A comparison of TG-43 and TG-186 dose calculation algorithms for treatment planning of intra-cavitary brachytherapy using tandem and ovoid applicator.

Purpose: The present study evaluated the dosimetric impact and compared the dose variations between the advanced collapsed cone engine (Task Group 186) and Task Group 43 plans for cervical cancer using tandem and ovoid applicators.

Material and methods: Thirty cervical cancer patients underwent iridium-192 (¹⁹²Ir) high-dose-rate (HDR) intra-cavitary brachytherapy using tandem and ovoid applicator. Original treatment plans for all patients were created using TG-43 dose calculation formalism. Subsequently, these plans were re-calculated using ACE (TG-186) algorithm and were not re-optimized, so that dwell time and dwell positions were identical in both plans. High-risk clinical target volume and organs at risk were contoured in each dataset. Significant air gaps within region of interest and use of high density applicator materials were also considered. The assessment encompassed a point-based evaluation, extraction of dosimetric parameters from dose-volume histogram (DVH), and plan evaluation indices for each algorithm.

Results: Compared with ACE (TG-186) plans, TG-43 plans predicted higher doses for point A, point B, D₉₀, D₁₀₀, V₁₀₀, V₁₅₀, V₂₀₀, and V₃₀₀ for HR-CTV (p < 0.05). Similarly, TG-43 plans indicated higher doses for bladder point, rectum point, D_0.1cm ³, D_10cm ³, and D_2cm ³ for bladder, rectum, and sigmoid (p < 0.05). Additionally, overall plan quality score (PQS) was significantly greater in plans calculated with ACE (TG-186) formalism than in TG-43 plans (p < 0.05). In TG-186 (ACE) plans, gradient index (GI) was found to be lower than that in TG-43 plans (p < 0.05).

Conclusions: TG-43 tends to overestimate doses compared with ACE (TG-186); nonetheless, both methods meet clinical standards. Material differences in the applicator are notable, and dose overestimations by TG-43 are within 5%.