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Image-guided radiation therapy (IGRT) is the process of frequent two and three-dimensional imaging, during a course of radiation treatment, used to direct radiation therapy utilizing the imaging coordinates of the actual radiation treatment plan.〔(IGRT, or Image Guided Radiation Therapy, is a sophisticated method of radiation treatment )〕 The patient is localized in the treatment room in the same position as planned from the reference imaging dataset. An example of IGRT would include localization of a cone beam computed tomography (CBCT) dataset with the planning computed tomography (CT) dataset from planning. IGRT would also include matching planar kilovoltage (kV) radiographs or megavoltage (MV) images with digital reconstructed radiographs (DRRs) from the planning CT. These two methods comprise the bulk of IGRT strategies currently employed circa 2013. This process is distinct from the use of imaging to delineate targets and organs in the planning process of radiation therapy. However, there is clearly a connection between the imaging processes as IGRT relies directly on the imaging modalities from planning as the reference coordinates for localizing the patient. The variety of medical imaging technologies used in planning includes x-ray computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) among others. The precision of IGRT is significantly improved when N-localizer technology is used in conjunction with these medical imaging technologies. Through advancements in imaging technology, combined with a further understanding of human biology at the molecular level, the impact of IGRT on radiotherapy treatment continues to evolve. ==Goals and Clinical Benefits== The goal of the IGRT process is to improve the accuracy of the radiation field placement, and to reduce the exposure of healthy tissue during radiation treatments. In years past, larger planning target volume (PTV) margins were used to compensate for localization errors during treatment. (Jaffray et al. 1999) This resulted in healthy human tissues receiving unnecessary doses of radiation during treatment. PTV margins are the most widely used method to account for geometric uncertainties. By improving accuracy through IGRT, radiation is decreased to surrounding healthy tissues, allowing for increased radiation to the tumour for control. (Jaffray et al. 1999) Currently, certain radiation therapy techniques employ the process of intensity-modulated radiotherapy (IMRT). This form of radiation treatment uses computers and linear accelerators to sculpt a three-dimensional radiation dose map, specific to the target’s location, shape and motion characteristics. Because of the level of precision required for IMRT, detailed data must be gathered about tumour locations. The single most important area of innovation in clinical practice is the reduction of the planning target volume margins around the location. The ability to avoid more normal tissue (and thus potentially employ dose escalation strategies) is a direct by-product of the ability to execute therapy with the most accuracy. (Jaffray et al. 1999) Modern, advanced radiotherapy techniques such as proton and charged particle radiotherapy enable superior precision in the dose delivery and spatial distribution of the effective dose. Today, those possibilities add new challenges to IGRT, concerning required accuracy and reliability (Selby et al. 2010). Suitable approaches are therefore a matter of intense research. IGRT increases the amount of data collected throughout the course of therapy. Over the course of time, whether for an individual or a population of patients, this information will allow for the continued assessment and further refinement of treatment techniques. The clinical benefit for the patient is the ability to monitor and adapt to changes that may occur during the course of radiation treatment. Such changes can include tumor shrinkage or expansion, or changes in shape of the tumor and surrounding anatomy. (Jaffray et al. 1999) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Image-guided radiation therapy」の詳細全文を読む スポンサード リンク
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