Advanced Technologies in Radiation Therapy: A New Beginning
Howard I. Amols, Ph.D.
Image Guided Radiation Therapy (IGRT) is often used to describe two different, but related new technologies which foretell significant improvements in radiation therapy (RT) treatment planning and treatment beam delivery. First, functional imaging (FI) modalities such as PET and MRI now permit quantification of tumor biology and radiosensitivity. In conjunction with anatomy based CT treatment simulation they are increasingly being used in RT treatment planning. Second, IGRT is often used to describe linear accelerator based kilovoltage (kV) imaging systems that are increasingly being used to monitor both inter and intrafraction changes in patient setup and internal anatomy offering the potential for real time adaptive RT.
Functional imaging offers the potential to more accurately diagnose tumors and in particular, identify aggressive heterogeneous subvolumes within tumors, which when coupled with intensity modulated radiation therapy (IMRT) and `dose painting’ have the potential to improve local control rates. The combination of FI based treatment planning plus IGRT therapy delivery may permit reduced treatment field margins, in turn leading to reduced normal tissue damage, which in turn may permit further dose escalation and improved clinical outcome. In particular the normal tissue dose sparing achievable with the combination of FI and IGRT may permit increased application of high dose hypofractionated radiosurgery to various extracranial tumor sites such as liver, lung, pelvis, abdomen, and soft tissues. Single fraction extracranial IGRT has also been proposed as a systemic treatment for oligometastases. Decreased treatment field margins and dose escalation place increasing importance on accurate treatment delivery, control of respiratory induced organ motion, and intrafractional monitoring of treatment delivery. The application of new technologies for these purposes is rapidly expanding in the clinical setting.
We present here an overview of these new technologies, a review of early reports of their clinical application, and goals for the future.