Design of a solid-state array detector prototype for small-field dosimetry in megavoltage photon beams

Recent developments in imaging techniques, medical linear accelerator (linac) design and treatment modalities in megavoltage photon-beam radiotherapy have been aimed at optimizing the delivery of highly conformal dose distributions, leading to an escalation in the use of small radiation fields. Modern radiotherapy delivered with small fields has more stringent requirements, in terms of quality assurance (QA), than conventional radiotherapy with broad fields. Additionally, accurate dosimetry, paramount for the safe and efficient use of radiation, becomes challenging in this context. Accidents, near misses and discrepancies between the results of different investigators confirm that dosimetry in small fields is complex. The factors contributing to this are broadly summarized as an absorbed dose distribution characterized by a lack of charged particle equilibrium (CPE) over most of the treatment target, partial source occlusion by the collimation system of the linac, and a measurement of absorbed dose which is highly dependent on radiation detector design and the perturbations it introduces to particles fluence. Starting from the currently available knowledge on the physics of small radiation fields, the aim of the research in the present dissertation was the design and test of a novel radiation detector prototype with the potential to address the shortcomings of currently available dosimeters.