Influence of applicator models on dose distribution in gynecologic high-dose-rate brachytherapy.

This study evaluated the influence of applicator models on dose distribution using Acuros BV (ABV) and the TG-43 protocol for high-dose-rate brachytherapy of gynecologic cancer. First, the dosimetric effects of a tandem and ovoid, tandem cylinder, and multichannel cylinder were evaluated on a water-equivalent phantom using the TG-43 protocol and two methods of applying ABV. One method calculated doses using a source model excluding the applicator model (ABVa), whereas the other included both source and applicator models (ABVb). Second, the doses calculated using ABV were compared with those obtained via TG-43 utilizing 53 clinical plans for gynecologic cancer. Dose-volume parameters were evaluated as per TG-43 for the high-risk clinical target volume (HR-CTV) and organs at risk (OARs). A three-dimensional gamma pass rate (GPR) analysis was also conducted between TG-43 and the ABV plans based on a 3%/2 mm criterion with a low-dose threshold of 10%. The dose calculated by TG-43 was the highest, followed by those of ABVa and ABVb. The maximum dose differences between TG-43 and ABVa and between ABVa and ABVb were 10.4% and 11.7%, respectively. Regarding clinical plans, the dose differences between TG-43 and ABV were − 4.6% for HR-CTV and − 5.7 to -4.0% for OARs (all p < 0.05). The median GPR value for the 3%/2 mm criterion was 99.9% (minimum–maximum: 98.7–100.0%). The applicator causes dose attenuation, which also affects the dose distribution within the patient. The transition from TG43 to ABV should be rigorously evaluated to provide an accurate clinical perspective.