Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
Med Phys. 2011 May;38(5):2318-23. doi: 10.1118/1.3572228.
To introduce a tool, termed distance to dose difference (DTD), which estimates the required spatial accuracy of displacement vector fields (DVFs) used for mapping four dimensional dose values.
Dose mapping maps dose values from an irradiated geometry to a reference geometry. DVF errors result in dose being mapped from the wrong spatial location in the irradiated geometry, with a dose error equal to the dose difference between the error-free and sampled spatial locations. The DTD, defined as the distance to observe a given dose difference in the irradiated geometry, quantifies the permitted DVF error to ensure a prespecified desired dose mapping accuracy is achieved. To demonstrate the DTD, a treatment plan is generated with a 5 mm internal target volume-to-planning target volume margin for an intensity modulated radiation therapy lung patient. The DTD is evaluated for mapping dose from the end of inhale image with a dose error tolerance of 3.30 Gy, which equals 5% of the 66 Gy prescription dose. The DTD is loaded into the treatment planning system to visualize positional dependencies of permissible DVF errors overlaid on the patient's anatomy and DTD-volume-histograms are generated.
DTD values vary with location in the patient anatomy. For the test case, DTD analysis indicates that accurate DVFs (approximately 1 mm) are required in high dose gradient regions while large DVF errors (>20 mm) are acceptable in low dose gradient regions. Within the clinical target volume (CTV), tolerated DVF uncertainties range from 1 to 12 mm, depending on location. Ninety percent of the CTV volume had DTD values less than 4 mm.
The DVF spatial accuracy required to meet a dose mapping accuracy tolerance depends on the spatial location within the dose distribution. For dose mapping, DVFs accuracy must be highest in dose gradient regions, while less accurate DVFs can be tolerated in uniform dose regions. The DTD tool provides a useful first estimate of DVF required spatial accuracy.
介绍一种工具，称为剂量差异距离（DTD），用于估计用于映射四维剂量值的位移矢量场（DVF）所需的空间精度。
剂量映射将剂量值从照射几何图形映射到参考几何图形。DVF 误差导致剂量从照射几何图形中的错误空间位置映射，剂量误差等于无误差和采样空间位置之间的剂量差。DTD 定义为在照射几何图形中观察给定剂量差的距离，它量化了允许的 DVF 误差，以确保达到预定的所需剂量映射精度。为了演示 DTD，为一位接受调强放疗的肺癌患者生成了一个具有 5 毫米内部靶区到计划靶区边缘的治疗计划。对于以 3.30 Gy 的剂量误差容限（等于 66 Gy 处方剂量的 5%）从吸气末图像映射剂量的情况，评估了 DTD。将 DTD 加载到治疗计划系统中，以可视化患者解剖结构上允许的 DVF 误差的位置依赖性，并生成 DTD-体积-直方图。
DTD 值随患者解剖结构中的位置而变化。对于测试案例，DTD 分析表明，在高剂量梯度区域需要精确的 DVF（约 1 毫米），而在低剂量梯度区域可以接受较大的 DVF 误差（>20 毫米）。在临床靶区（CTV）内，根据位置，允许的 DVF 不确定性范围为 1 至 12 毫米。90%的 CTV 体积的 DTD 值小于 4 毫米。
满足剂量映射精度容限所需的 DVF 空间精度取决于剂量分布内的空间位置。对于剂量映射，DVF 精度在剂量梯度区域必须最高，而在均匀剂量区域可以容忍较低精度的 DVF。DTD 工具提供了 DVF 所需空间精度的有用初步估计。
