Live implant dosimetry may be an effective replacement for postimplant computed tomography in localized prostate cancer patients receiving low dose rate brachytherapy

Brachytherapy. 2021 Apr 8:S1538-4721(21)00045-3. doi: 10.1016/j.brachy.2021.02.008. Online ahead of print.

ABSTRACT

PURPOSE: To determine if Live Implant Dosimetry (LIDO) utilizing intraoperative transrectal ultrasound (TRUS) is equivalent to postimplant CT dosimetry (either day 0 or day 30) in patients with localized prostate cancer (PC) treated with low dose rate (LDR) prostate seed brachytherapy.

METHODS AND MATERIALS: The treated population consisted of 628 men with localized (T1-T2) PC. All d’Amico risk categories (low, intermediate, and high) were included, and 437 patients were treated with monotherapy (160 Gy) [low and low tier intermediate], and the remainder (191) [high tier intermediate and high risk] with an implant boost (106 Gy) post external beam radiation, to a volume including the prostate and seminal vesicles (46 Gy). LIDO with intraoperative TRUS, postimplant CT (day 0 and day 30) were performed in all cases. Prostate volumes (V), V₁₀₀ (prostate) and dose (D) D₉₀ (prostate), D₃₀ (urethra), and Rectum D_2cc, were recorded. No urinary catheter was used on Day 30 CT.

RESULTS: More than 91.33% of monotherapy patients reached the target D₉₀ according to LIDO while only 82.99% of Day 0 CT and 92.82% of Day 30 CT achieved target D₉₀. When considering V₁₀₀, monotherapy patients recorded target dosimetry in 90.93%, 82.31%, and 92.02% of cases assessed by LIDO, Day 0 CT and Day 30 CT, respectively. Strong correlations are observed in D₉₀, Rectum D_2cc and Urethra D₃₀ across imaging modalities but V₁₀₀ and V₁₅₀ were poorly correlated due to the relative quantification of this parameter and high degree of error in measurement. Of all monotherapy patients with satisfactory dosimetry on LIDO, 94.82% reached target D₉₀ at day 30 CT and 94.19% reached target V₁₀₀.

CONCLUSIONS: LIDO and CT are both effective tools for assessing postimplant dosimetry. Patients with satisfactory LIDO dosimetry are highly likely to have equivalent dosimetry on CT at follow-up, indicating that postimplant CT may be eliminated in PC a patients implanted with this technique.

PMID:33840634 | DOI:10.1016/j.brachy.2021.02.008