目的：分析在不同剂量率条件下，调强计划的机器跳数（MU）和治疗时间的变化。方法从头颈部、胸部，腹部和中枢神经系统肿瘤中各选择一种典型病例，通过选择100～600 MU/min的剂量率，制定20例调强放疗计划，使用Varian计划系统对不同的剂量率计算MU数和出束时间。结果每增加100 MU/min的剂量率，MU数增加4.5%～7%，出束时间非线性减少，具体变化数值根据计划的复杂程度和靶区体积的变化有所不同。结论剂量率的增加对治疗计划实施方面产生影响，随着剂量率的增加，对于复杂的计划MU数会增加很快，但是出束时间会大量减少，因此可以增加单位加速器治疗的病人数，对于病人数较多的放疗单位具有较大的意义。%Objective To analyze of the different accelerator dose rate conditions and the change in the treatment time and the number of MUs. Methods We used Varian's Eclipse Treatment Planning System to calculate the number of MUs and beam-on times for a total of 20 different treatment plans across an array of common IMRT sites including head and neck, chest, abdomen and central nervous system cancers using dose rates of 100, 200, 300, 400 and 600 MU/min. Results We observed a 4.5%~7%increase in the number of MUs delivered and decrease in the beam-on time for each 100 MU/min of dose rate increase. The exact magnitude of the changes depended on treatment site and planning target volume. Conclusion Although the number of MUs increased more rapidly for more complex treatment plans, the absolute beam-on time savings was greater for these plans because of the higher total number of MUs required to deliver them. We estimate that increasing the IMRT dose rate has the potential to treat more people per day for each linear accelerator.
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