High-dose-rate stereotactic body radiation therapy for postradiation therapy locally recurrent prostatic carcinoma: Preliminary prostate-specific antigen response, disease-free survival, and toxicity assessment.

PURPOSE - Patients with locally recurrent adenocarcinoma of the prostate following radiation therapy (RT) present a challenging problem. We prospectively evaluated the use of "high-dose-rate-like" prostate stereotactic body RT (SBRT) salvage for this circumstance, evaluating prostate-specific antigen response, disease-free survival, and toxicity.

MATERIALS AND METHODS - Between February 2009 and March 2014, 29 patients with biopsy-proven recurrent locally prostate cancer >2 years post-RT were treated. Median prior RT dose was 73.8 Gy and median interval to SBRT salvage was 88 months. Median recurrence Gleason score was 7 (79% was ≥7). Pre-existing RT toxicity >grade 1 was a reason for exclusion. Magnetic resonance imaging-defined prostate volume including any suspected extraprostatic extension, comprising the planning target volume. A total of 34 Gy/5 fractions was given, delivering a heterogeneous, high-dose-rate-like dose-escalation pattern. Toxicities were assessed using Common Terminology Criteria for Adverse Events, version 3.0, criteria.

RESULTS - Twenty-nine treated patients had a median 24-month follow-up (range, 3-60 months). A median pre-SBRT salvage baseline prostate-specific antigen level of 3.1 ng/mL decreased to 0.65 ng/mL and 0.16 ng/mL at 1 and 2 years, respectively. Actuarial 2-year biochemical disease-free survival measured 82%, with no local failures. Toxicity >grade 1 was limited to the genitourinary domain, with 18% grade 2 or higher and 7% grade 3 or higher. No gastrointestinal toxicity >grade 1 occurred.

CONCLUSIONS - Two-year disease-free survival is encouraging, and the prostate-specific antigen response kinetic appears comparable with that seen in de novo patients treated with SBRT, albeit still a preliminary finding. Grade ≥2 genitourinary toxicity was occasionally seen with no obvious predictive factor. Noting that our only brachytherapy case was 1 of the 2 cases with ≥grade 3 genitourinary toxicity, caution is recommended treating these patients. SBRT salvage of post-RT local recurrence appears clinically feasible, with longer term evaluation required to assess ultimate efficacy and late toxicity rates.

Pract Radiat Oncol. 2015 Jun 6. pii: S1879-8500(15)00157-5. doi: 10.1016/j.prro.2015.04.009. [Epub ahead of print]

Fuller DB1, Wurzer J2, Shirazi R3, Bridge SS4, Law J2, Mardirossian G3.

1 Department of Radiation Oncology, Genesis Healthcare Partners, Inc., San Diego, California.
2 Department of Radiation Oncology, Atlanticare, Egg Harbor, New Jersey.
3 Department of Radiation Oncology, Genesis Healthcare Partners, Inc., San Diego, California.
4 Department of Urology, Genesis Healthcare Partners, Inc., San Diego, California.

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