3.1 Patients’ demographic and baseline characteristics
Patients’ demographic, clinical and pathological data are summarised in Table 1.There were 15 (39.5%) men and 23 (60.5%) women, with the mean age being 45.6 ± 12.3 years (range: 20–67 years). The distribution of patients (based on the eighth edition of the TNM staging system) was as follows: stage I: 18 (47.4%), stage II: 13 (34.2%), stage III: 1 (2.6%) and stage IV: 6 (15.8%). The TSH level in eight patients was lower than 30 mIU/l after 4 weeks of THW for the initial RAI therapy.Out of these eight patients, 99mTc-pertechnetate scans of the neck showed that there was no accumulation of radioactivity in the thyroid bed in 4 patients. The other 4 patients had radioactive uptake in the thyroid bed with uptake rates of 0.1–0.3%, which were lower than those of the extra-thyroid lesions, suggesting that there were only a small number of thyroid residuals. Among these patients, one patient’s TSH level at the second RAI therapy was higher than that at the time of the previous treatment; however, it still did not reach the treatment standard. In another patient, the TSH level only increased to above 30 mIU/l at the fourth RAI therapy. Among the 38 DTC patients, 35 (92%) had an sTg level higher than 10 ng/mlduring the first 131I treatment.
Table 1
Demographics, clinical, and pathological data for 38 patients
Characteristic | No. of patients | Percentage of patient |
Sex | | |
Female | 23 | 60.5 |
Male | 15 | 39.5 |
Age | | |
< 55y | 29 | 76.3 |
≥ 55y | 9 | 23.7 |
Histology | | |
Papillary | 26 | 68.4 |
Follicular | 8 | 21.1 |
Mixed papillary-follicular* | 3 | 7.9 |
Poorly differentiated | 1 | 2.6 |
TNM | | |
T | | |
T1a | 6 | 15.8 |
T1b | 8 | 21.1 |
T2 | 3 | 7.9 |
T3 | 8 | 21.1 |
T4a | 3 | 7.9 |
Tx | 10 | 26.2 |
N | | |
N0 | 7 | 18.4 |
N1a | 12 | 31.6 |
N1b | 13 | 34.2 |
Nx | 6 | 15.8 |
M | | |
M0 | 23 | 60.5 |
M1 | 15 | 39.5 |
AJCC stage | | |
I | 18 | 47.4 |
II | 13 | 34.2 |
III | 1 | 2.6 |
IVA | 0 | 0 |
IVB | 6 | 15.8 |
TSH (mIU/l) | | |
༜30 | 8 | 21.1 |
≥30 | 30 | 78.9 |
sTg(ng/mL) | | |
1 | 1 | 2.6 |
1–10 | 2 | 5.3 |
10–100 | 13 | 34.2 |
≥100 | 22 | 57.9 |
TgAb(IU/mL) | | |
negative(༜115) | 37 | 97.4 |
positive (≥ 115) | 1 | 2.6 |
* refer to papillary carcinoma and follicular carcinoma in the different lobe of the thyroid |
3.2 Distribution of extra-thyroid 99mTc-pertechnetate uptake
A total of 65 extra-thyroid 99mTc-pertechnetate uptake foci were detected in 38 patients, of which 50.77% (33/65), 38.46% (25/65) and 7.69% (5/65) were in the lymph nodes, lungs and bones, respectively. The distribution characteristics are summarised in Table 2. In the per-patient analysis, 34 showed abnormal 99mTc-pertechnetate uptake in the lymph nodes (26; 68.4%), lungs (4; 10.5%) and bones (4; 10.5%), and the corresponding uptake rates were 0.2% (0.1–0.35%), 0.2% (0.1–0.68%), and 0.8% (0.45–1.6%). Data on the relationship between the three subgroups showed that the uptake rate in the lymph node subgroup was significantly lower than that in the bone subgroup (Z = 2.722, p = 0.019), as shown in Table 3 and Fig. 1. Seven patients showed extra-thyroid 99mTc-pertechnetate uptake in two or more sites, five of whom showed simultaneous uptake in two or more lymph nodes, and each of the remaining two patients showed uptake in the lymph nodes and lung tissue (Figs. 2–4) and the lymph nodes and bone tissue. One patient with superior vena cava 99mTc-pertechnetate uptake underwent chest MRI scanning before 131I therapy and this showed that the superior vena cava was significantly enlarged, with abnormal mass in the blood vessels, high signal on T2-weighted images, enhanced scan lesions significantly enhanced and 131I uptake by Rx-WBS/SPECT/CT in this area, which was considered to be tumour thrombus. Another patient showed 99mTc-pertechnetate uptake in the supraclavicular vessel, but no abnormality was found on ultrasound, MRI or Rx-WBS/SPECT/CT. The distribution and uptake rates are shown in Table 3. Correlation analyses between the extra-thyroid 99mTc-pertechnetate uptake rate and sex, age, sTg, TgAb and TSH levels, pathological type and TNM stage showed a definite positive correlation between the sTg level and the uptake rate in Fig. 5 (r = 0.36, p = 0.027).
Table 2
Distribution of 65 extra-thyroid 99mTc-pertechnetate uptake lesions in 38 DTC patients
Organs | No. of lesions | Percentage of lesions(%) |
Lymph node(LN) | | |
mediastinum | 18 | 27.69 |
lateral cervical | 9 | 13.85 |
clavicular region | 5 | 7.69 |
axilla | 1 | 1.54 |
Lung | | |
nodular | 24 | 36.92 |
diffuse | 1 | 1.54 |
Bone | | |
sternum | 2 | 3.08 |
rib | 1 | 1.54 |
femur | 1 | 1.54 |
humerus | 1 | 1.54 |
Blood vessel | 1 | 1.54 |
Superior vena cava tumor thrombus | 1 | 1.54 |
Table 3
Distribution and 99mTc-pertechnetate uptake rate of extra-thyroid in 38 patients
Organs | No. of patients (Percentage, %) | 99mTc-pertechnetate uptake rate (%) | z | p |
Lymph node (LN) | 26(68.4) | 0.20(0.10–0.35) | -2.722 | 0.019 |
Lung | 4(10.5) | 0.20(0.10–0.68) | | |
Bone | 4(10.5) | 0.80(0.45–1.60) | | |
LN + Lung | 1(2.6) | 0.20 | | |
LN + Bone | 1(2.6) | 0.35 | | |
Superior vena cava tumor thrombus | 1(2.6) | 2.60 | | |
Blood vessels | 1(2.6) | 0.15 | | |
3.3 99mTc‑pertechnetate uptake and its relationship with 131I uptake
99mTc-WBS/SPECT/CT did not show 99mTc-pertechnetate uptake in the thyroid bed in 9 patients before the first RAI therapy, but RxWBS showed thyroid bed iodine uptake in 8 cases (indicating a small amount of thyroid residue), and only one case showed no obvious radioactive uptake in the thyroid bed in both examinations. The sensitivity and specificity of the 99mTc‑pertechnetate scan in evaluating thyroid residue were 82.22% and 100%, respectively. One patient showing 99mTc‑pertechnetate uptake in the axillary lymph node, and another patient showing uptake in blood vessels, both showed no obvious 131I uptake on RxWBS/SPECT/CT imaging. The other 36 patients showed 131I uptake at the extra-thyroid 99mTc-pertechnetate uptake foci, with the number of 131I uptake foci being significantly more than the foci showing 99mTc-pertechnetate uptake. 37.5% (39/104 foci) showed metastases with 131I uptake but without 99mTc-pertechnetate uptake (diffuse 131I uptake in the lungs was defined as a lesion), and there were no instances of 99mTc-pertechnetate uptake in the liver, kidneys or brainindicating 131I-avid metastases. Excluding physiological uptake, the presence of extra-thyroid131I uptake foci was used as the criterion for judging the presence of metastases, and 94.7% (36/38) of extra-thyroid 99mTc-pertechnetate uptake foci were DTC metastases.99mTc-pertechnetate scans were performed on all patients during the second 131I treatment, and only one patient showed a small amount of 99mTc-pertechnetate uptake in the extra-thyroid bed.
3.4 Evaluation of RAI therapy response
All patients underwent 131I therapy 1 to 10 times, with a cumulative dose of 3.7 to 57 GBq, and a single dose of 3.7–7.4 GBq. The initial evaluation of RAI therapy response indicated ER in 15 cases (39.5%), IDR in 4 cases (10.5%), BIR in 3 cases (7.9%) and SIR in 16 cases (42.1%). A statistically significant difference was found between the ER and NER groups for sTg level (Z = -2.947, p = 0.003) and pathological stage (Z = -2.348, p = 0.019), but not for age, sex, pathological type, TSH and TgAb levels and extra-thyroid 99mTc-pertechnetate uptake site and rate.