Dose-volume derived nomogram as a reliable predictor of radiotherapy-induced hypothyroidism in head and neck cancer patients

Figure 1

Figure 2

Figure 3

General characteristics of the study population; continuous variables are presented as mean ± SD and categorical ones as N (%)

	Euthyroidism N = 86		Hypothyroidism N = 70		P
Age	60.2	± 10.0	59.3	± 9.5	0.556
Male gender	79	(91.9)	58	(82.9)	0.087
Primary tumor					0.851
Unknown primary(C80)	5	(5.8)	2	(2.9)
Hypopharinx	16	(18.6)	12	(17.1)
Larynx	18	(20.9)	16	(22.9)
Nasopharynx	3	(3.5)	5	(7.1)
Oral cavity	11	(12.8)	9	(12.9)
Oropharynx	28	(32.6)	24	(34.3)
Other	5	(5.8)	2	(2.9)
T status					0.106
1	10	(11.6)	14	(20.0)
2	35	(40.7)	22	(31.4)
3	16	(18.6)	21	(30.0)
4	17	(19.8)	11	(15.7)
x	8	(9.3)	2	(2.9)
N status					0.508
N0	28	(32.6)	16	(22.9)
N1	16	(18.6)	10	(14.3)
N2a	1	(1.2)	3	(4.3)
N2b	25	(29.1)	23	(32.9)
N2c	12	(14.0)	13	(18.6)
N3	4	(4.7)	5	(7.1)
Neck metastases present	58	(67.4)	54	(77.1)	0.181
Chemotherapy	43	(50.0)	43	(61.4)	0.153
Surgery involving thyroid					0.758
None	18	(20.9)	14	(20.0)
Lobectomy	10	(11.6)	11	(15.7)
Non-thyroid	58	(67.4)	45	(64.3)

Dosimetric characteristics of the study population; continuous variables are presented as mean ± SD and categorical ones as n (%)

	Euthyroidism N = 86		Hypothyroidism N = 70		P
Dmin	4178	± 1652	5005	± 869	<0.001
Dmax	6298	± 704	6304	± 587	0.867
Dmean	5487	± 1055	5836	± 537	0.087
D02	6172	± 650	6222	± 582	0.765
D10	6041	± 663	6133	± 577	0.410
D20	5953	± 709	6062	± 567	0.373
D30	5818	± 884	5992	± 560	0.242
D40	5697	± 1003	5927	± 550	0.238
D50	5503	± 1168	5869	± 537	0.094
D60	5314	± 1414	5775	± 583	0.093
D70	5181	± 1495	5704	± 607	0.042
D80	5063	± 1540	5616	± 622	0.032
D90	4903	± 1595	5520	± 637	0.019
D98	4640	± 1663	5322	± 681	0.006
Total thyroid volume	15.951	± 8.399	11.461	± 4.513	<0.001
V10	96.85	± 11.27	100.00	± 0.00	0.005
V20	95.38	± 14.80	100.00	± 0.00	0.002
V30	94.40	± 16.57	99.64	± 2.99	0.005
V40	93.44	± 18.36	99.34	± 5.14	0.019
V45	92.70	± 19.66	98.99	± 5.51	0.040
V50	85.99	± 24.35	95.29	± 9.95	0.003
V55	53.15	± 41.84	65.72	± 40.89	0.053
V60	40.56	± 37.74	49.27	± 37.49	0.163
V65	12.82	± 25.13	13.61	± 26.67	0.888
V70	4.38	± 15.45	1.81	± 9.25	0.193
VS10	0.59	± 2.10	0.00	± 0.00	0.009
VS20	0.87	± 2.82	0.00	± 0.00	0.002
VS30	1.02	± 3.07	0.04	± 0.36	0.008
VS40	1.23	± 3.47	0.09	± 0.72	0.003
VS45	1.37	± 3.78	0.15	± 0.77	0.040
VS50	2.56	± 4.78	0.63	± 1.45	0.003
VS55	7.75	± 7.87	3.93	± 5.18	0.003
VS60	9.86	± 7.79	5.84	± 5.16	0.001
VS65	14.18	± 8.15	9.70	± 4.88	<0.001
VS70	15.32	± 8.00	11.23	± 4.62	<0.001

Area under the curve for each variable in predicting hypothyroidism

Variable(s)	AUC	SE	P	95% Confidence Interval
				Lower Bound	Upper Bound
Dmin	.673	.043	.000	.589	.757
Dmax	.508	.046	.867	.417	.599
Dmean	.580	.046	.087	.490	.669
D02	.514	.046	.765	.423	.605
D10	.538	.046	.410	.448	.629
D20	.542	.046	.373	.451	.632
D30	.555	.046	.242	.464	.645
D40	.555	.046	.238	.465	.645
D50	.578	.046	.094	.489	.668
D60	.578	.046	.093	.489	.668
D70	.595	.045	.042	.506	.683
D80	.600	.045	.032	.512	.688
D90	.609	.045	.019	.521	.697
D98	.627	.044	.006	.540	.714
VS
VS10	.547	.046	.318	.456	.637
VS20	.564	.046	.170	.474	.654
VS30	.557	.046	.218	.468	.647
VS40	.569	.046	.140	.479	.658
VS45	.556	.046	.233	.466	.646
VS50	.623	.044	.008	.536	.710
VS55	.637	.044	.003	.550	.723
VS60	.655	.044	.001	.569	.740
VS65	.684	.043	.000	.600	.768
VS70	.672	.043	.000	.588	.757
Total thyroid volume
TTV	.676	.043	.000	.592	.760
V
V10	.552	.046	.262	.462	.642
V20	.564	.046	.170	.474	.654
V30	.563	.046	.177	.473	.653
V40	.562	.046	.182	.473	.652
V45	.564	.046	.168	.475	.654
V50	.630	.044	.005	.543	.717
V55	.589	.046	.057	.498	.679
V60	.565	.046	.166	.474	.655
V65	.495	.047	.906	.403	.586
V70	.470	.046	.519	.379	.561

Pearson correlation coefficients between strongest predictive variables_ P< 0_001 for all correlations

	Dmin	TTV	VS65	V50
Dmin	1.000	-.398	-.537	.842
TTV	-.398	1.000	.853	-.331
VS65	-.537	.853	1.000	-.462
V50	.842	-.331	-.462	1.000

The incidence of hypothyroidism in the study population

Time (months)	N (%)
6	21 (13.5)
12	37 (23.7)
18	48 (30.8)
24	59 (37.8)
30	66 (42.3)
36	70 (44.9)
42	70 (44.9)