Savelyi Belkin, Abstract Co-Author: Nothing to Disclose

Nina A. Mayr MD, Presenter: Nothing to Disclose

Lanchun Lu PhD, Abstract Co-Author: Nothing to Disclose

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

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

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

There is controversy about the optimal delineation of breast tissue for 3D conformal breast radiation and IMRT. Delineation methods have been inconsistent and surface anatomy-based targeting is frequently employed. Our previous work has shown discrepancies between surface marker based and CT anatomy based breast delineation. The current study evaluated the effect such discrepancies on breast and boost volume coverage.

Clinical target volume (CTV) delineation methods were compared in 30 archived breast planning CT data sets: For the surface-marker method, the breast perimeter was outlined with radiopaque wire on the skin. On the planning CT the wire surface markers were used for contouring. Dosimetry was computed for 3D conformal therapy using segmented MLC technique. For the CT-defined method the breast was delineated based on the CT-defined breast configuration and location of fibroglandular breast tissue. Differences between surface-marker and CT-defined delineation, and differences in dose volume coverage of breast and tumor bed were assessed. Dosimetry plans were reviewed and judged for the need of replanning based on the CT-defined contours.

Breast CTVs were smaller with the CT-defined method compared to the surface-marker method (mean 956, range 394-1889 cm3 vs. mean 1004, range 357-1927 cm3; p=0.001). D90 and V100 of the breast were similar (mean, 92% vs. 91%; 64% vs. 64%, respectively). Tumor bed volumes ranged from 6-260 cm3, and the distance from the tumor bed to the lung ranged from 0.2-4.2 (mean, 1.5) cm. Based on the added information from the CT-defined delineation, repeat dosimetry plans were judged necessary in 10 of the 30 cases. The CT-defined plans showed higher D90 for the tumor bed volume in 7 of the 10 cases, and in 7 of the 8 cases with far-laterally located tumor beds that were within 2 cm of the chest wall (p=0.034).

These preliminary results confirm significant variations between surface marker-based and CT-defined breast delineation. Although whole breast dose coverage does not significantly change, the coverage of the boost target may improve with CT-defined internal anatomy criteria, particularly in patients with deep and far-laterally located tumor bed.

Understanding of discrepancies between surface marker-based versus CT-defined breast delineation.

Belkin, S, Mayr, N, Lu, L, Zhang, D, Lipari, A, Wang, J, CT-defined Target Delineation versus Surface Anatomy Marker Method in Breast Radiation Therapy: Impact on Boost Volume Coverage.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8009952.html