Dosimetry of ¹³¹I in remnant ablation and metastasis of differentiated thyroid cancer treated with high radioactivities and rhTSH

Abstract

Purpose: Ruling out that healthy organs receive doses higher than those allowed in treatments with Iodo-131 (¹³¹I) for ablation of thyroid remnant is crucial for the radiological protection of the patient who also received the recombinant human thyroid-stimulating hormone (rhTSH). So, the investigation aimed to determine the changes in energy imparted by ¹³¹I in multiple organs due to the rhTSH in thyroid remnants and metastases of patients treated with high ¹³¹I activities (≥ 5,550 MBq). Materials and methods: Nine patients were divided into three groups (three per group); Group I included thyroid hormone withdrawal (THW) patients, while patients in groups II and III were stimulated with rhTSH. The activity and absorbed dose in regions of interest (ROIs) was quantified using the conjugated views method using gamma camera images. Results and discussion: Dosimetric variations of ¹³¹I produced by using rhTSH in the remnant thyroid (groups II and III) were observed, absorbed doses were minor for groups treated with rhTSH. Conclusion: The application of the high activities > 5,500 MBq administered together with the application of rhTSH is safe in dosimetric terms, also for 9250 MBq do not exceed established limits of absorbed dose in the bone marrow. Furthermore, these high activities provide more than three times the radiation dose to remaining thyroid tissue and approximately 1.5 times to metastases.

KEYWORDS:

• Differentiated thyroid cancer
• ¹³¹I
• recombinant human thyroid-stimulating hormone (rhTSH)
• internal dosimetry

Disclosure statement

No potential conflict of interest was reported by the author(s).