title: Dosimetry for fractionated (131)I-mIBG therapies in patients with primary resistant high-risk neuroblastoma: preliminary results.
abstract: This paper describes the development of a protocol for SPECT-based tumor dosimetry for (131)I-mIBG therapy patients with high-risk neuroblastoma. The treatment aims to deliver a whole-body dose of 4 Gy in two fractions. Whole-body retention measurements taken during the first fraction are used to guide the second therapy administration. The tumor dose from 3 patients was assessed by acquiring a minimum of three SPECT scans. Dead-time and triple-energy window scatter corrections were applied. The images were reconstructed using filtered backprojection with a Chang attenuation correction, and a phantom-based calibration factor was used to convert to activity. A monoexponential fit was made to the data, and instantaneous uptake was assumed. Tumor absorbed-dose ratios were used to analyze intrapatient variations, and absolute tumor dosimetry was used to assess interpatient variation. The whole-body dose administered ranged from (3.7 +/- 0.1) Gy to (3.9 +/- 0.3) Gy. This method is more accurate than a weight-based administration method. Despite this, a variation in absorbed tumor dose of 10-103 Gy was observed. All repeat doses were in the same order of magnitude, although 2 patients received a lower tumor dose per MBq from the second therapy owing to a shorter biological half-life. The tumor dosimetry protocol was simple to apply and reproducible, but the errors in image quantitation needed to be evaluated.
authors.affiliation: Royal Marsden NHS Foundation Trust, Sutton, Surrey, UK. susan.buckley@icr.ac.uk
authors.forename: Susan E
authors.initials: SE
authors.lastname: Buckley
authors.forename: Frank H
authors.initials: FH
authors.lastname: Saran
authors.forename: Mark N
authors.initials: MN
authors.lastname: Gaze
authors.forename: Sarah
authors.initials: S
authors.lastname: Chittenden
authors.forename: Mike
authors.initials: M
authors.lastname: Partridge
authors.forename: Donna
authors.initials: D
authors.lastname: Lancaster
authors.forename: Andrew
authors.initials: A
authors.lastname: Pearson
authors.forename: Glenn D
authors.initials: GD
authors.lastname: Flux
mesh_terms: D019797:3-Iodobenzylguanidine / Q000737:chemistry / Q000627:therapeutic use*; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D008297:Male; D009447:Neuroblastoma / Q000188:drug therapy* / Q000473:pathology / Q000532:radiotherapy*; D011874:Radiometry; D013997:Time Factors
chemical_list: D007457:Iodine Radioisotopes; D019797:3-Iodobenzylguanidine