DETECTION OF AIR-GAPS AROUND THE CYLINDER BY POST-INSERTION COMPUTED TOMOGRAPHY IN VAGINAL VAULT BRACHYTHERAPY: NEW PROSPECTIVE DATA AND META-ANALYSIS

Purpose: Post-insertion computed tomography (CT) can identify air gaps (AGs) around the cylinder in vaginal cuff brachytherapy (VCB). This study investigates the incidence and location of AGs. METHOD I) Planning CTs of 22 prospectively-recruited patients (NCT02091050) treated with 2.6 cm (n=8) and 3.0 cm (n=14) cylinders were evaluated. II) Additionally, a systematic literature review (CRD42016032608) and meta-analysis was performed (PubMed and EMBASE), and the pooled incidence of AGs was calculated by using the random-effects model weighted by inverse variance. Results: I) prospective study In 18 (82%) cases, a total of 45 AGs were found: 26 within the 2 cm cranial length, and 19 between 2-4 cm of the cylinder. The mean AG diameter was 3.7 mm (range: 1.3-11.8). Cylinder diameter, primary tumor site, and use of external beam radiotherapy were not associated with AG incidence. II) meta-analysis Systematic literature review revealed 9 additional relevant studies, totaling 657 patients and 667 insertions. The pooled incidence of patients with ≥1 AG was 68.7% (95% confidence interval: 52.9-81.1). AGs were located at the apex in 43.4%-94.4% of cases. In patients with ≥1 AG (n=244), the pooled mean number of AGs was 2.18 per patient. The mean dose reduction varied from 9.6% to 29.3%. Conclusions More than two-thirds of VCB cases present with AGs, which are most commonly at the apex and can potentially reduce mucosal dose. By identifying AGs, post-insertion CT can facilitate selection of optimal cylinder size in VCB. References in press: Sapienza LG, N.S. Gutierrez, Ning MS, Pellizzon ACA, et al. Detection of air gaps around the cylinder by post insertion computed tomography in vaginal cuff brachytherapy: A prospectiveseries, system icreview, andmeta-analysis. Brachytherapy 2019. https://doi.org/10.1016/j.brachy.2019.04.272