Assessment of residual tumor viability in thymic carcinoma by sequential thallium-201 SPECT: comparison with CT and biopsy findings.

We present a case of 201TI accumulating thymic carcinoma, in which sequential CT scans demonstrated a steady decrease in tumor volume. The presence of a residual mass on CT scans after the completion of therapy presented the clinical dilemma of whether or not a viable tumor remained. Sequential 201TI SPECT images demonstrated a marked decrease in tumor uptake. At 2 wk after therapy, no significant accumulation of 201TI in the region of the residual mass was observed, indicating a lack of viable tumor. A biopsy specimen revealed no tumor cells. Sequential histopathologic findings were correlated well with the findings of 201TI SPECT rather than those of CT. Thallium-201 SPECT is of great clinical value in assessing tumor viability in the course of therapy.