Continuing Education Course Use of CT and PET in Radiation Therapy

The modern practice of radiation therapy relies on volumetric patient images. Computed tomography (CT) imaging has been the primary imaging modality used in radiation oncology for over two decades. However, magnetic resonance imaging (MRI) and positron emission tomography (PET) are increasingly becoming an important component of the treatment planning process. CT studies provide information not only about target volumes but about critical (normal) organs as well. Using CT images for radiation therapy treatment planning has enabled us to improve dose delivery to target volumes while reducing the dose to critical organs. CT images also provide density information for electron density corrected dose calculations. A major weakness of CT imaging is a relatively limited soft tissue contrast. This, limitation can be overcome by using CT images in conjunction with MRI studies. PET studies provide functional information about patient’s anatomy which can aid in target volume definition. The first portion of this refresher course reviews CT-simulation technology, tools, and process; and discusses the QA requirements for CT-simulation process and recommendations of the upcoming TG66 report on CT-simulation QA. The second part discusses registration of CT and PET images for treatment planning purposes and describes PET scanning process for radiation therapy. The third portion of presentation reviews the current status of PET based treatment planning for several treatment sites.