Combined use of transverse and scout computed tomography scans to localizeradioactive seeds in an interstitial brachytherapy implant

Various techniques have been developed to localize radioactive sources in b rachytherapy implants. The most common methods include the orthogonal film method, the stereo-shift film method, and recently, direct localization fro m a series of contiguous CT transverse images. The major advantage of the C T method is that it provides the seed locations relative to anatomic struct ures. However, it is often the case that accurate identification and locali zation of the sources became difficult because of partial source artifacts in more than one transverse cut and other artifacts on CT images. A new alg orithm has been developed to combine the advantages of using a pair of orth ogonal scout views with the advantages of using a stack of transverse cuts. In the new algorithm, a common reference point is used to correlate CT tra nsverse images and two orthogonal scout CT scans (AP and lateral). The radi oactive sources are localized on CT transverse images. At the same time, th e sources are displayed automatically on the two CT scout scans. In this wa y, the individual sources can be clearly distinguished and ambiguities aris ing from partial source artifacts are resolved immediately. Because of the finite slice thickness of transverse cuts, the longitudinal coordinates are more accurately obtained from the scout views. Therefore, the longitudinal coordinates of seeds localized on the transverse cuts an adjusted so that they match the position of the seeds on scout views. The algorithm has been tested on clinical cases and has proved to be a time saving and accurate m ethod. (C) 1999 American Association of Physicists in Medicine. [S0094-2405 (99)01604-1].