Department of Radiation Oncology, M. D. Anderson Cancer Center Orlando, 1400 South Orange Avenue, Orlando, FL 32806, USA.
Phys Med Biol. 2010 Jul 21;55(14):4187-202. doi: 10.1088/0031-9155/55/14/015. Epub 2010 Jul 5.
Intra-fraction organ motion during intensity-modulated radiation therapy (IMRT) treatment can cause differences between the planned and the delivered dose distribution. To investigate the extent of these dosimetric changes, a computational model was developed and validated. The computational method allows for calculation of the rigid motion perturbed three-dimensional dose distribution in the CT volume and therefore a dose volume histogram-based assessment of the dosimetric impact of intra-fraction motion on a rigidly moving body. The method was developed and validated for both step-and-shoot IMRT and solid compensator IMRT treatment plans. For each segment (or beam), fluence maps were exported from the treatment planning system. Fluence maps were shifted according to the target position deduced from a motion track. These shifted, motion-encoded fluence maps were then re-imported into the treatment planning system and were used to calculate the motion-encoded dose distribution. To validate the accuracy of the motion-encoded dose distribution the treatment plan was delivered to a moving cylindrical phantom using a programmed four-dimensional motion phantom. Extended dose response (EDR-2) film was used to measure a planar dose distribution for comparison with the calculated motion-encoded distribution using a gamma index analysis (3% dose difference, 3 mm distance-to-agreement). A series of motion tracks incorporating both inter-beam step-function shifts and continuous sinusoidal motion were tested. The method was shown to accurately predict the film's dose distribution for all of the tested motion tracks, both for the step-and-shoot IMRT and compensator plans. The average gamma analysis pass rate for the measured dose distribution with respect to the calculated motion-encoded distribution was 98.3 +/- 0.7%. For static delivery the average film-to-calculation pass rate was 98.7 +/- 0.2%. In summary, a computational technique has been developed to calculate the dosimetric effect of intra-fraction motion. This technique has the potential to evaluate a given plan's sensitivity to anticipated organ motion. With knowledge of the organ's motion it can also be used as a tool to assess the impact of measured intra-fraction motion after dose delivery.
调强放射治疗（IMRT）过程中的分次内器官运动可导致计划剂量分布与实际剂量分布之间的差异。为了研究这些剂量变化的程度，开发并验证了一种计算模型。该计算方法允许计算在 CT 容积中受刚性运动影响的三维剂量分布，因此可以基于剂量体积直方图评估分次内运动对刚性运动体的剂量影响。该方法是针对分步照射 IMRT 和固体补偿器 IMRT 治疗计划开发和验证的。对于每个射野（或束），从治疗计划系统中导出了剂量率图。根据从运动轨迹推导出的靶位置来移动剂量率图。然后，将这些移位的、运动编码的剂量率图重新导入治疗计划系统，并用于计算运动编码的剂量分布。为了验证运动编码剂量分布的准确性，使用程控式四维运动体模将治疗计划输送到运动的圆柱体模体。使用扩展剂量响应（EDR-2）胶片测量平面剂量分布，以便与使用伽马指数分析（3%剂量差异，3 毫米距离一致性）计算的运动编码分布进行比较。测试了一系列包含射野间阶跃函数移位和连续正弦运动的运动轨迹。对于所有测试的运动轨迹，该方法都能准确预测胶片的剂量分布，对于分步照射 IMRT 和补偿器计划均如此。对于静态输送，相对于计算的运动编码分布，测量的剂量分布的伽马分析通过率平均值为 98.3 +/- 0.7%。对于静态输送，胶片与计算的平均通过率为 98.7 +/- 0.2%。总之，已经开发了一种计算技术来计算分次内运动的剂量效应。该技术具有评估给定计划对预期器官运动的敏感性的潜力。如果了解器官的运动，它也可以用作评估剂量输送后测量的分次内运动影响的工具。
