Simultaneous CBCT Acquisition During Arc Radiotherapy

The cone beam image is a part of the radiotherapy treatment machine and uses lower energy xrays as the head of the radiotherapy machine moves around the patient in a circle. This takes pictures that give 3-dimensional information, somewhat like a CT scan. These images are better at showing the position of the tumour and surrounding soft tissues than the standard xrays that were previously used. Cone Beam Imaging Technology is not new and has been used regularly at The Christie for many years. The standard cone beam scan is taken before the actual radiotherapy treatment or after the treatment has been delivered. Volumetric Modulated Arc Therapy (VMAT or Arc Radiotherapy) is a novel method of delivering radiotherapy that involves the continuous movement of the radiotherapy treatment machine head around the patient and MLC during radiation. Arc radiotherapy has been clinically implemented at The Christie for prostate radiotherapy treatments and work is in progress for implementation in lung radiotherapy. The continuous gantry rotation inherent to VMAT delivery makes this simultaneous imaging possible, although there are concerns associated with the impact that this may have on patient dose and image quality. The aim of this research is to assess whether the image quality of cone beam scans taken during treatment are as good as standard cone beam scans taken before or after treatment used to determine the accuracy of patient position and the tumour coverage by radiotherapy.