Journal of Medical Physics
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Year : 1999  |  Volume : 24  |  Issue : 1  |  Page : 28-31

Evaluation Of Gafchromic MD-55 Film For Radiotherapy Dosimetry



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S.D Sharma


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Gafchromic MD-55 is a colourless, grainless and transparent thin film dosimeter which develops a blue colour after exposure to radiation without any physical, chemical or thermal processing. The colour intensity is a function of radiation exposure. Dosimetric characteristics such as sensitivity, linearity, uniformity, reproducibility and post irradiation stability of the film response were studied experimentally simulating the condition of radiotherapy dosimetry. The irradiation of film samples, each of size 1.5 cm x 1.5 cm, were carried out in a full scattering medium, Mix-D phantom, under a telecobalt beam. The pre-irradiation and post-irradiation optical densities (OD) of these film samples along directions parallel and perpendicular to media's coated direction were determined with the help of a scanning spectrophotometer using the light of wavelength 676 nm and slit width 0.5 nm. The uniformity of irradiated film samples along these two directions of the film was found to be within 4% and 8%, respectively. The variation of net mean oiptical density (NMOD) with radiation absorbed dose (D) was found to be linear in the dose range studied in this investigation and can be represented by the equation NMOD - 0.02268 + 0.05342 x D. The average rate of increase of OD of irradiated samples, 24 hours after iradiation, was observed to be 1.5% per week, and was independent of radiation absorbed dose. These results indicate that the film is suitable for absolute as well as relative dosimetry of radiation beams commonly encountered in radiotherapy treatment, provided the scanning of the film samples are done in a direction parallel to media's coated direction .


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