ESTRO 2021 Abstract Book

S1177

ESTRO 2021

central nervous system tumors. Materials and Methods

A systematic search was performed in PubMed database using the following search strategy: ("brain"[MeSH Terms] OR "brain"[All Fields]) AND ("pediatrics"[MeSH Terms] OR "pediatrics"[All Fields] OR "pediatric"[All Fields]) AND ("protons"[MeSH Terms] OR "protons"). Only papers in English reporting PT-induced toxicity were included. Results Among 144 articles screened for relevance, 19 studies were deemed eligible (five prospective and 14 retrospective), including 2,544 patients. Median follow-up ranged between 0.1 and 18.2 years (median 3.7 years). The most common late toxicities were neuroendocrine deficiency (6.0%), vasculopathy (2.9%), brainstem/brain necrosis (2.8%), ototoxicity (2.3%), radiological changes (1.5%), and visual symptoms (0.6%). Only 10 studies reported toxicity based on the CTCAE scale (G1: 5.9%, G2: 4.9%, G3: 2.0%, G4: 0.3%, and G5: 0.2%). Long-term outcomes were reported in 13 papers. Progression-free survival, reported as crude value, was 80% in one study, 48% as 2-year rate in one study, 76% as 3-year rate in one study, 83%-89% (in the subgroup of Germ Cell Tumors) and 82% (others) as 5-year rate in four papers, and 83% as 8-year rate in one study. Local control, reported as 3-year rate was 85% and 91% in two studies, and 83%-89% (Germ Cell Tumors) and 82%-77% (others) as 5-year rate in four studies. Two-year Overall Survival (OS) was 68%-91% as reported in two papers, 3-year OS was 90%-96% in three studies, 5-year OS was 87%-100% (Germ Cell Tumors) and 82%-83% (others) in five papers, 7-year OS was 80% in one paper, and 8-year OS was 100% in one study. Conclusion Although high-level evidence is lacking, this review confirms a relatively low risk of toxicity after PT in this setting. In terms of outcomes, the results are similar to the ones recorded with photon-based radiotherapy. Prospective controlled trials are needed to confirm these data. PO-1433 TBI as a Component Of Conditioning Regimen in AHCST for Pediatric ALL S. Kamer 1 , C. Hidimoglu 1 , S. Hoca 1 , G. Ozek 2 , S. Aksoylar 2 , Y. Anacak 1 1 Ege University, Radiation Oncology, IZMIR, Turkey; 2 Ege University, Pediatric Hematology Oncology, IZMIR, Turkey Purpose or Objective Current scientific literature recommends Allogeneic hematopoietic stem cell transplantation (AHSCT) with TBI (total body irradiation) as a promising method providing excellent outcome without increasing relapse or transplant-related mortality (TRM) for pediatric acute lymphoblastic leukemia (ALL). The aim of the present study was to evaluate the outcome and toxicity of TBI as a part of the conditioning regimen for AHSCT from the data of the Ege University Hospital. Materials and Methods 84 patients who underwent TBI between 2009-2020 were analyzed retrospectively. Their median age was 8 (1- 17) at the diagnosis and 10 (3-18) during the TBI. Until 2012 BFM-2003, and after 2012 BFM-2012 protocols were used for AHSCT. Hematopoietic stem cells obtained from 56 (66.7%) related and 28 (33.3 %) unrelated donors. Conditioning regimen included 12 Gy TBI in 6 fractions delivered in 3 days (-4th to -6th days), and etoposide. In the days prior to TBI 6 Gy whole cranial irradiation was administered to 14 patients who had CNS involvement. Results 12 patients (14.3%) died due to TRM. After a median follow-up of 49 months (1-139), relapse was occurred 8 (9.5%) patients; median time to relapse was 17 months (3-48). There were bone marrow relapse in 6 patients and CNS relapse in 2. All patients with relapse died of disease. 4-y OS was %75.1. Grade 2-3 acute side effects of TBI was recorded in 35 patients (41.6%) - Vomiting in 18, transient parotitis in 12, headache in 8. Late effects were as follows: secondary sarcoma in one patient after 79 th month, veno- occlusive disease in one, cataract in one and hypothyroidisim in 5 patients. Chronic GVHD was experienced in 8 (9.5%) patients. Conclusion Fractionated TBI including conditioning regimen for the AHSCT in pediatric ALL patients provides good OS and acceptable relapse rate and side effects. These patients are under risk of developing late side effects and secondary cancers, and should be followed forever PO-1434 Pencil beam scanning Proton therapy for Pediatric and young adults-Preliminary experience from India S. Chilukuri 1 , N. Burela 2 , R. Uppuluri 3 , D. Indumathi 4 , P. Panda 2 , R. Raj 3 , T. Raja 5 , D. Sharma 6 , R. Jalali 2 1 Apollo Proton Cancer Centreq, Radiation Oncology, Chennai, India; 2 Apollo Proton Cancer Centre, Radiation Oncology, Chennai, India; 3 Apollo Proton Cancer Centre, Pediatric Oncology, Chennai, India; 4 Apollo Proton Cancer Centre, Pediatric Anesthesia, Chennai, India; 5 Apollo Proton Cancer Centre, Medical Oncology, Chennai, India; 6 Apollo Proton Cancer Centre, Medical Physics, Chennai, India Purpose or Objective Proton beam therapy (PBT) has been a preferred modality in pediatric malignancies requiring radiotherapy. We report our preliminary experience of treating consecutive patients younger than 25 years with image- guided pencil beam scanning PBT from the first and only centre on the Indian subcontinent. Materials and Methods Patients were selected for PBT on the basis of a multidisciplinary tumor board decision. Patient demographic data, as well as tumor and treatment-related characteristics of the cohort, were captured. Patient and treatment-related factors and their association with acute toxicities were analyzed using univariable and