Prostate tumor alignment and continuous, real-time adaptive radiation therapy using electromagnetic fiducials: Clinical and cost-utility analyses
Received 9 February 2008; received in revised form 19 April 2008; accepted 19 April 2008. published online 14 July 2008.
Abstract
Objective
To evaluate the accuracy, utility, and cost effectiveness of a new electromagnetic patient positioning and continuous, real-time monitoring system, which uses permanently implanted resonant transponders in the target (Calypso® 4D Localization System and Beacon® transponders, Seattle, WA) to continuously monitor tumor location and movement during external beam radiation therapy of the prostate.
Materials and methods
This clinical trial studied 43 patients at 5 sites. All patients were implanted with 3 transponders each. In 41 patients, the system was used for initial alignment at each therapy session. Thirty-five patients had continuous monitoring during their radiation treatment. Over 1,000 alignment comparisons were made to a commercially available kV X-ray positioning system (BrainLAB ExacTrac, Munich, Germany). Using decision analysis and Markov processes, the outcomes of patients were simulated over a 5-year period and measured in terms of costs from a payer's perspective and quality-adjusted life years (QALYs).
Results
All patients had satisfactory transponder implantations for monitoring purposes. In over 75% of the treatment sessions, the correction to conventional positioning (laser and tattoos) directed by an electromagnetic patient positioning and monitoring system was greater than 5 mm. Ninety-seven percent (34/35) of the patients who underwent continuous monitoring had target motion that exceeded preset limits at some point during the course of their radiation therapy. Exceeding preset thresholds resulted in user intervention at least once during the therapy in 80% of the patients (28/35). Compared with localization using ultrasound, electronic portal imaging devices (EPID), or computed tomography (CT), localization with the electromagnetic patient positioning and monitoring system yielded superior gains in QALYs at comparable costs.
Conclusions
Most patients positioned with conventional tattoos and lasers for prostate radiation therapy were found by use of the electromagnetic patient positioning and monitoring system to have alignment errors exceeding 5 mm. Almost all patients undergoing external beam radiation of the prostate have been shown to have target organ movement exceeding 3 mm during radiation therapy delivery. The ability of the electromagnetic technology to monitor tumor target location during the same time as radiation therapy is being delivered allows clinicians to provide real time adaptive radiation therapy for prostate cancer. This permits clinicians to intervene when the prostate moves outside the radiation isocenter, which should decrease adverse events and improve patient outcomes. Additionally, a cost-utility analysis has demonstrated that the electromagnetic patient positioning and monitoring system offers patient outcome benefits at a cost that falls well within the payer's customary willingness to pay (WTP) threshold of $50,000 per QALY.
Conflict of interest notification: All funding for the research reported in this manuscript was provided by Calypso Medical Technologies, Seattle, WA, manufacturer of the Calypso® 4D Localization System with Beacon® transponders used in this research. MMQ is a paid consultant of Calypso Medical Technologies. Aequitas is a San Diego, CA-based consulting firm retained by Calypso Medical Technologies to perform a cost-utility analysis from the clinical trial data reported herein. T.P.M. and J.E.S. have received and continue to receive funding from Calypso Medical Technologies to support their ongoing research.
ABSTRACT