Feasibility study and optimum loading pattern of a multi-ring inflatable intravaginal applicator

Purpose: A cylinder applicator is the standard treatment device for intravaginal brachytherapy. However, they are limited in their ability to simultaneously spare the organs at risk (OAR), and reduce the hot spot in the vaginal mucosa, while achieving adequate dose conformality. This study aims to compare the dosimetric characteristics of single and multichannel cylinders, and utilizes volume point dose optimizations to investigate the feasibility and optimum loading method for a multi-ring inflatable intravaginal applicator. Material and methods: Studies were designed to: (1) test the feasibility of multi-ring applicators, (2) compare dose distributions between different multi-channel applicators and loading patterns, (3) test non-uniform prescription depths around the multi-ring cylinder. Results: Compared to a cylinder with a single central channel, a cylinder with 6 lumina arranged around the periphery, providing the lumina had adequate distance to the cylinder surface, could reduce dose beyond the prescription depth. However, when the number of outer lumina increased from 6 to 12, no further dose reduction could be achieved and the high dose volume close to the surface of the cylinder increased. Moreover, an additional ring, with lumina further away from the surface, provided increased dose shaping capabilities, allowing for individualized dose distributions. Conclusions: Dose could be reduced to normal tissue and the inner mucosa, and better conformity was seen to unique anatomical shapes. A modified peripheral loading pattern provided the optimum dose distribution, yielding good conformity, dose sparing at adjacent organs, and dose reduction in the high dose region of the vaginal mucosa.