Session Item

In patients with increasing PSA levels after primary radiotherapy for prostate cancer, 52% will present with a local recurrence. Radiorecurrent disease is often confined to the prostate and mostly located focally at the site of the index lesion. Patients can be treated with focal salvage, e.g. high dose rate (HDR) brachytherapy. This can decrease the risk of late toxicity, with a chance of cure and or deferral of androgen deprivation therapy. The purpose of this study was to look at recurrence characteristics in patients treated with focal salvage HDR brachytherapy. In addition, we aimed to compare recurrence characteristics with a group of patients who received primary focal HDR brachytherapy.

Patients treated with MRI-guided focal salvage HDR brachytherapy with a single 19 Gy dose to the recurrent tumor from July 2013 to October 2021 were prospectively included in the current study, alongside patients treated with MRI-guided focal primary HDR brachytherapy with a single 19 Gy dose to the primary tumor from May 2013 to April 2016. Imaging data were collected regarding the occurrence of local, regional and distant recurrences, including location of local recurrences in relation to the HDR radiotherapy field, predominantly using PSMA/PET-CT.

A total of 187 patients after focal salvage HDR and 30 patients after primary HDR treatment were included in the analyses. Median follow-up duration was 44 months (IQR 23-66). A total of 74 patients (40%) developed a local recurrence after focal salvage HDR, of which 38 (51%) only in-field, 13 (18%) only out-of-field, 8 (11%) in an overlapping region in- and out-of-field and 13 (18%) in multiple regions in- and out-of-field. In comparison, after primary HDR treatment 15 patients (50%) developed a local recurrence, of which 5 (33%) only in-field, 8 (53%) only out-of-field, 1 (7%) in an overlapping region in- and out-of-field and 1 (7%) in multiple regions in- and out-of-field. Univariable regression analyses showed no significant relation between an in-field recurrence and CTV D95%, post-salvage PSA nadir, GTV/CTV volume, pre-salvage PSA value or PSA doubling time. Regarding the focal salvage population, 29 patients (16%) developed regional lymph node metastases, 23 (12%) developed distant metastases and 90 patients (48%) developed any type of recurrence (local/regional/distant). Figure 1 displays the recurrence distribution in the focal salvage group.

Figure 1: Venn diagram showing the distribution of local and/or regional lymph node and/or distant recurrences since treatment, in the cohort of patients treated with focal salvage HDR brachytherapy. Each number represents the amount of patients in the corresponding category.

After focal salvage HDR brachytherapy with a dose of 1x19 Gy for local prostate cancer recurrence, subsequent recurrences are mostly local and in-field. Contrarily, local recurrences after primary HDR brachytherapy are predominantly out-of-field.