Bladder and rectum volume estimations using CT and stereology.

Twelve prostate cancer patients underwent a treatment planning CT prior to radiotherapy. Stereologic method based on Cavalieri principle was applied to CT images. Systematic and random sampling of CT slices were performed with alternative ways for assessing the volumes of bladder and rectum. The contribution of point counting to the precision of the obtained volume estimations was analysed. It was found that 100-150 test points counted on only 5-7 systematically sampled slices through bladder or rectum suffice for reliable volume estimations of the above organs. Also, the superiority of systematic vs random sampling was confirmed. The suggested volumetric method gives the possibility of generating unbiased and efficient bladder and rectum volume assessments directly from CT data with great saving in labour.