BOSTON—Stereotactic body radiotherapy (SBRT) offers excellent cancer-free survival rates for patients with intermediate-risk, organ-confined prostate cancer (PCa) and results in few long-term rectal side effects, data show.

The early PSA responses are promising, and suggest that SBRT could provide significant advantages in this patient population, said lead investigator Robert Meier, MD, a radiation oncologist at the Swedish Radiosurgery Center in Seattle.

“SBRT can complete treatment in five days instead of eight weeks and achieve what appears to be extremely high cancer-control rates with minimal reduction in long-term urinary or bowel function quality of life,” Dr. Meier told Renal & Urology News. “All the patients were treated with the CyberKnife, so it is unclear if this translates to other SBRT platforms.”

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Dr. Meier and his colleagues, who presented their findings at the annual meeting of the American Society for Radiation Oncology, evaluated the toxicity and efficacy of SBRT in 129 PCa patients with intermediate-risk, organ-confined disease. The median follow-up was 36 months. The four-year Kaplan-Meier progression-free survival rate was 99%. Only one patient experienced cancer recurrence. There were no reports of grade 4 to 5 toxicity.

Thirty patients (23%) experienced acute grade 2 genitourinary (GU) toxicity and 11 (8.5%) experienced acute gastrointestinal (GI) toxicity with SBRT.  Late grade 2 GU and GI toxicities occurred in 14 patients (11%) and three patients (2%), respectively. One patient had a grade 3 bladder neck injury one year after treatment.

This study also examined the effects on patients’ quality of life using the Expanded Prostate Cancer Index Composite (EPIC-26) questionnaire for urinary, bowel, and sexual function and determined that the results appear favorable compared with other radiotherapy modalities. EPIC-26 scores showed that patients’ urinary and bowel functions had diminished one month after treatment but returned to normal by 24 months. One patient required temporary catheter placement for acute urinary retention. At baseline, 52% of patients were potent; at 24 months, this declined to 36%.

The study included patients from 21 institutions who exhibited a pre-treatment median PSA level of 5.9 ng/mL, which decreased to 0.8, 0.4, and 0.2 ng/mL at one, two, and three years, respectively. Patients were treated for one week with a non-isocentric robotic SBRT platform using real-time tracking of implanted fiducials. Investigators used magnetic resonance imaging to assist in target localization. SBRT was administered to patients at 40 Gy in five fractions of 8 Gy to the prostate, and 36.25 Gy was delivered to seminal vesicles. No patient received androgen deprivation therapy. Researchers assessed toxicities using common terminology criteria for adverse events. Patients with erections “firm enough for intercourse” were scored as potent.

“In the sexual domain, there was a decrease in quality of life initially and there was a gradual reduction over the three-year study period,” Dr. Meier said. “This is typical of radiotherapy modalities. We have 17 patients out at four years, and we have had only one biochemical failure. For intermediate-risk patients that is extremely good.”

Dr. Meier and his team defined biochemical failure as a 2 ng/mL rise above nadir. The one case of biochemical failure, which was identified after three months of follow-up, was caused by biopsy-proven nodal metastasis.