Pappas E, Seimenis I, Angelopoulos A, Georgolopoulou P, Kamariotaki-Paparigopoulou M, Maris T, Sakelliou L, Sandilos P, Vlachos L
Physics Department, University of Athens. Greece.
Phys Med Biol. 2001 Mar;46(3):783-97. doi: 10.1088/0031-9155/46/3/313.
In this work, polymer gel-MRI dosimetry (using VIPAR gels), radiographic film and a PinPoint ion chamber were used for profile measurements of 6 MV x-ray stereotactic beams of 5 and 10 mm diameter. The VIPAR gel-MRI method exhibited a linear dose response up to 32 Gy. VIPAR gels were found to resolve the penumbra region quite accurately, provided that the in-plane image resolution of the related T2-map is adequate (< or = 0.53 mm). T2-map slice thickness had no significant effect on beam profile data. VIPAR measurements performed with a spatial resolution of 0.13 mm provided penumbra widths (80%-20% distance) of 1.34 and 1.70 mm for the 5 and 10 mm cones respectively. These widths were found to be significantly smaller than those obtained with the film (2.23 mm for the 5 mm cone, 2.45 mm for the 10 mm cone) and PinPoint (2.25 mm for the 5 mm cone, 2.52 mm for the 10 mm cone) methods. Regarding relative depth dose measurements, good correlation between VIPAR gel and PinPoint data was observed. In conclusion, polymer gel-MRI dosimetry can provide relatively accurate profile data for very small beams used in stereotactic radiosurgery since it can overcome, to some extent, the problems related to the finite size of conventional detectors.
在这项工作中，使用聚合物凝胶 - MRI剂量测定法（使用VIPAR凝胶）、放射照相胶片和PinPoint电离室对直径为5毫米和10毫米的6兆伏X射线立体定向束进行轮廓测量。VIPAR凝胶 - MRI方法在高达32戈瑞的剂量范围内呈现线性剂量响应。结果发现，只要相关T2图的平面内图像分辨率足够（≤0.53毫米），VIPAR凝胶就能相当准确地分辨半影区。T2图切片厚度对束轮廓数据没有显著影响。以0.13毫米的空间分辨率进行的VIPAR测量得出，5毫米和10毫米射束准直器的半影宽度（80% - 20%距离）分别为1.34毫米和1.70毫米。发现这些宽度明显小于用胶片（5毫米射束准直器为2.23毫米，10毫米射束准直器为2.45毫米）和PinPoint（5毫米射束准直器为2.25毫米，10毫米射束准直器为2.52毫米）方法获得的宽度。关于相对深度剂量测量，观察到VIPAR凝胶和PinPoint数据之间有良好的相关性。总之，聚合物凝胶 - MRI剂量测定法可为立体定向放射外科中使用的非常小的射束提供相对准确的轮廓数据，因为它在一定程度上可以克服与传统探测器有限尺寸相关的问题。
