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Five-Year Outcomes From a Multicenter Trial of Stereotactic Body Radiation Therapy for Low- and Intermediate-Risk Prostate Cancer

      Purpose/Objective(s)

      Single-institution studies suggest stereotactic body radiotherapy (SBRT) is a cost-effective alternative to IMRT as primary therapy for prostate cancer. We hypothesized that dose-escalated SBRT could be safely administered across multiple institutions, with grade 3+ toxicities not exceeding 10%. With median follow up greater than five years, we report toxicity, survival, and relapse-free survival (RFS) outcomes.

      Materials/Methods

      After completing rigorous credentialing requirements, 21 community, regional, and academic hospitals enrolled 309 evaluable patients with biopsy-proven adenocarcinoma of the prostate, confirmed by central pathologic review: 172 low-risk (CS T1-T2a, Gleason 6, PSA < 10 ng/mL) and 137 intermediate-risk (CS T1c-T2b with either Gleason = 7 and PSA < 10 ng/mL, or Gleason 6 and PSA between 10 and 20 ng/mL). All patients were treated with a non-isocentric robotic SBRT platform using real-time tracking of implanted fiducials. The prostate was prescribed 40 Gy in 5 fractions of 8 Gy and seminal vesicles received 36.25 Gy. Normal tissues were rigidly constrained (rectal V36 Gy <1 cc; bladder V37 Gy <5-10 cc). No patient had concomitant or adjuvant androgen ablation therapy. Toxicities were assessed using CTCAE v3 criteria. Patient-reported quality of life outcomes were recorded and reported elsewhere. Biochemical failure was assessed using the ASTRO consensus and the nadir + 2 definitions. Actuarial survival outcomes were calculated using Kaplan Meier methods. The study populations yielded a 90% power of identifying excessive (>10%) rates of grade 3+ GU or GI toxicities at the one-sided 5% significance level.

      Results

      Median follow-up was 61 months. Five grade 3+ toxicities (1.6%) were reported, far below the 10% rate deemed excessive. There were no grade 4 or 5 toxicities. All reported grade 3 toxicities were GU; these occurred between 11 and 51 months after treatment. Toxicities rates are summarized below. Five patients (1.6%) developed urinary retention which required a temporary catheter placement. Seven patients were diagnosed with bladder cancers between 21 and 50 months after treatment. For the entire population, actuarial 5-year overall survival was 95.6%. Actuarial 5-year nadir +2 RFS was 97.1% for all patients, and was 97.3% and 97.1% for the low- and intermediate-risk groups, respectively. Actuarial 5-year ASTRO RFS was 92.3% and 91.3% for these respective risk groups.

      Conclusion

      With appropriate treatment delivery and constraints, dose-escalated prostate SBRT can be safely administered across multiple institutions. Toxicity rates and RFS rates compare favorably to other radiotherapies. SBRT appears to be a suitable option for low- and intermediate-risk prostate cancer. ClinicalTrials.gov identifier NCT00643994.
      Tabled 1Abstract 74; Table 1
      GU ToxicityGI Toxicity
      Gr1Gr2Gr3Gr4+Gr1Gr2Gr3+
      Any time165 (53%)108 (35%)5 (2%)0183 (59%)31 (10%)0
      < 3 mos182 (59%)79 (26%)00169 (55%)25 (8%)0
      > 3 mos87 (28%)38 (12%)5 (2%)038 (12%)6 (2%)0

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