Design and evaluation of a methodology to perform personalized visual biofeedback for reducing respiratory amplitude in radiation treatment.

A methodology to perform personalized visual biofeedback aimed to the reduction of respiratory amplitude is here proposed. A custom-made software allows to adapt the biofeedback parameters to a patient's respiratory pattern by calculating a limiting range for respiratory amplitude obtained from data acquired during free breathing. The proposed methodology has been tested on ten healthy volunteers and on five lung cancer patients undergoing radiotherapy treatment. The protocol for volunteers consisted of 3 min of data acquisition during the subject's free breathing, 2 min of visual biofeedback within the limits, and 3 min of free breathing. The patients' free breathing was acquired in 3 min and the visual biofeedback performed during all the sessions of the radiotherapy treatment, i.e., an average of eight sessions and an average total treatment time of 2000 s each patient. All the volunteers and three patients of the five found the protocol comfortable. The settlement time needed for considering the limiting range stabilized during free breathing has been calculated as 120 +/- 10 s (p < 0.05). During visual biofeedback the baseline shift was removed and the average respiratory amplitude was reduced by about 40% for all the subjects. The variability of the breathing amplitude remained unaltered during biofeedback. Eight volunteers and three patients remained within the limiting range for more than 90% of the biofeedback period; all subjects remained within the limiting range for more than 80% of the biofeedback period. During the biofeedback period both groups, volunteers and patients, showed a significant increase in breathing frequency which was mostly doubled. Patients with shallow breathing performed comfortably the biofeedback.