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Internal Mammary Node Coverage - An Investigation of Presently-Accepted Techniques

John Han-Chih Chang, MD
OncoLink Assistant Editor
Last Modified: November 1, 1999

Presenter: Douglas Arthur, MD
Affiliation: Virginia Commonwealth University/Medical College of Virginia

Background:
The Internal mammary nodes (IMNs) are found lateral to the internal mammary vessels from the 1st rib to the 4th intercostal space. Radiation therapy (RT) to this area can be administered using various techniques. The purpose of this investigation was to determine which of the three accepted techniques would provide the most adequate IMN coverage with least dose to normal tissues.

Materials and Methods:

• Five patients who had CT scans for target planning purposes were evaluated for dose volume histograms of the target (breast and regional lymph nodes including special attention to the IMN's) and normal tissues (lung and heart).
• The three techniques investigated were:
  1. Extended tangents with a supraclavicular field,
  2. 5 field technique (with electrons and photons to the IMN region and medial breast) and,
     
  3. The partly wide tangents with a supraclavicular field.
     The standard tangent along with a supraclavicular field was also utilized for comparision.

• All of the approaches to treat the IMN's increase the irradiated lung and heart volume by 10 - 15%.
• The superior aspect of the IMN chain is the most difficult to get adequate coverage due to the patient anterior chest wall thickness in that region. Underdosing can be in the range of 15% to 35% in some techniques with some patients.
• The 5 field technique seemed to have the highest increase in dose to normal tissue volume, while the partly extended tangents had the best IMN coverage with the least increase lung and heart volume treated.

Clinical/Scientific Implications:

1. Multiple techniques exist in addressing IMN with RT. The authors demonstrated what can be accomplished with each in relation to standard tangents, which do not directly address IMNs.
2. Which is the "correct" technique remains unknown. It seems with the differences in patient's anatomy, each case must be individualized. Technique must be chosen based upon a careful planning.
3. Only further long term data will demonstrate whether IMN RT is required in all or any situation with the ongoing accrual of two European randomized trials addressing regional lymph node RT.

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