Département de physique, Université de Montréal, Complexe des sciences, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, QC, H2V 0B3, Canada.
Centre de recherche du CHUM, 900 Rue Saint-Denis, Montréal, QC, H2X 3H8, Canada.
Med Phys. 2021 May;48(5):2592-2603. doi: 10.1002/mp.14742. Epub 2021 Apr 1.
The goal of this work is to propose a new multichannel method correcting for systematic thickness disturbances and to evaluate its precision in relevant radiation dosimetry applications.
The eigencolor ratio technique is introduced and theoretically developed to provide a method correcting for thickness disturbances. The method is applied to EBT3 Gafchromic film irradiated with cobalt-60 and 6 MV photon beams and digitized with an Epson 10000XL photo scanner. Dose profiles and output factors of different field sizes are measured and analyzed. Variance analysis of the previous method of Bouchard et al. ["On the characterization and uncertainty analysis of radiochromic film dosimetry" Med Phys. 2009;36:1931-1946] is adapted to the new approach. Uncertainties are predicted for relevant applications.
Results show that systematic disturbances attributed to thickness variations are efficiently corrected. The method is shown efficient to identify and correct for dark spots which cause systematic errors in single-channel distributions. Applications of the method in the context of relative dosimetry yields standard uncertainties ranging between 0.8% and 1.9%, depending on the region of interest (ROI) size and the film irradiation. Variance analysis predicts that uncertainty levels between 0.3% and 0.6% are achievable with repeated measurements. Uncertainties are found to vary with absorbed dose and ROI size.
The proposed multichannel method is efficient for accurate dosimetry, reaching uncertainty levels comparable to previous publications with EBT film. The method is also promising for applications beyond clinical QA, such as machine characterization and other advanced dosimetry applications.
本研究旨在提出一种新的多通道方法，用于校正系统厚度干扰，并评估其在相关辐射剂量学应用中的精度。
引入并从理论上发展特征颜色比技术，以提供一种校正厚度干扰的方法。该方法应用于 EBT3 Gafchromic 胶片，用钴-60 和 6 MV 光子束照射，并使用 Epson 10000XL 照片扫描仪进行数字化。测量和分析了不同射野大小的剂量分布和输出因子。适应 Bouchard 等人的先前方法的方差分析[“放射性色迹胶片剂量学的特征和不确定度分析”，医学物理。2009；36:1931-1946]适用于新方法。预测了相关应用的不确定性。
结果表明，系统干扰归因于厚度变化得到了有效校正。该方法被证明可以有效地识别和校正暗点，暗点会导致单通道分布中的系统误差。在相对剂量学应用中，该方法的标准不确定度范围在 0.8%到 1.9%之间，具体取决于感兴趣区域（ROI）的大小和胶片的照射。方差分析预测，通过重复测量可以达到 0.3%到 0.6%的不确定度水平。发现不确定性随吸收剂量和 ROI 大小而变化。
所提出的多通道方法对于精确剂量测定是有效的，可以达到与 EBT 胶片相关文献相当的不确定度水平。该方法还有望应用于临床质量保证之外的领域，如机器特性和其他先进的剂量学应用。
