S1740
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
optic nerves, chiasm, and hy4pothalami; however, these increases remained within OAR dose constraints.
Digital Poster 2717
Toxicity Trade-Offs in Proton and (non-) coplanar Photon Radiotherapy for Pituitary Adenomas David J.A Palm 1 , John Paulissen 1 , Rik Emmah 1 , David Hofstede 1 , Nikolina E Birimac 1 , Ruud MA Houben 1 , Marlies E Granzier 1 , Marloes Nogarede 1 , Ans J Swinnen 1 , Jasper van Aalst 2 , Yasin Temel 2 , Marleen Kars 3 , Danielle BP Eekers 1 , Catharina ML Zegers 1 , Inge Compter 1 1 Department of Radiation Oncology (Maastro), GROW Research Institute for Oncology and Reproduction Institution: Maastricht University Medical Centre+, MAASTRO, Maastricht, Netherlands. 2 Department of Neurosurgery, Maastricht University Medical Center+, MUMC, Maastricht, Netherlands. 3 Department of Internal Medicine, Division of Endocrinology, Maastricht University Medical Center+, MUMC, Maastricht, Netherlands Purpose/Objective: Proton radiotherapy has been used in the treatment of pituitary adenomas (PAs) since the 1950s. While previous studies have shown that protons offer efficacy comparable to photons, definitive evidence of their clinical advantages remains limited which is a key concern given their higher cost and reduced availability. Therefore, we set-out to investigate whether we can determine whether protons confer advantages compared to photons in a cohort of PA patient in terms of dose and predicted toxicity. Material/Methods: In this study, treatment plans for 15 PA patients were made using intensity-modulated proton therapy (IMPT), coplanar photon therapy, and non-coplanar photon therapy. Dose distributions to organs at risk (OARs) were compared using the Radiation Oncology Collaborative Comparison Group’s Performance Scoring System (ROCOCO RPSS), which estimates predicted toxicity. Results: IMPT resulted in significantly lower overall predicted toxicity than both photon modalities (median RPSS: 1.09 vs. 1.24; p < 0.005). This reduction was due to significantly lower D40% to the hippocampi. For the right hippocampus, median D40% (EQD2) was 1.01 Gy with IMPT, compared with 4.96 Gy for coplanar photons and 3.18 Gy for non-coplanar photons. Both IMPT and non-coplanar plans were significantly lower than coplanar plans (p < 0.001). For the left hippocampus, IMPT achieved a median D40% of 0.68 Gy, compared with 5.02 Gy for coplanar and 2.67 Gy for non-coplanar photons. Non-coplanar was significantly lower than coplanar (p < 0.001), while IMPT was significantly lower than both photon modalities (p < 0.001). IMPT also delivered higher doses to the surface and interior of the brainstem,
Conclusion: This in-silico study demonstrates that both IMPT and non-coplanar FSRT can significantly reduce hippocampal dose compared with coplanar FSRT, suggesting a potential benefit for cognitive function preservation in patients with favourable prognosis. Among the modalities, IMPT achieved the lowest toxicity score (RPSS), indicating a promising balance between therapeutic management and normal tissue sparing. However, the higher doses observed in the optic apparatus and brainstem, together with uncertainties related to variable proton RBE, highlight the need for careful clinical consideration and patient selection. Keywords: Protons, Pituitary, Toxicity Assessing proton range estimation in photon- counting and dual-energy computed tomography with low imaging doses and using varying phantom sizes Didier Lustermans 1 , Gabriel Paiva Fonseca 1 , Vicki Trier Taasti 2 , Gloria Vilches Freixas 1 , Ilaria Rinaldi 1 , Eva Hoeijmakers 3 , Cécile Jeukens 3 , Katia Parodi 4 , Guillaume Landry 4 , Frank Verhaegen 1 1 Department of Radiation Oncology (Maastro), GROW Research Institute for Oncology and Reproduction, Maastricht University Medical Centre+, Maastricht, Netherlands. 2 Danish Centre for Particle Therapy, Digital Poster Highlight 2771
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