Microdosimetric measurements for LET monitoring in proton therapy. The development of engineered mini-TEPCs for clinical applications: First results

Innovative Treatment Planning Systems (TPS) in proton therapy based on a variable radiation quality with depth with respect to the conventional one with a fixed Relative Biological Effectiveness (RBE) of 1.1 are under study. Experimental methods are needed to verify the consistency between what is planned and what is delivered in terms of radiation quality. Microdosimetry studies the stochastics of the energy deposition process at micrometric and sub-micrometric level which is known to be related to the biological effectiveness of ionising radiation fields. For this reason, it is recognised by the scientific community that it is a useful tool to monitor the radiation quality of hadron therapy beams where the effectiveness varies with the penetration depth in patients. Detectors are needed to perform a microdosimetric characterization of a clinical beam and they need to satisfy specific requirements to enter the clinical practice as instruments for the Quality Assurance (QA). With this aim, at the Legnaro National Laboratories of the Italian National Institute for Nuclear Physics (LNL-INFN) a technological transfer project was carried out with the final goal of developing engineered miniaturized Tissue Equivalent Proportional Counters (mini-TEPCs) for clinical applications. This work presents the characterization performed on the new detectors and the results obtained in neutron and proton fields.