comparison of input values of shielding design parameters for medical linac with iaea safety report...

8/3/2019 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 deli

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Presented by Supervised by

M. Anwarul Islam

Medical Physicist

SQUARE Hospitals Ltd

Dhaka-Bangladesh

Email: [email protected]

Golam Abu Zakaria

Professor & Head

Gummersbach Hospital, AcademicTeaching Hospital of the University ofCologne Germany

Comparison of input values of shielding design parameters formedical linac with IAEA Safety Report Series 47 and calculated

values of shielding parameters with treatment delivered datafrom Square Hospitals.


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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 800 radiotherapy patients data

analyzed from SQUARE hospitals ltd

Analyzed field sizes, gantry angles, photonenergy, delivered monitor units and dose

Analyzed average treatment time for3DCRT and IMRT

Calculated maximum treatment capacitiesper dayfor all modalities


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Calculated possible maximum beam ONtime 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 CalculationParameters

Yearly radiation dose limit for radiationworker (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, outside of the barrier. Example: office, reception,shop-1, corridors-1/4, toilets, stairways-1/16 etc)

Energy of the machine

IAEA Shielding CalculationParameters


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Why more shielding required for IMRT ??

Shielding features Comments

Delivered dose tothe tumor perfraction

Similar for DCRT & IMRT. Workload isequal for both modalities for primaryshielding thickness calculation

Scattering radiationby 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


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Findings

Analyzed 1608 treatment fields

Average field size: 13.9cm 16.6 cm

Maximum field size: 22.6cm 27.4cm

IAEA recommendation: 40cm 40cm

Field Size (3DCRT/2D treatment with 6MV):


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Cont.

Treatment with 10MV beam

Average field size: 13.6cm 13.8 cm

Maximum field size: 24.8cm 24.8cm


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IAEA recommendation: 0.25 for primary beam ofall angle (0, 90, 180, 270)

Barrier Use Factors

Calculated dataModality Gantry Angle,

degPrimary barrier Calculated Use

factorIAEA

3DCRT

With

6MV and

10 MV

46-135 Vertical wall 0.33 0.25

136-225 Roof 0.15 0.25

226-315 Vertical wall 0.33 0.25

316-45 Floor 0.19 0.25

(Use factors calculated from angle wise MU delivery data)


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Cont.

VerticalWall

VerticalWall

Roof

Floor


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Workload depends on

- working hour per day

- no. patients treat per day

- working day per week

Workload


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The calculated maximum workload was found tobe 740 Gy / week and 500 Gy / week for 3DCRTwith 6MV and 10MV respectively

IAEA recommendation

Workload usually 1000Gy/week used with 6MV

for 3DCRT and 600Gy/week used for higherenerg

Calculated Workload


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Calculated IMRT factor, C1 = 4.36

Calculated workload = 1800 Gy/Week

The workload for IMRT is applicable to calculatethe shielding thickness against the head leakage

radiation only.Leakage radiation is generally (0.1-0.2)% of

useful beam

Cont.

Workload for IMRT center


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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)


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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


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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 IAEArecommendation 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

TreatmentModalities

Calculated IDR (in Sv/h) fordesign limit

Public Area Occupational Area

3DCRT center1 IDR


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Permissible design limit

TreatmentModalities

OccupancyArea Permisible Design Limit (in Sv/h)

IAEA UK USA Bangladesh

N/A

Public

---

IDR


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Conclusion

The IDR Survey (by NSRC) results in front of thedoor & linac control room was < 4 Sv/h

(FS= 40 40 cm2, E = 10MV, DR = 600 MU/Min,G.A = 0, 90, 180, 270)


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Cont.

The calculated radiation dose at the neardoor & control room of SQUARE hospital wasfound to be 0.2 mSv/year

(Data analyzed within the year of 2010 and 2011 inthe basis of the total MU delivered within this time

and NSRC survey data)

Finally, the study reveals that the radiotherapydepartment in Square hospital is sufficiently

radiation protected for radiation workers and public.


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comparison of input values of shielding design parameters for medical linac with iaea safety report...

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