Although widely used in external beam treatment planning, computed tomography scans are infrequent in incranial tumors by implanting of Radioactive isotope. This incranial brachytherapy has only become possible by using CT scans and stereotaxic operation methods. The coincidence of single source and tumor axes in brachytherapy is very important to determine the therapeutic dosages. Eventhough using the CT scan, according to spatial location of tumor lying, the section of tumor will be seen enlargement, cause the tumor will be cut off with slight angle to its axes. Correct analysis of tumor size from source is required for rotated axes in analytical geometry.