Marker-less intra-fraction organ motion tracking using hybrid asm

External beam radiation therapy attempts to deliver a high dose of ionizing radiation to destroy cancerous tissue, while sparing healthy tissues and organs at risk (OAR). Recent advances in intensity modulated radiotherapy treatment call for a greater understanding of uncertainties in the treatment process and more rigorous protocols leading to greater precision in treatment delivery. The degree to which this can be achieved depends largely on the cancer site. The treatment of organs comprises soft tissue (e.g. in the abdomen) and those subject to rhythmic movements (e.g. lungs) causing inter and intra-fraction motion artifacts that are particularly problematic. Various methods have been developed to tackle the problems caused by organ motion during radiotherapy treatment, e.g. Real-time position management respiratory gating (Varian) and synchronized moving aperture radiation therapy, developed by researchers at Harvard Medical School.