Radiological Assessment of the Anatomic Adequacy of Locoregional Lymphatic Radiotherapy Target Volumes for Locally Advanced Breast Cancer (LABC).
Authors: Dinniwell R. , Lee G. , Gregorio N. , Clemons M. 
Published: December 2010

Background: Women with LABC are at high risk of regional nodal metastases. Failure to control nodal disease can not only result in lymphedema and brachial plexopathy but may also reduce overall survival. Locoregional radiotherapy is typically delivered in an adjuvant manner using standard field borders. An analysis of the anatomic extent of lymphatic nodal disease at the time of presentation of LABC could provide insight into the adequacy of standard locoregional radiotherapy target volumes.Material and Methods: Staging CT and MRI DICOM image sets from a prospective LABC dataset were obtained for analysis. The locations of the lymph node metastases within the lymphatic nodal basins were transposed upon a reference CT DICOM image set in relation to relevant anatomic landmarks. The locoregional lymph nodes were classified into separate categories according to recognized boundaries (Dijkema et al.). Standard four-field borders to treat the breast/chest wall and regional lymphatics were defined and the percent coverage of the lymphatic nodal basins and the lymphatic metastases by 95% of the prescribed dose calculated. Radiotherapy treatment planning was completed using Pinnacle3 software (Version 8.0, Philips Medical System, Bothell, WA, USA).Results: From July 2006 to December 2008, 120 women with LABC were identified. Median age 52 years (range 27 to 93) with 64 left-sided and 56 right-sided primaries (1 cT1N1, 2 cT1N2, 6 cT2N0, 3 cT2N1, 3 cT2N2, 18 cT3N0, 30 cT3N1, 25 cT3N2, 2 cT3N3, 10 cT4N0, 9 cT4N1, 8 cT4N2, 1 cT4N3, 2 not available). The primary disease was situated within: all 4 quadrants and axillary tail in 14, centrally in 10, 3 quadrants in 1, 2 quadrants in 22 and 1 quadrant in 13 of the patients. Of the 60 woman analyzed to date, a total of 165 metastatic lymph nodes were identified by the radiographic staging investigations (127 level I axilla, 20 level II axilla, 4 level III axilla, 2 interpectoral, 2 medial supraclavicular, 1 lateral supraclavicular, 1 infraclavicular, 1 internal mammary, 7 intra-mammary lymph nodes). After placement of the four-field borders all of the lymphatic nodal basins were covered within the treatment fields except for the level I axillary, and lateral and medial supraclavicular regions, where the volume outside of the 95% prescribed dose was 18%, 6% and 28% respectively. With the exception of the level I axillary region, all of the metastatic lymph nodes were encompassed within each of the nodal basins and by the prescribed dose.Conclusions: Increased knowledge of the anatomical distribution of nodal disease in LABC patients prior to systemic therapy facilitates the validation of population based nodal clinical target volumes and affords assurance as to their adequacy. The lymph nodes identified in this series support the current definitions used to account for potential locoregional spread and may be used to further refine specific boundaries. With incorporation of the topographic distribution of gross nodal disease and the improving ability to detect micrometastatic disease, patient specific precision radiotherapy treatment planning is becoming possible.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4115.