Volumetric (3D) bladder dose parameters are more reproducible than point (2D) dose parameters in vaginal vault high-dose-rate brachytherapy

There is no consensus on the use of computed tomography in vaginal cuff brachytherapy (VCB) planning. The purpose of this study was to prospectively determine the reproducibility of point bladder dose parameters (D(ICRU) and maximum dose), compared with volumetric-based parameters. Twenty-two patients who were treated with high-dose-rate (HDR) VCB underwent simulation by computed tomography (CT-scan) with a Foley catheter at standard tension (position A) and extra tension (position B). CT-scan determined the bladder ICRU dose point in both positions and compared the displacement and recorded dose. Volumetric parameters (D0.1cc, D1.0cc, D2.0cc, D4.0cc and D50%) and point dose parameters were compared. The average spatial shift in ICRU dose point in the vertical, longitudinal and lateral directions was 2.91 mm (range: 0.10–9.00), 12.04 mm (range: 4.50–24.50) and 2.65 mm (range: 0.60–8.80), respectively. The D(ICRU) ratio for positions A and B was 1.64 (p < 0.001). Moreover, a decrease in Dmax was observed (p = 0.016). Tension level of the urinary catheter did not affect the volumetric parameters. Our data suggest that point parameters (D(ICRU) and Dmax) are not reproducible and are not the ideal choice for dose reporting.