Abstract
Simple SummaryThe purpose of the current in silico planning study is to compare radiation doses of whole-breast irradiation (WBI) and whole-breast plus regional lymph node irradiation (WBI+RNI) administered to the regional lymph nodes (RLN) in pN1 breast cancer. Twenty-four participating institutions were asked to create plans of WBI and WBI+RNI for two dummy cases. In all RLN regions including supraclavicular lymph node, axillary lymph node, and internal mammary lymph node, the radiation dose to the RLN was higher in WBI+RNI plan than WBI plan.The purpose of the current in silico planning study is to compare radiation doses of whole-breast irradiation (WBI) and whole-breast plus regional lymph node irradiation (WBI+RNI) administered to the regional lymph nodes (RLN) in pN1 breast cancer. Twenty-four participating institutions were asked to create plans of WBI and WBI+RNI for two dummy cases. To compare target coverage between the participants, an isodose line equal to 90% of the prescribed dose was converted to an isodose contour (contour90% iso). The relative nodal dose (RND) was obtained using the ratio of RLN dose to the target dose. The Fleiss’s kappa values which represent inter-observer agreement of contour90% iso were over 0.68. For RNI, 6 institutions included axillary lymph node (ALN), supraclavicular lymph node (SCN), and internal mammary lymph node (IMN), while 18 hospitals included only ALN and SCN. The median RND between the WBI and WBI+RNI were as follows: 0.64 vs. 1.05 (ALN level I), 0.27 vs. 1.08 (ALN level II), 0.02 vs. 1.12 (ALN level III), 0.01 vs. 1.12 (SCN), and 0.54 vs. 0.82 (IMN). In all nodal regions, the RND was significantly lower in WBI than in WBI+RNI (p < 0.01). In this study, we could identify the nodal dose difference between WBI and WBI+RNI.
Highlights
Whole-breast irradiation (WBI) after breast-conserving surgery (BCS) reduces locoregional recurrence and improves survival in patients with breast cancer [1]
In an evaluation of relative radiation dose for regional lymph nodes (RLN) in both treatment arms, we found that significant proportions of radiation were unintentionally delivered to axillary lymph node (ALN) level I and internal mammary lymph node (IMN) in the whole-breast irradiation (WBI) arm
Prophylactic irradiation of supraclavicular lymph node (SCN) and IMN was provided for patients with pN1 breast cancer to eliminate microscopic tumor foci in RLN regions [8]
Summary
Whole-breast irradiation (WBI) after breast-conserving surgery (BCS) reduces locoregional recurrence and improves survival in patients with breast cancer [1]. Including RNI was expected to prevent systemic spreading of cancer and to improve the survival of the patient [2]. RNI was significantly associated with improved disease-free survival (DFS) in patients with high-risk node-negative or pN1 breast cancer [5,6]. In these studies, only a small proportion of patients received contemporary systemic treatments such as taxane or anti-HER2 agents that have been proven to improve locoregional control. It is necessary to evaluate the prognostic impact of RNI in pN1 breast cancer patients receiving contemporary systemic treatments
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