Department of Radiation Oncology, Columbia University, New York, NY, 10032, USA.
Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, 10027, USA.
Med Phys. 2018 Jul;45(7):3330-3339. doi: 10.1002/mp.12955. Epub 2018 Jun 3.
The precise dosimetric and geometric characteristics of small animal irradiators are essential to achieving reproducible dose delivery, especially in cases where image-guidance is utilized. Currently, radiochromic film is the established measurement tool used to evaluate beam characteristics for these systems. However, only 2D information can be acquired with film. This study characterized both the dosimetric and geometric properties of the small animal research radiation platform (SARRP, Xstrahl) for commissioning purposes using a 3D radiochromic dosimetry system with a submillimeter resolution optical computed tomography (OCT) scanner.
Like a modern clinical linear accelerator, the SARRP features both a beam delivery system and a cone beam computed tomography (CBCT) imaging system. Dosimetric and geometric characteristics of the SARRP were studied using EBT3 radiochromic film and 3D PRESAGE dosimeters. Dosimetric measurements included percent depth dose (PDD) curves and beam profiles. For geometric evaluation, the isocenter sizes of the treatment stage and gantry rotations as well as their coincidence were measured using star shot patterns. A commercial Epson Expression 11000XL flatbed scanner was used for readout of irradiated EBT3 films at 300 dpi resolution. Each irradiated PRESAGE dosimeter was scanned using a submillimeter resolution single laser beam OCT scanner. Acquired data were reconstructed with a resolution of 0.3 mm/pixel.
PDD data measured from films and 3D dosimeters agree to within ±3% for depths up to 5 cm, for both 3 × 3 and 10 × 10 mm fixed collimation. Profiles were analyzed at 10, 20, and 30 mm depth for 3 × 3 mm and 10 × 10 mm fields. The FWHM measurements for both dosimeters agreed to within 0.01 mm, and the penumbras agreed to within 0.1 mm for 3 × 3 mm and 0.5 mm for 10 × 10 mm . Gantry and treatment stage isocenter sizes were determined to be 0.21 and 0.43 mm using EBT3 film, and 1.72 and 0.75 mm using PRESAGE dosimeters. Absolute isocenter shifts, evaluated with 3D phantoms, were 0.80 mm for the gantry rotation isocenter (treatment isocenter) with respect to the laser-defined setup isocenter, and 0.71 mm for the gantry rotation isocenter relative to treatment stage rotation isocenter (CBCT isocenter). The difference between CBCT isocenter and laser-defined setup isocenter was 0.68 mm.
This study demonstrated that 3D PRESAGE dosimeters can be used for verification of precise targeting for the SARRP. This 3D dosimetry system can be utilized to obtain information on both geometric and dosimetric properties, as well as acquire beam data parameters for the purpose of commissioning image-guided small animal irradiator systems.
对于实现可重复性剂量输送，小型动物辐照器的精确剂量学和几何特性至关重要，特别是在使用图像引导的情况下。目前，放射色迹胶片是用于评估这些系统光束特性的既定测量工具。然而，胶片只能获取 2D 信息。本研究使用具有亚毫米分辨率的光学计算机断层扫描（OCT）扫描仪的 3D 放射色迹剂量系统，对小型动物研究辐射平台（SARRP，Xstrahl）的剂量学和几何特性进行了表征，目的是为了进行调试。
与现代临床线性加速器一样，SARRP 具有束流输送系统和锥形束计算机断层扫描（CBCT）成像系统。使用 EBT3 放射色迹胶片和 3D PRESAGE 剂量计研究了 SARRP 的剂量学和几何特性。剂量学测量包括百分深度剂量（PDD）曲线和射束轮廓。对于几何评估，使用星状射束图案测量治疗台和旋转架的等中心大小及其重合度。使用商业 Epson Expression 11000XL 平板扫描仪以 300dpi 的分辨率读取辐照的 EBT3 胶片。使用亚毫米分辨率的单个激光束 OCT 扫描仪扫描每个辐照的 PRESAGE 剂量计。使用分辨率为 0.3mm/pixel 的重建采集数据。
对于 3×3mm 和 10×10mm 固定准直器，从胶片和 3D 剂量计测量的 PDD 数据在深度达 5cm 时的差异在±3%以内。在 10、20 和 30mm 深度处分析了 3×3mm 和 10×10mm 射野的射束轮廓。对于这两种剂量计，FWHM 测量值的差异在 0.01mm 以内，半影的差异在 3×3mm 时为 0.1mm，在 10×10mm 时为 0.5mm。使用 EBT3 胶片确定的旋转架和治疗台等中心尺寸分别为 0.21mm 和 0.43mm，使用 PRESAGE 剂量计确定的分别为 1.72mm 和 0.75mm。使用 3D 体模评估的绝对等中心偏移量，对于旋转架等中心（治疗等中心）相对于激光定义的设置等中心，为 0.80mm，对于旋转架等中心相对于治疗台旋转等中心（CBCT 等中心），为 0.71mm。CBCT 等中心与激光定义的设置等中心之间的差异为 0.68mm。
本研究表明，3D PRESAGE 剂量计可用于验证 SARRP 的精确靶向。该 3D 剂量系统可用于获取几何和剂量学特性信息，并获取光束数据参数，目的是为图像引导小型动物辐照器系统的调试。
