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Escalated-dose radiation does not improve OS in intermediate-risk prostate cancer
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Dose-escalated radiation therapy did not improve OS among men with intermediate-risk prostate cancer despite improvements in distant metastases and biochemical control, according to study results.
"Prior to the availability of modern radiation therapy techniques such as 3-dimensional conformal radiation therapy or intensity-modulated radiation therapy, it was difficult to safely deliver high doses of radiation to the prostate gland without excessive toxic effects,” Jeff M. Michalski, MD, MBA, distinguished professor in the department of radiation oncology at Washington University School of Medicine in St. Louis, and colleagues wrote. “Using modern technologies, prospective phase 3 dose escalation trials have demonstrated a dose response for improved biochemical and local tumor control.”
The researchers conducted a randomized clinical trial of 1,532 men with prostate cancer from 104 institutions. All men (median age, 71 years) had stage cT1b or T2b disease. Men had either Gleason scores between 2 and 6 and PSA levels that ranged from 10 ng/mL to less than 20 ng/mL, or a Gleason score of 7 and PSA levels lower than 15 ng/mL.
Most patients (70%) had PSA levels lower than 10 ng/mL and a Gleason score of 7 (84%). Fifty-seven percent had T1 disease.
Researchers randomly assigned men to 3-D conformal radiation therapy or intensity-modulated radiation therapy at doses of 79.2 Gy in 44 fractions or 70.2 Gy in 39 fractions.
OS served as the primary endpoint.
Michalski and colleagues used American Society for Radiation Oncology/Phoenix definitions to define biochemical failure, and they used NCI Common Toxicity Criteria to grade toxic effects.
Median follow-up was 8.4 years.
Men who received 79.2 Gy (n = 751) did not achieve significantly longer OS compared with men who received 70.2 Gy (n = 748; 8-year OS, 76% vs. 75%; HR = 1; 95% CI, 0.83-1.2).
The distant metastasis rate was lower among men who received 79.2 Gy (4% vs. 6%; HR = 0.62; 95% CI, 0.42-1.01).
ASTRO-defined biochemical failure rates were higher in the 70.2-Gy arm than 79.2-Gy arm at 5 years (40% vs. 25%) and 8 years (47% vs. 31%; HR = 0.59; 95% CI, 0.5-0.7). Phoenix-defined biochemical failure rates also were higher in the 70.2-Gy arm at 5 years (20% vs. 13%) and 8 years (35% vs. 20%; HR = 0.54; 95% CI, 0.44-0.65).
Patients assigned to the high-dose regimen appeared less likely to receive salvage therapy.
Men assigned the higher radiation dose experienced higher 5-year rates of late grade 2 or greater gastrointestinal toxic effects (21% vs. 15%; HR = 1.39; P = .006) or genitourinary toxic effects (12% vs. 7%; HR = 1.59; P = .003).
"Dose escalation has several clinical advantages, including improved rates of biochemical and clinical cancer control,” Michalski and colleagues wrote. “These benefits do not translate into improved OS. The decision to deliver high radiation dose must be balanced against the risk of mortality in the individual patient.” – by Andy Polhamus
Disclosures: Michalski reports no relevant financial disclosures. Please see the full study for all other authors’ relevant financial disclosures.
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