Lung cancer: intermittent irradiation synchronized with respiratory motion--results of a pilot study.

Purpose: To test the feasibility of a system for intermittent irradiation synchronized with respiratory motion in a clinical setting.
Materials and Methods: A newly developed gate pulse controller that starts and stops irradiation at a chosen phase of the respiratory cycle by controlling a linear accelerator was used in six patients with lung cancer. A laser displacement sensor was used for the detection of respiratory motion. Three patients underwent radiation therapy during the cycles between 50% expiration and 50% inspiration (step 1), and three patients underwent radiation therapy during the cycles between 70% expiration and 30% inspiration (step 2).
Results: The system functioned well; irradiation was verified with portal verification radiography in all six patients. The range of the tumor position during synchronized irradiation was detectable with fast portal localization radiography. The treatment times for steps 1 and 2 were 1.38-1.71 and 2.03-2.18 times longer, respectively, than those for conventional irradiation.
Conclusion: Synchronized irradiation with the authors' system allowed convenient and reliable reduction of the target volume. Further study is needed to standardize the system for clinical use.