It is essential to choose delivering the energy in electron irradiation and to determine the thickness of the lung tissue that is radiated in patients who has the indication of postoperative irradiation of the chest wall. For practical purposes ultrasonography has been used to find average values by measuring the thickness of the chest wall. For normal and thin patients the value following simple mastectomy was 2 cm, for obese patients it was 2.9 cm. The thickness to be irradiated following modified radical mastectomy has been determined as 1.5 cm in normal and thin patients; 2.5 cm in obese patients . For making a schedule of the treatment data from ultrasound and computerized tomography have been compared.