IDR Presentation

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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 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.

Transcript of IDR Presentation

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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.

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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

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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

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• 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

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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)

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• 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

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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

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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:

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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)

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• 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

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Angle wise MU delivered (3DCRT)

316º - 45º

226º - 315º

136º - 225º

46º - 135º

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Workload

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

Shielding features

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• 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

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• 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

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• 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

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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

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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

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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

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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

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• Regulatory authority assess the radiation safety requirements.

IAEA Guideline

Licensing Issue for RT operations

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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 ???

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Recommended Dose Limit

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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

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• 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

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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

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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

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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

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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

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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 . . .

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