Image-Guided Adaptive Brachytherapy

The use of imaging has an enormous impact on the workflow and use of brachytherapy. Imaging is used in the whole process from preparation for application to quality assurance during dose delivery. In cervix brachytherapy (BT), ultrasound (US) is commonly used for guidance during the application. For treatment planning, magnetic resonance imaging (MRI) is the modality of choice, because it incorporates all volumes of interest within one data set and gives the best information about the local and regional tumor extension. If MRI is not or less available, methods with use of computed tomography (CT)-scan or US are possible. In prostate BT, US is typically used for implantation. For treatment planning, other modalities, such as CT and MRI are also used. Particularly the use of MRI makes it possible to target the dose to visible intraprostatic lesions. This is done either as a BT boost dose or as a limited treated volume in the context of partial prostate BT. Besides imaging as a tool for assessment of tumor and organs, imaging is also needed to reconstruct the applicators inserted for BT. The accuracy of this reconstruction has an impact on the accuracy of the dosimetry. In certain cases, it is necessary to register different imaging modalities to each other in order to take advantages of differences in applicator and anatomical assessments. In modern BT, treatment planning is done on volumes and no longer on dose points. With this development, much better prediction of tumor control and toxicity is acquainted when considering dose-volume parameters.