Data from a 300+ patient series treated with CyberKnife


Stereotactic body radiotherapy (SBRT) — aka CyberKnife radiotherapy — is among the most recent methods developed for the treatment of prostate cancer using radiation. People have been waiting a while now to see early data from a large series of patients.

In a recent article, Katz et al. have reported such preliminary data on  a series of 304 patients, all of whom were treated for apparently organ-confined prostate cancer. Their patients received either five fractions of 7 Gy for a total dose 35 Gy (n = 50) or five fractions of 7.25 Gy  for a total dose 36.25 Gy (n = 254).

Katz and his colleagues report the following results to date.

  • For the 50 patients treated at the 35 Gy dose level:
    • Median follow-up is 30 months (range, 26 – 37 months).
    • At the 30-month median follow-up there were no biochemical failures among these patients.
    • Acute Grade II urinary and rectal toxicities occurred in 2/50 patients (4 percent).
    • There were no higher grade acute toxicities.
    • A late Grade II urinary toxicity occurred in 1/50 patients (2 percent).
    • There were no other Grade II or higher late toxicities.
  • For the 254 patients treated at the 36.25-Gy dose level:
    • Median follow-up is 17 months (range, 8 – 27 months).
    • At the 17-month median follow-up, biochemical fialures were observed in 2 low-risk and 2 high-risk patients.
    • Biopsy data suggested that the 2 low-risk and 1 high-risk patients with biochemical failure were disease-free in the gland.
    • Acute Grade II urinary and rectal toxicities occurred in 12/253 patients (4.7 percent) and 9/253 pastients (3.6 percent), respectively.
    • Among patients with a minimum of 12 months follow-up, 12/206 (5.8 percent) had late Grade II urinary toxicity and 6/206 (2.9 percent) had late Grade II rectal toxicities.
    • A late Grade III urinary toxicity occurred in a single patient.
    • There were no Grade IV toxicities. occurred.
  • At 17 months of follow-up, for patients treated at both dose levels:
    • Bowel and urinary quality of life (QOL) returned to baseline values.
    • Sexual QOL decreased by 10 percent compared to baseline values.

In their initial report, Katz et al. conclude that, “The low toxicity and maintained QOL are highly encouraging,” while recognizing that longer-term follow-up is still needed.

In additional commentary on this paper in “Beyond the Abstract” on the UroToday web site, Katz writes that, “In the year since we compiled the data, we have continued to be encouraged by the efficacy and toxicity profile. We still have not seen a local failure in the low or intermediate risk patients, with our early group treated with 35 Gy having a median follow-up of 42 months. For two reasons, we have decreased our dose back from 36.25 Gy to 35 Gy. First, 35 Gy has been very effective, with a 36-month median PSA of 0.15, which is highly predictive of excellent long-term control according to the literature. Secondly, our 36.25 group did experience a small increase in the rate of Grade 2-3 urethral toxicity.”

It has to be said that these early data in men with localized disease continue to demonstrate the potential of SBRT. However, the rubber will really only start to “hit the road” when we can see 5-year and 10-year follow-up data, and it will be a while before these are available.

For those readers who may be unfamiliar with SBRT, the great benefit of this external beam radiation technique from the patient’s point of view (assuming that it is at least as effective and safe as any other form of radiotherapy) is that it requires just five visits for treatment as opposed to the 35-40 visits needed for more traditional forms of radiation using IMRT or IGRT or even PBRT.

2 Responses

  1. How does CyberKnife’s data compare with Tomotherapy’s data?

  2. I am not aware of any analagous series of tomotherapy patients that would allow one to make such a comparison.

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