Higher Radiation Therapy Doses Over Shorter Time Show No Added Side Effects in Men with Prostate Cancer, Study Says

Delivering higher doses of radiation therapy over a shorter time period — an approach called stereotactic body radiation therapy (SBRT) — does not worsen side effects in men with localized prostate cancer, compared to conventional radiation therapy, a Phase 3 trial shows.

The study also suggests that SBRT delivered through the CyberKnife System is less toxic for the genitourinary system than conventional linear accelerators used for this kind of radiation therapy.

The research was published in an article, “Intensity-modulated fractionated radiotherapy versus stereotactic body radiotherapy for prostate cancer (PACE-B): acute toxicity findings from an international, randomised, open-label, phase 3, non-inferiority trial,” in the journal The Lancet Oncology.

Accuray’s CyberKnife is a robotic system that delivers SBRT to the prostate and other organs. This approach involves very high doses of radiation over a smaller number of treatment sessions compared to conventional radiation therapy.

As the prostate can move unpredictably during the course of treatment, tracking its position and correcting the radiation delivery site are key. CyberKnife offers continual imaging and automatic beam delivery corrections through its Synchrony technology, which helps increase treatment efficacy and spare healthy tissue, according to the company.

The international, Accuray-funded PACE-B Phase 3 trial (NCT01584258) was designed to compare SBRT to conventional radiation therapy in men who were ineligible for surgery, and to determine if the CyberKnife system provided any benefits over other SBRT delivery systems.

Patients assigned to SBRT received five sessions over one or two weeks, while those on conventional radiotherapy had either 39 sessions over eight weeks, or 20 sessions over four weeks.

The trial included 874 men and took place in the U.K., Ireland, and Canada. In both groups, 90% of the patients had intermediate-risk prostate cancer.

Patients receiving SBRT were assessed after the final dose, and at two, four, eight, and 12 weeks after the end of treatment. The participants in the control group were evaluated every other week.

Clinical assessments and patient-completed questionnaires showed that SBRT and conventional radiation therapy resulted in similar levels of acute gastrointestinal and genitourinary side effects over three months. No treatment-related deaths occurred in either group.

“It is reassuring to see from this trial that SBRT does not significantly impact patients’ quality of life in the short term, compared with the current standard of care,” Nicholas van As, the trial’s chief investigator and a consultant clinical oncologist at The Royal Marsden NHS Foundation Trust, said in a news release.

The researchers also found that moderate or worse genitourinary side effects were less common in CyberKnife users (12%) than in non-users (31%). Gastrointestinal side effects were similar in both groups.

“There are many reasons why there might be a systematic difference between CyberKnife and non-CyberKnife stereotactic body radiotherapy outcomes, including variations in dosimetry, image guidance, and treatment times (typically 45 min for CyberKnife and <5 min for conventional linear accelerators),” the researchers said.

In another news release, vas As said the results are “promising, and for the first time show in a large patient group that giving five large doses of SBRT is safe in the short term.”

Birgit Fleurent, Accuray’s chief marketing officer, said “there is robust clinical data supporting the safety and efficacy of CyberKnife SBRT for the treatment of patients with low- and intermediate-risk prostate cancer.”

“And now,” she added, “with the Accuray Precision Treatment Planning System and the CyberKnife VOLO Optimizer, clinicians are able to significantly reduce both the time to create high quality treatment plans and the time to deliver patient treatments.”

Of note, eight of the study’s authors received grants and/or personal fees from Accuray.