External radiation therapy for thyroid cancer: Variable dose to the neck

Radiation treatment plan for a 47-year-old patient who presented with locally advanced MTC involving the left recurrent nerve and with esophageal and tracheal invasion. They had bilateral neck dissection: 4 out of 24 nodes were involved on the right and 20 out of 23 on the left with extracapsular invasion.

IMRT allows for giving variable dose to the neck depending on the risk of recurrence, while sparing as much normal tissue as possible. In this image, the lateral necks were included in the clinical target volume because the surgeon felt that another surgical resection of a subsequent recurrence in the neck was not possible.

The red shaded area represents the volume where there was gross disease before surgery, orange represents the area of potential residual disease, and the blue and green shaded area represents the volume of potential residual nodal disease. The volume of tissue within each line (isodose line) receives a minimum dose represented by that line. The yellow line is the 66 Gy isodose line (eg, the orange and red volumes within that line receive a minimum of 66 Gy). The mauve line is the 53.2 Gy isodose line (blue and green volumes receive a minimum of 53.4 Gy). Similar technique may be used for differentiated thyroid cancer.