SBRT as Monotherapy or Boost for Intermediate or High-Risk Prostate Cancer: A Prospective Observational Study

Abstract

The high level of precision and accuracy of Stereotactic Body Radiotherapy (SBRT,) in addition to its unique radiobiologic characteristics, confer a potential therapeutic advantage with limited toxicity when compared with alternated radiation therapy treatment approaches. Stereotactic Body Radiation Therapy (SBRT) has become a standard treatment alternative to other treatment options such as laparoscopic-assisted robotic prostatectomy, intensity-modulated radiation therapy (IMRT) and brachytherapy in the management of low-risk prostate cancer. The efficacy and risk profile of SBRT in the setting of intermediate and high-risk prostate cancer are less well studied. The purpose of this project is to evaluate the efficacy and Health-Related Quality of Life (HRQOL) in intermediate and high-risk prostate cancer patients treated with SBRT as monotherapy or as a boost in combination with IMRT. 77 patients with intermediate and high-risk prostate cancer were enrolled in this prospective evaluation Intermediate-risk patients (n=47, 61%)) were treated with SBRT monotherapy, 36.25 Gy in 5 fractions, or with SBRT boost to the prostate, 21 Gy in 3 fractions followed by IMRT directed to the prostate and seminal vesicles, 45 Gy in 25 fractions, per physician discretion. High risk patients (n=30, 39%) were treated with SBRT boost to the prostate, 21 Gy in 3 fractions followed by IMRT directed to the prostate, seminal vesicles and pelvic lymph nodes, 45 Gy in 25 fractions. Androgen deprivation hormonal therapy (ADT) was administered to all patients in the high-risk group and per physician discretion in the intermediate-risk group. Biochemical disease-free survival (bDFS) was calculated per the Phoenix definition. Quality of Life (QOL) was assessed by the American Urological Association (AUA) symptom index, Expanded Prostate cancer Index Composite Short Form (EPIC-26), and the Sexual Health Inventory for Men (SHIM). Acute and late genitourinary (GU) and gastrointestinal (GI) toxicity were graded using the CTCAE version 3.0 and RTOG/ECOG definitions. QOL was estimated using least square means of fixed effects. The median follow-up time was 18 months. The bDFS was 96.43%, 100% and 92.59% for favorable-intermediate, unfavorable-intermediate, and high-risk groups, respectively. Late Grade 2 and 3 genitourinary toxicities were 24%, and 1.2 %, and late grade 2 gastrointestinal toxicities were 3% without grade 3 toxicities reported. Mean EPIC QOL scores declined modestly at 1-month post-treatment, plateaued until about 24 months, and recovering to levels close to baseline thereafter. SBRT as monotherapy or boost in the management of intermediate or high-risk patients with adenocarcinoma of prostate is a promising treatment approach, with excellent short-term bDFS and limited late toxicity. These outcomes will continue to be followed with the goals of confirming equivalence or superiority to alternative radiation therapy treatment approaches.