Speaker
Description
Alanine, as measured by electron paramagnetic resonance (EPR), has long been employed in medical dosimetry as either a secondary standard or a transfer dosimeter, due to its linear dose response over a wide absorbed-dose range, soft-tissue equivalence, and independence from dose rate. However, advances in radiotherapy, e.g., novel radiation qualities and delivery techniques, necessitate evaluating existing detectors under these conditions. The literature shows that the EPR signal of irradiated alanine comprises three distinct radical components (designated R1, R2, and R3), whose relative contributions are modulated by the linear energy transfer (LET) of the incident radiation. The present study, therefore, investigates the LET dependence of the EPR/alanine response by spectral decomposition. It estimates each radical’s fractional contribution and their paramagnetic parameters. For that, commercial alanine pellets (Harwell, UK) were irradiated with 6 MV photons delivered by a Versa HDTM linear accelerator (Elekta, UK) and with carbon ions delivered in pencil beam scanning (PBS) in a spread-out Bragg peak (SOBP) configuration, at San Matteo Hospital and Fondazione CNAO, respectively, both in Pavia, Italy. EPR spectra were recorded in the X-band using a Bruker ELEXSYS E580 spectrometer (Bruker, Germany). Simulated component spectra were generated with the EasySpin toolbox for MATLAB using the pepper function; literature-derived g-values and hyperfine coupling constants were used as initial parameters. Simulations incorporated weighting factors and both homogeneous and inhomogeneous (strain) broadening effects to reproduce the experimental lineshapes. For photon irradiation (LET ≈ 0.2 keV/µm), decomposition yielded fractional contributions of R1 = 35.0% and R2 = 50.6% of the total EPR signal, with the remainder assigned to R3. At increased LET values (35, 45, and 100 keV/µm), the R3 contribution increased to 28.3%, 28.9%, and 50.4%, respectively. Higher LET induced stronger inhomogeneous broadening, as shown by increased $g_\mathrm{strain}$ and $H_\mathrm{strain}$ values. This indicates that EPR/alanine can provide LET-discriminating information.