Durable efficacy of early postoperative radiation therapy for high-risk pT3N0 prostate cancer: the importance of radiation dose.

Objectives: To determine the durable efficacy of early postoperative radiation therapy (RT) in patients with pT3N0 prostate cancer who were at an increased risk of biochemical failure. We also evaluated the long-term benefit derived from using higher RT doses.
Methods: Seventy-nine patients with pathologic Stage T3N0 prostate cancer and high-risk postoperative features underwent RT within 6 months after surgery. No patient received prior hormonal therapy. Fifty-nine patients had positive surgical margin, 29 had pathologic seminal vesicle invasion, and 27 had persistently elevated postoperative prostate-specific antigen (PSA) levels. Freedom from biochemical relapse (bNED) was defined as an undetectable (less than 0.2 ng/mL) PSA level. Median follow-up time was 39 months, and the median radiation dose was 64.8 Gy. All patients were followed for at least 2 years to be considered biochemically controlled.
Results: Patients receiving adjuvant RT for an undetectable pre-RT PSA level had a 3-year bNED rate of 90%, compared with 44% for those receiving salvage RT for a detectable level (P < 0.0001). In the group of adjuvant patients, RT doses more than 61.2 Gy resulted in a 3-year bNED rate of 90% compared with 64% for those receiving a lower dose (P=0.015). The salvage patients irradiated with a dose of 64.8 Gy or greater had a 3-year bNED rate of 52% compared with 18% for those irradiated with lower doses (P=0.048). Severe late RT-related complications were infrequent and did not correlate with dose.
Conclusions: In patients with high-risk pT3N0 prostate cancer, an RT dose response may exist. Although some studies suggest limited durable efficacy for early postoperative RT, our data suggest that RT doses of 64.8 Gy or more appear superior to prevent future biochemical failures. A prospective randomized study evaluating a postoperative RT dose response is warranted.