Evaluation of Interfraction and Intrafraction Prostate Motion During the Treatment of Prostate Cancer Using the Calypso 4D Localization System

To evaluate interfraction and intrafraction prostate motion during the treatment of prostate cancer using the Calypso 4D Localization System. Between April 2007 and February 2008, 48 patients underwent external beam radiation therapy as a component of their prostate cancer treatment using an intensity modulated radiation therapy (IMRT) technique in conjunction with the Calypso 4D Localization System. A total of 1,327 treatment fractions were evaluated. The tolerance threshold for prostate motion was set at >3 mm for >5 seconds. Treatment was interrupted and patients were repositioned each time prostate motion exceeded the threshold. Patients received dietary instructions before and coaching during their treatment course. Localization data used for interfraction monitoring and tracking data for intrafraction monitoring from the Calypso 4D Localization System was analyzed. The average daily patient setup time was 49 seconds (range, 35-74). The average shifts from treatment isocenter in the X, Y, and Z directions were 0.43 cm (+/− 0.17), 0.34 cm (+/− 0.12) and 0.56 cm (+/− 0.40 cm). The average treatment time was 12.8 minutes (+/− 3.2) and the average number of treatment stops per fraction was 0.54 (range, = 0-4). All patients exceeded the tolerance threshold at least once during their treatment course. The percentage of fractions delivered requiring 0, 1, 2, 3, or 4 treatment stops were 61%, 26%, 9%, 3%, and 1%. The directional frequency of the shifts were X = 1%, Y = 31%, and Z = 77%. The average standard deviation of distance between each beacon transponder over the course of treatment was 0.5 mm. The Calypso 4D Localization System provides an efficient and accurate means to quantify interfraction and intrafraction prostate motion during external beam radiation therapy. These results indicate that real-time monitoring of prostate motion can minimize a significant amount of marginal target miss while keeping overall treatment times reasonable.