Stereotactic Body Radiation Therapy and High-Dose Rate Brachytherapy Boost in Combination with Intensity Modulated Radiation Therapy for Localized Prostate Cancer: A Single-Institution Cohort Study

Abstract

The use of dose-escalated external beam radiation (EBRT) and brachytherapy (BT) boost with ADT has emerged as an option with superior biochemical control compared to dose-escalated EBRT alone. BT is traditionally delivered using low-dose rate techniques, but more recently high-dose rate (HDR) BT has also emerged as a boost option for these patients with promise of low toxicity rates. SBRT is a favorable modality for monotherapy for low and intermediate risk group patients, however its safety and efficacy as a boost in combination with EBRT is less well understood. The aim of this study is to compare SBRT boost, HDR boost and LDR boost for localized prostate cancer. A single-institution retrospective chart review was performed of men receiving EBRT delivered using intensity modulated RT and either SBRT boost (650cGy x 3), HDR-BT boost (1500cGy x 1), or LDR boost with I-125 (110Gy). Of patients treated w/ SBRT boost, 39 (80%) were treated with an SIB to the MRI-detectable lesion(s) to 700cGy x 3. Treatment characteristics for each strategy were reviewed and on-treatment toxicity outcomes for each of the cohorts were compared using Chi-square tests. From 2017-2022, 49 patients were treated with EBRT+SBRT boost, 44 patients received EBRT+ HDR-BT boost, and 46 patients received EBRT+ LDR-BT boost. The average age of patients included in the study was 71.2 years (median age 69.55 years, range 51.42-83.70 years) with average baseline PSA of 11 (median 7.6, range 3.3-64). In addition, 55% of the patients had high-risk/very high-risk disease, 39% had unfavorable intermediate disease and 6% had favorable intermediate disease. 139 patients received androgen deprivation therapy (93%). There were no differences in these baseline demographics and clinical or treatment factors between SBRT, HDR and LDR boost (p>0.05). The median dose/fx of EBRT was 4500cGy/25 fx (range 4500-5040cGy/23-28 fractions). At the end of treatment, 69% of the patients had 0-1 change in nocturia. There is an increase in nocturia episodes of 2-3 from baseline in 27% of the patients, while 4% had an increase in nocturia episodes of 4 or more from baseline with no difference between the SBRT, HDR and LDR boost. At baseline 36 patients (26%) reported urinary frequency symptoms, increasing to 80 patients (58%) by end of treatment with no difference between the SBRT, HDR and LDR boost. Similarly, there was a trend to increased use of urinary modifiers at end of treatment in patients treated with EBRT+HDR boost compared to EBRT+SBRT and EBRT+ LDR boost (89% vs. 71% v 72% respectively). There was no significant difference in acute urinary toxicity and nocturia between SBRT, HDR and LDR boost (p>0.05).