1. A method of forming an applicator bad of an applicator for insertion into an anatomical cavity of a patient for delivering a treatment to the patient, the method comprising: receiving a first three-dimensional image of the anatomical cavity, the first three-dimensional image having been generated while the anatomical cavity contained an expandable container adjacent a tissue region of the patient, wherein the expandable container, when contained in the anatomical cavity, was filled with a fluid such that the container was expanded to substantially conform to the shape of at least a portion of the tissue region forming at least a portion of the anatomical cavity; isolating, from the first three-dimensional image, a first sub-image corresponding to an image of the filled expanded container; and using the first sub-image as a design template for forming the applicator body for use with the patient.