Hybrid inverse treatment planning optimization in gynecologic brachytherapy: Comparison with conventional method

To investigate a semi-automatic hybrid inverse treatment planning optimization (HIPO) approach for gynecological brachytherapy that preserves the pear-shaped dose distribution without relying on dummy structures.

We retrospectively analyzed 29 patients with gynecological cancers, who underwent combined intracavitary and interstitial (IC/IS) brachytherapy. HIPO enables optimization of dwell times for specific applicators, while other applicators are fixed in Oncentra^® Brachy. Clinical treatment plans (CPs) were compared based on manual adjustments using four HIPO methods: H_ovoid, H_free, H_MS, and H_MS*. H_ovoid optimized tandem and IS needles with ovoid dwell time fixed; H_free optimized all applicators with no fixation; H_MS optimized IS needles with fixation using modified Manchester system, with safe organs at risks (OARs) doses generated in advance by graphical optimization. In H_MS* plan, optimization parameters were adjusted to improve high-risk clinical target volume (HR-CTV) dose coverages based on comparisons between CPs and H_MS.

H_ovoid, H_free, H_MS, and H_MS* achieved clinically acceptable DVH parameters in terms of HR-CTV dose coverage and OARs sparing. However, considerable deviations from the conventional pear-shaped dose distributions were observed, particularly with H_free, which exhibited zero dose contribution from ovoid applicators. Among all HIPO plans, H_MS* with adjusted optimization parameters demonstrated the closest HR-CTV D_90% to that of the CP, while maintaining a conventional pear-shaped dose distribution.

We recommend applying the modified Manchester system with safe OARs doses as the object of fixation, given its consistency with the conventional pear-shaped dose distribution. The proposed method demonstrated clinically acceptable dose distribution and DVH parameters.