Radiotherapy planning techniques for thyroid cancer.

Abstract

External beam radiotherapy has a role in each histological type of thyroid cancer. For treatment confined to the thyroid bed, an antero--oblique wedged pair of beams is simple to apply. More frequently, however, the volume needs to include both sides of the neck and adequate dose must be given down to the level of the suprasternal notch, precluding use of lateral fields. Thus, anterior and posterior fields are usually necessary, extending from the tips of the mastoid processes or hyoid down to the carina and laterally to include both sides of the neck and supraclavicular fossae. The mandible and infraclavicular portions of both lungs are shielded, but there is no midline lead in the phase one volume. A mid-plane dose of 46 Gy given in 23 daily fractions results in an acceptable early radiation reaction and will avoid late damage to the spinal cord. Because of considerable variation of interplanar distance along the length of the volume, a lateral simulator film should be taken to determine the maximum cord dose. For most patients, a three-dimensional CT planned phase two volume will be required and should be determined prior to completing phase one. The optimum beam arrangement, usually incorporating conformal beam shaping assisted by use of a multileaf collimator, should avoid further dose to the cord. If there is additional dose to the spinal cord, this phase can be introduced before 46 Gy is reached.

The Role of Radiotherapy in the Management of Elevated Calcitonin After Surgery for Medullary Thyroid Cancer

“…The target volume for radiotherapy comprised the thyroid bed, both sides of the neck, and superior mediastinum. Patients were treated on a 5-or 6-mV linear accelerator with anterior and undercouched fields to 46 Gy for phase one, followed by a computerplanned reduced volume phase two to a total dose of 60 Gy in 30 daily fractions over 6 weeks (13). Three patients were treated with the same dose but with a wedged pair of fields to the thyroid bed only.…”

Medullary thyroid cancer

“…• Overall, MTC is a moderately radiosensitive tumor and a dose of 60 Gy is best when used over several weeks (hyperfractionated radiotherapy). The area of irradiation for locoregional MTC should encompass the cervical area (including the lateral cervical lymph node compartments) and the upper mediastinum [23]. The most severe complications from external beam radiotherapy is myelitis with an estimated risk of less than 0.5% for doses of 57 to 61 Gy [23].…”

“…The area of irradiation for locoregional MTC should encompass the cervical area (including the lateral cervical lymph node compartments) and the upper mediastinum [23]. The most severe complications from external beam radiotherapy is myelitis with an estimated risk of less than 0.5% for doses of 57 to 61 Gy [23]. When the dose is fractionated and delivered over 5 to 6 weeks, the risk of myelopathy is significantly lowered.…”

“…Other complications of external radiotherapy include esophagitis or laryngitis, which are usually acute and transient. Esophageal stricture or dysmotility occurs as a late complication in about 5% of patients when doses of 45 to 60 Gy are used [23]. …”

Treatment of advanced differentiated thyroid carcinoma with high activity radioiodine therapy

“…Recommended activities vary between 3.7 GBq and 11.1 GBq, with reported side effects becoming commoner with higher cumulative levels [2][3][4]. Apart from radioiodine treatment following initial thyroid surgery, adjuvant external beam radiotherapy and surgical removal of individual metastases still have important roles in the management of advanced DTC [5][6][7]. Chemotherapy is of limited value.…”