Calibration of mechanical systems of in-house dynamic thorax phantom for radiotherapy dosimetry

The purpose of this study is to calibration a mechanical system of In-house Dynamic Thorax Phantom so that it can be used as a dosimetry on the Radiotherapy Real-Time Position Management (RPM) technique. In order to ensure the RPM technique had properly function, we need to employ a quality control tool that represents moving objects on the human body. Inspired by the CIRS Dynamic Thorax Phantom model 008A, we developed an In-house Dynamic Thorax Phantom using three Nema-17 stepper motors with 200 steps in a cycle as a mechanical system. In addition, the first stepper motor was used to move objects in superior-inferior direction; the second one was used to move the RPM marker in anterior-posterior direction; while the third one was used to move objects in rotation. Calibration of mechanical system was performed by finding out the number of counts needed each direction. Especially for rotational system, they were calibrated with Optical Interrupt Device. The result of calibration of the mechanical system between the actual readings compared with the system specification is 0.0% and < 1% for the measurement testing.