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SAN ANTONIO – Fewer, higher-dose radiation treatments, said searchers said.
In a sample of 1,641 low and intermediate-risk men treated with stereotactic body radiation therapy (SBRT), 6% experienced biochemical recurrence and 0.6% experienced distant metastases, reported Amar U. Kishan, MD, of the University of California, Los Angeles, at the American Society for Radiation Oncology (ASTRO) meeting.
Patients were divided into three groups: low-risk, favorable intermediate-risk, and unfavorable intermediate-risk, the most aggressive form observed in this study. After 7-year follow-up, 95.5% of low-risk patients, 91.4% of favorable intermediate-risk patients, and 85.1% of unfavorable intermediate-risk patients were free of biochemical recurrence.
Overall survival rates were also high: 91.4% for low-risk patients, 93.7% for favorable intermediate-risk patients, and 86.5% for unfavorable intermediate-risk patients, the Kishan's group reported.
"Prostate cancer is more likely to be more sensitive to higher doses of radiation treatment, higher doses, and less effective treatments," Kishan said. "SBRT pushes this hypothesis to the limit by condensing treatment, also known as extreme hypofractionation."
Low-risk prostate cancer can be treated with external beam radiation therapy (EBRT), radical prostatectomy, brachytherapy, hormone therapy, and active surveillance. Radiation is one of the most effective treatment methods, reportedly curing 98% of prostate cancer cases. SBRT, also known as extreme hypofractionation, is a strong form of EBRT that delivers higher levels of radiation dose, in a shorter amount of time. Although it has been considered a form of treatment since 2000, long follow-up studies have been determined to determine the duration of this treatment.
Severe adverse events were rare in the sample of men, with only 0.6% of patients experiencing grade 3 acute genitourinary (genital or urinary) toxicity. There was one case of late grade 4 gastrointestinal toxicity (fistula-in-ano), Kishan reported.
In this study, very large prostates and preexisting transurethral resection of prostate (TURP) have been specifically associated with higher levels of toxicity, he said. However, Kishan noted that the results of this study are designed to determine the overall benefit and quality of life in the future. He also said it would be important to measure patient-reported outcomes in the future.
"If you are to embark on SBRT you have to be careful," Kishan said. "There have been signs in the literature of trials that have been used in the past. [image-guided radiation therapy]. "
Still, these results demonstrate that hypofractionation may be endorsed by the standardized approach, said Neha Vapiwala, MD, PhD, of the University of Pennsylvania.
"I think this work exemplifies the shifting paradigm towards hypofractionation in prostate cancer as the standard for low-and-intermediate-risk prostate cancer that's treated with external beam radiotherapy," said Vapiwala, who was not involved in the study.
This study observed 2,142 men from 2000 to 2012 across 10 institutional and large trials, multi-institutional studies. The majority of men had low-risk disease (55.3%), while 32.3% had favorable intermediate-risk disease, and 12.4% had unfavorable intermediate risk disease, classified by the presence of multiple intermediate risk factors, primary Gleason pattern 4 disease, or at least half positive cores. Patients were an average age of 67.9.
A nearly equal number of patients were treated every day, and 5.3% were treated once a week. Most patients received five fractions (88%), while the patients received 33.5 to 40 Gy doses. The average follow-up was 6.9 years, with the low-risk group followed for 7.1 years, the favorable intermediate-risk group for 6.2 years, and the unfavorable intermediate-risk cohort followed for 5.9 years.
Overall, none of the patients observed in this study died from prostate cancer, the authors reported.
Kishan disclosed no relevant relationships with industry.
1969-12-31T19: 00: 00-0500
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