The invention relates generally to methods of using a thiol-Michael addition hydrogel for providing intracavitary brachytherapy and/or displacing tissue and organs. The thiol-Michael addition hydrogel may be used as a packing material and an attenuation material for intracavitary brachytherapy applications. The invention also relates generally to a brachytherapy applicator, which may be used in conjunction with the thiol-Michael addition hydrogel and methods thereof. The invention also relates to a kit comprising at least one container containing the precursor materials of the thiol-Michael addition hydrogel.