Biomaterial Database

Monte Carlo dosimetry of the microselectron HDR 192Ir brachytherapy source using MCNP4A. 1998

S Wallace, and T Wong, and W Fernando

Radiotherapy Physics Department, Austin and Repatriation Medical Centre, Heidelberg West, Vic.

This study examines the transverse radial dose distribution around the Nucletron MicroSelectron high dose rate (HDR) 192Ir brachytherapy source using the Monte Carlo radiation transport code MCNP (Monte Carlo N Particle) version 4A. The geometry modeled consisted of an identical simulation of the geometry of the MicroSelectron HDR source within the centre of a cylindrical water phantom of 80 cm diameter and height. Doses were calculated at 0.1 cm intervals in the 1 cm closest to the source, whilst extending to 1 cm intervals 15 cm from the source. Conversion to the clinically relevant unit of air-kerma strength to describe source activity enables absolute comparison of Monte Carlo dose calculations to current treatment planning computer results. Most HDR brachytherapy planning computers utilise algorithms based on a point source with attenuation and scatter corrections based on the Van Kleffen and Starr or Meisberger equations. Significant differences between the planning computer algorithms and the Monte Carlo dose calculations occur in the near field (radius less than 1 cm) and the far field (radius greater than 8 cm) which in some cases may have important clinical consequences. These results are consistent with Monte Carlo calculations of previous authors examining the MicroSelectron HDR 192Ir source and also show that far field uncertainties are increased as the size of the phantom is reduced to a more realistic patient size.

UI	MeSH Term	Description	Entries
D007496	Iridium Radioisotopes	Unstable isotopes of iridium that decay or disintegrate emitting radiation. Ir atoms with atomic weights 182-190, 192, and 194-198 are radioactive iridium isotopes.	Radioisotopes, Iridium
D009010	Monte Carlo Method	In statistics, a technique for numerically approximating the solution of a mathematical problem by studying the distribution of some random variable, often generated by a computer. The name alludes to the randomness characteristic of the games of chance played at the gambling casinos in Monte Carlo. (From Random House Unabridged Dictionary, 2d ed, 1993)	Method, Monte Carlo
D011879	Radiotherapy Dosage	The total amount of radiation absorbed by tissues as a result of radiotherapy.	Dosage, Radiotherapy,Dosages, Radiotherapy,Radiotherapy Dosages
D011880	Radiotherapy Planning, Computer-Assisted	Computer-assisted mathematical calculations of beam angles, intensities of radiation, and duration of irradiation in radiotherapy.	Computer-Assisted Radiotherapy Planning,Dosimetry Calculations, Computer-Assisted,Planning, Computer-Assisted Radiotherapy,Calculation, Computer-Assisted Dosimetry,Calculations, Computer-Assisted Dosimetry,Computer Assisted Radiotherapy Planning,Computer-Assisted Dosimetry Calculation,Computer-Assisted Dosimetry Calculations,Dosimetry Calculation, Computer-Assisted,Dosimetry Calculations, Computer Assisted,Planning, Computer Assisted Radiotherapy,Radiotherapy Planning, Computer Assisted
D001918	Brachytherapy	A collective term for interstitial, intracavity, and surface radiotherapy. It uses small sealed or partly-sealed sources that may be placed on or near the body surface or within a natural body cavity or implanted directly into the tissues.	Curietherapy,Implant Radiotherapy,Plaque Therapy, Radioisotope,Radioisotope Brachytherapy,Radiotherapy, Interstitial,Radiotherapy, Intracavity,Radiotherapy, Surface,Brachytherapy, Radioisotope,Interstitial Radiotherapy,Intracavity Radiotherapy,Radioisotope Plaque Therapy,Radiotherapy, Implant,Surface Radiotherapy,Therapy, Radioisotope Plaque
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man