Does the imaging method have an influence on the measured tumor height in ruthenium plaque therapy of uveal melanoma?

Background And Purpose: For ruthenium plaque therapy of uveal melanoma the precise knowledge of the tumor height is necessary. The purpose of this analysis is to examine systematic differences between ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) measurements of tumor height in uveal melanoma.

Material And Methods: From 1993 to 2000, 208 patients with uveal melanoma were treated with ruthenium therapy. US was done in 190/208 patients, CT in 147/208 patients, and MRI in 81/208 patients. The measurements from the imaging modalities were compared to each other. Separate comparisons were carried out for tumor size and localization and between two-dimensional (2-D) and three-dimensional (3-D) measurements in reconstructed planes.

Results: In direct comparison, CT measurements (median: 4.5 mm; range: 1.6-10.5 mm) were nearly identical to MRI measurements (median: 4.5 mm; range: 2.0-11.4 mm), while US yielded the highest values (median: 5.2 mm; range: 2.5-13.4 mm). Linear regression yielded the following values: CT versus US (R(2) = 0.88, correlation coefficient = 1.04), MRI versus US (R(2) = 0.79, correlation coefficient = 0.92), MRI versus CT (R(2) = 0.84, correlation coefficient = 0.90), and "2-D" versus reconstructed "3-D" (R2 = 0.93, correlation coefficient = 0.98).

Conclusion: Differences between the measurements from all three modalities were generally acceptable, except for small tumors (< or =4 mm; limited spatial resolution of CT/MRI) and temporal or peripheral lesions (angular distortion in US). In special anatomic situations, CT/MRI measurements can also result in distortions. "3-D" measurements can sometimes help in these situations.