Proton Beam Therapy for Pancreas Cancer: PTCOG Consensus Recommendations for Simulation, Treatment Planning and Treatment Delivery

Abstract

<h3>Purpose/Objective(s)</h3> The proximity of gastrointestinal (GI) luminal organs-at-risk (OAR) poses a challenge to radiotherapy (RT) for pancreas cancer (PC). Proton beam therapy (PBT) may reduce toxicities compared to photon therapy by avoiding radiation exposure to large volumes of the abdomen while enabling safe dose escalation. The purpose of this study is to create recommendations for the safe treatment of PC with PBT. <h3>Materials/Methods</h3> The Particle Therapy Co-Operative Group (PTCOG) Gastrointestinal Subcommittee consisting of radiation oncologists and medical physicists with extensive clinical experience using PBT for GI cancers developed expert consensus recommendations for PC describing simulation, treatment planning, and treatment delivery through their collective experience and systematic review of the literature. <h3>Results</h3> The following general recommendations were established: <i>Simulation</i>: Indexed immobilization is recommended to reduce patient setup variability. Patients should be supine with arms above the head. Additional imaging such as PET/CT and/or MRI should be considered for target delineation. Contrast CT is recommended but should be performed subsequent to the planning CT at simulation to avoid the need to override Hounsfield Units. Dual-energy CT should be used, if available, to reduce CT-related proton range uncertainties. Motion management strategies are imperative, including 4DCT for motion accounting and breath-hold, or other techniques for motion mitigation. Patients should also have an empty stomach. <i>Treatment planning</i>: Beam angle selection is critical. Posterior and lateral beam angles are preferred to minimize the dosimetric impact of variable anatomy such as bowel. Robust optimization should be used for pencil beam scanning (PBS) techniques. When treating with PBS, single-field optimization (SFO) is often preferrable to increase robustness. If OAR constraints cannot be met with SFO, then multi-field optimization may be used. Higher linear energy transfer (LET) at the end of range should be considered in the context of sparing distal OARs. Increased beam angle separation should be used to reduce skin dose and mitigate the impact of higher LET. <i>Treatment delivery</i>: Volumetric image guidance, where available, should be used daily. Verification CT scans should be acquired <i>ad-hoc</i> as deemed necessary, or at least every other week, to assess the dosimetric impact of changes in anatomy, such as weight changes and variation in bowel gas and gastric filling. Adaptive re-planning should be performed as required. <h3>Conclusion</h3> The PTCOG Gastrointestinal Subcommittee has developed PBT expert consensus recommendations for PC. These recommendations enable PBT facilities to develop protocols for safe dose escalation studies.