Purpose: This study was undertaken to assess the accuracy and ability of endorectal ultrasound (ERUS) to predict changes in rectal tumor stage after a preoperative chemoradiation protocol.
Methods: Since December 1990, all rectal malignancies at our institution have been preoperatively staged with ERUS. ERUS has been an essential tool in preoperative staging of rectal cancer patients, possessing an overall accuracy of 84 percent for T stage and 81 percent for lymph node status in our hands (Williamson PR, unpublished data). Beginning in July 1992, all patients staged with T3 or T4 lesions on initial ERUS have been entered into a protocol consisting of preoperative chemoradiation therapy (CRT). This protocol consists of patients receiving 4,500 to 5,040 rads for five to eight weeks and concomitantly receiving sensitizing doses of 5-fluorouracil and/or leucovorin. All patients were scheduled for sphincter-saving or abdomino-perineal resections six to eight weeks following completion of CRT. A repeat ERUS was performed on each patient one week before surgery.
Results: The study group consisted of 15 patients who completed CRT, including 12 males and 3 females. Evidence of tumor shrinkage via ERUS measurement was seen in all patients. Average tumor shrinkage as assessed by ERUS was 16 percent by width and 32 percent by depth of invasion. Sonographic level of invasion and nodal status were each downstaged in 38 percent of patients. Pathologic evaluation comparison revealed that the level of invasion was downstaged in 47 percent and nodal status in 88 percent compared with initial ERUS staging. Of those patients downstaged, 4 of 11 (36 percent) revealed no tumor in the pathology specimen.
Conclusions: We conclude from our early experience that although ERUS offers a method for assessing degree of shrinkage and downstaging of T3 and T4 lesions after CRT, presently it does not closely predict the pathologic results. Results are strongly related to the experience of the ultrasonographer. The ability to distinguish tumor from radiation-induced changes to perirectal tissues is under continued investigation, and a new method of interpreting the data obtained by ERUS after CRT will need to be established.