Original Article Pattern of relapse and dosimetric analysis of a single dose 19 Gy HDR-brachytherapy phase II trial Alfonso Gomez-Iturriaga a,⇑ , David Buchser a , Esther Mayrata a , Iñigo San Miguel a , Alba Gonzalez a , Fernan Suarez a , Lorea Martinez-Indart b , Pablo Minguez a , Jose Espinosa a , Fernando Perez a , Jon Cacicedo a , Francisco Casquero a a Hospital Universitario Cruces/Biocruces Health Research Institute, Radiation Oncology; and b Hospital Universitario Cruces/Biocruces Health Research Institute, Clinical Epidemiology Unit, Barakaldo, Spain article info Article history: Received 25 September 2019 Received in revised form 24 January 2020 Accepted 25 January 2020 Keywords: Single-fraction Brachytherapy 19 Gy Monotherapy Prostate-cancer abstract Purpose: To report the pattern of relapse within the prostate with reference to the initial site of disease in patients treated with single fraction 19-Gy. Methods and materials: Forty-four patients were treated according to a prospective study of single- fraction HDR-brachytherapy. Treatment was delivered using 192Ir to a dose of 19 Gy prescribed to the prostate. Patients who experienced a biochemical failure underwent a re-staging multiparametric MRI (mpMRI) and MRI-TRUS fusion biopsy to rule-out local recurrence. In patients with visible Dominant intraprostatic lesions (DIL) on pretreatment mpMRI, the site of local relapse was compared with the initial site of disease. The dose received by the site of recurrence was investigated. Results: The median follow-up period was 48 months (range 29–63). The PSA nadir was reached at 24 months follow-up, with a median value of 1.07 ng/mL. To date, 14 patients (32%) have experienced bio- chemical failure (4 patients low-risk and 10 intermediate-risk; p = 0.013). Re-staging mpMRI was per- formed in 11/14 patients. Eleven patients underwent MRI-TRUS fusion biopsy confirming local relapse in all patients. The analysis of DVH of all 44 patients revealed that patients with biochemical failure had received sig- nificantly lower doses in terms of V100, V125 and D90 (p = 0.032, p = 0.018 and p = 0.018 respectively). In patients with DILs on diagnostic mpMRI, the mean D90 and D98 on DIL were lower for patients with biochemical failure. Conclusions: This dosimetric analysis demonstrates a dose-response relationship in patients treated with single fraction 19 Gy. Patients with intermediate risk disease, with visible DIL on mpMRI and patients treated with cooler implants have higher incidence of biochemical and local failure. Ó 2020 Elsevier B.V. All rights reserved. Radiotherapy and Oncology xxx (2020) xxx–xxx There is increasing interest in the use of High Dose Rate Brachytherapy (HDR-BT) alone as monotherapy, without supple- mental EBRT. Several studies demonstrate excellent biochemical relapse-free survival rates for men with low- and intermediate- risk disease when 2 or more fractions have been used [1,2]. However, multifraction regimens are logistically challenging, as patients require either inpatient admission or multiple implants, being both options demanding in terms of resource consumption. In last years, several studies have reported excellent results in terms of toxicity and quality of life after single fraction HDR-BT [3,4], however, in most of the studies with longer follow-up the results in biochemical and local control are not satisfactory [5–7]. In 2014, a phase II trial of single fraction 19 Gy HDR-BT was launched in the Radiation Oncology Department of the University Hospital with the hypothesis that a single fraction schedule was as efficacious as multifraction schedules in terms of biochemical and local control. The purpose of this analysis is first, to report biochemical and local control and second, to investigate the pattern of relapse within the prostate with reference to the initial site of disease in patients treated with single fraction 19 Gy and to determine dose delivered to these areas of recurrence. https://doi.org/10.1016/j.radonc.2020.01.025 0167-8140/Ó 2020 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Department of Radiation Oncology, Hospital Univer- sitario Cruces, Plaza Cruces Gurutzeta 12, 48903, Barakaldo, Spain. E-mail address: agomeziturriaga@gmail.com (A. Gomez-Iturriaga). Radiotherapy and Oncology 146 (2020) 16–20 Contents lists available at ScienceDirect Radiotherapy and Oncology journal homepage: www.thegreenjournal.com