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Variability of Target and Normal Structure Delineation for Breast-Cancer Radiotherapy: A RTOG Multi-Institutional and Multi-Observer Study

2007; Elsevier BV; Volume: 69; Issue: 3 Linguagem: Inglês

10.1016/j.ijrobp.2007.07.131

1879-355X

X.A. Li, D.W. Arthur, Thomas A. Buchholz, Stuart MacDonald, L.B. Marks, L.J. Pierce, Alphonse G. Taghian, F.A. Vicini, Wendy A. Woodward, Jared White,

Advances in Oncology and Radiotherapy

To quantify the multi-institutional and multi-observer variability of target and organ-at-risk (OAR) delineation for breast-cancer radiotherapy (RT), and its dosimetric impacts, as a part of a RTOG effort to establish a breast cancer atlas. Eight radiation oncologists specialized in breast RT from seven institutions independently delineated targets and OARs on the CT images of three representative patients of breast cancer, Case A: Stage I, left breast with lumpectomy to undergo breast RT, Case B: stage IIIB, left breast with mastectomy and planned for nodal and chest wall RT, and Case C: Stage IIIA, right breast with lumpectomy and planned for breast and nodal RT. The targets (e.g., lumpectomy cavity, lumpectomy PTV, breast, supraclavicular nodes, axillary nodes, internal mammary nodes, chest wall) and OARs (e.g., heart, lung) were delineated. Inter-observer differences in the delineation were quantified with regard to volume, distance between centers of mass (DCOM), percent overlap (PO), and average surface distance (ASD). The mean, median and standard deviation for theses quantities were calculated for all possible combinations. To assess the impact of these variations on treatment planning, representative dosimetric plans based on observer-specific contours were generated. The variations between the institutions/observers for selected target and OAR delineation are presented in the Figure below. These variations were generally substantial and related both to differences in opinion regarding clinical target boundaries as well as approach to incorporation of dosimetric limitations in target delineation. The difference in lumpectomy and breast volumes between different observers was as high as 35% and higher differences were observed for nodal volumes. These variations would result in substantial changes in dosimetric planning if fields were applied to cover targets as drawn. For example, tangential fields designed to treat the breasts, as defined by different observers for Case A, resulted in the heart V20 (percentage volume receiving 20 Gy) varying from 2% to 14%. The differences in target and OAR delineation for breast irradiation between institutions/observers appear to be clinically and dosimetrically significant. A systematic consensus on the delineation needs to be established, particularly in the era of IMRT and IGRT.