Radiation Therapy

The general indications for radiation therapy are given in Table 18-11. Other sources should be reviewed for details of the port, dose, and methods of irradiation.

Studies by Tubiana et al (536), Simpson (537), and Riccabona (538) have clearly established the efficacy of radiotherapy in all types of thyroid cancer. Although its therapeutic use is now well accepted, its prophylactic use (e.g., in papillary or follicular lesions with possible residual disease, or in papillary or follicular Stage III lesions after RAI ablation) is controversial. Currently, we would first treat all papillary or follicular invasive or possibly metastatic tumors with RAI. In patients under age 55, it is not clear that x-ray therapy should be added. Over age 55, 131I therapy should be followed by x-ray treatment for Stage III or potentially Stage III lesions, and any recurrence or metastasis not responding to 131I may also be treated (539).

The efficacy of external radiation therapy in the management of thyroid malignancy has been reviewed by Brierley et al, Lin et al , Farahati et al, and Tsang et al. (540-543). Brierley recommends X-ray therapy in addition to ¹³¹I therapy in patients with papillary or follicular cancer who have probable or definitive microscopic residual disease. They gave 30 to 50 Gy over four weeks with the spinal cord dose less than 80% of the total. Radiotherapy was also advised for treatment of anaplastic thyroid carcinoma, in an attempt to achieve local control, using hyperfractionation, possibly with the addition of doxorubicin. Radiotherapy was used for treatment of lymphomas, with a total dose of 35 – 40 Gy given over four weeks, and was typically preceded by the use of CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) delivered every three to four weeks in three to six cycles prior to the radiotherapy. Cause-specific survival was 82% in patients who received combined therapy and 63% in those who got X-ray alone. Combined therapies were given to all patients except those with small bulk disease under 3 cm in size confined to the thyroid, who received radiation alone. Lin et al (543.1) evaluated 699 patients with differentiated thyroid cancer. After surgery 172 patients  in clinical stages 2 and 3 at the time of treatment received no radiotherapy, while 32 did.  They found no evidence that radiotherapy improved survival rate of patients with well differentiated thyroid cancer. These were patients with either neck nodes or local invasion. Farahati et al looked at patients with para-thyroidal tumor invasion and found that adjuvant external radiotherapy improved recurrence-free survival in patients over 40 years of age. Benefit was confined to patients with papillary thyroid carcinoma. Tsang et al also confirmed the benefit of radiotherapy in patients with papillary tumors who have microscopic or macroscopic residual disease.

In a recent study, Hurthle cell carcinoma of the thyroid gland was found to be a radiosensitive tumor. Adjuvant radiation therapy was successful in preventing recurrence in 4 of 5 patients. Salvage radiation therapy was successful in 3 of 5 patients treated with external beam radiation therapy. Palliative radiation therapy provided sustained symptomatic relief at 67% of irradiated sites. Radiation therapy may provide palliative relief from symptomatic metastases, control recurrent tumors, and prevent recurrence of advanced resected tumors(543a).
    The indications for MTC have been described above. Stage I-E lymphomas may be treated by chemotherapy or radiotherapy. Anaplastic lesions are currently given radiotherapy after operation. It is possible that chemotherapy should be used instead of or in addition to radiotherapy in these lesions, but studies are needed to establish this point.
    The exact dose must be individually determined, but usually the maximal dose is 5,000-6,000 rads, using ortho- or megavoltage, and a fractionated technique over several weeks. Dosage must be planned to assure that the spinal cord receives less than 3500 rads in order to avoid myelopathy.

Note- Spinal cord dose not to exceed *3000 or ** 3500 rads.