Thyroid toxicity after radiotherapy of nasopharyngeal carcinoma

Abstract

Objectives To analyze retrospectively the risk factors for occurrence of thyroid toxicity after radiotherapy for nasopharyngeal cancer and to demonstrate the necessity of a long-term post-therapeutic screening. Patients and methods Between 1993 and 2004, 239 patients with non-metastatic nasopharyngeal carcinoma were treated by conventional radiotherapy with or without chemotherapy. Radiotherapy was delivered by a standard fractionation (2 Gy/fraction, 5 fractions/week) for 157 patients and hyperfractionation (1.6 Gy/fraction, 2 fractions/day, 5 days/week) for 82 patients. An evaluation of thyroid late toxicity was performed according to tumor stage, age, gender, time after treatment, irradiation method and association or not with chemotherapy. Results After a median follow up of 111 months, 72 patients (30%) had primitive and/or pituitary thyroid dysfunction. Fifty-seven patients (24%) experienced hypothyroidism, peripheral in 92% of cases (biological 73%, clinical 19%) and central in 8% of cases. Hypothyroidism was detected at a mean 37 months follow up. All patients received replacement treatment with l-thyroxin. The actuarial rate of hypothyroidism was 18.1%, 24.3% and 35% at respectively 3, 5 and 10 years. Only female gender was found as a risk factor for occurrence of hypothyroidism in univariate analysis. However, younger age and advanced tumor stage were associated with a higher risk but the difference was not significant ( P = 0.08 for each). There was no difference for other factors: nodal stage, modality of radiation and chemotherapy treatment. The multivariate analysis did not show any risk factor. Conclusion Thyroid dysfunction after radiotherapy for nasopharyngeal carcinoma is frequent and requires systematic screening to begin adequate treatment earlier. Only gender has been identified as risk factor in univariate analysis in this study.