Alanine dosimeters for LET measurement in proton radiotherapy

Abstract

Proton radiotherapy enables highly conformal dose delivery to the tumor while minimizing exposure to healthy tissues surrounding the target. However, to achieve the most optimal treatment plan, it is necessary to consider various parameters, including variable relative biological effectiveness (RBE) and linear energy transfer (LET) within the target and in the normal tissues. The proton treatment planning systems (TPS) currently under development incorporate both of these parameters. However, before introducing biologically guided treatment planning into the clinic, commissioning and end-to-end tests must be conducted. These procedures require specific tools to verify the planned LET distribution. The same tools will also be necessary for subsequent patient-specific quality assurance (QA).The objective of this work was to evaluate the alanine/EPR dosimetry system developed at the Cyclotron Center Bronowice at the Institute of Nuclear Physics (CCB IFJ PAN) for verifying LET values in therapeutic proton fields. The change in the shape of the EPR spectra of alanine irradiated in proton fields of different LETs, described by the ratio of the intensities of the satellite and central lines (x/y ratio), was used to discriminate LET values. The method does not provide absolute LET values. However, as demonstrated, it can verify the LET values calculated in the TPS after calibration using Monte Carlo (MC) simulation.