title: Feasibility of dosimetry-based high-dose 131I-meta-iodobenzylguanidine with topotecan as a radiosensitizer in children with metastatic neuroblastoma.
abstract: BACKGROUND
  (131)I-meta iodobenzylguanidine ((131)I-mIBG) therapy is established palliation for relapsed neuroblastoma. The topoisomerase-1 inhibitor, topotecan, has direct activity against neuroblastoma and acts as a radiation sensitiser. These 2 treatments are synergistic in laboratory studies. Theoretically, the benefit of (131)I-mIBG treatment could be enhanced by dose escalation and combination with topotecan. Haematological support would be necessary to overcome the myelosuppression, which is the dose-limiting toxicity.
  
  
  OBJECTIVE
  Firstly, one aim of this study was to establish whether in vivo dosimetry could be used to guide the delivery of a precise total whole-body radiation-absorbed dose of 4 Gy accurately from 2 (131)I-mIBG treatments. Secondly, the other aim of this study was to determine whether it is feasible to combine this treatment with the topotecan in children with metastatic neuroblastoma.
  
  
  METHODS
  An activity of (131)I-mIBG (12 mCi/kg, 444 MBq/kg), estimated to give a whole-body absorbed-radiation dose of approximately 2 Gy, was administered on day 1, with topotecan 0.7 mg/m(2) administered daily from days 1-5. In vivo dosimetry was used to calculate a 2nd activity of (131)I-mIBG, to be given on day 15 which would give a total whole-body dose of 4 Gy. A further 5 doses of topotecan were given from days 15-19. The myeloablative effect of this regimen was circumvented by peripheral blood stem cell or bone marrow support.
  
  
  RESULTS
  Eight children with relapsed stage IV neuroblastoma were treated. The treatment was delivered according to protocol in all patients. There were no unanticipated side-effects. Satisfactory haematological reconstitution occurred in all patients. The measured total whole-body radiation-absorbed dose ranged from 3.7 Gy to 4.7 Gy (mean, 4.2 Gy).
  
  
  CONCLUSIONS
  In vivo dosimetry allows for a specified total whole-body radiation dose to be delivered accurately. This schedule of intensification of (131)I-mIBG therapy by dose escalation and radiosensitization with topotecan with a haemopoietic autograft is safe and practicable. This approach should now be tested for efficacy in a phase II clinical trial.
authors.affiliation: Meyerstein Institute of Oncology, The Middlesex Hospital, London W1T 3AA, UK. mark.gaze@uclh.org
authors.forename: Mark N
authors.initials: MN
authors.lastname: Gaze
authors.forename: Yen-Ch'ing
authors.initials: YC
authors.lastname: Chang
authors.forename: Glenn D
authors.initials: GD
authors.lastname: Flux
authors.forename: Rob J
authors.initials: RJ
authors.lastname: Mairs
authors.forename: Frank H
authors.initials: FH
authors.lastname: Saran
authors.forename: Simon T
authors.initials: ST
authors.lastname: Meller
mesh_terms: D019797:3-Iodobenzylguanidine / Q000494:pharmacology*; D002648:Child; D002675:Child, Preschool; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000494:pharmacology; D008297:Male; D009362:Neoplasm Metastasis; D009447:Neuroblastoma / Q000628:therapy*; D011829:Radiation Dosage; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D011874:Radiometry / Q000379:methods*; D019275:Radiopharmaceuticals / Q000494:pharmacology*; D011879:Radiotherapy Dosage; D019772:Topotecan / Q000494:pharmacology*; D014915:Whole-Body Counting
chemical_list: D007457:Iodine Radioisotopes; D011838:Radiation-Sensitizing Agents; D019275:Radiopharmaceuticals; D019797:3-Iodobenzylguanidine; D019772:Topotecan