Purpose

To compare TG-43 and Acuros^® BV dose estimates in iridium-192 (¹⁹²Ir) high-dose-rate (HDR) gynecological brachytherapy across four applicator types and evaluate applicator-dependent differences. The novelty was the systematic comparison of multiple applicators within a single-institution workflow.

Material and methods

This retrospective dosimetric study included 40 patients and 121 treatment plans: tandem and ring (T&R, 34 plans), tandem and ovoid (T&O, 38 plans), segmented cylinder (SC, 23 plans), and universal multi-channel cylinder (UMC, 26 plans). All plans were generated in BrachyVision™ v. 15.6 using the TG-43 formalism and subsequently recalculated with Acuros^® BV, with identical dwell positions and dwell times. The main analysis included high-risk clinical target volume (HR-CTV) D₉₀, D₉₈, and V₁₀₀; organ-at-risk (OAR) D_2cc; Point A for T&R/T&O; and the SC 100% prescription-isodose position at 5 mm depth. Exploratory dwell-loading descriptors and a density-cap quality assurance audit supported physical and methodological interpretation.

Results

TG-43 yielded consistently higher dose estimates than Acuros^® BV. For HR-CTV D₉₀, relative differences were 2.9 ±0.5% for T&R, 3.7 ±0.8% for T&O, 3.2 ±0.4% for SC, and 4.9 ±2.2% for UMC. OAR D_2cc differences were also largest for UMC, ranging from 4.3% (3.4-7.1%) in bladder to 6.1 ±2.2% in small bowel. For SC, when the TG-43 100% prescription isodose was normalized to 5 mm from the applicator surface, the corresponding Acuros^® BV 100% isodose position was 4.6 ±0.1 mm, indicating an inward shift of 0.4 ±0.1 mm.

Conclusions

TG-43 systematically overestimated dose relative to Acuros^® BV in all applicator groups. Differences were smallest for T&R, largest and most variable for UMC, and intermediate for T&O and SC. Algorithm-related dose differences are applicator-dependent and should not be assumed uniform across treatment configurations.