Radiotherapy in the presence of contrast agents: a general figure of merit and its application to gold nanoparticles
Radiotherapy in the presence of contrast agents: a general figure of merit and its application to gold nanoparticles
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DOI：
10.1088/0031-9155/53/20/005
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发表时间：
2008-10-21
影响因子：
3.5
通讯作者：
Currell, Fred
中科院分区：
文献类型：
--
作者：
McMahon, Stephen J.;Mendenhall, Marcus H.;Currell, Fred
在保护周围组织的同时向肿瘤输送足够的剂量是放射治疗的主要挑战之一，在常规实践中，这通常是通过使用高穿透性的兆伏级（MV）光子束并对剂量进行空间塑形来实现的。然而，最近人们对使用高原子序数造影剂结合千伏级（kV）X射线来增加肿瘤内沉积剂量的可能性兴趣渐增，因为在这种能量下，重元素的高光电截面会使吸收显著增加。不幸的是，此类造影剂的引入使不同放射源类型治疗效果的比较变得极为复杂，因为现在沉积的剂量在很大程度上取决于射线谱的确切组成，这使得诸如射束品质等传统指标的价值降低。为了解决这一问题，有人提出了一个“品质因数”，它得出一个数值，能够直接比较患者体内不同深度肿瘤的不同放射源类型。通过分析方法以及数值模型，针对一个15 MV直线加速器源和两个150 kVp源（两者都使用钨靶，一个采用常规的铝过滤，另一个使用更强效的钍过滤器）对该品质因数进行了评估，同时考虑了使用具有实际浓度和摄取率的金纳米粒子造影剂（“肿瘤”体积内浓度为10 mg/ml，摄取率为10∶1）处理过的组织。最后，考虑了一个使用类似造影剂的人体颈部体模测试案例，将抽象的品质因数与更接近实际的治疗情况进行比较。在计算品质因数的不同方法之间，以及品质因数与更接近实际患者情况的有效性之间，都发现了良好的一致性。综合来看，这些观察结果表明，仅从剂量学考虑，造影剂增强的千伏级辐射有可能成为多种肿瘤的一种有用的治疗工具，并且它们表明在这一领域需要进一步研究。
Delivering sufficient dose to tumours while sparing surrounding tissue is one of the primary challenges of radiotherapy, and in common practice this is typically achieved by using highly penetrating MV photon beams and spatially shaping dose. However, there has been a recent increase in interest in the possibility of using contrast agents with high atomic number to enhance the dose deposited in tumours when used in conjunction with kV x-rays, which see a significant increase in absorption due to the heavy element's high-photoelectric cross-section at such energies. Unfortunately, the introduction of such contrast agents significantly complicates the comparison of different source types for treatment efficacy, as the dose deposited now depends very strongly on the exact composition of the spectrum, making traditional metrics such as beam quality less valuable. To address this, a 'figure of merit' is proposed, which yields a value which enables the direct comparison of different source types for tumours at different depths inside a patient. This figure of merit is evaluated for a 15 MV LINAC source and two 150 kVp sources (both of which make use of a tungsten target, one with conventional aluminium filtration, while the other uses a more aggressive thorium filter) through analytical methods as well as numerical models, considering tissue treated with a realistic concentration and uptake ratio of gold nanoparticle contrast agents (10 mg ml(-1) concentration in 'tumour' volume, 10: 1 uptake ratio). Finally, a test case of human neck phantom is considered with a similar contrast agent to compare the abstract figure to a more realistic treatment situation. Good agreement was found both between the different approaches to calculate the figure of merit, and between the figure of merit and the effectiveness in a more realistic patient scenario. Together, these observations suggest that there is the potential for contrast-enhanced kilovoltage radiation to be a useful therapeutic tool for a number of classes of tumour on dosimetric considerations alone, and they point to the need for further research in this area.