A case study on the use of cine MR images to create an ITV for the treatment of liver tumours with Stereotactic Ablative Radiotherapy (SABR)

Abstract

Liver tumours are rarely visible on CT imaging without the use of contrast. In addition to the need for contrast, the CT image must be acquired at a specific phase of the contrast injection. This presents difficulties for synchronization of the contrast injection with the acquisition of a 4dCT. Liver tumours move significantly due to respiration so a reliable method of measuring motion due to respiration is required. This work describes a method to measure tumour motion using cine MR images acquired in three sagittal planes and three coronal planes at two frames per second for 30 seconds. Images were then manually binned into different breathing phases by measuring the distance between a fixed and moving anatomical point. The images were binned into five phases and imported into the Eclipse TPS. The tumour was drawn on each MR image set and a composite tumour volume was constructed to create the ITV. For treatment planning, an end-expiration breath-hold CT simulation was acquired. This CT scan was registered with each MR image set and the ITV generated from the cine MR images was transposed onto the CT scan. This work has demonstrated that the use of cine MR images of liver tumours may be used to assess motion due to respiration and represents a valuable tool in the treatment planning of SABR for such tumours.