测量后装近距离放射治疗192Ir源参考空气比释动能方法学研究

目的 用NE2570剂量仪,2571指形电离室,测量 ¹⁹²Ir源空气比释动能支架,测量1m处 ¹⁹²Ir源参考空气比释动能。 方法将测量支架放在离墙、地面1m处,指形电离室插入有机玻璃测量支架夹具中,源中心距电离室中心的最佳距离是16cm, 源通过后装机的传输系统传输到施源器中,测量源参考空气比释动能。根据 ⁶⁰Co γ射线,250 kVΧ射线空气照射量刻度因子换算为空气比释动能刻度因子,再由内插公式计算 ¹⁹²Ir源空气比释动能刻度因子。对墙、地、空气、测量支架的散射校准因子,通过阴影屏蔽实验得到;对初始光子减弱校准因子;电离室壁产生的电子非均匀校准因子,均由IAEA的1079号报告(近距离放射治疗源的刻度)中查表得到。 结果在相同环境条件下,使用2种测量方法,指形电离室测量 ¹⁹²Ir源空气比释动能,经转换系数计算源外观活度为1.584×10¹¹Bq;井型电离室测量 ¹⁹²Ir源空气比释动能强度,经转换系数计算源外观活度为1.561×10¹¹ Bq,2个结果的相对偏差为 1.4%。结论指形电离室测量源空气比释动能,该物理量与源的结构、尺寸、壳材料、电离室形状、材质和尺寸无关,测量源空气比释动能与源的空气照射量比较,不确定度误差小。     

Flexitron后装机的临床调试

目的 为满足国家标准和临床需求,对Flexitron后装机的硬件和软件制定临床调试流程、项目内容和测试方法,并建立相关的质量控制规程。方法 临床调试分为硬件、治疗计划系统(TPS)和端对端(ETE)的全流程测试。采用源位置检测标尺测量放射源的到位精度;通过秒表计时、电离室测量、视频分析3种方法检测驻留时间的精度和线性;使用高精度尺测试模拟尺、连接管、源位置检测标尺等测量工具的精度;使用胶片校准标记丝和施源器;使用静电计和井型电离室校准放射源活度。通过实物图像对TPS的显示、重建精度进行评价。采用自制模体完成扫描、计划和剂量测量进行ETE测试。结果 调试项目中的精度检测结果均在可接受的限值之内,源活度测量结果偏差为0.21%,ETE点剂量测量偏差为2.32%,均满足临床使用要求。但精度检测项目中,核磁标记丝的标称和实测值存在2 mm差异,因此基于核磁影像采用标记丝进行管道重建时需要修正。结论 本研究通过总结Flexitron后装机的临床调试经验,制定了后装机、计划系统各项目的质量控制方法及结果的基线水平,为后装机投入临床使用前的调试工作提供了参考。     

后装治疗源192 Ir空气比释动能强度检测 与评价

目的 研究用井型电离室测量后装192Ir源空气比释动能强度的方法.方法 用CDX-2000A静电计和HDR 1000井型电离室,现场检测30台后装192Ir源空气比释动能强度,根据源外观活度与空气比释动能强度转换系数,计算源外观活度.用实测源活度与厂家给出的初始源活度比较,相对偏差应在±5%内符合要求.结果 对所有检测的30台后装192Ir源活度与厂家初始源活度比较,相对偏差在-0.1%～4.4%范围内.结论 井型电离室测量法简便,准确度高,在医院可用于质量控制检测.

Abstract：

Objective To study the method of measuring air kerma strength of afterloading units with 192Ir source by using well type ionization chamber.MethodsThe air kerma strength of 30 afterloading units with 192Ir source was measured using 2000A electrometer and 1000 plus well type ionization chamber,and apparent activity of the source was calculated with the air kerma strength and apparent activity conversion factor.The measured activity of the source was compared with the original value of the source provided by the manufacturer,and the relevant deviation should be within ± 5%.Results Theair kerma strength of afterloding units with 192Ir sources was tested.The relevant deviation of the measured activity and the original value was within -0.1%-4.4%.Conclusions The measurement method with a well type ionization chamber is convenient and highly accurate which can be used for the test of quality control in hospitals.     

井型电离室位置对放射性活度测量准确度和人员受照剂量的影响

单光子发射型计算机断层（single photon emission computed tomography，SPECT）显像是根据探测的放射性核素在人体内的分布情况，显示器官及病变组织的解剖结构、代谢和功能状态。在远离核素供应站的医院需用Mo-Tc发生器进行放射性核素（^99mTc）的淋洗、标记和分装，此时需用放射性活度计测量淋洗液的放射性核素浓度和标记药物的放射性核素活度，此项操作属近距离开放性放射性操作，必须考虑辐射防护问题。本研究是将放射性活度计之井型电离室放置不同位置，分别测量放射性活度和在一定距离（50cm）测量其空气比释动能，将测量结果进行对比，找出有利于辐射防护的最佳方法。     

符合线路显像与18F最佳活度的关系

目的探讨符合线路显像18F给药活度对随机符合比率及显像灵敏度的影响.方法 胸部模型充满不同18F活度的水溶液,用DST-Xli双探头SPECT仪符合采集发射影像,并进行图像处理.结果真符合减去随机符合,相应的18F活度之差越大显像效果越好,6次显像该差值由小变大再由大变小,在86 min时差值最大为8.9 MBq,单光子计数率3.65×105,18F相应活度17.8 MBq,随机符合比率25%,出现阳性结节最多,显像效果最好.6次显像的单光子计数率、随机符合比率等彼此间均存在直线相关性.活度(X,MBq)与随机符合比率(Y,%)的相关系数平方(R2)为0.9974,校正的R2为0.9967,P＜0.0001,直线方程Y=-1.893 79+1.550 685 X.结论模型显像可测出符合线路显像的最佳18F给药活度;当随机符合比率为25%时对应的18F活度为最佳活度,可取得最灵敏的显像效果.     

蒙特卡罗方法计算后装192Ir源散射校正因子研究

目的 研究一种方便、可行地推算医用后装192Ir源空气比释动能散射校正因子的方法,便于医院用指形电离室进行活度测量的QA工作的开展.方法 用指形电离室测量有铅挡块和无铅挡块192Ir源空气比释动能,根据国际原子能机构(IAEA)1079号报告,计算192Ir源散射校正因子.用蒙特卡罗(MC)方法模拟测量条件,计算192Ir源散射校正因子,并与实验结果进行比较验证,同时模拟几种不同电离室型号和房间尺寸,计算并给出不同192Ir源散射校正因子.结果 蒙特卡罗方法模拟192Ir源散射校正因子与实验测得的散射校正因子比较,相对误差为0.8%.利用蒙卡计算得散射校正因子推算出的源活度和用井型电离室测量推算出的源活度相差2.4%.MC模拟IAEA1079号报告中的两种球形电离室计算结果与报告中给出的结果比较,相对误差范围在0.3%～0.4%.模拟5种不同型号指形电离室,不同房间尺寸,相对误差范围在3%之内.结论 用蒙卡方法模拟计算后装192Ir源散射校正因子的方法是可行的,此方法方便了医院用指形电离室进行近距离治疗QA工作的开展.

Abstract：

Objective To facilitate activity measurement by using the thimble ionization chamber in hospitals,to obtain air kerma scatter correction factor of medical afterloading of 192Ir source by developing an available and convenient calculation method.Methods According to International Atomic Energy Agency (IAEA) 1079 Report to calculate the scatter correction factor of 192 Ir source,to measure air kenna of 192Ir source with and without lead shield using thimble ionization chamber.Simulation measurement conditions were used to calculate scatter correction factor of 192Ir source and comparison was made between experimental results and literature records.At the same time,the different ionization chamber models were simulated at different room sizes to obtain scattering correction factor of 192 Ir source.ResultsComparison was made between the simulation scatter correction factors of 192Ir source and experiment by the shadow shield,and the relative deviation was 0.8%.The deviation of the 192 Ir activity calculated according to the simulated scatter correction factor and measured by well type ionization chamber was 2.4%.By comparison between the calculated results by using two kinds of spherical ionization chamber and those ones deduced by IAEA 1079 Report,the relative deviations ranged within 0.3%-0.4%.Five different types of thimble ionization chamber and different room sizes were simulated and calculated by MC simulation,with the relative deviation within 3%.Conclusions Monte Carlo simulation method for calculating afterloading 192 Ir source's scatter correction factor is feasible,and this method is convenient for use in the thimble chamber for brachytherapy QA work in the hospital.     

近距离高剂量率192Ir源活度的质量控制

根据 2 0 0 2年 5月调查统计 ,我国现有后装机 3 79台 ,其中 3 1台使用13 7Cs ,6 0 Co和2 5 2 Cf,其余 3 4 8台使用192 Ir源。由于19 2 Ir源半衰期短 (74 2d) ,能谱复杂 ,测量仪器和技术等原因 ,长期以来 ,几乎所有医院仅根据厂家提供的源强标称活度制定放射治疗计划 ,存在医疗事故隐患。因此 ,开展192 Ir源活度质量控制检测 ,改善治疗剂量准确度非常必要。本文作者重点介绍两种测量方法和检测结果。一、材料和方法1 井型电离室法 :电离室高 15 6cm ,井口直径 3 6cm ,井深 12 1cm ,收集体积 2 45cm3 ,工作电压± 3 0 0V ,总漏电小于 10…     

二维空气电离室矩阵MatriXX系统的应用研究

目的 探讨二维空气电离室矩阵MatriXX系统应用于放疗质量控制中的特点。方法用MatriXX系统和自制的剂量测量体模,对临床放疗质量控制中的一些重要内容进行了初步的研究,主要包括MatriXX系统的刻度、X线虚拟楔形野的离轴比、半野和偏心野衔接、均整块的校准、放疗计划剂量分布的二维验证、散射屏对大面积电子线特殊野的影响、大野附加散射屏后铅挡块的遮挡效果和挡块的最佳位置和厚度的确定。结果 任意角度的虚拟楔形野的离轴比均可用MatriXX来测量,测量时只需要1次照射;半野和偏心野衔接位置可精确到小于1 mm;用MatriXX系统可对照射野内任一点的计算值与测量值,或整个射野内任意百分比的等剂量曲线分布以及任意方向离轴比进行对比分析;均整块校准后射野的平坦度和对称性分别为1.85%和0.98%;散射屏明显改变了电子线射野的剂量特性,大面积电子线特殊野照射时远距离遮挡难以达到遮挡目的,近距离或直接遮挡效果最佳。结论 二维空气电离室矩阵MatriXX系统用于放疗质量控制时,比普通指形电离室和胶片剂量测量更简便、高效,是放疗质量控制的理想工具。     

湖北省核查放射治疗非参考条件剂量学参数方法的验证

目的 研究用TLD核查医用电子加速器在非参考条件下,光子线束剂量随照射野、楔形板变化,电子线束剂量随照射野、源皮距变化的剂量学参数方法的可靠性。方法 在非参考条件下,用指形电离室测量光子线束水下10 cm处吸收剂量和电子线束最大剂量点处吸收剂量,并在同一位置放置TLD进行照射,将照射后的TLD邮寄到中国疾病预防控制中心辐射防护与核安全医学所进行测量并估算剂量。结果 光子线束剂量点共70个,其中58个点的TLD测量结果与指形电离室测量结果相对偏差在±7.0%以内（IAEA允许偏差±7.0%）,合格率为82.8%。经过P_S值修正后,合格点数达到62个,合格率上升为88.6%;电子线束剂量点为24个,其TLD测量结果与指形电离室测量结果相对偏差均在±5.0%以内（IAEA允许偏差±5.0%）,合格率为100%。结论 用TLD核查非参考条件电子线束剂量学参数方便,与指形电离室相互验证,可提高剂量测量的准确性。电子线束能量在5 MeV<E₀<10 MeV的范围内,用指形电离室测量吸收剂量参数,并用TLD验证,其结果精确可靠。     

测量方法对125I密封籽源活度值的影响研究

目的 研究各种因素(包括测量的几何位置、不同容器、自屏蔽、容器壁厚等)对125I密封籽源表观活度测量的影响,建立理想的测量条件。方法 将125I密封籽源直立在1ml尖底放免管中,放入CRC-15R活度计的小托盘中进行测量。结果 不同测量条件对125I密封籽源表观活度测量有影响。结论 在最佳测量条件下,测量的125I密封籽源表观活度比较准确。     

192Ir γ射线球形石墨空腔电离室室壁修正系数的模拟计算

目的 研究¹⁹²Ir放射源参考空气比释动能率基准电离室(NIM-Ir-SG-100型)的室壁修正系数。方法 利用蒙特卡罗程序计算经过放射源包壳和辐照器模型的光子光谱和电离室室壁修正系数,并对影响室壁修正系数结果的光子能量、壁厚和电离室内径进行了模拟。结果 经计算,球形石墨空腔电离室室壁修正系数模拟结果为1.037 7。控制单一变量,光子能量(0.3~1.3) MeV、壁厚(0.2~0.5) cm、电离室内径(0.5~15) cm对室壁修正系数结果的最大偏差分别为1.62%、3.30%、2.86%。结论 自制球形石墨空腔电离室性能良好,室壁修正系数k_wall值在合理范围内。室壁修正系数的完成为测量¹⁹²Ir放射源的参考空气比释动能率,建立计量基准完成重要的一步。     

Dosimetric consideration of individual 125I source strength measurement and a large-scale comparison of that measured with a nominal value in permanent prostate implant brachytherapy

Purpose We investigated the difference between measured and manufacturer's nominal source strength in a large sample of a single model of ¹²⁵I seeds. Physical characteristics of single seed measurement by the well-type ionization chamber were also investigated to provide dosimetric data. Materials and methods A well-type ionization chamber with a single seed holder was used to measure source strength of all 1935 ¹²⁵I seeds implanted in the initial 28 patients in our hospital. Physical characteristics including linearity of readings for different integral time intervals, reproducibility, isotropy, and axial positional sensitivity were assessed. To calculate the source strength, the integral charge during 30 s was measured and converted to air kerma strength. The nominal activity stated by the manufacturer was compared with the measured value. Results Linearity, reproducibility, and isotropy of the well-type ionization chamber were within 0.2%. Measured source strength was on average 2.1% (range −7.6% to +7.2%), lower than the nominal value. Standard deviation of all measured seeds was 2.0%. The maximum difference between the measured and the manufacturer's nominal source strength in each patient was −3.7%. The standard deviation averaged 1.6%. Conclusion The nominal source strength of the ¹²⁵I seeds agreed well with the measured value. Our study can be helpful as guidance for individual ¹²⁵I seed source strength measurement.     

Consistency of vendor-specified activity values for 192Ir brachytherapy sources

A long-term comparison was done between the manufacturer-stated ¹⁹²Ir activity and the measured ¹⁹²Ir activities determined with a well-type ionization chamber. Sources for a Nucletron Micro Selectron high-dose-rate (HDR) unit were used for this purpose. The radioactive sources reference activities were determined using a PTW well-type ionization chamber traceable to the National Institute of Standards and Technology Primary Calibration Laboratory. The measurements were taken in a period of 56 months with 17 different radioactive sources. The manufacturer stated activities were taken from the source calibration certificate provided by the manufacturer. These values were compared with the measured activities. The results have shown that both the percentage deviation of the monthly control measurements with the well-type chamber and the ratio between the measured activities to the manufacturer-stated value lie within ± 2.5%. These results were compared with similar published data and with uncertainty level (3% of the mean and 5% maximum deviation from mean) for brachytherapy sources calibration recommended by the AAPM. It was concluded that a threshold level of ±2.5% can be used as a suitable quality assurance indicator to spot problems in our department. The typical ±5% uncertainty as provided by the manufacturers may be tightened to ±3% to be more in line with published AAPM reports.     

HDR brachytherapy well chamber calibration and stability evaluated over twenty years of clinical use

PurposeThe purpose of the study was to establish, using a retrospective analysis of existing hospital records, the long-term stability and accuracy of a high-dose-rate brachytherapy well chamber. This should be assessed to determine reliability and appropriate calibration frequency. The accrual of long-term data that demonstrates the stability of our chamber may inform others of the performance they might expect from similar equipment.Methods and MaterialsWe evaluated air kerma strength measurements made with the PTW 32002 (Nucletron 077.091) high-dose-rate well chamber on 72 ¹⁹²Ir sources over an 18-year period and the seven calibrations of that chamber which span a 27-year period.ResultsConsecutive air kerma strength measurements agreed within 0.01% on average. The chamber measurement agreed with the source specification within 0.02% on average, but was up to 1.4% during some calibration periods. The chamber calibration coefficient varied by a maximum of 5% over seven chamber calibration measurements.ConclusionsThe constancy of the well chamber current compared with the source manufacturer suggests that our chamber has been stable to better than 2% over a period of 18 years. Although the chamber has received different calibration coefficients over time, these coefficients are within the combined uncertainties of any two calibrations and are consistent with the chamber being stable. The agreement we have observed between clinical measurements and the source manufacturer would justify an action level for further investigation of 1%, for this specific chamber.     

222Rn-220Rn分辨探测器参加国际比对结果分析

目的 提高²²²Rn与²²⁰Rn的累积测量水平,保证测量结果的准确性与可靠性。方法 采用中国疾病预防控制中心辐射防护与核安全医学所的氡课题组（以下简称本实验室）改进的LD-P型²²²Rn-²²⁰Rn分辨探测器参加日本放射线医学综合研究所（NIRS）组织的²²²Rn-²²⁰Rn累积探测器国际比对。将²²²Rn-²²⁰Rn分辨探测器寄往日本,在NIRS的²²²Rn室和²²⁰Rn室进行不同条件下的比对,暴露结束后再寄回本实验室进行蚀刻与分析,测量结果告知NIRS。最后NIRS将²²²Rn与²²⁰Rn暴露参考值回馈本实验室。结果 在高²²²Rn和低²²²Rn条件下,测量值与NIRS提供的参考值的相对百分偏差（RPD）分别为-12.0%、-11.8%;变异系数（COV）分别为3.0%、6.2%。在高²²⁰Rn和低²²⁰Rn条件下,测量值与NIRS提供的参考值的相对百分偏差（RPD）分别为-0.8%、-8.0%;变异系数（COV）分别为6.7%、4.5%。结论 本次比对LD-P型探测器²²²Rn与²²⁰Rn的测量结果均为NIRS规定的Ι级结果（PRD<10%）,比对结果较好。     

252Cf中子后装治疗机步进精度测量及其剂量偏差研究

目的 研究²⁵²Cf中子后装治疗机步进精度以及步进偏差引起的剂量偏差。方法 利用EBT3胶片测量²⁵²Cf中子源的步进,然后通过Image J软件测量光密度值找到每步²⁵²Cf中子源的中心,计算出每步之间的间隔;利用双电离室法测量²⁵²Cf中子源位置偏差引起的剂量偏差。结果 EBT3胶片测量²⁵²Cf中子源步进精度可达0.01 mm;²⁵²Cf中子源位置偏差<3 mm时,剂量偏差<2.5%。结论 对²⁵²Cf中子源步进精度以及位置偏差的研究可为制订²⁵²Cf中子后装治疗机质量控制标准提供参考。     

Direct measurement of 60Co and 125I activity by the sum-peak method in PTKMR-BATAN

The sum-peak method was successfully applied to the determination of the activity of ⁶⁰Co and ¹²⁵I sources measured by HPGe and well-type NaI(Tl) detectors in PTKMR-BATAN. The result of the ⁶⁰Co activity agrees with the activity value measured by using a calibrated ionization chamber within a range of about 0.35–0.5% and the activity result of ¹²⁵I agrees with the activity value measured using the photon–photon coincidence method within a range of 0.05–0.26%.     

基于电子射野影像系统与加速器日志文件重建模体内剂量的初步比较

目的 研究基于电子射野影像系统（EPID）与加速器日志文件（dynalogs file）重建模体内剂量的差异性。方法 收集12例盆腔患者的容积旋转调强（VMAT）计划,将计划信息复制到“Cheese”模体上重新计算剂量,而后在瓦里安加速器（RapidArc）上执行,“Cheese”模体置于等中心处获取射野影像（EPI）,将EPI传入EPIgray软件中重建剂量。同时利用Mobius软件调用加速器日志文件,实现对模体计划剂量的重建。以A1SL型号的电离室和配套的剂量仪测量整个计划执行结束后射野等中心（电离室中心）处剂量值,在计划系统（TPS）中读取电离室敏感体积体内的平均剂量值（设置电离室中心与等中心重合）。结果 电离室测量值与TPS中读取的等中心处剂量值相比,两者偏差为1.31%。两种方式重建的射野等中心的剂量分别与电离室测量数值相比,差异均无统计学意义（P>0.05）。结论 两种重建体内剂量的方法均能为VMAT在体剂量验证提供参考。     

Prospective Study of Systemic Yttrium-90 Elution during Radioembolization of Hepatic Metastases

PurposeTo evaluate total blood radioactivity (BR) after SIR-Spheres yttrium-90 (⁹⁰Y) radioembolization and differences in BR based on delivery method.Materials and MethodsTwenty participants with hepatic metastases undergoing first radioembolization were prospectively enrolled from December 2017 to June 2018. Blood samples were drawn at baseline and 0, 10, 20, 60, and 120 minutes after ⁹⁰Y administration. BR was measured with a γ-counter and scaled by estimated blood volume. Percentage of instilled radioactivity in the bloodstream was calculated as area under the fitted curve, and differences between delivery methods were examined with nonparametric statistical tests.ResultsIn 10 participants, resin microspheres were instilled with 50% Isovue 300 diluted in saline solution in the D line, and 10 others were treated with dextrose 5% in water (D5W) in the D line. Median administered activities were 944 MBq (range, 746–1,993 MBq) and 1,213 MBq (range, 519–2,066 MBq), respectively. Fraction of ⁹⁰Y in blood was significantly higher with dilute contrast agent than with D5W (median, 0.5% of injected activity vs 0.2%; P = .001). Among all participants, the maximum activity delivered was 2,066 MBq, and a maximum of 1% of administered radioactivity was measured as free ⁹⁰Y in blood. Assuming these highest-case values and complete decay of all free ⁹⁰Y in bone, a dose to red marrow of 132.3 mGy was calculated by Organ Level INternal Dose Assessment/EXponential Modeling.ConclusionsBlood sampling after radioembolization allowed for estimation of the time–activity curve and BR. Delivery with 50% contrast agent in saline solution resulted in a significant increase in BR vs D5W, even though the total BR for both groups was nominal.