Should SBRT be THE preferred treatment for intermediate-risk prostate cancer?

Last year, the American Society of Radiation Oncologists (ASTRO) looked at the available evidence comparing hypofractionated radiotherapy (either 60 Gy in 20 treatments or 70 Gy in 28 treatments) to standard fractionation (78 to 82 Gy in 40 to 44 treatments), and found it was at least as good in terms of oncological outcomes and toxicity. They found strong evidence for this recommendation (see this link). There are obvious benefits for the patient in terms of convenience and cost. They stopped short of strongly endorsing ultrahypofractionated radiation therapy (usually called SBRT), which is usually completed in only four or five treatments. There wasn’t enough published data at the time.

Since then, there have been several published clinical trials, some with randomized comparisons. Jackson et al. have now compiled data from 38 prospective clinical trials comprising 6,116 patients treated with SBRT for localized prostate cancer. Their meta-analysis found that:

  • 5-year biochemical recurrence-free survival (bRFS) was
    • 95 percent among all patients
    • 97 percent among low-risk patients
    • 92 percent among intermediate-risk patients
  • 7-year bRFS was 94 percent among all patients

They also reported that

  • More studies included intermediate-risk than low-risk patients.
  • There were not enough high-risk patients to reliably report yet.
  • bRFS increased with higher doses of SBRT
  • bRFS was not affected by the use of adjuvant androgen deprivation therapy (ADT)

In terms of physician-reported toxicity, Jackson et al. found that:

  • Acute Grade ≥ 3 (serious) urinary toxicity occurred in 0.5 percent of patients.
  • Acute Grade ≥ 3 (serious) rectal toxicity occurred in 0.1 percent of patients.
  • Late-term Grade ≥ 3 (serious) urinary toxicity occurred in 2 percent of patients
  • Late-term Grade ≥3 (serious) rectal toxicity occurred in 1 percent of patients
  • Late urinary toxicity increased with dose; rectal toxicity did not

In terms of patient-reported adverse effects of treatment:

  • Urinary and bowel scores returned to baseline within 2 years of treatment
  • Urinary and bowel scores remained at those baseline levels with 5 years of follow up
  • Sexual scores declined gradually over time

While the authors believe that their analysis provides enough evidence that SBRT should be considered a standard of care for low- and intermediate-risk patients, they stop short of recommending that SBRT be considered the standard of care for patients who choose radiotherapy. (Active surveillance or AS is appropriate for most low-risk patients).

There is an ongoing randomized clinical trial designed to explore whether SBRT or moderately hypofractionated radiation is superior to the other. First results are expected in 2025. The PACE trials in the UK, will compare outcomes of SBRT vs surgery (PACE A) and SBRT vs IMRT (PACE B). Early toxicity results of PACE B have been presented. Results are expected in 2021.

Editorial note: This commentary was written by Allen Edel for The “New” Prostate Cancer InfoLink. We thank Dr. Amar Kishan of the University of California, Los Angeles, for allowing Allen to review the full text of the analysis by Jackson et al.

One Response

  1. Had SBRT (5 sessions CyberKnife) in March 2013. PSA was over 8 with four image-confirmed tumors. Primary was 1.2 cc, Gleason 3 + 4; three smaller tumors were 3 + 3. Current PSA is 0.089. Recent Color Doppler/Tissue Harmonic Ultrasound (Bahn, Ventura) found no evidence of any tumors. Prostate uniform dense tissue, with clean, well-defined margins.

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