RADT-30. RADIOTHERAPY ALONE WITH REDUCED VOLUME AND DOSE FOR PURE INTRACRANIAL GERMINOMA: PRELIMINARY RESULTS FROM AN INTERNATIONAL MULTICENTER STUDY

Abstract INTRODUCTION Pure intracranial germinomas are highly curable due to their pronounced chemosensitivity and radiosensitivity. These features have allowed for radiotherapy (RT) dose reduction when combined with chemotherapy. However, concerns persist regarding the acute and long-term toxicities of chemotherapy. If reduced-dose RT alone can provide comparable outcomes, omitting chemotherapy would be preferable. This study aimed to evaluate the efficacy and safety of reduced-dose RT alone in patients with pure intracranial germinomas. METHODS We retrospectively reviewed 63 patients with pure intracranial germinoma treated with RT alone between 2012 and 2024. Of these, 59 (93.7%) were histologically confirmed, and 60 (95.2%) underwent spinal MRI for staging. All but one patient had serum human chorionic gonadotropin levels <100 mIU/mL. Solitary disease was observed in 49 patients (77.8%). The median total RT dose to the gross tumor was 36 Gy in 20 fractions (range, 30–40 Gy). RT fields included the whole ventricle, whole brain, or craniospinal axis depending on disease characteristics—solitary and localized, basal ganglia or thalamic location, or multifocal disease, respectively. The median neuraxial dose was 18 Gy. RESULTS The median follow-up duration was 73 months. The 5-year event-free survival and overall survival rates were 91.7% and 100%, respectively. Disease progression occurred in six patients. One patient developed an out-of-field recurrence at the biopsy tract entrance. Notably, three patients had evidence of direct invasion into the brain parenchyma, including the corpus callosum or basal ganglia/thalamus. Another patient who received 30 Gy developed local recurrence as a non-germinomatous germ cell tumor after 110 months and died of septic shock during salvage chemotherapy. No grade ≥3 RT-related toxicities were observed. CONCLUSION RT alone with reduced volume and dose appears effective and well tolerated in patients with pure intracranial germinoma. However, patients with parenchymal invasion may require more intensive treatment. An updated analysis with an expanded cohort is forthcoming.