Evaluation and Clinical Relevance of Plan Quality Indices in Intracavitary Brachytherapy for Cervical Cancer.

Abstract

Background: Cervical cancer remains to be a significant health concern globally, with India contributing to nearly one-quarter of cases worldwide. Intracavitary brachytherapy (ICBT) combined with external beam radiotherapy (EBRT) is the standard of care, optimizing tumour dose while sparing normal tissues. Plan quality indices such as Dose Homogeneity Index (DHI), Overdose Index (OI), Dose Non-uniformity Ratio (DNR), and Conformity Index (COIN) are crucial in evaluating treatment plans, yet their predictive clinical relevance remains underexplored.

Methodology: In this Retrospective study, 84 patients with histologically confirmed cervical cancer undergoing definitive chemoradiation followed by CT-based HDR ICBT (Co-60) were evaluated. Plan indices were calculated per ICRU 89 and GEC-ESTRO guidelines. Correlation with tumour response (RECIST v1.1), toxicity (≥ grade 2 bladder/rectal), and clinical factors (FIGO stage, HRCTV volume, EQD2, BED, treatment duration) was assessed using t-tests, regression analyses, and Pearson's correlation.

Results: Mean DHI was 0.403; OI 0.358; DNR 0.594; COIN 0.636. Higher DHI (p=0.019) and lower OI (p=0.004) were associated with tumour response; DNR and COIN were not significant. No plan index predicted ≥ grade 2 bladder or rectal toxicity. COIN correlated poorly with other indices. Multiple regression showed no consistent predictors of dosimetric indices. Logistic regression did not establish any index as a definitive predictor of 3-month response.

Conclusion: Plan quality indices provide useful quantitative insights into dose distribution in High dose rate intracavitary brachytherapy for cervical cancer. In this study, DHI and OI showed an association with early tumour response, while no significant correlation was observed between plan indices and treatment-related toxicity.