S760
Clinical - Lung
ESTRO 2026
Digital Poster Highlight 657
were treated with stereotactic ablative radiotherapy between March 2024 and August 2025.Case 1: A 58- year-old man with bilateral adrenal oligoprogression after first-line chemotherapy received SABR (45 Gy/5 fx right, 40 Gy/5 fx left) after 8 cycles of Tarlatamab, with a 17-day interval between treatments.Four months later, palliative RT (30 Gy/10 fx) was administered to the lumbosacral spine after decompressive laminectomy.Case 2: A 65-year-old man, previously treated with two RT courses (45 Gy BID, then SABR 30 Gy/5 fx), underwent reirradiation to the right upper lobe lesion (30 Gy/6 fx) after 13 Tarlatamab cycles.Case 3: A 64-year-old woman with brain progression after chemo-immunotherapy received Tarlatamab as second line and underwent radiosurgery for three subcentimetric brain metastases (infratentorial, periventricular, and cerebellar), treated with 18 Gy in a single fraction prescribed to the 95% isodose. Results:
Exploring Survival Heterogeneity in Randomised Trials of Stereotactic Ablative Radiotherapy (RT) vs Conventional RT in Early Stage NSCLC Zhi Xuan Ng 1 , David Ball 2 , Tabitha Chan 1 , Cheng Nang Leong 1 , Wee Yao Koh 1 , Ivy Weishan Ng 1 , Chia Ching Lee 1 , Yu Yang Soon 1 1 Radiation Oncology, National University Cancer Institute, Singapore, Singapore, Singapore. 2 Radiation Oncology, Peter MacMacallum Cancer Centre, Melbourne, Australia Purpose/Objective: Conflicting overall survival (OS) outcomes exist across randomised trials (RCTs) comparing stereotactic ablative radiotherapy (SABR) to conventional radiotherapy (CRT) for early-stage NSCLC. This study aimed to evaluate these possible explanations for the different effects on OS observed in the CHISEL, LUSTRE, and SPACE RCTs. Material/Methods: This comparative effectiveness study used reconstructed individual participant data from 3 RCTs. Aggregate baseline patient characteristics were obtained from the primary publication of the RCTs. The Cochran Q test was used to determine if the reported OS HR from these three RCTs differ from one another. We used the Kaplan-Meier method to compare OS between the SABR arms and, separately, between the CRT arms across the included RCTs. We used Cox proportional hazards regression to estimate hazard ratios (HRs) and their 95% confidence intervals (CI). Results: Across the three trials, participants were randomised to receive either SABR or CRT. The SABR regimens were 54Gy/3, 48Gy/4, 60Gy/8, or 66Gy/3 fractions. The CRT regimens were 50Gy/20, 66Gy/33, 60Gy/15, or 70Gy/35 fractions. Significant heterogeneity in reported OS HRs was identified among the three RCTs (Cochrane Q test P value (CQP) =0.06), localized specifically to the CHISEL-LUSTRE comparison (CQP=0.02) (Figure 1) instead of CHISEL-SPACE (CQP=0.39) and LUSTRE-SPACE (CQP=0.19) comparisons. This heterogeneity was driven by the differential performance of the CRT arms, not the SABR arms. While SABR outcomes were consistent between CHISEL and LUSTRE (HR 1.14, 95% CI 0.70– 1.86, p=0.59), CRT was associated with significantly longer survival in LUSTRE than in CHISEL (HR 0.42, 95% CI 0.24–0.74, p=0.003) (Figure 2). This discrepancy may also be explained by key differences in baseline characteristics, including biopsy-confirmed malignancy rates (CHISEL: 100% vs LUSTRE: 49%) and medical inoperability (CHISEL: 89% vs LUSTRE: 100%). Furthermore, CRT in the LUSTRE trial used a higher
Case 1: No acute or late abdominal toxicity was observed, except grade 2 nausea managed with antiemetics. Both adrenal lesions achieved a complete radiological response, which was maintained up to the last restaging performed 10 months after SABR. Palliative RT induced only mild grade 1 intestinal toxicity.Case 2: No acute or late toxicity occurred despite reirradiation. Eight weeks post-SABR, complete response was documented in the reirradiated lesion; systemic progression required chemotherapy rechallenge.Case 3: No acute or late toxicity or radionecrosis was detected. The treated lesions appeared necrotic on follow-up MRI. For hepatic progression, systemic therapy was modified. Conclusion: Tarlatamab is a promising agent for ES-SCLC. Evidence regarding its combination with radiotherapy is currently scarce. Our experience suggests that SABR, delivered during ongoing Tarlatamab therapy, is feasible and safe, without unexpected acute or late toxicities. Keywords: Tarlatamab, SABR, Lung
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