Following successful therapy with chemoradiation, the initially intermediate- to high-signal-intensity tumor on T2-weighted images decreases in both size and signal intensity, with eventual conversion to low-signal-intensity fibrotic tissue [7,31]. However, the main limitation of MRI in the very early posttreatment period (<2 months after completion) is its difficulty distinguishing early postradiation change from residual tumor, both of which can demonstrate intermediate- to high-signal T2-weighted intensity and avid gadolinium enhancement [33,34]. One retrospective study evaluating pelvic MRI at a median of 5 weeks after completion of chemoradiation for cervical cancer found that 37% (16 of 44) of MRI examinations were considered indeterminate for discriminating residual disease and fibrosis [34]. Despite diagnostic confidence in the remainder of cases, sensitivity and specificity for residual disease were 80% and 55%, respectively, indicating a high false-positive rate because of posttreatment change. A more recent retrospective study in cervical cancer patients found better performance of pelvic MRI at a later postchemoradiation time point (median 9 weeks) with strict objective diagnostic criteria, achieving sensitivity and specificity of 91% and 85%, respectively, for residual disease [33]. Therefore, for cervical cancer, the suggested time interval for determining posttherapy treatment response with pelvic MRI is 3 to 6 months after completion of therapy [27], although earlier imaging is sometimes used for interim assessment of tumor regression for prognostication and/or adaptive radiation planning. Because MRI relies primarily on size criteria for nodal evaluation, it has limitations similar to CT with respect to sensitivity and specificity for nodal metastases.
Staging and Follow up of Primary Vaginal Cancer. Following successful therapy with chemoradiation, the initially intermediate- to high-signal-intensity tumor on T2-weighted images decreases in both size and signal intensity, with eventual conversion to low-signal-intensity fibrotic tissue [7,31]. However, the main limitation of MRI in the very early posttreatment period (<2 months after completion) is its difficulty distinguishing early postradiation change from residual tumor, both of which can demonstrate intermediate- to high-signal T2-weighted intensity and avid gadolinium enhancement [33,34]. One retrospective study evaluating pelvic MRI at a median of 5 weeks after completion of chemoradiation for cervical cancer found that 37% (16 of 44) of MRI examinations were considered indeterminate for discriminating residual disease and fibrosis [34]. Despite diagnostic confidence in the remainder of cases, sensitivity and specificity for residual disease were 80% and 55%, respectively, indicating a high false-positive rate because of posttreatment change. A more recent retrospective study in cervical cancer patients found better performance of pelvic MRI at a later postchemoradiation time point (median 9 weeks) with strict objective diagnostic criteria, achieving sensitivity and specificity of 91% and 85%, respectively, for residual disease [33]. Therefore, for cervical cancer, the suggested time interval for determining posttherapy treatment response with pelvic MRI is 3 to 6 months after completion of therapy [27], although earlier imaging is sometimes used for interim assessment of tumor regression for prognostication and/or adaptive radiation planning. Because MRI relies primarily on size criteria for nodal evaluation, it has limitations similar to CT with respect to sensitivity and specificity for nodal metastases.