Isodose Volume Analysis in Postoperative High-Dose-Rate Brachytherapy: A Study on Total-Reference-Air-Kerma Correlations and Organ-at-Risk Doses

Introduction: High-Dose-Rate (HDR) Vaginal Brachytherapy (VBT) is a standard adjuvant treatment for early-stage endometrial cancer following surgery. While the Total-Reference-Air-Kerma (TRAK) reflects the overall radiation output, its relationship with the actual irradiated tissue volumes and Organ-At-Risk (OAR) exposure remains underexplored in treatments using cylindrical applicators. The aim of this study is to evaluate the correlation between TRAK, irradiated volumes, and doses to OARs. Material and Methods: This retrospective study included ۲۸ Iranian women with histologically confirmed endometrial carcinoma postoperatively treated with HDR brachytherapy using single-channel vaginal cylinder applicators. CT-based treatment planning was performed using Elekta Oncentra software. Prescribed doses were delivered over three weekly fractions. The volumes enclosed by the prescribed isodose surface (VISV) were quantified using ۳D Slicer software. TRAK, dosimetric parameters (D۹۰%, D۲cc, D۰.۱cc), and VISV were analyzed. The geometric volume of the applicator was subtracted to determine the actual irradiated tissue volume. Statistical analysis involved Pearson and Spearman correlation coefficients. Results: The mean TRAK was calculated as ۰.۴۵ ± ۰.۰۶ cGy·m². A significant positive correlation (R²=۰.۹۸۱) was found between TRAK/dprescribed and the irradiated volume (VISV). No significant correlation was observed between TRAK and D۲cc doses for the bladder and rectum (R²=۰.۰۷۵ and ۰.۴۶). Conclusion: This study demonstrates a strong association between TRAK and isodose volumes in HDR brachytherapy, suggesting TRAK could be a surrogate for overall dose delivery. However, its lack of correlation with OAR dose metrics emphasizes the need for comprehensive (Dose-Volume-Histogram) DVH assessments. Future research may explore incorporating TRAK into models for predicting toxicity and outcomes, enhancing brachytherapy planning and monitoring.

کلیدواژه ها:

Endometrial neoplasms ، Brachytherapy ، Radiotherapy ، isodose surface volume ، total reference air kerma