ESTRO 2021 Abstract Book

S1247

ESTRO 2021

patients were classified as PSP and 18 as ETP. After a median follow up of 41 months, OS rate at 2 years was 60.7% in PSP and 19.3% in ETP. Median survival was higher in PSP compared to ETP (25.2 months’ vs 20.3 months p=0.0092). There was no significant difference between groups in terms of gender, arm of treatment, type of surgery and MGMT status. Higher ratios of Lac/NAA and Cho/Cr were observed in ETP compared to those with PSP (median respectively 1.2 vs 0.5, p=0.006 and 3 vs 2.2, p=0.021) within the CE regions. ETP were characterized by Cho/Cr >2.33 with an AUC of 78%, sensibility (se)83%, specificity (sp)64%. Other parameters were Lac/NAA >0.61 and tumor volume (TV) >9.42 cc with respectively AUC of 81% and 81%, se of 100% and 100%, and sp of 63 % and 61%. Within the FLAIR edema, no significant predictor was retained after Bonferroni correction. TV was higher in ETP than in PSP (23.2cc vs 7.2cc p= 0.0075). After multivariable regression analysis, TV was the most significant predictor to classify ETP and PSP and the only one retained in the model (p=0.028). Conclusion In this analysis from a prospective trial including DWI, perfusion and MRSI, we describe significant spectroscopic ratios, particularly surrogate’s markers of hypoxia, i.e. lactate. TV remains the only predictive factor in the multivariate analysis. PO-1523 Real world outcomes in patients with oligometastases treated with SABR - a single centre experience. A. Fatimilehin 1 , S. Bowen Jones 1 , M. Bewley 1 , R. Hall 2 , C. Harris 2 , P. Whitehurst 2 , N. Bayman 1 , R. Colaco 1 , D. Woolf 1 , G. Radhakrishna 1 1 The Christie NHS Foundation Trust, Clinical Oncology, Manchester, United Kingdom; 2 The Christie NHS Foundation Trust, Physics, Manchester, United Kingdom Purpose or Objective Delivering Stereotactic Ablative Body Radiotherapy (SABR) to patients with extracranial oligometastatic disease has the potential to improve long-term disease control, survival and defer systemic therapies, by providing a high biologically equivalent dose (BED) whilst sparing normal tissue, in a small number of fractions compared with conventional fractionation.We present the outcomes from an audit of patients treated with SABR under the NHS Commissioning through Evaluation (CtE) scheme at a single centre in Manchester, United Kingdom. Materials and Methods A retrospective analysis was performed. Eligible patients were 18 years or older with up to 3 extracranial lesions. The onset of metastatic disease in this cohort was at least 6 months from the primary tumour diagnosis, and life expectancy had to be 6 months or over. Inclusion criteria also included having a WHO performance status of 2 or less. Prescribed doses ranged from 30–60 Gy in 3-8 fractions, delivered to lesions which were up to 6cm in size. The primary outcomes included local control at 1 and 2 years from SABR treatment, median overall survival and G3/4 toxicity. Results A total of 106 patients were treated between February 2016 and September 2019. The median age was 74 years and median follow up period was 12 months. The most common primary tumour was colorectal 33% (35/106), followed by renal 16.9% (18/106). The most common site of oligometastases treated was lung 49% (52/106). The local control rate was 96.2% (102/106) at 1 year and 86% (43/50) at 2 years. Of those patients who had disease progression, 19.6% (10/51) had local progression, and 80.4% (41/51) had distant progression. The overall survival rate at 1 year was 90.7%. One patient experienced grade 3 fatigue toxicity. No other grade 3 or 4 toxicities were reported. A Kaplan-Meier curve demonstrating overall survival is shown in Figure 1. A summary of the primary diagnoses and treated metastases is seen in Table 1. Prior to SABR, the majority of patients (84.9%) had 0 or 1 previous lines of systemic treatment. 1. Laprie A et al, BMC Cancer 2019

No of lines of treatment prior to SABR % 0

58.5%

1

26.4%

2

7.5%

3

3.8%

4

3.8%