Harnett A N, Hirst A, Plowman P N
Department of Radiotherapy, St. Bartholomew's Hospital, West Smithfield, London, U.K.
Radiother Oncol. 1987 Nov;10(3):195-202. doi: 10.1016/s0167-8140(87)80005-1.
The dose to the ocular lens during standard cranial irradiation prophylaxis in childhood acute lymphoblastic leukaemia (ALL) has been studied both in patients and in an anthropomorphic phantom. Doses to the lens depend on patient set-up and in order that this is minimised, a simple immobilisation technique is recommended. Surface thermoluminescent dosimeter (TLD) measurements seriously underestimate the dose received by the ocular lens. Previous measurements made in a phantom have used a large volume ionisation chamber and therefore the minimum cataractogenic dose of 400 cGy for a fractionated treatment is an underestimate. The exact position of the anterior orbital field margin and thus its distance behind the surface of the eye is also important as regards lens dose. Data from the phantom demonstrate accurately the dose gradient through the eye during standard cranial prophylaxis and may explain the lower incidence of leukaemic relapse in the posterior segment of the eye, and yet explain the persistence of isolated anterior chamber relapses.
在儿童急性淋巴细胞白血病（ALL）的标准颅脑照射预防期间，已对患者和人体模型的晶状体剂量进行了研究。晶状体的剂量取决于患者的摆位，为了将其降至最低，建议采用一种简单的固定技术。表面热释光剂量计（TLD）测量严重低估了晶状体所接受的剂量。先前在模型中进行的测量使用了大体积电离室，因此对于分次治疗，400 cGy的最小致白内障剂量被低估了。前眼眶野边缘的精确位置以及因此其在眼球表面后方的距离对于晶状体剂量也很重要。来自模型的数据准确地显示了标准颅脑预防期间通过眼睛的剂量梯度，这可能解释了眼后段白血病复发率较低的原因，但也解释了孤立性前房复发的持续存在。
