Department of Radiation Oncology, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA.
Phys Med. 2018 Jun;50:59-65. doi: 10.1016/j.ejmp.2018.05.019. Epub 2018 May 29.
To describe the design and clinical use of a rotational phantom for dosimetric verification of IMRT/VMAT treatment plans using radiochromic film.
A solid water cylindrical phantom was designed with separable upper and lower halves and rests on plastic bearings allowing for 360° rotation about its central axis. The phantom accommodates a half sheet of radiochromic film, and by rotating the cylinder, the film can be placed in any plane between coronal and sagittal. Calculated dose planes coinciding with rotated film measurements are exported by rotating the CT image and dose distribution within the treatment planning system. The process is illustrated with 2 rotated film measurements of an SRS treatment plan involving 4 separate targets. Additionally, 276 patient specific QA measurements were obtained with the phantom and analyzed with a 2%/2 mm gamma criterion.
The average 2%/2 mm gamma passing rate for all 276 plans was 99.3%. Seventy-two of the 276 plans were measured with the plane of the film rotated between the coronal and sagittal planes and had an average passing rate of 99.4%.
The rotational phantom allows for accurate film measurements in any plane. With this technique, regions of a dose distribution which might otherwise require multiple sagittal or coronal measurements can be verified with as few as a single measurement. This increases efficiency and, in combination with the high spatial resolution inherent to film dosimetry, makes the rotational technique an attractive option for patient-specific QA.
描述一种旋转体模的设计和临床应用，该体模可用于使用光致变色胶片对调强放疗/VMAT 治疗计划进行剂量验证。
设计了一个固体水圆柱形体模，由可分离的上下两部分组成，放置在塑料轴承上，可绕其中心轴旋转 360°。体模可容纳半张光致变色胶片，通过旋转圆柱体，胶片可以放置在冠状面和矢状面之间的任何平面上。与旋转胶片测量相吻合的计算剂量平面通过旋转 CT 图像和治疗计划系统内的剂量分布来导出。该过程通过对涉及 4 个独立靶区的 SRS 治疗计划的 2 个旋转胶片测量进行了说明。此外，使用该体模获得了 276 个患者特定的 QA 测量，并使用 2%/2mm 伽玛标准进行了分析。
所有 276 个计划的平均 2%/2mm 伽玛通过率为 99.3%。276 个计划中有 72 个计划的胶片平面在冠状面和矢状面之间旋转，平均通过率为 99.4%。
旋转体模可在任何平面上进行准确的胶片测量。通过这种技术，原本需要多个矢状面或冠状面测量的剂量分布区域，现在只需一次测量即可进行验证。这提高了效率，并且结合胶片剂量测量固有的高空间分辨率，使得旋转技术成为患者特定 QA 的一个有吸引力的选择。
