Biochemical control in intermediate- and high-risk prostate cancer after EBRT with and without brachytherapy boost

Abstract

Purpose: External beam radiotherapy (EBRT) with or without brachytherapy boost (BTB) has not been compared in prospective studies using guideline-recommended radiation dose and recommended androgen-deprivation therapy (ADT). In this multicenter retrospective analysis, we compared modern-day EBRT with BTB in terms of biochemical control (BC) for intermediate-risk (IR) and high-risk (HR) prostate cancer.

Methods: Patients were treated for primary IR or HR prostate cancer during 1999-2019 at three high-volume centers. Inclusion criteria were prescribed ≥ 76 Gy EQD2 (α/β = 1.5 Gy) for IR and ≥ 78 Gy EQD2 (α/β = 1.5 Gy) for HR as EBRT alone or with BTB. All HR patients received ADT and pelvic irradiation, which were optional in IR cases. BC between therapies was compared in survival analyses.

Results: Of 2769 initial patients, 1176 met inclusion criteria: 468 HR (260 EBRT, 208 BTB) and 708 IR (539 EBRT, 169 BTB). Median follow-up was 49 and 51 months for HR and IR, respectively. BTB patients with ≥ 113 Gy EQD_2Gy experienced a stable, good BC outcome compared with BTB at lower doses. Patients treated with ≥ 113 Gy EQD_2Gy also experienced significantly improved BC compared with EBRT (10-year BC failure rates after ≥ 113 Gy BTB and EBRT: respectively 20.4 and 41.8% for HR and 7.5 and 20.8% for IR).

Conclusions: In patients with IR and HR prostate cancer, BTB with ≥ 113 Gy EQD_2Gy offered a BC advantage compared with dose-escalated EBRT and lower BTB doses.

Fig. 1

Patients with high-risk prostate cancer treated with brachytherapy boost. The log hazard ratio function (red solid line) and a corresponding 95% pointwise confidence band (blue dashed lines) were estimated by a restricted cubic spline to quantify the effect of dose in EQD2 on time to biochemical control failure. Note that smaller log hazard ratios indicate superior biochemical control. A reference value of 113 Gy (grey vertical solid line) was applied. The three spline knots were placed at 86, 115, and 118 Gy

Fig. 2

Patients with intermediate-risk prostate cancer treated with brachytherapy boost. The log hazard ratio function (red solid line) and a corresponding 95% pointwise confidence band (blue dashed lines) were estimated by a restricted cubic spline to quantify the effect of dose in EQD2 on time to biochemical control failure. Note that smaller log hazard ratios indicate superior biochemical control. A reference value of 113 Gy (grey vertical solid line) was applied. The three spline knots were placed at 87, 114, and 118 Gy

Fig. 3

Cumulative incidence functions of patients with high-risk prostate cancer treated with either external beam radiotherapy (EBRT) or EBRT and an additional brachytherapy boost (BTB) of at least 113 Gy EDQ2

Fig. 4

Cumulative incidence functions of patients with intermediate-risk prostate cancer treated with either external beam radiotherapy (EBRT) or EBRT and an additional brachytherapy boost (BTB) of at least 113 Gy EDQ2