[In vivo determination of tumor volume: what does a CT-based calculation mean in recurrences of rectal carcinoma?].

The volumetric analysis of a tumour by CT is a reliable and clinically important method of examination which is rarely used. As for oncology, the importance of this method is based upon the determination of the stage of remission post-therapeutically, especially in those cases which respond to therapy without a roentgenologic change in comparison to pretherapeutic findings. This applies in particular for the evaluation of CT images. In this study 115 CT examinations of 38 patients with recurrent rectal cancer were evaluated and the tumour remission was measured by an exact determination of the tumour volume before and after radiotherapy. The results were compared with the CT findings without volumetric analysis. A change of the tumour size up to 20% of the pretherapeutic volume which eludes from the visual perception can be revealed by a subtle CT-assisted volumetric analysis. Formulas for calculation of the volume or the data concerning length, width and depth of a mass prove to be insufficient or incorrect. Therefore the correct evaluation of a tumour regression or progression should be done more often by CT-assisted volumetric analysis.