To analyse the dosimetric benefit of the hybrid inverse planning optimisation (HIPO) planning method over the graphical optimisation (GrO) planning method for 3D volume-based intravaginal brachytherapy (IVBT) in a mono-centre patient cohort.

Twenty-five patients surgically staged with endometrial cancer were considered for the study. All the patients had received adjuvant IVBT for three fractions with one-time computed tomography image-based planning. The data on the patient, tumour, plan, and treatment characteristics were retrieved from the database. All the plans were re-optimised with GrO and HIPO techniques for this comparison study. The different dosimetric parameters were compared between the two methods, and the collected data were tabulated and shown graphically. The statistical evaluation was performed with IBM SPSS version 26, and Origin Pro 8.5 was employed for plots.

HIPO plans show similar target coverage in terms of D 90(%), V 95(%) and conformity index with no significant statistical difference from the GrO plans with an acceptable increase in homogeneity index (0·087 ± 0·062%). It succeeds in achieving a statistically significant reduction of dose to organs at risk such as D0·1 cc, D1·0 cc and D2·0 cc for the bladder (11·59%, 4·8% and 3·99%), rectum (41·33%, 16·9% and 16·05%) and sigmoid (20·97%, 13·53% and 11·21%), respectively, in comparison with GrO optimisation.

Considering the dosimetric outcome of 3D-based IVBT, it is suggested to adopt inverse optimisation techniques like HIPO over GrO to achieve higher quality treatment plan in terms of adequate target dose and lesser dose to OARs.