Article

Radiation-induced hypothyroidism in head and neck cancer patients: A systematic review

Department of Radiation Oncology, University Medical Center Groningen, The Netherlands.
Radiotherapy and Oncology (Impact Factor: 4.86). 04/2011; 99(1):1-5. DOI: 10.1016/j.radonc.2011.03.002
Source: PubMed

ABSTRACT To review literature on the relationship between the dose distribution in the thyroid gland and the incidence of radiation-induced hypothyroidism in adults.
Articles were identified through a search in MEDLINE, EMBASE and the Cochrane Library. Approximately 2449 articles were screened and selected by inclusion- and exclusion criteria. Eventually, there were five papers that fulfilled the eligibility criteria to be included in this review.
The sample sizes of the reviewed studies vary from 57 to 390 patients. The incidence of hypothyroidism was much higher (23-53%) than would be expected in a non-irradiated cohort. There was a large heterogeneity between the studies regarding study design, estimation of the dose to the thyroid gland and definition of endpoints. In general, the relationship between thyroid gland volume absorbing 10-70Gy (V10-V70), mean dose (Dmean), minimal dose (Dmin), maximum dose (Dmax) and point doses with hypothyroidism were analysed. An association between dose-volume parameters and hypothyroidism was found in two studies.
Hypothyroidism is frequently observed after radiation. Although the results suggest that higher radiation doses to the thyroid gland are associated with hypothyroidism, it was not possible to define a clear threshold radiation dose for the thyroid gland.

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    • "It is also necessary to consider the influence on thyroid function because irradiation fields often include a part of the thyroid gland. Although it is well known that radiation exposure of the thyroid gland can induce hypothyroidism, its potential influence can be ignored in this study because radiation-induced hypothyroidism would be detected several years after completion of irradiation 48. Furthermore, possible influence of CDDP-based chemotherapy on thyroid function has been reported in children 49. "
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    • "Therefore, 200 samples (with at least 32 events, to avoid severe overfitting) appear to be a robust number to set as an efficient minimum data set size to obtain a model with high predictive power. This lower bound is within the relevant range of current practice, as, for example, in [12–14,17,18], and [24] [25] [26] the range of data set sizes is 94–529 patients (median 214) with a range of 11–122 events (median 50). Although the increase of predictive power is limited for data sets larger than 200 samples, the benefit is that more variables can be included in the model (see Fig. 4), which widens the potential applicability, as, for example , in [14]. "
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