High-dose rate endorectal brachytherapy (HDR-EBT) is mainly used as a palliative treatment modality. In this paper, we compare dosimetry distributions for a single-channel catheter (Miami) applicator with distributions of the inflatable multichannel (Novi Sad) endorectal applicator. The comparisons were made with respect to dose coverage to the clinical tumor volume as well as to the bladder, rectal wall, prostate, and bone marrow. Our results suggest that a multichannel applicator provides better sparing of the bone marrow by 50%, clinically uninvolved parts of the rectal wall by 70%, and bladder and prostate (in the case of male patients) by 100% in terms of ratio of median doses to critical organ volume for single- and multichannel endorectal applicators. Our results justify the advantage of using a multichannel endorectal brachytherapy applicator as a neo-adjuvant treatment of patients with locally advanced rectal cancer.