The purpose of this study was to assess mammographic and sonographic findings in a long-term follow-up (>or=3 years) after breast-conserving surgery (BCS) and IORT, either applied as boost or exclusively. Follow-up-findings of 54 patients were retrospectively evaluated and compared to a control group of 48 patients, treated with BCS and whole-breast radiotherapy. After IORT patients had a higher incidence of fat necroses manifesting as oil cysts in the late follow-up mammograms (n = 31 vs n = 8); furthermore, oil cysts were larger in the IORT group (median 4.5 vs 1.4 cm(2)). In 25 IORT patients the oil cysts arose from partially organized hematomas/seromas, which in this group were generally more frequent (n = 38 vs n = 9) and larger (median 3.6 vs 1.8 cm(2)). After IORT a decreasing incidence of hematomas/seromas was reciprocal to an increasing incidence of oil cysts, and the size of both entities correlated with each other. Liquid lesions with polypoid inner wall thickening on ultrasound, attributed to organized hematomas/seromas or fat necroses, appear more frequently after IORT (n = 15 vs n = 1). In conclusion, IORT is associated with a high incidence of large oil cysts, which arise from likewise large partially organized wound cavities. On ultrasound pronounced partial organization with polypoid inner wall thickening is a frequent finding in those cavities.

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