Steenbakkers R J, Altschuler M D, D' Angio G J, Goldwein J W, Kassaee A
State University of Groningen, The Netherlands.
Int J Radiat Oncol Biol Phys. 1997 Oct 1;39(3):589-94. doi: 10.1016/s0360-3016(97)00370-2.
The ideal lens-sparing radiotherapy technique for retinoblastoma calls for 100% dose to the entire retina including the ora serrata and zero dose to the lens. Published techniques, most of which use photons, have not accomplished this ideal treatment. We describe here a technique that approaches this ideal configuration using electron beam therapy.
Dose-modeling calculations were made using a computer program built around a proprietary algorithm. This program calculates 3D dose distribution for electrons and photons and uses the Cimmino feasibility method for the inverse problem of beam weighting to achieve the prescribed dose. The algorithm has been verified in the ocular region by measurements in a RANDO phantom. To search for an ideal lens-sparing beam setup, a stylized phantom of an 8-month-old infant was generated with built-in inhomogeneities, and a phantom of a 5-year-old child was generated from a patient CT series.
Of more than 100 different beam setups tested, two 9 MeV electron beams at gantry angles plus and minus 26 degrees from the optic nerve axis achieved the best distribution. Both fields have a lens block and an isocenter between the globe and origin of the optic nerve. When equal doses are given to both fields, the entire extent of the retina (including ora serrata) received 100%, while the lens received 10% or less.
The two-oblique-electron-beam technique here described appears to meet most of the stringent dosimetry needed to treat retinoblastoma. It is suitable for a range of ages, from infancy to early childhood years.
视网膜母细胞瘤理想的保留晶状体放疗技术要求对包括锯齿缘在内的整个视网膜给予100%剂量，而对晶状体给予零剂量。已发表的技术大多使用光子，尚未实现这种理想的治疗效果。我们在此描述一种使用电子束疗法接近这种理想配置的技术。
使用围绕专有算法构建的计算机程序进行剂量建模计算。该程序计算电子和光子的三维剂量分布，并使用西明诺可行性方法解决束流加权的逆问题，以实现规定剂量。该算法已通过在RANDO体模中的测量在眼部区域得到验证。为了寻找理想的保留晶状体束流设置，生成了一个具有内置不均匀性的8个月大婴儿的简化体模，以及一个从患者CT系列生成的5岁儿童体模。
在测试的100多种不同束流设置中，两个9兆电子伏的电子束，在与视神经轴成正负26度的机架角度下，实现了最佳分布。两个射野都有一个晶状体挡块，等中心位于眼球和视神经起始点之间。当两个射野给予相等剂量时，整个视网膜范围（包括锯齿缘）接受100%剂量，而晶状体接受10%或更少剂量。
本文所述的双斜电子束技术似乎满足治疗视网膜母细胞瘤所需的大多数严格剂量学要求。它适用于从婴儿期到幼儿期的一系列年龄段。
