(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: determine individual beta source characteristics and the subsequent loading pattern to be designated for each of two beta irradiation devices (BRDs) used for research of an animal model of radiation skin injury. To confirm the radiation characteristics of the two BRDs given particular source loading patterns.
Methods: Sr-90 beta sources, serial numbers sequenced from XX49 to XX62, with strength range from 100 +/-10 mCi were positioned in sequence at a fixed geometry above and orthogonal to a Markus chamber. Their relative activities were determined in both charge and current modes. All 14 sources were then separated into low and high activity cohorts of 7 sources each. Based on the 7-source geometry of each BRD, with one middle source symmetrically surrounded by 6 sources, loading patterns were determined with the lowest activity in the middle (central) slot, and the remaining 6 sources placed in alternating ranked order. This arrangement provides the most homogeneous distribution of sources. Three custom-made cone applicators with different heights are switchable to achieve different dose rates. To validate and assure the quality of the radiation characteristics for three BRD devices, dose maps and PDD were measured by GAFChromic™ EBT3 film with a multichannel method for inhomogeneity compensation and the relative dose rates were measured with the Markus chamber cross-calibrated by an extrapolation chamber.
Results: Measured BRD-2 and BRD-3 nominal dose rates of 3.5 Gy/min agreed with analytical modeling, relative to the BRD-1 dose rate of 2.7 Gy/min. Film results showed expected and acceptable performance for flatness and symmetry over the 10 cm² circular beta field, as well as for percent depth dose.
Conclusion: source loading patterns has been determined for two new BRDs. All measured quantities are within tolerance with minimum standard deviation for preclinical research irradiations for the study of cutaneous radiation injury.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by ASPR-BARDA-Argentum Medical, LLC, Contract No. HHS0100201800022C
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