Examination of the dynamic range of Sm-doped glasses for high-dose and high-resolution dosimetric applications in microbeam radiation therapy at the Canadian synchrotron

Abstract

Microbeam Radiation Therapy (MRT) is a promising cancer treatment technique. During the treatment, a micro-planar lattice of narrow X-ray beams called a microbeam (each narrow X-ray beam is typically 20–100μm wide separated by 100–400μm) delivers a very large dose (>1000Gy) onto a tumor. Sm3+-doped glasses that involve the reduction of the Sm-valency (Sm3+ → Sm2+) upon X-ray irradiation are one of the potential dosimetric detectors for this particular application. With this class of detectors, we use the extent of valency reduction as a measure of the delivered X-ray dose, and the response read out using a confocal microscopic technique via the Sm2+/Sm3+ photoluminescence. This method enables us to measure the dose distribution of the microbeam. In this paper, we show that both Sm3+-doped fluorophosphate and fluoroaluminate glasses exhibit a dynamic range for the conversion response from 1 to over 1000Gy, which satisfies the dose range for MRT applications. The dynamic range depends on the concentration of Sm3+ dopants as well as the detector glass composition. Moreover, X-ray induced absorbance, photobleaching and thermally-stimulated luminescence (TL) measurements suggest that the hole trapping process during X-ray irradiation is a dominant factor for the valency conversion, and the accommodation of precursor POHCs in fluorophosphate glasses gives rise to an acceleration of the conversion process.