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| Home > Publications database > Pseudo-3D IMRT Verification with Film and Its Sensitivity to Errors Compared to 2D Methods |
| Home > Publications database > Pseudo-3D IMRT Verification with Film and Its Sensitivity to Errors Compared to 2D Methods |
| Dissertation / PhD Thesis | DKFZ-2023-02462 |
2023
Abstract: With the advent of complex radiation therapy techniques like IMRT (intensity modulated radiation therapy) and VMAT (volumetric modulated arc therapy), the need to measure dose distributions in 3D has increased greatly. Several commercial systems have been released that attempt to measure and evaluate 3D dose distributions. None of them, however, is a real 3D dosimeter. All of them use software algorithms to model 3D dose distributions based on measured 2D data. Thus, the user canquantify discrepancies between the predicted and modeled 3D dose maps only. The only true 3D dosimeter is polymer or radiochromic gel, which is not yet suitable for routine clinical use.The aim of this work was to develop a simple dosimetric method that would enable quantitative 3D evaluation of measured data only, without the use of any reconstruction algorithms. Our method uses a water equivalent slab phantom and radiochromic film, so it is accessible to all clinics using their existing resources. Data are evaluated in MATLAB (The MathWorks, Inc., United States) and quantified both with 2D and 3D gamma analysis. However, commercial software available at hospitals could also be used for this purpose. The main advantages of our method are excellent spatial resolution within each plane and water equivalence of the detection system. The main disadvantage of the method is some extra time needed for each measurement compared tocommercial electronic devices. Compared to gel dosimetry, our method is more precise and less demanding.Another advantage of the method is the possibility to evaluate the very same measured data set in 2D and in 3D, using the same software code. This cannot be done with commercial equipment and no comparison of this sort has been performed in scientific literature to the author‘s best knowledge. Comparisons from literature are influenced by the inherent differences between the 2D and 3D data and corresponding software algorithms.Based on our findings, a 3D evaluation is recommended at least when new techniques or new detection equipment are introduced into clinical practice. It is also recommended for individual treatment plan verification where results obtained otherwise are questionable. Testing dose distributions in a single 2D plane in the 3D space or field-by-field might not be sufficient because of the interplay of different types of error
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