A novel approach to limit radiation toxicity is the use of high dose rate endorectal brachytherapy (Endo-HDR) (21). Endo-HDR involves the placement of a silicon multicatheter applicator within the rectum to deliver large doses to the rectal tumor and mesorectum with rapid dose fall off to the surrounding organs. An Iridium 192 high dose rate brachytherapy source attached to a wire is inserted into each catheter to deliver a high dose of radiation therapy the tumor. High dose rate brachytherapy has been well established in various malignancies (prostate, uterine, sarcoma, head and neck) to escalate radiation dose to the tumor over a short period of time while sparing normal tissue. Compared with NCRT and IMRT, Endo-HDR delivers treatment internally to the tumor without having to pass through surrounding normal tissue and organs. It requires smaller margins (CTV/PTV=~1 cm) on the tumor since the applicator is positioned under fiducial guidance over the tumor without need for a margin for organ motion allowing greater sparing of OARs (22). Furthermore, the area of the rectum exposed to high dose radiotherapy is surgically removed at the time of resection which further minimizes chronic toxicity. Important structures that may be spared include bone marrow, small bowel, bladder, the autonomic nerves, sexual organs, anal sphincter and skin. Considering that 1/3 of patients will develop metastases, limiting bone marrow toxicity may contribute to better compliance with systemic treatment and allow for a better treatment strategy to target systemic recurrence. Another distinct advantage of Endo-HDR is the shortened treatment time (1 versus 6 weeks). Endo-HDR therefore provides a major logistic advantage for patients who may benefit from neoadjuvant therapy but who are geographically distant from radiation centers, elderly, or medically infirmed.