Tests of a Compton imaging prototype in a monoenergetic 4.44MeV photon field - a benchmark setup for prompt gamma-ray imaging devices
Tests of a Compton imaging prototype in a monoenergetic 4.44MeV photon field - a benchmark setup for prompt gamma-ray imaging devices
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DOI：
10.1088/1748-0221/11/06/p06009
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发表时间：
2016-06-01
影响因子：
1.3
通讯作者：
Kormoll, T.
中科院分区：
文献类型：
--
作者：
Golnik, C.;Bemmerer, D.;Kormoll, T.
质子束在组织中的有限射程为放射治疗中高共形剂量分布的传输开辟了新的前景。然而，实际的粒子范围，因此准确的剂量沉积，对质子路径中的组织成分很敏感。由于对该组织成分或定位误差的有限了解而导致的范围不确定性以安全裕度的形式被考虑。因此，未经验证的粒子范围限制了质子治疗的主要好处。探测瞬发伽马射线是质子-组织相互作用的副产品，目的是在线和非侵入性地监测粒子范围，从而开发质子治疗的潜力。空间瞬发伽马射线发射的康普顿成像是一种很有前途的测量方法。瞬发伽马射线的发射能量为几兆电子伏特。因此，普通放射源不能提供即时伽马射线成像设备必须设计的能量范围。在这项工作中，介绍了一种用于生产本地化单能4.44 MeV伽马射线源的基准测量装置。在HZDR的坦德加速器上，使用了质子俘获共振反应N-15(p，α-伽马4.439)C-12。这种反应提供了与质子治疗中强烈的瞬发伽马射线线相同的核去激发(和伽马射线发射)。对排放产额进行了定量描述。示例性地在设置处测试专用于瞬发伽马射线成像的两级康普顿成像设备。除了成功的成像测试外，该样机在4.44 MeV下的探测效率也是由测量数据得出的。结合这一效率和瞬发伽马射线的发射产额，估计了在治疗方案中实施的原型的有效康普顿事件的数量，该事件由约4.44 MeV的能量区域中的伽马射线引起。因此，探测效率成为快速伽马射线康普顿成像的关键参数，限制了原型在当前实现中的适用性。
The finite range of a proton beam in tissue opens new vistas for the delivery of a highly conformal dose distribution in radiotherapy. However, the actual particle range, and therefore the accurate dose deposition, is sensitive to the tissue composition in the proton path. Range uncertainties, resulting from limited knowledge of this tissue composition or positioning errors, are accounted for in the form of safety margins. Thus, the unverified particle range constrains the principle benefit of proton therapy. Detecting prompt gamma-rays, a side product of proton-tissue interaction, aims at an on-line and non-invasive monitoring of the particle range, and therefore towards exploiting the potential of proton therapy. Compton imaging of the spatial prompt gamma-ray emission is a promising measurement approach. Prompt gamma-rays exhibit emission energies of several MeV. Hence, common radioactive sources cannot provide the energy range a prompt gamma-ray imaging device must be designed for. In this work a benchmark measurement- setup for the production of a localized, monoenergetic 4.44 MeV gamma-ray source is introduced. At the Tandetron accelerator at the HZDR, the proton-capture resonance reaction N-15(p, alpha gamma 4.439)C-12 is utilized. This reaction provides the same nuclear de-excitation (and gamma-ray emission) occurrent as an intense prompt gamma-ray line in proton therapy. The emission yield is quantitatively described. A two-stage Compton imaging device, dedicated for prompt gamma-ray imaging, is tested at the setup exemplarily. Besides successful imaging tests, the detection efficiency of the prototype at 4.44 MeV is derived from the measured data. Combining this efficiency with the emission yield for prompt gamma-rays, the number of valid Compton events, induced by gamma-rays in the energy region around 4.44 MeV, is estimated for the prototype being implemented in a therapeutic treatment scenario. As a consequence, the detection efficiency turns out to be a key parameter for prompt gamma-ray Compton imaging limiting the applicability of the prototype in its current realization.