Session Item

To determinate and evaluate long-term survival, dosimetric and gastrointestinal (GI) toxicity outcomes after rectal-spacer hyaluronic acid (HA) injection during high-dose-rate brachytherapy (HDR-BT) boost in treatment of high-risk prostate cancer patients.

Between january-2009 and december-2017, 234 patients with high-risk prostate cancer were treated in our institution with CT-based iridium192 15Gy HDR-BT boost and external beam radiotherapy (EBRT) combination schema. All patients received transrectal ultrasound-guided HA rectal-spacer injection in Denonvilliers fascia during HDR-BT procedure. After HDR-BT boost, all patients received EBRT 46Gy in 23 fractions of pelvic irradiation encompassing the prostate and seminal vesicles. Those patients with less than 3-year follow-up and less than 3 post treatment prostate-specific antigen (PSA) were excluded. Survival, dosimetric and GI toxicity outcomes were evaluated. Toxicity was evaluated using Common Terminology Criteria for Adverse Events (CTCAE) version 5.0.

About 202 from 234 patients satisfied inclusion criteria. Median follow-up was 8 years. Median age was 71 years (range: 49-83) and 85.1% of patients received androgen deprivation therapy (ADT), 55% long-term (36 months). Median PSA was 11ng/m and 67.7% of patients was Gleason 7 (4+3) or superior. T3 or superior clinical stage was 70.8%. All patients received at least 2cc of HA between prostate and rectum. Freedom from biochemical failure (FFBF) defined by Phoenix-criteria was 88.1% at 5 years and 76.1% at 10 years, respectively. Metastasis free survival (MFS) and Overall Survival (OS) was 95.9% and 92.7% at 5 years and 89.97% and 76.7% at 10 years, respectively. For HDR-BT boost target, median D90 was 109Gy and v100 98%. Analyzing rectum dosimetry, 2cc dose median was 8Gy and max dose median at 0.1cc was 10Gy. Combination of 15Gy HDR-BT and EBRT had a median BED (α/β=3) in rectum of 104Gy with a median equivalent dose of 62Gy. GI grade 2 late toxicity was 0.7% at 5 years and 1.1% at 10 years, respectively, and GI grade 3 or higher late toxicity was 0.1% for both 5 and 10 years. Subdivided according to injected HA quantity, GI grade 2 late toxicity was statistically unfavorable for those patients who were injected with 3cc or less HA. At 5 and 10 years, GI grade 2 late toxicity was 79.6% and 79.6% for 3cc injected, 95.8% and 88.7% for 4cc injected and 90.3% and 90.3% for 6cc or more injected, respectively. No significant difference was found in GI grade 3 or higher late GI toxicity between HA injection groups.

HA rectal-spacer injection during HDR-BT boost was well tolerated and provided excellent long-term toxicity and survival outcomes in patients with high-risk prostate cancer in combination with EBRT. Late grade 2 GI toxicity was statistically unfavorable for those patients with less quantity of HA injected. No significant difference was found in GI grade 3 or higher late GI toxicity.