FIVE-FRACTION SBRT TO PROSTATE AND PELVIC NODES IN HIGH-RISK PROSTATE CANCER. A SINGLE INSTITUTION EXPERIENCE

Purpose:

Stereotactic body radiation therapy (SBRT) is an attractive treatment alternative for high-risk prostate cancer. However, most prior studies have focused solely on SBRT targeting the prostate. This study aims to report on outcomes for patients with high-risk prostate cancer treated with SBRT to the prostate and pelvic lymph nodes in combination with androgen deprivation therapy (ADT).

Materials and Methods:

Patients with localized high-risk prostate cancer that received SBRT at a dose of 36.25 Gy in 5 fractions targeting the prostate, while the pelvic nodal regions received 25 Gy over the same 5 fractions, delivered, on alternate days, via a simultaneous integrated boost technique with intensity-modulated radiation therapy (Figure 1). We performed same-day MRI and CT simulations with urethrograms in all patients. Cone-beam CT was performed prior to each treatment session. The primary tumour clinical target volume (CTV) prostate included the entire prostate and the proximal 1cm of seminal vesicles. The primary tumour planning target volume (PTV) was CTV with a 5mm isotropic margin. The PTV for pelvic nodes included the pelvic nodes CTV with a 6-7mm margin. The bladder constraint was V38Gy[cc]<0.03; V18Gy<50%, and the rectum constraint was V36Gy[cc]<3; V18Gy<50%. ADT was initiated 2-3 months before SBRT and continued for 6-24 months at the treating physician’s discretion. Follow-ups were conducted every 3-6 months annually. Outcomes were calculated using Kaplan-Meier analysis, from the end of radiation treatment date to the event date.

Results:

The data analyzed were collected from the first 102 patients treated between August 2019 and December 2022. The median age at diagnosis was 73 years; median PSA=11.9ng/ mL. T-Stage and Gleason scores are summarized in Table 1. The median follow-up was 33.8 months (range: 15-55 months), and 43% of patients had follow-up beyond 36 months. The 3- and 4-year actuarial biochemical recurrence-free survival were 92.8% and 77.7%, respectively; the distant metastasis-free survival was 96.3% and 82%; and the overall survival were 95.5% and 89.9%. Acute gastrointestinal and genitourinary Grade 2 toxicity were 4% and 25% respectively. No Grade 3 or 4 acute toxicity were observed.

Conclusions:

Five-fraction SBRT for high-risk prostate cancer, at dose of 36.25 Gy to prostate and 25 Gy to pelvic nodes, appears both feasible, safe and convenient for patients and the healthcare system. This regimen is associated with promising early outcomes and appears safe. Continued longer follow-up with late-toxicity report. Randomized trials employing similar approaches are needed.