Background: The purpose of this study was to evaluate nodal irradiation with conventional three-field's technique. Materials and Methods: Fifty patients with breast cancer were enrolled in this study. Computed tomography scans in the supine treatment position were imported into a treatment planning system. Levels I-III axillary and supraclavicular nodes were identified and their depths to the anterior skin surface were measured. Two tangential fields and one anterior- posterior supraclavicular field were developed to treat all of the patients. Dose –volum histogram was evaluated for quality measurement. Results: The mean depths of the level I, II and III axillary and supraclavicular nodes varied widely (4.6, 5.7, 6.1 and 5.9 cm, respectively). Complete coverage of level II was not achieved by tangential fields. In some patients the optimal dose was not prescribed. The median dose administered to level I, II and III was 42.6 Gy (10 to 53 Gy), 41.9 Gy (8.3 to 54 Gy) and 41.3 Gy (5 to 52 Gy), respectively. The median dose to supraclavicular nodes was 46.9 Gy (from 38 to 51 Gy).The mean regional nodal volumes included in the 95% isodose were 47, 48, 45.7, and 65.1 percent for level I-III and supraclavicular, respectively. Conclusion: As the depth of regional nodes varies widely, thus using a fixed calculation depth for dose prescription is not optimal. Careful depth measurement for each patient is necessary. Moreover, the use of conventional three- field technique is not optimal for all patients. At least in some patients, adding posterior axillary boost field is necessary, to optimize axillary coverage.