Prediction of Intrafraction Prostate Motion: Accuracy of Pre- and Post-Treatment Imaging and Intermittent Imaging
Received 19 December 2007; received in revised form 22 April 2008; accepted 25 April 2008. published online 08 August 2008.
Purpose
To evaluate whether pre- and post-treatment imaging (immediately before and after a radiation therapy treatment fraction) and intermittent imaging (at intervals during a treatment fraction) are accurate predictors of prostate motion during the delivery of radiation.
Methods and Materials
The Calypso 4D Localization System was used to continuously track the prostate during radiation delivery in 35 prostate cancer patients, for a total of 1,157 fractions (28–45 per patient). Predictions of prostate motion away from isocenter were modeled for a pre- and post-treatment imaging schedule and for multiple intermittent intrafraction imaging schedules and compared with the actual continuous tracking data. The endpoint was drift of the prostate beyond a certain radial displacement for a duration of more than 30 s, 1 min, and 2 min. Results were used to evaluate the sensitivity and specificity of these models as an evaluation of intrafraction prostate motion.
Results
The sensitivity of pre- and post-treatment imaging in determining 30 s of intrafraction prostate motion greater than 3, 5, or 7 mm for all fractions was low, with values of 53%, 49%, and 39%, respectively. The specificity of pre- and post-treatment imaging was high for all displacements. The sensitivity of intermittent imaging improved with increasing sampling rate.
Conclusions
These results suggest that pre- and post-treatment imaging is not a sensitive method of assessing intrafraction prostate motion, and that intermittent imaging is sufficiently sensitive only at a high sampling rate. These findings support the value of continuous, real-time tracking in prostate cancer radiation therapy.
Reprint requests to: Parag J. Parikh, M.D., Department of Radiation Oncology, Washington University School of Medicine, 4921 Parkview Place, Lower Level, St. Louis, MO 63110. Tel: (314) 362-8525; Fax: (314) 362-8521
Presented at the 49th Annual Meeting of the American Society for Therapeutic Radiology and Oncology, Oct 28-Nov 1, 2007, Los Angeles, CA.
Conflict of interest: Lisa Levine, Ph.D., is an employee of Calypso® Medical Technologies.
ABSTRACT