A comprehensive national audit of radiotherapy retreatment numbers, sites and indications.

Background and purpose: Reirradiation has seen increased interest and clinical use; however, robust data on patient numbers and treatment indications are missing. As a precursor to a prospective national reirradiation registry, a comprehensive national audit of reirradiation was performed.

Patients/materials and methods: Radiotherapy retreatment courses in 2023 were audited by all (eight) radiotherapy centres in Denmark. Six centres extended the evaluation to include 2021-22, and three of these also evaluated preceding years. Reirradiation was defined according to the ESTRO/EORTC consensus (i.e. treatment volume overlap or cumulative dose toxicity risk) using 3 months threshold between the primary and reirradiation courses. Reirradiation courses were further stratified into curative/ablative and palliative treatments by prescription dose.

Results: The total number of radiotherapy patients at Danish centres in 2023 was 17,424. Of these, 3,163 received retreatment, including 1,471 reirradiation courses (1,035 palliative; 436 curative/ablative). From 2014 to 2023, absolute numbers for both retreatment and reirradiation increased. We found large variation in prescription doses and fractionation schedules used for reirradiation. Widely used palliative prescriptions were 8Gy/1 fraction (F), 20Gy/4F and 30Gy/10F; stereotactic prescriptions of 20Gy/1F or 27Gy/3F in brain and 45Gy/3F in lung; and a variety of curative treatments schedules. Palliative reirradiations were primarily thoracic (29%), spine (25%), and abdominal/pelvic (22%) and curative/ablative reirradiations were primarily breast (29%) and lung stereotactic (23%).

Interpretation: This is the first comprehensive national audit of reirradiation, demonstrating an increasing number of patients being treated, using a wide variety of dose prescriptions and fractionation schedules.