Beijing Key Lab of Medical Physics and Engineering, Peking University, Beijing, China.
Int J Radiat Oncol Biol Phys. 2012 Aug 1;83(5):1649-54. doi: 10.1016/j.ijrobp.2011.10.072. Epub 2012 Jan 26.
To develop a quantitative method for the estimation of kV cone beam computed tomography (kVCBCT) doses in pediatric patients undergoing image-guided radiotherapy.
Forty-two children were retrospectively analyzed in subgroups of different scanned regions: one group in the head-and-neck and the other group in the pelvis. Critical structures in planning CT images were delineated on an Eclipse treatment planning system before being converted into CT phantoms for Monte Carlo simulations. A benchmarked EGS4 Monte Carlo code was used to calculate three-dimensional dose distributions of kVCBCT scans with full-fan high-quality head or half-fan pelvis protocols predefined by the manufacturer. Based on planning CT images and structures exported in DICOM RT format, occipital-frontal circumferences (OFC) were calculated for head-and-neck patients using DICOMan software. Similarly, hip circumferences (HIP) were acquired for the pelvic group. Correlations between mean organ doses and age, weight, OFC, and HIP values were analyzed with SigmaPlot software suite, where regression performances were analyzed with relative dose differences (RDD) and coefficients of determination (R(2)).
kVCBCT-contributed mean doses to all critical structures decreased monotonically with studied parameters, with a steeper decrease in the pelvis than in the head. Empirical functions have been developed for a dose estimation of the major organs at risk in the head and pelvis, respectively. If evaluated with physical parameters other than age, a mean RDD of up to 7.9% was observed for all the structures in our population of 42 patients.
kVCBCT doses are highly correlated with patient size. According to this study, weight can be used as a primary index for dose assessment in both head and pelvis scans, while OFC and HIP may serve as secondary indices for dose estimation in corresponding regions. With the proposed empirical functions, it is possible to perform an individualized quantitative dose assessment of kVCBCT scans.
开发一种用于估算接受图像引导放疗的儿科患者千伏锥形束 CT（kVCBCT）剂量的定量方法。
回顾性分析了 42 名儿童，分为头颈部扫描组和骨盆扫描组。在 Eclipse 治疗计划系统中对计划 CT 图像上的关键结构进行勾画，然后将其转换为 CT 体模进行蒙特卡罗模拟。使用经过基准测试的 EGS4 蒙特卡罗代码，按照制造商预设的全扇高剂量头部或半扇低剂量骨盆协议，计算 kVCBCT 扫描的三维剂量分布。基于计划 CT 图像和以 DICOM RT 格式导出的结构，使用 DICOMan 软件对头颈部患者计算枕额周长（OFC）。对于骨盆组，获取髋周长（HIP）。使用 SigmaPlot 软件套件分析平均器官剂量与年龄、体重、OFC 和 HIP 值之间的相关性，其中回归性能用相对剂量差异（RDD）和确定系数（R²）进行分析。
kVCBCT 贡献的所有关键结构的平均剂量随研究参数单调下降，骨盆的下降幅度大于头部。针对头颈部和骨盆的主要危险器官，分别开发了剂量估算的经验函数。如果用年龄以外的物理参数进行评估，我们 42 名患者群体中所有结构的平均 RDD 高达 7.9%。
kVCBCT 剂量与患者体型高度相关。根据本研究，体重可作为头颈部和骨盆扫描剂量评估的主要指标，而 OFC 和 HIP 可作为相应区域剂量估算的次要指标。使用提出的经验函数，可以对头颈部和骨盆 kVCBCT 扫描进行个体化的定量剂量评估。
