Evaluation of in-beam PET treatment verification in proton therapy with different reconstruction methods

In-beam PET monitoring can provide early treatment assessment in proton therapy. However, open ring configurations and low positron emitter production yields degrade image quality, hampering the assessment accuracy. To achieve the highest precision for range monitoring, it is compulsory to mitigate image noise and compensate for data truncation. The goal of this work is to study the performance of state-of-the-art algorithms for in-beam PET image reconstruction, by evaluating the impact of the system response model and assessing the accuracy of range measurements. The approaches investigated here were Maximum-A-Posteriori algorithms combined with Total-Variation and Median-Root Priors. Maximum-Likelihood-Expectation-Maximization was used as reference. To compute the system matrix, different models were compared: a precise Monte Carlo model, and Single-Ray Tracing with and without Gaussian blurring in image space. The proposed methods were tested on simulations of Spread-Out-Bragg-Peaks delivered on phantoms. The I3PET scanner geometry was used as a case study. After image post-processing, the explored methods delivered similar results. Our work demonstrates the feasibility and reliability of using a simple and fast reconstruction method to perform range evaluations, given the correct image post-processing.