Correlation of Dose-reporting Parameters in Two-dimensional and Three-dimensional Image-guided Brachytherapy for Cancer of the Cervix Uteri: a Single-Institution Experience

Objective: Different dose-reporting parameters are suggested for two-dimensional and three-dimensional image-guided brachytherapy for cancer of the cervix uteri. We aimed to determine if there is any correlation between these dose-reporting parameters in three-dimensional image-guided brachytherapy plans. Methods: A computed tomographic (CT) scanner has been installed in the brachytherapy room in our department so that patients can undergo imaging in the same room immediately following insertion of applicators while being maintained under anaesthesia or sedation. Between January 2014 and September 2015, 34 patients underwent CT-based brachytherapy (number of plans, 136). High-risk clinical target volume (HR-CTV) and rectum were contoured according to GEC-ESTRO guidelines. Point A and ICRU rectal points were also determined. The correlations of D90 of HR-CTV with Point A, and also of D2cc of rectum with ICRU rectal points were determined. Two-sided paired t-test was used to determine if there were any statistically significant differences between HR-CTV D90 and Point A, and also between D2cc of rectum and ICRU rectal points. Results: Comparison of the dose of Point A and D90 of HR-CTV revealed a statistically significant difference (p < 0.001) with a weak negative correlation (R = -0.32; p < 0.0001). Comparison of the dose of ICRU reference rectal point and D2cc of rectum revealed a statistically significant difference (p < 0.01) with a positive correlation (p < 0.001). Conclusion: HR-CTV D90 and Point A appear to show a random relationship. ICRU rectal point, however, may tend to underestimate the dose to the rectum in a plan that is CT imaging-based compared with D2cc.