Dose response of selected solid state detectors in applied homogeneous transverse and longitudinal magnetic fields
Dose response of selected solid state detectors in applied homogeneous transverse and longitudinal magnetic fields
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DOI：
10.1118/1.4893276
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发表时间：
2014-09-01
期刊：
影响因子：
3.8
通讯作者：
Rathee, S.
中科院分区：
文献类型：
--
作者：
Reynolds, M.;Fallone, B. G.;Rathee, S.
目的：全球正在开发的MR-LINAC设备将需要标准校准、调试和质量保证。固态辐射探测器通常用于剂量分布和深度百分比剂量测量。因此，选择的固态探测器在不同的横向和纵向磁场中进行剂量响应评估。方法：使用蒙特卡罗程序Penelope模拟了PtW-60003金刚石探测器和IBAPFD二极管探测器在磁场作用下的剂量响应。场本身的强度是不同的，并且相对于入射的光子束既有横向的，也有纵向的。探测器的长轴方向与光子束平行或垂直。对每个探测器在空气中的有效体积的剂量进行评分，并将其与磁场强度为零的剂量之比确定为磁场中的“剂量响应”。为了评估模拟的准确性，在横向磁场中对两个探测器进行了低场测量。在水模中进行了额外的模拟，以获得几个具有代表性的束流剖面和深度百分比剂量测量的点。结果：模拟显示出显著的剂量响应作为横场几何中磁场的函数。在1.5T时，这种响应可以接近20%，并且它高度依赖于探测器相对于磁场的相对取向、光子束的能量和探测器的组成。在低横向磁场下的测量验证了两种探测器相对于辐射束方向的模拟结果。纵向磁场则表现出较小的剂量响应，随磁场的增加而缓慢上升，在1.5T时达到0.5%~1%，与探测器取向无关。在存在横向电子平衡的情况下，水箱和空气中的模拟结果是相同的，只是在横场方向上在束流边缘有预期的不同。由于设计的不同，两种探测器的性能也有所不同。结论：在横向磁场存在的情况下，使用钻石或二极管探测器时应格外小心。剂量响应随探测器的相对取向、磁场强度和探测器之间的不同而变化。这种响应可能是相当大的(类似于两个探测器的20%)。纵场中的两个探测器都很少或没有表现出作为磁场的函数的剂量响应。水箱模拟似乎表明，二极管探测器更适合于一般的束流调试，每个探测器都必须单独进行研究。(C)2014年美国医学物理学家协会。
Purpose: MR-Linac devices under development worldwide will require standard calibration, commissioning, and quality assurance. Solid state radiation detectors are often used for dose profiles and percent depth dose measurements. The dose response of selected solid state detectors is therefore evaluated in varying transverse and longitudinal magnetic fields for this purpose.Methods: The Monte Carlo code PENELOPE was used to model irradiation of a PTW 60003 diamond detector and IBA PFD diode detector in the presence of a magnetic field. The field itself was varied in strength, and oriented both transversely and longitudinally with respect to the incident photon beam. The long axis of the detectors was oriented either parallel or perpendicular to the photon beam. The dose to the active volume of each detector in air was scored, and its ratio to dose with zero magnetic field strength was determined as the "dose response" in magnetic field. Measurements at low fields for both detectors in transverse magnetic fields were taken to evaluate the accuracy of the simulations. Additional simulations were performed in a water phantom to obtain few representative points for beam profile and percent depth dose measurements.Results: Simulations show significant dose response as a function of magnetic field in transverse field geometries. This response can be near 20% at 1.5 T, and it is highly dependent on the detectors' relative orientation to the magnetic field, the energy of the photon beam, and detector composition. Measurements at low transverse magnetic fields verify the simulations for both detectors in their relative orientations to radiation beam. Longitudinal magnetic fields, in contrast, show little dose response, rising slowly with magnetic field, and reaching 0.5%-1% at 1.5 T regardless of detector orientation. Water tank and in air simulation results were the same within simulation uncertainty where lateral electronic equilibrium is present and expectedly differed at the beam edge in transverse field orientations only. Due to the difference in design, the two detectors behaved differently.Conclusions: When transverse magnetic fields are present, great care must be taken when using diamond or diode detectors. Dose response varies with relative detector orientation, magnetic field strength, and between detectors. This response can be considerable (similar to 20% for both detectors). Both detectors in longitudinal fields exhibit little to no dose response as a function of magnetic field. Water tank simulations seem to suggest that the diode detector is better suited to general beam commissioning, and each detector must be investigated separately. (C) 2014 American Association of Physicists in Medicine.