Dose Escalation for Prostate Cancer Radiotherapy: Predictors of Long-Term Biochemical Tumor Control and Distant Metastases–Free Survival Outcomes

Abstract

BackgroundHigher radiation dose levels have been shown to be associated with improved tumor-control outcomes in localized prostate cancer (PCa) patients. ObjectiveIdentify predictors of biochemical tumor control and distant metastases–free survival (DMFS) outcomes for patients with clinically localized PCa treated with conformal external-beam radiotherapy (RT) as well as present an updated nomogram predicting long-term biochemical tumor control after RT. Design, setting, and participantsThis retrospective analysis comprised 2551 patients with clinical stages T1–T3 PCa. Median follow-up was 8 yr, extending >20 yr. InterventionPrescription doses ranged from 64.8 to 86.4Gy. A total of 1249 patients (49%) were treated with neoadjuvant and concurrent androgen-deprivation therapy (ADT); median duration of ADT was 6 mo. MeasurementsA proportional hazards regression model predicting the probability of biochemical relapse and distant metastases after RT included pretreatment prostate-specific antigen (PSA) level, clinical stage, biopsy Gleason sum, ADT use, and radiation dose. A nomogram predicting the probability of biochemical relapse after RT was developed. Results and limitationsRadiation dose was one of the important predictors of long-term biochemical tumor control. Dose levels <70.2Gy and 70.2–79.2Gy were associated with 2.3- and 1.3-fold increased risks of PSA relapse compared with higher doses. Improved PSA relapse–free survival (PSA-RFS) outcomes with higher doses were observed for all risk groups. Use of ADT, especially for intermediate- and high-risk patients, was associated with significantly improved biochemical tumor-control outcomes. A nomogram predicting PSA-RFS was generated and was associated with a concordance index of 0.67. T stage, Gleason score, pretreatment PSA, ADT use, and higher radiation doses were also noted to be significant predictors of improved DMFS outcomes. ConclusionsHigher radiation dose levels were consistently associated with improved biochemical control outcomes and reduction in distant metastases. The use of short-course ADT in conjunction with RT improved long-term PSA-RFS and DMFS in intermediate- and high-risk patients; however, an overall survival advantage was not observed.