Department of Radiology, Hyogo College of Medicine, 1-1, Mukogawa-cho, Nishinomiya City, Hyogo, 663-8501, Japan.
J Radiat Res. 2013 Nov 1;54(6):1153-9. doi: 10.1093/jrr/rrt059. Epub 2013 May 17.
We validated 3D radiochromic film dosimetry for volumetric modulated arc therapy (VMAT) using a newly developed spiral water phantom. The phantom consists of a main body and an insert box, each of which has an acrylic wall thickness of 3 mm and is filled with water. The insert box includes a spiral film box used for dose-distribution measurement, and a film holder for positioning a radiochromic film. The film holder has two parallel walls whose facing inner surfaces are equipped with spiral grooves in a mirrored configuration. The film is inserted into the spiral grooves by its side edges and runs along them to be positioned on a spiral plane. Dose calculation was performed by applying clinical VMAT plans to the spiral water phantom using a commercial Monte Carlo-based treatment-planning system, Monaco, whereas dose was measured by delivering the VMAT beams to the phantom. The calculated dose distributions were resampled on the spiral plane, and the dose distributions recorded on the film were scanned. Comparisons between the calculated and measured dose distributions yielded an average gamma-index pass rate of 87.0% (range, 91.2-84.6%) in nine prostate VMAT plans under 3 mm/3% criteria with a dose-calculation grid size of 2 mm. The pass rates were increased beyond 90% (average, 91.1%; range, 90.1-92.0%) when the dose-calculation grid size was decreased to 1 mm. We have confirmed that 3D radiochromic film dosimetry using the spiral water phantom is a simple and cost-effective approach to VMAT dose verification.
我们使用新开发的螺旋水模体对容积旋转调强弧形治疗（VMAT）的三维辐射变色胶片剂量学进行了验证。该水模体由主体和插入盒组成，其各自的丙烯酸壁厚度为 3 毫米，内部填充水。插入盒包括用于剂量分布测量的螺旋胶片盒和用于定位辐射变色胶片的胶片夹。胶片夹有两个平行的壁，其相对的内表面配备有镜像配置的螺旋槽。胶片通过其边缘插入螺旋槽中，并沿着它们在螺旋平面上定位。通过将临床 VMAT 计划应用于螺旋水模体，使用商业基于蒙特卡罗的治疗计划系统 Monaco 进行剂量计算，而剂量则通过将 VMAT 束传输到模体进行测量。在螺旋平面上对计算出的剂量分布进行重采样，并扫描胶片上记录的剂量分布。在 3 毫米/3%标准下，对 9 个前列腺 VMAT 计划进行比较，计算剂量分布和测量剂量分布的平均伽玛指数通过率为 87.0%（范围，91.2-84.6%），剂量计算网格尺寸为 2 毫米。当剂量计算网格尺寸减小到 1 毫米时，通过率提高到 90%以上（平均 91.1%；范围 90.1-92.0%）。我们已经证实，使用螺旋水模体的三维辐射变色胶片剂量学是一种简单且具有成本效益的 VMAT 剂量验证方法。
