Comparison of single catheter vs. dual catheter-based EBT3 film calibration for the Ir-192 beam energy.

PURPOSE: Films and TLDs have been the common choices for passive in-vivo dose measurement in radiotherapy. This study was carried out to introduce a new and accurate calibration method for GafChromic EBT3 films irradiated using Ir-192 photon energy from a miniature High Dose Rate (HDR) Brachytherapy source.

MATERIALS AND METHODS: A film holder made of Styrofoam was used to hold the EBT3 film at its center. It was placed inside the mini water phantom and the films were irradiated by Ir-192 source of microSelectron HDR afterloading brachytherapy system. Two different setups: Single catheter-based film exposure and dual catheter-based film exposure were compared. The films were analyzed in three different color channels: red, green, and blue using Image J software. The dose calibration graphs were generated using the third-order polynomial equations fitted on the data points from two different methods of the calibration procedure. mean dose difference between TPS calculated and measured was analyzed.

RESULTS: The measured dose difference from the TPS calculated doses were evaluated for the three groups of dose ranges (low, medium, and high). In the high dose range, the standard uncertainty of dose difference is ±2.3%, ±2.9%, and ±2.4% respectively for the red, green, and blue color channel when the TPS calculated dose was compared with single catheter-based film calibration equation. Whereas it is observed as 1.3%, 1.4%, and 3.1% for the red, green, and blue color channels respectively when compared with the dual catheter-based film calibration equation.

CONCLUSION: Source miniature size, reproducible positioning of the film, and catheter system inside the water medium are the major challenges in the film calibration with Ir-192 beam. To overcome these situations dual catheter-based film calibration was found more accurate and reproducible as compared to single catheter-based film calibration. Keywords- Film calibration, Brachytherapy, ImageJ software, GafChromic EBT3 films, TG235.