“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,” lead author Dr. Christopher King, from Stanford University School of Medicine, California, said in a statement.

The findings, reported in the International Journal of Radiation, Oncology, Biology, Physics for March 15, come from a study of 41 men who received a 7.25-Gy daily dose of image-guided SBRT for 5 days delivered with the CyberKnife (Accuracy Inc., Sunnyvale, California).

During a median follow-up period of 33 months, no RTOG (Radiation Therapy Oncology Group) grade 4 early (<3 months) or late (>6 months) rectal/urinary complications were noted. No grade 3 rectal complications were noted either, but two patients had grade 3 late urinary complications.

These toxicities are on par with what is seen with other radiation treatments for prostate cancer, the authors note. Moreover, they found that giving the SBRT doses every other day rather than every day helped reduce the rate of rectal complications: 0% vs. 38% (p = 0.0035).

No PSA failures were noted at latest follow-up, regardless of how biochemical failure was defined. In 25 of 32 patients with at least 1 year of follow-up, the lowest PSA was 0.4 ng/mL or less. Further monitoring for up to 3 years suggested that PSA nadirs continue to fall.

While the findings are encouraging, Dr. King acknowledged that longer follow-up of these patients is needed. “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.”

Int J Radiat Oncol Biol Phys 2009;73:1043-1048