The high dose rate sensing potential of a radiotherapy optical fiber dosimeter

Abstract

Abstract A perceived need exists for real-time dosimeters offering pulse-by-pulse temporal resolution to validate the delivery of the prescribed dose from clinical electron linear accelerators (linacs). In the case of linacs working at conventional (100–600 cGy/min) dose rates and operating in the bremsstrahlung mode, radioluminescence-emitting Ge-doped silica optical fibers have been shown to satisfy such demand. Ge-doped silica optical fiber scintillators measurements are made for a linac operating in the electron mode, delivering at dose rates up to 600 cGy/min. The radioluminescence response of the material as a function of dose has been measured using a Photomultiplier Tube (PMT) with a photon-counting circuit capable of 1-200 µs gating time, demonstrating dose linearity (R2 = 0.99971). Time-resolved radiation dosimetry measurements for a wide range of electron beam energies (6, 9, 12, 15 and 18 MeV) are reported. Measurements using a Multi Pixel Photon Counter (MPPC) connected to an oscilloscope shows the absence of saturation in the time resolved signal, freedom from performance limitations of residual memory or afterglow effects. Individual pulses at different energies have been analysed in terms of rise- and decay-times. While obtaining a qualitative assessment of the variation in pulse sub-structure, the variations likely arising from internal pulse manipulation for handling linac power delivery. The results point not only to the use of Ge-doped optical fiber scintillator in time-resolved dosimetry at conventional dose rates but also potential for use at the greater dose-rates of FLASH radiotherapy.