Reynoso Francisco J, Curcuru Austen, Green Olga, Mutic Sasa, Das Indra J, Santanam Lakshmi
Department of Radiation Oncology, Washington University School of Medicine, St. Louis, Missouri 63110.
Department of Radiation Oncology, New York University Langone Medical Center, New York, New York 10016.
Med Phys. 2016 Dec;43(12):6552. doi: 10.1118/1.4967486.
Magnetokinetic changes may affect crystal orientation and polymerization within the active layer of radiochromic film (RCF). This effect is investigated in a magnetic resonance image-guided radiotherapy unit within the context of film dosimetry.
Gafchromic EBT2 RCF was irradiated in a 30 × 30 × 30 cm solid water phantom using a Co-60 MRI guided radiotherapy system (B = 0.35 T) under normal operating conditions, and under the exact conditions and setup without a magnetic field. Fifteen 20.3 × 25.4 cm EBT2 film sheets were placed at three different depths (d = 0.5, 5, and 10 cm) using five different treatment plans. The plans were computed using the MRIdian (ViewRay, Inc.) treatment planning system to deliver doses between 0 and 17.6 Gy. Films were analyzed before and after irradiation to obtain the net optical density (netOD) for each color channel separately. Scanning electron microscope (SEM) images were obtained to compare the active layer of selected samples.
The results indicated that the red channel netOD decreased between 0.013 and 0.123 (average of 0.060 ± 0.033) for doses above 2.8 Gy, with a linear increase in this effect for higher doses. Green channel netOD showed similar results with a decrease between 0.012 and 0.105 (average of 0.041 ± 0.027) for doses above 3.5 Gy. The blue channel showed the weakest effect with a netOD decrease between 0.013 and 0.029 (average of 0.020 ± 0.006) for doses above 8.0 Gy. SEM images show changes in crystal orientation within active layer in RCF exposed in a magnetic field.
The presence of a magnetic field affects crystal orientation and polymerization during irradiation, where netOD decreased by an average of 8.7%, 8.0%, and 4.3% in the red, green, and blue channels, respectively. The under response was dependent on dose and differed by up to 15% at 17.6 Gy.
磁动力学变化可能会影响放射变色薄膜（RCF）活性层内的晶体取向和聚合。在磁共振图像引导放射治疗单元的薄膜剂量测定背景下，对这种效应进行了研究。
使用钴 - 60磁共振成像引导放射治疗系统（B = 0.35 T），在正常操作条件下，以及在没有磁场的精确条件和设置下，在30×30×30 cm的固体水模体中对Gafchromic EBT2 RCF进行照射。使用五种不同的治疗计划，将15张20.3×25.4 cm的EBT2薄膜片放置在三个不同深度（d = 0.5、5和10 cm）处。使用MRIdian（ViewRay公司）治疗计划系统计算计划，以输送0至17.6 Gy之间的剂量。在照射前后对薄膜进行分析，分别获得每个颜色通道的净光密度（netOD）。获得扫描电子显微镜（SEM）图像以比较选定样品的活性层。
结果表明，对于高于2.8 Gy的剂量，红色通道netOD下降了0.013至0.123（平均为0.060±0.033），随着剂量增加，这种效应呈线性增加。绿色通道netOD显示出类似的结果，对于高于3.5 Gy的剂量，下降了0.012至0.105（平均为0.041±0.027）。蓝色通道的效应最弱，对于高于8.0 Gy的剂量，netOD下降了0.013至0.029（平均为0.020±0.006）。SEM图像显示了在磁场中暴露的RCF活性层内晶体取向的变化。
磁场的存在会影响照射期间的晶体取向和聚合，其中红色、绿色和蓝色通道的netOD分别平均下降了8.7%、8.0%和4.3%。响应不足取决于剂量，在17.6 Gy时差异高达15%。
