The threshold of hypothyroidism after radiation therapy for head and neck cancer: a retrospective analysis of 116 cases

Abstract

The purpose of the present study was to determine the risk factors for developing thyroid disorders based on a dose–volume histograms (DVHs) analysis. Data from a total of 116 consecutive patients undergoing 3D conformal radiation therapy for head and neck cancers was retrospectively evaluated. Radiation therapy was performed between April 2007 and December 2010. There were 108 males and 8 females included in the study. The median follow-up term was 24 months (range, 1–62 months). The thyroid function was evaluated by measuring thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels. The mean thyroid dose, and the volume of thyroid gland spared from doses ≥10, 20, 30 and 40 Gy (VS10, VS20, VS30 and VS40) were calculated for all patients. The thyroid dose and volume were calculated by the radiotherapy planning system (RTPS). The cumulative incidences of hypothyroidism were 21.1% and 36.4% at one year and two years, respectively, after the end of radiation therapy. In the DVH analyses, the patients who received a mean thyroid dose <30 Gy had a significantly lower incidence of hypothyroidism. The univariate analyses showed that the VS10, VS20, VS30 and VS40 were associated with the risk of hypothyroidism. Hypothyroidism was a relatively common type of late radiation-induced toxicity. A mean thyroid dose of 30 Gy may be a useful threshold for predicting the development of hypothyroidism after radiation therapy for head and neck cancers.

A dosimetric study on radiation‑induced hypothyroidism following intensity‑modulated radiotherapy in patients with nasopharyngeal carcinoma

“…The present ROC curve analysis demonstrated that 5,160 cGy was a predictive threshold value, and the increased 3-year cumulative incidence of RIHT in the Dmean >5,160 cGy cohort confirmed this data (67.8% for Dmean >5,160 cGy and 44.6% for Dmean <5,160 cGy; P=0.036). Notably, the threshold value in the present study was >30 Gy reported by Fujiwara et al (29). Possible explanations are as follows: i) The dose in the target region was 54-60 Gy, and the prescribed dose was 59.4-66 Gy for PTV and 70-74.9 Gy for GTV boost, whereas the total dose in the Fujiwara et al (29) study was 60-66 Gy; and ii) The difference in the tumor types (NPC vs. head and neck malignancy types) and physicians may result in variations in the target area delineations.…”

“…Notably, the threshold value in the present study was >30 Gy reported by Fujiwara et al (29). Possible explanations are as follows: i) The dose in the target region was 54-60 Gy, and the prescribed dose was 59.4-66 Gy for PTV and 70-74.9 Gy for GTV boost, whereas the total dose in the Fujiwara et al (29) study was 60-66 Gy; and ii) The difference in the tumor types (NPC vs. head and neck malignancy types) and physicians may result in variations in the target area delineations. In the present study, 30.6% (range, 1-88.2%) of thyroid tissues were exposed to radiation, resulting in the exposure of increased radiation doses to the thyroid gland.…”

“…The Dmean has also been reported as an independent predictor for RIHT (27,28); however, the associated threshold value has rarely been studied. Fujiwara et al (29) estimated the threshold value as 30 Gy, based on the incidence of RIHT being significantly reduced in patients with Dmean <30 Gy compared with the other groups (P<0.05). The present ROC curve analysis demonstrated that 5,160 cGy was a predictive threshold value, and the increased 3-year cumulative incidence of RIHT in the Dmean >5,160 cGy cohort confirmed this data (67.8% for Dmean >5,160 cGy and 44.6% for Dmean <5,160 cGy; P=0.036).…”

Nomogram for radiation-induced hypothyroidism prediction in nasopharyngeal carcinoma after treatment

“…We found that female gender and D mean were risk factors, as was found in previous studies. 8,9,13,14,25 The role of chemotherapy as a risk factor of RHT is unclear; 10,43,44 however, in our nomogram, chemo plays a significant role in RHT prediction (Figure 2, .70 points) because there was only 1 patient diagnosed with RHT who did not receive chemotherapy [(11.6%) 19 patients]. The study by Sachdev et al 23 identified V 50 as the only risk factor using a receiver-operating characteristic curve to obtain the cut-off point of V 50 for patients with RHT.…”

“…However, predictors and dose constraints varied according to the study. 13,14,[16][17][18][19][20][21][22][23][24][25] Nasopharyngeal carcinoma (NPC) is a prevalent cancer in southern China. Irradiation to the bilateral neck is a regular practice because of a high incidence 26 of neck node involvement.…”