Prompt gamma-ray imaging for on-line tracking of the bragg peak in proton radiation therapy

Proton therapy (PT) requires reliable in-vivo beam range verification methods and techniques to ensure safe and accurate dose delivery to the targeted region while sparing critical organs-at-risk during the treatment delivery. Secondary prompt gamma (PG) rays emitted during PT have been proposed for on-line tracking and monitoring of the Bragg peak (BP) of the proton beam in real-time. The general principle of using PG imaging for in-vivo beam range verification has recently been proven. However, PG detection presents a great challenge since PG rays are generated from different nuclear reaction channels and have a broad energy range with strong interference backgrounds from the secondary neutrons and stray gamma rays. Currently there is a lack of detailed knowledge and quantitative methodology for clinically feasible PG imaging system development. The purpose of this study is to investigate PG detection strategies for optimal PG image formation in PT. The novelty of the work performed in my thesis is such that a systematic study of PG ray emission in water and PMMA phantoms from high energy proton beam irradiations has been carried out, which provides broad information of PG signal characteristics in spectral, spatial and timing aspects as compared to the main background signal from neutrons. To my knowledge, this kind of study has not yet been reported from any literature. Specific aims include: (i) quantifying the correlation between the longitudinal PG emission and the position of the BP in the patient; (ii) characterising PG detection dependencies on PG energy and timing properties; (iii) modelling PG detection with a proposed BGO detector.