document: Reproducibility of mammary gland structure during repeat setups in a supine position Purpose : In breast conserving therapy , complete excision of the tumor with an acceptable cosmetic outcome depends on accurate localization in terms of both the position of the lesion and its extent . We hypothesize that preoperative contrast-enhanced magnetic resonance -LRB- MR -RRB- imaging of the patient in a supine position may be used for accurate tumor localization and marking of its extent immediately prior to surgery . Our aims in this study are to assess the reproducibility of mammary gland structure during repeat setups in a supine position , to evaluate the effect of a breast immobilization device , and to derive reproducibility margins that take internal tissue shifts into account occurring between repeat setups . Materials Methods : The reproducibility of mammary gland structure during repeat setups in a supine position is estimated by quantification of tissue shifts in the breasts of healthy volunteers between repeat MR setups . For each volunteer fiducials are identified and registered with their counter locations in corresponding MR volumes . The difference in position denotes the shift of breast tissue . The dependence on breast volume and the part of the breast , as well as the effect of a breast immobilization cast are studied . Results : The tissue shifts are small with a mean standard deviation on the order of 1.5 mm , being slightly larger in large breasts -LRB- V > 1000 cm/sup 3 / -RRB- , and in the posterior part -LRB- toward the pectoral muscle -RRB- of both small and large breasts . The application of a breast immobilization cast reduces the tissue shifts in large breasts . A reproducibility margin on the order of 5 mm will take the internal tissue shifts into account that occur between repeat setups . Conclusion : The results demonstrate a high reproducibility of mammary gland structure during repeat setups in a supine position
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extractive_keyphrases: repeat setups supine position breast conserving therapy accurate tumor localization breast immobilization device reproducibility margins internal tissue shifts
abstractive_keyphrases: mammary gland structure reproducibility contrast-enhanced magnetic resonance imaging localization methods