Radt-07. Clinical Results, Acute and Early Late Toxicity After Proton Radiotherapy for Pediatric Medulloblastoma, Retrospective Analysis

Abstract Craniospinal irradiation with boost to primary tumor site (and metastatic sites) is current radiotherapy standard for most patients diagnosed with medulloblastoma (MB). This treatment is effective, but survivors frequently develop long-term toxicity affecting the quality of life. Proton radiotherapy has the same efficacy compared to conventional photon-based techiques, but might achieve lower risk of toxicity. We retrospectivelly analyzed our cohort of patients irradiated for MB in our institution, using IMPT (intensity modulated proton therapy). Between May 2013 and December 2023 eighty patients (50 male, 30 female, median age at radiotherapy 8 years/range 3-17/) with primary or recurrent MB (not previously irradiated) were treated and included into analysis. 36 patients were treated for high-risk MB (mostly metastatic), 44 pts for SR disease. Neoadjuvant, concurrent and adjuvant systemic treatment was applied according to the protocol selected by the pediatric oncologist. All but one patients completed their treatment, acute toxicity including hematological was mild and lead to treatment interruption in seven cases. With a median of follow-up 39,6 months (range 3-119) 62 pts were in complete remission, 3 pts alive with disease, 14 died from disease progression and one died from complication (intracranial hemorrhage). We were able to identify two secondary malignancies potentially associated with IMPT (thyroid cancer, radiation induced high-grade glioma). Most common endocrinopathy observed in our patients was hypothyroidism and growth-hormon decifit. Due to lack of data, we were not able to analyze cognitive functions and quality of life. There was one case of severe brainstem necrosis with persistent neurological deficit, treated with corticosteroids and bevacizumab. Proton radiotherapy using IMPT for craniospinal irradiation in MB is feasible, treatment outcomes and toxicity are encouraging, although a longer follow-up is needed.