Evaluation of a MapCHECK2(TM) Diode Array for High Dose Rate Brachytherapy Quality Assurance

Despite continuous improvements in design of HDR brachytherapy delivery systems, the position of the source is still verified only through the HDR afterloader hardware/software based on the length of the wire reeled out relative to the parked position. The position of the source is not independently monitored during the treatment, potentially opening the door to misadministrations. We investigate the feasibility of using dose maps acquired with a two-dimensional diode array to verify the relative source locations and confirm delivered dose during an HDR treatment.;Dose maps for the source located at selected distances in air and depths in solid water were acquired with a MapCHECK2(TM) diode array and the Varian VariSource(TM) Ir-192 HDR afterloader. The peak location of the measured dose profile for each dwell position provided the X and Y coordinates while the full width at half maximum (FWHM) of each peak was used to calibrate the source distance along the Z axis. Two treatment orientations were considered with the source moving along 1) the rectangular surface of a solid water phantom and 2) the inclined plane of a paraffin wax wedge to verify the method for both coplanar and non-coplanar source and detector geometries for three source positions. Acquired dose maps were used to restore coordinates of dwell positions.;Although the spatial resolution is 10 mm along a row or column of diode detectors, the accuracy in determining dwell position coordinates was found to be within +/-2 mm in the X and Y directions of the diode plane using a polynomial fit to interpolate the values at distances between the measured points. The FWHM was found to increase linearly with source depth/distance, making it a suitable parameter for determining the source Z coordinate. Our studies have verified that the dose maps can be used as a routine QA tool for HDR treatment delivery verification.