Stereotactic Body Radiation Therapy For Low- And Intermediate-Risk Prostate Cancer: Disease Control And Quality Of Life At 8 Years

Stereotactic body radiation therapy (SBRT) takes advantage of the prostate’s low α/β ratio to deliver a large biological radiation dose in a few fractions. Initial studies on small groups of low-risk patients support SBRT’s potential for clinical efficacy while limiting treatment-related morbidity and maintaining quality of life (QOL). This prospective study expands upon prior studies to further evaluate SBRT efficacy and QOL for a patient population that includes low- and intermediate-risk prostate cancer patients treated a minimum of 7 years ago. Two hundred and seventeen patients with organ-confined prostate cancer (195 T1c and 22 T2a, all N0M0) were treated with robotic SBRT. The median age was 69 years and the median prostate-specific antigen (PSA) was 5.5 ng/mL. One hundred fifty-seven patients were low risk (PSA ≤ 10 ng/mL and Gleason < 7) and 60 were intermediate risk (PSA 10-20 ng/mL or Gleason = 7). Androgen deprivation therapy was administered to 34 patients for up to 6 months. The first 50 patients received 35 Gy delivered in 5 daily fractions. These patients were either low risk or low-intermediate risk (Gleason scores of <4+3). The remaining patients, from both risk groups, received a total dose of 36.25 Gy in 5 daily fractions. The dose was prescribed to a planning target volume (PTV) created by a 5-mm expansion of the prostate gross tumor volume (GTV), with a 3-mm posterior expansion. The proximal seminal vesicles were included for intermediate patients. The PTV was covered by the 83% to 87% isodose line. Biochemical failure was assessed using the Phoenix criterion. Toxicity was scored by Radiation Therapy Oncology Group (RTOG) criteria. With a median follow-up of 84 months (range, 9-99 months), the actuarial 8-year biochemical disease-free survival (bDFS) was 95.8% and 90% for the low and intermediate groups, respectively. The median PSA fell to 0.11 ng/mL at 48 months and remains there at 96 months. For low- and low-intermediate-risk patients, there was no difference in bDFS between doses of 35 Gy and 36.25 Gy. Late RTOG toxicity was mild, occurring at a frequency of 3.7% Grade 2 rectal, 8.7% Grade 2 urinary, and 1.8% Grade 3 urinary. Incidence of late Grade 2 or 3 urinary toxicity trended lower for 35 Gy than 36.25 Gy (6% vs 12.7%, P=.22). Mean EPIC urinary and bowel QOL scores declined at 1 month posttreatment and returned to baseline by 2 years, where they remain. Mean EPIC sexual QOL declined by 23% at 12 months and by 34% at 7 to 8 years. Sixty-two percent of the patients sexually potent at baseline remain potent at last follow-up. Robotic SBRT produces excellent biochemical control rates at up to 8 years with minimal impact on QOL. PSA control rates, toxicity, and QOL compare favorably to other radiation modalities. Median PSA nadir was reached at 4 years and has remained unchanged for up to 8 years, suggesting that the response is durable. These results also strongly suggest that 35 Gy is as effective as 36.25 Gy for low- and low-intermediate-risk patients.