Rubinstein Ashley E, Liao Zhongxing, Melancon Adam D, Guindani Michele, Followill David S, Tailor Ramesh C, Hazle John D, Court Laurence E
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 and The University of Texas Graduate School of Biomedical Sciences, Houston, Texas 77030.
Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
Med Phys. 2015 Sep;42(9):5510-6. doi: 10.1118/1.4928600.
Magnetic fields are known to alter radiation dose deposition. Before patients receive treatment using an MRI-linear accelerator (MRI-Linac), preclinical studies are needed to understand the biological consequences of magnetic-field-induced dose effects. In the present study, the authors sought to identify a beam energy and magnetic field strength combination suitable for preclinical murine experiments.
Magnetic field dose effects were simulated in a mouse lung phantom using various beam energies (225 kVp, 350 kVp, 662 keV [Cs-137], 2 MV, and 1.25 MeV [Co-60]) and magnetic field strengths (0.75, 1.5, and 3 T). The resulting dose distributions were compared with those in a simulated human lung phantom irradiated with a 6 or 8 MV beam and orthogonal 1.5 T magnetic field.
In the human lung phantom, the authors observed a dose increase of 45% and 54% at the soft-tissue-to-lung interface and a dose decrease of 41% and 48% at the lung-to-soft-tissue interface for the 6 and 8 MV beams, respectively. In the mouse simulations, the magnetic fields had no measurable effect on the 225 or 350 kVp dose distribution. The dose increases with the Cs-137 beam for the 0.75, 1.5, and 3 T magnetic fields were 9%, 29%, and 42%, respectively. The dose decreases were 9%, 21%, and 37%. For the 2 MV beam, the dose increases were 16%, 33%, and 31% and the dose decreases were 9%, 19%, and 30%. For the Co-60 beam, the dose increases were 19%, 54%, and 44%, and the dose decreases were 19%, 42%, and 40%.
The magnetic field dose effects in the mouse phantom using a Cs-137, 3 T combination or a Co-60, 1.5 or 3 T combination most closely resemble those in simulated human treatments with a 6 MV, 1.5 T MRI-Linac. The effects with a Co-60, 1.5 T combination most closely resemble those in simulated human treatments with an 8 MV, 1.5 T MRI-Linac.
已知磁场会改变辐射剂量沉积。在患者接受使用磁共振成像直线加速器（MRI-Linac）的治疗之前，需要进行临床前研究以了解磁场诱导剂量效应的生物学后果。在本研究中，作者试图确定适合临床前小鼠实验的束流能量和磁场强度组合。
使用各种束流能量（225 kVp、350 kVp、662 keV [铯 - 137]、2 MV 和 1.25 MeV [钴 - 60]）和磁场强度（0.75、1.5 和 3 T）在小鼠肺部模型中模拟磁场剂量效应。将所得剂量分布与用 6 或 8 MV 束流和正交 1.5 T 磁场照射的模拟人体肺部模型中的剂量分布进行比较。
在人体肺部模型中，作者观察到对于 6 MV 和 8 MV 束流，在软组织与肺部界面处剂量分别增加 45%和 54%，在肺部与软组织界面处剂量分别降低 41%和 48%。在小鼠模拟中，磁场对 225 或 350 kVp 剂量分布没有可测量的影响。对于 0.75 T、1.5 T 和 3 T 磁场，铯 - 137 束流的剂量增加分别为 9%、29%和 42%。剂量降低分别为 9%、21%和 37%。对于 2 MV 束流，剂量增加分别为 16%、33%和 31%，剂量降低分别为 9%、19%和 30%。对于钴 - 60 束流，剂量增加分别为 19%、54%和 44%，剂量降低分别为 19%、42%和 40%。
使用铯 - 137、3 T 组合或钴 - 60、1.5 T 或 3 T 组合在小鼠模型中产生的磁场剂量效应与使用 6 MV、1.5 T MRI-Linac 的模拟人体治疗中产生的效应最为相似。使用钴 - 60、1.5 T 组合产生的效应与使用 8 MV、1.5 T MRI-Linac 的模拟人体治疗中产生的效应最为相似。
