Real-time lung tumour motion modeling for adaptive radiation therapy using LEGO Mindstorms

An anthropomorphic phantom was built using LEGO Mindstorms® and programmed in LabVIEW® for Adaptive Radiation Therapy (ART) purpose, to simulate the processes of breathing in the lung district during treatments. A thoracic cavity is prototyped by means of an 8 ribs apparatus and 2 artificial tumor masses, driven by intelligent brick LINUX® OS CPU. An optical surface tracking system (VisionRT®) and a QUASAR™ phantom allow correlation between physiological, robotic motion and surrogated signal. Patient's breathing phases are acquired instantaneously by InfraRed/UltraSound sensors. Through 4DCT images, tumor center of mass are individuated and tracked during respiration, to link internal-external organs motion. To quantify the degree of divergences due to dynamics organs deformation, a 4D function was obtained and simulated by our phantom. Sinusoidal signals (6, 10, 12, 15 and 17 Breaths per Minute-BPM) were used for evaluating and commissioning, thereby obtained a correlation coefficient (0.90-0.94) between QUASAR and LEGO. Validated on ideal conditions, phantom was tested in clinical practice. Breaths and CT study of 12 patients were analyzed. Fitting of real breath sinograms returned a mean R value of 0.94 (0.83-0.98) with best model performance achieved in signals with respiratory frequency less than 20 BPM. By using LEGO it is possible to reproduce real patients conditions and simulate normal and even abnormal behavior during the course of therapy, allowing spatial motion estimation.