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

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 20-100 mu m wide separated by 100-400 mu m) delivers a very large dose (>1000 Gy) 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 1000 Gy, 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. (C) 2012 Elsevier B.V. All rights reserved.