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Absorbed-Dose Energy Dependence of EBT3 Radiochromic Film Measurements for Ru-106 Eye Plaques

J Hansen

J Hansen*, W Culberson, L DeWerd, Univ of Wisconsin-Madison, Madison, WI


TU-FG-205-1 (Tuesday, August 1, 2017) 1:45 PM - 3:45 PM Room: 205

Purpose: The purpose of this work was to use Monte Carlo methods to simulate the electron energy spectrum from a ¹⁰⁶Ru eye plaque and quantify the expected absorbed-dose energy dependence for EBT3 radiochromic film measurements.

Methods: A custom flat ¹⁰⁶Ru CCB eye plaque was acquired from BEBIG (Berlin, Germany) to carry out planar extrapolation chamber measurements. This source was modeled in the EGSnrc cavity Monte Carlo user code, including beta decay from ¹⁰⁶Ru and ¹⁰⁶Rh as well as gamma decay, characteristic x-rays, Auger electrons, and internal conversion electrons from excited ¹⁰⁶Pd. The electron fluence spectrum was tallied at various depths in a water phantom, and the average electron energy was calculated at each depth. Additionally, simulations were performed to quantify the absorbed-dose energy dependence for surface film measurements with the ¹⁰⁶Ru plaque compared to ⁶⁰Co calibration. Dose was tallied to the active layer of un-laminated EBT3 film and compared with simulated dose to the same volume of water.

Results: Electron energy spectra from the ¹⁰⁶Ru source simulated in EGSnrc exhibited a sharp rise in low energy electrons that decreased with depth in water. The average electron energy ranged from 693 keV at the surface to 291 keV at 1 cm in water. The absorbed-dose energy dependence showed that the ratio of dose-to-film to dose-to-water was 0.972±0.1% for ¹⁰⁶Ru, which agreed closely with the ratio for ⁶⁰Co found previously as 0.973±0.3% for EBT3 film.

Conclusion: Though the shape of the electron fluence spectrum differed from that of secondary charged particles from a ⁶⁰Co beam used for film calibration, the Monte Carlo predicted absorbed-dose energy dependence for film-to-water was found to be the same for ¹⁰⁶Ru surface irradiation and ⁶⁰Co calibration for EBT3 film.

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