title: Patient-specific dosimetry for intracavitary 32P-chromic phosphate colloid therapy of cystic brain tumours.
abstract: OBJECTIVE
  (32)P-chromic phosphate colloid treatments of astrocytoma and craniopharyngioma cystic brain tumours in paediatric patients are conventionally based on a sphere model under the assumption of uniform uptake. The aims of this study were to determine the distribution of the absorbed dose delivered by (32)P on a patient-specific basis and to evaluate the accuracy with which this can be predicted from a pretherapy administration of (99m)Tc-Sn colloid.
  
  
  METHODS
  Three patients were treated with (32)P-chromic phosphate colloid following (99m)Tc-Sn colloid administrations. Convolution dosimetry was performed using pretherapy and posttherapy sequential SPECT imaging, and verified with EGSnrc Monte Carlo radiation transport simulations. Mean absorbed doses to the cyst wall and dose-volume histograms were also calculated and compared with those obtained by the sphere model approach.
  
  
  RESULTS
  Highly nonuniform uptake distributions of both the (99m)Tc and (32)P colloids were observed and characterized by dose-volume histograms to the cyst wall. Mean absorbed doses delivered to the cyst wall, obtained with the convolution method, were on average 21 % (SD 18 %) and 50 % (SD 30 %) lower than those predicted by the (99m)Tc distribution and the uniform assumption of the sphere model, respectively.
  
  
  CONCLUSIONS
  Absorbed doses delivered to the cyst wall by (32)P are more accurately predicted from image-based patient-specific convolution dosimetry than from simple sphere models. These results indicate the necessity to perform personalized treatment planning and verification for intracavitary irradiation of cystic brain tumours treated with radiocolloids. Patient-specific dosimetry can be used to guide the frequency and levels of repeated administrations and would facilitate data collection and comparison to support the multicentre trials necessary to progress this therapy.
authors.affiliation: Joint Department of Physics, Institute of Cancer Research, Sutton, London, SM2 5NG, UK, ana.denisbacelar@icr.ac.uk.
authors.forename: Ana M
authors.initials: AM
authors.lastname: Denis-Bacelar
authors.forename: Marina
authors.initials: M
authors.lastname: Romanchikova
authors.forename: Sarah
authors.initials: S
authors.lastname: Chittenden
authors.forename: Frank H
authors.initials: FH
authors.lastname: Saran
authors.forename: Henry
authors.initials: H
authors.lastname: Mandeville
authors.forename: Yong
authors.initials: Y
authors.lastname: Du
authors.forename: Glenn D
authors.initials: GD
authors.lastname: Flux
mesh_terms: D001254:Astrocytoma / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D002648:Child; D017608:Chromium Compounds / Q000493:pharmacokinetics* / Q000627:therapeutic use; D003102:Colloids / Q000493:pharmacokinetics / Q000627:therapeutic use; D003397:Craniopharyngioma / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D003560:Cysts / Q000000981:diagnostic imaging / Q000532:radiotherapy; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008954:Models, Biological; D010710:Phosphates / Q000493:pharmacokinetics* / Q000627:therapeutic use; D010911:Pituitary Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011874:Radiometry; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics*; D017556:Technetium Compounds / Q000493:pharmacokinetics / Q000627:therapeutic use; D017971:Tin Compounds / Q000493:pharmacokinetics / Q000627:therapeutic use; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D017608:Chromium Compounds; D003102:Colloids; D010710:Phosphates; D019275:Radiopharmaceuticals; D017556:Technetium Compounds; D017971:Tin Compounds; C033493:technetium Tc 99m tin colloid; C509370:chromic phosphate, 32P-labeled