Our experience of high dose I-131 therapy in 75 patients with well differentiated carcinoma thyroid followed up over 5 years

Thyroid cancer is the most common endocrine malignancy. The epidemiology of thyroid cancer is variable, depending on the geographic location of the patient population. Well differentiated thyroid cancer (WTC), is responsive to high dose I-131 treatment, and is the most accepted form of therapy, even though the dose administered for ablation of residual thyroid tissue maybe controversial. At our centre, 75 patients of WTC, mean age 42.4 years, 22 males and 53 females (M:F 1:2.4), were treated with high dose oral I-131 therapy with a Total Mean Dose (TMD) of 263.6 mCi, 4 - 6 weeks post thyroidectomy. They were followed up over a period of 6 years. Twenty ( 26.7%) patients had follicular cancer (FC), 47 (62.7%) papillary cancer (PC) and 8 (10.7%) were mixed (MC), on histopathology, at presentation. 38 (50.7%) patients had only residual thyroid tissue (RTT) on I-131 whole body bone scan (WBS) and 37 (49.3%) presented with metastatic disease (MD) at the time of therapy. Of the 37 patients with MD, 21 (56.8%) had metastases to the lymph nodes, 6 (16.2%) to the lungs, 4 (10.8%) to bone, 3 (8.1%) to bone and lung, and 4 (10.8%) to lung plus lymph nodes. Twenty-three patients (7 FC , 13 - PC and 3 MC; 6 RTT, 17 - MD) , received more than one dose of I-131 with a TMD of 422.7 mCi (Range 88 1590 mCi ). 52 patients (13 FC, 34 PC, 5 MC; 20 MD and 32 RTT) received a single TMD of 104.4 (Range 39.5 219 mCi). On follow-up, 3 patients of FC with MD (2 lung metastasis and 1 with extensive lymph node metastasis), died within 3 months 2 years of therapy. 3 patients of MD (2 FC, 1-MC; 2 bone metastasis and 1 bone with lung metastasis) died after 5 .5 years, Of the 6 patients who died, 5 were FC and only 1 was MC. 2 patients with MD to lungs and bone had received a single dose and were lost to follow up. All patients with PC and FC with only RTT, were surviving at the end of 5 years. None of the patients with MD to lymph nodes died at the end of 5 years, either receiving single or multiple doses. In our study group, the TMD for ablation used in RTT was 100.4mCi, and 5 year mortality was zero. The patients with MD involving lungs and bone had the worst prognosis, despite multiple doses of I-131 (TMD of 442.7 mCi). 33.3% patients with lung metastasis died before the end of 5 years. Only bone MD had slightly better prognosis than either lung or lung plus bone metastasis. Lymph node involvement did not increase the mortality, and it remained zero at 5 years