title: Dose distribution outside of a sphere of P-32 chromic phosphorous colloid.
abstract: OBJECTIVE
  To evaluate the dose distribution outside of a cyst instilled with phosphorous-32 (P-32, an electron emitter with a short effective range of 2-8 mm and average energy of 0.69 MeV, used to treat cystic craniopharyngioma) as a function of cyst size with and without plating (migration and adhesion of P-32 to the cyst surface).
  
  
  METHODS
  A cystic craniopharyngioma treated with instillation of P-32 was approximated by a sphere of uniformly distributed and plated chromic P-32 colloid. The percent depth dose was calculated along a radial position vector exterior to the sphere with a three-dimensional convolution integral and a dose point kernel.
  
  
  RESULTS
  The percent depth dose variation of surface or volume source external to a family of spheres was plotted. Complex cyst geometry is amenable to evaluation by approximation with simple spheres. Error estimates are calculated for the dose outside of truncated sphere segments. Plating might occur and raise the dose outside the cyst by more than a factor of 5.0. This has the potential to cause damage to adjacent tissues, including the optic chiasm.
  
  
  CONCLUSIONS
  Clinicians are faced with a number of treatment options for cystic craniopharyngioma, including intracystic instillation of colloid P-32. Unfortunately, plating might occur and potentially damage adjacent normal tissues. It is recommended that the propensity for a craniopharyngioma to plate be evaluated before full treatment, especially after previous treatment.
authors.affiliation: Department of Radiation Oncology, Washington University School of Medicine, and the Alvin J. Siteman Cancer Center, St. Louis, MO 63110, USA. ckhechtman@aol.com
authors.forename: Charles D
authors.initials: CD
authors.lastname: Hechtman
authors.forename: Zuofeng
authors.initials: Z
authors.lastname: Li
authors.forename: David B
authors.initials: DB
authors.lastname: Mansur
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Perez
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Myerson
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Simpson
authors.forename: Jon C
authors.initials: JC
authors.lastname: Anders
authors.forename: Catherine
authors.initials: C
authors.lastname: Wu
authors.forename: Cindy A
authors.initials: CA
authors.lastname: Palucci
mesh_terms: D000465:Algorithms; D003397:Craniopharyngioma / Q000473:pathology / Q000532:radiotherapy*; D003560:Cysts / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D010761:Phosphorus Radioisotopes / Q000627:therapeutic use*; D010911:Pituitary Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000517:prevention & control; D011874:Radiometry / Q000379:methods
chemical_list: D010761:Phosphorus Radioisotopes