Posters— Surgical Treatment of Sarcomas

THALLIUM 201 UPTAKE IN CHONDROID LESIONS

Templeton KT, Raveill T, Tawfik O (University of Kansas Medical Center, Kansas City, Kansas 66160).

Heterogeneity seen in cartilagenous lesions can make grading and surgical planning difficult. Low-grade lesions may potentially be treated with less aggressive surgery. However, if higher-grade lesions are missed, the local recurrence rate can be high. In conjunction with standard imaging modalities, thallium 201 scans have been utilized in the evaluation of tumors to distinguish benign from malignant lesions. In chondroid lesions, Thallium 201 may help to differentiate low- from high- grade lesions.

METHODS: Thallium 201 scans were utilized to evaluate 25 patients (15 females, 10 males) who had cartilagenous lesions noted on standard radiographs. Four patients were felt to have low-grade lesions on open biopsy. Thallium 201 scans were obtained to evaluate for the presence and location of higher-grade areas in these lesions. 5mCi of thallium 201 was injected, with images obtained early (20 minutes) and late (3 hours). SPECT imaging was used for pelvic lesions. 18 patients underwent either surgical excision/wide resection if they had positive scans or curettage if their scans were negative but they remained symptomatic. The remainder of the patients was followed with routine clinical and radiographic exams.

RESULTS: The areas noted on histologic exam of the operated lesions to be benign or grade I malignancies demonstrated an average thallium 201 uptake (compared to the normal contralateral side) of 1.005 +/-0.125 (range 0.90-1.10). This was unchanged on delayed images. All have been followed radiographically and clinically for over 12 months, without evidence of recurrence. In comparison, those patients found to have grade II or III lesions histologically had mean uptake ratios of 1.485 +/-0.255 (range 1.26-1.64) cts/pixel compared to an equivalent anatomic location on the contralateral normal side (p=0.0001). All four patients who were felt to have low-grade lesions on initial biopsy had thallium 201 ratios of greater than 1.3 in some area of their tumors. All underwent wide resection and were found to have grade II-III lesions. In addition, seven other patients with chondroid lesions diagnosed radiographically and having negative thallium scans have been followed with serial clinical exams and roentgenograms. All of these patients remain asymptomatic and with no change in their radiographs (follow-up 4 months to 5 years).

CONCLUSION: Thallium 201 uptake, mediated through the Na-K ATPase dependent pump, is dependent not only on blood flow but also on tumor cell viability and activity. A greater degree of uptake is seen in more active regions of tumors. With the heterogeneity seen in chondroid lesions, Thallium 201 may help elucidate those tumors, or regions within tumors, that are more aggressive and, therefore, need more aggressive surgical management.