Introduce 4π dynamic spot-scanning proton arc therapy (SPArc-4 π) for pancreatic cancer: a comparative planning study with IMPT
TL;DR
SPArc-4 π provides a promising proton planning strategy for pancreatic SBRT-SIB by preserving robust target coverage while improving gastrointestinal organ sparing and reducing predicted toxicity, and support further investigation of SPArc-4 π for safer dose escalation in LAPC.
Abstract
Objective. Stereotactic body radiotherapy with a simultaneous integrated boost (SBRT-SIB) for locally advanced pancreatic cancer (LAPC) is constrained by the proximity of serial gastrointestinal organs at risk (OARs). Conventional intensity-modulated proton therapy (IMPT) relies on a limited number of fixed beam angles, which may restrict dose shaping around these critical structures. This study evaluated whether non-coplanar spot-scanning proton arc therapy (SPArc-4 π) could improve OAR sparing while preserving robust target coverage. Approach. 10 patients with LAPC were retrospectively selected in this study. For each patient, SBRT-SIB plans were generated using conventional IMPT and SPArc-4 π. Plan robustness was assessed across 21 uncertainty scenarios. Target coverage, conformity, OAR doses, estimated delivery time, and Lyman–Kutcher–Burman normal tissue complication probability for four gastrointestinal endpoints were compared using the Wilcoxon signed-rank test. Main results. SPArc-4 π maintained target coverage comparable to IMPT, with similar clinical target volume (CTV) and boost-volume coverage, while CTV conformity improved with SPArc-4 π (conformity index: 0.50 vs. 0.56; p = 0.02). SPArc-4 π significantly reduced maximum dose (Gy(RBE)) to the stomach (30.01–24.53), duodenum (35.14–33.14), bowel (32.60–28.91), and spinal cord (15.38 to 5.58; all p ⩽ 0.01). Predicted toxicity decreased across all four gastrointestinal endpoints: gastric bleed risk decreased from 8.19% to 6.15%, grade ⩾3 gastrointestinal toxicity from 3.91% to 3.81%, ulceration/perforation from 0.03% to 0.01%, and diarrhea from 24.14% to 22.34% (all p⩽0.005). All plans met robustness criteria. The main trade-off was delivery efficiency, with SPArc-4 π requiring approximately 2–3 min longer delivery time than IMPT. Significance. SPArc-4 π provides a promising proton planning strategy for pancreatic SBRT-SIB by preserving robust target coverage while improving gastrointestinal organ sparing and reducing predicted toxicity. These findings support further investigation of SPArc-4 π for safer dose escalation in LAPC.