Dose-Response Relationship in Differentiated Thyroid Cancer Patients Undergoing Radioiodine Treatment Assessed by Means of 124I PET/CT

The dose–response relationship in a fixed-activity approach generally applied in the treatment of differentiated thyroid cancer was assessed using ¹²⁴I PET/CT. Methods: Pretherapeutic ¹²⁴I PET/CT images of 47 patients scheduled for radioiodine therapy were retrospectively analyzed. ¹²⁴I PET/CT images were acquired 24 and 96 h after oral administration of approximately 28 MBq of ¹²⁴I-sodium iodide. Lesions were identified as thyroid remnants or metastases (lymph node, lung, bone). After a neoteric segmentation technique allowing accurate volume estimation down to the ¹²⁴I PET spatial resolution of 0.15 mL was applied, lesions were divided into a known-volume group and a small-volume group. For the known-volume group, average lesion-absorbed dose (AD) values were calculated, whereas for the small-volume group a minimum lesion AD was estimated. Lesion response was determined on the basis of ¹²⁴I PET/CT and ¹³¹I SPECT/CT follow-up images. A lesion not detectable on any of the follow-up images was considered a completely responding lesion. Differences in lesion AD estimations between completely and incompletely responding lesions were evaluated by Mann–Whitney U test. Moreover, receiver-operating-characteristic curves were used to test the performance of pretherapeutic ¹²⁴I PET/CT lesion AD for prediction of complete lesion response. Results: In the approach of fixed radioiodine activity (3.0 ± 1.0 GBq), 89% of thyroid remnants and 69% of metastases responded completely. Except for the small-volume groups, the lesion AD of completely responding lesions was significantly higher than that of incompletely responding lesions. Using receiver-operating-characteristic curve analysis, it was shown that for the known-volume group, pretherapeutic ¹²⁴I PET/CT lesion dosimetry can be used as a prognostic tool to predict lesion-based ¹³¹I therapy response with an area under the curve of 0.76 for remnants and 0.97 for metastases. The corresponding lesion AD threshold value maximizing correct complete response prediction was 90 Gy for remnants and 40 Gy for metastases. Conclusion: In a fixed-activity approach, a statistically significant dose–response relationship for both thyroid remnants and metastases using pretherapeutic ¹²⁴I PET/CT lesion dosimetry was found. The findings may be useful in patient management.

from #MedicinebyAlexandrosSfakianakis via xlomafota13 on Inoreader http://ift.tt/29h0gra
via IFTTT