Abstract
The dose profile of a prototype IS 125 I-125 brachytherapy seed was measured using MD-55 radiochromic film. Irradiated films were scanned by a document scanner and results were compared with results obtained when a densitometer was used. Images produced by a document scanner were converted to dose with several graphic related programs. Advantages of scanning the films with a document scanner versus with a densitometer include: no diffraction from the film holder used in densitometer scans, shorter scanning times and smaller experimental error. Experimental precision of 0.35 % relative standard deviation was obtained using the document scanner, but only 9 % could be achieved with the densitometer. As expected, the measured dose profiles showed this new brachytherapy seed to be similar to the commercially available model 6711 seed because of similar source geometry. Exposures with the seed embedded in a paraffin medium produced different profiles from when the seed was embedded in Plexiglas because of the difference of properties in these media. Unequal thickness at the two ends of the seed contributed to anisotropy in the dose distribution. Anisotropy in Plexiglas was a factor of 2 more than in paraffin for both longitudinal axes. Radial dose fall-off in paraffin was similar in shape to MCNP calculations out to 1 cm. The use of a document scanner for measurement of radiochromic film was shown to be an acceptable and convenient method for low-energy I-125 brachytherapy seed dosimetry. Further study is needed to evaluate the measurement of dose at extended distances from the seed, and to allow comparison to commercially available sources in accordance with AAPM TG43.
Lee, Sung-Woo (1999). Dose profile establishment of new I-125 brachytherapy seed by radiochromic film. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1999 -THESIS -L447.