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Aims To evaluate focal high dose rate (HDR) brachytherapy in locally recurrent prostate cancer. Materials and methods Patients with biochemical relapse after non-surgical primary treatment for localised prostate cancer were selected after a negative screen for metastatic disease. Template mapping biopsies combined with multiparametric magnetic resonance imaging were used to identify the location of the tumour and the focal clinical target volume. The planning aim dose prescription was 19 Gy. Outcome measures were biochemical relapse-free survival and toxicity using International Prostate Symptom Score and Common Terminology Criteria for Adverse Events (version 4.0) scores. Results Between March 2013 and December 2018, 50 patients underwent salvage HDR brachytherapy. The median follow-up was 21 months (range 1–53). Biochemical progression-free survival at 2 and 3 years was 63% and 46%, respectively. On multivariate analysis, only prostate-specific antigen nadir ≤0.5 ng/ml post-salvage (P = 0.03, hazard ratio 0.04) was associated with biochemical progression-free survival. Relapse was associated with distant metastases in 11/13 patients in whom this was investigated. Late grade 3 genitourinary toxicities were gross haematuria (three patients), severe lower urinary tract symptoms (two patients), erectile dysfunction (one patient) and urethral stricture requiring surgery (four patients). No acute and late grade 4 or 5 genitourinary and no grade 3 or higher gastrointestinal toxicities were recorded. Conclusions Focal salvage HDR monotherapy achieves biochemical control in 46% of patients at 3 years with acceptable toxicity rates in selected patients. Biochemical relapse was related to a post-salvage prostate-specific antigen nadir of ≥0.5 ng/ml. Long-term outcomes are needed to assess the impact on the natural history of prostate cancer in these patients.

The application of magnetic resonance imaging (MRI) in image-guided brachytherapy has expanded rapidly over the past two decades. In cervix cancer, significant improvements in overall survival, local control and long-term morbidity have been shown in patients treated with MRI-guided brachytherapy, changing clinical practice and directing an international approach to standardise the technique; unifying adaptive target volume definition and dose reporting. MRI-guided prostate brachytherapy has significantly improved the accuracy of tumour and organ-at-risk delineation, facilitating targeted implantation and dose optimisation. It also has potential to improve clinical outcomes through enhancement of the therapeutic ratio and the identification of dominant lesions that can be the targets of sub-volume boosting and salvage therapy. However, MRI-guided brachytherapy presents a number of logistical and financial challenges in modern healthcare systems, requiring technologically advanced imaging and planning techniques, as well as robust safety and quality assurance procedures. A collaborative, multidisciplinary approach involving clinical oncologists, radiologists, medical physicists, therapy radiographers, nurses and technical staff is therefore critical to its successful incorporation into any clinical brachytherapy workflow. In this overview we evaluate the current role of MRI in image-guided brachytherapy, primarily in cervix and prostate cancer, but also in other tumour sites, and review its potential future developments in the context of both clinical and research spheres.