Portal imaging and image analysis

Summary form only given. Electronic portal imaging performs verification of radiotherapy by taking patient images with the treatment beam which show the bony anatomy in relation to the treatment beam. For effective portal imaging, image acquisition equipment, reference images, image analysis software, and decision rules for minimizing setup errors are required. The past few years, the quantum efficiency of existing EPID systems has been improved, but the advent of solid-state flat panel imaging systems (almost all based on a scintillating screen coupled to an amorphous silicon light detector), is the most promising development. These devices take high quality images with acceptable dose. Quantitative analysis of portal images is a prerequisite for accurate decision making. The objectives of portal image analysis are: (1) verify that the treatment field has the right shape, (2) verify that the patient is in the correct position. As reference image a simulated radiograph from the CT data (for 2D analysis), or even the CT data itself (for 3D analysis). Finally, the measured deviations are fed into computerized decision protocols that reduce systematic (average) setup errors as much as possible with limited workload. User friendly implementation in commercial products, in particular of the image analysis software and decision rules, remains to be done