Dose optimization comparison study of inverse planning simulated annealing [IPSA] and hybrid inverse planning optimization [HIPO] in interstitial brachytherapy of head and neck cancer

Abstract

This study was a retrospective dose optimization comparison of two commercially available inverse planning algorithms, the inverse planning simulated annealing (IPSA) and hybrid inverse planning optimization (HIPO) for head and neck cancer interstitial brachytherapy. Seven patients with head and neck cancer were selected (4 with tongue cancer, 2 with buccal mucosa cancer and 1 with carcinoma lip) who were previously treated with interstitial brachytherapy using a flexible nylon tube catheter and graphical optimization/geometric optimization technique. All seven patients were retrospectively re-planned using both IPSA as well as HIPO algorithms available in the Oncentra Brachytherapy Treatment Planning System (TPS) version V4.5.3.30. The dosimetric parameters [PTV-V100, V150, V200, D90; mandible-D2cc, parotid-D2cc, conformity index (CI), dose homogeneity index (HI), overdose volume index (ODI)] were chosen for evaluation in compliance with the objective function and organ at risk dose constraints. Using the paired sample T test in chosen parameters (PTV-V100, V150, V200, D90; mandible-D2cc, CI, HI, ODI both the inverse planning algorithms), it was found that IPSA and HIPO were comparable. Even though both IPSA and HIPO are largely comparable in most of the dosimetric parameters for inverse planning in brachytherapy of head and neck cancers, differences in the algorithms can be exploited to improve certain parameters in specific situations such as D2cc parotid.