Development of micro-collimators for highly precise irradiation of ophthalmic tumours with I-125 brachytherapy eye applicators

眼部肿瘤放射治疗的目的是完全控制肿瘤，并尽可能最大限度地保护眼睛功能。目标体积以外的所有区域都必须幸免于难，特别是视神经、血管和睫状体等有风险的结构。由于这些结构通常位于距离目标体积几毫米的范围内，甚至邻近目标体积，这些区域之间的大剂量梯度对于成功的治疗是必不可少的。使用低能量光子发射器I-125和测试型发射器Ru-106的传统眼斑的场梯度和几何形状只能以有限的方式满足这些要求。因此，人们经常试图通过昂贵的质子放射治疗来获得更好的眼睛功能结果。为了克服眼科近距离放射治疗的这一重大缺点，我们开发了由金属和塑料薄片组成的微型准直器的新概念，用于I-125种子。由于它们的体积很小，它们可以被插入到典型的眼斑中。尽管结构非常简单，但正如原型的测量所显示的那样，微型准直器发出的辐射具有精确定义的方向和角度。在0.5毫米范围内，横向场边界的剂量梯度可以达到一个数量级以上--这个值甚至超过了昂贵的质子束。因此，可以更有效地保护处于危险中的结构。因此，微准直器提供了一种高精度的适形近距离放射治疗，可以根据患者的情况进行调整。为了确定应用范围，并为临床常规使用该技术做准备，仍有必要进行广泛的基础研究。必须研究微准直器的结构参数对其剂量分布的影响，以及使用几个准直器的斑块及其所产生的辐射场的优化。对于这项研究，必须使用最近开发的微型塑料闪烁体进行数值模拟和高精度剂量测量。还必须开发一种足够准确和可重复的方法来建造微型准直器和敷贴器，并为手术室的眼科医生提供集成的定位工具，以及制定有效的治疗计划的方法。拟议的研究项目的目标是立即将微准直器应用于眼部肿瘤的放射治疗。因此，与目前使用的技术相比，旨在通过减少副作用来从根本上改善患者的生活质量。

The aim of radiation therapy of ocular tumours is a complete tumour control combined with the best possible conservation of the eye functionality. All regions outside of the target volume have to be spared, especially structures at risk such as the optic nerve, blood vessels and the ciliary body. Since these structures are often located within a few millimetres from the target volume, or even adjacent to it, large dose gradients between these regions are essential for a successful therapy. Field gradients and geometry of conventional eye plaques with the low-energy photon emitter I-125 and the beta emitter Ru-106 fit these requirements only in a limited way. Thus, it is often tried to get better functional results of the eye by an expensive proton radiation therapy. To overcome this substantial disadvantage of ophthalmic brachytherapy we developed the novel concept of micro collimators consisting of metal- and plastic sheets, for usage with I-125 seeds. Due to their small size they could be inserted into typical eye plaques. In spite of their quite simple structure, micro collimators emit the radiation with exactly defined direction and angle, as measurements of prototypes showed. The dose gradient at the lateral field boundaries can reach more than one order of magnitude within 0.5 mm - a value even surpassing that of expensive proton beams. Thus, a more effective sparing of structures at risk can be reached. Hence, micro collimators offer the possibility of a highly precise conformal brachytherapy that can be adjusted to the situation of the individual patient. In order to determine the range of application and to prepare the technique for a usage in the clinical routine, extensive basic investigations are still necessary. The influence of constructive parameters of the micro collimators on their dose distribution and the optimisation of plaques with several collimators and their resulting radiation field have to be investigated. For this research, numerical simulations and highly precise dosimetric measurements with recently developed miniature plastic scintillators are mandatory. A sufficiently exact and reproducible way of the construction of micro collimators and applicators, with integrated positioning tools for the ophthalmologist in the operational theatre, and approaches for an effective therapy planning have to be developed, as well. The objective of the proposed research project is the immediate implementation of micro collimators into the radiation therapy of ocular tumours. An essential improvement of the patient's life quality by reduction of side effects is thereby intended, compared to the techniques used so far.