title: Assessment of lesion response in the initial radioiodine treatment of differentiated thyroid cancer using 124I PET imaging.
abstract: (124)I 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 (124)I 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 (131)I 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.
  
  
  CONCLUSIONS
  In the known-volume group, the response rate for TRs matched well with historical data derived using (131)I 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.
authors.affiliation: Klinik für Nuklearmedizin, Universität Duisburg-Essen, Essen, Germany; and walter.jentzen@uni-duisburg-essen.de.
authors.forename: Walter
authors.initials: W
authors.lastname: Jentzen
authors.affiliation: Fontys University of Applied Sciences, Eindhoven, The Netherlands.
authors.forename: Jan
authors.initials: J
authors.lastname: Hoppenbrouwers
authors.affiliation: Fontys University of Applied Sciences, Eindhoven, The Netherlands.
authors.forename: Paul
authors.initials: P
authors.lastname: van Leeuwen
authors.affiliation: Fontys University of Applied Sciences, Eindhoven, The Netherlands.
authors.forename: Daan
authors.initials: D
authors.lastname: van der Velden
authors.affiliation: Fontys University of Applied Sciences, Eindhoven, The Netherlands.
authors.forename: Rudie
authors.initials: R
authors.lastname: van de Kolk
authors.affiliation: Klinik für Nuklearmedizin, Universität Duisburg-Essen, Essen, Germany; and.
authors.forename: Thorsten Dirk
authors.initials: TD
authors.lastname: Poeppel
authors.affiliation: Klinik für Nuklearmedizin, Universität Duisburg-Essen, Essen, Germany; and.
authors.forename: James
authors.initials: J
authors.lastname: Nagarajah
authors.affiliation: Klinik für Nuklearmedizin, Universität Duisburg-Essen, Essen, Germany; and.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Brandau
authors.affiliation: Klinik für Nuklearmedizin, Universität Duisburg-Essen, Essen, Germany; and.
authors.forename: Andreas
authors.initials: A
authors.lastname: Bockisch
authors.affiliation: Klinik für Nuklearmedizin, Universität Duisburg-Essen, Essen, Germany; and.
authors.forename: Sandra
authors.initials: S
authors.lastname: Rosenbaum-Krumme
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008175:Lung Neoplasms / Q000473:pathology / Q000556:secondary; D008207:Lymphatic Metastasis / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D011829:Radiation Dosage; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000627:therapeutic use*; D011879:Radiotherapy Dosage; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals
keywords: 124I; dosimetry; radioiodine therapy; thyroid carcinoma