The use of appropriate equipment during the measurements required for a treatment planning system (TPS) directly affects the quality of treatment. The present study investigates the effect of small field output factors (OF) obtained with ion chambers of different volumes on intensity-modulated radiotherapy (IMRT) treatment plans. Three different beam models (BM65, BM13, BM04) were created at TPS using small fields OFs measured by ion chambers with three different volumes, i.e. 0.65, 0.13 and 0.04 cc respectively. IMRT plans with the same features were designed for these models. The difference between the calculated and measured doses at dose distributions for each IMRT plan was investigated using point-dose measurement and gamma index method. The OF values obtained with a 0.65 cc ion chamber were significantly different, especially in small fields. The greatest difference in point-dose measurements made in IMRT plans was observed in the plans produced in the BM65 beam model. There was no significant difference in gamma passing rate (GPR) values in 2D array measurements. Inaccurate OF values obtained during small-field measurements is one of the important parameters that affect dosimetric accuracy. Therefore, using different dosimetric methods in quality assurance during TPS commissioning may allow to detect measurement errors, especially in small-field measurements.

中文翻译：

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电离室容积对调强放疗小野剂量测定的影响

在治疗计划系统 (TPS) 所需的测量过程中使用适当的设备直接影响治疗质量。本研究调查了不同体积电离室获得的小场输出因子 (OF) 对调强放射治疗 (IMRT) 治疗计划的影响。使用由三种不同体积（即分别为 0.65、0.13 和 0.04 cc）的离子室测量的小视场 OF，在 TPS 上创建了三种不同的射束模型（BM65、BM13、BM04）。具有相同功能的 IMRT 计划是为这些模型设计的。使用点剂量测量和伽马指数方法研究了每个 IMRT 计划剂量分布的计算剂量和测量剂量之间的差异。使用 0.65 cc 离子室获得的 OF 值存在显着差异，尤其是在小视场中。在 IMRT 计划中进行的点剂量测量的最大差异是在 BM65 射束模型中生成的计划中观察到的。二维阵列测量中的伽马通过率 (GPR) 值没有显着差异。小视场测量过程中获得的OF值不准确是影响剂量测量精度的重要参数之一。因此，在 TPS 调试期间使用不同的剂量测定方法进行质量保证可以检测测量误差，特别是在小场测量中。