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(in total) and clinical outcome and then compared with results of the ACRIN6668/RTOG 0235 study. Results PET/CT data from 161 stage IIIA/IIIB NSCLC patients were analysed. Uni- and multivariable analysis failed to identify MTV as prognostic factor for overall survival. The hazard ratio associated with MTV was 1.000 (0.997 to 1.002) (p>0.5, chi2-test). The distribution of MTV in the ESPATUE cohort was similar to that in ACRIN6668/RTOG 0235 with a median MTV of 53.7 ml (upper quartile 93.3 ml). The ACRIN6668/RTOG 0235 defined three MTV tertiles (low-, middle- and high-risk tertile: <39.2 ml, 39.2≤89.8 ml and >89.8ml) with associated median times for overall survival of 29.7, 21.2 and 13.6 months, respectively (Ohri JNCI2015;107, doi:10.1093). In the ESPATUE trial, survival was good, especially for patients with MTV>89.8ml (median: 37.7months; 95% CI: 19.9-71 m) with no differences in comparison to patients with tumors < 89.8ml (median survival: 35.7months; 95% CI: 27.9-48m) (p>0.5, log rank test). No differences existed for patients randomised to trimodality or definitive RCT after induction chemotherapy in the stratified comparison according to MTV. Conclusion We examined the prognostic value of MTV and tracer activity uptake in FDG-PET before treatment. The finding of the ACRIN6668/RTOG 0235 trial of MTV as a prognostic factor could not be validated. The intense treatment schedule of induction chemotherapy andbhyperfractionated accelerated RCT in either neoadjuvant or definitive setting might mitigate prognostic significance of MTV for OS in NSCLC patients. OC-0494 Randomized clinical trial on 7-days-a-week radiotherapy in non-small cell lung cancer R. Suwinski 1 , K. Galwas-Kliber 1 , M. Giglok 1 , G. Plewicki 1 , B. Jochymek 2 , D. Sygula 2 , B. Maciejewski 2 , L. Miszczyk 2 1 Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Radiotherapy Clinic and Teaching Hospital, Gliwice, Poland 2 Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Radiation Oncology, Gliwice, Poland Purpose or Objective To compare the tolerance and effectiveness of conventional 5-days-a-week (CF) vs. continuous 7-days-a- week (CAIR) radiotherapy given after induction chemotherapy in locally advanced non-small cell lung cancer (NSCLC). Overall survival (OS), including the planned subset analysis, was considered as primary Between September 2009 and May 2017 189 patients with histologically confirmed, inoperable, Stage IIIA N2 or III B NSCLC were enrolled. They were given induction platin- based chemotherapy (2-4 cycles) and randomized to receive CF (n=90) or CAIR (n=99). Total radiation dose was 67.2-69.2 in both arms given in 35-36 fractions over 7 (CF) vs 5 (CAIR) weeks. Squamous cell cancer was diagnosed in 120 pts (63.5%), adenocarcinoma in 23 pts (12.2%), NOS in 43 pts. There were 137 males (72.5%) and 52 females (27.5%). Median age was 62 years, median follow-up was 2.7 years. The groups were well balanced with respect to the major prognostic factors. Results Curative doses of radiotherapy were delivered in 78/90 (86.7%) of patients in CF compared to 79/99 (79.8%) of patients treated in CAIR. Ten patients in CF (11.1%) and 16 patients in CAIR (16.2%) received palliative radiotherapy (20-30 Gy in 5-10 fractions), mostly due to the presence of metastatic disease detected at the diagnostic procedures before radiotherapy. No major differences in treatment toxicity between CF and CAIR were observed. The 2-year actuarial overall survival was endpoint of the study. Material and Methods

39.8% in CF vs. 45.7% in CAIR, the difference was not statistically significant (p=0.84, RR=0.71, intention to treat analysis). No significant differences in locoregional control or metastases-free survival were observed between the arms. The subset analysis revealed that patients with GTV volume below the median of 66 cm 3 had significantly better OS in CAIR compared to CF (2- year OS 66.6% vs 33.7%, p=0.04). Likewise, younger patients (age below the median of 62) had significantly better OS in CAIR compared to CF (2-year OS 53.2% vs 29.8%, p=0.04). Tumour type had major impact on OS in both trial arms, with 2-year OS of 58.% for non-squamous cancer, compared to 31.5% in squamous cancer (p<0.001). The analysis according to actual treatment did not alter the qualitative outcome of the study. Conclusion 7-days-a-week radiotherapy did not improve OS in the analysed group of patients with Stage IIIA N2 or III B NSCLC, after induction therapy. A significant improvement in OS attributable to CAIR fractionation was, however, detected in subsets of patients younger than 62 years, or with GTV smaller than 66 cm 3 . Such outcome may advocate future evidence-based selection of candidates for accelerated treatment. Non-squamous histology entailed a favourable survival in both trial arms. OC-0495 Early PD-1 blockade improves disease control for NSCLC brain metastases treated with radiosurgery A. Srivastava 1 , C.Abraham 1 , E. Filiput 1 , J. Huang 1 1 Washington University School of Medicine, RADIATION ONCOLOGY, Saint Louis, USA Purpose or Objective PD-1 inhibitors have shown single-agent activity against brain metastases in patients with metastatic melanoma as well as metastatic non-small cell lung cancer (NSCLC). Prior studies have demonstrated a synergistic effect between stereotactic radiosurgery (SRS) and concurrent PD-1 blockade on disease control in melanoma intracranial brain metastases. However, this relationship is less clear in individuals with metastatic NSCLC. The purpose of this study was to evaluate whether the timing of anti-PD-1 therapy when combined with SRS for NSCLC brain metastases may affect treatment outcomes. Material and Methods For this retrospective study, an institutional database of NSCLC patients with intracranial metastases treated with SRS between 2015 and 2017 was reviewed for individuals who had received immunotherapy (IT) with PD-1 inhibitors. Using the methods of Contal and O’Quigley, a cutpoint analysis was completed to determine the optimal timing of IT relative to SRS to optimize disease control. Patients were then divided into two cohorts based on this cutpoint. Concurrent IT was defined as initiation of anti-PD-1 agents prior to or within four weeks of SRS, and adjuvant IT was defined as administration of PD-1 inhibitors at least four weeks after SRS. Fisher’s exact test was utilized to compare baseline clinical and demographic covariates. The Kaplan-Meier method and log-rank test were used to estimate and compare local control (LC), distant brain control (DBC), and overall survival (OS) between these two cohorts, and Cox regression was used to identify predictors of these outcome metrics. Results Forty-two patients were eligible for this analysis, and cutpoint analysis demonstrated a significant difference in disease control at four weeks. Based on this cutoff, Twenty patients (47.7%) received concurrent IT, and 22 (52.3%) received adjuvant IT (median time from SRS 2.3 months, range 0.3 months – 10.1 months). Ten patients (25%) had previously undergone whole brain radiation therapy, and 34 patients (85%) had received prior chemotherapy. Mean follow-up time was 14.3 months.