Intercepting radiotherapy using a fluoroscopic real-time tumor-tracking radiotherpy system.

Abstract

Purpose: To reduce uncertainty due to setup error and organ motion during radiotherapy of tumors in or near the lung, by means of real-time tumor tracking system and gating of a linear accelerator for intercepting radiotherapy .Methods and Materials: The real-time tumor-tracking system consists of two sets of diagnostic X-ray television systems, an image processor unit, a gating control unit, and an image display unit. The system recognizes the position of a 1.5-mm gold marker in the human body 30 times per second using two X-ray television systems. The marker is inserted in or near the tumor using image guided implantation. The linear accelerator is gated to irradiate the tumor only when the marker is within 1 - 2 mm from its planned coordinates relative to the isocenter. Results: The phantom experiment demonstrated that the geometric accuracy of the tumor-tracking system is better than 1.5 mm for moving targets up to a speed of 100 mm/s. The dose due to the diagnostic X-ray monitoring ranged from 0.01% to 1% of the target dose for a 2.0-Gy irradiation of a chest phantom. In 16 patients with Stage IA non-small celllung cancer, the 4-year survival was 95% by givign 48 Gy in fractions in 4-6 days.Conclusion: We successfully implemented and applied a tumor-tracking system for gated radiotherapy. The system significantly improves the accuracy of irradiation of targets in motion at the expense of an acceptable amount of diagnostic X-ray exposure.