Dosimetric characteristics of unflattened 6 MV photon beams of a clinical linear accelerator: a Monte Carlo study.

The purpose of this study is to evaluate the dosimetric properties of a flattening filter free 6 MV photon beam. The 6 MV photon beam of a Varian Clinac 21 EX linac was modeled using the MCNP4C Monte Carlo (MC) code. Dosimetric features including central axis absorbed doses, beam profiles and photon energy spectra were calculated for flattened and unflattened 6 MV photon beams. A substantial increase in the dose rate was seen for the unflattened beam, which was decreased with field size and depth. The penumbra width was decreased less than 0.2 mm (about 5%) and a 25% decrease in out-of-field dose was observed for the unflattened beam. The photon energy spectra were softer for the unflattened beam and the mean energies of spectra were higher for smaller field size. Our study showed that increase in the dose rate and lower out-of-field dose could be considered as practical advantages for unflattened 6 MV beams.

[1]  J. F. Briesmeister.  MCNP-A General Monte Carlo N-Particle Transport Code , 1993 .

[2]  Jianrong Dai,et al.  Delivery time comparison for intensity-modulated radiation therapy with/without flattening filter: a planning study. , 2004, Physics in medicine and biology.

[3]  David I Thwaites,et al.  Development and commissioning of a Monte Carlo photon beam model for Varian Clinac 2100EX linear accelerator. , 2006, Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine.

[4]  P F O'Brien,et al.  Radiosurgery with unflattened 6-MV photon beams. , 1991, Medical physics.

[5]  D. Sheikh-Bagheri,et al.  Sensitivity of megavoltage photon beam Monte Carlo simulations to electron beam and other parameters. , 2002, Medical physics.

[6]  Radhe Mohan,et al.  WE‐E‐T‐617‐03: Flattening Filter Free IMRT ‐ First Experimental Results , 2005 .

[7]  W. Lutz,et al.  The effect of flattening filter design on quality variations within an 8-MV primary x-ray beam. , 1984, Medical physics.

[8]  Radhe Mohan,et al.  Properties of unflattened photon beams shaped by a multileaf collimator. , 2006, Medical physics.

[9]  Robert Jeraj,et al.  Radiation characteristics of helical tomotherapy. , 2004, Medical physics.

[10]  Frank Verhaegen,et al.  Monte Carlo modelling of external radiotherapy photon beams. , 2003, Physics in medicine and biology.

[11]  U Titt,et al.  A flattening filter free photon treatment concept evaluation with Monte Carlo. , 2006, Medical physics.

[12]  Radhe Mohan,et al.  Dosimetric properties of photon beams from a flattening filter free clinical accelerator , 2005, Physics in medicine and biology.

[13]  Radhe Mohan,et al.  Monte Carlo study of photon fields from a flattening filter-free clinical accelerator. , 2006, Medical physics.

[14]  P C Lee,et al.  Monte Carlo simulations of the differential beam hardening effect of a flattening filter on a therapeutic x-ray beam. , 1997, Medical physics.

[15]  Asghar Mesbahi,et al.  Monte Carlo calculation of Varian 2300C/D Linac photon beam characteristics: a comparison between MCNP4C, GEANT3 and measurements. , 2005, Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine.