Novel Online PET Imaging for Intrabeam Range Verification and Delivery Optimization: A Simulation Feasibility Study

Online positron emission tomography (PET) image-based method uses an initial particle beam to measure the particle beam range (BR) within the same fraction so that any measured range-shift with respect to the predicted BR can be compensated before the rest therapeutic beam deliveries. However, the method requires to use a low-dose initial beam to minimize the risk of beam overshooting, which leads to low image count and inaccurate BR measurement. In this in-silico study, we evaluate the feasibility of a new online PET imaging method that measures BR at the mid-plane of a target volume with part of the high-dose therapy beams to verify BR and guide adaptive treatment replanning. Simulations included various processes of proton beam radiations to a tumor inside a human-brain phantom, positron, and PET image generation at the mid-plane with initial beams, activity range measurement, and range-shift compensated beam delivery. The results demonstrated that the new method, under the simulated conditions, can achieve 1.1-mm mid-plane BR measurement accuracy and closely match the delivered range-shift compensated dose distribution with the planned one. Overall, it is promising that this new method may significantly improve the particle therapy accuracy.