Comparison of dose volume histogram parameters of high dose rate tandem-ovoids brachytherapy plans generated with manuel and inverse optimizatian methods

Comparison of Dose Volume Histogram Parameters of High Dose Rate Tandem-Ovoids Brachytherapy Plans Generated with Manuel and Inverse Optimization Methods. Different types of optimization methods can be used for brachytherapy planning. In this study, dose-volume histogram (DVH) parameters obtained with manual and inverse optimization methods were compared. Fifteen patients treated with Ir 192 high dose rate brachtherapy device (Varisource) after tandem ovoid application were included in the study. Target volumes (GTV; Gross Target Volume, HR CTV; High Risk Clinical Volume) and organs at risk (rectum and bladder) were contoured on treatment planning computed tomography (CT). Two optimization plans were generated for each patient with manual and inverse optimization methods, the dose was prescribed to the HR CTV. Rectum, bladder, right and left A point doses were calculated according to ICRU38 on these plans. The DVH for target volumes and critical organs were generated for comparison. The minimum doses received by 90% of the HR CTV (p= 0.046) and GTV (p=0.001) volumes were found to be higher with inverse optimization when compared to manual optimization. Right and left A point doses were significantly lower in plans obtained with inverse optimization (p=0.04). Rectum D2cc doses tended to be lower for the plans generated with inverse optimization but the reduction was not statistically significant. Bladder D2cc was found to be lower with inverse optimization (p=0.001). The treatment times were shorter for the plans generated with inverse optimization (p=0.01). The time differences were found to be related to tandem applicator treatment times. Inverse optimization method produced improved plans with better dose distribution in target volume while reducing the dose to organs at risk. Inverse optimization method also generated treatment plans with shorter treatment times. Key Words: Brachytherapy, cervical cancer, high-dose-rate, inverse planning, Iridyum-192