A new irradiation system for lung cancer combining linear accelerator, computed tomography, patient self-breath-holding, and patient-directed beam-control without respiratory monitoring devices

Abstract Purpose To introduce and assess a new irradiation technique for lung cancer that utilizes a linear accelerator and computed tomography (CT) scanner combination, along with a novel switching mechanism, which enables patients to synchronize the duration of irradiation with self-breath-holding without respiratory monitoring devices. Methods and materials A newly developed treatment unit, a linear accelerator combined with a CT scanner (CT-linac), was used for irradiation. A novel switching mechanism, connected directly to the console of the linear accelerator, enabled the patient to control the radiation beam to correspond with the duration of self-breath-holding during a session determined by a radiation technologist. Twenty patients with lung cancer were enrolled in this study. All patients were instructed in the technique of breath-holding during the inspiration phase using visualization of respiratory motion through fluoroscopy as a teaching aid. CT scans under patients’ self-breath-holding were repeated three times, and differences in tumor position on CT images were measured. The reproducibility of tumor position was visually evaluated on electronic portal images (EPI). Results Mean maximum differences in tumor position under patients’ self-breath-holding were 2.2 mm in the cranial-caudal direction, 1.4 mm in the anterior-posterior direction, and 1.3 mm in the right-left direction. Switching of the radiation beam was delayed less than 0.1 s behind patient switching. EPIs were used to determine that reproducibility of tumor position was satisfactorily accurate. Conclusion The reproducibility of tumor position, during patient self-breath-holding synchronized with patient-initiated radiation and without a respiratory monitoring device, was sufficiently accurate. This novel irradiation technique for lung tumors using a combination CT-linac offers reduced PTV, sufficient reproducibility, and decreased duration of treatment.