Prompt gamma-ray spectroscopy in conjunction with the Monte Carlo Library Least Squares approach: applications to range verification in proton therapy

Prompt Gamma-ray Spectroscopy (PGS) in conjunction with the Monte Carlo Library Least Squares (MCLLS) approach was investigated for the purposes of range monitoring in proton therapy through Monte Carlo simulations. Prompt gamma-rays are produced during treatment and can be correlated to the range of the proton beam in the tissue. In contrast to established approaches, MCLLS does not rely on the identification of specific photopeaks. Instead it treats each individual constituent as a library spectrum and calculates coefficients for each spectrum, and therefore takes both the photopeaks and the Compton continuum into account. It can thus be applied to organic scintillators traditionally not used for energy spectroscopy due to their low Z number and density. Preliminary results demonstrate that the proposed approach returns a strong linear correlation between the range of the primary proton beam and the calculated library coefficients, depending on the composition of libraries. This can be exploited for range monitoring.