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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 MapCHECK2TM diode array and the Varian VariSourceTM 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.

The aims of this dissertation were to develop a method with improved accuracy for various heterogeneous geometries and to evaluate the feasibility of using EPID transit dosimetry for error detection. This dissertation examined phantom geometries with an emphasis on a tumor-in-lung geometry that may occur in hypo-fractionated SBRT treatments. For dose investigation in heterogeneous geometries, a multi-planar film measurement system was used with a measurement accuracy (within 3%) by using specific procedures to reduce the film perturbation in a low density medium. Measurements were used to validate a Monte Carlo (MC) method, and the results indicated that this MC method can be used as a reference to validate other calculation algorithms or to evaluate the doses delivered to patients for lung treatment. For developing an error detection method, a commercial electronic portal imaging device (EPID) composed of amorphous silicon was characterized for dosimetry application. A general calibration method was explored to use this device as a water-equivalent dosimeter, allowing for direct comparison to calculated doses from treatment planning systems. The calibration method was validated for a range of situations, field shapes, and intensities. The EPID transit dosimetry was sensitive to delivery errors, such as variations in treatment field shape, machine output and patient setup. The correlation between in-patient and transit dose variations may be established and used to determine acceptance or rejection criteria when the error is found. This dissertation showed the potential of using EPID dosimetry during treatment for on-line error correction and for estimating the in-patient dose error.