AMERICIUM-241 SOURCES FOR INTRACAVITARY IRRADIATION

密封的镅-241源主要发射60 keV的光子， 多康普顿散射的产生在水中的剂量分布， 与Ra-226或Cs-137相当。 然而，镅伽马射线 可以被高原子序数材料的薄层屏蔽， 半值层的厚度只有1/8毫米的铅的镅 与Ra-226伽马射线的12 mm值相比， 这 允许对关键器官的有效体内屏蔽，例如， 膀胱可以部分地被Hypaque溶液屏蔽，直肠和 乙状结肠造影。 此外，接触医疗 参与腔内应用和患者护理的人员可以 通过使用相对较薄的铅围裙和 重量便携式护盾 该项目旨在继续对 镅来源的可行性和发展。 剂量测量 妇科菌斑涂敷器的原型证实了 在水中的分布与镭或铯产生的分布非常相似 可以获得涂抹器，并且可以获得高效的屏蔽， 通过少量的高原子序数材料来实现。 在这 项目，我们建议设计和制造一个临床妇科串联 和牙菌斑涂药器，以对其进行剂量测定 应用程序，开发计算机化治疗计划的方法， 有和没有屏蔽的应用，并开发和测试探头， 体内剂量测定。 根据这些物理学研究，我们建议 第一代镅敷贴器临床应用 用于治疗妇科恶性肿瘤，最初实施阶段 晚期复发性宫颈癌患者的I-II试验 子宫颈癌、术后子宫内膜癌等。 根据剂量分布和临床经验， 第一代镅施放器，第二代镅施放器将 设计和制造用于进行II-III期临床研究， 早期和中期宫颈癌和子宫内膜癌。

Sealed sources of americium-241 emit primarily 60 keV photons which because of multiple Compton scattering produce dose distributions in water that are comparable to those from Ra-226 or Cs-137. However, americium gamma rays can be shielded by thin layers of high atomic number materials since the half value layer thickness is only 1/8th of a mm of lead for americium gamma rays as compared to a value of 12 mm for Ra-226 gamma rays. This allows effective in-vivo shielding of critical organs, for example, the bladder can be partially shielded by hypaque solution, and the rectum and sigmoid colon by barium sulfate. In addition, the exposure to medical personnel involved in intracavitary application and patient care can be reduced substantially by the use of relatively thin lead aprons and light weight, portable shields. This project seeks to continue an on-going investigation into the feasibility and development of americium sources. Dosimetry measurements around a prototype gynecological plaque applicator confirm that the dose distributions in water very similar to those produced by radium or cesium applicators can be obtained, and that highly effective shielding can be achieved by small amounts of high atomic number materials. In this project, we propose to design and fabricate a clinical gynecological tandem and plaque applicator, to perform dosimetry measurements on this applicator, to develop methods for computerized treatment planning for applications with and without shields, and to develop and test a probe for in-vivo dosimetry. Following these physics studies, we propose to introduce a first-generation americium applicator into clinical practice for treatment of gynecological malignancies, initially carrying out Phase I-II trials in patients with recurrent carcinoma of the cervix, late stage carcinoma of the cervix, post surgical carcinoma of the endometrium, etc. Based on the dose distributions and clinical experience with the first-generation applicator, a second-generation americium applicator will be designed and fabricated to carry out Phase II-III clinical studies on early and intermediate stage carcinoma of the cervix and endometrium.