Clinical experience using respiratory gated radiation therapy: Comparison of free-breathing and breath-hold techniques

To investigate the clinical use of a commercially available gating system for minimizing respiratory-induced anatomic motion over a range of treatment sites. The gating system consists of a reflective marker placed on the patient's anterior surface. The motion of the marker is tracked using a camera interfaced to a computer. Gated intervals were defined that limited the motion of the diaphragm to less than 1 cm during free breathing. Patients underwent a computed tomography virtual simulation using a breath-hold technique. At the time of treatment, verification of patient position and gating interval were performed using electronic portal imaging. Between September 2000 and January 2002, 136 patients were simulated with respiratory gating. Of these, 108 patients were treated to 110 sites for a total of 2301 treatment sessions. Ninety-seven percent of patients completed their entire course of therapy with gated treatment delivery. Respiratory gating is a practical and achievable solution for minimizing respiratory-induced target motion during both simulation and treatment. With proper patient selection and training, it can be successfully implemented in a clinical radiation therapy department.