Prototype Development of an A-Mode Ultrasound Based Intrafraction Motion Management System

Abstract: Owing to the steep dose fall-off curves of high precision and accuracy radiation therapy (RT) modalities such as stereotactic body RT (SBRT), treatment plans with extraordinarily small margins to organs at risk (OARs), such as the spinal cord, has been made possible. With this development, patient movements during treatment, i.e. intrafraction motion (IFM), must be monitored more closely. This master thesis was aimed at developing an A-mode ultrasound prototype to detect the motions of the cervical spine as part of an IFM management (IFMM) system. Current IFMM systems have several drawbacks, including invasiveness and indirect measurements. The existing prototype was tested in order to identify areas of improvement. The prototype developed was equipped with a preconditioning circuit that retains the frequency information of the signal. Furthermore, software was developed based on wavelet filtering and enveloping using the Hilbert transform. Multiple logic algorithms were added in order to handle lost signals, competing echoes, echoes from soft tissues etc. The newly-developed prototype was found to have higher accuracy and precision than the pre-existing prototype. It was also more robust when measuring distance to the spine. A difficulty in segmenting the echo for bone arises for low quality signals. Therefore a compromise exists between setup time, including probe adjustment, and signal quality. Future work includes the manufacturing of a new neck rest to enable robust probe adjustment and fixation.