Gelover Reyes, E; (2013) The application of active pixel sensors to proton imaging. Doctoral thesis , UCL (University College London).

Abstract

Proton therapy is one of the most precise modalities of cancer treatment, but some of its benefits cannot be fully exploited due to the uncertainties during treatment planning and dose delivery. The clinical implementation of imaging techniques such as proton radiography or proton computed tomography have been prevented by detector technology. The major challenges for the development of a device intended for proton detection are: high energy resolution, high speed data acquisition rates, single particle tracking and large area sensors with sufficient radiation hardness. Complementary metal oxide semiconductor (CMOS) active pixel sensors (APS) can be designed to meet all these demands. Preliminary experiments were performed to evaluate the feasibility of using CMOS APS technology for proton detection. This was done in an attempt to identify the parameters that will lead to the design of an ideal application specific CMOS APS. It was found that the detector used in this thesis has a dependence on proton intensity and it is not radiation hard. Proton transmission radiographs were successfully acquired at the Clatterbridge Centre for Oncology. A detailed description of the image formation process is given analysing the process of energy loss on the detector. Single proton detection was achieved using a region of interest of 1 mm2 and an acquisition rate of 1100 frames per second. Some limitations in the detector performance were identi ed when comparing these results with the Landau theory of particle identification. A series of modifications to the pixel architecture are listed to overcome issues such as pixel cross talk and to improve radiation hardness. The Most likely Path (MLP) method was applied on the data obtained by simulating the passage of protons through an arrangement of CMOS detectors. It was demonstrated that, CMOS APS in combination with the MLP method, can be used to correct for Multiple Coulomb scattering in proton radiography images. The performance of CMOS APS for beam monitoring and dosimetry was also studied. It was found that the detector tested can be used to perform beam monitoring since low doses were measured accurately and that its application could be escalated to 2D measurements for monoenergetic protons.

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