Robotic radiosurgery found safe, feasible in low-risk prostate cancer

Seattle-Early results from the first multicenter trial of stereotactic robotic radiosurgery are in, with researchers from the Swedish Cancer Institute at Northwest Hospital, Seattle reporting that toxicity is acceptable and PSA responses are favorable.

This is a relatively new technology, and more time must pass before the procedure's impact on long-term efficacy can be reliably assessed.

"Based on our early outcomes, we can say that it is feasible to deliver brachytherapy-equivalent doses of radiation using an external beam platform, and we can complete the treatment in a week," first author Robert Meier, MD, medical director of the Swedish Cancer Institute, told Urology Times.

The tool used for the treatment is the CyberKnife (Accuray Inc., Sunnyvale, CA), a radiosurgery system that employs three advanced technologies: a compact X-band linear particle accelerator (LINAC), a robot, and a real-time x-ray-based imaging and guidance system that surrounds the patient. The LINAC is mounted on the robot, which allows it to deliver precise doses of radiation to a target organ or tumor within that organ from any perspective.

The imaging system controls the robot arm via a sophisticated computer program. This allows soft, often mobile organs and tissues such as the prostate gland to be treated without the need for framework to keep the patient immobile. The system adjusts instantly to any movement in the target. This allows it to paint the organ or tumor with a radiation field that replicates the shape of the organ almost perfectly, even when it is moving.

"There is a lot of motion in the prostate during any procedure. That is one of the reasons why we could not use standard external beam technology to delivery brachytherapy-like radiation doses," Dr. Meier told Urology Times.

He added that the CyberKnife delivers a more homogenous dose and avoids some of the problems that can arise from misplaced or mobile brachytherapy seeds.

This multi-institutional trial involved 17 institutions enrolling patients with low-risk (T1b-T2a, N0, M0, PSA <10.0 ng/mL, Gleason ≤6) or intermediate-risk prostate cancer (T1c-T2b, with either Gleason 7, PSA >10.0 ng/mL or Gleason ≤6, PSA 10.0 to 20.0 ng/mL).

No grade 3 toxicities observed

A total of 198 patients were evaluable at 3 months. Of these, 98 in the ongoing study were evaluable at 1 year. Using Common Terminology Criteria for Adverse Events criteria, no acute grade 3 toxicities were reported, although one patient did present with a grade 3 genitourinary toxicity (bladder neck necrosis) 1 year postoperatively. The cohort's mean PSA fell from 5.5 ng/mL to 1.2 ng/mL. One patient presented with PSA progression and developed regional metastatic disease but with no evidence of regional failure.

A treatment lasts less than 1 hour. The full procedure usually involves one treatment per day over a 5-day period, as compared to the up-to-9 weeks of treatment often required by external beam radiation, said Dr. Meier. He also noted that despite the advanced technology and computerized delivery system, there is currently a rather steep learning curve associated with the procedure. That curve results from the need for urologists and radiation oncologists to learn to accurately read magnetic resonance images.

Dr. Meier is a meeting participant/lecturer for Accuray, which provided a grant for the trial.