Predictors for Post-treatment Biopsy Outcomes after Prostate Stereotactic Body Radiotherapy.

To investigate predictors associated with post-treatment biopsy outcomes after stereotactic body radiotherapy (SBRT) for localized prostate cancer.

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.

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).

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.

Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology. 2021 Feb 12 [Epub ahead of print]

Michael J Zelefsky, Debra A Goldman, Margaret Hopkins, Attapol Pinitpatcharalert, Sean McBride, Daniel Gorovets, Behfar Ehdaie, Samson W Fine, Victor E Reuter, Neelam Tyagi, Laura Happersett, Achiraya Teyateeti, Zhigang Zhang, Marisa A Kollmeier

Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, USA. Electronic address: ., Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York, USA., Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, USA., Division of Radiation Oncology, Thammasat University Hospital, Pathumthani, Thailand., Department of Urology, Memorial Sloan Kettering Cancer Center, New York, USA., Department of Pathology, Memorial Sloan Kettering Cancer Center New York, USA., Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, USA., Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, USA; Division of Radiation Oncology, Department of Radiology, Bangkok, Thailand.