Comparing multichannel cylinder and 3D-printed applicators for vaginal cuff brachytherapy with preliminary exploration of post-hysterectomy vaginal morphology

Introduction
To compare dosimetric parameters of multichannel cylinder (MCC) and 3-dimensional (3D)-printed plans for high-dose-rate vaginal cuff brachytherapy (VBT) and to explore vaginal morphologies after hysterectomy.

Material and methods
Forty-eight patients with gynecological cancer who required VBT after hysterectomy were investigated. To develop a 3D-printed applicator, computed tomography images were obtained with contrast-soaked vaginal gauzes placed in situ to mould vaginal anatomy. 3D digital model of vaginal gauze was then generated and subsequently converted into a prototype 3D-printed applicator, and optimized source catheters were placed in the applicator. Post-hysterectomy vaginal configurations were classified via morphometric analysis of 3D-printed applicators.

Results
In terms of clinical target volume (CTV) coverage, V100 was slightly larger in 3D-printed plans than in MCC plans (90.02% vs. 90.01%, p < 0.001), and D98 in 3D-printed group (429.11 cGy) was higher than that in MCC group (400.08 cGy, p < 0.001). Quality indices were superior in 3D-printed plans than in MCC plans. When evaluating proximal 1 cm of CTV from the vaginal apex (CTV-1 cm), difference in V100 was significant and favored 3D-printed plans (81.85% vs. 72.47%, p < 0.001). 3D-printed applicators demonstrated superiority over MCC in terms of bladder and rectum protection. However, it would cause higher undesired doses to sigmoid. Post-hysterectomy vaginal configurations were classified into five different types, including dome-column, Gothic arch-column, two dog ears-column, one dog ear-column, and ‘up wide and low narrow’.

Conclusions
Compared with MCC, 3D-printed applicators delivered a higher dose and larger volume, and offered more homogeneous and conformal target coverage. Further research on vaginal morphology will be valuable to help screen out patients who need 3D-printed applicators, and to provide guidance for designing new applicators.