To introduce computed tomography for the detection of post-surgical intramammarian lesions, exposing risk factors for subsequent radiation therapy. 104 patients with breast cancer were treated. They previously underwent breast conserving carcinoma treatment and were subsequently irradiated. The techniques were planned individually based on a CTdata set. All the acquired slices were evaluated with regard to seromas, larger tissue defects or organized hematomas. Seromas and tissue defects are raising the rate of byeffects during radiation therapy and deteriorating the cosmetic results. Pretherapeutical CT allows the puncture of hidden seromas and the individual adaptation of the irradiation technique in order to avoid overdosage due to tissue defects. Therefore CT is valuable for all patients prior to radiation therapy.