Abstract
Intensity modulated radiation therapy (IMRT) for head and neck cancers and brain tumors was started in December 2000 at our hospital. Methods of quality assurance (QA) in IMRT at our hospital are reported. IMRT was given by 4 MV X-ray with a dynamic multi-leaf collimator (MLC) method. Treatment planning was obtained by an inverse planning method. It took two days to select an appropriate treatment plan among various plans obtained by inverse planning, and three days to perform dosimetry in phantoms for each beam and the total beams and to determine an isocenter of fields. The measured dose distribution in phantoms were consistent with the calculated dose distribution, although the measured doses were 2-4% lower than the calculated doses. The accuracy of MLC is the most important point in QA of IMRT. Beam profiles were obtained for all beams by a semiconductor profiler before IMRT every day. In addition, position of MLC was checked by a test pattern of a film method once a week. This method is very accurate and the slight deviation of MLC position as small as 0.2 mm could be detected by the method. A guideline of QA for IMRT should be established as soon as possible in Japan to perform IMRT safely and effectively.
