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Table 3 Univariate analyses with respect to dosimetric factors and the risk of HT

From: Predictors of radiation-induced hypothyroidism in nasopharyngeal carcinoma survivors after intensity-modulated radiotherapy

Variable

Univariate analyses

p value

HR (95% CI)

Dtmean, per Gy increase

1.000 (1.000–1.001)

0.000*

Dtmin, per Gy increase

1.000 (1.000–1.000)

0.000*

Dtmax, per Gy increase

1.000 (1.000–1.000)

0.551

Thyroid Vt30, per % increase

7.735 (2.648–22.594)

0.000*

Thyroid Vt40, per % increase

7.394 (2.979–18.353)

0.000*

Thyroid Vt45, per % increase

7.544 (3.054–18.639)

0.000*

Thyroid Vt50, per % increase

7.042 (2.781–17.832)

0.000*

Thyroid Vt60, per % increase

0.901 (0.225–3.601)

0.883

Dpmin, per Gy increase

1.000 (1.000–1.000)

0.360

Dpmean, per Gy increase

1.000 (1.000–1.000)

0.391

Dpmax, per Gy increase

1.000 (1.000–1.000)

0.979

Pituitary Vp50, per % increase

1.136 (0.708–1.822)

0.596

Thyroid VS45, per cm3 increase

0.855 (0.815–0.898)

0.000*

Dichotomous (< 5cm3 vs ≥ 5cm3)

0.474 (0.352–0.639)

0.000*

Thyroid VS50, per cm3 increase

0.863 (0.827–0.902)

0.000*

Dichotomous (< 8cm3 vs ≥ 8cm3)

0.445 (0.326–0.607)

0.000*

Thyroid VS55, per cm3 increase

0.886 (0.855–0.918)

0.000*

Dichotomous (< 12cm3 vs ≥ 12cm3)

0.437 (0.318–0.601)

0.000*

Thyroid VS60, per cm3 increase

0.904 (0.877–0.932)

0.000*

Dichotomous (< 15cm3 vs ≥ 15cm3)

0.482 (0.354–0.655)

0.000*

  1. Thyroid Vt30, Vt40, Vt45, Vt50 and Vt60 = percentages of thyroid volume receiving 30 Gy, 40 Gy, 45 Gy, 50 Gy and 60 Gy; Vp50 = percentage of pituitary volume receiving 50 Gy; Thyroid VS 45, 50, 55 and 60 = spared volume of thyroid receiving 45 Gy, 50 Gy, 55 Gy and 60 Gy
  2. *Means p < 0.05