Determine prostate intrafraction motion with Cine-magnetic resonance imaging (MRI) and deformable registration.
A total of 68 cine-MRI studies were done in 17 different series with 4 scans per series in 7 patients. In without rectal balloon (WORB) scans, 100 mL of water was infused in the rectum. Each series consisted of supine and prone, with a rectal balloon (WRB) and WORB. Each scan was performed over 4 minutes. Automatic deformable registration software developed by View Ray, Inc., Cleveland, Ohio was employed to segment the prostate for each cine-MRI image. A time-based analysis was done for the different positions and the use of the rectal balloon.
The variation/standard deviation of the prostate position during 240 seconds was: supine WRB: 0.55 mm, WORB: 1.2 mm, and prone WRB: 1.48 mm, WORB: 2.15 mm (P < 0.001). A strong relationship was observed between time and prostate motion. For the initial 120 s the standard deviation was smaller than for the second 120 s supine WRB 0.54 mm versus 1.37 mm; supine WORB 0.61 mm versus 1.70 mm; prone WRB 0.85 mm versus 1.85 mm; and prone WORB 1.60 mm versus 2.56 mm. The probabilities for prostate staying within ±2 mm to its initial position are: 94.8% supine WRB; 91.5% supine WORB; 92.3% prone WRB; 79.2% prone WORB.
Intrafraction prostate motion was found dependent on time, patient position, and the use of a rectal balloon. Relatively stable positions can be obtained for 4 minutes or less especially in the supine position with a rectal balloon.
From the *Boca Radiation Oncology Associates, Boca Raton, FL; †Department of Science, View Ray, Inc, Cleveland, OH; ‡Department of Radiology, Juntendo University School of Medicine, Tokyo, Japan; §Department of Radiation Oncology, University of Florida of Medicine, Gainesville, FL, and the University of Florida Proton Therapy Institute, Jacksonville, FL; and ¶Department of Mathematics, University of Florida, Gainesville, FL.
Carlos Vargas, MD, is an advisor for ProCure Treatment Centers, Inc. Anneyuko I Saito, MD, is a former employee of ViewRay, Inc. Jim Dempsey, PhD, is the Chief Scientific Officer of ViewRay, Inc.
Reprints: Wen Chien Hsi, PhD, University of Florida Proton Therapy Institute, 2015 N. Jefferson St, Jacksonville, FL 32206. E-mail: firstname.lastname@example.org.