SBRT in men with intermediate-risk, localized prostate cancer


Data reported by Meier et al. and presented at the recent annual meeting of the American Society for Radiation Oncology (ASTRO) provide some early guidance on the efficacy and safety of sterotactic body radiation therapy (SBRT) in treatment of men with intermediate-risk, localized prostate cancer.

This prospective, multi-center, Phase II study enrolled patients at 21 institutions between 2007 and 2011. All eligible patients needed to have biopsy-proven, organ-confined prostate cancer meeting one or other of the following set of criteria indicating intermediate-risk disease:

  • Clinical stage T1c-T2b; Gleason score 7; PSA < 10 ng/ml
  • Clinical stage T1c-T2b; Gleason score 6; PSA 10-20 ng/ml

The patients were all hormone therapy-naive (i.e., they had received no form of androgen deprivation therapy) and were treated using the Accuray CyberKnife system, with real-time tracking of implanted fiducial markers. The dose delivered to the prostate itself was 40 Gy (in five fractions each of 8 Gy). The dose delivered to the seminal vesicles was 36.25 Gy.

Here are the results reported by Meier et al.:

  • 129 eligible patients were recruited and treated.
  • Average (median) follow-up after treatment was 30 months (range, 10 to 42 months).
  • Acute toxicities were observed in
    • 0/129 patients (0 percent) who had acute toxicities of Grade 3 or higher.
    • 26/129 patients (20 percent) who had acute Grade 2 genitourinary toxicities.
    • 11/129 patients (8.5 percent) whohad accute Grade 2 gastrointestinal toxicities.
  • Late toxicities were observed in
    • 1/129 patients (< 1 percent) who had a late Grade 3 toxic event (bladder neck injury 1 years post-treatment)
    • 13/129 patients (10 percent) who had late Grade 2 genitourinary toxic events.
    • 3/129 patients (2 percent) who had late Grade 2 gastrointestinal toxic events.
  • Average (mean) urinary and bowel scores (measured using the Expanded Prostate Cancer Index Composite  or EPIC-26 questionnaire)
    • Fell at 1 month post-treatment
    • Returned to baseline by 24 months post-treatment.
  • With respect to erectile function
    • 52 percent of patients were potent (meaning that they had erections that were “firm enough for intercourse”) at baseline
    • 35 percent of patients were potent at 24 months post-treatment.
  • The patients’ average (median) PSA levels were
    • 5.93 ng/ml at baseline
    • 0.80 ng/ml at 1 year post-treatment
    • 0.38 ng/ml at 2 years post-treatment
    • 0.20 ng/ml at 3 years post-treatment
  • 1/129 patients (< 1 percent) had a biochemical failure at 3 months post-treatment (with biopsy-proven nodal metastasis)
  • The 3-year Kaplan-Meier biochemical progression-free survival rate was 99.2 percent.

Clearly these data are derived from a relatively brief follow-up of “just” 129 patients with intermediate-risk disease, but they do appear to show some promise regarding the potential applicability of SBRT in treatment of this set of patients. The authors conclude that “… serious acute and late toxicities have been minimal. EPIC urinary, bowel and sexual function responses appear favorable compared to other radiation therapy modalities. Early PSA responses are promising.”

It should be noted that this study was supported by Accuray, the manufacturer of CyberKnife technology.

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