Guo W Y
Department of Neuroradiology, Karolinska Institute, Stockholm, Sweden.
Acta Radiol Suppl. 1993;388:1-34.
The aims of the thesis were to investigate stereotaxic procedures in radiosurgery for cerebral arteriovenous malformations (AVMs) and radiation effects of single session high-dose irradiation delivered by gamma knife on the human brain. Investigation of gamma knife radiosurgery in 1,464 patients constitutes the data base of this thesis. High quality stereotaxic angiography is the gold standard targeting imaging in radiosurgery for cerebral AVMs, particularly for small AVMs or residual AVMs after other treatments. For medium and large size AVMs, stereotaxic MR techniques can improve targeting precision and decrease irradiation volume as compared to stereotaxic angiography in selected cases provided that proper pulse sequences are used. Combined treatments, where embolization precedes radiosurgery, can improve amenability of the treatment for large AVMs. This is on condition that the partially embolized nidi are well delineated and the volume of the residual nidi has been decreased to a level where an optimum irradiation can be safely prescribed. Radiologically, adverse radiation effects (ARE) of gamma knife radiosurgery for cerebral AVMs are observed in 16% (131/816) of the patients. The ARE are observed as a focal low attenuation on CT or as a focal high signal on MR image without enhancement in 47% (61/131), and as a peripheral or homogeneous enhancing lesion in 48% (63/131). MR imaging is more sensitive than CT in detecting the ARE. 91% of the ARE are observed within 18 months after radiosurgery and 89% are seen to regress within 18 months. Clinically, symptomatic ARE are only observed in 6% (51/816) and only in half of them, i.e. 3%, are the symptoms permanent. The risk of ARE in radiosurgery for venous angiomas is higher as compared to AVMs. Other mechanisms have probably been employed. In gamma capsulotomy, the necrotic lesions and reaction volumes created by using multiple isocentres of 4 mm collimators are less predictable as compared to that by single isocentre. Volume effects and depreciation of the steep isodose gradient are hypothesised as the leading factors of the inconsistency. Based on the in vivo assessment of the radiation effects observed on the basically normal human brain it is concluded that irradiation volume is strongly related to the radiation effects and is one of the important considerations in decision making for radiosurgery. Volume of brain tissue exposed to irradiation could be minimised and precision of targeting could be maximised provided that a proper stereotaxic imaging is used.(ABSTRACT TRUNCATED AT 400 WORDS)
本论文的目的是研究脑动静脉畸形（AVM）放射外科中的立体定向程序，以及伽马刀单次大剂量照射对人脑的辐射效应。对1464例患者进行伽马刀放射外科治疗的研究构成了本论文的数据库。高质量的立体定向血管造影是脑AVM放射外科治疗中靶区成像的金标准，尤其适用于小型AVM或其他治疗后的残留AVM。对于中大型AVM，在使用适当脉冲序列的情况下，与立体定向血管造影相比，立体定向磁共振技术在某些病例中可提高靶区定位精度并减少照射体积。先行栓塞再进行放射外科的联合治疗可提高大型AVM的治疗顺应性。前提是部分栓塞的病灶巢要清晰界定，且残留病灶巢的体积已减小到可安全给予最佳照射剂量的水平。在放射学上，脑AVM伽马刀放射外科治疗的不良辐射效应（ARE）在16%（131/816）的患者中被观察到。47%（61/131）的ARE表现为CT上的局灶性低密度影或磁共振图像上无强化的局灶性高信号，48%（63/131）表现为周边或均匀强化的病灶。磁共振成像在检测ARE方面比CT更敏感。91%的ARE在放射外科治疗后18个月内被观察到，89%在18个月内消退。临床上，有症状的ARE仅在6%（51/816）的患者中被观察到，且其中只有一半（即3%）的症状是永久性的。与AVM相比，静脉瘤放射外科治疗中ARE的风险更高。可能还涉及其他机制。在伽马刀内囊切开术中，与单等中心相比，使用4毫米准直器的多个等中心产生的坏死病灶和反应体积更难以预测。体积效应和陡峭剂量梯度的衰减被认为是不一致的主要因素。基于对基本正常的人脑观察到的辐射效应的体内评估，得出结论：照射体积与辐射效应密切相关，是放射外科决策中的重要考虑因素之一。如果使用适当的立体定向成像，可将受照射的脑组织体积最小化，并将靶区定位精度最大化。（摘要截断于400字）
