P09.15.b Acute Toxicity and Early Late Toxicity With Proton Radiotherapy in CNS Tumors: The Pro-CNS Study

Abstract BACKGROUND Proton radiation was implemented in cancer therapy with minimal evidence of its superiority to photon radiation from RCTs. A minority of clinical cohorts on proton radiotherapy (PRT) report worrying side effects. As the use of PRT expands, further evaluation of its effect and safety is needed. This abstract reports on acute toxicity and early late toxicity in proton radiotherapy for CNS tumors. MATERIAL AND METHODS The Skandion Clinic in Uppsala, Sweden, opened in 2015. Accrual for this multicenter, prospective observational study began in August 2015 and continued through August 2020. Adults in performance status (ECOG ≤2), diagnosed with primary CNS tumors with a good prognosis and with indication for radiotherapy, where the proton plan was deemed superior or equal to the photon plan according to the national treatment planning committee, were eligible for inclusion. Toxicity was recorded before, during and after proton radiotherapy according to the CTCAE 4.0 scale. RESULTS A majority of the included 262 patients were male, the most common diagnosis was glioma grade 2 and the median total radiation dose was 54 Gy (RBE), given in fractions of 1,8 Gy (RBE). At the last week of radiation 14% of patients had fatigue grade 1, 46% of patients had radiation dermatitis grade 1, and 32% of patients had alopecia grade 2. In total, 288 toxicity grade 1 and 121 toxicity grade 2 cases were reported in the last week of PRT. After 4-6 weeks the numbers were 211 and 120, respectively. At the first-year follow-up there were 98 cases of grade 1 toxicity, and 43 of grade 2 toxicity, in total. There was no grade 3 or higher toxicity the last week of radiation. At 4-6 weeks after radiotherapy, 11 (4,2%) grade 3 toxicities were registered, including headache, fatigue, radiation dermatitis, nausea and impaired hearing. The total number of grade 3 toxicity was 10 (3,8%) at 3 months post-radiotherapy and 7 (2,7%) after 1 year. At the first-year follow-up, only 2 (0,8%) grade 4 toxicities were reported (impaired hearing and stroke). No grade 5 toxicity was reported. CONCLUSION In this heterogeneous cohort of primary CNS tumors, PRT on average seems tolerable and safe regarding acute and early late toxicity. However, with a higher radiation dose or specific diagnoses, toxicity with PRT needs to be further investigated. Reports on late toxicity from the PRO-CNS study will ensue after 5- and 10-year follow-up.