Long-term outcome of magnetic resonance spectroscopic image-directed dose escalation for prostate brachytherapy.

PURPOSE - To report the long-term control and toxicity outcomes of patients with clinically localized prostate cancer, who underwent low-dose-rate prostate brachytherapy with magnetic resonance spectroscopic image (MRSI)-directed dose escalation to intraprostatic regions.

MATERIALS AND METHODS - Forty-seven consecutive patients between May 2000 and December 2003 were analyzed retrospectively. Each patient underwent a preprocedural MRSI, and MRS-positive voxels suspicious for malignancy were identified. Intraoperative planning was used to determine the optimal seed distribution to deliver a standard prescription dose to the entire prostate, while escalating the dose to MRS-positive voxels to 150% of prescription. Each patient underwent transperineal implantation of radioactive seeds followed by same-day CT for postimplant dosimetry.

RESULTS - The median prostate D90 (minimum dose received by 90% of the prostate) was 125.7% (interquartile range [IQR], 110.3-136.5%) of prescription. The median value for the MRS-positive mean dose was 229.9% (IQR, 200.0-251.9%). Median urethra D30 and rectal D30 values were 142.2% (137.5-168.2%) and 56.1% (40.1-63.4%), respectively. Median followup was 86.4 months (IQR, 49.8-117.6). The 10-year actuarial prostate-specific antigen relapse-free survival was 98% (95% confidence interval, 93-100%). Five patients (11%) experienced late Grade 3 urinary toxicity (e.g., urethral stricture), which improved after operative intervention. Four of these patients had dose-escalated voxels less than 1.0 cm from the urethra.

CONCLUSIONS - Low-dose-rate brachytherapy with MRSI-directed dose escalation to suspicious intraprostatic regions exhibits excellent long-term biochemical control. Patients with dose-escalated voxels close to the urethra were at higher risk of late urinary stricture.

Brachytherapy. 2016 Mar 18 [Epub ahead of print]

Martin T King, Nicola J Nasser, Nitin Mathur, Gil'ad N Cohen, Marisa A Kollmeier, Jasper Yuen, Hebert A Vargas, Xin Pei, Yoshiya Yamada, Kristen L Zakian, Marco Zaider, Michael J Zelefsky

Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY., Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY., Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY., Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY., Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY., Department of Radiation Oncology, The Carlo Fidani Regional Cancer Centre, Mississauga, Ontario., Department of Radiology, Memorial Sloan-Kettering Cancer Center, New York, NY., Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY., Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY., Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY., Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY., Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY.