Correlation between Obesity and Treatment Failure Following Stereotactic Body Radiation Therapy (SBRT) for Clinically Localized Prostate Cancer

Abstract

<h3>Purpose/Objective(s)</h3> Cancer control outcomes are significantly worse in obese prostate cancer patients. Over the past decade, stereotactic body radiation therapy (SBRT) has been established as a safe and effective treatment for localized prostate cancer. Accurate delivery of external beam radiation could be adversely affected by increased pelvic adipose tissue and result in worse biochemical control. Data reporting on the efficacy of SBRT stratified by BMI is limited. This single-institution study sought to evaluate oncologic outcomes following SBRT for prostate cancer in men based on BMI. <h3>Materials/Methods</h3> A retrospective chart review was performed on all patients with localized prostate cancer treated with SBRT at a single institution between 2006 to 2021. Treatment was delivered using robotic SBRT with doses of 35-36.25 Gy in 5 fractions, per institutional protocol. Biochemical recurrence was defined by the Phoenix definition (PSA rise ≥ 2 ng/mL above nadir). Multiple regression Cox proportional hazard analysis was performed. <h3>Results</h3> 1306 patients were identified, with a mean follow-up of 47 months. The patients were elderly (Median age = 70 years) and overweight (Median BMI = 27.6 kg/m²). The majority were low to intermediate risk (88%) according to the D'Amico classification. Median pre-treatment PSA was 7.4 ng/mL. 23.7% received neoadjuvant ADT. BMI (kg/m²) was calculated prior to initiation of treatment and patients were stratified as thus: BMI < 25, 25 – 29.9, 30 – 34.9, ≥ 35. There was no statistically significant difference between pre-treatment PSA or Gleason's score between BMI groups. A multiple regression Cox proportional hazard analysis was performed, with BMI < 25 set as the reference. There was no statistically significant difference in biochemical disease-free survival, distant metastasis-free survival, or disease-specific survival between BMI subgroups. <h3>Conclusion</h3> In the general population, cancer control following prostate SBRT is equivalent to other standard radiation options. In this analysis, increased BMI did not portend worse oncologic outcomes following SBRT when analyzing bDFS, DMFS, or DSS. Thus, in the opinion of the authors, obesity should not be considered a contraindication to prostate SBRT.