Evaluating the variability of depth of supraclavicular and axillary lymph nodes in patients with breast cancer and its role in radiotherapy treatment planning

Introduction: Radiation therapy has traditionally been used to treat patients at high risk formicroscopic residual disease of the supraclavicular (SCV) and axillary level III regions,resulting in rates of regional failure as first failure of only 0.0%–1.5%. Historically, the SCVnodes and the axillary level III have been treated by using a single anterior field, with fulldose prescribed to a point in the SCV fossa 30mm deep to the surface of the skin. Uniformdosing to a depth of 30mm in all patients for an arbitrarily defined nodal volume is ofconcern, given the range in body habitus, weights, and depth of subcutaneous adipose tissueamong individuals. Thus, the goals of this study were to delineate on CT scans the anatomicregions containing the SCV and axillary level III nodal groups, to measure their depth andfind a relation between BMI and these measures.Materials and Methods: CT scans with 2mm intervals were obtained in 35 patients at ImamHossein Hospital from Jan 2012 till Apr 2012. All patients were treated in the supine positionwith the ipsilateral arm elevated above the head. Then, patients were divided into threegroups based on Body Mass Index (BMI) measurements: class 1 (BMI ≤24.9), class 2 (BMI=25-29.9), and class 3 (BMI≥30).Results: Depths of lymph nodes between class 3 and classes 1 and 2 were statisticallysignificant. Although class 2 patients had deeper lymph nodes, their difference with class 1was not statistically significant. All patients had maximum supraclavicular nodes’ depth of<38.8mm. Therefore, it seems that treating this area at the depth of 30mm would result inproper lymph node coverage. However, treating axillary level III nodes at the depth of 30mmwould result in underdosage in the majority of patients. Based on BMI, in class 1 patientsdepth of 47 mm, in class 2 patients depth of 53 mm, and in class 3 patients depth of 60 mmwould properly cover > 90% of axillary level III lymph nodes.Conclusions: Axillary level III nodes are best treated by individual CT-based planning. Forextremely busy centers, determining the depth of lymph nodes by using patients’ BMI seemsto be an appropriate alternative.

Keywords:

Breast radiotherapy , axillary , lymph node