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Quantitative assessment of inter-observer consistency in target volume delineation following breast-conserving
An Yi1,2, Lihong He1,2, Zijie Wang3
1Jiangxi Medical College, Nanchang University, Nanchang, China.
Background:
Consistent clinical target volume (CTV) delineation is vital for breast cancer radiotherapy. While organs-at-risk definitions are increasingly automated, manual CTV delineation of complex post-surgical volumes remains highly observer-dependent, potentially compromising treatment homogeneity.
Objective:
To quantify inter-observer discrepancies in postoperative breast cancer CTV contouring among regional oncologists and to qualitatively analyze the reasons for these contouring discrepancies to promote standardization and quality assurance.
Methods:
Based on CT datasets of two representative post-surgical breast cancer cases (BCS and MRM), 22 frontline radiation oncologists from regional municipal hospitals independently contoured the required CTVs. Inter-observer contouring discrepancies across these manual target volumes were quantitatively evaluated via Dice similarity coefficients (DSC) and Hausdorff distances (HD) against a consensus reference standard established through a two-expert consensus workflow.
Results:
A total of 20 completed datasets, each for both the BCS and MRM cases, were successfully retrieved and analyzed. The large volumes achieved the highest overlap (CTVp_breast and CTVp_thoracic wall DSC mean: 0.80 ± 0.07 and 0.63 ± 0.08, respectively), though mean 95% Hausdorff distances (HD95) were elevated at 42.84 ± 50.62 mm and 45.73 ± 60.44 mm. Post-BCS focal volumes (CTV_tb and CTV_boost) showed intermediate overlap (both DSC mean: 0.56) but restricted boundary deviations (mean HD95: 11.51 mm and 19.94 mm). For nodal stations, consistency was moderate for the supraclavicular volume (CTVn_L4 DSC mean: 0.57 ± 0.15, HD95: 26.21 ± 15.08 mm) but dropped substantially for axillary Level III (CTVn_L3 DSC mean: 0.38 ± 0.26, HD95: 37.95 ± 37.94 mm) and internal mammary nodes (CTVn_IMN DSC mean: 0.42 ± 0.14, HD95: 42.67 ± 25.70 mm).
Conclusion:
Delineation consistency is acceptable for large volumes (CTVp_breast and CTVp_thoracic wall) but poor for regional nodal stations, demonstrating that standardized anatomical training is crucial to improve radiotherapy uniformity.
