在 1.5T、0.35T 和 0T 磁场强度下，MR/CT 可见材料中 TLD 和 EBT3 的性能研究。
Investigation of TLD and EBT3 performance under the presence of 1.5T, 0.35T, and 0T magnetic field strengths in MR/CT visible materials.
机构信息
Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX, 77030, USA.
Department of Imaging Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX, 77030, USA.
出版信息
Med Phys. 2019 Jul;46(7):3217-3226. doi: 10.1002/mp.13527. Epub 2019 May 15.
PURPOSE
The aim of this study was to investigate thermoluminescent dosimeters (TLD) and radiochromic EBT3 film inside MR/CT visible geometric head and thorax phantoms in the presence of: 0, 0.35, and 1.5 T magnetic fields.
METHODS
Thermoluminescent Dosimeters reproducibility studies were examined by irradiating IROC-Houston's TLD acrylic block five times under 0 and 1.5 T configurations of Elekta's Unity system and three times under 0 and 0.35 T configurations of ViewRay's MRIdian Cobalt-60 ( Co) system. Both systems were irradiated with an equivalent 10 × 10 cm field size, and a prescribed dose of 3 Gy to the maximum depth deposition (dmax). EBT3 film and TLDs were investigated using two geometrical Magnetic Resonance (MR)-guided Radiation Therapy (MRgRT) head and thorax phantoms. Each geometrical phantom had eight quadrants that combined to create a centrally located rectangular tumor (3 × 3 × 5 cm ) surrounded by tissue to form a 15 × 15 × 15 cm cubic phantom. Liquid polyvinyl chloride plastic and Superflab were used to simulate the tumor and surrounding tissue in the head phantom, respectively. Synthetic ballistic gel and a heterogeneous in-house mixture were used to construct the tumor and surrounding tissue in the thorax phantom, respectively. EBT3 and double-loaded TLDs were used in the phantoms to compare beam profiles and point dose measurements with and without magnetic fields. GEANT4 Monte Carlo simulations were performed to validate the detectors for both Unity 0 T/1.5 T and MRIdian 0 T/0.35 T configurations.
RESULTS
Average TLD block measurements which, compared the magnetic field effects (magnetic field vs 0 T) on the Unity and MRIdian systems, were 0.5% and 0.6%, respectively. The average ratios between magnetic field effects for the geometric thorax and head phantoms under the Unity system were -0.2% and 1.6% and for the MRIdian system were 0.2% and -0.3%, respectively. Beam profiles generated with both systems agreed with Monte Carlo measurements and previous literature findings.
CONCLUSIONS
TLDs and EBT3 film dosimeters could potentially be used in MR/CT visible tissue equivalent phantoms that will experience a magnetic field environment.
目的
本研究旨在调查在 0、0.35 和 1.5 T 磁场存在下，热释光剂量计（TLD）和放射性 EBT3 薄膜在可见磁共振/计算机断层扫描（MR/CT）头部和胸部体模中的性能。
方法
通过在 Elekta 的 Unity 系统的 0 和 1.5 T 配置下对 IROC-Houston 的 TLD 丙烯酸块进行五次照射，并在 ViewRay 的 MRIdian 钴-60（Co）系统的 0 和 0.35 T 配置下进行三次照射，对 TLD 重复性进行了研究。两个系统均采用相同的 10×10 cm 射野大小和最大深度沉积（dmax）处 3 Gy 的规定剂量进行照射。EBT3 薄膜和 TLD 采用两个几何形状的磁共振引导放射治疗（MRgRT）头部和胸部体模进行了研究。每个几何体模有八个象限，组合成一个位于中心的矩形肿瘤（3×3×5 cm），周围是组织，形成一个 15×15×15 cm 的立方体模。液态聚氯乙烯塑料和 Superflab 分别用于模拟头部体模中的肿瘤和周围组织。合成弹道凝胶和内部混合不均匀材料分别用于构建胸部体模中的肿瘤和周围组织。EBT3 和双载 TLD 用于体模中，比较有无磁场时的射束轮廓和点剂量测量。采用 GEANT4 蒙特卡罗模拟对 Unity 0 T/1.5 T 和 MRIdian 0 T/0.35 T 配置的探测器进行了验证。
结果
与 Unity 和 MRIdian 系统相比，TLD 块测量的平均磁场效应（磁场与 0 T 相比）分别为 0.5%和 0.6%。Unity 系统下，几何胸部和头部体模的磁场效应平均比值分别为-0.2%和 1.6%，MRIdian 系统下的比值分别为 0.2%和-0.3%。两种系统生成的射束轮廓与蒙特卡罗测量值和先前的文献结果一致。
结论
TLD 和 EBT3 薄膜剂量计可能可用于将经历磁场环境的磁共振/CT 可见组织等效体模中使用。
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