ESTRO 38 Abstract book

S351 ESTRO 38

Data from ten anonymized pediatric craniopharyngioma patients (midline tumor, median clinical target volume (CTV) of 16 cm 3 [range: 8-37 cm 3 ]) were used in this study, including CT/MRI scans, clinical structure set as well as the clinically delivered double scattering proton therapy (DSPT) plans. The total prescription dose was 54Gy(GyRBE) delivered via a two-phase sequential boost approach. Temporal lobe sparing volumetric modulated arc therapy (VMAT) and pencil beam scanning proton therapy (PBS) plans were optimized to deliver the same dose to the CTV, maintaining consistent target coverage metrics. The VMAT plans consisted of three non-coplanar arcs, while two anterior and one posterior field were used for the PBS plans. Thirty unique BSCs were delineated (using CT/MRI), including temporal lobe substructures (i.e. amygdala, hippocampus, entorhinal cortex) as well as BSCs outside of this region. For each BSC, the difference between modalities in the fractions of volume receiving low (V10Gy, V20Gy), intermediate (V30Gy, V40Gy) and high (V50Gy) doses were analyzed. A logistic dose-response model, derived from published odds ratio of memory impairment and temporal lobe doses, as well as a model associating left hippocampus V20Gy and delayed verbal memory were applied to compare the different modalities. Results Temporal lobe doses were lower in the PBS plans than in the DSPT and VMAT plans. The volumes of temporal lobe substructures exposed to all dose levels were consistently reduced with PBS compared to DSPT, e.g. from 41% to 0% for the left hippocampus V10Gy or from 43% to 24% for the left amygdala V40Gy. For the BSCs outside of the temporal lobes, the volumes exposed to low doses were in general smaller with both proton modalities compared to VMAT, while intermediate and higher dose levels to the ventricular substructures were reduced in the VMAT plans due to field configurations for both DSPT and PBS (Fig. 1). Overall, the reduced doses to the temporal lobes and hippocampus translated into lower estimated risks of memory impairment with proton therapy, particularly with PBS (Fig. 2).

Conclusion A MRI-based TPS for ocular proton therapy was developed. For the first time in eye proton therapy treatment planning, a trade-off for OARs sparing was implemented, while maintaining the tumor coverage. OC-0670 Temporal lobe sparing radiotherapy for cognitive preservation in pediatric brain tumor patients L. Toussaint 1 , D.J. Indelicato 2 , L.P. Muren 1 , Z. Li 2 , Y. Lassen-Ramshad 3 , K. Kirby 2 , C. Pedro 4 , R. Mikkelsen 5 , M. Di Pinto 2 , M. Høyer 3 , C.H. Stokkevåg 6 1 Aarhus University Hospital, Department of Medical Physics, Aarhus, Denmark; 2 University of Florida Health Proton Therapy Institute, Department of Radiation Oncology, Jacksonville, USA ; 3 Danish Center for Particle Therapy, Department of Oncology, Aarhus, Denmark; 4 Instituto Português de Oncologia Francisco Gentil, Department of Radiotherapy, Lisbon, Portugal; 5 Aarhus University, Department of Biomedicine, Aarhus, Denmark; 6 Haukeland University Hospital, Department of Oncology and Medical Physics, Bergen, Norway Purpose or Objective Pediatric brain tumor patients are at risk of cognitive impairment, as most tumors are located close to several brain substructures associated with cognition (BSCs). Reducing radiation exposure to the temporal lobes is beneficial due to their association with cognitive functions such as memory. However, the implications of this strategy on other BSCs (both within and outside the temporal lobes) have not been reported. The aim of this study was therefore to investigate the dose patterns across a broad range of BSCs in suprasellar pediatric brain tumor patients in photon and proton therapy plans intended to spare the temporal lobes, and to predict subsequent memory impairments. Material and Methods This abstract is part of the media p ogramme and will be released on the day of its presentation