE-secondary
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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
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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*
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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
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FF shielding > FFF shielding
FFF new vault designs
Conservative assumption FF
6. Conclusions