ESTRO 2021 Abstract Book

S959

ESTRO 2021

Purpose or Objective In this study we report the retrospective data of a cohort of patients who received stereotactic body radiotherapy for pulmonary oligometastases and we assess the clinical factors potentially affecting the clinical outcomes. Materials and Methods The present series reports the outcomes of a cohort of 88 patients with pulmonary oligometastases. All patients were treated with SBRT performed with image-guided volumetric modulated arc therapy (VMAT- IGRT), up to 5 secondary lesions. Concurrent systemic therapy was allowed. Local control (LC), distant- progression free survival (DPFS) and overall survival (OS) were assessed using Kaplan-Meier method. Univariate and multivariate analyses were performed to assess any potential predictive factor for survival outcomes. A p<0.05 was assumed as statistically significant .All statistical analyses were carried out using Graphpad Prism v9.0.2 (Graphpad, San Diego, CA, USA) Results A total of 117 lesions in 88 patients were treated from February 2014 to August 2020: 77 lesions were oligorecurrent, 28 were oligoprogressive, 12 were oligopersistent. The most frequent histology subtypes were: colon in 30.5%, lung cancer (both small and non-small cell lung cancer) in 40%, gynecological cancer (ovary and endometrium) in 7%, bladder in 8%, head and neck cancer in 6%, breast in 2.5%. Median patients’ age was 61 (range, 32-86 years). Concurrent systemic therapy was administered in x%. Median total dose was 58 Gy Gy (range, 48 – 70 Gy) delivered in 5-10 fractions for a median BED 10 =118 Gy (range, 96-151 Gy) ). Median PTV volume was 5.9 cc (range, 0.4-29). Median follow-up was 43 months (range, 3-71); acute and late toxicity was negligible with no G≥2 adverse event. Our LC rates at 2 and 3-years were both 94.3%. DPFS rates at 2- and 3- years were 74% and 68%; the number of oligometastases treated was found to be related to worse DPFS outcomes (p=0.03); similarly, also the absence of concurrent systemic therapy was associated to a higher incidence of distant metastases (p=0.001). The most frequent site of relapse was lung in 31 cases (35%). A second SBRT course was proposed in 25 cases (28%) . The 2- and 3- OS rates were 84% and 71%. Conclusion SBRT is feasible for pulmonary oligometastasis with favorable local control and minimal toxicity. Preliminary clinical outcomes are promising and more mature data are warranted. PO-1154 Respiratory admissions following RT in relation to pulmonary function and lung doses in lung cancer F. Sun 1 , A. Abravan 2 , A. McWilliam 2 , K. Banfill 2 , J. Lilley 1 , B. Wheller 1 , F. Corinne 2 , K. Franks 1 1 Leeds cancer centre, Oncology, Leeds, United Kingdom; 2 University of Manchester, Oncology, Manchester, United Kingdom Purpose or Objective Radiation pneumonitis is a well-known side effect for patients treated with thoracic radiotherapy. However, clinical diagnosis of radiation pneumonitis can be difficult, often compounded by co-existing respiratory diseases such as chronic obstructive pulmonary disease (COPD) and chest infections. This project aims to assess the relationship between baseline pulmonary function test, COPD diagnosis, alongside lung RT dosimetric parameters and respiratory hospital admission within a first year after RT in lung cancer. Materials and Methods 1113 non-metastatic lung cancer patients who received curative-intent RT at a large regional cancer centre, between 2010 and 2016 with available RT planning images were identified. Pulmonary function test parameters including FEV1 (forced expiratory volume in 1 second), FVC (forced vital capacity) and DLCO (diffusing capacity of the lungs for carbon monoxide) were collected. COPD diagnosis and lung dosimetric parameters such as lung V10, V20, V30 and mean lung dose were obtained from RT dose images. The end point was respiratory type admission, identified using WHO ICD-10 codes and obtained from Hospital Episode Statistics/Public Health England, from day 1 of RT up to 1 year after RT completion. Frequency of admissions within the first year categorized into no admission, low number of admission (1-2 admissions), and high number of admission (3 admissions or higher). Lung dosimetric parameters were bootstrapped 100 times into elastic net least absolute shrinkage and selection operator along with other important factors. Variables with highest magnitude and frequency were included into the Ordinal logistic regression to predict the frequency of respiratory admission after RT. Results 601 with available pulmonary function test and hospital admissions following RT were analysed. Percentages of patients with no admission, low number of admission, and high number of admission were 61%, 26%, and 13%, respectively. From multivariable ordinal regression, odds ratio (OR) between no admission to low admission, and no admission to high admission was 2.5 for COPD, 0.98 for DLCO, 1.9 for performance status and 1.03 for lung V20, adjusted for gender (OR = 0.74) and age (OR= 1.01) (Table 1). Table 1: Multivariable ordinal logistic regression for no admission, low, and high number of admissions.