OSTEOGENIC SARCOMA: ASSESSMENT OF TUMOR NECROSIS WITH DYNAMIC MR IMAGING AFTER NEOADJUVANT CHEMOTHERAPY - WORK IN PROGRESS

Panicek DM, Dyke JP, Ballon DJ, Koutcher JA, Schwartz LH, Healey JH, Meyers PA, Huvos AG (Memorial Sloan-Kettering Cancer Center, New York, NY 10021).

PURPOSE: To compare estimates of the relative amount of necrosis present within osteogenic sarcoma after neoadjuvant chemotherapy as determined at histopathologic examination and at dynamic gadolinium-enhanced MR imaging with high temporal resolution.

METHOD/MATERIALS: Seven patients (mean age, 17.6±7 yr) with osteogenic sarcoma of an extremity underwent MR imaging with a fast multiplanar spoiled gradient-echo sequence on a 1.5T scanner before, during, and after bolus IV injection of gadolinium-DTPA. The entire tumor was imaged with 5-8 longitudinal sections at a temporal resolution of 6.7-9.5 sec/section for a total of 20-30 time points. The initial uptake slope was used to characterize perfusion in each voxel of the image according to the equation %SI/min = slopex100/SI. The fraction of tumor voxels in the central slice through the tumor having an initial enhancement slope threshold below 100%/minute was considered to represent the necrotic fraction. The necrotic fractions in the central section through the tumor determined at dynamic MR imaging and at histopathologic examination were compared, as were the corresponding tumor necrosis grades based on the Huvos method.

RESULTS: The ranges of necrotic fractions obtained at dynamic MR imaging and at histopathologic assessment were 5-75% and 20-100%, respectively. The correlation between necrotic fractions determined at dynamic MR imaging and at histopathologic examination was moderate (r²=0.49), whereas the correlation between Huvos tumor necrosis grades determined by both methods was strong (r²=0.84).

CONCLUSIONS: Dynamic gadolinium-enhanced MR imaging with high temporal resolution appears useful for grading the relative amount of tumor necrosis present in osteogenic sarcoma after neoadjuvant therapy. Such information is valuable in planning the surgical approach and in determining the specific type of adjuvant therapy to be given. Long-term follow-up will be needed to determine whether the results of this MR imaging technique correlate with patient outcome as well as, or better than, the results of the Huvos system assessment.