title: Developing a Treatment Planning Software Based on TG-43U1 Formalism for Cs-137 LDR Brachytherapy.
abstract: BACKGROUND
  The old Treatment Planning Systems (TPSs) used for intracavitary brachytherapy with Cs-137 Selectron source utilize traditional dose calculation methods, considering each source as a point source. Using such methods introduces significant errors in dose estimation. As of 1995, TG-43 is used as the main dose calculation formalism in treatment TPSs.
  
  
  OBJECTIVE
  The purpose of this study is to design and establish a treatment planning software for Cs-137 Solectron brachytherapy source, based on TG-43U1 formalism by applying the effects of the applicator and dummy spacers.
  
  
  METHODS
  Two softwares used for treatment planning of Cs-137 sources in Iran (STPS and PLATO), are based on old formalisms. The purpose of this work is to establish and develop a TPS for Selectron source based on TG-43 formalism. In this planning system, the dosimetry parameters of each pellet in different places inside applicators were obtained by MCNP4c code. Then the dose distribution around every combination of active and inactive pellets was obtained by summing the doses. The accuracy of this algorithm was checked by comparing its results for special combination of active and inactive pellets with MC simulations. Finally, the uncertainty of old dose calculation formalism was investigated by comparing the results of STPS and PLATO softwares with those obtained by the new algorithm.
  
  
  RESULTS
  For a typical arrangement of 10 active pellets in the applicator, the percentage difference between doses obtained by the new algorithm at 1cm distance from the tip of the applicator and those obtained by old formalisms is about 30%, while the difference between the results of MCNP and the new algorithm is less than 5%.
  
  
  CONCLUSIONS
  According to the results, the old dosimetry formalisms, overestimate the dose especially towards the applicator's tip. While the TG-43U1 based software perform the calculations more accurately.
authors.affiliation: Radiation Research Center, Shiraz University, Shiraz, IR Iran.
authors.forename: Sedigheh
authors.initials: S
authors.lastname: Sina
authors.affiliation: Radiation Research Center, Shiraz University, Shiraz, IR Iran ; Department of Nuclear Engineering, Shiraz University, Shiraz, IR Iran.
authors.forename: Reza
authors.initials: R
authors.lastname: Faghihi
authors.affiliation: Department of Nuclear Engineering, Shiraz University, Shiraz, IR Iran ; Comprehensive Cancer Center of Nevada, Las Vegas, Nevada, USA.
authors.forename: Ali
authors.initials: A
authors.lastname: Soleimani Meigooni
authors.affiliation: Department of Radiation Medicine, Shahid Beheshti University, Tehran, IR Iran.
authors.forename: Zahra
authors.initials: Z
authors.lastname: Siavashpour
authors.affiliation: Center for Research in Medical Physics and Biomedical Engineering, Shiraz University of Medical Sciences, Shiraz, IR Iran ; Department of Radiotherapy and Oncology, Shiraz University of Medical Sciences, Shiraz, IR Iran.
authors.forename: Mohammad Amin
authors.initials: MA
authors.lastname: Mosleh-Shirazi
keywords: Intracavitary Brachytherapy; Monte Carlo Method; PLATO