The Role of High-Dose-Rate Brachytherapy (Interventional Radiotherapy) in the Reirradiation of Liver Metastases

Background: This study aimed to analyse treatment outcomes, determine prognostic factors and assess the toxicity of reirradiation using high-dose-rate (HDR) brachytherapy for liver metastases in the oligometastatic stage of disease. Materials and Methods: The study included 59 patients who had previously undergone SBRT (stereotactic body radiation therapy) or HDR brachytherapy and experienced progression within (type 1) or outside (type 2) the irradiated area, but in a different location within the liver. Patients were divided according to the type of reirradiation and the reason for treatment. Local control (LC), progression-free survival (PFS) and overall survival (OS) were analysed in relation to the following factors: age; gender; performance status; tumour type; line of systemic treatment; location of extrahepatic metastases; type of reirradiation; time since previous irradiation; indication for treatment; size and number of metastases; dose; and degree of response to treatment. Treatment toxicity and the influence of dose, irradiation volume, number of metastases, time since previous radiotherapy and dose to the non-irradiated part of the liver on hepatic toxicity were also assessed. Results: With a median follow-up period of 13 months, the median LC, PFS and OS were 9, 8 and 13 months, respectively. The respective rates of partial regression (PR), stable disease (SD) and progressive disease (PD) were 32%, 44% and 12%. The most significant factors influencing LC were the degree of tumour shrinkage, with PFS influenced by the degree of tumour shrinkage and a low number of metastases, and OS influenced by the degree of tumour shrinkage, a low number of metastases and one to two lines of systemic therapy. Treatment toxicity was low, and there was no strong correlation between the dosimetric parameters of the treatment plan and the biochemical parameters of liver function. Conclusions: Brachytherapy is a safe and effective method of re-irradiating liver metastases. However, due to the limitations of the study, further investigation is required.