Prostate cancer less likely to spread when treated with higher dose of radiation

A new study from Fox Chase Cancer Center finds that higher doses of 74 to 82 Gray (Gy) greatly reduce the risk that the cancer will spread later–even 8-10 years after treatment. The results of the study were presented today at the 48th Annual Meeting of the American Society for Therapeutic Radiology and Oncology in Philadelphia.

“There is a comprehensive body of evidence demonstrating that prostate cancer treated with higher doses of radiation is less likely to grow back in the prostate or cause a rising PSA, and now, we know it is also less likely to spread later to other parts of the body,” explained Peter Morgan, M.D., a resident in the Radiation Oncology Department at Fox Chase Cancer Center.

Generally, treatment centers that offer 3D conformal radiation therapy or a newer system of radiation delivery called IMRT (intensity modulated radiation therapy) treat men with the higher levels of radiation shown in this study to prevent the cancer's spread.

Morgan said that no published data from prospective randomized trials have shown a significant reduction in distant metastasis with higher radiation dose, likely because patients have not been followed for long enough to see the reduced of late-wave of metastasis. The current study shows that the risk of cancer spreading 8-10 years after treatment is lower when doses >74 Gray of radiation are given.

When asked how more radiation to the prostate protects the rest of the body from the cancer, Dr. Morgan replied, “That's what is so important about this work. We believe that the late wave of distant metastasis is due to the persistence of cancer in the prostate itself, which subsequently seeds tumor cells to other parts of the body. Because higher dose radiation more effectively kills cancer in the prostate, the source for future metastases is eliminated.”

From 1989 to 1999, 667 men with intermediate- to high-risk prostate cancer were treated consecutively with 3D conformal radiation therapy. The outcomes of men who received less than 74 Gy, 74-75.9 Gy and greater than 76 Gy were compared. These groups had a median follow-up of 84, 84 and 65 months, respectively. The 10-year rate of the cancer spreading outside of the prostate (distant metastasis) was 16 percent for radiation doses less than 74 Gy, 7 percent for 74-75.9 Gy, and 3 percent for greater than 76 Gy.

Morgan said, “At our institution the policy for several years has been to treat prostate cancer to a dose of 76 to 80 Gy using IMRT. This study confirms that we are doing the right thing.”