The success rate of I-131 ablation in differentiated thyroid cancer: comparison of uptake-related and fixed-dose strategies

Abstract

Introduction: The aim of the study was to compare the success rate of an uptake-related ablation protocol in which the dose depends on an I-131 24-h neck uptake measurement and a fixed-dose ablation protocol in which the dose depends on tumour stage. Methods: All differentiated thyroid carcinoma patients with M0 disease who had undergone (near-) total thyroidectomy followed by I-131 ablation were included. In the uptake-related ablation protocol, 1100 (uptake O10%), 1850 (uptake 5-10%) and 2800 MBq (uptake !5%) were used. In the fixeddosage ablation strategy, 3700 (T1-3, N0 stage) and 5550 MBq (N1 and/or T4 stage) were applied. We used I-131 uptake on whole-body scintigraphy and thyroglobulin-off values to evaluate the ablation 6-12 months after treatment. Results: In the uptake-related ablation protocol, 60 out of 139 (43%) patients were successfully treated versus 111 out of 199 for the fixed-dose ablation protocol (56%) (PZ0.022). The differences were not statistically significant for patients with T4 (PZ0.581) and/or N1 (PZ0.08) disease or for patients with T4N1 tumour stage (PZ0.937). Conclusion:The fixed-dose I-131 ablation protocol is more effective in ablation of the thyroid remnant in differentiated thyroid carcinoma patients than an uptake-related ablation protocol. This difference is not observed in patients with a N1 and/or T4 tumour stage.

Postsurgical thyroid remnant estimation by 99mTc‐pertechnetate scintigraphy predicts radioiodine ablation effectiveness in patients with differentiated thyroid carcinoma

“…6,13 In contrast, a population treated with the same fixed activities after diagnostic 131 I scintigraphy showed a 50% reduction of the ablation success rate. 18 This comparison shows that, like 123 I, 99m Tc-pertechnetate does not induce stunning and is, therefore, excellently suited for preablative assessment of the size of thyroid remnants; as the current study shows, the outcome of ablation is clearly related to the uptake in 99m Tc-pertechnetate scintigraphy.…”

Impact of histopathology of non-neoplastic thyroid tissue on ablation outcome in patients with papillary thyroid cancer

“…As a matter of fact, we should differentiate between the I-131 activity administered and the absorbed dose of radiation in thyroid tissue that causes the ablation effect. This dose depends on several factors, such as uptake of I-131, retention time in the remnant, mass of residual thyroid tissue, different TSH levels, the initial activity given, and the preparation of patient [29]. This is obvious in our study; despite the fact that if a standard amount of radioactivity is given, it results in different ablation outcomes denoting the presence of many factors affecting the radiation-absorbed dose in remnant thyroid tissue.…”

“…The presence of T4 tumor has a negative impact on ablation outcome as there seems to be a high chance of residual malignant cells in the thyroid remnants. Moreover, the presence of N1 lesions would adversely affect ablation outcome, as micrometastases in left lymph nodes cannot be excluded even after adequate neck dissection [29]. Many researchers have described that thyroid carcinoma cells take up and process iodine less efficiently than normal thyroid cells because of lower expression of NIS [36][37][38]; hence, both N1 and T4 tumor stages significantly correlated with a high chance of local tumor recurrences [39].…”

“…Many researchers have described that thyroid carcinoma cells take up and process iodine less efficiently than normal thyroid cells because of lower expression of NIS [36][37][38]; hence, both N1 and T4 tumor stages significantly correlated with a high chance of local tumor recurrences [39]. It was reported that in patients with T4N1 disease, complete ablation was achieved in only one out of 10 and nine patients using uptake-related and fixed-dose strategies, respectively [29]. These findings are in agreement with data published by Rosario et al [40], who found a clear relationship between ablation failures and presence of metastases and tumors larger than 4 cm in diameter.…”

La medicina nuclear y el cáncer diferenciado de tiroides

“…Sin embargo, para fines prácticos, la aplicación de yodo 131 suele clasificarse en ablación y tratamiento. La eficiencia del yodo 131 es inversamente proporcional al volumen de tejido tiroideo residual y directamente proporcional a los niveles de TSH, por lo que debe eliminarse quirúrgicamente toda la enfermedad macroscópica 33 . A la fecha existen tres enfoques para definir la dosis de yodo 131: dosis fijas, dosis determinada por el límite superior de la sangre y dosimetría tumoral cuantitativa.…”