Residual vital ratio: predicting regrowth after radiofrequency ablation for benign thyroid nodules

Figures & data

Figure 1. Flowchart of patient enrollment.

Table 1. Clinical characteristics of patients before RFA.

Characteristics	Data
No. of patients	189
Age (years)	46.56 ± 11.88 (18–79)
Sex (F/M)	168/21 (88.89/11.11)
No. of nodules	206
No. of patients with number of treated nodules
One nodule	175 (92.59)
Two nodules	11 (5.82)
Three nodules	3 (1.59)
Largest diameter (cm)	2.99 ± 1.33 (1.1–6.7)
Initial volume (ml)	10.09 ± 12.90 (0.40–71.39)
Small (N = 139)	3.52 ± 2.71 (0.40–9.41)
medium (N = 50)	16.43 ± 5.47 (10.01–29.16)
Large (N = 17)	45.17 ± 13.02 (30.20–71.39)
Location
Right lobe	107 (51.94)
Left lobe	97 (47.09)
Isthmus	2 (0.97)

Values are presented as mean ± SD (range) or number of tumors (percentages).

Figure 2. The changes of VRR at each follow-up point after RFA.

Table 2. Changes of VRR in the subgroups at each follow-up period after RFA.

Time (months)	Total	Small (N = 139)	Medium (N = 50)	Large (N = 17)	p Value
1	51.11 ± 18.13 (15.10–90.23)	49.02 ± 17.79 (15.10–88.24)	55.15 ± 19.01 (17.19–90.23)	56.09 ± 16.59 (23.79–79.41)	.098
3	70.85 ± 16.70 (23.54–100)	71.28 ± 18.14 (23.54–100)	71.09 ± 12.00 (37.32–91.87)	63.68 ± 15.06 (36.29–81.60)	.354
6	80.86 ± 12.70 (44.35–100)	82.63 ± 12.26 (52.30–100)	78.24 ± 13.41 (44.35–99.30)	74.38 ± 12.07 (50.59–87.89)	.057
12^a	84.90 ± 14.11 (32.33–100)	87.82 ± 12.83 (37.52–100)	80.45 ± 13.64 (32.33–98.60)	71.13 ± 17.17 (40.80–94.28)	<.001
24^b	89.29 ± 12.43 (54.09–100)	93.08 ± 10.57 (57.52–100)	82.02 ± 10.36 (63.20–95.64)	70.38 ± 9.25 (54.09–76.95)	<.001
Last follow-up time^c	85.26 ± 15.02 (32.23–100)	89.21 ± 12.74 (37.52–100)	79.80 ± 15.11 (32.33–99.30)	68.96 ± 16.79 (40.10–94.28)	<.001

Values are presented as mean ± SD (range).

^aCompared to the small subgroup, p values were significantly different from: the medium subgroup (p = .001), the large subgroup (p = .002).

^bCompared to the small subgroup, p values were significantly different from: the medium subgroup (p = .003), the large subgroup (p = .001).

^cCompared to the small subgroup, p values were significantly different from: the medium subgroup (p < .001), the large subgroup (p < .001).

Figure 3. The changes of Vt, Va and Vv in each subgroup at each follow-up point after RFA (A: small subgroup; B: medium subgroup; C: large subgroup).

Table 3. Changes of Vt, Va and Vv in the subgroups at each follow-up period after RFA.

Time (months)	Small			Medium			Large
	Vt	Va	Vv	Vt	Va	Vv	Vt	Va	Vv
Baseline	3.52 ± 2.71	3.17 ± 2.51		16.43 ± 5.47	13.45 ± 5.55		45.17 ± 13.02	35.83 ± 11.35
1	1.93 ± 1.64	1.37 ± 1.18	0.57 ± 0.99	7.69 ± 4.64	4.68 ± 2.97	3.01 ± 2.64	18.73 ± 6.08	10.65 ± 5.70	8.09 ± 5.01
3	1.05 ± 1.18	0.59 ± 0.72	0.46 ± 0.71	4.42 ± 2.08	2.15 ± 1.44	2.27 ± 2.07	15.31 ± 3.58	7.74 ± 2.99	7.58 ± 5.44
6	0.75 ± 0.88	0.41 ± 0.59	0.35 ± 0.53	3.45 ± 2.14	1.41 ± 1.27	2.03 ± 1.74	11.53 ± 5.60	5.42 ± 3.02	6.11 ± 5.01
12	0.57 ± 0.86	0.25 ± 0.44	0.32 ± 0.73	3.38 ± 3.10	0.86 ± 0.85	2.53 ± 3.02	13.04 ± 8.70	3.76 ± 3.60	9.28 ± 7.79
24	0.38 ± 0.80	0.13 ± 0.31	0.24 ± 0.62	3.44 ± 2.73	0.78 ± 0.95	2.66 ± 2.38	13.69 ± 3.33	2.96 ± 2.12	10.73 ± 2.01

Values are presented as mean ± SD.

Table 4. Univariate and multivariate logistic regression analyses for nodule regrowth.

	Non-regrowth group (N = 180)	Regrowth group (N = 26)	Univariate		Multivariate
			OR (95%CI)	p Value	OR (95%CI)	p Value
Age (years)	47.08 ± 11.80	42.78 ± 12.04	0.969 (0.933–1.007)	.106
Female (%)	159 (88.33)	20 (76.92)	0.440 (0.159–1.220)	.115
Initial volume (ml)	9.05 ± 11.77	17.25 ± 17.71	1.037 (1.011–1.063)	.005	1.033 (1.000–1.066)	.048
Solid (%)	129 (71.67)	15 (57.69)	0.539 (0.232–1.252)	.151
Location close to critical structure (%)	28 (15.56)	9 (34.62)	2.874 (1.165–7.089)	.022	5.967 (1.898–18.760)	.002
Energy applied per volume (J/ml)	527.55 ± 544.50	472.78 ± 715.91	1.000 (0.999–1.001)	.646
Vascularity	2.46 ± 0.92	2.96 ± 0.87	1.954 (1.155–3.306)	.013	2.216 (1.185–4.143)	.013
RVR (%)	31.24 ± 21.75	55.76 ± 16.72	1.052 (1.030–1.075)	<.001	1.050 (1.025–1.075)	<.001

Values are presented as mean ± SD or number of tumors (percentages).

Figure 4. The ROC curve for RVR to predict regrowth.

Figure 5. The conventional US and CEUS images of a 48-year-old male with a benign thyroid nodule. (A) Before RFA, a solid thyroid nodule located in the right thyroid lobe with an initial volume of 22.27 ml. Color Doppler showed the vascularity was grade 3. (B) CEUS performed immediately after RFA showed a lack of enhancement on the treated area(arrow). (C, D) At one months after RFA, conventional US showed the treated nodule began to shrink and total volume(Vt) was 5.28ml. CEUS showed the treated nodule was divided into the centrally non-enhancement area(ablated volume, Va) and peripheral iso-enhancement area(vital volume, Vv). Va was 2.59ml and Vv was 2.69ml. RVR was 50.95%. (E, F) At 3 months after RFA, conventional US showed Vt was 3.48ml and the echogenicity of nodule was heterogeneous. Va decreased to 1.11ml on CEUS and Vv was 2.37ml. (G, H) At 6 months after RFA, conventional US and CEUS showed Vt decreased to 2.89 ml and Va decreased to 0.27ml, respectively. However, Vv began to enlarge to 2.62ml.(I, J) At 12 months after RFA, conventional US showed nodule regrowth and Vt was 4.34ml. Va decreased to 0.20ml on CEUS and thus Vv increase also occurred and Vv was 4.13ml.