shielding design
TRANSCRIPT
Rota%on 13: Shielding Design (Mentors: Edward C Pennington,
Sarah McGuire) By
Vibha Chaswal, Ph.D.
The Problem
40I x 125I area design layout and shielding: • A Dual energy Linear Accelerator room: 6 MV low-‐energy and 18 MV high-‐energy facility.
(IMRT and TBI capable)
• A High Dose rate Brachytherapy Suite: Ir-‐192 • A PET/CT Area
The facility designed
Assump%ons: Linac room Overes%ma%ons in workload
• 8 h day, 5 d week–1, 50 pa%ents per week • Average absorbed dose of 3 Gy delivered at isocenter per pa%ent • 40 % pa%ents 18 MV beam, 60 % treated using 6 MV beam • Maximum absorbed dose output rate at 1 m of 15 Gy/min, and the normal
rate used is 5 Gy/ min • The isocenter is at 1 m from the radia%on source for this facility. • IMRT WorkLoad:
– 80 % of 6MV pa%ents – 24 pa%ents per day treated as IMRT – 40 % of 18 MV pa%ents – 8 pa%ents per day treated as IMRT
• 6 MV TBI beam • Future increase of 18 MV beam to 60% usage Use factor of walls: • Lateral walls: 0.3 as opposed to 0.25 (IMRT usage) Sca`er and Leakage angle of incidence: All sca`er and leakage taken at the minimum angle of incidence
Linac Room
Tedious calcula%ons: watch out for errors!
• The wall adjacent to the HDR vault is calculated for design dose of 0.02 mSv/week, i.e., that of an uncontrolled area.
• This is DEFINITELY a control area in a Radia%on Oncology department. The primary wall thickness for the control area design dose is 173 cm as opposed to 202 cm calculated in the report.
• However, this error lead to an overes%ma%on. An error of the opposite kind will lead to an underes%ma%on of shielding.
• Since this wall is also TBI wall, overes%ma%on is good.
Linac room roof design
4.8 m
6.44 m
1.3m
3.3 m 0.72 m
R Q
2.7 m
1.83 m 2.12 m 2.22 m
2.1 m
Assump%ons: HDR and PET/CT
HDR • HDR Pa%ents per week = 25 • Dose per pa%ent = 10 Gy at 1 cm from the source.
PET/CT
• PET/CT pa%ents: 15 pa%ents/week • F-‐18 FDG dose is 555 MBq (15 mCi) with an uptake %me of 60 min
HDR-‐room
PET holding area and PET-‐CT
Thank You!