Design and applications of a 4D simulator for respiratory motion

Purpose: To design, construct, and evaluate a pneumatic respiratory‐motion simulator for 4D radiotherapy. The device should be able to operate in dynamic mode for real‐time simulation of patient breathing motion as well as snapshot mode for static dose measurement. Method and Materials: A simulator incorporating a cylindrical air reservoir with a piston was constructed as a tool in 4D radiotherapy studies. The piston movement is controlled by a programmable logic controller (PLC) which is interfaced to custom software written in Visual Basic (VB). The air reservoir is connected to a lung phantom made of two pulmonary simulation balloons. The pressure inside the lung phantom is monitored by a detector whose input is feedback to the PLC. The lung phantom is immersed in a water‐filled box to simulate the normal tissue surrounding actual human lungs. The box is connected to a water reservoir to allow breathing of the lung phantom. A rubber ball is attached to the inner side of the phantom to simulate a lung tumor and gold seeds are implanted into it for seed‐tracking studies. Spirometer‐based patient respiratory waveform data in ASCII format were obtained from our department's breath‐hold clinical study. The waveform data are input to the VB program and sent to the simulator for controlling the simulation. Results: Preliminary evaluation of the simulator using several patient waveforms has been conducted. The respiratory motion of the lung phantom is found to be reproducible. Conclusion: A prototype respiratory‐motion simulator has been built which should prove valuable for 4D radiotherapy and related studies (gating, respiratory‐induced organ deformation). Its unique design of using pneumatic means to simulate breathing motion allows more realistic simulation studies including those involving animal lung models. © 2005, American Association of Physicists in Medicine. All rights reserved.