The role of external beam radiotherapy in the management of medullary carcinoma of the thyroid: A systematic review

Objective: In order to clarify the role of external beam radiotherapy in the management of medullary thyroid cancer (MTC), a systematic review was undertaken.

Patients and interventions: Patients with MTC of any stage receiving radiotherapy, either as adjuvant postoperative treatment or as primary treatment for unresectable disease.

Design: Electronic searching Medline and ProQuest databases for randomised or non-randomised studies. A risk of bias assessment (ROBINS-I) was carried out for each study.

Main outcome measures: Overall survival, rates of locoregional recurrence, locoregional relapse-free survival.

Results: There were no randomised studies. Twenty-seven non-randomised studies were identified. Within four cohort studies, radiotherapy had no significant effect on overall survival. Within one prospective and 22 retrospective studies (of approximately 1200 patients), radiotherapy similarly had no consistent effect on overall survival but there was evidence that radiotherapy reduces the risk of locoregional relapse, particularly in those with nodal involvement, extrathyroidal extension or residual disease. In a meta-analysis of patients within four studies, radiotherapy reduced the risk of locoregional relapse by at least 38%. Evidence supports the use of doses of 60 Gy or greater and an interval between surgery and radiotherapy of less than two months. Thirteen of 63 patients (21%) treated for unresectable disease achieved a complete response. Acute morbidity was observed in relation to difficulty swallowing, xerostomia and skin reactions. Late morbidity was infrequent with a low incidence of xerostomia.

Conclusions: Radiotherapy should be considered for those at high risk of locoregional relapse, in particular those with nodal involvement, extrathyroidal extension or residual disease (microscopic or macroscopic).