Image-guided radiation therapy: part 3 - stereotactic body radiation therapy. Medical Dosimetrists

摘要

Three-dimensional conformal radiation therapy (3DCRT) requires that the field outline of each radiation beam just covers the target, and intensity-modulated radiation therapy (IMRT) requires that the exact 3D shape of the targets be defined. This has led to the realization that the location of the target relative to the critical surrounding normal tissues must be determined prior to dose planning. It is also not sufficient to know the location of the target itself but also the shape of the target in 3 dimensions. As such, patients undergoing radiation therapy are initially scanned by an imaging modality, such as computed tomography (CT) or magnetic resonance imaging (MRI), for target and relative organs-at-risks (OARs) information for the dose planning purposes. The current tools available for target localization prior to and during treatment are less than satisfactory. As a result, there has been an emergence of the concept of image-guided radiation therapy (IGRT) as a methodology to devise more accurate ways of localizing target volumes, positioning these targets relative to the isocenter of the medical linear accelerator, and also tracking the target during dose delivery. Recently, there have been dramatic developments of positioning and/or tracking devices, which were described in the first and second special issues of the IGRT series (Medical Dosimetry Volume 31, Spring and Summer 2006). A clinical paper by Pawlicki et al. for hypofractionated prostate radiotherapy, illustrating the use of the imaging system, is included in this third issue of the IGRT series.