Low-risk PCa: Higher radiation dose shows no benefit

July 31, 2015

Higher radiation doses don’t confer a survival benefit in men with low-risk prostate cancer, although they do increase survival rates for men with medium- and high-risk cancers, the authors of a new study report.

Higher radiation doses don’t confer a survival benefit in men with low-risk prostate cancer, although they do increase survival rates for men with medium- and high-risk cancers, the authors of a new study report.

The retrospective, nonrandomized study, which was published online in JAMA Oncology (July 15, 2015), used information from the National Cancer Database to evaluate 42,481 men diagnosed with non-metastatic prostate cancer between 2004 and 2006. Researchers followed the men through 2012. They divided patients into three cohorts: low-risk (12,229 men), intermediate-risk (16,714 men), and high-risk (13,538 men), and categorized the members of each cohort according to whether they were treated with standard-dose or escalated-dose external beam radiation therapy (EBRT). The standard dose was 68.4 Gy to <75.6 Gy (1 Gy=100 rad); the escalated dose was 75.6 Gy to 90 Gy.

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The authors then compared overall survival rates between treatment groups in each cohort and performed a secondary analysis of dose response for survival. Men in the low-risk cancer group showed no difference in survival regardless of radiation dose. The intermediate-risk group showed a 7.8% decrease in the risk of death for every incremental increase of about 2 Gy in radiation dose, and the high-risk group showed a 6.8% reduction for each incremental dosage increase.

The 7-year adjusted survival rate for low-risk men was 86% in both the standard- and escalated-dose groups. Intermediate-risk men in the escalated-dose group had an 82% survival rate compared with 78% for men in the standard-dose group. Survival rates for high-risk men were 74% in the escalated-dose group and 69% in the standard-dose group.

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The findings suggest that “physicians should strongly consider disease risk when weighing the risks and benefits of dose-escalated EBRT,” said lead author Anusha Kalbasi, MD, of the Perelman School of Medicine of the University of Pennsylvania, Philadelphia, who worked on the study with Justin E. Bekelman, MD, and co-authors.

Dr. Kalbasi notes that the study raises the issue of whether low-risk patients could minimize the risk of treatment side effects, which increase as the radiation dosage rises, while benefiting from cure rates similar to those achieved at escalated doses. Patients undergoing prostate radiation may experience fatigue, urinary frequency and urgency, changes in bowel habits, and erectile dysfunction.

For intermediate- and high-risk patients, the study is the first to show a survival benefit with dose-escalated EBRT. In previous studies, higher-dose EBRT improved biochemical and local control of prostate cancer, but evidence regarding overall survival was scarce.

“Our findings show that the dose of radiation should be personalized to the specific characteristics of the prostate tumor,” Dr. Bekelman said in a press release from the University of Pennsylvania. “For some patients, personalized treatment will lower the chances of toxicity while maintaining similar survival rates; for other patients, personalized treatment will mean escalating radiation dose to achieve the highest survival while protecting normal tissues, like the bladder and rectum.”

The study was funded by the National Cancer Institute.

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