DAVID系统探测MLC叶片位置误差的能力测试与评估

Test and Evaluation on DAVID System′s Ability to Detect Location Error of MLC Leaves

目的:检测DAVID系统对叶片位置误差的探测能力并加以评估。方法:以射野10 cm×10 cm为参考,每次照射100 MU。改变X和Y方向射野大小,移动射野中单个叶片位置,射野分别沿X和Y方向向上整体移动,射野位于边角和侧边时改变射野大小,利用DAVID系统进行参考值测量并读取测量结果。结果:射野在X方向上增大1~4 mm,DAVID系统检测到的平均偏差分别为0.98%、2.04%、3.03%和4.11%;在Y方向上增大1~2 mm,平均偏差为5.11%和10.45%。31号叶片移动1~7 mm,偏差范围为-0.41%^-2.59%。40号叶片朝射野内移动1~7 mm,偏差范围为-0.88%^-3.37%;朝射野外移动1~7 mm,偏差范围为0.42%~2.22%。在X和Y方向上分别移动5 mm,偏差为-0.51%和1 184.11%;在X和Y方向同时移动5 mm,偏差为1 368.56%。射野位于边角和一侧时,射野扩大1 mm,探测到的偏差分别为1.25%和1.15%。结论:DAVID系统对MLC射野和单个叶片的位置误差探测能力分别为1和2 mm,对中心轴和偏一侧的射野具有同等探测能力,但其没有位置判断能力。

Objective To test and evaluate the ability of DAVID system to detect the location error of MLC leaves. Methods With a referential field size of 10 cm×10 cm and a single dose of 100 MU, the reference values were measured by DAVID system when the field sized was modified along the directions of X axis and Y axis, some single leave was moved in the mobile field, the overall field was shifted along the directions of X axis and Y axis and the field size was changed in ease that it was located at the comer and broadside. Results The mean deviations along the X axis were 0.98%, 2.04%, 3.03% and 4.11% respectively with the amplification of the field along X axis between 1 and 4 mm, were 5.11% and 10.45% respectively with the amplification along Y axis between 1 and 2 mm, were from -0.41% to -2.59% with the displacement of No. 31 leave between 1 and 7 mm, were from -0.88% to -3.37% with the intruded displacement of No. 40 leave between 1 and 7 mm, and were from 0.42% to 2.22% with the extruded displacement of No. 40 leave between 1 and 7 mm. With the displacement of 5 mm along X axis or Y axis, the deviation was -0.51% or 1 184.11% respectively; with the displacements along both X axis and Y axis, the deviation was 1 368.56%. When the field was located at the comer or broadside, the deviations were 1.25% and 1.15% respectively with the amplification of the field of 1 mm. Conclusion DAVID system can detect 1 mm position error for MLC field and 2 mm error for some single leave, and behaves similarly when used to detect the field at central axis and broadside, while has no capability for location Judgment.