Radiation Oncology Center, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences, Beijing, China.
Radiation Oncology Center, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital (Langfang campus), Chinese Academy of Medical Sciences, Langfang, China.
J Appl Clin Med Phys. 2024 Oct;25(10):e14471. doi: 10.1002/acm2.14471. Epub 2024 Aug 5.
To investigate the dose rate dependence of MapCHECK3 and its influence on measurement accuracy, as well as the effect of dose rate correction.
The average and instantaneous dose rate dependence of MapCHECK2 and MapCHECK3 were studied. The accuracy of measurements was investigated where the dose rate differed significantly between dose calibration of the MapCHECK and the measurement. Measurements investigated include: the central axis dose for different fields at different depths, off-axis doses outside the field, and off-axis doses along the wedge direction. Measurements using an ion chamber were taken as the reference. Exponential functions were fit to account for average and instantaneous dose rate dependence for MapCHECK3 and used for dose rate correction. The effect of the dose rate correction was studied by comparing the differences between the measurements for MapCHECK (with and without the correction) and the reference.
The maximum dose rate dependence of MapCHECK3 is greater than 2.5%. If the dose calibration factor derived from a 10 × 10 cm open field at 10 cm depth was used for measurements, the average differences in central diode dose were 0.8% ± 1.0% and 1.0% ± 0.8% for the studied field sizes and measurement depths, respectively. The introduction of wedge would not only induce -1.8% ± 1.3% difference in central diode dose, but also overestimate the effective wedge angle. After the instantaneous dose rate correction, above differences can be changed to 1.9% ± 8.1%, 0.2% ± 0.1%, and 0.0% ± 0.9%. The pass rate can be improved from 98.4% to 98.8%, 98.3%-100.0%, and 96.3%-100.0%, respectively.
Compared with MapCHECK2 (SunPoint1 diodes), the more pronounced dose rate dependence of MapCHECK3 (SunPoint2 diodes) should be carefully considered. To ensure highly accurate measurement, it is suggested to perform the dose calibration at the same condition where measurement will be performed. Otherwise, the dose rate correction should be applied.
研究 MapCHECK3 的剂量率依赖性及其对测量精度的影响，以及剂量率校正的效果。
研究了 MapCHECK2 和 MapCHECK3 的平均和瞬时剂量率依赖性。在 MapCHECK 的剂量校准与测量之间存在显著剂量率差异的情况下，研究了测量的准确性。研究的测量包括：不同深度不同野中心轴剂量、野外离轴剂量以及楔形方向的离轴剂量。使用电离室进行的测量作为参考。使用指数函数拟合 MapCHECK3 的平均和瞬时剂量率依赖性，并用于剂量率校正。通过比较 MapCHECK（校正前后）与参考之间的测量差异来研究剂量率校正的效果。
MapCHECK3 的最大剂量率依赖性大于 2.5%。如果使用源自 10×10cm 开野在 10cm 深度的校准因子进行测量，对于研究的射野大小和测量深度，中央二极管剂量的平均差异分别为 0.8%±1.0%和 1.0%±0.8%。引入楔形不仅会导致中央二极管剂量出现-1.8%±1.3%的差异，还会高估有效楔形角。进行瞬时剂量率校正后，上述差异可分别变为 1.9%±8.1%、0.2%±0.1%和 0.0%±0.9%。通过率可分别从 98.4%提高到 98.8%、98.3%-100.0%和 96.3%-100.0%。
与 MapCHECK2（SunPoint1 二极管）相比，MapCHECK3（SunPoint2 二极管）的剂量率依赖性更为显著，应予以谨慎考虑。为确保高精度测量，建议在进行测量的相同条件下进行剂量校准。否则，应应用剂量率校正。
