ESTRO 2021 Abstract Book

S892

ESTRO 2021

Figure 2

Conclusion While appearance of abnormalities after proton radiotherapy seems to be multifactorial and not necessarily related to LET, we identified common characteristics related to planning technique for those cases in which LET is significantly higher in abnormal areas. More studies would be desirable to confirm whether the use of plans with arrangements with few beams and incidence directions may increase the effect of LET over normal tissue.

PO-1071 Hypofractionated stereotactic radiotherapy of brain metastases: a retrospective analysis. L. Marco 1 , M. Trignani 2 , G. Ingrosso 3,4 , F.C. Di Guglielmo 2 , G. Centofanti 3 , D. Fasciolo 2 , V. Bini 5,6 , D. Genovesi 2,7 , C. Aristei 3,4 1 General Hospital, Radiation Oncology , Perugia, Italy; 2 SS Annunziata Hospital, Radiation Oncology, Chieti, Italy; 3 General Hospital, Radiation Oncology, Perugia, Italy; 4 University of Perugia, Radiation Oncology, Perugia, Italy; 5 General Hospital, Internal Medicine, Endocrinology & Metabolism, Perugia, Italy; 6 University of Perugia, Internal Medicine, Endocrinology & Metabolism, Perugia, Italy; 7 G. D'Annunzio University, Neuroscience, Imaging and Clinical Sciences, Chieti, Italy Purpose or Objective Brain metastases (BM) are the primary cause of intracranial malignancies, affecting 20–40% of patients (pts) with malignant neoplasms. Hypofractionated stereotactic radiotherapy (HSRT) and stereotactic radiosurgery provided high tumor control without severe radiation-induced toxicity. Our aim is to evaluate the HSRT feasibility, effectiveness and toxicity. Materials and Methods We retrospectively reviewed medical records of pts with BM treated at two Radiation Oncology Centers. Between January 2015 and June 2020 a total of 78 lesions in 58 consecutive pts underwent HSRT. The median age was 60 years (35%>65 years); 50 (86%) pts had a KPS > 80. The most common primary tumor were lung (57%) and breast (20%). Forty-six (79%) pts were in the RTOG-RPA class II and 55% of cases had a DS-GPS score between 1.5 and 2.5. Forty-one (70%) pts had a single lesion and 57 (73%) of BM were telencephalic. Median lesion diameter was 1.8cm (range 0.5-5). HSRT was delivered in 3-5 fractions. Median total dose was 27 Gy (range 24-35) and median dose per fraction 8 Gy (range 6-9). To compare the different schedules, we used the corresponding BED 10 for each fractionation, which had a median value of 48 Gy 10 (range 42.3-59.5). Twenty- five pts underwent Linac-based volumetric-modulated arc therapy (VMAT), and 33 Tomotherapy. Neurological status and toxicity were scored according to Common Terminology Criteria for Adverse Events (CTCAE) v4.0. Study end-points were overall survival (OS), cancer-specific survival (CSS), brain progression-free survival (brain-PFS) defined as the occurrence of in-field and/or out-field progression. About the 78 HSRT-treated lesions, we evaluated local control (LC), out-field progression and radionecrosis (RN) occurrence. The Kaplan- Meier method and log-rank test were used for univariate analysis. Results Median follow-up was 13.3 months (IQR, 4.2-21). Median OS was 16.5 months (95%CI, 10.6-22.4), the 1-year and 2-year rates were 65% and 40%, respectively. Median CSS was 19.5 months (95%CI, 13.6-25.5), the 1- and 2-year rates were 71% and 43%, respectively. One- and 2-year brain-PFS were 44% and 29%, with a median value of 9.6 months (95%CI, 4.8-14.3). At univariate analysis, OS and CSS were positively correlated with KPS ≥ 90, RPA class I and controlled primary tumor. Moreover, age (>60 years) resulted as a prognostic factor for OS (p=0.03). After HSRT, 1- and 2-year LC were 74% and 42% with corresponding values of out-field progression of 82% and 70%, respectively. No severe acute toxicity was observed. RN was reported in 4 (7%) pts; it was symptomatic in 2 cases requiring steroids. Conclusion