Another area of great interest at Martha Jefferson Hospital is respiratory gating for women with left-sided breast cancer. In some patients the heart is immediately adjacent to the chest wall that is targeted for external beam radiation. These patients will also have a 4-D CT scan performed in a supine position at the time of simulation and be coached to take exaggerated breaths. This will increase the amplitude of diaphragmatic excursion and increase the distance between the heart and chest wall at peak inspiration. The treatment is again gated, now at end inhalation, to take advantage of this increased physical distance between target (chest wall) and normal, critical structure (heart).

Patient selection is important. The treatment position is with the patient supine with one or both arms overhead and immobilized for reproducibility. A small, lightweight gating box is placed on the patient's chest, and its movement is traced by a video camera. A regular respiratory phase must be established and maintained. In lung patients normal, uncoached breathing has been optimal. In breast patients the exaggerated breath has been beneficial, and therefore, adequate pulmonary function is required to maintain this during the 15 minutes needed for setup and treatment delivery. As treatment delivery is limited to a portion of the respiratory cycle, treatment times increase. Some patients with irregular breathing patterns, significant respiratory compromise, or frequent cough are not optimal candidates for respiratory gating. In those who are, the addition of respiratory gating to their radiation therapy is enhancing the delivery of high-dose, precision radiation with enhanced sparing of normal critical structures.