Needle position during 125I seed implantation: accurately recognized by sagittal transrectal ultrasonography

Purpose. The aim of this study was to assess the variation of probe rotation angles for detecting a single needle using sagittal images of transrectal ultrasonography (TRUS). Materials and methods. A phantom study was performed. One needle was inserted through each of 10 holes of the template, and variations in the probe rotation angles for detecting the needle were measured. Results. The mean variation of probe rotation for detecting a single needle was 17.0 degrees (range 4 degrees-25 degrees). Slightly broader variation was seen for the needle in holes farther away from the probe. Conclusion. Probe rotation angles for detecting a single needle displayed considerable variation. Seed locations recognized on sagittal imaging by TRUS are thus indeterminate, and real-time dose calculations using TRUS for I-125 seed implantation should be used with care.