[Dosimetric analysis of different optimization algorithms for three-dimensional brachytherapy for gynecologic tumors]

To investigate the dosimetric difference between manual and inverse optimization in 3-dimensional (3D) brachytherapy for gynecologic tumors.

This retrospective study was conducted among a total of 110 patients with gynecologic tumors undergoing intracavitary combined with interstitial brachytherapy or interstitial brachytherapy. Based on the original images, the brachytherapy plans were optimized for each patient using Gro, IPSA1, IPSA2 (with increased volumetric dose limits on the basis of IPSA1) and HIPO algorithms. The dose-volume histogram (DVH) parameters of the clinical target volume (CTV) including V₂₀₀, V₁₅₀, V₁₀₀, D₉₀, D₉₈ and CI, and the dosimetric parameters D_2cc, D_1cc, and D_0.1cc for the bladder, rectum, and sigmoid colon were compared among the 4 plans.

Among the 4 plans, Gro optimization took the longest time, followed by HIPO, IPSA2 and IPSA1 optimization. The mean D₉₀, D₉₈, and V₁₀₀ of HIPO plans were significantly higher than those of Gro and IPSA plans, and D₉₀ and V₁₀₀ of IPSA1, IPSA2 and HIPO plans were higher than those of Gro plans (P < 0.05), but the CI of the 4 plans were similar (P > 0.05). For the organs at risk (OARs), the HIPO plan had the lowest D_2cc of the bladder and rectum; the bladder absorbed dose of Gro plans were significantly greater than those of IPSA1 and HIPO (P < 0.05). The D_2cc and D_1cc of the rectum in IPSA1, IPSA2 and HIPO plans were better than Gro (P < 0.05). The D_2cc and D_1cc of the sigmoid colon did not differ significantly among the 4 plans.

Among the 4 algorithms, the HIPO algorithm can better improve dose coverage of the target and lower the radiation dose of the OARs, and is thus recommended for the initial plan optimization. Clinically, the combination of manual optimization can achieve more individualized dose distribution of the plan.