基于DAO算法的重离子放射治疗技术的相关研究

发布时间：2018-04-28 08:39

本文选题：重离子治疗 + 调强放疗　；参考：《中国科学院大学(中国科学院近代物理研究所)》2017年硕士论文

【摘要】：重离子束(heavy ion beam)相比于放射治疗常用射线(光子)主要有两方面优势:在物理学上重离子具有倒转的深度剂量分布,即Bragg曲线,可以通过对束流能量的调节实现对肿瘤靶区高剂量的精确辐照,并且重离子束在穿越人体组织时能量损失小使入射通道上的正常组织受到较少的剂量;在生物学上重离子束在Bragg峰区具有高的传能线密度(linear energy transfer,LET)因而具有高的相对生物学效应(relative biological effectiveness,RBE),而在坪区的LET较低,其生物学效应与常规放疗中的X射线相似,可以保证对肿瘤靶区具有高剂量辐照的同时实现对附近正常组织和危及器官(organ at risk,OAR)的有效保护。因此基于以上两方面优势,重离子束被誉为二十一世纪的最佳放疗用射线。在传统的光子放疗中,基于逆向计划(inverse planning)的调强放疗(Intensity Modulated Radiation Therapy,IMRT)逐渐发展成为一种成熟的治疗技术而被广泛应用于各大放射治疗中心。IMRT通过调节入射束流的强度对靶区进行非均匀照射,不同入射方向的束流叠加最终得到理想的剂量分布,相比于正向计划而言,对肿瘤靶区的辐照强度与对正常组织或危机器官的保护效果都得到了极大的提高。并且随着技术的发展与日益完善,不断有新的调强技术被提出,其中Shepard教授提出的基于模拟退火原理的直接射野孔径优化(direct aperture optimization,DAO)算法可以实现对照射野(beam’s eye view,BEV)方向上多叶光栅(Multileaf Collimator,MLC)叶片位置与孔径权重的同时优化,在优化子野时不再需要预先计算出强度通量图(intensity map),达到通过较少子野数量即可实现高度适形的照射效果。但是在重离子治疗中,真正意义上的调强技术仍未实现,因此为了将常规放疗中的DAO-IMRT技术应用到重离子治疗中来,本论文基于被动式束流配送系统开展了一系列针对改进DAO模型的模拟研究,发展基于DAO原理的重离子放射治疗技术。考虑到光子与重离子束流模型的区别,本论文工作在每个BEV方向上提出纵向分层的概念,并考虑重离子治疗的横向散射因素建立高斯形束流模型,对不同的靶区模型进行模拟优化得到一系列较为理想的优化结果。结果显示重离子治疗中基于DAO原理的剂量优化可以实现使用少量子野达到较高的剂量适形效果,直接得到每个子野的MLC叶片位置与相应的权重。对于标准的凹形靶体(TG119测试模型的简化模型),本论文工作模拟了多个BEV方向束流的叠加照射,结果显示在基于被动式束流配送系统重离子治疗下可以初步实现调强放疗技术。在对展宽布拉格峰(spread-out Bragg peak,SOBP)纵向展宽的研究中,考虑到放射生物学模型中RBE随深度的变化对肿瘤靶区生物有效剂量的影响,在被动式束流配送系统下采用基于不同展宽的微型脊型过滤器(mini ridge filter,mini-RF)的双微小展宽峰(mini-SOBP)组合照射方法针对重离子的分层照射治疗方式进行优化。理论计算显示对于不同初始能量的12C离子束,利用较大和较小两种半高宽(full width at half maximum,FWHM)的mini-SOBP组合叠加,得到了按生物有效剂量和物理吸收剂量均匀两种方式展宽的SOBP,实现了在减少照射分层数缩短治疗时间的同时,减小SOBP远端剂量跌落距离(distal dose fall-off distance,通常为SOBP远端剂量80%-20%之间的纵向距离),使肿瘤靶区后方正常组织或危及器官得到最大程度的保护。
[Abstract]:The heavy ion beam (heavy ion beam) has two main advantages compared with the radiation therapy of radiation (photons). In physics, the heavy ion has a deep dose distribution in reverse, that is, the Bragg curve. The high dose of the tumor target area can be accurately irradiated by the regulation of the beam energy, and the heavy ion beam is energy through the body tissue. The low loss caused the normal tissue on the incident channel to be less dose; the biological heavy ion beam has a high energy transfer line density (linear energy transfer, LET) in the Bragg peak region, thus having a high relative biological effect (relative biological effectiveness, RBE), while the LET of the plateau region is low, and its biological effect and conventional radiotherapy Similar to the X ray, it can ensure the high dose radiation of the tumor target area and the effective protection of the nearby normal tissue and the endanger organ (organ at risk, OAR). Therefore, based on the above two advantages, the heavy ion beam is known as the best radiotherapy line in twenty-first Century. In the traditional photon radiotherapy, the reverse plan (INV) is based on the reverse plan (INV). Erse planning (Intensity Modulated Radiation Therapy, IMRT) has gradually developed into a mature treatment technology and is widely used in large radiation therapy center.IMRT to irradiate the target region by adjusting the intensity of incident beam, and the ideal dose distribution is finally obtained by the superposition of the beam of different incident directions. Compared with the forward plan, the radiation intensity of the tumor target area and the protection effect on the normal tissue or the crisis organ have been greatly improved. And with the development and improvement of the technology, the new technique of intensity modulation has been put forward, in which the direct field aperture optimization based on the simulated annealing principle is proposed by Professor Shepard (direc The T aperture optimization, DAO) algorithm can achieve the simultaneous optimization of the position of the multileaf raster (Multileaf Collimator, MLC) blade and the weight of the aperture in the direction of the contrast field (beam 's eye view, BEV). The intensity flux graph is no longer needed in the optimization of the subfield. However, in heavy ion therapy, the true intensity modulation technology is still not realized, so in order to apply the DAO-IMRT technology in conventional radiotherapy to heavy ion therapy, this paper develops a series of simulated research on the improved DAO model based on the passive beam distribution system, and develops heavy ions based on the principle of DAO. Radiation therapy technology. Considering the difference between photon and heavy ion beam model, this paper proposes the concept of longitudinal stratification in every BEV direction, and considers the Gauss beam model for the transverse scattering factors of heavy ion therapy. A series of more ideal optimization results are obtained by simulating and optimizing the different target area models. The results show that the results show a series of ideal results. The dose optimization based on the DAO principle in the heavy ion therapy can achieve a high dose conformal effect with a small number of subfields, and directly obtain the MLC blade position and the corresponding weight of each subfield. For the standard concave target (the simplified model of the TG119 test model), the work of this paper simulates the superposition of multiple BEV direction beams. The results show that the intensity modulated radiation therapy can be implemented initially under the heavy ion therapy based on the passive beam distribution system. In the study of the longitudinal broadening of the spread-out Bragg peak (peak, SOBP), the effect of RBE on the biological effective dose of the tumor target area in the radibiologic model is taken into account in the passive beam flow distribution. The double micro broadening peak (mini-SOBP) combined irradiation method based on the mini ridge filter (mini-RF) based on the transmission system is used to optimize the treatment of stratified irradiation of heavy ions. The theoretical calculation shows that the 12C separated beams with different initial energy use two large and smaller half wide width (full width a). The mini-SOBP combination of T half maximum and FWHM is superimposed, and the SOBP is broadened in two ways, namely, the biological effective dose and the physical absorption dose. It reduces the distance of the SOBP distal dose drop distance (distal dose fall-off distance, usually between the distal SOBP dosages) while reducing the treatment time for reducing the number of radiation stratification. To the distance, the normal tissue or organ endangering the tumor target area can be protected to the greatest extent.

【学位授予单位】：中国科学院大学(中国科学院近代物理研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：R730.55;TP18

【参考文献】