Intensity-modulated radiotherapy using implanted fiducial markers with daily portal imaging: assessment of prostate organ motion.

Abstract

To assess our single institutional experience with daily localization, using fiducials for prostate radiotherapy. From January 2004 to September 2005, 33 patients were treated with 1,097 intensity-modulated radiation treatments, using three implanted fiducials. Daily portal images were obtained before treatments. Shifts were made for deviations > or =3 mm in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP) dimensions. Of 1,097 treatments, 987 (90%) required shifts. Shifts were made in the LR, SI, and AP dimensions in 51%, 67%, and 58% of treatments, respectively. In the LR dimension, the median distance shifted was 5 mm. Of 739 shifts in the SI dimension, 73% were in the superior direction for a median distance of 6 mm, and 27% were shifted inferiorly for a median distance of 5 mm. The majority of shifts in the AP dimension were in the anterior direction (87%). Median distances shifted in the anterior and posterior directions were 5 mm and 4 mm, respectively. The median percentage of treatments requiring shifts per patient was 93% (range, 57-100%). Median deviations in the LR, SI, and AP dimensions were 3 mm, 4 mm, and 3 mm, respectively. Deviations in the SI and AP dimensions were more often in the superior rather than inferior (60% vs. 29%) and in the anterior rather than posterior (70% vs. 16%) directions. Interfraction prostate motion is significant. Daily portal imaging with implanted fiducials improves localization of the prostate, and is necessary for the reduction of treatment margins.