Enhancement of prompt gamma response for treatment planning verification

Abstract

In this project I present the results of a feasibility study on a novel strategy for real-time dose verification using secondary prompt γ-ray emissions produced by way of proton–nuclear interactions within selected materials during proton irradiation. To provide a proof-of principle of this methodology, Monte Carlo simulations were performed using an approximately mono-energetic 70 MeV proton beam, irradiating different materials in salt and solution form. The choice of the target element is the key to obtaining a prompt γ-ray spectrum significantly different from the background produced by the human body, as well as for physiological considerations (such as uptake and toxicity effects). The promising candidates were: 63Cu, 89Y and 31P. I investigated the emission spectra of γ-rays exiting the target and assessed the enhancement of the γ-ray yield with respect to the background, comparing simulation and experimental results as conducted by the research group of the Trento University, Italy. I demonstrated how proton reactions with a solution containing the target elements can produce signature prompt γ-rays related to the material irradiated despite the significant background. The minimum material concentration required to obtain a significant enhancement was also studied. The results show that the prompt γ-ray spectra differ significantly for each type of target studied. The relative intensity of the characteristic γ-rays emitted from a given solution containing the target elements was shown to be proportional to the concentration of each element in that material. Based on these results, I discuss the potential use of prompt γ-ray emission as a method to verify the accuracy and efficacy of doses delivered with proton radiotherapy