James C. H. Chu, PhD
Rush University Medical Center
Chicago, IL 60612
Total body irradiation is often used to eradicate diseased bone marrow and leukemic cells and/or to provide immunosuppression for patients receiving bone marrow transplant. The treatment can be delivered with a variety of techniques using megavoltage photon beams. The need to achieve a uniform dose distribution over a very large treatment volume while maintaining low doses to the critical organs presents a difficult challenge to a medical physicist. In addition, a physicist should be prepared to deal with many other technical issues. For example, the radiation beams are usually projected over a large distance to encompass the entire patient during TBI. However, this treatment geometry may not be possible for facilities with only small treatment rooms. Other medical physics issues related to TBI include, among others, the need of a large phantom for beam data acquisition, the validity of inverse square fall off over a large distance, the effect of scatter when the patient is positioned close to the wall, the dose to marrow when the bone is relatively superficial, the establishment of a dose prescription system, the use of in vivo dosimetry, the use of beam spoiler and bolus, and the shielding of lungs and kidneys.
TB19-全身照射
James C. H. Chu, PhD
Rush University Medical Center
Chicago, IL 60612
全身照射常用于根治病变骨髓和白血病细胞，对接受骨髓移植的患者进行免疫抑制。治疗采用高能（兆伏）光子照射技术，要在全身获得均匀剂量分布同时使重要器官的剂量低，这是物理师需要解决的难题。此外物理师还要处理其它的技术问题，例如，在治疗时，射野要照射整个身体，源到患者的距离要延长，然而小的治疗室可能不具备这样的几何条件。全身治疗还需要考虑一些其它物理问题，包括采集射野数据需要大的模体；需要确认距离平方反比定律在长距离时是否有效；当患者接近墙壁时，散射线对剂量的影响；浅部骨骼的骨髓剂量；剂量处方系统的建立；活体剂量测量；使用射野均整滤过(spoiler)、组织补偿材料，以及肺和肾的屏蔽。