Five-Year Reliability Assessment of In-Air Film Dosimetry Approach for Quality Assurance of Cs-137 Blood Irradiators
Abstract
Purpose
To assess the long-term reliability of in-air film dosimetry approach for quality assurance (QA) of Cs-137 blood irradiators using the measured data accumulated over 5 years.
Methods
A new approach based on in-air film dosimetry was developed in 2021 to replace the conventional approach based on in-water film dosimetry for periodic QA of Cs-137 blood irradiators. In the new in-air film dosimetry approach, the air-to-water dose conversion factors were derived from in-water and in-air film measurements performed sequentially using the custom-made film cassette made of two thin Lexan sheets contained seven dose measurement regions; one at the center and six at off-center locations (2.5 and 5cm lateral to the center, and 8 cm above and below the center). Specifically, a GAFChromic EBT3 film was sandwiched within the cassette and placed vertically inside the canister. The canister was filled with water for standard in-water measurements and left empty for in-air measurements. Since its introduction, the new in-air film dosimetry approach has been successfully applied to periodic QA of commercial Cs-137 blood irradiators, providing immediately realizable benefits such as relatively simple, quick, and hassle-free measurements, compared to in-water film measurements. In this work, the long-term reliability of the new approach was assessed based on analysis of our in-air measurement results accumulated over the past 5 years as well as comparison with independent in-water measurement results available from commercial dose mapping service providers.
Results
The central dose rate measured in-air, after conversion to that in water, agreed well (within ~1%) with the reference data. The off-center %doses also agreed well (within ~3%) with the reference data.
Conclusion
The new in-air film dosimetry approach was found to result in consistently good agreement over the past 5 years with the reference data, confirming its effectiveness/robustness for periodic QA of Cs-137 blood irradiators.