Evaluation of Radical Thoracic Re-Irradiation: A Single Institution Retrospective Study

Abstract

<h3>Purpose/Objective(s)</h3> The ability to deliver radical thoracic re-irradiation is limited by the balance between efficacy and potential toxicity. The aim of our study was to evaluate the safety and efficacy of radical thoracic re-irradiation. <h3>Materials/Methods</h3> A single institution retrospective analysis was performed on all patients who received two or more courses of radical thoracic radiotherapy, for sequential malignancies, between January 2011 and October 2019. All radical dose-fractionation schemes were included. The dose was converted to a Biologically Equivalent Dose, to ensure the cumulative dose delivered to the organs at risk (OAR) with re-irradiation did not exceed standard limits. The primary endpoint was the rate of acute (within 6 weeks) and late (within 1 year) toxicity as assessed by CTCAE V4.0. Secondary endpoints included progression free survival and overall survival which were calculated from the date of last radiotherapy using the Kaplan-Meier method. The study was approved by the institutional ethics board and patients provided informed consent. <h3>Results</h3> 43 patients had received at least one prior course of radical thoracic radiotherapy. 7/43(16%) and 2/43(5%) had received two and three prior courses respectively. The median follow-up from last completed radiotherapy was 19.8 months (0 - 64 months). The median age was 73 and 23/43(53%) of the cohort were female. Stereotactic Ablative Body Radiotherapy and External Beam Radiotherapy techniques were used in 48/97(49%) and 49/97(51%) of the treatment courses respectively. The primary tumor was non-small cell lung cancer in 78/97(80%), small cell lung cancer in 8/97(8%), head and neck cancer in 6/97(6%) and breast cancer in 5/97(5%). The median time from 1^st to 2^nd radiotherapy was 19 months. Following last re-irradiation, acute grade 1 and 2 toxicities were observed in 30/43(70%). The acute toxicities were cough 14/43(33%), dyspnea 9/43(21%), esophagitis 11/43(26%), fatigue 24/43(56%), erythema 6/43 (14%) and chest wall pain 2/43(5%). One patient had a fatal event during re-irradiation after an acute upper gastrointestinal hemorrhage but causality could not be established. Another patient had a grade 3 respiratory infection. Cumulative late grade 1 and 2 toxicities were observed in 7/31(23%) of the evaluable cohort including hemoptysis 1/31 (3%), cough 2/31(6%), dyspnea 3/31(10%), chest wall pain 3/31(10%) and fatigue 3/31(10%). There was no other grade 3 or higher acute or late toxicities. At time of analysis 33/43(77%) of patients had died. One-year overall survival and progression free survival were 64% (95%CI: 50-79%) and 49% (95%CI: 33-64%) respectively. Limitations of the study include its retrospective nature and patient heterogeneity. <h3>Conclusion</h3> Radical thoracic re-irradiation was generally well tolerated in a typical clinical setting when the cumulative dose delivered to OAR did not exceed standard constraints.