Normal organ dosimetry for thyroid cancer patients treated with radioiodine as part of the multi-centre multi-national Horizon 2020 MEDIRAD project

Purpose Dosimetry is rarely performed for the treatment of differentiated thyroid cancer patients with Na[^131I]I (radioiodine), and information regarding absorbed doses delivered is limited.

Collection of dosimetry data in a multi-centre setting requires standardised quantitative imaging and dosimetry.

A multi-national, multi-centre clinical study was performed to assess absorbed doses delivered to normal organs for differentiated thyroid cancer patients treated with Na[^131I]I. Methods Patients were enrolled in four centres and administered fixed activities of 1.1 or 3.7 GBq of Na[^131I]I using rhTSH stimulation or under thyroid hormone withdrawal according to local protocols.

Patients were imaged using SPECT(/CT) at variable imaging time-points following standardised acquisition and reconstruction protocols.

Whole-body retention data were collected.

Dosimetry for normal organs was performed at two dosimetry centres and results collated.

Results One hundred and five patients were recruited.

Median absorbed doses per unit administered activity of 0.44, 0.14, 0.05 and 0.16 mGy/MBq were determined for the salivary glands of patients treated at centre 1, 2, 3 and 4, respectively.

Median whole-body absorbed doses for 1.1 and 3.7 GBq were 0.05 Gy and 0.16 Gy, respectively.

Median whole-body absorbed doses per unit administered activity of 0.04, 0.05, 0.04 and 0.04 mGy/MBq were calculated for centre 1, 2, 3 and 4, respectively.

Conclusions A wide range of normal organ doses were observed for differentiated thyroid cancer patients treated with Na[^131I]I, highlighting the necessity for individualised dosimetry.

The results show that data may be collated from multiple centres if minimum standards for the acquisition and dosimetry protocols can be achieved.