Subacute neuropathological effects of microplanar beams of x-rays from a synchrotron wiggler.

Microplanar beam radiation therapy has been proposed to treat brain tumors by using a series of rapid exposures to an array of parallel x-ray beams, each beam having uniform microscopic thickness and macroscopic breadth (i.e., microplanar). Thirty-six rats were exposed head-on either to an upright 4-mm-high, 20- or 37-microns-wide beam or to a horizontal 7-mm-wide, 42-microns-high beam of mostly 32- to 126-keV, minimally divergent x-rays from the X17 wiggler at the National Synchrotron Light Source at Brookhaven National Laboratory. Parallel slices of the head, separated at either 75 or 200 microns on center, were exposed sequentially at 310-650 grays (Gy) per second until each skin-entrance absorbed dose reached 312, 625, 1250, 2500, 5000, or 10,000 Gy. The rats were euthanized 2 weeks or 1 month later. Two rats with 10,000-Gy-entrance slices developed brain tissue necrosis. All the other 10,000- and 5000-Gy-entrance slices and some of the 2500- and 1250-Gy-entrance slices showed loss of neuronal and astrocytic nuclei and their perikarya. No other kind of brain damage was evident histologically in any rat with entrance absorbed doses < or = 5000 Gy. Brain tissues in and between all the 312- and 625-Gy-entrance slices appeared normal. This unusual resistance to necrosis is central to the rationale of microplanar beam radiation therapy for brain tumors. IMAGES:

微平板束放射治疗（Microplanar beam radiation therapy）已被提出用于脑肿瘤的治疗，其通过一系列快速照射多组平行X射线束实现，每一束射线均具有均匀的微观厚度与宏观宽度（即微平板束）。本研究共纳入36只大鼠，使其头部正对射线接受照射：一组采用垂直取向的4毫米高、20或37微米宽的射线束，另一组采用水平取向的7毫米宽、42微米高的射线束；所用射线均主要为32~126千电子伏特（keV）的微发散X射线，源自布鲁克海文国家实验室（Brookhaven National Laboratory）国家同步辐射光源（National Synchrotron Light Source）的X17波荡器（wiggler）。以中心间距75或200微米的方式依次制备大鼠头部的平行切片，并以每秒310~650戈瑞（Gy）的剂量率进行连续照射，直至每个皮肤入射吸收剂量分别达到312、625、1250、2500、5000或10000戈瑞。分别于照射后2周或1个月对大鼠实施安乐死。其中，接受10000戈瑞入射剂量切片照射的2只大鼠出现了脑组织坏死。其余所有接受10000戈瑞与5000戈瑞入射剂量切片照射的样本，以及部分接受2500戈瑞和1250戈瑞入射剂量切片照射的样本，均出现神经元与星形胶质细胞核及其胞体的缺失。对于入射吸收剂量≤5000戈瑞的所有大鼠，组织学检查均未发现其他类型的脑损伤。所有接受312戈瑞与625戈瑞入射剂量切片照射的样本及其周边脑组织均表现正常。这种独特的抗坏死特性，正是微平板束放射治疗用于脑肿瘤的核心理论依据。图像（IMAGES）：