What anatomical landmarks are important for surface marking in palliative radiotherapy (RT) for bone metastasis, pelvic, head and neck region Squamous Cell Carcinoma (SCC), and thoracic regions?

Anatomical Landmarks for Surface Marking in Palliative Radiotherapy

The most critical anatomical landmarks for surface marking in palliative radiotherapy vary by treatment site and must be precisely identified to ensure accurate treatment delivery while minimizing radiation exposure to surrounding healthy tissues.

Bone Metastases Surface Marking

Key Anatomical Landmarks

• Spine:

  • Spinous processes for vertebral alignment
  • Iliac crests to identify L4-L5 junction (superior border)
  • Sacroiliac joints as reference points for field borders 1
  • Intertrochanteric line of femur for inferior border when treating pelvic metastases

• Pelvis:

  • Anterior-inferior iliac spine as lateral border reference 1
  • Inguinal crease for inferio-lateral border
  • Saphenofemoral junction (1.5-2 cm distal margin needed) 1
  • Femoral heads and necks (to be spared when possible)

• Long Bones:

  • Bony prominences (greater trochanter, epicondyles)
  • Joint spaces (proximal and distal to lesion)
  • 2-5 cm margins beyond radiographically visible disease

Head and Neck SCC Surface Marking

Primary Site Landmarks

• External Surface Markers:
  • Wire placement to define skin borders and gross tumor volume 1
  • Markers on anus, urethra, clitoris for perineal lesions
  • Radio-opaque markers on key landmarks during simulation 1

Nodal Regions Landmarks

• Cervical Lymph Nodes:

  • Mandible and mastoid process (superior border)
  • Hyoid bone and thyroid cartilage (mid-neck reference)
  • Clavicles and suprasternal notch (inferior border)
  • Sternocleidomastoid muscle borders

• Head and Neck Specifics:

  • Risk of false-negative sentinel lymph node biopsy is higher due to aberrant lymph node drainage 1
  • Multiple sentinel node basins often present 1
  • Radiation field for primary site often overlaps with draining lymph node beds

Thoracic Region Surface Marking

Key Anatomical Landmarks

• Lung Fields:

  • Sternal notch and clavicles (superior border)
  • Xiphoid process (inferior central reference)
  • Mid-axillary line (lateral border)
  • Vertebral bodies (posterior reference)

• Mediastinum:

  • For centralized tumors: assessment of esophageal toxicity required 1
  • For lateralized tumors: skin and lung toxicity assessment 1

Technical Considerations for Surface Marking

General Principles

• CT or MRI planning with image fusion technology recommended for all sites 1
• Radio-opaque markers should be placed on key landmarks during simulation 1
• Bolus should be used to ensure adequate dosing to superficial target volumes 1

Field Border Determination

• Superior field border: no lower than bottom of sacroiliac joints or higher than L4/L5 junction unless pelvic nodes involved 1
• If pelvic nodes involved: upper border can be raised 5 cm above most cephalad-positive node 1
• Inferior border: at least 2 cm below most distal part of target volume 1

Special Considerations by Region

Bone Metastases

• Anatomical sites for bone metastases vary widely, requiring individualized field design 1
• For spine lesions: include one vertebral body above and below the involved segment
• For pelvic metastases from head and neck SCC: thoracolumbar spine (34%) and pelvis (24%) are most common sites 2
• Notably, metastases to bones above the clavicle account for only 3% of all bone lesions in head and neck SCC 2

Palliative Dose Considerations

• For bone metastases: less protracted fractionation schedule (e.g., 30 Gy in 10 fractions) 1
• For head and neck palliation: consider anatomical limitations when determining dose and fractionation

Common Pitfalls to Avoid

1. Inadequate margins: Ensure wide margins (5 cm when possible) around primary site 1
2. Failure to account for patient positioning: Use immobilization devices appropriate for treatment site
3. Missing subclinical disease: Consider irradiating nodal beds even when clinically negative 1
4. Improper bolus use: Required for adequate skin dose in superficial lesions 1
5. Inadequate identification of bony landmarks: Can lead to geographic miss of target volume 3

Quality Assurance

• Consider using thermoluminescent dosimeter (TLD) at first treatment to confirm dose to target areas 1
• For electron beam treatments, select appropriate energy and isodose line (e.g., 90%) to deliver adequate lateral and deep margins 1

Surface marking accuracy is essential for palliative radiotherapy success, with proper identification of anatomical landmarks directly impacting treatment efficacy and patient quality of life.