背景和目的：

目前，动态调强放疗广泛地应用于肿瘤的放射治疗，并且越来越多地应用于胸腹部肿瘤的治疗。随着临床上对剂量分布等要求的不断提高，动态调强射野的子野越来越小，呼吸等生理运动引起的剂量学差异越来越显著。

对于呼吸运动引起的剂量学差异的研究目前主要集中在对单次治疗剂量分布或全疗程的剂量分布在有无呼吸运动时差异比较，和呼吸管理方面的研究。并未对具体的子野参数进行研究。本研究首次针对动态调强射野的两个重要特性：子野宽度（射野宽度）与MLC叶片移动速度（叶片速度）来设计、研究呼吸运动对动态调强射野剂量学的影响。并分析动态调强技术能否应用于乳腺癌的放疗。

材料和方法：

使用Quasar驱动平台驱动调强验证模体模拟呼吸运动。

设计一组不同射野宽度和不同叶片速度的照射野照射调强验证模体。

在验证模体中放置辐射自显影胶片分别在有无呼吸运动时采集一个呼吸周期内射野剂量分布。

处理胶片并生成剂量分布曲线分析胶片，对运动模式、叶片速度、射野宽度等多个因素分组进行比对并分析原因。

使用一组实际患者的动态调强射野对验证模体进行照射。在连续呼吸情况下，分别在有无呼吸运动时采集射野中心的剂量分布。处理胶片并生成剂量分布曲线后对比并分析原因。

结果:

在单次呼吸模式下，不同的运动模式对剂量分布影响差异显著不同。随着叶片速度的增大，射野内剂量波动幅度随之显著增大；随着射野宽度的增大，射野内剂量波动幅度随之减小；射野宽度小叶片速度高，对剂量分布的影响最为显著。模式A中最大剂量无统计学意义，但最小剂量为49.93%±13.49%；在模式B中最大剂量为204.79%±49.35%，最小剂量为 27.53%±6.96%。在实际射野中射野照射范围内剂量波动幅度明显减小，剂量分布曲线相似，剂量差异主要表现为剂量分布的偏移。

结论:

有呼吸运动影响时，应通过提高射野宽度和（或）减小叶片速度等方法来减小呼吸运动对SW调强射野剂量分布的影响。

Background and Purpose

Currently，dynamic modulated radiation therapy (IMRT) is widely used in radiotherapy，and is increasingly applied in the treatment for thoracic and abdominal tumors. With the ever-growing clinical requirements for dose distribution, the subfields of dynamic IMRT are getting smaller and smaller. and the dosimetric differences caused by physiological movements, such as respiration, are becoming significant.

At present, researches on dosimetry differences as a result of respiratory movement are mainly focuses on difference comparison of dose distribution for a single treatment or the whole course with or without respiratory movement. Specific subfield parameters have not been researched. This study focuses on two important characteristics of dynamic IMRT field for the first time the width of subfield (field width) and the speed of MLC leaf moving (leaf speed) are used to design and research the effects of respiratory on dynamic IMRT field dosimetry. Moreover, whether dynamic intensity modulated technology can be applied in the radiotherapy of breast cancer will be analyzed.

Materials and Methods

Quasar drive platform was used to drive the IMRT verification phantom to simulate respiratory movement.

A set of sliding window field with different field width and leaf speed was designed to radiate IMRT phantom.

Placing EBT2 film in the IMRT phantom to collect the dose distribution during a breathing cycle with or without respiratory motion.

Analyzing the film by processing the film and generating a curve analysis film of dose distribution. Comparing the factors such as movement mode, leaf speed and field width, and analyze the reasons.

A set of patients’ dynamic IMRT field was used to radiate the IMRT phantom, and the dose distributions at the center field were collected with or without respiratory motion in the case of continuous breathing, then comparing and analyzing the reasons by processing the film and generating a dose distribution curve.

Results

In the single breathing mode, different modes have significantly different effects on the dose distribution; as the leaf speed increases, the amplitude of the dose fluctuation in the field increases significantly; as the width of the field increases, the amplitude of the dose fluctuation is reduced. Small field width and high leaf speed have the most significant effect on the dose distribution. The maximum dose in mode A is not statistically significant, but the minimum dose is 49.93% ± 13.49%; in mode B, the maximum dose is 204.79% ± 49.35%, and the minimum dose is 27.53% ± 6.96%. However, in the actual radiation field, the dose fluctuation range is significantly reduced in the irradiation field with similar dose distribution curve, and the dose difference is mainly represented by the dose shift.

Conclusion

With respiratory motion, its effect on the dose distribution of SW field should be reduced by increasing the radiation field width and/or reducing the leaf speed.