Post on 03-Jun-2015
Presented by Supervised by
M. Anwarul Islam
Medical Physicist
SQUARE Hospitals Ltd
Dhaka-Bangladesh
Golam Abu Zakaria
Professor & Head
Gummersbach Hospital, Academic Teaching Hospital of the University of Cologne Germany
Comparison of input values of shielding design parameters for medical linac with IAEA Safety Report Series 47 and calculated values of shielding parameters with treatment delivered data
from Square Hospitals.
Comparison of input values of shielding design parameters for medical linac with IAEA Safety Report Series 47 and calculated values of shielding parameters with treatment delivered data
from Square Hospitals.
Objectives
• Optimal protection to the radiation worker & public
• Easy handling to regulatory compliance
• Feasibility check to IMRT up gradation
• Optimal RT service delivery with 3DCRT & IMRT
• Avoidance the unnecessary shielding cost
Method & Materials
• More than 800 radiotherapy patient’s data analyzed from SQUARE hospitals ltd
• Analyzed field sizes, gantry angles, photon energy, delivered monitor units and dose
• Analyzed average treatment time for 3DCRT and IMRT
• Calculated maximum treatment capacities per day for all modalities
• Calculated possible maximum beam ON time for 1 year of treatments
• Calculated Instantaneous Dose Rate (IDR) to follow the IAEA protocol
(1mSv/y for public and 20mSv/y for occupational dose limit)
Method & Materials
IAEA Shielding Calculation Parameters
• Yearly radiation dose limit for radiation worker (≤20mSv/year) & public (≤1mSv/year)
• Maximum workload of the machine /week- depends on the number of patients treating / week
- treatment modalities (3DCRT/IMRT)
• Use factor of the barrier (primary -1/4 & secondary -1)
• Occupancy factor (occupational nature, out side of the barrier. Example: office, reception, shop-1, corridors-1/4, toilets, stairways-1/16 etc)
• Energy of the machine
IAEA Shielding Calculation Parameters
Why more shielding required for IMRT ??
Shielding features Comments
Delivered dose to the tumor per fraction
Similar for DCRT & IMRT. Workload is equal for both modalities for primary shielding thickness calculation
Scattering radiation by patient
Similar for 3DCRT & IMRT
Scattered radiation by primary barrier
Similar for both modalities
Linac head leakage 3 - 5 times more for IMRT than 3DCRT
FindingsFindings
Analyzed 1608 treatment fields Average field size: 13.9cm х 16.6 cm
Maximum field size: 22.6cm х 27.4cm
IAEA recommendation: 40cm х 40cm
Field Size (3DCRT/2D treatment with 6MV):
Cont.Cont.
Treatment with 10MV beam
Average field size: 13.6cm х 13.8 cm Maximum field size: 24.8cm х 24.8cm
IAEA recommendation: 0.25 for primary beam of all angle (0º, 90º, 180º, 270º)
Barrier Use FactorsBarrier Use Factors
Calculated dataCalculated data
Modality Gantry Angle, deg
Primary barrier Calculated Use factor
IAEA
3DCRTWith6MV and10 MV
46º-135º Vertical wall 0.33 0.25
136º-225º Roof 0.15 0.25
226º-315º Vertical wall 0.33 0.25
316º-45º Floor 0.19 0.25
(Use factors calculated from angle wise MU delivery data)
Cont.Cont.
Ver
tical
Wal
l
Ver
tical
Wal
l
Roof
Floor
• Workload depends on
- working hour per day
- no. patients treat per day
- working day per week
Workload
The calculated maximum workload was found to be 740 Gy / week and 500 Gy / week for 3DCRT with 6MV and 10MV respectively
IAEA recommendation Workload usually 1000Gy/week used with 6MV for
3DCRT and 600Gy/week used for higher energ
Calculated Workload
• Calculated IMRT factor, C1 = 4.36
• Calculated workload = 1800 Gy/Week
The workload for IMRT is applicable to calculate the shielding thickness against the head leakage radiation only.
Leakage radiation is generally (0.1-0.2)% of useful beam
Cont.
Workload for IMRT centerWorkload for IMRT center
Treatment time basis workload
Average treatment time/patient was 9.64 Min
Average MU delivered /treatment was 297
2D/3DCRT treatment capacity per day (8h) = 50
Workload = 148Gy/Day i.e 740Gy/week
(3DCRT/2D treatments)(3DCRT/2D treatments)
Cont.
Average treatment time/patient was 16.92 Min
Average MU delivered /treatment was 1285
IMRT treatment capacity per day (8h) = 28
Workload = 360Gy/day i.e 1800Gy/week
IMRT treatmentsIMRT treatments
• Considering Maximum dose rate = 600MU/Min1 MU ≈ 1cGy at isocenter of the machine
• Max. Beam ON time for 3DCRT/2D = 102 hour/year(when machine fully occupied with 3DCRT/2D treatment only)
• Max. Beam ON time for IMRT = 253 hour/year(when machine fully occupied with IMRT treatment only)
The proposed design limit for IDR is following an IAEA recommendation with 1 mSv/year for public and 20
mSv/year for occupational workers
IDR calculation for design limit
Calculated IDR for design limit
Treatment Modalities
Calculated IDR (in µSv/h) for design limit
Public Area Occupational Area
3DCRT center1 IDR<10 IDR<194
IMRT center2 IDR<4 IDR<80Output dose rate of the machine = 600MU/Min
1 facilities available only for 3DCRT / 2D
2 if all treatments with IMRT
Permissible design limit
Treatment Modalities
Occupancy Area Permisible Design Limit (in µSv/h)
IAEA UK USA Bangladesh
N/A
Public---
IDR<7.5TADR<0.5TADR2000<0.15
1mSv/yIDR<20
IDR<10
Occupational---
6 mSv/yIDR<7.5
10mSv/y
(Output dose rate of the machine is not mentioned here)
(Reference: IAEA Safety Series No. 47)
Conclusion
The IDR Survey (by NSRC) results in front of the door & linac control room was < 4 μSv/h
(FS= 40 х 40 cm2, E = 10MV, DR = 600 MU/Min, G.A = 0º, 90º, 180º, 270º)
Cont.
The calculated radiation dose at the near door & control room of SQUARE hospital was found to be 0.2 mSv/year
(Data analyzed within the year of 2010 and 2011 in the basis of the total MU delivered within this time
and NSRC survey data)
Finally, the study reveals that the radiotherapy department in Square hospital is sufficiently
radiation protected for radiation workers and public.