Pleuramesothelioma is malignant tumor on the pleura, caused by asbestos exposure. Computer-assisted diagnosis system shall support physicians to assess the growth rate of detected pleural thickenings from CT data. This paper describes a new, improved method to automatically assess the size of detected thickening using thin plate spline interpolation which then leads to the 3D modeling of thickening. First, we detect each pleural thickening. Second, an automatic coordinate transformation is applied to enable the numeric calculation of the spline. Next, the appropriate landmark points are then automatically selected by using the newly applied chain-code concavity analysis and used as the constraint points for the interpolation. Numerical integration is applied to calculate area by slice. In the final step, the spline interpolation between layers is applied to calculate volume of each thickening. The resultsshow that the thin plate spline interpolated boundary is suitable for 3D modeling of the thickening.