Stereotactic body radiation therapy (SBRT) for localized prostate cancer (PCa) offers high rates of long-term oncologic control with mild toxicity, according to study results presented at the American Society for Radiation Oncology (ASTRO) virtual annual meeting.
Alan J. Katz, MD, JD, of St Francis Hospital in Roslyn, New York, and Josephine Kang, MD, PhD, of New York-Presbyterian/Weill Cornell Medicine in New York, New York, reported findings of a 12-year study of 560 patients with organ-confined PCa treated with robotic SBRT between 2006 and 2009. Of these, 324, 154, and 82 patients had low-, intermediate-, and high-risk PCa, respectively, according to National Comprehensive Cancer Network criteria.
A total of 515 patients received a 35-36.25 Gy dose in 5 daily fractions and 45 received external beam radiation therapy (EBRT, 45 Gy) followed by an SBRT boost (18-21 Gy).
Androgen deprivation therapy of up to 9 months was administered to 102 patients.
The 12-year biochemical disease-free survival (bDFS) was 92.0%, 79.1%, and 64.0% for the low-, intermediate-, and high-risk groups, respectively, according to the investigators. Local control rates were 97.0%, 91.7%, and 88.0%, respectively.
The 12-year bDFS rate did not differ significantly between the favorable intermediate-risk and low-risk patients (89.8% and 92.0%, respectively). The unfavorable intermediate-risk patients had a 12-year bDFS rate similar to that of the high-risk group (67.5% and 64.0%).
Unfavorable intermediate-risk PCa was defined as Gleason 4+3 disease or more than 1 intermediate risk factor (cT2b-c, PSA 10-20 ng/mL, Gleason 7). Biochemical failure was defined by the Phoenix definition (PSA nadir plus 2 ng/mL).
Toxicities were mild, according to the investigators. A dose of 36.25 Gy was associated with significantly more grade 2-3 late urinary toxicity than 35 Gy (13.8% vs 6%). EBRT and ADT did not improve long-term control in higher-risk patients.
“This study suggests that early excellent control rates for SBRT for prostate cancer remain durable over 12 years,” Dr Katz and Dr Kang concluded in a study abstract.
For patients receiving SBRT alone, 35 Gy is as effective as 36.25 Gy, with less toxicity, suggesting that 35 Gy may be the optimal dose, they noted.
Katz AJ, Kang J. Efficacy and toxicity of stereotactic body radiation therapy for localized prostate cancer: A twelve year study. Presented at: ASTRO 2020 virtual annual meeting, October 25 to 28. Poster 4026.