Head Neck target Delineation


Applied Anatomy

Newer techniques of radiation therapy, specifically Intensity Modulated Radiotherapy (IMRT ), require detailed anatomical knowledge. Drawing the gross tumor volume requires interpretation of Computed tomography scans, Magnetic Resonance Imaging and FDG Positron Emission Tomography scans. Both clinical findings and imaging findings are taken together to define the gross tumor volume. For demonstration click here.

The major challenge for a radiation oncologist is to draw the clinical target volume. The questions that need to be asked prior to drawing CTV are

  1. What is the pattern of lymphatic spread?
  2. Which are the nodal levels most commonly involved?
  3. What is the frequency of involement in each nodal level?
  4. What are the anatomical boundaries of each nodal level?.
  5. How are these boundaries drawn on computed tomography scans?

This section focuses on the basic anatomy of the neck in reference to nodal levels.

The nomenclature used is as decscribed by Robbins, i.e., Levels I to VI. In addition, retropharyngeal nodes,which are not included in Robbins classification, are also described. The anatomical boundaries of nodal levels defined by Robbins are based on surgical procedures and the structures used to define the specific boundaries are not easily recognized on CT scans. The RTOG has published guidelines and an atlas which detail the procedure of drawing nodal levels on CT scans. Detailed anatomical description as per the nodal levels is given below.

Headneck Nodal Levels

  • Level 1a
  • Level 1b
  • Level II
  • Level III
  • Level IV
  • Level V
  • Level VI
  • Retropharyngeal Nodes