What are the recommended two‑dimensional radiotherapy field borders and margins for treating supraglottic carcinoma?

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2D Radiotherapy Field Borders for Supraglottic Cancer

For supraglottic carcinoma treated with 2D radiotherapy, field margins should be 1.5-2 cm beyond the gross tumor volume for tumors >2 cm, and 1-1.5 cm for smaller lesions, with field sizes generally larger than 7×7 cm to adequately cover bilateral cervical lymphatics at risk. 1, 2

Field Size and Margin Recommendations

Primary Tumor Coverage

  • Tumors <2 cm: Use 1-1.5 cm field margins around the gross tumor volume 1
  • Tumors ≥2 cm: Use 1.5-2 cm field margins around the gross tumor volume 1
  • Minimum field size: Fields smaller than 7×7 cm result in significantly higher neck failure rates (18% vs 3%, p=0.00005), particularly in early-stage disease 2

Critical Anatomic Considerations

  • Superior border: Must include the base of tongue and valleculae, as the tongue base-supraglottic complex develops from one central embryologic region 3
  • Inferior border: Should extend to cover the supraglottic larynx adequately 4
  • Lateral borders: Must encompass bilateral cervical lymphatics, as supraglottic tumors have bilateral lymphatic drainage patterns 5

Nodal Coverage Requirements

Bilateral Neck Treatment

  • Bilateral neck irradiation is mandatory for supraglottic carcinomas due to high risk of bilateral nodal involvement (44% incidence in clinically N0 patients) 5
  • Field size significantly impacts regional control: larger fields (>7×7 cm) reduce neck failure from 18% to 3% 2
  • Even in clinically N0 necks, 30% harbor occult metastases, with 100% involving level II and 82% involving level I nodes 5

Specific Nodal Levels

  • Levels I-IV must be included bilaterally in the radiation field for adequate coverage of regions at highest risk 5
  • The submandibular triangle (level I) and upper jugular nodes (level II) are consistently involved and require coverage 5

Dose Considerations

Primary Site Dosing

  • T1-T2 lesions: 50-55 Gy in conventional fractionation (1.8-2.0 Gy per fraction) 1, 2
  • T3-T4 lesions: 66-70 Gy for definitive treatment 1
  • No significant dose-response relationship exists over the range of 1650-2300 ret for supraglottic cancer 2

Regional Nodal Dosing

  • Clinically negative but at-risk nodes: 50 Gy over 5 weeks 1
  • Clinically evident adenopathy: 66-70 Gy over 6.6-7 weeks 1

Critical Pitfalls to Avoid

Field Size Errors

  • Avoid undersized fields: The most common technical error is using fields <7×7 cm, which dramatically increases neck failure rates from 3% to 18% 2
  • This applies particularly to early-stage disease where the temptation to use smaller fields is greatest 2

Inadequate Nodal Coverage

  • Do not treat unilaterally: Even for lateralized tumors, bilateral neck treatment is required due to the 44% bilateral involvement rate 5
  • Include level I nodes: Failure to include the submandibular triangle results in inadequate coverage, as 82% of occult disease involves this level 5

Treatment Outcomes by Stage

Local Control Rates with Adequate Fields

  • T1: 92-100% local control 4, 6
  • T2: 80-88% local control 4, 6
  • T3: 68-79% local control 4, 6
  • T4: 56% local control 4, 6

Regional Control

  • N1 disease: 71% control 4
  • N2 disease: 38% control 4
  • N3 disease: 25% control 4
  • Preoperative radiotherapy with radical neck dissection prevents recurrence in the dissected neck 4

Technical Setup Parameters

Beam Arrangement

  • Use opposed lateral fields (AP-PA or lateral-lateral technique) for 2D planning 1
  • Megavoltage photons with energies of 4-6 MV are recommended 1
  • All fields should be treated daily, 5 days per week 1

Margin Expansion for Setup Error

  • Add 0.5 cm uniform expansion for setup uncertainty 1
  • Provide 0.7 cm margin from planning target volume to block edge to account for beam penumbra 1

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Research

Supraglottic laryngeal carcinoma: an analysis of dose-time-volume factors in 410 patients.

International journal of radiation oncology, biology, physics, 1983

3
Research

Carcinoma of the tongue base.

Folia medica, 2005

5
Research

Patterns of nodal metastasis and surgical management of the neck in supraglottic laryngeal carcinoma.

Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery, 1999

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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