Ertl A, Zehetmayer M, Schöggl A, Kindl P, Hartl R
Department of Neurosurgery, University of Vienna, Austria.
Phys Med Biol. 1997 Nov;42(11):2137-45. doi: 10.1088/0031-9155/42/11/009.
Between March 1993 and January 1997, stereotactic radiation techniques were used to irradiate 66 intraocular tumour patients with the Gamma Knife (Leksell Gamma Knife, model B unit) at the University of Vienna, Austria. This study investigates the dosimetry for stereotactic irradiation of ocular structures. For the dosimetry program KULA 4.4, Gamma Knife stereotactic irradiation of the eye represents an extreme frontal skull position. In addition, irradiation of the eye may be performed in the usual supine position in exceptional cases only. With the patient in the prone position, the dose planning program has to calculate with a significantly large number of single-beam extrapolations. In our first experiment we measured the isocentre dose for eight different gamma-angle positions, both in prone and supine positions, using TLD measurements in an Alderson head phantom. We found a maximum deviation of +/- 1.6% using these individually calibrated TLDs. In the second experiment we examined the dose cross profiles for the two most frequently used treatment positions (supine position, gamma = 65 degrees, and prone position, gamma = 140 degrees). For this purpose we implanted a specially designed TLD array into the orbit of a human cadaver head. We found excellent agreement of the dose values measured for the isocentre as well as the posterior part of the eye with orbit with deviations of less than -2.7%. However, for the anterior part of the eye, deviations between computer-generated calculations and the TLD measurements were found to range up to -30%. These differences were noticed both for supine and prone positions. For the Gamma Knife stereotactic irradiation of ocular tumours or pathologies, precautions should be taken to avoid significant underdosage in the anterior part of the radiation field.
1993年3月至1997年1月期间，奥地利维也纳大学使用立体定向放射技术，用伽玛刀（Leksell伽玛刀，B型单元）对66例眼内肿瘤患者进行了照射。本研究调查了眼部结构立体定向照射的剂量学。对于剂量学程序KULA 4.4，伽玛刀对眼睛的立体定向照射代表了一种极端的额部颅骨位置。此外，仅在特殊情况下才可以在通常的仰卧位进行眼部照射。患者处于俯卧位时，剂量规划程序必须进行大量的单束外推计算。在我们的第一个实验中，我们在Alderson头部模型中使用热释光剂量测量法，测量了俯卧位和仰卧位八个不同伽马角位置的等中心剂量。使用这些单独校准的热释光剂量计，我们发现最大偏差为±1.6%。在第二个实验中，我们检查了两个最常用治疗位置（仰卧位，伽马 = 65度；俯卧位，伽马 = 140度）的剂量交叉剖面。为此，我们在一具人类尸体头部的眼眶内植入了一个专门设计的热释光剂量计阵列。我们发现等中心以及眼眶与眼球后部的测量剂量值吻合良好，偏差小于-2.7%。然而，对于眼球前部，计算机生成的计算值与热释光剂量测量值之间的偏差高达-30%。仰卧位和俯卧位均出现了这些差异。对于伽玛刀立体定向照射眼内肿瘤或病变，应采取预防措施，以避免辐射野前部出现明显的剂量不足。
