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

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.

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.

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 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

• 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 Comments

Delivered 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 3DCRT & IMRT

Scattered radiation by primary barrier

Similar for both modalities

Linac head leakage 3 - 5 times more for IMRT than 3DCRT

FindingsFindings

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):

Cont.Cont.

Treatment with 10MV beam

Average field size: 13.6cm х 13.8 cm Maximum field size: 24.8cm х 24.8cm

IAEA recommendation: 0.25 for primary beam of all angle (0º, 90º, 180º, 270º)

Barrier Use FactorsBarrier Use Factors

Calculated dataCalculated data

Modality Gantry Angle, deg

Primary barrier Calculated Use factor

IAEA

3DCRTWith6MV and10 MV

46º-135º Vertical wall 0.33 0.25

136º-225º Roof 0.15 0.25

226º-315º Vertical wall 0.33 0.25

316º-45º Floor 0.19 0.25

(Use factors calculated from angle wise MU delivery data)

Cont.Cont.

Ver

tical

Wal

l

Ver

tical

Wal

l

Roof

Floor

• Workload depends on

- working hour per day

- no. patients treat per day

- working day per week

Workload

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 1000Gy/week used with 6MV for

3DCRT and 600Gy/week used for higher energ

Calculated 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

Cont.

Workload for IMRT centerWorkload for IMRT center

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)(3DCRT/2D treatments)

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 treatmentsIMRT treatments

• 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 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<194

IMRT center2 IDR<4 IDR<80Output dose rate of the machine = 600MU/Min

1 facilities available only for 3DCRT / 2D

2 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<10

Occupational---

6 mSv/yIDR<7.5

10mSv/y

(Output dose rate of the machine is not mentioned here)

(Reference: IAEA Safety Series No. 47)

Conclusion

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

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

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.