ESTRO 2025 - Abstract Book

S1356

Clinical - Lung

ESTRO 2025

Material/Methods: A retrospective analysis of electronic medical records for patients treated between 01/07/2020 and 31/12/2023 was conducted. Patients were included if they had undergone a second course of radiation to the thorax with overlapping treatment fields from their prior course. Cases were categorised into low, moderate or high dose overlap. Moderate dose overlap was defined as overlap of 40% isodose lines, whereas high dose overlap was defined as PTV overlap, or overlap with a structure which had previously been irradiated to full tolerance e.g. spinal cord. Patient demographics, radiotherapy intent and dose (curative intent defined as minimum PTV dose >39Gy EQD2), adverse effects in the curative-intent cohort, treatment response, and adherence to eligibility guidelines (see Table 1) were assessed. Results: Out of 195 patients identified to have received reirradiation, 102 remained after excluding those with low dose overlap, considered to pose minimal clinical concern. Adherence rates to eligibility guidelines are shown in Table 1.

Median age was 73.4 years and median follow-up was 9.3 months. 66 (64.7%) patients received curative-intent doses and 36 (35.3%) patients palliative doses. In the curative-intent group, median GTV and PTV volumes were 29.5 cm³ (3-352.84 cm³) and 102.35 cm³ (13.72-1070 cm³). Grade 3 and above toxicities peaked at 3 months post treatment with an incidence of 15.1%. Toxicity within and beyond 3 months is shown in Figure 1A and 1B. 55/66 patients (85%) had a complete/partial response or stable disease on first response assessment. Median progression-free survival was 9.8 months. Of the 29/66 patients who progressed, only 8 were within the radiation field. Overall survival was significantly better after curative-intent treatment, with median survival of 13.6 vs 4.3 months respectively.