Analysis on the Dosimetric Characteristics of Tangential Breast Intensity Modulated Radiotherapy

Yoon, Mee Sun; Kim, Yong Hyeob; Jeong, Jae Uk; Nam, Taek Keun; Ahn, Sung Ja; Chung, Wong Ki; Song, Ju Young

Abstract

The tangential breast intensity modulated radiotherapy (T-B IMRT) technique, which uses the same tangential fields as conventional 3-dimensional conformal radiotherapy (3D-CRT) plans with physical wedges, was analyzed in terms of the calculated dose distribution feature and dosimetric accuracy of beam delivery during treatment. T-B IMRT plans were prepared for 15 patients with breast cancer who were already treated with conventional 3D-CRT. The homogeneity of the dose distribution to the target volume was improved, and the dose delivered to the normal tissues and critical organs was reduced compared with that in 3D-CRT plans. Quality assurance (QA) plans with the appropriate phantoms were used to analyze the dosimetric accuracy of T-B IMRT. An ionization chamber placed at the hole of an acrylic cylindrical phantom was used for the point dose measurement, and the mean error from the calculated dose was 0.7+/-1.4%. The accuracy of the dose distribution was verified with a 2D diode detector array, and the mean pass rate calculated from the gamma evaluation was 97.3+/-2.9%. We confirmed the advantages of a T-B IMRT in the dose distribution and verified the dosimetric accuracy from the QA performance which should still be regarded as an important process even in the simple technique as T-B IMRT in order to maintain a good quality.