The Use of Sectional Imaging with CT and MRI for Image-Guided Therapy

Sectional imaging is integrated in each link of the modern radiotherapy chain, from diagnostic procedures to target volume definition to treatment planning, dose delivery, and verification. While CT is widely used for modern EBRT, including intensity modulated radiotherapy (IMRT) and image-guided radiotherapy (IGRT), MRI represents the gold standard for IGBT for gynecological malignancies (see Chap. 5, Sect. 5.4). High-precision radiotherapy techniques offer the option of enhancement of the therapeutic ratio, because the dose to the target is escalated and the normal organs are spared. However, in order to increase conformity, accurate target and organ delineation performed according to standardized protocols is required. Additionally, inter-/intrafraction variation due to tumor shrinkage and changes in dimensions and topography of the normal organs has to be taken into account, thus representing the main challenge for successful application of IGRT. To reduce contouring uncertainties and to identify inter-/intrafraction variation with high accuracy, a radiation oncologist has to apply image acquisition protocols adapted to the needs of image-guided therapy, to analyze sectional images with particular attention to tumor regression, regions of potential tumor spread, and lymph nodes regions. This chapter aims to cover important issues of CT and MRI application for image-guided therapy.