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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.
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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.

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  • 1. 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. Golam Abu Zakaria Professor & Head Gummersbach Hospital, Academic Teaching Hospital of the University of Cologne Germany M. Anwarul Islam Medical Physicist SQUARE Hospitals Ltd Dhaka-Bangladesh Supervised by Presented by
  • 2. 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
  • 3. 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
  • 4.
    • 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
  • 5. 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)
  • 6.
    • 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
  • 7. Why more shielding required for IMRT ?? 3 - 5 times more for IMRT than 3DCRT Linac head leakage Similar for both modalities Scattered radiation by primary barrier Similar for 3DCRT & IMRT Scattering radiation by patient Similar for DCRT & IMRT. Workload is equal for both modalities for primary shielding thickness calculation Delivered dose to the tumor per fraction Comments Shielding features
  • 8. Findings
    • 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):
  • 9. Cont.
    • Treatment with 10MV beam
    • Average field size: 13.6cm х 13.8 cm
    • Maximum field size: 24.8cm х 24.8cm
  • 10.
    • IAEA recommendation: 0.25 for primary beam of all angle (0º, 90º, 180º, 270º)
    Barrier Use Factors Calculated data (Use factors calculated from angle wise MU delivery data) 0.25 0.19 Floor 316º-45º 0.25 0.33 Vertical wall 226º-315º 0.25 0.15 Roof 136º-225º 0.25 0.33 Vertical wall 46º-135º 3DCRT With 6MV and 10 MV IAEA Calculated Use factor Primary barrier Gantry Angle, deg Modality
  • 11. Cont. Vertical Wall Vertical Wall Roof Floor
  • 12.
    • Workload depends on
    • - working hour per day
    • - no. patients treat per day
    • - working day per week
    Workload
  • 13.
    • 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 1000 Gy/week used with 6MV for 3DCRT and 600 Gy/week used for higher energ
    Calculated Workload
  • 14.
    • Calculated IMRT factor, C 1 = 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 center
  • 15. 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)
  • 16. 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 treatments
  • 17.
    • Considering Maximum dose rate = 600MU/Min
    • 1 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
  • 18. Calculated IDR for design limit Output dose rate of the machine = 600MU/Min 1 facilities available only for 3DCRT / 2D 2 if all treatments with IMRT IDR<80 IDR<4 IMRT center 2 IDR<194 IDR<10 3DCRT center 1 Occupational Area Public Area Calculated IDR (in µSv/h) for design limit Treatment Modalities
  • 19. Permissible design limit (Output dose rate of the machine is not mentioned here) (Reference: IAEA Safety Series No. 47) 10mSv/y 6 mSv/y IDR<7.5 --- Occupational IDR<10 1mSv/y IDR<20 IDR<7.5 TADR<0.5 TADR2000<0.15 --- Public N/A Bangladesh USA UK IAEA Permisible Design Limit (in µSv/h) Occupancy Area Treatment Modalities
  • 20. Conclusion
    • The IDR Survey (by NSRC) results in front of the door & linac control room was < 4 μ Sv/h
    • (FS= 40 х 40 cm 2 , E = 10MV, DR = 600 MU/Min, G.A = 0º, 90º, 180º, 270º)
  • 21. 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.
  • 22.  

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