A method for obtaining three-dimensional measurements of HDR brachytherapy dose distributions using Fricke gel dosimeters and optical computed tomography

This study aimed to develop a method for performing accurate, high-resolution, three-dimensional (3D) Fricke gel dosimetry measurements of high dose rate (HDR) brachytherapy dose distributions using optical computed tomography (CT). A multi-needle brachytherapy gel phantom was purpose-built to contain four stainless-steel brachytherapy needles and a sample of Fricke Xylenol gel. A Paris-style HDR brachytherapy treatment was planned and delivered to the gel, which was then read out using a novel optical CT scanning method; all the brachytherapy needles were removed prior to scanning and replaced with a refractive index matched fluid. The removal of the stainless-steel needles during pre- and post-irradiation scanning minimised the potential for artefacts caused by missing ray-sum data. Results showed good agreement between measured and calculated doses (within 1%) at all positions greater than 0.1 cm from each needle. This study demonstrated that 3D Fricke gel phantoms may be valuable tools in verifying HDR brachytherapy treatments. The phantom construction and optical CT scanning method proposed in this work has the potential to enable routine quality assurance measurements of complex HDR brachytherapy treatment deliveries via accurate and detailed three-dimensional dose measurements.