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

Publication date: Available online 20 April 2016
Source:Brachytherapy
Author(s): 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
PurposeTo 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.Methods and MaterialsForty-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.ResultsThe 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.ConclusionsLow-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.



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