四种探测器测量射波刀离轴比曲线的比较分析

目的 比较分析不同探测器测量射波刀离轴比曲线，为正确选择和应用探测器提供参考。方法 应用PTW-60017、PTW-60018、PTW-60019和IBA-SFD 4种探测器分别平行和垂直于射束中心轴方向测量射波刀不同孔径准直器、不同深度的离轴比曲线，分析不同探测器测量的离轴比曲线差异及探测器固定方式对测量结果的影响。结果 探测器平行于射束中心轴方向时，4种探测器测得的半高宽（full width at half maximum，FWHM）均比实际射野偏大，最大偏差为1.9 mm，偏差随测量深度增加而增大。4种探测器测得的FWHM之间最大偏差为0.2 mm。4种探测器测得的半影最大偏差为0.3 mm，IBA-SFD测得半影最小，PTW-60019最大。测得的半影均随准直器孔径和深度增加而增大。准直器孔径大于30 mm时，IBA-SFD在射野外存在过响应现象。探测器垂直于射束中心轴方向时，PTW-60017、PTW-60018、PTW-60019测得的FWHM和半影比探测器平行于射束中心轴方向时小，准直器孔径5 mm时尤为明显。而IBA-SFD测得的结果相反。随着准直器孔径增加，4种探测器测得的左右半影间差异增加，杆效应明显。结论 4种探测器测量的射波刀离轴比曲线相近，但应用时需考虑各自特点，并注意探测器固定方式和杆效应的影响。

Comparative analysis of four detectors for the profile measurement using CyberKnife

Objective To evaluate four detectors for the off-axis ratio profile measurements of a CyberKnife system, and provide reference and suggestions for selecting and using the correct detectors.Methods Profiles were acquired by using four detectors, PTW-60017, PTW-60018, PTW-60019 and IBA-SFD, at different depths for different collimator sizes, with the detector stem being oriented both perpendicular and parallel to the central beam axis. The differences of profiles and the influence of detector orientation on measurement result were analyzed.Results All full width at half maximum (FWHM) of field measured by four detectors in parallel orientation was larger than that in actual field size. The deviation was increased with the size of collimator and measurement depth, with the maximum deviation of 1.9 mm. The maximum deviation of FWHM among four detectors was 0.2 mm. The penumbra was the smallest for IBA-SFD, and the largest for PTW-60019. The maximum deviation of penumbra was 0.3 mm. The IBA-SFD tended to over-respond in the out-of-field region when the collimator size was larger than 30 mm. Both FWHM and penumbra in perpendicular orientation were smaller than those in parallel orientation for PTW-60017, PTW-60018 and PTW-60019, especially at 5 mm collimator. However, the trend was opposite for IBA-SFD. With the increase of collimator aperture, the difference between the right and left penumbra acquired by four detectors was increased, with more obvious stem effects.Conclusions Similar profiles were acquired by four detectors, but the detector characteristics and effects of detector orientations should be considered.