Abstract
Purpose: Postoperative radiotherapy has been delivered with wedged tangential fields, optimized isodose distribution without inhomogeniety corrections in a single central-axis. Three-dimensional radiation treatment planning systems (3D-RTPS) is now available and its utility for breast irradiation should be evaluated. We evaluated MLC segment technique whether it improves dose uniformity within target volume and reduces the dose delivered in normal tissue.
Methods and Materials: Twenty-four consecutive patients with breast cancer undergoing lumpectomy and adjuvant breast radiotherapy were treated in our hospital from April to September 2000. Using 3D-RTPS, standard wedge technique and MLC segment technique were evaluated according to the following parameters; maximum absorbed dose in field, dose conformity in PTV (volume of PTV with dose outside 95-105% of the prescribed dose), absorbed dose in ipsilateral lung (volume with dose larger than 100% of the prescribed dose), and absorbed dose in contralateral breast (maximum dose and mean dose).
Results: Significant improvement in the doses PTV and critical structures were achieved using MLC segment technique. Compared with standard wedge technique, MLC segment technique decreased 6% of the maximum absorbed dose, improved 50% of dose homogeneity within the planning target volume, and decreased 50% of the maximum dose and 25% of mean dose to the contralateral breast. The ipsilateral lung volume receiving more than 100% of the prescribed dose was not significantly changed.
Conclusion: MLC segment technique can significantly improve dose uniformity within PTV and decrease the maximum dose in the field and the dose of critical structures. It is suggested that customized 3D treatment planning for breast irradiation should be clinically applied to improve treatment outcome.
