Nina A. Mayr MD, Presenter: Nothing to Disclose

Jian Z. Wang PhD, Abstract Co-Author: Nothing to Disclose

Dongqing Zhang PhD, Abstract Co-Author: Nothing to Disclose

Edward Y. Kim MD, Abstract Co-Author: Nothing to Disclose

Kaile Li PhD, Abstract Co-Author: Nothing to Disclose

Adele Lipari DO, Abstract Co-Author: Nothing to Disclose

Rachel M Layman MD, Abstract Co-Author: Nothing to Disclose

et al, Abstract Co-Author: Nothing to Disclose

Delineation of breast tissue for breast radiation is becoming increasingly important with 3D conformal and IMRT planning. However, methods of delineation have been variable and inconsistent. This study evaluated the discrepancies among a surface marker based and CT-defined delineation of the breast target for 3D planning.

Two target delineation methods were compared in 20 archived planning CT data sets: (1) for the surface-marker method, the visible breast perimeter was wired on the skin, followed by 3-mm slice non-contrast CT imaging. The breast was contoured as delineated by the wire surface marker for medial and lateral, and by the chest wall for deep extent. (2) For the CT-defined method the breast was delineated based on CT-defined breast configuration, internal breast anatomy of fibroglandular breast tissue and tumor bed alone, and included the chestwall. Dosimetry was computed for 3D conformal therapy using segmented MLC technique for dose homogeneity. The two methods were compared with respect to breast target volume, extent of delineation in the medial, lateral, superior and inferior direction, and DVH parameters.

Mean target volumes were larger with the CT-defined method compared to the surface-marker method, 923 (357-1857) cm3 vs. 868 (394-865) cm3 (p=0.010). CT-defined delineation resulted in increased lateral contour extent in 10% and in increased medial contour extent 15%. Fibroglandular breast tissue was clearly identified and differentiated from non-glandular fat on CT in most, but in in 15% of patients, the internal breast anatomy was poorly defined and CT provided no significant guidance for breast delineation. Despite the significant differences in volumes and D90 among the surface-marker and CT-defined methods (46.78 vs. 47.49 Gy, p=0.040), V100 remained consistent within 1% among the two methods.

These preliminary results suggests wide variations between surface-marker delineation and CT-defined methods based on internal breast anatomy, but dosimetric consequences are small. Larger volumes for the CT-defined method may be related to inclusion of CT-defined breast tissue not appreciable by surface anatomy. A combination of the two methods may be most useful, particularly in patients with poorly visualized breast tissue.

Understanding of discrepancies between and optimal use of surface marker-based versus CT-imaging based breast delineation.

Mayr, N, Wang, J, Zhang, D, Kim, E, Li, K, Lipari, A, Layman, R, et al, , Surface Anatomy Maker Method versus CT-defined Target Delineation for Breast Radiation Therapy.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6019455.html