Adaptive Proton Therapy for Pediatric Patients: Improving the Quality of the Delivered Plan With On-Treatment MRI

PurposePencil-beam scanning proton therapy is particularly sensitive to anatomic changes, which may affect the delivered dose distribution. This study examined whether offline adaptation using on-treatment magnetic resonance imaging (MRI) scan during could improve plan quality for pediatric patients.Methods and MaterialsPediatric patients with at least 1 MRI in treatment position (MRItx) between January 2017 July 2019 were retrospectively reviewed. Patients underwent computed tomography simulation. Cases planned scenario-based optimization 3 mm/3% positional/range uncertainty. demonstrating change on MRItx recontoured. The original plans applied anatomy-of-the-day recalculation (delivered plans). Plans subsequently reoptimized offline, beam angles dose-volume constraints (adapted Delivered compared adapted detect significant changes quality, defined as a ?5% decrease clinical target volume (CTV) receiving 95% of prescription (V95) or increase parameter used an organ-at-risk constraint.ResultsSeventy-three eligible, 303 scans (73 simulation 230 scans) available analysis. median per patient was (range, 1-7). Twenty (27%) showed change, 11 (55%) quality. Significant noted from week 2 (n = 3) 8). Seven these (64%) had significantly reduced CTV V95 (median decrease, 7.6%; range, 5%-16%). Four (36%) increased brain stem, hippocampus, and/or optic apparatus. Eight suprasellar low-grade glioma head neck rhabdomyosarcoma.ConclusionOn-treatment useful detecting therapy. MRI-based improved most changes. Further studies should determine value adaptive patients. Pencil-beam Pediatric constraint. Seventy-three rhabdomyosarcoma. On-treatment