Characterization of alanine EPR detectors response in clinical carbon ion beams

Abstract

Heavy-ions beams offer several advantages compared to other radiation such as low lateral scattering and high biological effectiveness (RBE) in the Bragg peak region, making them particularly attractive for the treatment of radio-resistant tumors localized close to organs at risk [1]. Although ion beam radiotherapy ultimately requires dose prescription in terms of biological dose or cell survival, absorbed dose is still the quantity mostly used in clinical quality assurance and to dosimetrically characterize the beam. Moreover, the nuclear projectile fragmentation of heavy ions because of inelastic nuclear interactions with medium produces secondary particles with lower Z. The detailed knowledge of the resulting mixed radiation field at each point of the treatment area is crucial for an accurate estimate of the biological dose. Among solid state detectors the alanine EPR detectors present several advantages such as: tissue equivalence, linearity of its dose-response over a wide range, high stability of radiation induced free radicals, no destructive read-out procedure, no sample treatment before EPR signal measurement. These features associated with the possibility of recognizing the various components of a mixed radiation fields makes alanine a good candidate for Quality Assurance of clinical particle beams [2] and also for dosimetry in space radiation. The main goal of the present work is to investigate the response behaviour of alanine EPR pellets in clinical carbon ion beams. In particular, alanine dose response at selected locations within a carbon ion radiation field has been measured with alanine dosimeters in water and in presence of medium inhomogeneities (such as bone-water) to simulate different quasi-clinical scenarios. Furthermore, we aim at understanding the influence of fading and the variations in the shape and the power saturation characteristics of the EPR signal in alanine pellets exposed to different carbon ions LET.