School of Medicine, Klinikum rechts der Isar, Department of Radiation Oncology, Technical University of Munich, Munich, Germany; Institute for Radiation Medicine, Helmholtz Centre Munich, Munich, Germany; Physics Department, Technical University of Munich, Garching, Germany.
School of Medicine, Klinikum rechts der Isar, Department of Radiation Oncology, Technical University of Munich, Munich, Germany; Institute for Radiation Medicine, Helmholtz Centre Munich, Munich, Germany.
Int J Radiat Oncol Biol Phys. 2021 Feb 1;109(2):626-636. doi: 10.1016/j.ijrobp.2020.09.039. Epub 2020 Oct 7.
Microbeam radiation therapy is a preclinical concept in radiation oncology. It spares normal tissue more effectively than conventional radiation therapy at equal tumor control. The radiation field consists of peak regions with doses of several hundred gray, whereas doses between the peaks (valleys) are below the tissue tolerance level. Widths and distances of the beams are in the submillimeter range for microbeam radiation therapy. A similar alternative concept with beam widths and distances in the millimeter range is presented by minibeam radiation therapy. Although both methods were developed at large synchrotron facilities, compact alternative sources have been proposed recently.
A small-animal irradiator was fitted with a special 3-layered collimator that is used for preclinical research and produces microbeams of flexible width of up to 100 μm. Film dosimetry provided measurements of the dose distributions and was compared with Monte Carlo dose predictions. Moreover, the micronucleus assay in Chinese hamster CHO-K1 cells was used as a biological dosimeter. The focal spot size and beam emission angle of the x-ray tube were modified to optimize peak dose rate, peak-to-valley dose ratio (PVDR), beam shape, and field homogeneity. An equivalent collimator with slit widths of up to 500 μm produced minibeams and allowed for comparison of microbeam and minibeam field characteristics.
The setup achieved peak entrance dose rates of 8 Gy/min and PVDRs >30 for microbeams. Agreement between Monte Carlo simulations and film dosimetry is generally better for larger beam widths; qualitative measurements validated Monte Carlo predicted results. A smaller focal spot enhances PVDRs and reduces beam penumbras but substantially reduces the dose rate. A reduction of the beam emission angle improves the PVDR, beam penumbras, and dose rate without impairing field homogeneity. Minibeams showed similar field characteristics compared with microbeams at the same ratio of beam width and distance but had better agreement with simulations.
The developed setup is already in use for in vitro experiments and soon for in vivo irradiations. Deviations between Monte Carlo simulations and film dosimetry are attributed to scattering at the collimator surface and manufacturing inaccuracies and are a matter of ongoing research.
微束放射治疗是放射肿瘤学中的一种临床前概念。与传统放射治疗相比，它在同等肿瘤控制效果下能更有效地保护正常组织。放射场由数百格雷的峰值区域组成，而峰间（低谷）的剂量低于组织耐受水平。微束放射治疗的光束宽度和距离在亚毫米范围内。毫米范围内的类似替代概念是微束放射治疗。尽管这两种方法都是在大型同步加速器设施中开发的，但最近已经提出了紧凑型替代源。
一台小型动物辐照仪配备了特殊的 3 层准直器，用于临床前研究，可产生灵活宽度达 100μm 的微束。胶片剂量测定法提供了剂量分布的测量结果，并与蒙特卡罗剂量预测进行了比较。此外，还使用中国仓鼠 CHO-K1 细胞的微核测定作为生物剂量计。修改了 X 射线管的焦点尺寸和射束发射角度，以优化峰值剂量率、峰谷剂量比（PVDR）、射束形状和场均匀性。配备最大 500μm 狭缝宽度的等效准直器可产生微束，并允许比较微束和微束场特性。
该装置实现了 8Gy/min 的峰值入口剂量率和>30 的 PVDR 用于微束。对于较大的光束宽度，蒙特卡罗模拟和胶片剂量测定的一致性通常更好；定性测量验证了蒙特卡罗预测结果。较小的焦点尺寸提高了 PVDR，并减少了射束半影，但大大降低了剂量率。减少射束发射角度可改善 PVDR、射束半影和剂量率，而不会影响场均匀性。与微束相比，在相同的光束宽度和距离比下，微束显示出相似的场特性，但与模拟结果的一致性更好。
所开发的装置已投入使用进行体外实验，不久将用于体内照射。蒙特卡罗模拟和胶片剂量测定之间的偏差归因于准直器表面的散射和制造不准确，这是正在进行的研究的一个课题。
