Department of Radiation Oncology, Cancer Hospital, Department of Oncology, Shanghai Medical college, Fudan University, Shanghai, China.
Radiat Oncol. 2010 Apr 19;5:29. doi: 10.1186/1748-717X-5-29.
To evaluate the accuracy of using kilovoltage x-ray cone-beam computed tomography (kV-CBCT) imaging for in vivo dose calculations.
A Region-of-Interest (ROI) CT number mapping method was developed to generate the cone-beam CT number vs. relative electron density calibration curve for 3D dose calculations. The stability of the results was validated for three consecutive months. The method was evaluated on three brain tumors and three head-and-neck tumor cases. For each patient, kV-CBCT images were acquired on the first treatment day and two-week intervals on the Elekta XVI system. The delivered dose distributions were calculated by applying the patients' treatment plans to the kV-CBCT images. The resulting dose distributions and dose volume histograms (DVHs) of the tumor and critical structures were compared to the original treatment plan.
The kV-CBCT electron density calibration was stable within 1.5% over a three-month period. The DVH and dose distribution comparison based on the planning CT and the initial kV-CBCT showed good agreements for majority of cases. The doses calculated from the planning CT and kV-CBCT were compared on planes perpendicular to the beam axes and passing through the isocenter. Using gamma analysis with a criterion of 2 mm/2% and a threshold of 10%, more than 99.5% of the points on the iso-planes exhibited gamma <1. For one patient, kV-CBCT images detected 5.8% dose variation in the right parotid due to tumor shrinkage and patient weight loss.
ROI mapping method is an effective method for the creation of kV-CBCT electron density calibration curves for head-and-neck and brain tumor patients. Dose variations as monitored using kV-CBCT imaging suggest that some patients can benefit from adaptive treatment plan re-optimization.
评估千伏锥形束 CT（kV-CBCT）成像在体内剂量计算中的准确性。
开发了一种感兴趣区域（ROI）CT 数映射方法，以生成锥形束 CT 数与相对电子密度校准曲线，用于 3D 剂量计算。该方法的稳定性已连续三个月得到验证。该方法已在三个脑肿瘤和三个头颈部肿瘤病例中进行了评估。对于每个患者，在 Elekta XVI 系统上于治疗的第一天以及每两周采集一次 kV-CBCT 图像。通过将患者的治疗计划应用于 kV-CBCT 图像，计算出所传递的剂量分布。将肿瘤和关键结构的所得剂量分布和剂量体积直方图（DVH）与原始治疗计划进行比较。
kV-CBCT 电子密度校准在三个月内的稳定性在 1.5%以内。基于计划 CT 和初始 kV-CBCT 的 DVH 和剂量分布比较，大多数情况下吻合较好。在与束轴垂直并通过等中心的平面上比较了来自计划 CT 和 kV-CBCT 的剂量。使用 2mm/2%和 10%阈值的伽马分析标准，等平面上的 99.5%以上的点的伽马值<1。对于一名患者，由于肿瘤缩小和患者体重减轻，kV-CBCT 图像检测到右腮腺 5.8%的剂量变化。
ROI 映射方法是为头颈部和脑肿瘤患者创建 kV-CBCT 电子密度校准曲线的有效方法。使用 kV-CBCT 成像监测到的剂量变化表明，一些患者可以从自适应治疗计划重新优化中受益。
