Medium-term outcome data on CyberKnife SBRT for localized prostate cancer

A paper in the May issue of the journal Radiation Oncology has provided 6-year outcome data (including quality of life and complications of treatment) after the use of stereotactic body radiation therapy (SBRT) using the CyberKnife system (from the Flushing Radiation Oncology group in Flushing, New York).

This paper by Katz et al. provides data on a total of 304 men treated with SBRT as first-line, definitive therapy for localized prostate cancer. The patients included

  • 211 men with low-risk disease
  • 81 men with intermediate-risk disease
  • 12 men with high-risk disease

We should note that these are probably only about 30 percent of all the patients treated by Katz and his group to date, and they do represent many of the earliest patients to undergo CyberKnife radiation therapy. One has to assume that patients treated later may have benefited from the accumulated experience of the treating physicians and their support staff.

It is clear that one immediate question has to be what percentage of the patients with low-risk disease might have done just as well (or perhaps even better) on a careful monitoring program of some type (e.g., active surveillance). However, at present this is an unanswerable issue.

The authors are careful to point out that:

  • Their first 50 patients received a total of 35 Gy of radiation in 5 fractions of 7 Gy each.
  • All other patients received a very slightly higher dose (36.25 Gy in 5 fractions of 7.25 Gy each).
  • 57/304 men received neoadjuvant androgen deprivation therapy (ADT) for up to a maximum of 1 year.

It is probably safe to assume that the men being treated with neoadjuvant ADT were probably all men in the intermediate- and high-risk groups.

Patients were considered to have biochemical failure based on the Phoenix definition (i.e., a rise in  the patient’s PSA by 2 or more ng/ml over the lowest or nadir PSA level after completion of radiation therapy).

Here are the data reported by Katz and his colleagues:

  • The average (median) PSA of the patients at time of presentation was 5.8 ng/ml.
  • No patients exhibited acute Grade III or IV acute complications.
  • Among the patients treated to a total of 35 Gy
    • No patients exhibited acute Grade III or Grade IV complications.
    • 2/50 patients (4 percent) exhibited Grade II urinary tract complications.
    • 1/50 patients (2 percent) exhibited late Grade II rectal complications.
  • Among the patients treated to 36.25 Gy
    • No patients exhibited acute Grade III or Garde IV complications.
    • 23/254 patients (9 percent) exhibited Grade II urinary tract complications.
    • 5/254 patients (2 percent) exhibited late Grade III urinary toxicities.
    • 13/254 patients (5 percent) exhibited late Grade II rectal complications.
  • Bowel and urinary quality of life (QOL) scores initially decreased, but later returned to baseline values.
  • Sexual quality of life scores exhibited an overall decrease of 20%.
  • Among those patients who were potent prior to treatment, 75% stated that they remained sexually potent.
  • PSA levels fell to a median of 0.12 ng/ml at 5 years (and radiation dose had no impact on median PSA levels post-treatment).
  • Actuarial 5-year biochemical recurrence-free survival was
    • 97.0 percent for low-risk patients
    • 90.7 percent for intermediate-risk patients
    • 74.1 percent for high-risk patients.

Katz and his colleagues conclude that, in what is the largest published series of patients with 6 years of follow-up, they “found excellent biochemical control rates and low and acceptable toxicity, outcomes consistent with those reported for from high dose rate brachytherapy (HBR BT).” They also state that, “Provided that measures are taken to account for prostate motion, SBRT’s distinct advantages over HDR BT include its noninvasiveness and delivery to patients without anesthesia or hospitalization.”

It appears clear that CyberKnife radiation therapy is a very viable form of first-line treatment for low-risk patients and perhaps for some intermediate-risk patients with localized prostate cancer. We say this with the previously stated provision that the need for any form of therapy among men with low-risk disease is now highly debatable. The “New” Prostate Cancer InfoLink would congratulate Dr. Katz and his colleagues for providing  a thorough summary of both the oncologic and the quality of life outcomes associated with this series of men.

The great advantage of CyberKnife from a patient’s perspective is that it takes a much shorter time to execute than most other forms of external beam radiation therapy. From a payer’s perspective, it is also significantly less expensive than IMRT or proton beam radiation therapy.

9 Responses

  1. It would be important to know the median time to nadir in order to meaningfully interpret this data. Was it reported?

  2. It may be in the full text of the paper. I have only seen the abstract.

  3. Median PSA levels of 0.12 ng/ml are shown twice, once for overall results and once for high-risk patients. Reading the abstract it seems that the is a reference to the overall results, and not for high-risk patients. Would be great to see the the results for each of the three risk groups.

  4. Sorry Wolfram … The second reference to the PSA levels after treatment has now been deleted. My error.

  5. I just finished SBRT at UNM in Albuquerque, NM. Six weeks after treatment my PSA is 11.6 which startled me. Has anyone else had this experience …? I’m shocked.

  6. Dear Jim:

    I can’t imagine why anyone was giving you a PSA test just 6 weeks after completion of radiation therapy. Since serum PSA is an assay of how much PSA is leaking from the prostate into the blood stream, and dying cells in the prostate might well leak a lot of PSA into the blood stream, it also doesn’t surprise me that at 6 weeks you have an elevated PSA like this.

    It is normal to wait more like 12 weeks after completion of therapy to get an initial PSA level — even after surgery, let alone after radiation therapy.

  7. Thank you for your reply. Prior to radiation, my PSA was 10.8 ng/ml. For the past 48-hours, I’ve been extremely bothered. I honestly thought that at the very least, it would be cut in half. So, are you saying that this PSA reading is not indicative to a “failure” yet …? I will watch for your reply, again, thanks. I waited 5 years to do the SBRT.

  8. Jim:

    What I am saying is that you need to talk to your doctor about what s/he thinks this PSA level means because it is my understanding that a PSA level taken just 6 weeks after completion of radiation is not necessarily an accurate indicator of clinical outcome. I am in no position to make promises about whether this reading is or is not indicative of “failure”. I am not a doctor and I don’t have all sorts of other relevant information anyway. I do think you should tell the doctor that this reading is making you very anxious!

  9. And this was published in early December 2013.

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