ESTRO 2023 - Abstract Book

S1066

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ESTRO 2023

patients were eligible for assessment of local control. Local recurrences occurred in 2 patients (4%), manifesting at 9.4 months and 37.3 months post-SABR, respectively. Acute toxicity within 90 days post-SABR was observed in 2 patients (1 patient with grade 2 radiation pneumonitis and 1 with severe temporary back pain due to the duration of SABR delivery).

Conclusion The early results of MR guided SF-SABR delivered in breath-hold reveal high tumor control rates, indicating that the use of automatic beam gating with a 3 mm gating boundary is safe for patients with peripheral lung tumors.

PO-1332 Risk factors for intracranial metastasis in stage III NSCLC after chemoradiation

S. Thibodeau 1 , M. Meem 1 , S. Sandhu 2 , W. Hopman 3 , G. Digby 4 , S. Al-Ghamdi 4 , T. Owen 1 , A. Ashworth 5 , A. Fung 6 , A. Kartolo 7 , A. Robinson 6 , O. Zalay 8 , F. Ynoe de Moraes 1 1 Queen's University, Department of Oncology, Division of Radiation Oncology, Kingston, Canada; 2 Queen's University, Faculty of Medicine, Kingston, Canada; 3 Queen's University, Department of Public Health Sciences, Kingston, Canada; 4 Queen's University, Department of Medicine, Division of Respirology, Kingston, Canada; 5 Queen's University , Department of Oncology, Division of Radiation Oncology, Kingston, Canada; 6 Queen's University, Department of Oncology, Division of Medical Oncology, Kingston, Canada; 7 McMaster University, Department of Oncology, Division of Medical Oncology, Hamilton, Canada; 8 University of Ottawa, Department of Radiology, Division of Radiation Oncology, Ottawa, Canada Purpose or Objective Around 30% of patients with non-small cell lung cancers (NSCLC) are diagnosed with stage III disease at presentation, of which about 85% are treated with definitive chemoradiation (CRT). Approximately 40% of patients will eventually develop intracranial metastases (IM), though associated risk factors are not clearly described. We report survival outcomes and risk factors for development of IM in a cohort of patients with stage III NSCLC treated with CRT at a tertiary Cancer Centre. Materials and Methods We identified 195 patients with stage III NSCLC treated with CRT from January 2010 to May 2021. Multivariable logistic regression was used to generate odds ratios for covariates associated with development of IM. Kaplan-Meier analysis with the Log Rank test was used for unadjusted time-to-event analyses. P-value for statistical significance was set at < 0.05 with a two-sided test. Results Out of 195 patients, 108 (55.4%) had stage IIIA disease and 103 (52.8%) had adenocarcinoma histology. The median age and follow-up (in months) was 67 (IQR 60-74) and 21 (IQR 12-43), respectively. 148 patients (75.9%) were treated with 60 Gy in 30 fractions concurrent with chemotherapy. Of the 77 patients who received treatment since immunotherapy was available and standard at our Cancer Centre, 45 (58.4%) received at least one cycle. During follow-up, 84 patients (43.1%) developed any metastasis, and 33 (16.9%) developed IM (either alone or with extracranial metastasis). 150 patients (76.9%) experienced a treatment delay (interval between diagnosis and treatment > 4 weeks). Median OS was not reached for the overall cohort, and was 43.1 months for patients with IM and 40.3 months in those with extracranial-only metastasis (p=0.968). Factors associated with developing any metastasis included higher overall stage at diagnosis (p=0.013) and higher prescribed dose (p=0.022). Factors associated with developing IM included higher ratio of involved over sampled lymph nodes (p=0.001) and receipt of pre-CRT systemic or radiotherapy for any reason (p=0.034). On multivariate logistical regression, treatment delay (OR 4, p=0.032) and overall stage at diagnosis (IIIA vs. IIIB/IIIC) (OR 2.4, p=0.034) predicted development of IM. Conclusion In patients with stage III NSCLC treated with definitive CRT, the risk of intracranial metastasis appears to increase with overall stage at diagnosis and, importantly, treatment delay (> 4 weeks). Survival was better in patients without metastases. No difference in survival was observed between patients who developed either intracranial (alone or with extracranial metastasis) or extracranial-only metastasis. Metastatic disease remains the primary life-limiting prognostic factor in patients with stage III NSCLC treated with CRT. Further research is needed to better understand factors associated with survival and development of metastasis after CRT in the immunotherapy era.

PO-1333 MR-guided radiotherapy ablates ultracentral lung tumors with favorable long-term outcomes

S. Regnery 1 , E. Katsigiannopulos 1 , P. Hoegen 1 , F. Weykamp 1 , E. Sandrini 1 , T. Held 1 , M. Deng 1 , T. Eichkorn 1 , C. Buchele 1 , C. Rippke 1 , C.K. Renkamp 1 , L. König 1 , K. Lang 1 , S. Adeberg 1 , S. Klüter 1 , J. Debus 1 , J. Hörner-Rieber 1

1 Heidelberg University Hospital, Radiation Oncology, Heidelberg, Germany