What are the differences and similarities between Radiation Therapy (RT) contouring guidelines by Radiation Therapy Oncology Group (RTOG), European Society for Radiotherapy and Oncology (ESTRO), and the Danish Breast Cancer Cooperative Group in treating breast cancer?

Comparison of RT Contouring Guidelines for Breast Cancer

The ESTRO consensus guideline provides the most detailed and anatomically precise target volume delineation with specific vessel-based landmarks, while RTOG guidelines offer broader regional definitions, and the Danish Breast Cancer Cooperative Group (DBCG) provides practical national consensus with quantified inter-observer agreement metrics. 1, 2

Key Structural Differences

Target Volume Definition Approach

• ESTRO guidelines utilize a vessel-based approach with 5mm margins around large veins running through regional lymph node levels, providing anatomically precise boundaries for clinical target volumes (CTVs) 1
• RTOG guidelines define target volumes by anatomical regions (supraclavicular, infraclavicular, axillary, internal mammary) with prescription depth varying based on patient size 3
• DBCG guidelines developed through iterative dummy-runs with seven experienced radiation oncologists, achieving consensus through quantified Dice similarity coefficient (DSC) measurements to ensure reproducibility 2

Regional Nodal Coverage Specifications

Guideline	Supraclavicular Field	Internal Mammary Nodes	Axillary Coverage	Special Features
ESTRO	Includes caudal lymph nodes surrounding subclavicular arch and base of jugular vein [4,1]	5mm margin around internal mammary vessels [1]	Levels 1-4 individualized based on risk [3]	Vessel-based anatomical landmarks [1]
RTOG	Paraclavicular area with variable prescription depth [3]	Internal mammary artery/vein as surrogate for nodal location [3]	Standard axillary apex coverage [3]	Prescription depth varies by patient size [3]
DBCG	Consensus-based delineation with DSC validation [2]	Standardized contouring atlas provided [2]	Post-ALND coverage specified [2]	National consensus with online atlas [2]

Dosimetric and Clinical Implications

Thyroid Dose Differences

• RTOG contouring results in significantly higher thyroid doses across all treatment modalities (higher Dmax, Dmean, V30, V45, EUD, and NTCP) compared to ESTRO guidelines 5
• This difference persists across IMRT and VMAT techniques 5

Target Coverage Variations

• ESTRO guidelines with VMAT technique produce significantly higher equivalent uniform dose (EUD) and tumor control probability (TCP) for planning target volume (PTV) 5
• ESTRO-based plans demonstrate superior conformity index (CI) when using VMAT compared to RTOG-based plans 5
• Other organs-at-risk (OAR) doses remain similar between guidelines except for thyroid 5

Inter-Observer Variability

DBCG Consensus Impact

• Before consensus implementation, DSC values were modest for most volumes except breast CTV and heart 2
• After consensus adoption, DSC increased for all volumes, demonstrating improved inter-delineator agreement 2
• The DBCG provides the only guideline with quantified reproducibility metrics 2

Areas of Greatest Variability

• Supraclavicular CTV represents the highest risk area for geographical miss across all guidelines 6
• Major differences in anatomical and radiological delineation exist among physicians without standardized protocols 7
• Simplified written delineation protocols significantly improve consistency 7

Clinical Application Recommendations

Guideline Selection by Clinical Scenario

• For regional nodal irradiation in advanced disease: ESTRO guidelines provide the most comprehensive and individualized approach, specifying that in regionally advanced disease, individualization is required 3
• For standardized clinical trial protocols: DBCG guidelines offer validated reproducibility with quantified inter-observer agreement 2
• For routine practice with variable patient anatomy: RTOG guidelines accommodate prescription depth variation based on patient size 3

Technical Planning Considerations

• CT-based treatment planning is mandatory across all guidelines to identify lung and heart volumes and minimize exposure 3
• ESTRO vessel-based landmarks (5mm margin around large veins) provide the most reproducible anatomical boundaries 1
• Internal mammary node delineation uses internal mammary artery/vein location as surrogate in RTOG, while ESTRO specifies precise vessel-based margins 3, 1

Critical Pitfalls to Avoid

Supraclavicular Field Coverage

• The supraclavicular CTV is the most common site of geographical miss when guidelines are not followed precisely 6
• ESTRO specifies inclusion of the most caudal lymph nodes surrounding the subclavicular arch and base of jugular vein 4, 1
• Inadequate superior border definition leads to underdosing of at-risk nodal regions 6

Post-Surgical Considerations

• After ALND, the resected axilla should not be irradiated except with clear residual disease, per ESTRO recommendations 3
• After positive SLNB without ALND, regional RT extent varies: lowest risk receives no RT, intermediate risk receives level 1-2 RT, highest risk receives full level 1-4 RT including internal mammary nodes 3

Neoadjuvant Chemotherapy Impact

• Target volumes should be based on worst stage pre-treatment or post-treatment characteristics in patients receiving neoadjuvant chemotherapy per NCCN/RTOG approach 3
• ESTRO allows individualization based on clinical tumor stage combined with tumor response 3