DOSIMETRY OF BRACHYTHERAPY SOURCES IN MILLIMETER RANGE

描述：(改编自申请人的摘要)：再狭窄是指 冠状动脉成形术的主要局限性。最近，近距离放射治疗已经 作为一种潜在的治疗再狭窄的方法，使用光子发射器 作为192Ir、125I、103Pd和贝塔发射体，如32P、90Sr和90Y。二 正在研究的血管内近距离放射治疗方法有：(I)使用 导管末端的放射源；(Ii)永久性的 在闭塞部位植入放射性支架。第一个是一个 放射源临时腔内近距离放射治疗的例子 被放置在目标病变附近的体腔中；另一个是示例 将放射源植入脑部的永久性近距离放射治疗 目标损伤。众所周知，即刻的剂量梯度 放射源的附近非常高，因为几何形状 和组织衰减效应。传统上，靶子的剂量是 指定与震源的距离为1厘米。在此参考距离处 近距离治疗源的剂量测定已经建立得相当好了。 然而，血管内近距离放射治疗的预期照射靶点 要小得多，在1-3毫米的范围内。在这么短的距离内， 剂量学具有高度的不确定性，需要改进。其中一个主要的 短距离剂量不确定的原因可能是 低能二次辐射，如荧光X射线、β粒子、 二次电子等，主要在源中被吸收 包被或围绕来源的组织的前几毫米。他们的 在传统的近距离放射治疗剂量学中，影响在很大程度上被忽略了，因为 只有一小部分目标体积会受到它们的影响。这是, 然而，对于血管内近距离放射治疗来说并非如此，在这种情况下，整个靶点 可能在震源的几毫米范围内。目前已有多项调查 正在进行中，主要是在商业支持下，以确定 血管内近距离放射治疗，不仅有巨大的需求，而且 规范剂量处方，更重要的是要确定 短距离投放的剂量。这种剂量学很可能是 显著不同取决于特定的放射性核素以及设计 来源和施肥者。在这个项目中，血管内的物理学 将研究治疗再狭窄的近距离放射治疗剂量学 使用热释光剂量计芯片和薄片，放射变色薄膜， 聚合物凝胶剂量计，用于微剂量测量的Rossi型正比室， 和蒙特卡洛模拟。最后，组织异质性和 导管和支架对光子和β光子的自我屏蔽效应 还将对粒子进行调查。

DESCRIPTION: (Adapted from the applicant's abstract): Restenosis is the major limitation of coronary angioplasty. Recently brachytherapy has emerged as a potential treatment for restenosis using photon emitters such as 192Ir, 125I, 103Pd and beta emitters such as 32P, 90Sr, and 90Y. Two approaches under investigation for intravascular brachytherapy are: (i) use of a radioactive source at the end of a catheter, (ii) permanent implantation of a radioactive stent at the occlusion site. The first is an example of temporary intracavitary brachytherapy where radioactive sources are placed in a body cavity near the target lesion; the other is an example of permanent brachytherapy where radioactive sources are implanted in the target lesion. It is well known that dose gradients in the immediate vicinity of the radioactive sources are very high because of the geometric and tissue attenuation effects. Traditionally, the dose to the target is specified at a distance of 1 cm from the source. At this reference distance the dosimetry of brachytherapy sources is reasonably well established. However, the intended target for irradiation in intravascular brachytherapy is much smaller, in the range of 1 - 3 mm. At these short distances, the dosimetry is highly uncertain and needs improvement. One of the major reasons for dose uncertainty at short distances may be the contribution from low energy secondary radiations, such as fluorescent x rays, beta particles, secondary electrons etc., which are primarily absorbed in the source encapsulation or the first few mm of tissue around the source. Their effects are largely ignored in traditional brachytherapy dosimetry because only a small fraction of the target volume is affected by them. This is, however, not true for intravascular brachytherapy where the entire target may be within millimeters of the source. With many investigations currently underway, mostly with commercial support, to determine the efficacy of intravascular brachytherapy, there is a tremendous need to not only standardize the prescription of dose, but importantly to also determine the dose delivered over short distances. This dosimetry may well be significantly different depending on specific radionuclide as well as design of source and applicators. In this project, the physics of intravascular brachytherapy dosimetry for treatment of restenosis will be investigated using thermoluminescent dosimeter chips and sheets, radiochromic film, polymer gel dosimeters, Rossi-type proportional chamber for microdosimetry, and Monte Carlo simulations. Finally, effects of tissue heterogeneity and self-shielding effects of catheters and stents for photons and beta particles will also be investigated.