Department of Radiation Oncology, Vanderbilt University School of Medicine, Vanderbilt-Ingram Cancer Center, B-902, TVC, Preston Research Building, Nashville, Tennessee 37232-5671, USA.
Med Phys. 2007 Jul;34(7):2985-94. doi: 10.1118/1.2745923.
The purpose of this study is to assess the real target dose coverage when radiation treatments were delivered to lung cancer patients based on treatment planning according to the RTOG-0236 Protocol. We compare calculated dosimetric results between the more accurate anisotropic analytical algorithm (AAA) and the pencil beam algorithm for stereotactic body radiation therapy treatment planning in lung cancer. Ten patients with non-small cell lung cancer were given 60 Gy in three fractions using 6 and 10 MV beams with 8-10 fields. The patients were chosen in accordance with the lung RTOG-0236 protocol. The dose calculations were performed using the pencil beam algorithm with no heterogeneity corrections (PB-NC) and then recalculated with the pencil beam with modified Batho heterogeneity corrections (PB-MB) and the AAA using an identical beam setup and monitor units. The differences in calculated dose to 95% or 99% of the PTV, between using the PB-NC and the AAA, were within 10% of prescribed dose (60 Gy). However, the minimum dose to 95% and 99% of PTV calculated using the PB-MB were consistently overestimated by up to 40% and 36% of the prescribed dose, respectively, compared to that calculated by the AAA. Using the AAA as reference, the calculated maximum doses were underestimated by up to 27% using the PB-NC and overestimated by 19% using the PB-MB. The calculations of dose to lung from PB-NC generally agree with that of AAA except in the small high-dose region where PB-NC underestimates. The calculated dose distributions near the interface using the AAA agree with those from Monte Carlo calculations as well as measured values. This study indicates that the real minimum PTV dose coverage cannot be guaranteed when the PB-NC is used to calculate the monitor unit settings in dose prescriptions.
本研究旨在根据 RTOG-0236 协议评估肺癌患者放射治疗时基于治疗计划的实际靶区剂量覆盖。我们比较了在肺癌立体定向体部放射治疗计划中更精确的各向异性分析算法（AAA）和笔形束算法的计算剂量学结果。10 例非小细胞肺癌患者采用 6 和 10 MV 射线，8-10 野，60 Gy 分 3 次给予。患者根据肺部 RTOG-0236 协议选择。剂量计算分别采用无不均匀性校正的笔形束算法（PB-NC）和修正后的 Batho 不均匀性校正的笔形束算法（PB-MB），以及采用相同射束设置和监测单位的 AAA 进行。使用 PB-NC 和 AAA 计算 95%或 99%PTV 的剂量差异在 10%以内，与规定剂量（60 Gy）相符。然而，与 AAA 相比，使用 PB-MB 计算 95%和 99%PTV 的最小剂量分别被高估了 40%和 36%。使用 AAA 作为参考，使用 PB-NC 计算的最大剂量被低估了高达 27%，而使用 PB-MB 计算的最大剂量被高估了 19%。PB-NC 计算的肺剂量分布与 AAA 基本一致，只是在小剂量高剂量区域低估。使用 AAA 计算的界面附近的剂量分布与蒙特卡罗计算以及测量值吻合。本研究表明，在使用 PB-NC 计算剂量处方的监测单位设置时，无法保证真实的最小 PTV 剂量覆盖。
