Incidence of Lung Malignancy After Loose Brachytherapy Seed Migration Outside the Prostate: A Retrospective Cohort Study

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Abstract
Purpose of the researchPulmonary seed migration is a rare complication of low‑dose‑rate prostate brachytherapy. This retrospective study evaluated whether it is associated with an increased risk of lung cancer.Patients and MethodsWe conducted a single‑center cohort study of patients treated with low‑dose‑rate prostate brachytherapy between 2004 and 2015 who experienced seed migration, assessed 30 days post‑implant. The primary endpoint was lung cancer incidence, based on clinical and radiological data. We estimated cumulative incidences at 5, 10, and 20 years, and analyzed the anatomical correspondence between migrated seeds and tumours. We evaluated predictors of lung cancer using univariate Fine‑Gray regression accounting for competing risks. We followed the Strengthening the reporting of observational studies in epidemiology guidelines and received ethics approval.ResultsAmong 1,386 patients, 98 (7.1%) experienced seed migration, corresponding to 125 of 71,316 seeds (0.18%), and were included in the analysis. Mean age was 62 years, and median follow‑up was 178 months. On day 30 post‑implant, most migrated seeds were detected in the thorax. Five patients developed lung cancer, all with a smoking history. Tumours occurred 6.3 to 20.3 years after implantation. Cumulative incidence of lung cancer was 0% at 5 years, 2.84% at 10 years, and 6.38% at 20 years. Only one tumour was in direct contact with a migrated seed. On univariate competing‑risk analysis, age was the only variable significantly associated with lung cancer risk.ConclusionIn this cohort with extended follow‑up, pulmonary seed migration after low‑dose‑rate prostate brachytherapy was not associated with an increased risk of lung cancer beyond that expected based on age and smoking status.