Table 3.

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

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*

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

*Means p < 0.05