Stereotactic body radiotherapy (SBRT) may offer an effective and non-invasive treatment option for low-risk prostate cancer that is both shorter and results in lower toxicity than standard therapies, according to a study published Jan. 10 in Radiation Oncology.
With evidence indicating that the alpha/beta ratio in prostate cancer is lower than in some other cancers, researchers have directed attention to SBRT as a method for achieving therapeutic gains by administering fewer, high-dose fractions, according to Debra E. Freeman, MD, of Naples Radiation Oncology in Naples, Fla., and Christopher R. King, MD, of Stanford University School of Medicine in Palo Alto, Calif. "SBRT has recently emerged as an alternative technique to deliver hypofractionated radiotherapy to the prostate, comparable in many respects to high-dose rate brachytherapy, but with a non-invasive approach."
A pooled cohort of 41 patients with low-risk prostate cancer underwent SBRT at the authors' respective institutions. No patients had received either hormone therapy or transurethral resection of the prostate. Patients treated at Stanford received five fractions of 7.25 Gy, while Naples patients were administered five fractions of 7.00 Gy each, for totals of 36.25 Gy and 35 Gy, respectively. The treatments were given over five consecutive days, except in three patients.
The treatment delivered a median progression-free survival rate of 92.7 percent. Prostate-specific antigen levels fell from a pre-treatment mean of 5.4 ng/ml to a mean post-treatment value of .34 ng/ml for non-recurring patients.
"Comparing non-recurring Stanford patients (treated with 36.25 Gy) to Naples patients (treated with 35 Gy), the mean PSA at last followup was significantly lower for the Stanford group (0.18 ± 0.14 ng/ml vs. 0.51 ± 0.46 ng/ml, p=0.002)," the authors wrote. Freeman and King also reported that patients were able to resume normal activity after one week, stating that "patients tolerated treatments very well."
In addition, the authors reported that no patient experienced grade three or greater late rectal toxicity. One patient developed late grade three urinary toxicity, while 25 percent of patients reported grade one and 7 percent grade two post-treatment urinary symptoms.
"Our five-year progression-free survival rate of 93 percent compares favorably with that obtained with surgery, low-dose rate or high-dose rate brachytherapy," the authors reported.
"The current analysis is the first report of five-year outcomes of SBRT for low-risk prostate cancer, and biochemical disease control is comparable to other available therapies, with equal to or better toxicity profiles. In addition, the treatment can be completed in a time period that is notably shorter (one to two weeks) than conventional radiotherapy (eight to nine weeks) and neither hospitalization nor surgical recovery is involved," Freeman and King concluded.