(UroToday.com) The 2022 ASTRO annual meeting featured a prostate cancer session, including a presentation by Dr. Enrique Gutierrez discussing results of a prospective clinical trial assessing focal MR-guided high-dose-rate brachytherapy for localized prostate cancer. Focal therapy has gained traction in the management of localized prostate cancer based on the promise of equivalent oncologic outcomes with minimal toxicity compared to whole gland therapy. However, 20-45% of patients have persistent/recurrent disease within the first 2-5 years after most commonly-used ablative methods (e.g., HIFU, cryotherapy). Based on brachytherapy’s well-established and long track-record of efficacy for prostate cancer, Dr. Gutierrez and colleagues sought to test the focal therapy hypothesis in a prospective clinical trial of MR-guided HDR for men with localized prostate cancer.
This prospective trial was approved in 2016 (NCT02918253) for patients with clinically low- and favorable intermediate-risk prostate cancer, and a conspicuous lesion on mpMRI consistent with the area of pathological involvement. The CTV was derived from the mpMRI-defined GTV plus a 7 mm isotropic expansion, with 2 mm superior/inferior added for the PTV. Implant and planning were performed with an MR-only workflow, and delivery with HDR brachytherapy. As follows is an example of isodose distributions in the axial, coronal, and sagittal views with MRI-only guidance:
Treatment consisted of two separate implants within 14 days, to a prescription dose of 33-36 Gy in 2 sessions (biologically effective dose ≥ 200 Gy). Biochemical recurrence, defined as > 2 ng/mL above nadir was calculated using the Kaplan Meier method. Local failure, distant metastasis, and toxicity events are reported as absolute rates.
Nineteen patients have been treated, with a median age of 73 years (range 48-84), and median follow-up of 24 months (range 8-63). The median PSA was 6.1 ng/mL, and 17/19 patients had Grade Group 2 disease:
On average, the GTV and PTV corresponded to 3.56% (range 1.58-12.07%) and 23.16% (range 13.71-40.75%) of the median prostatic volume (40.49 cc [range 25.57-97.6]). The median number of catheters was 7 (range 4-11), and the median GTV D99 and PTV D95 per fraction were 23.82 Gy (range 18.50-31.89) and 18.71 Gy (range 16.01-20.64), respectively. Nine patients have undergone the 2-year local control ascertainment: 7 with mpMRI plus biopsies, and 2 with mpMRI only. At 2-years, local control and biochemical recurrence-free survival were 100%; a single biochemical recurrence event has been recorded 34 months after treatment:
No distant metastasis or death events have occurred. The rate of treatment-related acute and late toxicities that were graded ≥ 2 was 0%.
Dr. Gutierrez concluded his presentation discussing results of a prospective clinical trial assessing focal MR-guided high-dose-rate brachytherapy for localized prostate cancer with the following concluding messages:
- Focal MRI-guided HDR brachytherapy as monotherapy appears to have a high therapeutic ratio and is a promising technique for localized prostate cancer
- Further follow-up will determine the durability of outcomes with this approach and the need for collaborative randomized studies
Presented by: Enrique Gutierrez, MD, MHA, Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada
Co-Authors: M. Ramotar1,2, J. Helou1,3, S. Raman2,3, R. Glicksman1,3, A. Rink2, P. Chung1,3, R. A. Weersink3, and A. Berlin1,3; 1Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, 2Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Canada, Toronto, ON, Canada, 3Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada
Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia, @zklaassen_md on Twitter during the 2022 American Society of Radiation Oncology (ASTRO) Annual Hybrid Meeting, San Antonio, TX, Sat, Oct 22 – Wed, Oct 26, 2022.