Characterization of a Fiber Optic Coupled Dosimeter for Clinical Electron Beam Dosimetry

摘要

Fiber-optic-coupled dosimeters (FOCDs) are a relatively new method in which to obtain in-vivo dose concomitant with radiation treatment. Accurate live dosing can be achieved virtually anywhere due to their small dimensions (0.2 mm) which can be accommodated by a catheter. The purpose of this experiment is to characterize the electron response of FOCDs with the intent of commissioning a total skin electron therapy (TSE) program. The FOCD system, created by Brian Justus and Alan Huston at the Naval Research Laboratory in Washington, D.C., are composed of copper-doped fused quartz coupled to an optical fiber. The scintillation properties of the copper atoms make it an attractive element to use in radiation therapy based on the current pulse properties of most linear accelerators (linac). System linearity, reproducibility, energy, output dependence on dose rate, field size, and cable effect were characterized at 6, 9, 12, 16 and 20 MeV electron energy ranges. The FOCDs demonstrated excellent linearity with an R2 value of 1.00, electron energy dependence within +/- 1.67% and the reproducibility of the FOCD system was within +/- 0.55% for all energies in comparison to a reference ionization chamber, but fell short in the TSE commissioning process. The FOCDs exhibited a drop in signal when not positioned directly within the beam. The most likely cause for the dropped signal is due to its small cross-sectional area, rendering the system insensitive to scatter radiation. The results did, however, suggest that the FOCDs could prove highly valuable to integrate real-time in- vivo dose information concurrent with clinical electron radiation therapy.