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Re-irradiation (reRT) is increasingly attempted for patients with lung cancer recurrence or a new second lung primary after past thoracic radiotherapy. Data on outcomes for this patient group remain sparse, however. We aimed to evaluate cancer outcomes and toxicities for a large retrospective cohort of patients receiving curative dose reRT for recurrent lung malignancy at a tertiary cancer centre.  

Patients were identified by automatic search of radiotherapy electronic patient records, with additional manual review for eligibility. All patients received at least two courses of radiotherapy to the thorax between 2010 – 2020 for lung malignancy (either recurrence or new primary), with ≥6 months between treatments, with potential overlap between treatment fields (targets on same level or within 2cm cranio-caudal), and radiotherapy dose >30 Gy for both treatments. Treatment and demographic data were extracted automatically; outcome data collected manually from patient records. First site of disease progression after reRT was classified as ‘site of re-treatment’, ‘elsewhere in lung’, or ‘distant metastasis’. Death was split into cancer and non-cancer deaths. Overall survival (OS) and cancer-specific survival were calculated using Kaplan-Meier estimators, with all times calculated from end of reRT. A competing risk framework was used to estimate the 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

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.  

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.