IDR Presentation
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Transcript of IDR Presentation
Presented by Supervised byM. Anwarul IslamMedical PhysicistSQUARE Hospitals LtdDhaka-Bangladesh
Golam Abu ZakariaProfessor & HeadGummersbach Hospital, Academic Teaching Hospital of the University of Cologne Germany
Justification of Instantaneous Dose Rate (IDR) basis design limits for radiation shielding calculation and determination of a formula for workload calculation
applicable for all treatment modalities.
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 400 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 CommentsDelivered 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 DCRT & IMRT
Scattered radiation by primary barrier
Similar for both modalities
Linac head leakage 3 - 5 times more for IMRT than 3DCRT
Shielding features
• IAEA recommendation: 40cm х 40cm
• Calculated data from SQUARE Hospitals:We analyzed 756 fields with 3DCRT /2D treatments
Average field size: 13.81cm х 15.55cmMaximum field size: 27.4cm х 24.8cm
Field Size:
Shielding featuresField Size Effects:
Field Size VS Shielding Thickness
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 200 400 600 800 1000 1200 1400 1600 1800
Field Size (F)
Shie
ldin
g Th
ickn
ess
(S)
• IAEA recommendation: 0.25 for primary beam of all angle (0º, 90º, 180º, 270º)
Shielding featuresBarrier Use Factor:Barrier Use Factor:
Calculated data from Calculated data from SQUARESQUARE Hospitals: Hospitals:3DCRT3DCRT IMRTIMRT
Use factor for Use factor for 0º0º (316º-45º) = 0.19 (316º-45º) = 0.19 0.200.20Use factor for Use factor for 90º90º (46º-135º) = 0.33 (46º-135º) = 0.33 0.310.31Use factor for Use factor for 180º180º (136º-225º) = 0.15 (136º-225º) = 0.15 0.290.29Use factor for Use factor for 270º270º (226º-315º) = 0.33 (226º-315º) = 0.33 0.210.21
Combined use factor ≈ 0.25Combined use factor ≈ 0.25
Angle wise MU delivered (3DCRT)
316º - 45º
226º - 315º
136º - 225º
46º - 135º
Workload
• Workload depends on- working hour per day- no. patients treat per day- working day per week
Shielding features
• Workload usually 1000Gy/week used with 6MV for 3DCRT and 600Gy/week used for higher energy
• We calculated maximum workload 740Gy / week for 3DCRT
Shielding features
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
Shielding featuresWorkload for IMRT center
• The calculated workload is √2 times more for 6MV than 10MVThe relation between the workload for 6MV and 10MV is W6mv = √2 W10mv
where W6mv is the workload for 6MV energy W10mv is the workload for 10MV energy
Workload for 6MV & 10MV
Treatment time basis workload
RT data analyzed from SQUARE Hospitals Ltd
• Average treatment time/patient for 3DCRT/2D is 9.64 Min
• Average MU delivered /treatment for 3DCRT/2D = 297
2D/3DCRT treatment capacity per day (8h) = 50
Workload = 148Gy/Day i.e 740Gy/week
Treatment time basis workload
RT data analyzed from SQUARE Hospitals Ltd
• Average treatment time/patient for IMRT is 16.92 Min
• Average MU delivered /treatment for IMRT = 1285
IMRT treatment capacity per day (8h) = 28
Workload = 360Gy/Day i.e 1800Gy/week
Combined workload for IMRT & 3DCRT
We obtained the following formula to calculate the combined workload or the no. of 3DCRT / IMRT patients reserved for treatment.
WT = 18 T3d + 26 Timrt Gy/dayWhere,
WT = Total workload / dayT3d = Time reserved for 3DCRT/2DTimrt = Time reserved for IMRT
Licensing Issue for RT operations
• Regulatory authority is responsible for license.
• IAEA member country follow the IAEA protocol or national regulations
• Bangladesh follows the Nuclear Safety and Radiation Control Act, 1993 which is similar to the IAEA protocol
• Regulatory authority assess the radiation safety requirements.
IAEA Guideline
Licensing Issue for RT operations
Radiation survey by regulatory authority
• Regulatory authority check the Instantaneous Dose Rate (IDR) around the radiation facilities.
• Permissible IDR limit for photon (Bangladesh) is < 10μSv/h ?? IAEA ??
• Neutron: Regulatory authority expect 0 count /second ??? IAEA ???
Recommended Dose Limit
IDR calculation for design limitCalculated Data from SQUARE Hospitals
• 3DCRT/2D per treatment time = 9.64 Min• IMRT per treatment time = 16.9 Min• MU used per frac. for 3DCRT/2D = 297• MU used per frac. for IMRT = 1285• Total working time = 8 hour = 480 Min
• Machine dose rate during survey = 600MU/Min1 MU ≈ 1cGy at isocenter of the machine
• Beam ON time for 3DCRT/2D = 102 hour/year(when machine fully occupied with 3DCRT/2D treatment only)
• 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<194IMRT center2 IDR<4 IDR<80Output dose rate of the machine is 600MU/Min1 facilities available only for 3DCRT / 2D2 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<10Occupational
--- 6 mSv/yIDR<7.5 10mSv/y
Output dose rate of the machine is not mentioned
Conclusion
• Duration: 7 March, 2010 – 8 March, 2011• Total MU delivered (with all energies &
modalities + IMRT QA) = 3601059• Total dose delivered to the patients &
cubic phantom = 2108655 cGy
Radiotherapy Data Analyzed from SQUARE Hospitals Ltd
Conclusion
• Survey (by NSRC) maxi. IDR in front of the door & linac control room = 02 μS/h(FS= 40 х 40 cm2, E = 10MV, DR = 600 MU/Min, Angles = 0º, 90º, 180º, 270º)
• Calculated dose to the near door & control room = 0.2 mSv for 01 year.
Radiotherapy Data Analyzed from SQUARE Hospitals Ltd
Conclusion• Linac control room & In front of the door completely
“Controlled” area and permissible dose limit = 20mSv/year but radiation dose level is 100 times less. Obviously it is a very safe for us but . . .