Purpose: CivaSheetâ„¢ is a directional low-dose rate brachytherapy source array which has been used recently for different cancer treatments. The device can be implanted in several configurations based on the treatment site. This work aims to evaluate the dosimetric impact of a curvature on the CivaSheet dose distribution using measurements and Monte Carlo (MC) methods.
Methods: A custom Virtual Waterâ„¢ phantom (20Ã—20Ã—20 cmÂ³) was fabricated to perform dose-to-water measurements using a film-stack dosimeter. A CivaSheet (5Ã—5 cmÂ²) comprising of thirty-six CivaDots was used. The CivaSheet dose distribution was measured using EBT3 films in a flat, concave, and convex configuration with a 4 cm radius of curvature. Ten films were placed at depths ranging from 0.3 to 5 cm on the hot-side of the source and two films on the cold-side (0.5 and 1 cm). MC simulations of the CivaSheet device and measurement setup were performed using MCNP6 code.
Results: MC-predicted ratio of the dose value at the 0.5 cm depth (hot-side) on the central axis of the concave configuration to the flat configuration was 1.08 and for the convex configuration was 0.93. All measured PDD values for the flat configuration were within Â±4.1% of the MC-predicted PDD values, with most values within Â±2.0%. For the concave configuration, the measured PDD value was within Â±3.0% of the MC-calculated PDD value for all depths, with most values within Â±1.5%. The measured PDD values for all depths agreed to within Â±1.2% of the MC-calculated PDD values for the convex configuration. The agreement between the measured PDD and the CivaDot MC-calculated superposition PDD was within Â±4.0%, Â±2.8% and Â±1.6% respectively for the flat, concave and convex configurations for all depths.
Conclusion: There is a substantial dosimetric impact of using the CivaSheet in a curved configuration which should be taken into consideration for clinical applications.