Arrays of point detectors can be configured for linear, planar and 3D measurements. This approach has been commonly used for producing commercially available clinical dosimetry products. The performance of these devices is ultimately limited by the performance of the individual detectors. Which systems are most useful will depend on accuracy of the dosimetry. Spatial resolution is not a significant factor since lower resolution systems could be scanned. Higher resolution can be achieved using a step and shoot approach. Several of the issues being discussed at this meeting with respect to gel dosimetry such as accuracy, dose rate and fractionation effects are common issues for other chemical dosimeters such as films. Techniques, for improving densitometric accuracy can be adapted to improving optical CT accuracy as well. Since the root physical issues are the same. For example, spectral analysis becomes important when more than one chemical species is formed. In the push to reach a goal of 1 mm isotropic spatial resolution and 3percent dose accuracy for 3D gel dosimetry other techniques such as ion chambers and films have been used for comparison. As the quality of gel data approaches these target levels the question of the most appropriate measurements to compare with need to be addressed since recent reports have shown that errors of 2percent with film and 1percent with ion chambers are easily possible. Dosimetry may be approaching the stage where calculations are more accurate than measurements for low doses, low dose rates, small fields, low energy radiation (less than 100 keV) and regions of high gradients.
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