Acute toxicity of adjuvant radiotherapy in locally advanced differentiated thyroid carcinoma. First results of the multicenter study differentiated thyroid carcinoma (MSDS).

BACKGROUND AND PURPOSE

The indication for adjuvant postoperative radiotherapy in patients with differentiated thyroid carcinoma (DTC) extending beyond the thyroid capsule has been an issue of controversy during the past 2 decades. No randomized studies evaluating the benefit of radiotherapy have been published so far. In the Multicenter Study Differentiated Thyroid Carcinoma (MSDS), a randomization has been performed concerning external-beam radiotherapy in patients with DTC extending beyond the thyroid capsule (pT4 pN0/1/x cM0, TNM classification, 5th edition, 1997) following surgery and radioiodine therapy. Radiation-associated toxicity has been prospectively evaluated.

PATIENTS AND METHODS

Radiotherapy was performed with 50.4 Gy (pN0) or 54.0 Gy (pN1/x) to the cervical, supraclavicular and upper mediastinal lymph nodes. A total dose of 59.4 Gy (R0 resection) or 66.6 Gy (R1) was used to treat the tumor bed. Conventional fractionation was used with 1.8 Gy/d. At the time of the analysis, 36 patients were randomized or allocated to treatment arm A (with external-beam radiotherapy). Of these, 22 were treated with radiotherapy, and documentation of acute toxicity was available. Toxicity was evaluated prospectively according to the RTOG/EORTC criteria.

RESULTS

The maximal acute toxicity observed during radiotherapy was grade I in four patients, grade II in 16 patients, and grade III in two patients (9.1%; 95% confidence interval [95% CI] 1.1-29.2%). Toxicity was mainly observed at the pharynx, larynx, and skin. In 19 patients, residual toxicity within 100 days following radiotherapy was evaluated. No residual toxicity was observed in two patients. Maximal residual toxicity was grade I in 13 patients and grade II in four. No further grade III toxicity could be observed.

CONCLUSION

The majority of patients experience mild to moderate side effects from adjuvant external-beam radiotherapy. At the first follow-up examination, most side effects have subsided. Acute toxicity is tolerable in these patients.