Langen Katja M, Lu Weiguo, Ngwa Wilfred, Willoughby Twyla R, Chauhan Bhavin, Meeks Sanford L, Kupelian Patrick A, Olivera Gustavo
Department of Radiation Oncology, M. D. Anderson Cancer Center Orlando, 1400 South Orange Av., Orlando, FL 32806, USA.
Phys Med Biol. 2008 Dec 21;53(24):7073-86. doi: 10.1088/0031-9155/53/24/005. Epub 2008 Nov 18.
The dosimetric impact of intrafraction prostate motion was investigated for helical tomotherapy treatments. Measured motion tracks were used to calculate the dosimetric impact on delivered target dose distributions. A dynamic dose calculation engine was developed to facilitate this evaluation. It was found that the D95% (minimum dose to 95% of the volume) changes in the prostate were well correlated with D95% changes in the PTV. This means that the dosimetric impact of intrafraction motion is not restricted to the periphery of the target. The amount of motion was not well correlated with the dosimetric impact (measured in target D95% changes) of motion. The relationship between motion and its dosimetric impact is complex and depends on the timing and direction of the movement. These findings have implications for motion management techniques. It appears that the use of target margins is not an effective strategy to protect the prostate from the effects of observed intrafraction motion. The complex relationship between motion and its dosimetric effect renders simple threshold-based intervention schemes inefficient. Monitoring of actual prostate motion would allow the documentation of the dosimetric impact and implementation of corrective action if needed. However, when motion management techniques are evaluated, it should be kept in mind that the dosimetric impact of observed prostate motion is small for the majority of fractions.
研究了螺旋断层放射治疗中分次内前列腺运动的剂量学影响。使用测量的运动轨迹来计算对所给予的靶区剂量分布的剂量学影响。开发了一种动态剂量计算引擎以促进该评估。结果发现，前列腺内的D95%（95%体积的最小剂量）变化与计划靶体积（PTV）中的D95%变化密切相关。这意味着分次内运动的剂量学影响并不局限于靶区周边。运动幅度与运动的剂量学影响（以靶区D95%变化衡量）相关性不佳。运动与其剂量学影响之间的关系复杂，取决于运动的时间和方向。这些发现对运动管理技术具有启示意义。看来使用靶区边界并不是保护前列腺免受观察到的分次内运动影响的有效策略。运动与其剂量学效应之间的复杂关系使得基于简单阈值的干预方案效率低下。监测实际前列腺运动将能够记录剂量学影响，并在需要时实施纠正措施。然而，在评估运动管理技术时，应牢记对于大多数分次而言，观察到的前列腺运动的剂量学影响较小。
