Scatter dose from tangential breast irradiation to the uninvolved breast

Thermoluminescent dosimeters (TLDs) were used to measure scatter radiation to the uninvolved breast in 30 patients who received tangential breast or chest-wall radiation with a technique in which the deep edges of the tangential fields were aligned. In most patients, measurements were made during the 1st week of radiation therapy, after port radiographs were obtained to ensure proper field position and accurate alignment of the posterior tangential field edges. Phantom measurements were made simultaneously with TLD measurements to systematically assess the scatter dose as a function of the wedging, number of fields, type of accelerator, beam energy, and bolus used in each treatment. For most patients, the scatter dose to the contralateral breast at a point on the skin 5 cm outside the edge of the medial beam was 8%-13% of the prescribed dose. However, higher doses (up to 36% of the therapeutic dose) were recorded in some patients.