Results of CyberKnife

In this section I will talk about studies that have the largest numbers of patients, or the longest followup time, or some interesting findings.  Stereotactic radiation for prostate cancer is relatively new, so there are not many long term study results yet.

When reviewing these studies it is important to know that it is difficult to directly compare the results of two studies: for instance the “high risk” patient group in one study may have more aggressive cancer on average than patients in another study.  The follow-up schedule may be different or the way they determine if someone has a cancer recurrence may also be different.

Research studies typically divide patients into low-risk, intermediate-risk, and high-risk.

CyberKnife Alone

Dr.Katz (Flushing, NY) published 5-year results on 304 patients (PMID: 23668632).   The complete article is also available online.   At the 5-year mark the rate of cancer control was 97% for low-risk, 91% for intermediate-risk, and 74% for high-risk.  PSA fell to an average of 0.1 by the five year mark.  Only 25% developed erectile dysfunction, and only 2% developed serious long term urinary symptoms.   He concluded that these results were similar to the excellent results obtained by using HDR brachytherapy, but that CyberKnife has a distinct advantage because it doesn’t require hospitalization.

Dr. Katz recently updated his results for his stage 1 patients (low risk) who had reached 10-years.  93% of the men had cancer control at 10-years.  The cancer was found to come back in the prostate gland in only 1.6% of men.  Using the EPIC survey, the urinary, rectal, and sexual function were given an score pre-treatment and in followup visits.  Over the 10 years urinary score worsened by 10%, rectal score worsened by 4%, and sexual function worsened by 40%.

A study by King in 2013 pooled together the results from multiple different studies involving a total of 1100 patients who underwent CyberKnife (PMID: 24060175).  The complete article is also available online.  At the 5-year mark the rate of cancer control was 95% for low-risk, 84% for intermediate-risk, and 81% for high-risk.  PSA fell to an average of 0.2 by the three year mark. Hormonal therapy was used in some patients and this did not improve the treatment success.  A PSA bounce (a jump in the PSA after treatment that later drops back down) was seen in 16% of patients.   A common CyberKnife dosage is 7.25 Gy x 5 treatments, and in this study they did not notice a difference in success with doses ranging between 7.0 and 8.0 Gy per treatment.

Preliminary results were presented on a poster at a symposium by Fuller, regarding 259 patients who were treated at 14 different hospitals with CyberKnife.  They used a higher dose than typical, 9.5 Gy x 4 treatments,  which is about 30% higher than the usual 7.25 Gy x 5 treatments.  They used heterogenous dosing which means that different areas of the prostate received different dosages –  see chapter on Treatment Planning.  At the 5-year mark the rate of cancer control was 100% for low-risk, and 89% for intermediate-risk.  They unfortunately did not include high-risk men.  PSA fell to an average of 0.1 by the five year mark.  54% developed erectile dysfunction.  3% of patients had serious long term urinary symptoms, and 8% developed incontinence requiring pad use.  In the group as a whole, less than 2% developed a recurrence within the prostate gland by the 7 year mark.  The side effects seem worse than other studies, likely due to to the increased dose.

A study by Yu compared stereotactic radiation (SBRT) versus IMRT, looking at 4000 patients in the Medicare database (PMID: 24616315).  They found that the average cost for SBRT was 35% lower then for IMRT.   They found that 2 years after treatment 44% of SBRT patients had some urinary side effects, versus 36% of IMRT patients.

Combination treatment with CyberKnife and IMRT

A study by Anwar in 2016 gave 2 fractions of CyberKnife along with 25 fractions of IMRT to 48 patients    A complete article is available online.  This study only included patients with intermediate and high risk prostate cancers.  71% of patients had high-risk.  At the 5-year mark the rate of cancer control was 83%.

CyberKnife Compared to Other Treatments

If you take the average results of all the CyberKnife-alone studies in the last section, you get the following results:

  • Five year cancer control rates are 97% for low risk, 89% for intermediate risk, and 77% for high risk.
  • PSA drops down to 0.1 by the 5-year mark
  • Serious late urinary side effects occur in 2%
  • Erectile dysfunction occurs in 40%

There are no randomized head-to-head studies of CyberKnife compared with other treatment methods.  Therefore, it is difficult to accurately compare the results to other methods.

Surgery Results

There are some very long term results available for surgery, unlike the situation for CyberKnife.  Dr. Walsh has been considered one of the world’s leading experts on radical prostatectomy.    He published his 10 year results on 955 men (PMID: 7523730), and these results can perhaps can be considered the “gold standard” for surgery in expert hands.  Only low-risk and some intermediate-risk men with Gleason 6 or lower cancer were included in this study.  At 10 years the chance of having an undetectable PSA was 70%.  Biochemical failure (elevated PSA, but cannot find the recurrence) occurred in 23%.  Distant metastases (spread to bone / nodes) occurred in 7%, and proven recurrence within the region where the prostate used to be was 4%.   Again, these are 10 year results, not 5 year results, and for mostly low-risk patients.  These are very good results by one of the world’s best prostate cancer surgeons, but I think they emphasize that surgery is not a cure-all.

Currently many prostatectomies are being done with a robotic approach.  These have a better recovery time and possibly fewer side effects, but the cancer control rates are not any better compared with the older open prostatectomies.  In addition there is a significant learning curve with the robotic prostatectomies, meaning there can be different results between surgeons with different experience levels.