A Matched-Pair Analysis Of Dose-Escalated Adaptive Image-Guided Radiotherapy (Igrt) Vs. Pelvic Irradiation With Brachytherapy Boost For Intermediate- And High-Risk Prostate Cancer

The purpose of this study was to compare clinical outcomes in a cohort of intermediate and high risk prostate cancer patients treated with either dose escalated adaptive IGRT or pelvic external beam RT with high dose rate brachytherapy boost (EBRT+HDR). One thousand five hundred twenty patients with clinical stage T1-T3 N0 M0 prostate cancer were treated with either CT-based offline adaptive IGRT (n = 1037) or EBRT+HDR, n = 438) at a single institution (1994-2008). Risk groups were defined based on NCCN criteria. For IGRT, the CTV included the prostate and proximal seminal vesicles only. A patient-specific confidence-limited PTV (cl-PTV) was constructed based on 5 CT scans. Median dose (minimum to cl-PTV) delivered via 3D conformal RT or intensity-modulated RT was 75.6 Gy (range, 73.8-79.2 Gy, median isocenter dose = 79.7 Gy). For EBRT+HDR, the whole pelvis was treated to 46 Gy + 2 HDR implants with a median of 10.5 Gy (8.75-11.5 Gy) per implant. Two hundred eight EBRT+HDR patients were randomly matched with 208 IGRT patients based on criteria of pre-treatment PSA ± 4 ng/mL, same Gleason score, T stage ± 2 sublevels, and use of neoadjuvant androgen deprivation therapy (ADT). Mean follow-up was 5.1 years for IGRT vs. 7.0 years for EBRT+HDR. Mean pretreatment PSA was 9 for both groups. Mean Gleason was 7 for both groups. EBRT+HDR patients were younger (67 vs. 71 years, p < 0.01) with a higher percentage of positive biopsy cores (51% vs. 39%, p < 0.01). Intermediate risk patients comprised 78% and 76% for IGRT and EBRT+HDR, respectively (p = 0.56). 42% in each treatment group received neoadjuvant or concurrent ADT. Median nadir was 0.2 vs. 0.1 ng/mL (p = 0.20). 5-year biochemical control (BC) based on the Phoenix definition was 91% for IGRT vs. 87% for EBRT+HDR (p = 0.60). For intermediate-risk, 5-year BC was 94% vs. 87% (p = 0.71) and was 86% vs. 86% (p = 0.83) for high-risk patients. No significant differences were noted for all patients between the 2 groups for local recurrence (0.5% vs. 1.5% at 2 years), distant metastasis (1% vs. 2%), clinical failure (2% vs. 5%), overall survival (84% vs. 90%), and cause-specific survival (98% vs. 100%). No significant differences were noted in any endpoint when examining either risk group. In this matched-pair analysis of 416 patients, treatment of intermediate and high-risk prostate cancer with either offline adaptive IGRT or EBRT+HDR yielded similar excellent clinical outcomes without detectable significant differences. The omission of pelvic radiotherapy in the IGRT patients did not appear to be associated with poorer clinical outcomes with modern high-dose RT.