Evaluation of Air-Kerma and Absorbed Dose to Water for External Radiotherapy Beam Using Ionization Chamber

Radiotherapy is the most widely applied oncologic treatment modality utilizing ionizing radiation. A high degree of accuracy, reliability and reproducibility is required for a successful treatment outcome. Measurement using ionization chamber is a prerequisite for absorbed dose determination for external beam radiotherapy. Calibration coefficient is expressed in terms of air kerma and absorbed dose to water traceable to Secondary Standards Dosimetry Laboratory. The objective of this work was to evaluate the level of accuracy of ionization chamber used for clinical radiotherapy beam determination. Measurement and accuracy determination were carried out according to IAEA TRS 398 protocol. Clinical farmers type ionization chamber measurement and National Reference standard from Secondary Standards Dosimetry Laboratory were both exposed to cobalt-60 beam and measurement results compared under the same environmental conditions. The accuracy level between National Reference Standard and clinical radiotherapy standard was found to be −1.92% and −2.02% for air kerma and absorbed dose to water respectively. To minimize the effect of error and maximize therapeutic dose during treatment in order to achieve required clinical outcome, calibration factor was determined for air kerma (Nk) as 49.7 mGy/nC and absorbed dose to water ND, as 52.9 mGy/nC. The study established that radiotherapy beam measurement chain is prone to errors. Hence there is a need to independently verify the accuracy of radiation dose to ensure precision of dose delivery. The errors must be accounted for during clinical planning by factoring in calibration factor to minimize the systematic errors during treatment, and thereby providing enough room to achieve ±5% dose delivery to tumor target as recommended by ICRU.

Similar therapeutic effects of ^(125I) seed radiotherapy andγ-ray radiotherapy on lacrimal gland adenoid cystic carcinoma

AIM:To evaluate the survival outcomes of patients with lacrimal gland adenoid cystic carcinoma who underwent eye-sparing surgery combined with ^(125I)seed implantation radiotherapy or local externalγ-ray radiotherapy.METHODS:In this retrospective comparative case series,the clinical records of 27 primary and 8 recurrent patients were reviewed.Univariate and multivariate analyses were used to identify risk factors associated with distant metastasis(DM),and the overall survival(OS)after the initial surgery was analyzed.RESULTS:The median follow-up after radiotherapy was 36 mo(range 6-120 mo).At the last follow-up after radiotherapy,26(74.3%)patients had no evidence of disease,7(20%)patients had DM,2(5.9%)patients died of DM,and 1 patient with DM was lost to follow-up.Univariate analyses showed that duration of symptoms,bone destruction,T stage classification,and wide excision surgery were risk factors influencing DM(P<0.05).The 5-year and 10-year OS rates after the initial surgery were 95.8%and 79.9%,respectively.The 5-year DM-free survival and disease-free survival rates after radiotherapy were 66.4%and 52.7%,respectively.CONCLUSION:^(125I)seed radiotherapy and local externalγ-ray radiotherapy may have similar therapeutic effects in preventing DM.Patients with T1/T2 stage disease have a better prognosis than those with T3/T4 stage disease.

Study on γ-ray source from the resonant reaction ^19F(p,αγ)^16O at Ep=340 keV

High energyγ-ray can be used in many fields,such as nuclear resonant fluorescence,nuclear medicine imaging.One of the methods to generate high-energyγ-ray is nuclear resonant reaction.The 19F(p,αγ)16O reaction was used to generate 6.13-MeVγ-ray in this work.The angular distribution of 6.13-MeVγ-ray was measured by six LaBr3 detectors.The thick-target yield curve of 6.13-MeVγ-ray had been measured.The maximum yield was determined to be(1.85±0.01)×10^-8γ/proton,which was measured by HPGe detector and LaBr3 detector.The absolute efficiency of all the detectors was calibrated using 60Co and 27Al(p,γ)^28Si reaction at Ep=992 keV.The cross section and total resonant width of the reaction were determined to be 95.1±1.0 mb(1 b=10^-24 cm^2)andΓCM=2.21±0.22 keV,respectively.

Photo-transmutation based on resonance γ-ray source

High intensity γ-ray source can be obtained through resonance reaction induced by protons. In this work, the possibility of using such high intensity MeV-range γ-ray source to transmute nuclear waste is investigated through Mont Carlo simulation.197 Au(γ, n)196Au experiment is performed to obtain the transmutation rate and compared with the simulation result. If the current of the proton beam is 10 mA at the resonance energy of 441 keV, with the γ photons emitted from7 Li(p, γ)8 Be, then the corresponding transmutation yield for129I in 2π direction can reach 9.4 × 109 per hour. The result is compared with that of LCS γ-ray source.

Clinical study on gefitinib combined with γ-ray stereotactic radiotherapy for senile patients with adenocarcinoma of lung as the first-line regimen

Objective: The aim of our study was to evaluate the efficacy and safety of gefitinib combined with γ-ray stereo-tactic radiotherapy for senile patients with adenocarcinoma of lung as the first-line regimen. Methods: The 153 senile patients with adenocarcinoma of lung were divided into 4 groups according to the therapy method. Group A was the 35 patients treated with gefitinib combined with γ-ray stereotactic radiotherapy. Group B was the 45 patients treated with γ-ray stereotactic radio-therapy. Group C was the 42 patients treated with gefitinib. Group D was the 31 patients treated with best supportive therapy. The patients received gefitinib of 250 mg/d from the first day until disease progression or other reasons. The patients were treated with γ-ray stereotactic radiotherapy from the second day. Dose curve of this group of cases was 50%-80%. Encircled dose was 4.0-6.5 Gy per fraction and the range of total dose was 36-48 Gy. The total number of treatment was 8-12 and treated six times every week. Results: All the patients were examined by enhanced double helix CT at the second month. The tumor response rate (RR) of group A was 68.6% (24/35). Disease control rate (DCR) was 88.6% (31/35). The median survival time (MST) was 13.4 months (range 3-34 months ) and the progression-free survival (PFS) was 7.8 months. The overall 1-year survival rate was 40.0% (14/35). The main side effects included skin rash and diarrhea. The RR of group B was 51.1% (23/45). DCR was 71.1% (32/45). MST was 9.6 months (range, 3-18 months ) and PFS was 5.3 months. The overall 1-year survival rate was 15.6 % (7/45). The RR of group C was 40.5 % (17/42). DCR was 61.9% (26 /42). MST was 10.3 months (range, 3-26 months ) and PFS was 5.1 months. The overall 1-year survival rate was 35.7 % (15/42). The main side effects included skin rash and diarrhea. The MST of group D was 5.6 months (range, 2-11 months ) and PFS was 1.7 months. The overall 1-year survival rate was 0. The short-term therapeutic effects (RR) of group A was higher than group C (P = 0.014 < 0.05, χ2 = 6.053) but has no significant difference with group B (P = 0.116 > 0.05, χ2 = 2.477). The long-term therapeutic effects (overall 1-year survival rate) of group A was higher than group B (P = 0.014 < 0.05, χ2 = 6.077) but has no significant difference with group C (P = 0.642 > 0.05, χ2 = 0.216). Conclusion: Gefitinib combined with γ-ray stereotactic radiotherapy is feasible and effective for treatment in senile patients with adenocarcinoma of lung as the first-line regimen.

Design of CsI(TI) detector system to search for lost radioactive source

This report presents a design system based on the use of CsI(TI) detectors to search for lost radioactive sources that are dangerous and harmful to individuals, including searching persons. For this purpose, the GEANT4 simulation toolkit was utilized to develop a system based on three detectors. Various simulated analyses were performed on the dose rates of the three detectors using different source–detector distances and detector separation. There were good agreement between the simulated results and the experimentally measured data. A new method was discussed to detect and search for radioactive sources based only on the dose rates in detectors with source activity. Numerical analyses were performed based on the measured dose rates and the difference of distances to determine the actual location of the lost single or multiple γ-ray sources at a specific angle. The detection limit was calculated from the background radiation to establish the sensitivity and capability of the proposed detector system. This system can be applied in fields in which it is necessary to locate unknown radioactive sources.

Highly efficientγ-ray generation by 10 PW-class lasers irradiating heavy-ion plasmas

10 PW-class lasers irradiating overcritical plasmas in the quantum electrodynamics regime promise to generate ultrabrightγ-ray sources in the laboratory.Here using two-dimensional particle-in-cell simulations,we report highly efficientγ-ray generation in the parameter regime of 10 PW-class lasers at an intensity level of 10^(23)W cm^(–2)interaction with heavy-ion plasmas which have large-scale preplasmas.The laser-to-γ-ray(>1 MeV)energy conversion efficiency reaches close to 60%with an above 10^(14)γ-photons/pulse.The averageγ-photon energy is about 14 MeV with the highest photon energy exceeding 1 GeV.The high-energyγ-photons are mainly directed in the forward direction.We also find that plane target geometry is efficient enough for high powerγ-ray radiation,which is beneficial for easing the difficulty of complex target manufacturing and alignment in experiments.

10 MeV、>80 Gy/s@1 m的光子FLASH放疗射线源

报道了基于常温射频直线加速器建成的10 MeV光子FLASH放疗射线源样机,采用高平均电流电子束轰击高速旋转辐射转化靶,在距离靶点1 m远处的固体水模内,X射线剂量率达到80.5 Gy/s,达到未来临床实验与推广所需剂量率阈值。

On the surface brightness radial profile of the extendedγ-ray sources

The morphology of the extendedγ-ray source is governed by the propagation process of parent relativistic particles.In this paper,we investigate the surface brightness radial profile of extendedγ-ray sources illuminated by cosmic ray protons and electrons,considering the radiation mechanisms,projection effects,and the response of instruments.We find that the parent particle species and the propagation process can cause considerable differences in the observed radial profiles.Thus,the surface brightness profile can be used as a unique tool to identify the radiation mechanism and the propagation process of the parent particles.In addition,we also discuss the possible implications regarding the latest discoveries from very/ultra-high energyγ-ray instruments like LHAASO and HAWC.

An updated search of steady TeV γ-ray point sources in northern hemisphere using the Tibet air shower array

Using the data taken from Tibet II High Density （HD） Array （1997 February-1999 September） and Tibet-III array （1999 November--2005 November）, our previous northern sky survey for TeV γ-ray point sources has now been updated by a factor of 2.8 improved statistics. From 0.0° to 60.0° in declination （Dec） range, no new TeV T-ray point sources with sufficiently high significance were identified while the well-known Crab Nebula and Mrk421 remain to be the brightest TeV γ-ray sources within the field of view of the Tibet air shower array. Based on the currently available data and at the 90% confidence level （C.L.）, the flux upper limits for different power law index assumption are re-derived, which are approximately improved by 1.7 times as compared with our previous reported limits.

改变测量模体源皮距在大面积射野调强验证中的应用

目的探讨改变测量模体源皮距(SSD)在大面积射野调强验证中的应用效果。方法选取2018—2022年医院收治的15例鼻咽癌Ⅱ期患者作为研究对象,均接受放射治疗。先行CT模拟定位,然后将图像传输至Monaco治疗计划系统,物理师按照医师要求设计治疗计划,计算所有射野在模体中的剂量分布,并传输至验证系统进行分析,将所有射野角度设置为0°,在SSD为90、91、92、93、94、95、96、97、98、99、100 cm时分别进行模拟照射,运用软件分析相对剂量γ通过率。结果当SSD为93、94、95、96、97、98、99cm时,γ通过率均≥95.0%,当SSD为90、91、92、100 cm时,γ通过率均<95.0%。结论大面积射野的调强验证可通过改变SSD大小实现,建议SSD设置在93~99cm范围内。

基于MCNP源子程序的放射治疗剂量计算验证方法

目的:蒙特卡罗方法可以精确地对放射治疗过程所涉及到的物理过程进行模拟而在放射治疗领域有很大应用前景,本文发展了基于蒙特卡罗程序MCNP的剂量计算验证方法。用户只需要设置加速器源的位置参数和放疗计划参数就可以方便的调用MCNP源子程序完成放疗计划的剂量计算。方法:首先确定源的位置,根据加速器机头的位置和等中心点的位置来确定源粒子的位置信息。其次根据代表射野形状和强度的强度矩阵来抽样源粒子的方向信息,然后根据加速器能谱的抽样概率随机抽选能量段,然后在能量段内均匀抽样,得到该次抽样的源粒子能量信息,得到源粒子的所有信息后即可进行粒子在人体的蒙卡输运模拟。结果:本文通过对一例真实的宫颈癌病例的放疗计划进行模拟计算剂量分布,通过剂量偏差分析得到与MCFSPB在目标区域的平均误差为1.12%,γ分析值为94.55%,剂量计算结果符合的很好,比临床上的标准要求要高,完全满足临床要求。结论:本方法的计算精度能满足临床放射治疗验证的要求,能作为放疗计划的验证工具。

关于《放射治疗机房的辐射屏蔽规范第3部分:γ射线源放射治疗机房》(GBZ/T 201.3—2014)技术指标解析

目的对《放射治疗机房的辐射屏蔽规范第3部分:γ射线源放射治疗机房》(GBZ/T 201.3—2014)中的主要技术指标进行解析,为放射治疗机房的屏蔽估算和防护评价提供技术指导。方法以GBZ/T 201.3—2014标准文本为主线,结合常规γ射线源治疗机房的辐射屏蔽技术资料和屏蔽设计实例,阐释治疗机房屏蔽计算原则及屏蔽估算的考虑因素,剖析屏蔽估算方法相关技术指标。结果明确了常规γ射线源治疗机房的辐射屏蔽估算方法。60Co远距治疗机房辐射屏蔽估算中应分别针对主屏蔽区、与主屏蔽区直接相连的次屏蔽区、侧屏蔽墙、迷路外墙和机房入口考虑辐射束;后装治疗机房的屏蔽估算应考虑治疗源4π发射的γ射线对墙和室顶的直接照射及其散射辐射在机房入口处的照射;头部γ刀机房屏蔽只需考虑散射辐射,某些体部γ刀机房屏蔽还需考虑旋转照射时单个源的有用线束,两者在屏蔽计算中应尽可能利用已有实测的机房内散射辐射剂量场数据。结论 GBZ/T 201.3—2014提出的γ射线源放射治疗机房辐射屏蔽估算方法是可行的,在实际应用中应遵循屏蔽计算的基本原则,结合治疗装置的剂量学参数和治疗机房的具体物理模型以及辐射束类型等屏蔽计算影响因素,并对机房辐射屏蔽效果进行验证。

深圳大学微型反应堆的改进

介绍深圳大学核技术所近年来对微型反应堆进行的一系列改进 ,包括 :采取特殊措施 ,延长微堆安全运行时间 ,从原来的 6～ 8h ,延长至 40h左右 ,成功研制了治疗肝癌的含稀土元素的放射性玻璃微球 ;建立了超热辐照管和计算机控制的循环跑兔装置 ,扩展了微堆活化分析范围和领域 ;研制出一种新颖、简单、准确 ,且无需添置任何设备的测量堆芯绝对中子通量密度的方法———氙中毒法 .尽管深大微堆具有固有的安全性 ,但它目前处于运行后期 .因腐蚀、疲劳等原因 ,核燃料元件包壳破损的可能性将越来越大 ,为此研制了安全监测计算机系统 ,一旦发生核燃料元件包壳破损时 ,系统能很快监测放射性泄漏 ,这对控制核污染起到十分重要的作用 .但这并不说明深大微堆已安全无事 .国外发生的一系列核泄漏事件昭示人们 ,在核安全管理中 ,人员因素至关重要 .不管放射性物质泄漏多与少 ,影响都很大 。

深圳大学微型反应堆改进

介绍深圳大学核技术所几年来对微型反应堆（ 简称微堆） 进行的一系列改进，包括： 采取特殊措施， 延长微堆安全运行时间， 从原６ ～８ｈ ， 延长至４０ｈ 左右； 成功研制了治疗肝癌的含稀土元素的放射性玻璃微球； 建立了超热辐照管和计算机控制的循环跑兔装置， 扩展了微堆活化分析范围和领域； 研究成功一种新颖、简单、准确， 又无需添置任何设备的测量堆芯绝对中子通量密度的方法———氙中毒法． 尽管深大微堆具有固有的安全性， 但它目前处于运行后期． 由于腐蚀、疲劳等原因， 核燃料元件包壳破损的可能性将越来越大，为此研制了安全监测计算机系统， 一旦发生核燃料元件包壳破损时， 系统能很快监测放射性泄漏， 这对控制核污染起到十分重要的作用． 但应指出， 这并不是说深大微堆已安全无事．由最近国外发生的一系列核泄漏事故说明， 核安全管理、人员因素至关重要． 不管放射性物质泄漏多少， 影响都很大， 万万不能麻痹大意．

SGS-I立体定向伽玛线全身放疗系统源体定位系统的改进

目的我院立体定向全身伽玛线全身放疗系统在使用一段时间后,出现了源体定位系统中源体定位插销不能动作故障,造成整个系统的全自动化运行终止,必须进行维修改进。根据对设备结构和工作原理的消化理解,我们通过增加销驱动马达电源的改进,非常简便地实现设备正常运行,并很好地提高了原系统的可靠性和稳定性。

双源CT双能量成像在非小细胞肺癌放化疗疗效评估中的价值

目的:探究双源CT双能量成像在非小细胞肺癌放化疗疗效评估中的价值。方法:选择2017年6月—2019年6月期间我院收治的非小细胞癌患者80例,所有患者均接受放化疗治疗,并于放化疗前后采用双源CT双能量扫描。按照治疗效果,将患者分为有效组与无效组,记录两组治疗前后病灶直径、病灶平扫CT均值、病灶动脉强化分数(AEF)、动静脉期碘覆盖与碘浓度值等指标。结果:有效组与无效组病灶直径变化率以及平均CT值变化率对比差异显著(P<0.05),动脉期,两组患者标准化碘浓度与碘覆盖值治疗前后对比差异显著(P<0.05)。两组静脉期内标准碘化与碘覆盖值治疗前后对比差异不显著(P>0.05),有效组治疗后AEF水平较无效组明显降低(P<0.05)。结论:双源CT双能量成像可作为非小细胞肺癌放化疗疗效评价依据。

近距治疗的新进展

简要回顾了放射治疗的发展史。从治疗设备、核素选择、制源技术和照射技术四个方面阐述了近距治疗在近年来国内外取得的进展 ,并对其前景作了预测。

利用源皮距验证食管癌放疗摆位误差可行性的探讨

目的:利用源皮距验证多点固定摆位精度可行性。方法:使用常规模拟机和加速器对25食管例放疗前、中时期所拍摄射野图像与计划系统生成的射野数字重建(DRR)图像进行配准比较,并对病人摆位时机架角源皮距(GSSD)偏差进行了测量。结果:系统误差:G0°SSD为(1.80±1.3)mm、G45°SSD为(2.04±1.3)mm、G315°SSD为(2.10±2.3)mm;随机误差:距离为G0°SSD为(2.53±1.7)mm、G45°SSD为(2.41±2.3)mm、G315°SSD为(2.33±3.0)mm。结论:源皮距验证技术只是提供放疗技师在线摆位验证。快捷、参考方法,而不是放疗摆位验证的可靠方法。

利用源皮距验证头部肿瘤放疗摆位误差可行性的研究

目的验证源皮距法保证头部肿瘤患者精确摆位的可行性。方法使用Varian Acuity8.6模拟机对21例头部肿瘤病人拍片,并从治疗计划系统中得到相应位置的标准射野数字重建(DRR)图像,应用Acuity的二维匹配功能,得出摆位误差;观察其与射野角度为0°.45°.315°时源皮距误差的对应关系。结果21例患者左右、头脚、前后方向系统误差分别为(1.1±1.6)mm、(0.7±1.2)mm、(0.9±1.5)mm,随机误差分别为(1.51±3.1)mm、(1.05±3.3)mm、(1.60±2.3)mm。各角度源皮距系统误差为(1.25±1.3)mm、(1.04±1.3)mm、(1.10±2.3)mm,随机误差为(2.03±1.7)mm、(2.81±2.3)mm、(2.33±3.0)mm。结论源皮距法简易可行,可以作为其他位置验证手段的辅助。