• in-beam PET
• range monitoring
• range verification
• hadrontherapy

Hadrontherapy is a cancer treatment that aims at eradicating tumour cells by using charged particle beams (protons and other ions). Charged particles release most of the energy at the end of their range in tissue. Due to range uncertainties, large safety margins are introduced to avoid underdosing the tumour target or overdosing organs at risk located near the target.
Therefore, range monitoring and verifcation are crucial aspects of hadrontherapy. Positron Emission Tomography (PET) imaging is the most consolidated technique used to this purpose. In-beam PET is one of the options for real-time monitoring of the range and is based on the usage of dedicated PET detectors, compatible to the beam delivery system and treatment room geometry,
to perform acquisitions during the treatment session. In this work I have investigated the implementation of different analysis
methods of PET images for range monitoring and verifcation in hadrontherapy. The work has been carried out in the framework of the Innovative Solution for Inbeam Dosimetry in hadronthErapy (INSIDE) project, whose aim was to develop and validate a bimodal range monitoring system, composed of an in-beam PET scanner and a charged particles tracker. In particular, I have studied some dedicated range monitoring techniques to evaluate the performances of the INSIDE PET system in view of the upcoming clinical trial at the Centro Nazionale di Adroterapia Oncologica (CNAO) in Pavia. The reconstructed images were analyzed with three methods: Pearson's Correlation Coefficient (PCC) test, that evaluates the overall statistical agreement between the activity distributions compared; Beam's Eye View (BEV) method, that evaluates range deviations in the beam direction; Overall View (OV) method, that evaluates range deviations without a preferential direction. The last two methods are specific of PET range monitoring and were applied in a dedicated procedure for the INSIDE PET images with the aim of obtaining a quantitative tool for the evaluation of differences between the planned and the actual irradiation. Moreover, a Gamma index analysis algorithm, usually applied in conventional radiother-apy for quality test, was suitably adapted to compare activity distributions from different acquisitions.
The tests allowed to assess the performance of the INSIDE in-beam PET system as a tool for range monitoring and verification. In particular, the PCC test allows to establish if two activity distributions have enough statistical significance for more specific evaluations and can be used preliminarily on the images set. If the PCC output is positive, BEV and OV methods can
be applied to get local information about the range. Given that the OV method does not have a preferential direction, it can be used to evaluate the tolerance limits for the measured range deviations; only values of range differences that exceeds the so calculated limits can be considered statistically relevant. The obtained results with OV method allow to define a tolerance
limit of about 4 mm for the range deviations in a clinical irradiation with the INSIDE PET system. Basing on this result, it was possible to propose a clinical procedure for the automated range monitoring and verification with this system, involving the three methods presented.