Supine craniospinal irradiation in pediatric patients by proton pencil beam scanning

Background and purpose: Proton therapy is the emerging treatment modality for craniospinal irradiation (CSI) in pediatric patients. Herein, special methods adopted for CSI at proton Therapy Center of Trento by pencil beam scanning (PBS) are comprehensively described. Materials and methods: Twelve pediatric patients were treated by proton PBS using two/three isocenters. Special methods refer to: (i) patient positioning in supine position on immobilization devices crossed by the beams; (ii) planning field junctions via the ancillary-beam technique; (iii) achieving lens-sparing by three-beams whole-brain-irradiation; (iv) applying a movable-snout and beam-splitting technique to reduce the lateral penumbra. Patient-specific quality assurance (QA) program was performed using two-dimensional ion chamber array and gamma-analysis. Daily kilovoltage alignment was performed. Results: PBS allowed to obtain optimal target coverage (mean D98% > 98%) with reduced dose to organs at-risk. Lens sparing was obtained (mean D1 similar to 730 cGyE). Reducing lateral penumbra decreased the dose to the kidneys (mean Dmean < 600 cGyE). After kilovoltage alignment, potential dose deviations in the upper and lower junctions were small (average 0.8% and 1.2% respectively). Due to imperfect modeling of range shifter, QA showed better agreements between measurements and calculations at depths >4 cm (mean gamma > 95%) than at depths < 4 cm. Conclusions: The reported methods allowed to effectively perform proton PBS CSI. (C) 2017 Elsevier B.V. All rights reserved.