Role of IGRT in patient positioning and verification

Image-guided radiation therapy is 'Frequent imaging in the treatment room during a course of radiotherapy to guide the treatment process'. Instrumentation related to IGRT is highlighted. Focus of the lecture was on clinical experience gained by NKI-AVL, such as the use of EPID (electronic portal imaging devices) and CBCT (cone beam computed tomography) and their comparison: good results for head and neck and prostate/bladder patients: portal imaging was replaced by CBCT. After further investigation convincing results for lung patients were obtained: portal imaging was replaced by CBCT. Scan protocols were developed for these patient groups. Since February 2004 CBCT-based decision rules have been developed for: Head and Neck (Bony anatomy); Prostate (Bony anatomy; Soft tissue registration); Lung (Bony anatomy, Soft tissue registration); Brain (Bony anatomy); and Breast, bladder and liver (in progress). Final remarks are as follows: The introduction of various IGRT techniques allowed 3D verification of the position of target volumes and organs at risk just before or during treatment. Because the information is in 3D, or sometimes even in 4D, in principle these IGRT approaches provide more information compared to the use of 2D verification methods (e.g. EPIDs). Clinical data are becoming available to assess quantitatively for which treatment techniques IGRT approaches are advantageous compared to the use of conventional verification methods taking the additional resources (time, money, manpower) into account. (P.A.)