Mark C. Smith MD, Presenter: Nothing to Disclose

Several methods for prostate localization prior to treatment with external beam radiation therapy have been developed. Two systems have been used at The University of Iowa over the last year. One system uses daily ultrasound imaging (Varian SonArray). The other system uses megavoltage conebeam CT (Siemens M-Vision). The purpose of this study is to compare the average displacement and the variability of displacement with daily conebeam CT and ultrasound imaging.

25 patients with organ confined prostate cancer were treated at the University of Iowa between May 2006 and March 2007. For the first 11 patients, prostate localization was achieved with daily ultrasound imaging. Daily megavoltage conebeam CTs were obtained for prostate localization for the next 14 patients. Displacement, the distance from setup isocenter to corrected isocenter, was recorded daily for each patient. Average displacement and the standard deviation of displacements for each patient were calculated. A two-tailed t Test was used to compare the average displacement and average standard deviation for the conebeam CT and ultrasound groups.

305 ultrasound displacements and 468 conebeam CT displacements were recorded and analyzed. Each patient had at least 15 ultrasound or conebeam CT displacements measured (range: 15 - 41). The average displacement was 6.4 mm and 7.9 mm (p = NS) for the conebeam CT and the ultrasound groups respectively. The average standard deviation of displacement was 2.5 mm and 3.6 mm (p = 0.007) for the conebeam CT and the ultrasound groups respectively.

There was no statistically significant difference in average displacement between conebeam CT and ultrasound imaging. However, less daily variation in displacement was found with conebeam CT. This finding may be the result of more accurate interpretation by the attending physician of conebeam CT images compared to ultrasound images.

Smith, M, Comparison of Daily Conebeam CT and Ultrasound Imaging for Prostate Localization.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/6000676.html