X Chang*, L Huang, Y Cao, J Liu, J Chang, Northwell Health, Lake Success, NY

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  X Chang

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PO-GePV-T-29 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: To study the energy dependence of EBT-3 films for dosimetric measurements of a Y-90 disc source by comparing the measured percent depth dose (PDD) curves with that obtained from Monte Carlo simulations.

Methods: The PDD curve along the central axis was measured in water with Gafchromic EBT-3 (type1: Palmer) films. Monte Carlo simulations using Geant4 were performed for PDD calculations for the same (source, water phantom, EBT-3 films) geometry. Simulations were also performed for another type (type2: Bekerat, with different contents in the active layer) of EBT-3 film to study the energy dependence. Data from multiple measurements for small and large depths were combined to minimize the influences from film aging and background noise.

Results: The code was first validated by comparing the simulated PDDs of other sources already published in TG43/ICRU72; the agreements were very good (better than 1%), The simulated PDD curves along the central axis of the Y-90 disc agreed well with the measurements for the first 4.5 millimeters (maximum difference +/-10%). The simulated PDDs for the two types of EBT-3 films agreed well with each other up to 6 mm (better than +/- 10 %), and the shapes of energy spectrum were similar for water, two film types. The mean energy was 589, 465, and 341 keV at 3, 5, and 7 mm for electrons and 150 +/- 10 keV for photons at depth > 3 mm.

Conclusion: EBT-3 films can be used to measure the PDD curve of this new Y-90 disk source up to 6 mm where the film energy dependent response is minimal. The simulated PDD curves agreed well with film measurements up to 4.5 mm. Deviation from 4.5-7 mm might be caused by the relative larger uncertainties of measurements in this region.

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