Early outcomes of high-dose-rate brachytherapy combined with ultra-hypofractionated radiation in higher-risk prostate cancer

Abstract

Purpose: This study evaluated outcomes associated with a high-dose-rate (HDR) brachytherapy boost combined with stereotactic body radiation therapy (SBRT) for patients with higher-risk localized prostate cancer.

Materials and methods: We identified 101 patients with National Comprehensive Cancer Network high-risk, unfavorable intermediate-risk, or favorable intermediate-risk with probable extra-prostatic extension treated with HDR brachytherapy (15 Gy x 1 fraction) followed by SBRT (5 Gy x 5 daily fractions to the prostate and/or seminal vesicles and/or pelvic lymph nodes). Androgen deprivation therapy was used in 55.4% of all patients (90% of high-risk, 33% of intermediate-risk). Toxicities according to Common Terminology Criteria for Adverse Events (CTCAE) v4.0 and International Prostate Symptom Scores were prospectively documented at each followup visit. Biochemical relapse was defined as PSA nadir +2ng/mL.

Results: The median follow-up time after SBRT was 24.1 months. No grade ≥3 toxicities were observed. The incidence of acute and late grade 2 gastrointestinal toxicities was both 0.99%. Acute and late grade 2 genitourinary (GU) toxicities were observed in 5.9% and 9.9%, respectively. Median time to a grade 2 GU toxicity was 6 months with a 14% 2-year actuarial rate of grade 2 GU toxicity. Median International Prostate Symptom Scores at 24 months was not significantly different than baseline (6 vs. 5; p = 0.24). Inclusion of pelvic lymph nodes and absence of a rectal spacer were significantly associated with more frequent grade ≥1 GU toxicity, but not grade ≥2 GU or gastrointestinal toxicity. The 2-year biochemical relapse free survival was 97%.

Conclusions: HDR brachytherapy combined with SBRT was associated with a favorable early toxicity profile and encouraging cancer control outcomes.

Keywords: CTCAE, Common Terminology Criteria for Adverse Events; CTV, clinical target volume; EBRT, external beam radiation therapy; EPE, extra-prostatic extension; EPIC, Expanded Prostate Cancer Index Composite; GI, gastrointestinal; GU, genitourinary; HDR, high-dose rate; High dose rate brachytherapy; IMRT, intensity-modulated radiation therapy; IPSS, International Prostate Symptom Score; LDR, low-dose rate; NCCN, National Comprehensive Cancer Network; OARS, organs at risk; PET, positron emission tomography; PFS, progression-free survival; PRO, patient-reported outcomes; PSA, prostate-specific antigen; PSMA, prostate-specific membrane antigen; PTV, planning target volume; Prostate cancer; SBRT, stereotactic body radiation therapy; Stereotactic radiosurgery; Toxicity. Abbreviations: ADT, androgen deprivation therapy.