Thyroid dose‐volume thresholds for the risk of radiation‐related hypothyroidism in nasopharyngeal carcinoma treated with intensity‐modulated radiotherapy—A single‐institution study

Abstract

BackgroundTo identify thyroid dose‐volume thresholds for radiotherapy (RT)‐related hypothyroidism (HT) in patients with nasopharyngeal carcinoma (NPC) treated with intensity‐modulated RT (IMRT). In this way, we desired to guide the design of treatment plans and, finally, lower HT prevalence.MethodsIn total, 345 NPC patients treated with IMRT were evaluated retrospectively during a median follow‐up of 45.2 (range, 11.3‐64.9) months. Serum‐based assessments of thyroid function before and after IMRT were monitored periodically. Thyroid dose‐volume parameters were analyzed for their association with HT risk.ResultsIn total, 44.1% of patients (152/345) developed primary HT. Analyses of thyroid dose‐volume parameters identified a stringent dose‐volume histogram (DVH) threshold defined by V 25Gy (the percentage thyroid volume that receives >25 Gy, not the absolute volume) ≤60%, V 35Gy ≤ 55%, and V 45Gy ≤ 45%. Patients whose thyroid DVHs satisfied these constraints had a lower prevalence of 2‐year HT compared with the overall prevalence (13.2% vs 25.8%, P < .001). Another DVH was defined by V 25Gy > 95%, V 35Gy > 90%, and V 45Gy > 75%, and patients whose thyroid DVHs satisfied with these constraints had a higher prevalence of 2‐year HT than the overall incidence (36.0% vs 25.8%, P < .001).ConclusionWe recommend V 25Gy ≤ 60%, V 35Gy ≤ 55%, and V 45Gy ≤ 45% as the “stringent” DVH line, and V 25Gy > 95%, V 35Gy > 90%, and V 45Gy > 75% as the “inhibition” DVH line, under the precondition of not compromising the target coverage. These findings could help in the design of individual treatment plans and, eventually, to lowering of HT prevalence.

Dysphagia, hypothyroidism, and osteoradionecrosis after radiation therapy for head and neck cancer

“…35 The incidence of radiation-induced hypothyroidism in HNC patients at 3-year follow-up has varied from 25.8% to 56.6%. 36,37,38,39,40 Our result (29%) is in line with these findings.…”

Research progress of radiation-induced hypothyroidism in head and neck cancer

“…By contrast, some scholars have found no correlation between age and hypothyroidism 13 , 25 , 56 ; however, the difference in age boundary values was one of the main reasons for disagreement. Huang et al 44 showed that younger age (≤ 44 years old) was associated with hypothyroidism, while age was not significantly associated in multivariate analysis. One study found that the independent risk factors for radiation-induced hypothyroidism included younger age; the incidence of hypothyroidism decreased 0.9 times with every increase in age 2 .…”

“…Compared with other studies, this dose limit is not strict. Huang et al 44 believed that thyroid dose parameters should be individually limited, such as V25 ≤ 60%, V35 ≤ 55%, and V45 ≤ 45%, which could strictly control the thyroid dose and reduce the incidence of hypothyroidism, making it suitable for patients with a small tumor and those at the early clinical stages. They noted that V25 > 95%, V35 > 90%, and V45 > 75% are risk factors for hypothyroidism and should be avoided as far as possible.…”

An Underestimated Toxicity Radiation-Induced Hypothyroidism in Patients Multimodally Treated for Breast Cancer

“…A V45 value of <50% and the sparing at least 5 cm 3 of thyroid gland to receive lesser than 45 Gy, but also a 45 Gy mean dose for the thyroid gland of are the most common recommended dose-volume constraints in order to reduce the risk of hypothyroidism in radio-treated patients in the neck region [ 25 , 26 , 27 , 28 ]. After analysis of dose-volume-toxicity correlations on 345 cases of nasopharyngeal cancer treated by IMRT technique, with a median follow-up of 45.2 months, Huang and collaborators proposed V25 Gy ≤ 60%, V35 Gy ≤ 5 5%, and V45 Gy ≤ 45% for thyroid, as recommended constraints [ 29 ].…”