Abstract
To reproduce and keep the position of field alignment decided during treatment planning, it is necessary to immobilize and position the patients with exactness. Until now portal films have been used to verify and control the accuracy of fields alignment. For the study of deviation of field alignment, this article reviews the data published over the 10 or so years, and analyzes the extent of displacement from an intended position. From this analysis, it was shown that the extent of systematic and random errors had been at the same level. Therefore, it is effective in excluding systematic errors during the first session of radiotherapy, and then, it is expected to improve the uncertainty during the localization of fields. When a biteblock and plastic cast are used during patient setup, the extent of errors obviously decreased. Recently, electronic portal imaging devices are becoming available for radiotherapy. In this paper, advantage of these was discussed regarding use for patients setup. It is also important to improve the environment of radiotherapy (units and staff) as well as quality control. In Japan, especially, there are many problems with respect to radiotherapy staff. It is of urgent necessity in solving this problem.
