Preliminary evaluation of Time-of-flight (ToF) imaging system for monitoring DIBH radiotherapy

The study focusses on evaluation of a Time-of-flight (ToF) camera for monitoring breath-hold (BH) level during voluntary deep inspiration breath-hold radiotherapy (vDIBH-RT). A commercial Argos 3D P330 ToF camera (Bluetechnix, Austria) was used to provide the distance of the patient imaged based on the light reflected from the illuminated surface. A volunteer was recruited in this study to preliminary evaluate the performance of the ToF camera for optical surface imaging. The vDIBH-RT was simulated by instructing the patient to perform DIBH for 15 seconds during ToF imaging. A small region was selected on the image of the patient's chest surface, mid-way between the nipples. 200 consecutive ToF images of the selected area were captured during the DIBH. Imaging was repeated during free breathing (FB). These were performed for two times (representing fractions) to evaluate the inter-fraction variability. MATLAB (MathWork, Natick, MA) was used to calculate the average distance and standard deviation (SD) across each set of images acquired during a DIBH representing the BH level and BH stability, respectively. The inter-fraction variability defined as the difference between fraction-1 and fraction-2 was 4.5 mm ± 0.86. The BH stability for both sessions were within 1 mm. The distance measured during free breathing shows traces similar to the respiratory pattern obtained when using spirometry system. In conclusion, the ToF camera has potential in monitoring BH during DIBH-RT for breast cancer.