AMERICIUM-241 SOURCES FOR INTRACAVITARY IRRADIATION

Am-241的密封源主要发射60keV光子，这是因为 在水中产生的剂量分布是 可与Ra-226或Cs-137的化合物相媲美。然而，Am伽马射线 可以被薄层的高原子序数材料屏蔽，因为 对于Am来说，半值层厚度只有1/8毫米的铅 伽马射线，而Ra-226伽马射线的值为12毫米。这 允许对关键器官进行有效的体内屏蔽，例如 膀胱可被菌丝素溶液部分屏蔽，直肠和 乙状结肠用硫酸巴比妥钠。此外，接触到的医疗保健 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质围裙和灯光大大减少 重量轻，携带防护罩。 这项计划旨在继续对 碲源的可行性和发展前景。剂量学测量 围绕着一个妇科斑块涂抹器原型确认了剂量 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，并且可以获得高效屏蔽 由少量的高原子序数材料实现。在这 项目，我们建议设计和制造一个临床妇科串联 和斑块涂布器，对此进行剂量测量 开发计算机化治疗计划的方法 有屏蔽和无屏蔽的应用，并开发和测试探头 体内剂量学。在完成这些物理研究后，我们建议 将第一代Am敷贴器引入临床 针对妇科恶性肿瘤的治疗，初步开展阶段 晚期宫颈癌复发患者的I-II试验 宫颈癌、术后子宫内膜癌等。 根据剂量分布和临床经验 第一代敷贴器，第二代Am敷贴器将 被设计和制造以进行II-III期临床研究 早、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.