ESTRO 2022 - Abstract Book

S1046

Abstract book

ESTRO 2022

From Abril'18 to December'20, 28 patients were treated with SBRT.Central lung lesions were defined according to RTOG 0813 criteria. Immobilization systems were used. ITV was defined by 4D RPM-Varian™.PTV was generated by a 5mm isotropic expansion of the ITV.Two regimens were used: 7.5Gy in 8 fractions or 10-11Gy in 5 fractions.We contoured and retrospectively reviewed the dosimetry of 17 heart substructures according to Feng et al. heart atlas and cardiac toxicity based on CTCAE v5.0. UK constraints were applied. Results 10 patients with early-stage non-small cell lung cancer, 5 non-biopsed lesions and 14 lung metastases were analysed. 21 were central and 4 ultra-central. Mean follow-up was 16 months(3-33). Mean age was 70y (52-89). Mean GTV/PTV size was 26/57.6cc (0.8-100/6.1-219). Local control was 96% at 12 months. In the 8 fractions group, median D0,5cc at each substructure was: right and left atrium, 7.5Gy(1-20) and 17,2Gy(1-48); right and left ventricle, 6.5Gy(1-12) and 3.5Gy(1-17); superior vena cava, 48Gy(6.8-52.8); pulmonary artery, 17Gy(1- 43); ascending and descending aorta, 17.1Gy(1-39) and 18.8Gy(1-54.8); aortic valve, 2Gy(0-19.5); pulmonic valve, 4.5Gy(0- 10); mitral valve, 0.5Gy(0- 14); tricuspid valve, 0.5Gy(0-13.5); left main coronary artery, 7Gy(0-13.8); left anterior descending artery, 5Gy(0-15.6); left circumflex, 3Gy(0-18.5); right coronary artery, 2.5Gy(0-10) and AV node, 1.5Gy(1- 12.6). Median D0,5cc and mean dose in heart were 47Gy(1-51.5) and 2,9Gy(0.1-10.8) respectively. In the 5 fractions group, median D0,5cc at each substructure was: right and left atrium, 3Gy(1-39) and 5Gy(1-31.5); right and left ventricle, 1.5Gy(1-14.3) and 3Gy(1-37.5); superior vena cava, 12Gy(1.7-53.1); pulmonary artery, 13.75Gy(0,7- 28.8); ascending and descending aorta, 12.2Gy(5-33) and 13.3Gy(5.9-49.6); aortic valve, 0.5Gy(0-15.5); pulmonic valve, 1.5Gy(0.3-13); mitral valve, 0.5Gy(0-11); tricuspid valve, 0.4Gy(0-12); left main coronary artery, 0.9Gy(0.1-10); left anterior descending artery, 0.6Gy(0.1-8.8); left circumflex, 0.6Gy(0.1-15.7); right coronary artery, 0.5Gy(0-12.8) and AV node, 0.4Gy(0.2-9.8). Median D0,5 cc and heart mean dose were 16Gy(0.8-43.1) and 1.1Gy(0.1-10) respectively. Six deaths were reported at the time of the analysis. No > G3 toxicities were found. Conclusion No cardiovascular related deaths were observed with the doses reported above. Heart dose constraint used were safe. No consensus for each heart substructure constrains have been met yet. Knowing the dose that each substructure of the heart can tolerate might be useful for the treatment of central and ultracentral lesions in certain clinical situations (e.g. multiple lesions or re-irradiation). Prospective trials are needed to elucidate cardiac toxicity at each heart substructure. We are performing one at our center. 1 MAASTRO Clinic, Maastricht University Medical Center, GROW school for Oncology and Developmental Biology, Department of Radiation Oncology, Maastricht, The Netherlands; 2 Maastricht University Medical Center+, Department of Pulmonology, Maastricht, The Netherlands; 3 Maastricht University Medical Center+, Department of Cardiothoracic Surgery, Maastricht, The Netherlands; 4 University of Campania "L. Vanvitelli" , Department of Precision Medicine - Radiation Oncology Unit, Naples, Italy Purpose or Objective Current guidelines on radiotherapy (RT) dose for thymic epithelial tumors (TET) based on old and small studies using 2D-RT with low levels of evidence IV-V (1). We aim to shed light on the optimal RT doses for TET patients treated with modern RT techniques through a systematic review of more recent literature. Materials and Methods We first designed and registered the protocol (PROSPERO ID: CRD42021241826) for review and followed PRISMA guidelines. A comprehensive search of 4 databases was conducted. The literature search included retrospective and prospective studies on humans affected by TETs undergoing external beam radiation with modern techniques such as IMRT/VMAT, SBRT, 3D- CRT, or proton therapy, published in English from 1990-2021. Inclusion criteria were information on RT dose-response, a sample size of ≥ 20 patients, follow-up time of ≥ 5 years, and treatment outcomes (overall survival, progression-free survival, toxicity). Duplicates, reviews and studies reporting only 2D-RT were excluded. Two researchers (AA, SP) independently screened and reviewed all citations, after an interrater-reliability-test (Cohen’s Kappa). A 3rd person (DR) provided final arbitration if consensus on inclusion could not be reached. Risk of bias assessment was done for the selected studies using the New Castle-Ottawa scale. AA and SP independently extracted all the data, and a narrative synthesis without meta-analysis of the collected data was carried out. Results The online database search identified 966 citations, and 179 of these were selected for a full-text review (Fig. 1). Interrater reliability test based on 66 abstracts showed a very high agreement between the investigators (Cohen’s K = 0,91). Only two studies fulfilled all inclusion criteria. With a less stringent minimal follow-up time of 3 years, 3 additional studies could be included. These 5 studies with a total of 357 patients were synthesized according to stage, histology, and intervention (Table 1). Only 1 prospective study was found, including patients of all stages and histology (Fan X. et al, 2020) which showed a better OS and PFS with RT dose ≥ 60Gy using IMRT and concurrent chemotherapy. A retrospective study on postoperative RT (PORT) in stage II thymoma showed no significant results when PORT doses were compared (Chen et al, 2010). For stage III TET, 2 studies were found: for primary or definitive RT (dRT) an improved OS was found with a total dose of 54 Gy or higher (Fan C. et al, 2020), but not for PORT (Fan C et al, 2013). One study on salvage RT in recurrences showed a significantly better OS and PFS with ≥ 52 Gy compared to <52Gy (Yang et al, 2019). PO-1240 “Radiotherapy for Thymic Epithelial Tumors: What Is The Optimal Dose? A Systematic Review.” A. Angrisani 1,4 , R. Houben 1 , F. Marcuse 2 , M. Hochstenbag 2 , J. Maessen 3 , D. De Ruysscher 1 , S. Peeters 1