Positional Variability of a Tandem Applicator System in HDR Brachytherapy for Primary Treatment of Cervix Cancer

Abstract

Intraindividual applicator variability is significantly smaller than interindividual variability. Applicator-related procedures such as midline shielding or dose matching of tele- and brachytherapy should be performed with information on at least one individual applicator position.

Comparison of the Dosimetric Influence of Applicator Displacement on 2D and 3D Brachytherapy for Cervical Cancer Treatment

“…To evaluate the influence of applicator displacement on the dose to the CTV and OARs, the applicators in the 2D-BT and 3D-BT plans were virtually moved in 3 directions: left (+ X ) or right (−X ), cranial (+ Y ) or caudal (− Y ), and anterior (+ Z), or posterior (−Z). Since most of the current studies reported displacement measurements of less than 1 cm in clinical practice, [9][10][11][16][17][18] we set the simulated shift distances as ± 0.15, ± 0.2, ± 0.4, ± 0.6, ± 0.8, and ± 1 cm in this study. After changing the spatial position of T&O, the dwell times and relative positions of the radiation sources in the applicators remained the same as those in the original plans for both 2D-BT and 3D-BT.…”

“…Both target coverage and OAR sparing are then evaluated accurately in the brachytherapy treatment planning system (TPS). 7 In current practice, both brachytherapy techniques include the process of transferring the patient from the gynecological room to the X-ray/CT/MRI imaging room, and then to the brachytherapy room, which inevitably causes applicator displacement [8][9][10] even with an immobilization device. Wulf et al 10 investigated the intrafractional applicator displacement and found that the standard deviations (SD) of variability were 2.5 mm (minimum/maximum, − 17/ + 19 mm), 5.5 mm (minimum/maximum, − 21/+ 23 mm), and 4.2 mm (minimum/maximum, − 15/+ 18 mm) in the right-left (X-axis), caudal-cranial (Y-axis), and anterior-posterior (Z-axis) directions, respectively.…”

“…7 In current practice, both brachytherapy techniques include the process of transferring the patient from the gynecological room to the X-ray/CT/MRI imaging room, and then to the brachytherapy room, which inevitably causes applicator displacement [8][9][10] even with an immobilization device. Wulf et al 10 investigated the intrafractional applicator displacement and found that the standard deviations (SD) of variability were 2.5 mm (minimum/maximum, − 17/ + 19 mm), 5.5 mm (minimum/maximum, − 21/+ 23 mm), and 4.2 mm (minimum/maximum, − 15/+ 18 mm) in the right-left (X-axis), caudal-cranial (Y-axis), and anterior-posterior (Z-axis) directions, respectively. On the basis of 2D radiographs, a maximum applicator displacement of 12 mm has been demonstrated even with an applicator immobilization device, 9 while a 0.94-cm shift in the caudal-cranial direction has been reported by Ebruli et al 8 Previous studies have demonstrated that applicator displacements can result in significant dose changes in 2D-BT 11,12 or 3D-BT plans.…”