灵活调控笔形束参数的点扫描照射新方法研究

发布时间：2018-05-08 16:17

本文选题：重离子治癌 + 点扫描　；参考：《中国科学院大学(中国科学院近代物理研究所)》2016年博士论文

【摘要】：相比于传统光子放疗,重离子束放射治疗具有物理学和生物学两方面的优势:一是重离子束具有独特的倒转深度剂量分布(Bragg峰);二是传能线密度(linear energy transfer,LET)和相对生物学效应(relative biological effectiveness,RBE)在Bragg峰区较高,在坪区LET较小。因此重离子束在杀死肿瘤细胞的同时保护了正常组织细胞,达到精准放疗。目前运用于重离子放射治疗的束流配送系统有被动式束流配送方式和主动式束流配送方式两种。基于主动式束流配送方式有栅扫描和点扫描照射方法。点扫描照射方法中,采用横向和纵向尺寸比较宽的笔形束不利于肿瘤靶区的三维适形,而采用横向和纵向尺寸比较窄的笔形束会大大增加扫描点数目,延长剂量优化时间,并且对照射参数控制精度的要求较高。为解决以上矛盾,本文提出了在横向和纵向上采用两种尺寸笔形束的组合式点扫描照射方法:利用横向尺寸(束斑FWHM、sigma)较小、纵向尺寸(初级SOBP的FWHM)较窄的碳离子笔形束对肿瘤靶区边缘进行照射,利用横向尺寸(束斑FWHM、sigma)较大、纵向尺寸(初级SOBP的FWHM)较宽的碳离子笔形束对肿瘤靶区边缘进行照射。便于该照射方法中两种尺寸碳离子笔形束的灵活切换,本文还提出了沿束流配送方向倾斜微型脊形过滤器来调节笔形束纵向尺寸和插入不同厚度散射体改变笔形束横向尺寸的方法。基于HIRFL装置CSR深部肿瘤治疗终端的主动式点扫描束流配送系统,利用蒙特卡罗模拟工具SHIELDHIT-HIT12A模拟研究发现:束流配送距离越短,束斑FWHM越小,但剂量均匀性越差;微型脊形过滤器结构周期是影响剂量均匀性的关键因素,周期越小,剂量平坦度越好。因此,在HIRFL装置重离子治疗终端将真空窗设置在距等中心距离小于125cm、采用结构周期为2mm微型脊形过滤器时,碳离子笔形束的束斑FWHM和靶区的剂量均匀性可以满足放射治疗的临床要求。在优化后的重离子主动式点扫描束流配送系统下,本文建立了点扫描照射方法的碳离子笔形束数据库。通过蒙特卡罗工具SHIELDHIT12A模拟和MATLAB拟合等获得了碳离子笔形束射程-能量关系、物理吸收剂量随深度的分布和束斑sigma随深度的分布。根据LQ模型,利用剂量平均LET和LET对α、β的依赖关系计算了HSG细胞存活率为0.1时碳离子笔形束的相对生物学效应。通过碳离子笔形束物理吸收剂量随深度的分布和相对生物学效应最终计算出碳离子笔形束生物有效剂量随深度的分布。倾斜微型脊形过滤器30度,45度和60度可分别将初级SOBP宽度展宽到原来的约1.16倍,1.42倍和2倍,达到灵活调节碳离子笔形束的纵向尺寸的效果。在束流配送系统的真空窗下游插入0.15mm~0.4mm不同厚度Ta散射体可以将180MeV/u~360MeV/u能量碳离子束束斑sigma从3mm放大到5mm,有效调节碳离子笔形束的横向尺寸(束斑FWHM、sigma)。倾斜微型脊形过滤器和插入不同厚度Ta散射体的的操作可以在加速器改变束流能量时执行,因此这种笔形束参数的被动式调节方法不会额外增加放射治疗时间。本论文通过蒙特卡罗模拟和理论计算建立了大小束斑笔形束组合式点扫描照射方法。该方法中横向尺寸较小、纵向尺寸较窄的小束斑碳离子笔形束和横向尺寸较大、纵向尺寸较宽的大束斑碳离子笔形束之间切换是通过倾斜微型脊形过滤器60度和插入不同厚度的散射体的方式获得的。相比传统单一大束斑笔形束点扫描照射方法和单一小束斑笔形束的点扫描照射方法,大小束斑笔形束组合式点扫描照射方法具有:较小的剂量半影和较小剂量远端跌落距离、照射参数精度易于控制、剂量均匀性稳健性好和治疗时间短等优势。
[Abstract]:Compared to traditional photon radiotherapy, heavy ion beam radiotherapy has two advantages in physics and biology: first, heavy ion beam has a unique reverse depth dose distribution (Bragg peak); two is the energy transmission line density (linear energy transfer, LET) and the relative biological effect (relative biological effectiveness, RBE) in the Bragg peak region is higher, The LET is smaller in the Ping area. So the heavy ion beam protects the tumor cells and protects the normal tissue cells to achieve accurate radiotherapy. The current beam distribution system used in heavy ion radiation therapy has two kinds of passive beam distribution and active beam distribution. Based on the active beam distribution, there are grid scanning and point scanning illumination. In the point scanning method, the pen shaped beam with wide transverse and longitudinal dimensions is not conducive to the three-dimensional conform of the tumor target area. The number of scanning points will be increased greatly by using the narrow transverse and longitudinal dimensions, and the dose optimization time is prolonged, and the requirements of the control precision of the reference number are higher. In order to solve the above contradiction, In this paper, a combined point scanning method of two sizes of pencil beams is proposed in the transverse and longitudinal directions: the transverse size (beam spot FWHM, sigma) is smaller, and the longitudinal size (primary SOBP FWHM) is smaller than the narrow carbon ion beam to irradiate the edge of the tumor target area. The transverse size (the beam spot FWHM, sigma) is larger and the longitudinal size (primary SOBP). FWHM) a wide carbon ion pencil beam irradiates the edge of the tumor target area. It is convenient for the flexible switching of two kinds of carbon ion beam in the irradiation method. This paper also proposes that the longitudinal size of the pencil shaped beam is adjusted along the direction of the distribution of the beam in the beam distribution direction and the transverse size of the pen shaped beam is changed by inserting different thickness scatters. Method. The active point scanning beam distribution system based on the treatment terminal of the HIRFL CSR deep tumor treatment terminal, using the Monte Carlo simulation tool SHIELDHIT-HIT12A simulation study found that the shorter the beam distribution distance, the smaller the beam spot FWHM, the worse the dose uniformity; the period of the micro ridge filter is the key factor affecting the dose uniformity, and the cycle is the key factor. The better the dose flatness is, the better. Therefore, when the distance of the vacuum window is set at the distance of the center of the distance less than 125cm and the structure cycle is 2mm minitype ridge filter, the dose uniformity of the beam spot FWHM of the carbon ion pencil beam and the target area can meet the clinical requirement of the radiation therapy in the HIRFL device. In the point scanning beam distribution system, a carbon ion beam database with point scanning irradiation is established in this paper. Through the Monte Carlo tool SHIELDHIT12A simulation and MATLAB fitting, the relationship between the beam range and energy of the carbon ion beam is obtained, the distribution of the physical absorbed dose with the depth and the distribution of the beam spot Sigma with the depth. The use of the LQ model is used. The dependence of the average dose of LET and LET on alpha and beta was calculated for the relative biological effect of the carbon ion pencil beam with the HSG cell survival rate of 0.1. The distribution of the effective dose of the carbon ion pencil beam with the depth distribution was calculated by the physical absorption dose of the carbon ion beam and the relative biological effects. The filter 30 degrees, 45 degrees and 60 degrees can widen the primary SOBP width to about 1.16 times, 1.42 times and 2 times, respectively, to adjust the longitudinal size of the carbon ion pencil beam flexibly. The 180MeV/u~360MeV/u energy carbon beam spot Sigma can be sigma from 3mm in the downstream of the vacuum window of the beam distribution system. It is amplified to 5mm to effectively regulate the transverse size of the carbon ion pencil beam (beam spot FWHM, sigma). The operation of the inclined micro ridge filter and the insertion of different thickness Ta scatterers can be performed at the accelerator's beam energy. Therefore, the passive adjustment method of this pencil beam parameter will not increase the time of radiation therapy. This paper is adopted in this paper. Monte Carlo simulation and theoretical calculation set up a small beam spot beam combination point scanning irradiation method. In this method, the small transverse size, the narrow longitudinal size of the small beam spot carbon ion beam and the larger transverse size, the wide beam spot carbon ion beam with a wider longitudinal dimension are 60 degrees through the inclined micro ridge filter. Compared with the traditional single large beam spot beam point scanning method and the single beam spot pencil beam point scanning irradiation method, the size beam spot pencil beam combination point scanning method has the smaller dose penumbra and the smaller dose distal drop distance, and the precision of the irradiation parameter is easy to control. The system has the advantages of good uniformity, good stability and short treatment time.

【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】：博士
【学位授予年份】：2016
【分类号】：R730.55

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