ESTRO 2023 - Abstract Book

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ESTRO 2023

cumulative incidence of different failure types. Clinically relevant toxicity after reRT was retrospectively assessed from patient records (CTCAE v5.0, grade 2+ for dyspnoea, grade 3+ for all others), and cumulative incidences estimated Results 82 patients were identified, with median age 74 years (IQR 67-82), 44 male / 38 female. Key demographic and treatment data are summarised in Table 1. Stereotactic ablative radiotherapy (SABR) was the most common radiotherapy technique, with 51% receiving it for first course and 54% for reRT. Median potential follow-up was 40 months. 31 patients (41%) had progression after reRT: 12 (15%) local recurrence at the site of reRT; 12 (15%) recurrence elsewhere in the lung/thorax; 9 (10%) distant metastasis in another organ. OS was 48% (95% CI 38% - 60%) and 21% (11% - 37%) at 2 and 4 years, respectively. Cancer-specific survival was 66% (55% - 79%) and 50% (30% - 67%) at 2 and 4 years. Figure 1 illustrates the cumulative risk of different types events as first failure. Thirty-one (38%) patients developed CTCAE grade 2+ toxicity post reRT, with dyspnoea grade 2+ (N=15) being the most common. The 2-year cumulative incidences were 18% for dyspnoea, 8% for chest pain, 8% for oesophagitis, 5% for pneumonitis, and 2% for cough. There was one grade 5 toxicity. Conclusion This represents the reported largest cohort of patients treated with reRT for lung malignancies. We demonstrate excellent local control (19% failures at 4 years), and good cancer-specific survival (50% at four years), with acceptable toxicity. This may help guide clinicians when considering the risks and benefits of lung reRT. 1 Seoul National University College of Medicine, Radiation Oncology, Seoul, Korea Republic of; 2 Seoul National University, Cancer Research Institute, Seoul, Korea Republic of; 3 Seoul National University, Cancer Research Institute, Seoul, Korea Republic of; 4 Seoul National University Hospital, Radiation Oncology, Seoul, Korea Republic of; 5 Seoul National University College of Medicine, Radiation Oncology , Seoul, Korea Republic of; 6 Seoul Metropolitan Government Seoul National University Boramae Medical Center, Radiation Oncology, Seoul, Korea Republic of; 7 Seoul National University College of Medicine, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective Thoracic radiotherapy (TRT) has been demonstrated to improve local control and have survival benefits in patients with extensive-stage small cell lung cancer (ES-SCLC) in the chemotherapy era. However, there are no prospective data on the role of TRT in the era of chemoimmunotherapy, which has become the new standard of care for ES-SCLC. The purpose of this study is to compare the pattern of intrathoracic progression changed before and after the introduction of immunotherapy. Materials and Methods We retrospectively reviewed 294 patients with ES-SCLC who were treated at two institutions from January 2016 to June 2021. In total, 62.2% (n = 183) underwent chemotherapy alone (CTx), 13.3% (n =39) underwent CTx followed by consolidative TRT (TRT group), and 24.5% (n = 72) underwent CTx with immune check inhibitor (ICI) without TRT (ICI group). TRT was administered with a median dose and fractions of 50 Gy (interquartile range [IQR], 45-54 Gy) and 25 (IQR, 15-27), respectively. Propensity score matching (PSM) was performed to compare the three groups of patients. Results In patients with an objective response (n = 245), the proportion of intrathoracic progression among the first relapse sites was 83.0% in the CTx alone group and 77.5% in the ICI group (p = 0.40); however, it was significantly lower in the TRT group (58.3%, p = 0.02). At a median follow-up duration was 10.4 months (IQR, 6.9-16.1 months), the median intrathoracic progression-free survival (PFS) and PFS was 5.8 and 5.4 months in the CTx alone group, 11.0 and 9.2 months in the TRT group, and 6.9 and 6.0 months in the ICI group, respectively. Before matching, the TRT group showed improved intrathoracic-PFS compared to both the CTx alone and the ICI group (all p < 0.001). Also, the TRT group showed better PFS compared to both the CTx alone and the ICI group (p = 0.005 and p < 0.001, respectively). After PSM analysis, the TRT group maintained significantly better intrathoracic-PFS compared to both the CTx alone group and the ICI group (p <0.001 and p = 0.01, respectively); however, in terms of PFS, there was no significant benefit compared to the ICI group (p = 0.17). Conclusion In patients with ES-SCLC, intrathoracic tumor progression showed the most dominant pattern of failure even after immunotherapy. In the era of chemoimmunotherapy, consolidative TRT can still be considered a useful treatment strategy for locoregional control. PO-1317 Intrathoracic Failure Pattern in the ES-SCLC Following the 1st-line Immunotherapy D. Kim 1 , H.J. Kim 1,2 , H. Wu 1,3 , J.H. Lee 1,4 , S. Kim 5,6 , B.H. Kim 7,6

PO-1318 Pneumonitis after chemoRT and durvalumab: lung damage on CT is confined to the irradiated region

G. Defraene 1 , X. Verbeke 2 , S. Verfaillie 2 , P. Berkovic 3 , W. De Wever 4 , E. Wauters 2 , M. Lambrecht 3

1 KU Leuven – University of Leuven, Department of Oncology – Laboratory of Experimental Radiotherapy, Leuven, Belgium; 2 University Hospitals Leuven, Department of Pneumology, Leuven, Belgium; 3 University Hospitals Leuven, Department of Radiation Oncology, Leuven, Belgium; 4 University Hospitals Leuven, Department of Radiology, Leuven, Belgium Purpose or Objective Immune checkpoint inhibitors (ICI) entail an increased risk of pneumonitis when combined with chemo radiotherapy (RT) in locally-advanced non-small cell lung cancer (NSCLC). This often leads to discontinuation of ICI which was shown to affect