Target localization for post-prostatectomy patients using CT and ultrasound image guidance

Abstract

ABSTRACT: We conducted a study comparing BAT ultrasound alignments based on CT data in the postoperative setting. CT scans were obtained with a Primatom CT-on-rails on 9 patients. Two CT scans were obtained each week, while set up error was minimized by BAT ultrasounds. For the first 3 patients, a direct comparison was performed. For the next 6 patients, a template based on the shifts from the week 1 CT during treatment was used for subsequent set up. Comparison of isocenter shifts between the BAT ultrasound and CT was made by the difference, absolute difference and improvement (using CT alignments as the reference technique).
A total of 90 image comparisons were made. The average inter-fraction motion was 3.2 mm in the lateral, 3.0 mm in the longitudinal and 5.1 mm in the AP direction. Ultrasound alignments were improved when a CT template was implemented by reducing the average and standard deviation of the residual shift, thereby reducing both systematic and random errors. Improvement was limited by the initial displacement of the target. Statistically significant improvements were seen when the displacements was greater than 4 mm.