The prototype

The prototype has an optical camera, an infrared source, and a reflective fiducial. It also has a mechanical stabilization system, which controls the vibrations caused by the movement of the CT scanner and the linear accelerator couch (Fig. 1).

Prototype for the deep inspiration breath hold (DIBH) technique implementation. The system is fixed to the computed tomography (CT) simulator couch. A reflective fiducial is placed in the xiphoid appendix of the patient to reflect the respiratory motion. The optic camera and infrared detector detect the fiducial. The signal is transmitted to the monitor that displays the movement of the respiratory cycle and a band that turns green when the patient reaches a certain amplitude of inspiration that is individualized for each patient. This amplitude, with a maximum range of 6 mm, is recorded and should be reproduced throughout the treatment. The therapist and patient can view the monitor to control the process

The prototype was designed to be versatile, providing sub-millimeter accuracy and processing 30 frames per second in real-time. The developed software can modulate the infrared sensitivity and optically increase the noise/signal ratio.

Furthermore, it allows movement in two axes to focus on the target fiducial. Accuracy was certified using solid water phantoms of different thicknesses at varying distances from the camera measured by the lap laser of the CT scanner, a certified ruler, and by checking the reproducibility during CT simulation in 3 series of DIBH. The system would be considered safe if the value indicated by the equipment and the physical measures presented a Pearson’s correlation coefficient (‘r’) ≥ 0.9. After several iterations, the system proved robust and safe for clinical use with r = 1 (100% correlation).