[Intensity Modulated Radiation Therapy (IMRT)].

Radiotherapy plays an important role in the management of cancer patients, and half of the patients with malignant tumors are treated with radiotherapy in the United States. In Japan, the necessity of radiation therapy has come to be widely acknowledged in cancer treatment, and more and more cancer patients are being treated with radiation. External beam radiation is the most-used radiotherapy at the present time. The advantage is that this treatment modality can be used in a short time, although the problem is that not only the cancer lesion but also the surrounding normal tissue is irradiated,causing an adverse effect on normal tissue. In order to solve this problem,treatments such as 3D-Conformal Radiation Therapy (3D-CRT), Intensity Modulated Radiation Therapy (IMRT), Stereotactic Radiation Surgery (SRS) and Stereotactic Radiation Therapy (SRT) are clinically used as an extremely precise radiotherapy, thanks to the advances in computer technology in recent years. Therefore, the purpose of these extremely precise radiation therapies is to administer a high dose to the tumor intensively, and to suppress quantities of magnetism to normal tissues. IMRT treatment results for prostate cancer patients and head and neck cancer patients are reportedly better than with other irradiation methods. In this chapter,we explain the external irradiation method with the focus on IMRT and the extremely precise radiotherapy preformed in the Tokyo Women's Medical University Hospital.