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Radiother Oncol. 2019 Dec;141:144-148. doi: 10.1016/j.radonc.2019.09.011. Epub 2019 Sep 26.

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

Author information

1
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.
2
Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Canada.
3
Department of Radiation Oncology, University of Toronto, Princess Margaret Cancer Centre, Canada.
4
Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Canada; Department of Radiation Oncology, University of Toronto, Canada.
5
Mount Sinai Hospital, Toronto, Canada.
6
Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Canada; Department of Radiation Oncology, University of Toronto, Canada. Electronic address: andrew.loblaw@sunnybrook.ca.

Abstract

PURPOSE:

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.

METHODS:

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.

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.

CONCLUSIONS:

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.

KEYWORDS:

DIL; Dose escalation; HDR; MRI; Monotherapy

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