EBT3 film dose verification method for ⁹⁰Sr-⁹⁰Y applicator

Objective To measure the EBT3 film dose of brachytherapy with ⁹⁰Sr-⁹⁰Y applicator to provide a rapid dose verification method for clinical application.

Methods EBT3 films with good energy response were selected and compared with a solid water phantom. The gray scale dose curve of 0–500 cGy film was established using a linear accelerator, and its tissue equivalence was detected. Twenty 6 cm × 6 cm EBT3 films (0.28 mm thickness) were overlapped, and a ⁹⁰Sr-⁹⁰Y applicator was placed on the top and irradiated for 4 min. The absorbed dose near the central axis of each film was calculated using the gray scale dose curve. The radiation dose and isodose distributions at different distances from the applicator were calculated according to film thickness. Non-parametric independent sample U-test was used to compare the differences in absorbed doses measured before and after exposure to electron rays with different energies.

Results The measurement results of film replacement with equal thickness solid water molds were slightly higher than those of pure solid water molds, but the difference was not statistically significant (Z=−0.31, P=0.84). The absorbed dose in the central region corresponding to different film depths decreased rapidly with decreasing gray values, and the dose at a depth of 0.5 cm was only 7.0 cGy. After irradiation for 4 min, the absorbed dose at different depths from the applicator met the fitting curve, y=739.07e^−0.56x−44.8, and the range of isodose line initially increased and then decreased with the increasing depth.

Conclusion EBT3 film verification can well meet the dose verification of ⁹⁰Sr-⁹⁰Y applicator, which is simple, easy, and accurate and is suitable of primary medical institutions.