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Analysis of the photon beam treatment planning data for a scanning beam machine
Author(s) -
Lovelock D. M. J.,
Chui C. S.,
Kutcher G. J.,
Mohan R.
Publication year - 1994
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.597229
Subject(s) - monte carlo method , fluence , photon , optics , beam (structure) , dosimetry , physics , photon energy , computational physics , nuclear medicine , statistics , mathematics , medicine , laser
The characteristics of photon beams from the Scanditronix MM50 radiation therapy machine that are necessary for treatment planning are described. The MM50 uses a scanning beam instead of a conventional flattening filter to achieve flat dose distributions. At each beam energy, a scan pattern is chosen, depending on the field size; the small scan pattern ( S ) is used for field sizes up to 10×10 cm, the medium scan pattern ( M ) is used for field sizes up to 20×20 cm, and the large scan pattern ( L ) is used for the larger field sizes. The dose distributions of the beams associated with the 10 MV S , M , and L scan patterns, the 25 MV S , M , and L patterns, and the 50 MV S and M patterns are described. The data reported includes central axis data, beam profiles, and output factors. In addition to the measured data, our dose calculation model requires a pencil beam kernel for each beam. The kernel is constructed using the average photon energy spectrum, which is generated using a Monte Carlo simulation of the MM50. The simulation, based on EGS4 , is also used to generate the radial variation of fluence and energy fluence, which is required by a new dose calculation model that does not require the measurement of beam profiles. The Monte Carlo generated data; the photon energy spectrum, the fluence, and the energy fluence are presented.