Verification of high dose rate brachytherapy dose distributions with EBT3 Gafchromic film quality control techniques

It is essential that quality control (QC) techniques are developed to keep pace with modern high dose rate (HDR) brachytherapy. Current QC methods may be insufficient to fully assure the accuracy of 3D-optimized dose delivery. This work presents an evaluation of Gafchromic EBT3 film, with multi-channel analysis, in HDR dose environments for advanced QC and commissioning. 'Film-array in water' and 'three-channel Solid Water block' purpose-designed phantoms are utilized. Dose and dose-rate dependency and practical film usage has been evaluated. EBT3 measurements of dose with radial distance from a HDR source are compared to Monte Carlo data. Semi-3D dose distributions around clinical HDR applicators are compared to treatment plans. The measurement of delivery accuracy for inverse-planned pseudo-clinical test cases, with correct delivery and simulated treatment errors, has also been investigated. Local gamma criteria of 3%, 3 mm is recommended with passing rates of at least 96% typically achieved. The system is sensitive to simulated errors in HDR delivery, with significant reductions of passing rate. It has been demonstrated that EBT3 Gafchromic film, in combination with multi-channel analysis, is appropriate for applicator, treatment unit and planning system commissioning measurements as well as practical routine QC to confirm agreement of planned and delivered complex HDR brachytherapy dose distributions.