Predictors for Post-treatment Biopsy Outcomes after Prostate Stereotactic Body Radiotherapy
(2021, MSK study)
• SBRT dose levels of 35–37.5 Gy of SBRT were associated with a higher likelihood of a positive post-treatment biopsy at 2 years.
• Two-year positive post-treatment biopsies pre-dated the development of PSA failure in the majority of these patients.
• Among patients with positive post-treatment biopsies, the PSA level at the time of 2-year biopsy was ≤ 1.00 in 52.5% of patients.
• Patients with a positive biopsy had a significantly higher cumulative incidence of BCR at five years compared to patients who had a negative post-RT biopsy (57% versus 7%; p<0.001).Abstract
To investigate predictors associated with post-treatment biopsy outcomes after stereotactic body radiotherapy (SBRT) for localized prostate cancer.Materials and methods
257 patients treated with prostate SBRT to dose levels of 32.5 Gy to ≥40 Gy in 5–6 fractions underwent a post-treatment biopsy performed approximately two years after treatment to evaluate local control status. 73 had% intermediate-risk disease (n=187) and the remaining 17% (n=43) and 10% (n=27) had low-risk and high-risk disease, respectively.Results
The incidence of positive, negative, and treatment-effect post-treatment biopsies were 15.6%, 57.6%, and 26.8%, respectively. The incidence of a positive biopsy according to dose was 37.5% (n=9/24), 21.4% (n=6/28), 19.4% (n=6/31), and 10.9% (n=19/174) for 32.5 Gy, 35 Gy, 37.5 Gy, and ≥40 Gy, respectively. In a multivariable model, patients treated with SBRT doses of <40 Gy and those with unfavorable-intermediate-risk or high-risk disease had higher likelihood of a positive post-treatment biopsy. A positive post-SBRT biopsy was associated with a significantly higher likelihood of subsequent PSA relapse at five years (Positive biopsy: 57%, 95% CI: 29-77% compared to negative biopsy: 7%, 95% CI: 3-14%; p<0.001).Conclusion
Based on two-year post-SBRT biopsies, excellent tumor control was achieved when dose levels of 40 Gy or higher were used. Standard SBRT dose levels of 35–37.5 Gy were associated with a higher likelihood of a positive post-treatment biopsy. Two-year positive post-treatment biopsies pre-dated the development of PSA failure in the majority of patients.