Calculated and measured radiation dose in water for the low energy Xoft Axxent eBT X-ray source

Abstract

Abstract Purpose This study aims at evaluating the functionality of different dose fractions for the Xoft Axxent electronic brachytherapy (eBT) system and analyzing the system in terms of radiation dosimetry in water. Materials and Methods Different dose fraction schemes for the Xoft Axxent eBT system were calculated for different balloon applicator volumes based on dwell positions and dwell times. EBT-XD Gafchromic film was calibrated at 6MV photon energy and a calibration curve was devised for it which were used for dosimetric measurements. In the first phase, a balloon applicator filled with 0.9% isotonic sodium chloride (NaCl) solution was used for dosimetric measurements with the ability to deliver 20 Gy, 16 Gy, 10 Gy radiation dose in one fraction. Afterward, the balloon applicator was filled with water and the same measurements were performed. Finally, the balloon applicator was irradiated at different distances in the water tank and the simulation of dose distribution in the water was obtained so as to analyze the dose distribution in the tissue. Results At the time the balloon applicator was filled with 0.9% NaCl solution, the absorbed dose was approximately 23 Gy for 30 cc balloon volume, 22.8 Gy for 35 cc and 22 Gy for 40 cc balloon volume. On the other side, when the applicator was filled with water, the absorbed dose is approximately 20.5 Gy for 30 cc, 21 Gy for 35 cc, and 20,7 Gy for 40 cc balloon applicator. As a result, provided the balloon applicator was filled with water, the difference between the planned dose and the absorbed dose was ~ 2% for 30 cc, ~ 5% for 35 cc and ~ 3,5% for 40 cc. Accordingly, the fact that 0.9% NaCl solution caused an increase in the absorbed dose from the photoelectric effect was determine. Finally, the absorbed dose at a distance of 1 cm from the applicator surface was measured as 9.63 Gy which was obtained in accordance with the manufacturer’s criteria. Conclusion Different dose fraction schemes were created in the Xoft Axxent eBT system based on the standard atlas plan. In addition, this study shows that photoelectric effect in low energy photons increases the difference between the planned dose and the absorbed dose depending on the effective atomic number. By measuring the dose distributions at different distances from the balloon applicator surface, the absorbed dose in tissue equivalent medium was determined and the dose distribution characteristics was simulated.