Comparison of Outcomes from Adjuvant Radiation Including Pelvic Lymph Nodes Versus Prostate Bed Only Radiation for Prostate Cancer after Prostatectomy and Interaction with Pelvic Lymph Node Dissection

Abstract

For prostate cancer patients, adjuvant radiation after prostatectomy is considered for pathologic risk factors including positive margins, extension outside the prostatic capsule (extracapsular extension or ECE), and seminal vesicle invasion (SVI). Studies have shown improved biochemical progression free survival with adjuvant radiation therapy. However, the appropriate treatment volume has not been determined prospectively, so whether to add pelvic lymph nodes to the radiation field for high risk patients remains controversial. We studied the impact of adding pelvic lymph nodes to the treatment field in post-prostatectomy patients undergoing adjuvant radiation. We evaluated 25,784 non-metastatic prostate cancer patients who underwent prostatectomy followed by adjuvant radiation therapy from the National Cancer Database from 2004 to 2015. The data was managed and analyzed in SAS 9.4. Analysis was carried out using Kaplan-Meier survival analysis. Median follow-up was 67 months (41.3-96.1). Mean age at diagnosis was 61.2 years old. 10,233 patients received radiation to the prostate only, 9,891 received radiation to the prostate and pelvis, and 5,660 did not have radiation fields available. A total of 8,487 patients (32.9%) had ECE on pathology, 9,601 patients (37.1%) had SVI, and 3,571 (14.1%) had positive surgical margins; 19,210 patients (74.5%) had at least one of these risk factors. A total of 20,374 patients (79.4%) of patients had regional lymph nodes examined with a lymph node dissection.A total of 3,286 patients (16.1%) had positive lymph nodes on pathology.For all patients, there was increased hazard of death for those who received radiation to the prostate and pelvis versus prostate alone (HR = 1.21, p =0.05). When patients were stratified by risk factors, for patients with positive margins, ECE, SVI, or positive lymph nodes, radiation field size was not significantly associated with overall survival. Patients who did not have ECE, SVI, positive margins, or positive lymph nodes had an increased hazard of death with radiation to the prostate and pelvis versus prostate alone (HR 1.18, p = <0.0001). For patients on androgen deprivation therapy and patients who had not undergone pelvic lymph node dissection, there was also no significant change in overall survival with radiation field size. For all patients, there was increased hazard of death for those who received radiation to the prostate and pelvis versus prostate alone. This effect was still seen in patients without ECE, SVI, positive margins, or positive pelvic lymph nodes. In patients with ECE, SVI, positive margins, positive lymph nodes, on ADT, or patients who had not undergone pelvic lymph node dissection, no change in overall survival was correlated with radiation fields. This data does not support a benefit for post-prostatectomy radiation fields including pelvic lymph nodes. It is possible that with a longer follow-up, an overall survival benefit would be seen in specific subpopulations.