ESTRO 2024 - Abstract Book

S4623

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTR0 2024

LET variations in a European proton therapy planning comparison of pediatric posterior fossa tumors

Peter Lægdsmand 1,2 , Witold Matysiak 3,4 , Ludvig P Muren 1,2 , Yasmin Lassen-Ramshad 1 , John Maduro 3 , Anne Vestergaard 1 , Roberto Righetto 5 , Erik Pettersson 6 , Ingrid Kristensen 7 , Charlotte Demoor-Goldschmidt 8,9 , Frances Charlwood 10 , Gillian Whitfield 10,11 , Marta M Feijoo 12 , Pauline Dutheil 8 , Sabina Vennarini 13 , Alfredo Mirandola 14 , Ester Orlandi 14 , Barbara Rombi 15 , Anneleen Goedgebeur 16 , Damien Weber 17 , Karen van Beek 16 , Agata Bannink-Gawryszuk 3 , Fernando C Campoo 12 , Jacob Engellau 7 , Laura Toussaint 1,2 1 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus N, Denmark. 2 Aarhus University, Department of Clinical Medicine, Aarhus N, Denmark. 3 University Medical Centre Groningen, Department of Radiation Oncology, Groningen, Netherlands. 4 Mayo Clinic, Department of Radiation Oncology, Rochester, USA. 5 Hospital S. Chiara, APSS, Medical Physics Unit, Trento, Italy. 6 Sahlgrenska University Hospital, Department of Therapeutic Radiation Physics, Gothenburg, Sweden. 7 Skåne University Hospital, Hematology, Oncology and Radiation Physics, Lund, Sweden. 8 Centre Regional Francois Baclesse, Department of Radiation Oncology, Caen, France. 9 Angers University Hospital, Department of Paediatric Oncology, Angers, France. 10 University of Manchester, The Christie NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, United Kingdom. 11 University of Manchester, Royal Manchester Children’s Hospital, The Children’s Brain Tumour Research Network, Manchester, United Kingdom. 12 Quironsalud, Centro de Protonterapia, Madrid, Spain. 13 Fondazione IRCCS Instituto Nazionale Tumori, Paediatric Radiotherapy Unit, Milano, Italy. 14 CNAO National Centre for Oncological Hadrontherapy, Medical Physics Unit, Clinical Department, Pavia, Italy. 15 Trento Proton Therapy Centre, Department of Radiation Oncology, Trento, Italy. 16 Particle UZLeuven, Department of Radiation Oncology, Leuven, Belgium. 17 Paul Scherrer Institute, Centre for Proton Therapy, ETH Domain, Villigen, Switzerland

Purpose/Objective:

The risk of injury to the brainstem and spinal cord is a concern in treatment of posterior fossa tumors in children with proton therapy. The Relative Biological Effectiveness (RBE) of protons has preclinically been shown to correlate with the physical quantity Linear Energy Transfer (LET). Minimizing LET in the brainstem and spinal cord could therefore be important in reducing the risk of injury. To assess the clinical practice in Europe, we have performed a planning comparison across proton centers treating pediatric patients with spot-scanning delivery. However, LET assessment is not yet an integral part of clinical practice. Therefore, this study aimed to present variations in LET distributions in the brainstem and spinal cord across the centers according to their current practice.

Material/Methods:

Centers involved in the treatment planning study planned the two same pediatric posterior fossa cases according to their own clinical practice: An Atypical Teratoid Rhabdoid Tumor (ATRT) overlapping with the dorsal side of the brainstem prescribed 54 Gy(RBE) (1.8 Gy(RBE)/fraction), and an ependymoma tumor wrapping around the brainstem prescribed 54 Gy(RBE) and a 5.4 Gy(RBE) boost to a total dose of 59.4 Gy(RBE) (Figure 1). Both CTVs extended partially into the C1 segment of the spinal cord. For both cases, dose-averaged LET (LETd) distributions were provided by ten of the centers, using their own beamline Monte Carlo implementation either in Raystation 11B, TOPAS, or GATE (agreement between these calculation methods has previously been verified in a phantom study [1]). LETd was evaluated inside the 50 Gy(RBE=1.1) isodose overlapping with either the spinal cord or the brainstem, as the risk of injury depends mainly on doses above this threshold [2]. To translate the differences in LETd distributions, we