The immobilization devices consist of polyurethane fixtures and thermoplastic plates. The fixtures and plates are personalized for each patient before CT scanning for treatment planning. The patient is usually treated in the supine position. If the tumor is in the posterior lung, the patient assumes a prone position.

Irradiation is typically administered from four directions. As the beam lines are fixed in vertical and horizontal directions, the other two directions are achieved by tilting the patient to the left or right (Fig. 21.1).

CT images for treatment planning are taken in synchronization with the respiratory motion. Because the displacement of a tumor is generally lowest at the end of the expiratory phase, this timing is applied for the actual irradiation. The respiratory sensing system uses a position-sensitive detector (PSD) as a camera, along with an infrared light-emitting diode (LED). The LED is attached to the patient’s body around the chest wall, and the light spot from the LED is focused on the PSD through a lens system [20]. A change in position is amplified by the zoom lens of the camera. The analog signals of the PSD are directly proportional to the spot position, without the need for a software program to calculate the position. The camera is typically mounted on the treatment couch at the feet of the patient, where it does not disturb the irradiation and does not interfere with the patient’s fixation device. Setup of the respiratory sensor takes less than 30 s (Fig. 21.1). Prompt starting and stopping of the beam extraction according to the gate signal are achieved by a special extraction method that provides an efficiency of more than 85 % of that of the standard extraction at the heavy ion medical accelerator in Chiba (HIMAC)[20, 21].

For patient positioning, fluoroscopic images are used, along with the superposition of the respiration waveform. Each treatment room of the HIMAC has a pair of orthogonal fluoroscopic devices. Fluoroscopic images of the patient in the optimal position are digitized and transferred to the positioning computer. They are displayed on the computer monitor screen, together with reference images, such as simulation images or digital reconstruction radiography, which are calculated based on the planning CT images. Fluoroscopy is performed from the beam’s eye view. The patient’s respiration waveform and the gate signal are also superimposed on the TV screen. The treatment couch is then moved to the matching position until the largest deviation from the field edge and the isocenter position is less than 2 mm. The whole procedure, including irradiation, takes about 20–30 min.

Most patients underwent clinical examinations for follow-up, and CT scans of the thorax were carried out at our institute. Patients in whom follow-up testing could not be carried out until completion underwent periodic CT scanning at another institute. The clinical outcomes of all patients have been confirmed.

The first follow-up examinations were performed 4 weeks after C-ion RT and were repeated every 3–4 months. It is difficult to distinguish the changes in normal tissues due to radiation from tumor regrowth. We therefore defined transitorily enlarged densities observed after approximately 3 months as locally controlled tumors. Local recurrence was defined by an enlarging tendency of the tumor, as well as based on the findings of CT images, PET scans, tumor marker levels, and biopsy results.