Stereotactic body radiation: early data from a trial of CyberKnife therapy

The ‘New” Prostate Cancer InfoLink has previously stated the importance of having more data about the potential of CyberKnife therapy in the treatment of localized prostate cancer. The first such data are now available.

King et al. have reported interim data from a prospective Phase II clinical trial of stereotactic body radiotherapy (SBRT) in the treatment of 41 patients with localized, low-risk prostate cancer.

All patients received a dose of 36.25 Gy in five fractions of 7.25 Gy each, using image-guided SBRT alone delivered by CyberKnife. Patients were followed for a minimum of 6 months. Early (<3 months) and late (>6 months) urinary and rectal toxicities were assessed using validated quality of life questionnaires (International Prostate Symptom Score, Expanded Prostate Cancer Index Composite) and the Radiation Therapy Oncology Group (RTOG) toxicity criteria. PSA response data were also collected and analyzed.

The authors report the following results to date:

  • The median follow-up was 33 months.
  • There were no RTOG Grade 4 acute or late rectal/urinary complications.
  • Two patients demonstrated RTOG Grade 3 late urinary toxicity but there were no cases of RTOG Grade 3 rectal complications.
  • A significantly reduced rate of severe rectal toxicities was observed with treatment every other day as compared to treatment over 5 consecutive days  (0 vs. 38 percent).
  • A PSA “bounce” (median, 0.4 ng/ml) was observed in 12 patients (29 percent) at a median of 18 months after treatment. (The authors describe this PSA bounce as “benign.”)
  • No patient had demonstrated PSA failure, regardless of how biochemical failure is defined.
  • 25/32 patients (78 percent) with 12 months of minimum follow-up have achieved a PSA nadir of ≤ 0.4 ng/ml.
  • A PSA decline to progressively lower nadirs up to 3 years after treatment has been noted.

The authors conclude that, “The early and late toxicity profile and PSA response for prostate SBRT are highly encouraging. Continued accrual and follow-up will be necessary to confirm durable biochemical control rates and low toxicity profiles.”

Quoted in a media release from the American Society for Radiation Oncology (ASTRO), the lead author of the study, Dr. Christopher King, has said that, “There is great enthusiasm in reducing the length of treatment for prostate cancer while also possibly improving its effectiveness, and these early results are very promising for men with early-stage prostate cancer.” He continues, ” However, it can often take as long as 10 years to see late side effects and recurrences, so we will have to monitor these men closely and cautiously pursue these treatments further before we can confidently say that SBRT is as good as other proven prostate cancer treatments, like external beam radiation therapy, brachytherapy or surgery.”

The adverse events reported in this study at this stage would appear to be neither better nor worse than those seen in trials of other forms of prostate cancer radiation therapy, but this is not a comparative trial and so it is difficult to make absolute statements about compartive effectiveness or safety of the competing forms of radiotherapy.

5 Responses

  1. Here is something I don’t understand about this very small very short study:

    It is stated that

    — There were no RTOG Grade 4 acute or late rectal/urinary complications.

    — Two patients demonstrated RTOG Grade 3 late urinary toxicity but there were no cases of RTOG Grade 3 rectal complications.

    which sounds pretty good but then it is said that:

    — A significantly reduced rate of severe rectal toxicities was observed with treatment every other day as compared to treatment over 5 consecutive days (0 vs. 38 percent).

    Does this mean that 38% of the men who had treatment every day had “severe rectal toxicities”? Is a severe rectal toxicity different to a rectal complication. Please excuse my ignorance here.

  2. Terry: I have only read the abstract, not the complete paper, but I think that what the authors are suggesting is there there are short term “toxicities” and longer term “toxicities” that lead to complications. By giving the treatment over 10 days instead of over 5 days, the frequency of the short-term toxicities (tiredness, diarrhea, etc.) was lowered because people had the ability to recover between doses, but I would have to read the full paper to get any clarity.

  3. After much research on treatments, I was successfully treated (even with stage II and a PSA of 20) by CyberKnife with zero side effects. Guys diagnosed with prostate cancer need to do their research. To do so, these sites should be included in that research:

    Is CyberKnife ready for prime time in prostate cancer?
    — The Accuray corporate web site
    — The CyberKife web site

    All the best. David.

    [Editorial comment: Please note that the CyberKnife and the Accuray web sites are commercial sites owned by Accuray, the manufacturers of the CyberKnife system, who clearly have a commercial interest in maximizing the use of this system.]

  4. Thank you for the opportunity to submit comments on my prostate cancer treatment experience with stereotactic body radiation therapy (SBRT)/CyberKnife.

    I am a prostate cancer (PCa) patient who was treated with the CyberKnife and am also a founding member of ZERO — The Project to End Prostate Cancer.

    ZERO is a patient advocacy organization that is committed not only to reduce prostate cancer or alleviate the pain from the disease but to end it.

    My father had advanced PCa diagnosed (in 1980) when he was 69. His treatment was barbaric when compared with to today’s options. His experience motivated me to understand as much as possible about PCa prevention, detection and treatment. When my PSA increased (0.75 ng/ml 2006 to 2007) I had a biopsy which confirmed early stage (Gleason 3 + 3) PCa, just like my father.

    I thought I knew all the options: surgery, brachytherapy, cyrotherapy, ADT/chemo, HIFU, proton RT, EBRT by IMRT until I went to Stanford University Hospital in California. I feel very fortunate to have consulted with doctors at Stanford, who offered several surgical options (nerve sparing, robotic, etc.) and radiation oncology options including IMRT and SBRT/CyberKnife. The doctors answered my questions about every option. I had researched all options except the CyberKnife.

    Dr. Christopher King commented that he was conducting a clinical trial using the CyberKnife which I might want to include in the research I was doing for the treatment of my prostate cancer and he referred me to an early CyberKnife report.

    After a week of research, it was clear (in my opinion) that the CyberKnife offered the best chance of cure and lowest rate of side effects. The only downside was limited treatment history (3.5 years at the time). However, the physics and science of the CyberKnife treatment process has been well documented (from HDR brachytherapy) so the lack of platform-specific, long-term data was not a major concern compared with the benefit of cure and low risk of side effects. The ability of the CyberKnife to track prostate movement during treatment allowing reduced dose margins was very impressive and an important consideration in my research. All treatment options are a compromise of risk and benefit, which include an element of the unknown in terms of how each patient will respond in both the short- and long-term.

    In my opinion the CyberKnife is the ultimate treatment for localized PCa. As demonstrated by the Stanford experience, it appears to have one of the lowest, if not the lowest biological failure rate to date for of all options treating early stage localized PCa. And the toxicity rate is no worse than other external beam treatments, as measured by the side effects.

    As it turned out the hardest part of this treatment option was dealing with the denial of treatment by my insurance company. I appealed the insurance company denial for 7 months. The appeal denial was covered by CBS/SF. Here is a link to that story.

    My appeal with the state of California (IMR) overturned the 7-month denial of my insurer. On July 23, 2008 (approximately 2 months after the CBS story was aired) the insurer added the CyberKnife to their policy for treating prostate cancer.

    I was treated by Dr. Christopher King, and 14 days post-treatment there were minimal side effects. I am amazed by the improvements is radiation delivery and their impact on biological failure rate and reduction in side effects. CyberKnife treatment was completed May 7, 2008. I have had zero side effects for the last year.

    As a cancer patient I want all treatment options, not the just the ones special interests advocate. I feel very strongly about a patient’s right to make an informed choice for their treatment. Every treatment has risk and, from my research, every other option has higher risk of death, infection, or biological failure. It is the cancer patients’ quality of life at risk. It must be our choice in consultation with our doctors to select the treatment that best meets our specific limitations or medical needs.
    In my opinion, the CyberKnife/SBRT treats early stage PCa better than other option while maximizing the patient’s quality of life and ease of treatment.

    Thanks for giving us a voice.

    Best Regards,

  5. I recently completed my 1-year follow-up after being treated using CyberKnife for prostate cancer. PSA before treatment was 20 ng/ml; PSA is now 0.67.
    In my case, Cyberknife treatment was successful with minimal side effects.

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