Radioiodine (I-131) application in the management of differentiated thyroid cancer (DTC) audit

Full text: Differentiated thyroid cancer (DTC) remains one of the curable of all cancers. All literature reviews and clinical experiences regarding I131 use in DTC conclude the beneficial effects, better prognosis, longer survival time and an assurance for cure. The Overall prognosis of patients with DTC is excellent if treat scientifically, adequately and timely. The management of thyroid cancer depends on the resources available in different institutions. Nuclear Medicine unit (NMU), Faculty of Medicine Peradeniya, Sri Lanka is in the process of uplifting the services for thyroid cancer management. Clinical audit was carried out in NMU on patients who utilized the Nuclear Medicine facilities in the management of DTC. It is important to identify deficiencies in current practice to improve our services. During January 2004 to March 2005, 126 DTC patients were referred for radioiodine Whole body scan (WBS) and therapy. Their age, sex, histology, extent of surgery, adequacy of thyroxine suppression treatment, monitoring with serum thyroglobulin levels (Tg), WBS results and radioiodine therapy were analyzed. There were 104(82.5%) females and 22(17.5%) males giving sex ratio of 4.7: 1. The Mean age was 35.5 years (range 9-58 years). The commonest histological types were papillary carcinoma 55.5% (n=70), follicular carcinoma 35% (n=44) and follicular variant of papillary carcinoma 9.5% (n=12). Seventy five percent (n=95) had total thyroidectomy (TT), 17 %(n=21) had near total thyroidectomy (NTT) and 8%(n=10) had subtotal thyroidectomy (STT). Sixty-nine patients (54.8%) were on thyroid suppression therapy. Thirty-six patients (28.6%) were referred to the WBS soon after surgery without initiation of thyroxine treatment. Another twenty-one patients (16.6%) were not on thyroxine therapy since surgery. Serum thyroglobulin was assessed on 20.6% (n=26). WBS done using 3-4 mCi liquid radioiodine showed residual functioning thyroid tissues in 41% (n=52). Lymph nodes or bone metastases were detected in 16% (n=21). Of 52 patients with residual thyroid tissues, fourteen patients (30%) received residual ablation dose of 30 mCi of radioiodine. All 21 patients who exhibit abnormal WBS were referred to the cancer unit for high dose therapy. This study showed DTC is more common in young females than in males and Papillary carcinoma is the commonest histological type in Sri Lanka. Though the preferred surgical management is TT or NTT (92%) this study showed inadequacy of excision. In Sri Lanka we have very few experienced thyroid surgeons. Inadequate surgical excision could be due to inexperience and lack of facilities for surgical management in peripheral hospitals. Inadequate surgical excision will directly interfere with the long-term follow up of DTC. Presence of remnant thyroid tissues makes detection and treatment of nodal or distant metastases difficult. High TSH levels necessary to enhance tumor I131 uptake and assessment of Tg levels, the most sensitive test for detection of recurrences cannot be achieved with a large thyroid remnants. This results indicative of low sensitivity of the WBS and serum Tg measurements in our set up. We have detected 16% of patients with distant metastases but the actual number may be higher than this figure. Monitoring with Tg is grossly inadequate. Serum Tg test is expensive in our set up prevent us using this facility. Approximately 2/3 of this study group were not received residual ablation partly due to unawareness, not enough radioiodine in the government hospitals and poor follow up in our set up. Management of DTC is still debatable. There is no agreement on extent of surgery, optimal time for WBS, residual ablation and long-term fallow up. Today highly effective method of treatment for DTC is the combination of thyroid surgery (TT/NTT) followed by RAI residual ablation and thyroxine suppression therapy. 30 mCi of radioiodine is the highest permissible activity for out patient treatment according to the local Atomic Energy Agency, Sri Lanka. We prefer to use 30 mCi RAI for residual ablation as it can be used effectively on an out patients basis with associated low cost, convenience and low whole body radiation absorbed dose to the patient. Review of current practice in time to time is justified. Several deficiencies in the management of DTC as a whole were identified. Extent of surgery, radioiodine residual ablation, TSH suppression after surgery and monitoring with serum Tg are grossly inadequate. Guidelines should be introduced to promote the cost effective use of Nuclear Medicine facilities in the management of DTC. Locally agreed protocols are needed to minimize these deficiencies and uplift the existing facilities in the diagnosis, treatment and follow up of DTC patients in Sri Lanka. (author)