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Evaluation of TG‐43 recommended 2D‐anisotropy function for elongated brachytherapy sources
Author(s) -
Awan Shahid B.,
Meigooni Ali S.,
Mokhberiosgouei Ramin,
Hussain Manzoor
Publication year - 2006
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 - 10.1118/1.2357024
Subject(s) - brachytherapy , dosimetry , anisotropy , interpolation (computer graphics) , point source , function (biology) , physics , linear interpolation , nuclear medicine , computational physics , mathematics , optics , radiation therapy , medicine , mathematical analysis , radiology , motion (physics) , classical mechanics , evolutionary biology , biology , polynomial
The original and updated protocols recommended by Task Group 43 from the American Association of Physicists in Medicine (i.e., TG‐43 and TG‐43U1, respectively), have been introduced to unify brachytherapy source dosimetry around the world. Both of these protocols are based on experiences with sources less than 1.0 cm in length. TG‐43U1 recommends that forPd103sources, 2D anisotropy function F ( r , θ ) , should be tabulated at a minimum for radial distances of 0.5, 1.0, 2.0, 3.0, and 5.0 cm . Anisotropy functions defined in these protocols are only valid when the point of calculation does not fall on the active length of the source. However, for elongated brachytherapy sources (active length > 1 cm ), some of the calculation points with r < 1 2active length and small θ may fall on the source itself and there is no clear recommendation to handle this situation. In addition, the linear interpolation technique recommended by TG‐43U1 is found to be valid for seed types of sources as the difference between F ( r , θ ) for two consecutive radii is < 10 % . However, in the present investigations it has been found that values of F ( r , 5 ° ) for a 5 cm long RadioCoil ™Pd103source at radial distances of 2.5, 3.0, and 4.0 cm were 2.95, 1.74, and 1.19, respectively, with differences up to about a factor of 3. Therefore, the validity of the linear interpolation technique for an elongated brachytherapy source with such a large variation in F ( r , θ ) needs to be investigated. In this project, application of the TG‐43U1 formalism for dose calculation around an elongated RadioCoil ™Pd103brachytherapy source has been investigated. In addition, the linear interpolation techniques as described in TG‐43U1 for seed type sources have been evaluated for a 5.0 cm long RadioCoil ™Pd103brachytherapy source. Application of a polynomial fit to F ( r , θ ) has also been investigated as an alternate approach to the linear interpolation technique. The results of these investigations indicate that the TG‐43U1 formalism can be extended for elongated brachytherapy sources, if the two‐dimensional (2D) anisotropy function is tabulated at a minimum for radial distances of 0.2, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 cm , L ∕ 2 , and L ∕ 2 ± 0.2 cm . Moreover, with the addition of recommended radial distances for 2D anisotropy functions, the linear interpolation technique more closely replicates Monte Carlo simulated data than a polynomial fit.