医用加速器水吸收剂量测量研究及国际比对

介绍了量热法测量水吸收剂量的方法,着重论述了石墨量热计和水量热计的绝对测量过程和核心装置,讨论了主要发达国家的量热计装置和当前的不确定度水平。给出了各国计量实验室的医用加速器辐射质参数,申报国际计量局校准测量能力情况,以及加速器水吸收剂量国际比对进展和最新结果。     

60Co γ辐射空气比释动能基准的研究进展和相关国际比对

60Coγ辐射空气比释动能基准是医用加速器光子水吸收剂量的重要溯源基准之一.近三年来,中国计量科学研究院(NIM)先后就60Co γ辐射空气比释动能参加了国际原子能机构(IAEA)的国际比对,以及国际计量局(BIPM)组织的新一轮的关键比对,最新的关键比对数据库(KCDB)结果表明,NIM的比对结果与国际计量研究机构及地区基准实验室的结果之间的一致性较好.     

水量热法加速器光子水吸收剂量绝对测量与国际比对

为实现加速器光子水吸收剂量绝对测量,研制了水量热计系统,在此基础上取得国际互认并建立加速器光子水吸收剂量基准,进一步提高了我国放疗剂量量值传递能力。通过水浴与半导体制冷系统二级控温,将量热计水模体的温度漂移控制在0.5μ℃/s。利用惠斯通交流电桥测量辐射所致的热敏探针阻值变化,逐次校准热敏探针和交流电桥,实现了医用加速器光子水吸收剂量的绝对测量,合成标准不确定度为0.30%。参加了国际计量局加速器光子水吸收剂量关键比对,复现的6MV和10MV光子水吸收剂量值与比对参考值之比分别为0.9917和0.9949,在不确定度允许的范围内一致。     

医用加速器光子水吸收剂量量值体系的研究与应用

研制石墨空腔电离室,搭建电离电流测量系统,复现Co-60γ射线水吸收剂量(u=0.37%),参加国际比对取得等效互认,建立了国家基准;研制开放式量热芯,搭建惠斯登交流电桥,通过H_2/N_2饱和水体系和热损定量评估,复现加速器光子水吸收剂量(u=0.35%@10MV),并参加国际比对取得等效互认。建立了我国医用加速器光子水吸收剂量量值体系,并实现了临床放疗剂量的量值溯源。     

医用加速器高能光子束水吸收剂量测量及不确定度分析

针对电离室的⁶⁰Co水吸收剂量校准因子使用中存在的问题,对NIM在⁶⁰Co辐射场下校准电离室的水吸收剂量进行了研究。针对校准电离室和校准医用加速器时所考虑修正项的差异,对各修正项进行分析。通过不确定度分析得出⁶⁰Co辐射场下校准电离室的不确定度为0.71%,传递到加速器高能光子束下水吸收剂量的不确定度为1.30%。最后,给出医用加速器高能光子束水吸收剂量校准时的建议和注意事项。     

医用电子束水吸收剂量测量及其不确定度讨论北大核心CSCD

目前医用电子束水吸收剂量测量不确定度超过3%,很难满足临床治疗和医用电子加速器辐射源检定规程的要求。中国计量科学研究院采用水量热法开展了电子束辐射剂量学的研究,实现了电子束水吸收剂量绝对测量相对标准不确定度为0.35%,同时也开展了医用电子束的同质溯源工作,总结了电子束水吸收剂量测量的5个方案,相对标准不确定度包含最高的3.7%和最低的1.4%。为方便临床电子束水吸收剂量测量,给出了电离室剂量计选取、送检和使用不同校准系数的注意事项。     

基于医用电子直线加速器的参考辐射装置的初步设计

作为参考辐射的医用电子直线加速器,其实验场地要求、技术指标、验收方法和配套设备不同于商用加速器.在参考医用电子直线加速器的IEC和国家标准基础上,结合水吸收剂量基准和量传的要求,完成了参考辐射装置的方案设计,并提出了专门的技术要求和验收方法.     

~(60)Coγ辐射的空气比释动能及水吸收剂量的NIM-IAEA双边比对

在中国计量科学研究院(NIM)~(60)Coγ基准实验室,将~(60)Coγ辐射的空气比释动能及水吸收剂量基准值传递到国际原子能机构(IAEA)的FC65-G-2869电离室,给出了此电离室的~(60)Coγ辐射的空气比释动能和水吸收剂量的校准因子,并且比较了这2个物理量的校准因子与IAEA提供的相关结果的差异。实验结果表明,NIM给出的FC65-G-2869电离室的~(60)Coγ辐射的空气比释动能和水吸收剂量的校准因子相对IAEA提供的结果分别偏差0.5%和0.1%,比对结果达到了相关要求。为NIM参与国际计量局(BIPM)组织的正在进行中的一轮~(60)Coγ辐射的空气比释动能及水吸收剂量的关键比对作了前期准备。     

高能X射线下水等效材料对水的等效性研究

针对水等效材料校准医用加速器中存在的问题,通过对比法测量水体模和3种水等效材料校准医用加速器的剂量学差异,分别给出PTW 30013和IBA FC65-G两种类型探测器在校准深度为5 cm和10 cm的修正因子。针对加速器日稳定性校准的必要性,通过近7个月的日稳定性测量结果,给出加速器漂移量和引起漂移的可能原因;针对水等效材料在相对测量中对水的等效性,通过测量12个辐射野的输出因子,得出水等效材料在相对测量中与水一致。最后给出水等效材料在高能X射线下水吸收剂量校准时的建议和注意事项。     

中能X射线水吸收剂量量值复现方法研究北大核心CSCD

中能X射线应用于癌症的辐射诊断和深、浅层肿瘤的治疗,而X射线沉积在人体内的辐射剂量用水吸收剂量表征。现有的中能X射线水吸收剂量的测量方法有量热法、电离法和化学剂量法,水量热法是通过测量某种辐射射束在水中的能量沉积引起的温升来确定其水吸收剂量。为了测量中能X射线水吸收剂量,建立了100~220kV下的5个治疗水平X射线辐射质,用空腔圆柱型水量热计直接测量了各辐射质下的水吸收剂量。初步实现了中能X射线水吸收剂量的量值复现,为建立中能X射线水吸收剂量基准或标准装置提供了基础。     

Photon beam audits for radiation therapy clinics: a pilot mailed dosemeter study in Turkey

A thermoluminescent dosemeter (TLD) mailed dose audit programme was performed at five radiotherapy clinics in Turkey. The intercomparison was organised by the University of Wisconsin Radiation Calibration Laboratory (UWRCL), which was responsible for the technical aspects of the study including reference irradiations, distribution, collection and evaluation. The purpose of these audits was to perform an independent dosimetry check of the radiation beams using TLDs sent by mail. Acrylic holders, each with five TLD chips inside and instructions for their irradiation to specified absorbed dose to water of 2 Gy, were mailed to all participating clinics. TLD irradiations were performed with a 6 MV linear accelerator and (60)Co photon beams. The deviations from the TL readings of UWRCL were calculated. Discrepancies inside the limits of ±5 % between the participant-stated dose, and the TLD-measured dose were considered acceptable. One out of 10 beams checked was outside this limit, with a difference of 5.8 %.     

Studies on the response of the TLD badge for high-energy photons

Absorbed tissue dose measurements are carried out for high-energy photon beams using CaSO4:Dy thermo-luminescence dosemeter (TLD) badge and the results are also verified using ionisation chamber used in radiation therapy. The photon beams generated using linear accelerator at 6 and 18 MV photon beam energies have been used and the absorbed doses are measured at the surface as well as at various depths. It has been found that the depth at which maximum dose is delivered increases with the increase in photon energy and the depth of maximum absorbed dose in tissue occurs beyond 10 mm. It has also been found that the evaluation of the absorbed dose (or Hp(10) as well) using thermoluminescence readout of disc D1 clearly shows that the current TLD badge provides a reasonable estimate of the effective dose for photon fields from 6 to 18 MV linacs for anterior-posterior incidence. The paper also provides information regarding the misinterpretation of radiation pattern in multi-element/filter TLD badge.     

加速器辐射质测量方法的比较分析

针对加速器高能光子辐射质的不同测量方法,在剂量比(D20/D10)通过公式计算法和组织模体比(TPR20,10)直接实验法的基础上,提出了定剂量率和定剂量的测量方法.在中国计量科学研究院加速器实验室分别对6 MV、10 MV、25 MV光子的辐射质进行测量.实验结果表明:在测量加速器辐射质时,采用定剂量法比定剂量率法不确定度明显变小;采用定剂量法时,6 MV、10 MV、25 MV采用公式法计算的值比实际测量值分别偏小0.27％、0.31％、0.35％,采用剂量率法进行修正后和此结果一致.     

A measuring system with a recombination chamber for neutron dosimetry around medical accelerators

A measuring system for dosimetry of neutrons generated around medical electron accelerators is proposed. The system consists of an in-phantom tissue-equivalent recombination chamber and associated electronics for automated control and data acquisition. A second ionization chamber serves as a monitor of photon radiation. Two quantities are determined by the recombination chamber--the total absorbed dose and the recombination index of radiation quality. The ambient dose equivalent, H*(10), or neutron absorbed dose in an appropriate phantom, can be then derived from the measured values. Tests of the system showed that a 0.5% dose contribution of neutrons to the absorbed dose of photons could be detected and estimated under laboratory conditions. Preliminary tests at the 15 MV Varian Clinac 2300C/D medical accelerator confirmed that the measuring system could be used under clinical conditions. The H*(10) of the mixed radiation was determined with an accuracy of approximately 10%.     

用于放疗量传的照射量、空气比释动能和水吸收剂量量值体系比较

用照射量和空气比释动能校准的电离室进行剂量测量时,依据IAEA TRS 277报告,需要经历四级量值转换过程,不确定度也较大,但目前仍是国内使用的量值体系.我国正在建立60Co γ射线以及高能光子下的水吸收剂量基准装置并进行国际比对,之后将拥有水吸收剂量的量值复现的能力.在60Co γ射线参考辐射场和加速器高能X射线辐射场下,使用NE2571和NE2570/1A、PTW TW30013和PTW UNIDOS两套电离室剂量仪,分别按照277和398报告的要求计算并比较2种方法计算出的水吸收剂量值,从而验证了277报告和398报告的一致性.     

Multichannel dosemeter and Al2O3:C optically stimulated luminescence fibre sensors for use in radiation therapy: evaluation with electron beams

This article proposes an innovative multichannel optically stimulated luminescence (OSL) dosemeter for on-line in vivo dose verification in radiation therapy. OSL fibre sensors incorporating small Al(2)O(3):C fibre crystals (TLD(500)) have been tested with an X-ray generator. A reproducible readout procedure should reduce the fading-induced uncertainty ( approximately - 1% per decade). OSL readouts are temperature-dependent [ approximately 0.3% K(-1) when OSL stimulation is performed at the same temperature as irradiation; approximately 0.16% K(-1) after thermalisation (20 degrees C)]. Sensor calibration and depth-dose measurements with electron beams have been performed with a Saturne 43 linear accelerator in reference conditions at CEA-LNHB (ionising radiation reference laboratory in France). Predosed OSL sensors show a good repeatability in multichannel operation and independence versus electron energy in the range (9, 18 MeV). The difference between absorbed doses measured by OSL and an ionisation chamber were within +/-0.9% (for a dose of about 1 Gy) despite a sublinear calibration curve.     

Experimental simulation of A-bomb gamma ray spectra: revisited

It has been reported recently that the A-bomb gamma ray spectra received by the colon of the average Japanese survivor of Hiroshima and Nagasaki may be experimentally simulated using a hospital-based Philips SL15 linear accelerator. The simulated A-bomb gamma radiation may be used in radiobiology experiments to determine, amongst other things, the biological effectiveness of the A-bomb gamma radiation. However, in that study, the electron beams from the linear accelerator were poorly defined and photon contamination was ignored. In the study reported here, a Varian Clinac 2100C linear accelerator has been used for the same purpose but with photon contamination included in better defined output electron beams. It is found that the A-bomb gamma radiation can still be matched to an acceptable degree (<10%). The cause of the slightly poorer fit was due mainly to the different ranges of energies available from the linear accelerators used. The absorbed dose received by model breasts was also estimated in this study for the same situations as in the previous study. The ratio of the breast to colon doses was found to be only (3.9 +/- 4.0)% low compared with the expected values of 1.17 and 1.16 for Hiroshima and Nagasaki, respectively. These results provide further confirmation of the acceptability of the simple cylindrically symmetrical body models employed in these studies to represent the average Japanese survivor.