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

Document Type : Original Paper

Authors

1 Department of medical physics, Mashhad University of Medical sciences, Mashhad, Iran

2 medical physics department, medical faculty, Mashhad University of Medical Sciences, Mashhad, Iran.

3 Nuclear Medicine Research Center, Mashhad University of Medical Sciences, Mashhad, Iran

4 Cancer Research Center, Mashhad University of Medical Sciences, Mashhad, Iran.

5 Medical Physics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran

10.22038/ijmp.2025.90069.2592

Abstract

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 28 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 3D Slicer software. TRAK, dosimetric parameters (D90%, D2cc, D0.1cc), 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 0.45 ± 0.06 cGy·m². A significant positive correlation (R²=0.981) was found between TRAK/dprescribed and the irradiated volume (VISV). No significant correlation was observed between TRAK and D2cc doses for the bladder and rectum (R²=0.075 and 0.46).
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.

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Main Subjects

References

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Iranian Journal of Medical Physics
Volume 22, Issue 6 - Serial Number 6
November and December 2025
Pages 389-394

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History

  • Receive Date: 30 July 2025
  • Revise Date: 08 December 2025
  • Accept Date: 28 December 2025

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