Linac-based stereotactic radiosurgery or stereotactic body radiotherapy via online dynamic tracking

Stereotactic body radiotherapy (SBRT) is widely applied to treat patients with medically inoperable peripheral early-stage non-small cell lung cancer (NSCLC) and spine metastases. The tracking technology applied in SBRT has undergone profound changes over the last decades. The dose delivery accuracy has been significantly improved with the implementation of real-time motion management. High delivery accuracy allows higher target dose with sufficient normal tissue sparing which will further improve the tumor control probability. The general principle of the state-of-the art respiratory motion tracking techniques were introduced and discussed including tracking with multi-leaf collimator (MLC), optical imaging, portal X-ray imaging, radio-frequency markers, and positron emission tomography (PET) imaging. Implementation of the real-time tracking includes the application of external or internal imaging to build a correlation between tumor position and marker signals, using a predictive model to provide the tracking details for the linear accelerator (Linac), and control of the Linac to compensate for the respiratory motion. As the tracking technology is involving more advanced imaging modalities, the traditional radiation therapy workflow must be revised to ensure motion tracking efficiency and accuracy.