Supine craniospinal irradiation in pediatric patients by proton pencil beam scanning

Radiotherapy and Oncology, 2017, 123, (1), pag. 112-118

Farace P¹, Bizzocchi N¹, Righetto R¹, Fellin F¹, Fracchiolla F¹, Lorentini S¹, Widesott L¹, Algranati C¹, Rombi B¹, Vennarini S¹, Amichetti M¹, Schwarz M^1,2.
1    Proton Therapy Center, Hospital of Trento, Azienda Provinciale per I Servizi Sanitari (APSS), Italy.

2    Trento Institute for Fundamental Physics and Applications (TIFPA), National Institute of Nuclear Physics (INFN), Trento, Italy.

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 c-analysis. Daily kilovoltage alignment was performed. Results: PBS allowed to obtain optimal target coverage (mean D98% > 98%) with reduced dose to organsat-risk. Lens sparing was obtained (mean D1 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 c > 95%) than at depths < 4 cm. Conclusions: The reported methods allowed to effectively perform proton PBS CSI. 2017 Elsevier B.V. All rights reserved. Radiotherapy and Oncology 123 (2017) 112–118