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

Abstract

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. 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, V150%, V200%, HI, and CI), and (bladder, rectum, and intestines) D1cc, D2cc 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. Compared with IPSA and HIPO2, HIPO1 had better V150% and V200% (p < 0.05). Compared with IPSA and HIPO1, HIPO2 had better D100 and CI (p < 0.05). The doses to the bladder D1cc (4.72 ±0.33 Gy)/D2cc (4.47 ±0.29 Gy) and rectum D1cc (4.50 ±0.61 Gy)/D2cc (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. 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.