MRI assisted focal boost integrated with HDR monotherapy study in low and intermediate risk prostate cancer (MARS): Results from a phase II clinical trial.

There is growing concern that single-fraction HDR monotherapy to a dose of 19 Gy is suboptimal for the treatment of localized prostate cancer. We report the results of a phase II prospective trial of single-fraction 19 Gy HDR monotherapy with MRI-guided simultaneous focal boost.

Eligible patients had low or intermediate risk prostate cancer and an identified lesion on MRI. TRUS based single-fraction HDR monotherapy with MRI fusion was delivered. The dose prescribed was 19 Gy to the prostate and ≥23 Gy to the dominant intraprostatic lesion (DIL). ADT was not used. The purpose is to report early efficacy results.

60 patients were enrolled, with a median follow-up of 39 months. With MRI T-stage incorporated into the risk-group criteria, 8% had low-risk, 35% had favorable intermediate-risk and 57% had unfavorable intermediate-risk disease. The median dose to 90% of the DIL (D90) was 27.2 Gy, and the median prostate V100% was 96.9%. No acute or late grade ≥3 bowel or urinary toxicity was observed. The cumulative BF probability was 15.2% at 36 months and 31.6% at 48 months. All patients that were fully investigated had local failure only, and 88% of the local failures were at the site of original DIL. The median PSA nadir was 0.79 ng/ml, with a median time to nadir of 32 months.

Focal boost to the MRI-specified gross tumor was well tolerated, but did not adequately improve local control. Single-fraction HDR monotherapy to 19 Gy for prostate cancer provides suboptimal local control, and should not be offered outside of clinical trials.

Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology. 2019 Sep 26 [Epub ahead of print]

Yasir Alayed, Laura D'Alimonte, Joelle Helou, Ananth Ravi, Gerard Morton, Hans T Chung, Masoom Haider, Merrylee McGuffin, Liying Zhang, Andrew Loblaw

Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Canada; Department of Radiation Oncology, University of Toronto, Canada; Division of Radiation Oncology, College of Medicine, King Saud University, Riyadh, Saudi Arabia., Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Canada., Department of Radiation Oncology, University of Toronto, Princess Margaret Cancer Centre, Canada., Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Canada; Department of Radiation Oncology, University of Toronto, Canada., Mount Sinai Hospital, Toronto, Canada., Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Canada; Department of Radiation Oncology, University of Toronto, Canada. Electronic address: .