Pérez Lara, Maria Laura; (2025) Development of a compact Compton camera using HEXITEC detectors for online treatment verification during particle therapy. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Accurate in vivo verification remains a significant challenge in particle therapy. This work explores the potential of using pixellated semiconductor detectors as the core component of a compact Compton camera, designed for applications in Boron Neutron Capture Therapy (BNCT) and Proton Therapy (PT). BNCT is an emerging cancer treatment that targets tumour cells through the interaction of boron-enriched agents with (epi)thermal neutrons, while PT offers highly localised dose delivery that spares healthy tissue. In both modalities, secondary gamma particles are emitted from the patient, providing valuable spatial information on dose deposition. This research combines Monte Carlo simulations in Geant4 with experimental measurements using commercial HEXITEC detectors. The Stochastic Origin Ensemble (SOE) algorithm is used to reconstruct gamma origins, demonstrating successful imaging of both point and volumetric sources. The HEXITEC detector is shown to detect prompt gammas in complex radiation fields such as those found in PT, which can later be identified using post-processing algorithms like cluster size analysis and energy discrimination. Simulation studies indicate that a 3-layer HEXITEC configuration could enable verification for PT, while a 2-layer setup with commercial geometries shows promise for BNCT. Further Monte Carlo simulations in realistic BNCT and PT scenarios highlight the potential of the HEXITEC Compton camera and SOE algorithm for in vivo verification. Nonetheless, challenges remain in quantifying boron concentrations and dose from gamma counts in BNCT, and in optimising detection efficiency at PT energies. A first-generation Compton camera prototype was built and experimentally evaluated for spatial resolution and coincidence performance, although limitations in its triggering mechanism and detector synchronisation were found to significantly hinder reliable event pairing and image reconstruction. These findings lay the groundwork for future hardware improvements and highlight the need for integrated acquisition systems in high-resolution gamma imaging.

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