SU‐C‐207A‐06: On‐Line Beam Range Verification with Multiple Scanning Particle Beams: Initial Feasibility Study with Simulations

Abstract

Purpose:To investigate the feasibility and requirement for intra‐fraction on‐line multiple scanning particle beam range verifications (BRVs) with in‐situ PET imaging, which is beyond the current single‐beam BRV with extra factors that will affect the BR measurement accuracy, such as beam diameter, separation between beams, and different image counts at different BRV positions.Methods:We simulated a 110‐MeV proton beam with 5‐mm diameter irradiating a uniform PMMA phantom by GATE simulation, which generated nuclear interaction‐induced positrons. In this preliminary study, we simply duplicated these positrons and placed them next to the initial protons to approximately mimic the two spatially separated positron distributions produced by two beams parallel to each other but with different beam ranges. These positrons were then imaged by a PET (∼2‐mm resolution, 10% sensitivity, 320×320×128 mm^3 FOV) with different acquisition times. We calculated the positron activity ranges (ARs) from reconstructed PET images and compared them with the corresponding ARs of original positron distributions.Results:Without further image data processing and correction, the preliminary study show the errors between the measured and original ARs varied from 0.2 mm to 2.3 mm as center‐to‐center separations and range differences were in the range of 8–12 mm and 2–8 mm respectively, indicating the accuracy of AR measurement strongly depends on the beam separations and range differences. In addition, it is feasible to achieve ≤ 1.0‐mm accuracy for both beams with 1‐min PET acquisition and 12 mm beam separation.Conclusion:This study shows that the overlap between the positron distributions from multiple scanning beams can significantly impact the accuracy of BRVs of distributed particle beams and need to be further addressed beyond the established method of single‐beam BRV, but it also indicates the feasibility to achieve accurate on‐line multi‐beam BRV with further improved method.