When Should IGRT Be Done?
The therapeutic window of radiotherapy is defined by the balance between the tumor control probability (TCP) and the normal tissue complication probability (NTCP). The tremendous evolution from bony-landmark two-dimensional radiotherapy over CT-based thre
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K. Haustermans and I. Joye
23.1 Introduction
23.2 Definition
The therapeutic window of radiotherapy is defined by the balance between the tumor control probability (TCP) and the normal tissue complication probability (NTCP). The tremendous evolution from bony-landmark two-dimensional radiotherapy over CT-based three-dimensional radiotherapy towards highly-conformal radiotherapy techniques such as intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) has broadened the therapeutic window substantially. The steep dose gradients of IMRT and VMAT allow for a better sparing of the normal tissues, but demand rigorous quality assurance to ensure that the highly-conformal dose distributions are accurately delivered to the target. Therefore, simultaneously with the evolution in dose conformality, advanced imaging modalities have been gradually introduced into daily practice.
Image-guided radiotherapy (IGRT) refers to the integration of imaging technology during the radiation course in order to increase the precision and accuracy of radiation delivery. From a broader point of view, IGRT also refers to the use of imaging throughout the radiotherapy process in general: from target delineation, treatment planning and delivery to response monitoring and prediction.
K. Haustermans (*) • I. Joye Department of Radiation Oncology, University Hospitals Leuven, Herestraat 49, 3000 Leuven, Belgium e-mail: [email protected]
23.3 IGRT Technologies Guidance of radiotherapy delivery is not a new concept. In the early radiotherapy days, marks were placed on the skin once the area of treatment was determined. The purpose of the ink marks was to align and to position the patient for treatment and to improve the reproducibility of the field placement. By aligning the markings with the radiation field in the treatment room, the correct position of the treatment field could be identified. Treatment planning was verified by film dosimetry. A major advance in radiotherapy guidance was the introduction of portal imaging, which refers to the acquisition of images using the radiation treatment beam. The portion of the beam that passes through the patient may be used to produce images of the patient.
© Springer-Verlag Berlin Heidelberg 2018 V. Valentini et al. (eds.), Multidisciplinary Management of Rectal Cancer, https://doi.org/10.1007/978-3-319-43217-5_23
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Nowadays, there are plenty of image-guidance technologies that can be applied for patient setup verification and correction [1]. They can be classified as ‘on-board solutions’ that are physically attached to the treatment delivery system and as ‘peripheral solutions’, referring to devices that are not directly mounted to the treatment machine. Examples of ‘peripheral solutions’ are room-mounted X-ray imaging systems, in-room diagnostic CT scanners that are connected by rails, and ultrasound devices. The most wide-spread on-board IGRT technology is the Electronic Portal Imaging Device (EPID). A major advantage of EPID is the u
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