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Session: Therapy General ePoster Viewing [Return to Session]

Development of In-Air Film Dosimetry Approach for Quality Assurance of Cs-137 Blood Irradiators

H Moktan, S H Cho*, UT MD Anderson Cancer Center, Houston, TX


PO-GePV-T-84 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: To develop in-air film dosimetry approach for quality assurance (QA) of Cs-137 blood irradiators with radiochromic film measurements in air.

Methods: The custom-made film cassette made of two thin (0.8mm) Lexan sheets contained seven dose measurement regions; one at the center (rectangular - 9.7cm above the bottom of the stainless steel canister) and six at off-center locations (circular - 2.5 and 5cm lateral to the center, and 8 cm above and below the center). To measure the dose rate/distribution of Cs-137 blood irradiators, a GAFChromic EBT3 film was sandwiched within the cassette and placed diametrically vertical inside the canister. The canister was filled with water for standard in-water measurements and left empty for in-air measurements. The films were irradiated to deliver the desired dose (~8 Gy) based on the manufacturer-quoted dose rate. 24 hours after the irradiation, the films were read using a commercial scanner. The film optical densities corresponding to the dose measurement regions were converted to the doses using the film calibration curve that was verified on the date of measurement by exposing two pieces (2cm x 2cm each) of the same film to a known dose (~8 Gy) using the reference Cs-137 irradiator. The in-water and in-air measurements were used to estimate the air-to-water dose conversion factors for respective dose measurement regions. These air-to-water dose conversion factors were applied to subsequent in-air dosimetry measurement results.

Results: The central dose rate measured in the air-filled canister with EBT3 and converted to that in the water-filled canister, agreed well (within ±1%) with the manufacturer-stated value. The off-center %doses also agreed well (within ±3%) with the manufacturer-stated values.

Conclusion: The developed in-air film dosimetry approach was found to be reliable, and allowed for in-air film measurements, eliminating the need for in-water measurements thereby facilitating QA of Cs-137 blood irradiators.


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