Focal irradiation and image fusion techniques (IGRT)--Part IV.

摘要

Image-guided radiation therapy (IGRT) is currently an emerging technology and is undergoing rapid transformation. There have been different interpretations of this technology. Medical Dosimetry journal has devoted 4 special volumes on this topic. With the recent development in positron emission tomography (PET), in particular, the commercial availability of PET-CT hybrid scanner, the advancement of IGRT has been perceived as the integration of images from various medical imaging modalities to support the delineation of targets for three-dimensional (3D) treatment planning. Another interpretation has been toward the application of medical imaging modalities to set up patients prior to dose delivery to reduce patient setup uncertainties. Various technologies have been developed to support this concept including (a) ultrasound imaging, (b) in-room CT (also known as CT-on-rail), (c) mobile kilovoltage x-ray unit, and (d) cone-beam CT technology using kilovoltage and megavoltage radiation beams. The integration of these IGRT technologies to the dose delivery systems has been described in the first IGRT special volume of the Medical Dosimetry journal. Of particular interest in the integration of IGRT technologies to the dose delivery system is the implementation of cone-beam CT techniques. This cone-beam CT technique allows patient data to be acquired volumetrically by rotating the gantry of the dose delivery system around the patient. The patient data are then reconstructed to obtain transaxial and/or multiplanar CT images. Along with the advancement of medical imaging modalities for diagnostic radiology and radiation oncology, there have been increasing concerns about the impact of voluntary and involuntary patient movements. Static in silico treatment plans may have little resemblance to the dose distributions achieved in living, breathing, fidgeting patients who may gain or lose 10% of their body weight over a 7-week course of fractionated treatments. Involuntary patient movement such as breathing hasbeen addressed using (a) forced breathing technique, (b) shallow breathing technique, and (c) motion-gating techniques. Motion-gating techniques and the technology of cone-beam CT has been reviewed in the second IGRT special volume of Medical Dosimetry.