RT Journal Article SR Electronic T1 Assessment of Lesion Response in the Initial Radioiodine Treatment of Differentiated Thyroid Cancer Using 124I PET Imaging JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1759 OP 1765 DO 10.2967/jnumed.114.144089 VO 55 IS 11 A1 Jentzen, Walter A1 Hoppenbrouwers, Jan A1 van Leeuwen, Paul A1 van der Velden, Daan A1 van de Kolk, Rudie A1 Poeppel, Thorsten Dirk A1 Nagarajah, James A1 Brandau, Wolfgang A1 Bockisch, Andreas A1 Rosenbaum-Krumme, Sandra YR 2014 UL http://jnm.snmjournals.org/content/55/11/1759.abstract AB 124I PET/CT images from differentiated thyroid cancer patients were retrospectively analyzed to assess the relationship between absorbed radiation dose (AD) to lesions and their response after radioiodine therapy. Methods: Patients received serial 124I PET/CT scans before and after their first radioiodine treatment. The pretherapy PET data were used to segment the lesion volumes and to predict the therapy-delivered ADs after administration of the therapeutic 131I activity. The segmentation method’s lower volume limit of determinability was a sphere of 0.80 mL, which classified the lesions into a known-volume group (>0.80 mL) or a small-volume group (≤0.80 mL) with their respective average and minimum ADs. The posttherapy PET data were used to assess the lesion-based therapy success. In the known-volume group, the response rate was calculated on the basis of lesions that received average ADs above the generally accepted threshold of 85 Gy for metastases and 300 Gy for thyroid remnants (TRs) and was expressed as the percentage of completely responding lesions. In the small-volume group, the metastasis and TR responses were evaluated for 3 minimum-AD groups: 5 to 10 Gy (TR, 5 to 30 Gy), >10 to 85 Gy (TR, >30 to 300 Gy), and >85 Gy (TR, >300 Gy). Their response rates were calculated in terms of the percentage of completely responding lesions in each minimum-AD group. Results: In total, 59 lesions in 17 patients were amenable to reliable volume estimation. The response rates were 63%, 88%, and 90% for lymph node metastases (LMs), pulmonary metastases, and TRs, respectively. The response rates of 168 small lesions in 34 patients were more than 82% for LMs and more than 91% for TRs in each of the 3 minimum-AD groups; all small pulmonary metastases responded completely. Conclusion: In the known-volume group, the response rate for TRs matched well with historical data derived using 131I scintigraphy imaging, whereas the response rate for LMs was not as high as expected, which may be explained by too short a follow-up time for a few LMs and a higher sensitivity of PET imaging. Small lesions were treated effectively, suggesting that they are considerably smaller than 0.80 mL.