Radiation, especially subtherapeutic doses, has been proven to be carcinogenic. During therapeutic irradiation, normal tissue is exposed to some dose due to internal and external scatter from the primary beam. The dose to the contralateral breast during primary irradiation may cause secondary breast malignancies. For example, studies have shown that half-beam block techniques can dramatically increase the opposite breast dose. An attempt has been made to calculate the dose delivered during primary breast irradiation. Materials used will include previously published articles in medical and science journals. Preliminary results from a study currently being done by Marilyn Stovall will also be utilized. Isodose distributions demonstrating various treatment techniques will be shown.