[Current status and future prospects of 3D treatment planning in radiation therapy, focusing on IMRT]

The ultimate goal of radiation therapy is to confine a high dose to the target area while sparing the surrounding normal structures in order to increase the delivered dose and decrease the likelihood of organ injuries. In Japan, the rotational conformal technique, which is a combination of gantry rotation and dynamic movement of multi-leaf collimators (MLC), has been widely used as a standard method for high-precision radiation therapy. The non-coplanar technique in which radiation beams are given in three dimensions has the advantage of dose concentration as well as organ sparing. In intensity modulated radiotherapy (IMRT), an uneven intensity map within a beam is generated with various methods such as "sliding window technique" and "stop and shoot technique". Several intensity modulated beams are combined to create arbitrary dose distribution including concave distribution. Although a substantial number of proton therapy facilities are planned in this country, IMRT should be considered as a competitive rival from the viewpoint of cost-benefit analysis as well as clinical effectiveness.