Comparative analysis of dosimetric and radiobiological models of IPSA and HIPO algorithms in combined intra-cavitary/interstitial brachytherapy for cervical cancer.

Purpose: To compare inverse planning simulated annealing (IPSA) and hybrid inverse planning optimization (HIPO) using dosimetric and radiobiological models, and provide a basis for selecting the optimization method for cervical cancer.

Material and methods: This was a retrospective study including 32 patients with radical cervical cancer. Brachytherapy treatment plans were re-optimized using IPSA, HIPO1 (with a locked uterine tube), and HIPO2 (with an unlocked uterine tube). Dosimetric data, including isodose lines, HR-CTV (D₁₀₀, V_150%, V_200%, HI, and CI), and (bladder, rectum, and intestines) D_1cc, D_2cc for organs at risk (OARs) were also collected. Additionally, TCP, NTCP, BED, and EUBED were calculated, and differences were analyzed using matched samples t-test and Friedman test.

Results: Compared with IPSA and HIPO2, HIPO1 had better V_150% and V_200% (p < 0.05). Compared with IPSA and HIPO1, HIPO2 had better D₁₀₀ and CI (p < 0.05). The doses to the bladder D_1cc (4.72 ±0.33 Gy)/D_2cc (4.47 ±0.29 Gy) and rectum D_1cc (4.50 ±0.61 Gy)/D_2cc (4.11 ±0.63 Gy) were lower in HIPO2 than in IPSA and HIPO1. EUBEDs for HR-CTV were higher in HIPO1 and HIPO2 than in IPSA by 1.39-1.63%. However, TCPs were not remarkably different among the three plans (p > 0.05). Also, the NTCP for the bladder was lower in HIPO2 than in IPSA and HIPO1 by 13.04% and 16.67%, respectively.

Conclusions: Although the dosimetric parameters of IPSA, HIPO1, and HIPO2 are comparable, HIPO2 provides better dose conformability and lower NTCP. Therefore, HIPO2 is recommended as an optimization algorithm in IC/ISBT for cervical cancer.