A New Model for Predicting Hypothyroidism After Intensity-Modulated Radiotherapy for Nasopharyngeal Carcinoma.

Liang Peng,Wei-Ping Wen,Rui Guo,Jun Ma,Cheng-Long Huang,Yan-Ping Mao,Ling-Long Tang

doi:10.3389/fonc.2020.551255

Abstract

ObjectivesTo develop a model that can predict the risk of hypothyroidism (HT) after intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC), and to accordingly recommend dose constraints.Materials and MethodsNPC patients treated between 2011 and 2015 were retrospectively reviewed. HT was defined by an abnormally high level of thyrotropin. The dosimetry parameters Vx (percentage of thyroid volume receiving more than x Gy of radiation) and Va,b (percentage of thyroid volume receiving >a Gy, while ≤b Gy radiation) were calculated. The primary endpoint was the development of HT within the first 2 years after IMRT. The least absolute shrinkage and selection operator and multivariate logistic regression were used to identify predictors of HT.ResultsA total of 545 patients were included in the analyses, with a median follow-up of 36 months. Of the 545 patients, 138 developed HT within 2 years, and the 2-year incidence of HT was 25.3%. In patients with thyroid volume >20 cm3, the 2-year incidence of HT was 11.7% (16/137); in patients with thyroid volume ≤20 cm3 and V30,60 ≤ 80%, the 2-year HT incidence was 19.9% (33/166); in patients with thyroid volume ≤20 cm3 and V30,60 > 80%, the 2-year incidence of HT was 36.8% (89/242).ConclusionThyroid volume and V30,60 could be reliable predictors of HT after IMRT for NPC. For patients with thyroid volume ≤20 cm3, thyroid V30,60 ≤ 80% might be a useful dose constraint to adopt during IMRT planning.

Highlights

Radiation-induced hypothyroidism (HT) is frequent after radiotherapy (RT) of the head and neck region, with an incidence of 20–50% [1]
Radiation above a specific threshold dose will damage these follicles, and dysfunction of too many follicles results in HT. Dosimetry parameter depicting both the threshold dose of follicle and the number of influenced follicles will be a promising predictor for HT after RT, and that is the parameter Vx, defined as the percentage of thyroid volume receiving more than a to-be-determined threshold dose, x Gy
We have investigated the incidence of radiation-induced HT in a large cohort of Nasopharyngeal carcinoma (NPC) patients who underwent intensity-modulated radiotherapy (IMRT), with the aim of determining the dosimetry parameters that could be used as predictors of HT

Summary

Introduction

Radiation-induced hypothyroidism (HT) is frequent after radiotherapy (RT) of the head and neck region, with an incidence of 20–50% [1]. Nasopharyngeal carcinoma (NPC) tends to metastasize through the lymphatic network to the neck [2]; definitive or prophylactic RT of the neck region can affect the thyroid gland and result in HT. The survival of NPC patients has improved significantly after the introduction of chemotherapy and intensity-modulated radiotherapy (IMRT) during the last two decades [3]. With IMRT, it is possible to achieve sufficient dose coverage of the tumor and improve tumor control. Radiation above a specific threshold dose will damage these follicles, and dysfunction of too many follicles results in HT. In order to minimize the influence of collinearity, we have proposed a prediction model based on novel dosimetry parameters which are generated by subtractions between Vx

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Conclusion