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Regional Lymph Node Delineation variability and its Dosimetric Impact in Breast Cancer Radiotherapy
1National Radiotherapy Trials Quality Assurance (RTTQA) Group, UK; Mount Vernon Cancer Centre, Northwood, UK.
Clinical Oncology (Royal College of Radiologists (Great Britain))
|April 19, 2025
Summary
Interobserver variability in breast cancer radiotherapy lymph node contouring was quantified. While all plans met dose constraints, variations impacted optimal dose objectives, indicating a need for improved delineation consistency.
Area of Science:
- Radiation Oncology
- Medical Physics
- Oncology
Background:
- Accurate delineation of clinical target volumes (CTVs) is crucial for effective radiotherapy (RT).
- Interobserver variability in contouring can impact treatment consistency and outcomes.
- The FAST-Forward (FF) trial aims to optimize breast cancer radiotherapy through standardized protocols.
Purpose of the Study:
- To quantify interobserver variability in regional lymph node delineation for breast cancer RT.
- To assess the relationship between contouring variations and dosimetric parameters using FF benchmark cases.
- To evaluate the concordance of nodal CTVs against a gold standard volume.
Main Methods:
- Principal investigators (PIs) delineated axillary lymph node CTVs (levels 1-4) as part of RT quality assurance (QA).
- Contouring concordance was evaluated against a consensus gold standard (GS) using conformity indices (CI): discordance index (DI), geographical miss index (GMI), Jaccard index (JCI), and mean distance to conformity (MDC).
- Dosimetric parameters were compared between plans conforming to GS and individual PI volumes using Wilcoxon signed-rank tests.
Main Results:
- Data from 29/33 PIs were analyzed, revealing a median submitted LNCTV volume of 131.4 cc versus a GS volume of 105.46 cc.
- Conformity indices indicated moderate agreement, with a median Jaccard index of 0.53, and evidence of both over- and under-contouring.
- All plans met mandatory dose constraints, but not all optimal dose objectives. Statistically significant dosimetric differences were observed for 7/13 organs at risk when comparing PI versus GS volumes.
Conclusions:
- Significant interobserver variability exists in axillary nodal CTV delineation for breast cancer RT.
- Despite moderate agreement based on conformity indices, contouring variations influenced the achievement of optimal dosimetric objectives.
- Standardization of lymph node contouring in RT is essential to ensure consistent treatment delivery and maximize therapeutic efficacy.
