Locally advanced rectal carcinomas were increasingly treated by preoperative combined radiochemotherapy. Alterations of the rectal wall and the lymph nodes that were caused by the treatment make the assessment of the success of the therapy during the preoperative staging extremely difficult. Methods such as endorectal ultrasound, CT and MRI used for the estimation of the depth infiltration of the tumor achieved an exactness of only approximately 50%. It is thus essential to develop new criteria for the assessment of the success of the therapy.