Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, USA; The University of Texas MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, USA.
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, USA; Department of Physics, University of Houston, USA.
Radiother Oncol. 2017 Dec;125(3):426-432. doi: 10.1016/j.radonc.2017.08.027. Epub 2017 Sep 27.
The strong magnetic field of integrated magnetic resonance imaging (MRI) and radiation treatment systems influences secondary electrons resulting in changes in dose deposition in three dimensions. To fill the need for volumetric dose quality assurance, we investigated the effects of strong magnetic fields on 3D dosimeters for MR-image-guided radiation therapy (MR-IGRT) applications.
There are currently three main categories of 3D dosimeters, and the following were used in this study: radiochromic plastic (PRESAGE®), radiochromic gel (FOX), and polymer gel (BANG™). For the purposes of batch consistency, an electromagnet was used for same-day irradiations with and without a strong magnetic field (B, 1.5T for PRESAGE® and FOX and 1.0T for BANG™).
For PRESAGE®, the percent difference in optical signal with and without B was 1.5% at the spectral peak of 632nm. For FOX, the optical signal percent difference was 1.6% at 440nm and 0.5% at 585nm. For BANG™, the percent difference in R MR signal was 0.7%.
The percent differences in responses with and without strong magnetic fields were minimal for all three 3D dosimeter systems. These 3D dosimeters therefore can be applied to MR-IGRT without requiring a correction factor.
集成磁共振成像（MRI）和放射治疗系统的强磁场会影响二次电子，从而导致三维剂量沉积发生变化。为了满足体积剂量质量保证的需求，我们研究了强磁场对用于磁共振图像引导放射治疗（MR-IGRT）应用的三维剂量计的影响。
目前有三种主要类型的三维剂量计，本研究中使用了以下三种：光致变色塑料（PRESAGE®）、光致变色凝胶（FOX）和聚合物凝胶（BANG™）。为了批次一致性，使用电磁铁进行了同一天的有和无强磁场（B，PRESAGE®和 FOX 为 1.5T，BANG™为 1.0T）的照射。
对于 PRESAGE®，在 632nm 的光谱峰值处，有和无 B 时的光信号差异百分比为 1.5%。对于 FOX，在 440nm 处的光信号差异百分比为 1.6%，在 585nm 处为 0.5%。对于 BANG™，R MR 信号的差异百分比为 0.7%。
对于所有三种三维剂量计系统，有和无强磁场时的响应差异百分比均很小。因此，这些三维剂量计可用于 MR-IGRT，而无需校正因子。
