Kim H, Chang A, Park Y, Ye S
Soon Chun Hyang University Hospital, Seoul.
Soul National University Hospital, Seoul.
Med Phys. 2012 Jun;39(6Part18):3826. doi: 10.1118/1.4735613.
To investigate the effect of CT contrast enhancement (CE) on the 3D dose distributions of non-coplanar small field beams in the CyberKnife (CK) treatment planning system.
Twenty patients treated by pre-CE CT plans were recruited to this retrospective plan study. Their post-CE CT plans were based on the pre-CE CT plan data and calculated using the same MU and beam paths in either Ray-Tracing or Monte Carlo (MC) algorithms. The differences in doses of the beam path and the reference point and in DVHs of target and OARs between the pre-CE CT and the post-CE CT plans were compared. The minimum dose, the maximum dose, the mean dose, and the dose received to 50% of the target and OARs volumes, and the target volume coverage were also compared.
The dose differences between the pre-CE and post-CE plans in a single beam path were less than 50 cGy in both calculation algorithms. At the center of target volume, it was 1.9% (maximum 6.2%) in Ray-Tracing and 1.5% (maximum 4.0%) in MC, with respect to the prescription dose. The post-CE plans showed on average 2% decrease in the OAR maximum dose (maximum 6.4% in Ray-Tracing and 5.8% in MC). Regardless of the algorithms, the dose to the target and the target volume coverage of post-CE plans were on average reduced by 2% and 1 %, respectively, with a maximum reduction of 6.1% (in Ray-Tracing) in the minimum target dose.
The CK treatment plan using the post-CE CT could generally result in a few % dose differences from the pre-CE CT plan. However, it could be more than 6%, depending on the target positions in the body and the calculation algorithms. Thus the post-CE CT in CK treatment plans should be used with a caution.
研究CT对比增强（CE）对射波刀（CK）治疗计划系统中非共面小射野束流三维剂量分布的影响。
本回顾性计划研究纳入了20例接受CE前CT计划治疗的患者。他们的CE后CT计划基于CE前CT计划数据，并使用光线追踪或蒙特卡罗（MC）算法，在相同的MU和射线路径下进行计算。比较了CE前CT计划和CE后CT计划在射线路径和参考点剂量以及靶区和危及器官剂量体积直方图（DVH）方面的差异。还比较了最小剂量、最大剂量、平均剂量、靶区和危及器官体积50%所接受的剂量以及靶区体积覆盖率。
在两种计算算法中，单条射线路径上CE前和CE后计划的剂量差异均小于50 cGy。在靶区体积中心，相对于处方剂量，光线追踪算法中为1.9%（最大6.2%），MC算法中为1.5%（最大4.0%）。CE后计划显示危及器官最大剂量平均降低2%（光线追踪算法中最大降低6.4%，MC算法中最大降低5.8%）。无论采用何种算法，CE后计划的靶区剂量和靶区体积覆盖率平均分别降低2%和1%，最小靶区剂量最大降低6.1%（光线追踪算法）。
使用CE后CT的CK治疗计划通常与CE前CT计划存在几个百分点的剂量差异。然而，根据靶区在体内的位置和计算算法，差异可能超过6%。因此，在CK治疗计划中使用CE后CT应谨慎。
