Experimental measurement of radiological penumbra associated with intermediate energy x-rays (1 MV) and small radiosurgery field sizes.
Experimental measurement of radiological penumbra associated with intermediate energy x-rays (1 MV) and small radiosurgery field sizes.
复制标题
与中等能量 X 射线 (1 MV) 和小放射外科野尺寸相关的放射半影的实验测量。
作者：
B. Keller;D. Beachey;J. Pignol
立体定向放射外科用于治疗颅内病变，具有高度的准确性。目前，使用的X射线能量等于或高于Co-60伽马射线。先前的Monte Carlo模拟已经证明，中等能量X射线光子或IEP（定义为能量范围为0.2-1.2 MeV的光子）与小射野尺寸相结合，产生减少的放射半影，导致更尖锐的剂量梯度，改善剂量均匀性并保留邻近靶体积的关键解剖结构。该假设基于以下事实：对于小的X射线场，治疗体积之外的剂量主要由X射线光子运动的电子范围决定。本工作的目的是：（1）使用失谐医用直线加速器产生中能X射线，（2）表征该射束的能量，（3）测量IEP和小野的放射性半影，以与6 MV X射线或Co-60产生的半影进行比较，以及（4）将这些实验测量与Monte Carlo计算机模拟进行比较。我们的IEP X射线光谱的最大光子能量被测量为1.2 MeV。照射Gafchromic EBT膜（ISP Technologies，韦恩，新泽西州），并使用具有高空间分辨率的新型数字显微成像系统读取。在相同的照射条件下，对于0.3 x 0.3至4.0 x 4.0 cm 2的射野尺寸，测量的放射性半影宽度（80%-20%距离）在0.3-0.77 mm（1.2 MV）和1.1-2.1 mm（6 MV）之间变化。当比较90%-10%或95%-5%宽度时发现的差异更显着，这实际上在放射治疗中更显着。Monte Carlo模拟与实验结果吻合良好。放射学半暗带的减少对于特定的临床情况可能是实质性的，例如在治疗邻接黄斑的眼部黑素瘤或治疗功能性疾病如三叉神经痛（一种非致死性神经病理学）时，其中治疗不应诱导长期副作用。
Stereotactic radiosurgery is used to treat intracranial lesions with a high degree of accuracy. At the present time, x-ray energies at or above Co-60 gamma rays are used. Previous Monte Carlo simulations have demonstrated that intermediate energy x-ray photons or IEPs (defined to be photons in the energy range of 0.2-1.2 MeV), combined with small field sizes, produce a reduced radiological penumbra leading to a sharper dose gradient, improved dose homogeneity and sparing of critical anatomy adjacent to the target volume. This hypothesis is based on the fact that, for small x-ray fields, a dose outside the treatment volume is dictated mainly by the range of electrons set into motion by x-ray photons. The purpose of this work is: (1) to produce intermediate energy x rays using a detuned medical linear accelerator, (2) to characterize the energy of this beam, (3) to measure the radiological penumbra for IEPs and small fields to compare with that produced by 6 MV x rays or Co-60, and (4) to compare these experimental measurements with Monte Carlo computer simulations. The maximum photon energy of our IEP x-ray spectrum was measured to be 1.2 MeV. Gafchromic EBT films (ISP Technologies, Wayne, NJ) were irradiated and read using a novel digital microscopy imaging system with high spatial resolution. Under identical irradiation conditions the measured radiological penumbra widths (80%-20% distance), for field sizes ranging from 0.3 x 0.3 to 4.0 x 4.0 cm2, varied from 0.3-0.77 mm (1.2 MV) and from 1.1-2.1 mm (6 MV). Even more dramatic were the differences found when comparing the 90%-10% or the 95%-5% widths, which are in fact more significant in radiotherapy. Monte Carlo simulations agreed well with the experimental findings. The reduction in radiological penumbra could be substantial for specific clinical situations such as in the treatment of an ocular melanoma abutting the macula or for the treatment of functional disorders such as trigeminal neuralgia (a nonlethal neurological pathology) where no long-term side effect should be induced by the treatment.