ESTRO 2021 Abstract Book

S680

ESTRO 2021

consortium. S. Badellino 1 , H. Chen 2 , I. Poon 2 , D. Erler 2 , M. Levis 1 , R. Dagan 3 , M. Foote 4 , A.V. Louie 2 , K.J. Redmond 5 , T. Biswas 6 , A. Sahgal 2 , U. Ricardi 1 1 University of Torino, Department of Oncology, Torino, Italy; 2 Sunnybrook Odette Cancer Center, University of Toronto, Department of Radiation Oncology, Toronto, Canada; 3 University of Florida, Department of Radiation Oncology, Jacksonville, USA; 4 University of Queensland, Princess Alexandra Hospital, Department of Radiation Oncology, Queensland, Australia; 5 Johns Hopkins University, Department of Radiation Oncology and Molecular Radiation Sciences, Baltimore, USA; 6 Case Western Reserve University, University Hospitals Seidman Cancer Center, Cleveland, USA Purpose or Objective Stereotactic ablative radiotherapy (SABR) is increasingly used in the treatment of extra-cranial oligometastatic Non-Small cell lung cancer (NSCLC). Clinical evidence supporting the use of SABR in this setting demonstrated significant benefit in local control and progression-free survival. We report clinical outcomes of patients with oligometastatic (OM) NSCLC treated with SABR using a large multi-institutional database. Materials and Methods Six international centers registered a retrospective database in which all patients were treated with SABR between 2008 and 2016 for OM disease from any kind of tumor. For the purpose of this analysis, we identified all NSCLC patients without brain metastases who underwent SABR. The primary outcome was Overall Survival (OS), while secondary outcomes included Progression-free Survival (PFS) and Local Control (LC). Survival was analyzed using the Kaplan-Meier method. Univariable regression analysis was used to investigate the relationship between study outcomes and variables. Variables that passed the univariable screen were entered into a multivariable model. The variables used in regression analysis included stage at diagnosis, histology, systemic therapy, metastatic interval, synchronous and early metachronous (<= 24 months)/ late metachronous (> 24 months), site and number of metastases. All analysis was performed in R (R Foundation for Statistical Computing, version 4.0.2). Results We identified 255 patients with a total of 369 OM-NSCLC lesions. The mean age was 70.2 ± 10.6 years and 137 (53.7%) patients were male. At the time of first SABR, 193 patients (75.7%) were treated for a single lesion, 43 (16.9%) for 2 lesions and 19 (7.5%) for 3–5 metastases. The most common site of metastatic involvement was the lung (n=169, 66.3%). With a median follow-up time of 23.8 months, median OS was 32.5 months, while 2- year OS rate was 62.9%. The 2-year PFS and LC rate were 34.2% and 86%, respectively. On multivariable analysis, late metachronous onset predicted for improved OS (HR 0.52, 95% CI 0.35-0.76), while a total PTV volume (summed PTV of all treated lesions) > 68 cc, and the presence of non-spine bone metastases were associated with worse OS (HR 1.56, 95% CI 1.06-2.29, and HR 2.75, 95% CI 1.75-4.33, respectively). In terms of PFS, late metachronous onset predicted better outcome (HR 0.71, 95% CI 0.52-0.96), while a total PTV volume > 68 cc, and T stage 3/4 at diagnosis were detrimental (HR 1.49, 95% CI 1.06-2.10, and HR 1.44, 95% CI 1.04- 2.00, respectively). Moreover, Individual PTV volume > 57 cc predicted a worse LC (HR 2.37, 95% CI 1.37-4.09). We recorded one case of death, possibly related to acute pneumonitis, while most of the patients experienced mild toxicity. Conclusion This large multi-institutional analysis found that SABR for OM NSCLC has encouraging outcomes with acceptable toxicity. Patients with low disease burden and late onset of metachronous disease may have a better prognosis. PD-0846 Tumor match and adaptive radiotherapy reduce risk of radiation pneumonitis and increase survival D.S. Møller 1 , C.M. Lutz 1 , M. Alber 2 , A.A. Khalil 3 , M.I. Holt 4 , H.H. Schmidt 3 , A.L. Appelt 5 , M.M. Knap 3 , L. Hoffmann 1 1 Aarhus University Hospital, Department of Medical Physics, Aarhus, Denmark; 2 Heidelberg University Hospital, Heidelberg Institute for Radiation Oncolocy (HIRO), Heidelberg, Germany; 3 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 4 Vejle Hospital, part of Lillebælt Hospital, Department of Clinical Genetics, Vejle, Denmark; 5 University of Leeds, Leeds Institute of Medical Research at St James’s, Leeds, United Kingdom Purpose or Objective Tumor match and adaptive radiotherapy (ART) based on on-treatment imaging increases the precision of RT, thus allowing for a reduction of treatment volume and, consequently, of the dose to organs at risk. We investigate the effect of ART on recurrence, survival and radiation pneumonitis (RP) in a retrospective patient cohort of locally advanced non-small cell lung cancer (LA-NSCLC) patients. Materials and Methods Between 2010 and 2018, 439 consecutive LA-NSCLC patients received definitive chemo-radiotherapy treatment with RT doses between 50 and 66Gy in 25 to 33 fractions, 5 fractions/week. ART based on daily cone-beam CT tumor match was introduced for all patients in 2013, and the higher precision allowed reduction of the PTV margins. To investigate the effect of ART on recurrence, survival and RP, the 439 patients were divided in two groups, pre-ART (184 patients) and ART (255 patients). RP was scored retrospectively according to CTCAEv3 and date of maximum RP grade was recorded. Differences in clinical, treatment-specific and dosimetric variables were compared with c 2 tests (categorical variables) and Mann Whitney U tests (continuous variables). Progression-free and overall survival as well as RP in the two groups were compared with log-rank tests. Hazard ratios were estimated from Cox proportional hazard regression. Results With our ART strategy, median PTV volumes decreased significantly from 456 [71;1262] cm3 (preART) to 270 [31;1166] cm3 (ART), p<0.001. No significant differences in stage (p=0.36), histology (p=0.35), PS (p=0.12) and