IDR Presentation

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    04-Dec-2014
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Transcript of IDR Presentation

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.

Presented byM. Anwarul Islam Medical Physicist SQUARE Hospitals Ltd Dhaka-Bangladesh

Supervised byGolam Abu Zakaria Professor & Head Gummersbach Hospital, Academic Teaching Hospital of the University of Cologne Germany

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 patients 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

Method & Materials 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)

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)

IAEA Shielding Calculation Parameters Use factor of the barrier (primary -1/4 &secondary -1)

Occupancy factor (occupational nature, outside of the barrier. Example: office, reception, shop-1, corridors-1/4, toilets, stairways-1/16 etc)

Energy of the machine

Why more shielding required for IMRT ??Shielding featuresDelivered dose to the tumor per fraction

CommentsSimilar for DCRT & IMRT. Workload is equal for both modalities for primary shielding thickness calculation

Scattering radiation Similar for DCRT & IMRT by patient Scattered radiation Similar for both modalities by primary barrier Linac head leakage 3 - 5 times more for IMRT than 3DCRT

Shielding featuresField Size: IAEA recommendation: 40cm 40cm Calculated data from SQUARE Hospitals: We analyzed 756 fields with 3DCRT /2D treatments Average field size: 13.81cm 15.55cm Maximum field size: 27.4cm 24.8cm

Shielding featuresField Size Effects:Field Size VS Shielding Thickness0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 200 400 600 800 1000 1200 1400 1600 1800

Shielding Thickness (S)

Field Size (F)

Shielding featuresBarrier Use Factor:

IAEA recommendation: 0.25 for primary beam of all angle (0, 90, 180, 270)Calculated data from SQUARE Hospitals:3DCRT IMRT

Use factor for 0 (316-45) = 0.19 0.20 Use factor for 90 (46-135) = 0.33 0.31 Use factor for 180 (136-225) = 0.15 0.29 Use factor for 270 (226-315) = 0.33 0.21 Combined use factor 0.25

Angle wise MU delivered (3DCRT)316 - 45

226 - 315

46 - 135

136 - 225

Shielding featuresWorkload Workload depends on - working hour per day - no. patients treat per day - working day per week

Shielding featuresWorkload 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 featuresWorkload for IMRT center

Calculated IMRT factor, C1 = 4.36 Calculated workload = 1800 Gy/WeekThe 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

Workload for 6MV & 10MV The calculated workload is 2 times more for 6MV than 10MV The relation between the workload for 6MV and 10MV is W6mv = 2 W10mv whereW6mv is the workload for 6MV energy W10mv is the workload for 10MV energy

Treatment time basis workloadRT 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 workloadRT 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 & 3DCRTWe 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 / day T3d = Time reserved for 3DCRT/2D Timrt = 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

Licensing Issue for RT operations Regulatory authority assess the radiation safety requirements. IAEA Guideline

Radiation survey by regulatory authority Regulatory authority check the Instantaneous Dose Rate (IDR) around the radiation facilities. Permissible IDR limit for photon (Bangladesh) is < 10Sv/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

IDR calculation for design limit Machine dose rate during survey = 600MU/Min 1 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

Calculated IDR for design limitTreatment Modalities 3DCRT center1 Calculated IDR (in Sv/h) for design limit Public Area IDR