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Brachytherapy alone can control intermediate-risk prostate cancer
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The addition of external beam therapy to brachytherapy did not significantly extend PFS among men with intermediate-risk prostate cancer, according to the initial report of a phase 3 study presented at the ASTRO Annual Meeting.
Thus, radiation treatment with brachytherapy alone may provide adequate cancer control for this population, resulting in fewer long-term adverse events, results showed.
“Low-risk prostate cancer can be treated by either surgery, external beam therapy or brachytherapy, equally successfully. In fact, in recent years many investigators and doctors in clinical practice have elected to do active surveillance on patients and hold off on treatment completely until the patient progresses,” Bradley Prestidge, MD, medical director of the Bon Secours Cancer Institute at DePaul Medical Center in Norfolk, Virginia, said during a press conference. “But, patients with intermediate-risk prostate cancer have conventionally received external beam therapy alone or sometimes with hormone therapy, or in combination with brachytherapy, but traditionally not brachytherapy alone.”
Prestidge and colleagues hypothesized that patients with intermediate-risk prostate cancer who received external beam therapy in addition to brachytherapy — or the insertion of radioactive seed implants into a patient’s tissue to limit radiation exposure to surrounding, healthy tissue — would have a 10% improvement in 5-year PFS compared with patients who received brachytherapy alone.
The analysis included data from 579 men (median age, 67 years) with intermediate-risk prostate cancer. Patients had clinical stage T1c (67%) to T2b disease and a Gleason score between 2 and 6 with a PSA between 10 and 20, or a Gleason score of 7 and a PSA less than 10 (89%).
Researchers randomly assigned patients to receive brachytherapy alone (n = 292) or with 45 Gy partial external beam therapy to the pelvic area (n = 287). Brachytherapy used radioactive Iodine-125 or Palladium-103 in 110- or 100-Gy doses for patients who also received external beam therapy, and 146-Gy or 125-Gy doses for patients who received that treatment alone.
PFS served as the study’s primary endpoint. The incidence of short-term acute and long-term late side effects also served as an outcome measure.
Median follow-up was 6.7 years.
Researchers were able to evaluate data from 443 patients at 5-year follow-up.
Sixty-six patients experienced a first failure, 34 of whom were in the combination arm and 32 of whom received brachytherapy alone.
Overall, rates of 5-year PFS were 85% (95% CI, 80-89) among men who underwent external beam therapy plus brachytherapy, and 86% (95% CI, 81-90) among men who received brachytherapy alone (HR = 1.02; P for futility = .0006). Based on these results, the data monitoring committee recommended early release of the findings.
The rates of acute grade 2 or worse toxicity (28% vs. 27%) and acute grade 3 or worse toxicity (8% for both) were comparable in the combination and brachytherapy arms. However, more patients in the combination arm experienced late grade 2 or worse toxicity (53% vs. 37%; P = .0001) and late grade 3 or worse toxicity (12% vs. 7%; P = .039). More patients in the combination arm experienced grade 3 or worse genitourinary toxicity (7% vs. 3%), but rates of grade 3 or worse gastrointestinal toxicity were comparable (3% vs. 2%).
“This means men with intermediate-risk prostate cancer may be quite well managed with brachytherapy alone,” Prestidge said. “That represents a bit of a paradigm shift compared with when the study was originated. It is going to require further analysis to look at subsets, such as more favorable vs. less favorable intermediate risk, to see if heterogeneity in the groups leads to any differences between the two. And, of course, longer follow-up will be even more meaningful.”– by Alexandra Todak
Reference:
Prestidge BR, et al. Abstract 7. Presented at: ASTRO Annual Meeting; Sept. 25-28, 2016; Boston.
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Colleen Lawton, MD, FASTRO
I am very excited about these results. This is a paradigm shift for us. When this study opened up, there were factions that believed you could not treat intermediate-risk prostate cancer — which isn’t the best, isn’t the worse, but is somewhere in the middle — with anything but the combination. This shows that is not true; patients only need the implants. For the subset of patients defined in this study, the vast majority of intermediate-risk patients do not need the cost or the toxicity of external beam therapy. These data are really exciting.
Perspective
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Mark A. Hallman, MD, PhD
There are many effective approaches in the treatment of prostate cancer with unique advantages, disadvantages and limitations of each. Many men have options of intensity-modulated radiation therapy (IMRT), stereotactic body radiation therapy, brachytherapy and radical prostatectomy. Counseling patients to select the appropriate treatment should be based upon strong evidence. From a social perspective, cost and value are also important concerns. The investigators of NRG Oncology/RTOG 0232 should be commended for the most recent significant contribution to that evidence base.
For men with intermediate-risk prostate cancer, there have been conflicting reports regarding the appropriate use of low-dose rate brachytherapy as monotherapy among these men. Although low-dose rate monotherapy has several potential advantages including lower toxicity, shorter treatment time and lower cost, it has not been an adopted standard of care due to concerns of lower efficacy compared with IMRT alone or a combined modality approach. Low-dose rate monotherapy has been a high value option for men with low-risk prostate cancer. Despite this, there has been declining use of low-dose rate in favor of other radiation modalities that are equivalent but less cost-effective.
The NRG Oncology/RTOG 0232 trial was a multi-institutional study, in which researchers randomly assigned 588 men with intermediate-risk prostate cancer and favorable-risk features to low-dose rate monotherapy or combined modality with a freedom-from-progression endpoint.
The findings of this early report suggest that low-dose rate monotherapy provides high-quality care with comparable disease control and lower rates of late toxicity. This opens consideration of low-dose rate monotherapy to a broader group of men, now including those with favorable intermediate-risk disease. Not only would this provide additional treatment options, but low-dose rate monotherapy has potential to decrease the cost, improve patient quality of life and improve the value of high-quality care for these men.
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