A non-invasive beam current monitor for a medical accelerator

Abstract

Proton or heavy ion beams are a very attractive and promising tool in cancer therapy. They offer much localised and better controlled dose distributions in comparison to X-rays, thus, decreasing damage sustained by healthy tissue. Diagnostics of these beams is particularly interesting as interference with the beam, especially in the case of the ocular treatment, leads to a significant degradation of essential parameters of beam, therefore, non-interceptive methods of monitoring are preferred. In this work, a novel method of a proton beam current monitor was devised, relaying on non-invasive measurements, investigating the proton beam halo region. The method required adaptation of the LHCb VELO detector to allow its operation as a stand-alone device. The performance of the detector was tested in conjunction with a dedicated Faraday Cup, optimised to suit the clinical proton beam characteristics at the Clatterbridge Cancer Centre (CCC). To perform theoretical predictions of the proposed monitor, auxiliary measurements were completed that involved other instrumentation such as scintillating screens. They were used in the beam profile measurements that sourced information used afterwards to create a model of the existing beamline, which was used to find the extent of and nature of the beam halo extent. The thesis presents results of theoretical studies and modelling of different parts of the experimental set-up leading to the final design of the mentioned monitor, followed by a first successful run with a proton beam at CCC. A discussion on the outcomes of data analysis is presented with indication for possible future development of the method. Although the monitor was prepared and tested with a 60 MeV proton beam, the instrumentation can used with higher energy hadron therapy beams, including other particle species than protons once additional adaptation to their properties has been performed.