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Interobserver Variation Within Planning Target Volume and Organs at Risk in a Patient with Oropharyngeal Carcinoma: A
Fabian Baier1, Oliver Koelbl1, Felix Steger1
1Klinik und Poliklinik für Strahlentherapie, Universitätsklinikum Regensburg, 93053 Regensburg, Germany.
Current Oncology (Toronto, Ont.)
|January 27, 2026
Summary
Interobserver variability in radiotherapy contouring for oropharyngeal cancer is significant, particularly for lymph nodes and organs at risk. Structured anatomical assessment can improve consistency and patient outcomes.
Area of Science:
- Radiation Oncology
- Medical Imaging
- Anatomical Delineation
Background:
- Interobserver variability (IOV) in radiotherapy planning impacts treatment quality.
- Contouring guidelines and advanced imaging have not eliminated IOV in target and organ delineation.
Purpose of the Study:
- To examine variations in planning target volume (PTV) and organs at risk (OARs) delineation.
- To assess variability in lymph node level inclusion within the PTV.
Main Methods:
- Ten radiation oncologists contoured PTVs and 16 OARs for an oropharyngeal carcinoma patient.
- Interobserver variation was quantified using volume statistics, coefficient of variance (CoV), and conformity index (CI).
Main Results:
- High agreement in delineating ipsilateral lymph node levels Ib-IVa and VIIa+b.
- Significant discrepancies noted for cervical triangle and supraclavicular nodes.
- Greatest variability in OARs involved the inner ears (volume ranges 0.11-2.84 cm³).
Conclusions:
- Significant IOV persists in PTV and OAR delineation for oropharyngeal cancer.
- Elective lymph node inclusion and margin definition are key factors contributing to IOV.
- Structured anatomical assessment can minimize variability and enhance treatment consistency.
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