螺旋断层放疗系统物理性能的验收测试与质量保证

Acceptance Testing and Quality Assurance of Physics Performance in Helical Tomotherapy System

目的:验收测试新装螺旋断层放疗系统的主要物理性能。方法:参照设备厂家验收手册及AAPM TG148号报告,测试验证螺旋断层放疗系统的剂量学、射束几何学精度及兆伏CT影像测试等物理性能。结果:经测试,多叶光栅T&G测试数值为0.87%;次级准直器Shift/Sweep测试数值为0.05 mm;射束中心轴几何精度偏差数值为-0.377 mm,偏转角度为0.03°;旋转模式下,射束输出稳定性偏差为0.1%;能量测试稳定性偏差为0.8%;固定与移动激光灯精度偏差均小于0.5 mm;多叶光栅中心精度误差为0.86 mm;多叶光栅IEC Y方向平行度偏转角度为0.01°;次级准直器对称性精度偏差值为0.12 mm;射束横向、纵向离轴曲线及百分深度剂量分布与参考数据作γ分析比较,在标准为ΔDD=2%、ΔDTA=1 mm的条件下,γ值均<1;兆伏CT模体吸收剂量<3 cGy,重建影像无伪影,影像分辨率可见密度棒第三排小孔。结论:设备符合各项验收标准,可投入临床使用。

Objective To check the main physics performance of a new helical tomotherapy system. Methods With reference to the acceptance testing procedures of equipment manufacturers and AAPM TG148 report, the acceptance testing was executed for the physics performances of the system in dosiology, geometric accuracy of beam, MVCT image testing and etc. The measurement value of multi-leaf grating T＆G was 0.87%, the value of secondary collimator Shift/Sweep was 0.05 mm, the value of geometric accuracy offset of beam axis was -0.377 mm with the angle of 0.03°, the value of beam output stability offset was 0.1% in case of rotating mode, the value of energy test stability offset was 0.8%, the precision offsets of fixed and mobile laser lights were both less than 0.5 mm, the center precision error of multi-leaf grating was 0.86 mm, the angle of parallelism offset along Y direction of multi-leaf grating was 0.01°, and the deviation value of secondary collimator symmetry was 0.12 mm. With the standards of ADD = 2% and △DTA = 1 mm, γ values were all less than 1 when γ analysis was performed for beam off-axis curves along X axis and Y axis, percent depth dose distribution as well reference data. The phantom absorbed dose of MVCT was less than 3 cGy. There were no obvious artifacts in reconstructed image, and the third row of holes in the intensity rod could be distinguished in image resolution. The helical tomotherapy system meets all acceptance standards, and is worth of clinical application.