Usefulness of intensity-modulated radiation therapy for breast conserving radiation therapy: a three-dimensional treatment planning system comparison of irradiation methods

Until recently, conservative radiation therapy of breast cancer using a wedge-filter combined with rectangular tangential irradiation was widely carried out. This method of irradiation creates uniform dose distribution in the target, minimizing the radiation dose to the lung. However, this method of irradiation results in many cases in which the amount of dose in the irradiated area differs as a result of the shape and size of the breast. It is necessary to prevent excessive doses from reaching the lung. IMRT ensures a uniform dose to the target. Therefore, IMRT was examined because of the possibility that the normal tissue dose can be effectively utilized in cases of conservative radiation therapy of breast cancer by providing a minimum dose. To compare the irradiation of each method of rectangular tangential irradiation, an electronic compensator (ELC), and IMRT, which uses Dynamic MLC, we evaluated target dose uniformity, standard deviation, and target differential DVH in 13 examples. We evaluated the lung dose of the irradiated side (V(30), 30 Gy volume) of the lung to the volume of the lung on the irradiated side based on the report of Hernando.(6)) With this method of irradiation, irrespective of the difference in the shape and size of the target, dose uniformity with ELC was very good. IMRT can reduce the lung dose in comparison with the other irradiation methods. However, it is apt to cause a high-dose area in the irradiation field. In addition, it affects the target and the skin-extracting contour, and the dose to the skin surface declines. Although ELC cannot offer lung doses that are as low as those of IMRT, most of the 13 examples planned for cure with ELC showed rates of 22% of V(30) and below. In conservative radiation therapy of breast cancer, ELC is more effective than the rectangular tangential irradiation method and IMRT.