title: Patient dosimetry for 131I-MIBG therapy for neuroendocrine tumours based on 123I-MIBG scans.
abstract: Pre-therapeutic metaiodobenzylguanidine (MIBG) scans can be performed using labelling with either iodine-123 or iodine-131. (123)I-MIBG scans provide better image quality and count statistics, while (131)I-MIBG allows registration of tracer kinetics over a longer period. The aim of this study was to determine how much information about the (131)I-MIBG therapy total body dose according to the MIRD formalism can be gathered from (123)I-MIBG pre-therapy scans. Thirty-eight (131)I-MIBG therapies administered to a total of 15 patients suffering from neuroblastoma ( n=6), carcinoid tumours ( n=5), phaeochromocytoma ( n=3) and medullary thyroid carcinoma ( n=1) were included. The mean administered activity was 5.3 GBq (SD 2.4 GBq). Three biplanar (123)I-MIBG total body scans were taken only once before a series of therapies while three biplanar (131)I-MIBG scans were taken after each therapy. Attenuation correction was performed taking into account the difference in attenuation between (123)I and (131)I. Using the MIRD formalism, the total body dose to the patient was calculated on the basis of: (1) a single exponential fit drawn through the data from the (123)I-MIBG pre-therapy scans, (2) a bi-exponential fit through the combined data of (123)I-MIBG pre-therapy and (131)I-MIBG post-therapy scans. The mean total body dose calculated in our study was significantly higher for patients suffering from neuroblastoma (mean+/-SD 0.37+/-0.21 mGy/MBq) than for patients suffering from phaeochromocytoma (0.08+/-0.02 mGy/MBq), carcinoid tumours (0.07+/-0.01 mGy/MBq) and medullary thyroid carcinoma (0.09 mGy/MBq). The correlation coefficient between the dose calculated on the basis of the (123)I-MIBG pre-therapy scans and the subsequent (131)I-MIBG therapy was 0.93 when a correction factor of 1.26 was taken into account. When considering all following therapies, the correlation was 0.85 and the correction factor, 1.20. Our results show that it is feasible to use data from pre-therapy (123)I-MIBG scans to calculate the total body dose of the subsequent (131)I-MIBG therapy.
authors.affiliation: Department of Medical Physics and Radiation Protection, Ghent University, Proeftuinstraat 86, 9000 Ghent, Belgium. myriam.monsieurs@rug.ac.be
authors.forename: Myriam
authors.initials: M
authors.lastname: Monsieurs
authors.forename: Boudewijn
authors.initials: B
authors.lastname: Brans
authors.forename: Klaus
authors.initials: K
authors.lastname: Bacher
authors.forename: Rudi
authors.initials: R
authors.lastname: Dierckx
authors.forename: Hubert
authors.initials: H
authors.lastname: Thierens
mesh_terms: D019797:3-Iodobenzylguanidine / Q000627:therapeutic use*; D000293:Adolescent; D000328:Adult; D000368:Aged; D001822:Body Burden; D002648:Child; D002675:Child, Preschool; D005240:Feasibility Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D018358:Neuroendocrine Tumors / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D011874:Radiometry / Q000379:methods; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000627:therapeutic use; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014915:Whole-Body Counting / Q000379:methods
chemical_list: D019275:Radiopharmaceuticals; D019797:3-Iodobenzylguanidine