MRI response to focal salvage HDR prostate brachytherapy for locally recurrent prostate cancer after external-beam radiotherapy.

e631 Background: For local recurrence after external-beam radiotherapy, salvage therapy options include surgery, brachytherapy, cryotherapy or high-frequency ultrasound, though there is a significant risk of serious complications (e.g. fistula, incontinence, bladder neck contracture). In the meantime, MRI technology has evolved (e.g. DCE and DWI) such that the sensitivity of detecting viable cancer within the prostate is now more than 70%. Therefore, we initiated a pilot study of focal salvage HDR prostate brachytherapy in patients screened with a MRI with the hypothesis that focal treatment, rather than whole gland, would lead to less complications but similar local control. The MRI response is presented here. Methods: This study was approved by the institution’s research ethics board. Eligible patients included: biopsy-confirmed local recurrence > 30 months after completing XRT, MRI demonstrating solitary recurrence confined to the prostate, negative metastatic workup, IPSS < 15, post-XRT PSA < 10ng/mL, prostate volume ≤ 50cc. Salvage ultrasound-based HDR brachytherapy was performed with a prescription dose of 27Gy divided over two implants separated by 1 week to the target volume (TV) as seen on MRI with dose constraints to the urethra and rectum. All MRI scans were completed with 3T and included T2W, DCE and DWI. Lesions suspicious for cancer were scored using PI-RADS methodology pre-brachytherapy, and using a 5-point scale post-brachytherapy. Results: Fifteen patients were accrued. Thus far, 6 of 15 patients have completed a post-brachytherapy MRI (median 530 days; range 307-653). The baseline MRI characteristics of these 5 patients include: PI-RADS 4 (n = 1), 5 (n = 4), not specified (n = 1); median size 9 mm (range 7-9); T2 (n = 5) and T3a (n = 1); median prostate volume 28mL (20-63). In the post-brachytherapy MRI, the treated intraprostatic lesion no longer showed areas of cancer in 5 patients. Two patients developed a new focus of cancer in the prostate. Patients were not routinely biopsied after brachytherapy. Conclusions: Preliminary data from MRI suggests that there is a treatment response in most patients after focal salvage brachytherapy. Clinical trial information: NCT01583920.