# Dosimetric divergence in ICBT vs. IC/ISBT configurations: Comparative analysis of three optimization algorithms for cervical cancer brachytherapy

## TL;DR

This study compares three brachytherapy planning methods for cervical cancer, showing that hybrid inverse optimization offers better dosimetric outcomes and faster treatment times in combined therapy settings.

## Contribution

The study introduces a comparative analysis of three optimization algorithms in both ICBT and IC/ISBT configurations for cervical cancer brachytherapy.

## Key findings

- Inverse optimization methods (IPSA and HIPO) reduced doses to organs at risk compared to manual planning.
- HIPO significantly shortened treatment time and improved conformity index in IC/ISBT patients.
- HIPO provided better rectal protection in IC/ISBT compared to IPSA.

## Abstract

To compare dosimetric differences among graphical-based manual planning (MA), simulated annealing inverse optimization (IPSA), and hybrid inverse optimization (HIPO) for cervical cancer in both intra-cavitary brachytherapy (ICBT) and interstitial brachytherapy combined with ICBT (IC/ISBT) settings, providing evidence for clinical optimization method selection.

This study consisted of 60 cervical cancer patients undergoing CT-guided three-dimensional brachytherapy, including 30 ICBT patients and 30 IC/ISBT patients. Plans were generated using MA, IPSA, and HIPO. The dosimetric parameters for the high-risk clinical target volume (HRCTV) including D100%, V150%, V200%, conformity index (CI), homogeneity index (HI) were compared. Meanwhile, the dosimetric parameters D1cc, D2cc for the bladder, rectum, sigmoid, and total treatment time were evaluated.

Compared with MA, both IPSA and HIPO delivered lower doses to organs at risk (OARs). The total treatment time was significantly shorter for HIPO compared to IPSA and MA (P < 0.05). In ICBT patients, the D1cc and D2cc of OARs were lower for IPSA compared to HIPO (P > 0.05), while the CI was significantly better for HIPO (P < 0.05). Nevertheless, in IC/ISBT patients, D2cc of rectum for HIPO was significantly lower compared to IPSA (P < 0.05), with better CI.

Inverse optimization effectively reduces doses to OARs while maintaining target coverage. HIPO appears to be the preferred choice for IC/ISBT, due to shortened treatment time, superior CI and rectal protection compared with IPSA.