Dose distribution outside of a sphere of P-32 chromic phosphorous colloid.
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.
Hechtman
Charles D
CD
Department of Radiation Oncology, Washington University School of Medicine, and the Alvin J. Siteman Cancer Center, St. Louis, MO 63110, USA. ckhechtman@aol.com
Li
Zuofeng
Z
Mansur
David B
DB
Perez
Carlos A
CA
Myerson
Robert J
RJ
Simpson
Joseph R
JR
Anders
Jon C
JC
Wu
Catherine
C
Palucci
Cindy A
CA
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
D010761:Phosphorus Radioisotopes