A novel continuous beam energy selector for photon intensity-modulated radiotherapy

A photon synthesis method was developed recently which can generate photon beam of any equivalent energy from only two energies. In this work, a novel continuous beam energy selector for photon intensity-modulated radiotherapy (IMRT) was proposed and validated. Based on the effective path length of the target and organs at risk, a model based on dose reference points was proposed and optimized to choose beam energy which could be continuously adjusted between high energy (15 MV) and low energy (6 MV). An in-house inverse planning system using quadratic optimization objective was then employed to optimize the IMRT plan with Optimally selected Beam Energy (IMRT-OBE) per beam. The feasibility of the proposed method was tested on a sample of ten pancreatic cancer cases. Traditional single-energy IMRT and IMRT-OBE plans were evaluated using dose-volume metrics for PTV and the organs at risk (OARs). There were no clear differences in the HIs of the PTV among the different plans. The CIs for IMRT-OBE plans were superior to that of the 6 MVand 15 MVIMRT plans. Compared to 6MV-IMRT, IMRT-OBE reduced the non-target tissue integral dose in all ten cases. There were reduction in the dose metrics for the majority of the organs at risk (OARs) for IMRT-OBE when compared with both single-energy IMRT. In summary, IMRT-OBE has certain dosimetric advantages and can be effectively used in radiation treatment planning, thus providing another degree of freedom for planners to improve treatment plan quality.