One year of experience with alanine dosimetry in radiotherapy

Commercially available alanine dosimeters from different manufacturers were purchased for this study. The response of the detectors was evaluated with ⁶⁰Co gamma radiation in the dose range 0.2–200 Gy, using a small EPR spectrometer dedicated to dosimetry. The batch sensitivity, inter-specimen scattering and background signal for the different selection of dosimeters were evaluated. The usefulness of the alanine dosimetry system for clinical routine is illustrated by in vivo measurements during ¹⁹²Ir brachytherapy of cervix carcinoma.     

Application of an alanine dosimetry system for industrial irradiation and radiation protection

This paper reports the application of alanine dosimetry in radiation processing. Continuous checks of the EPR measuring conditions as well as using high-quality alanine dosimeters and consistent technique for dose determination guarantee an accuracy of about ±3% intermediate dose levels. The alanine dosimetry system was applied for dose mapping measurements during irradiator qualification and performance qualification of different products, routine dosimetry, and special radiation protection application within the gamma irradiator.     

K-band EPR dosimetry: small-field beam profile determination with miniature alanine dosimeter.

The use of small-size alanine dosimeters presents a challenge because the signal intensity is less than the spectrometer sensitivity. K-band (24 GHz) EPR spectrometer seems to be a good compromise between size and sensitivity of the sample. Miniature alanine pellets were evaluated for small-field radiation dosimetry. Dosimeters of DL-alanine/PVC with dimensions of 1.5 mm diameter and 2.5 mm length with 5 mg mass were developed. These dosimeters were irradiated with 10 MV X-rays in the dose range 0.05-60 Gy and the first harmonic (1h) spectra were recorded. Microwave power, frequency and amplitude of modulation were optimized to obtain the best signal-to-noise ratio (S/N). For beam profile determination, a group of 25 dosimeters were placed in an acrylic device with dimensions of (7.5 x 2.5 x 1)cm3 and irradiated with a (3 x 3)cm2 10 MV X-rays beam field size. The dose at the central region of the beam was 20 Gy at a depth of 2.2 cm (build up for acrylic). The acrylic device was oriented perpendicular to the beam axis and to the gantry rotation axis. For the purposes of comparison of the spatial resolution, the beam profile was also determined with a radiographic film and 2 mm aperture optical densitometer; in this case the dose was 1 cGy. The results showed a similar spatial resolution for both types of dosimeters. The dispersion in dose reading was larger for alanine in comparison with the film, but alanine dosimeters can be read faster and more directly than film over a wide dose range.     

Numerical signal treatment for optimized alanine/ESR dosimetry in the therapy-level dose range

Electron spin resonance (ESR) spectra of alanine detectors irradiated to absorbed doses below 5 Gy are affected by a varying non-linear background which mainly influences the lower limit of detection in alanine/ESR dosimetry. A mathematical method based on fast Fourier transform is described capable of filtering simultaneously background and noise in the frequency domain of ESR spectra. It provides clearer alanine/ESR signals down to 50 mGy. Even in non-irradiated but long-term stored alanine detectors an ESR signal could be observed similar to irradiated alanine (pre-signal). A linear ESR signal vs absorbed dose relationship was found above 200 mGy, after correction for background and pre-signal. The number of repeated ESR read-out cycles and hence the time required for a precise and reliable low-dose evaluation have significantly been reduced. The method has been worked out for the therapy-level dosimetry range and tested on a Bruker ESP 300 and for comparison Bruker EMS 104 ESR spectrometer.     

An automated system for the measurement of alanine/EPR dosimeters

NPL for several years has offered mailed reference dosimetry services based on alanine/EPR dosimeters, both at industrial and therapy dose levels. Compared to other methods of reference dosimetry, operator involvement in alanine/EPR has been found to be relatively high, and contributes significantly to the overall economics of the process. Commercially available sample changers are not suitable for high accuracy applications, and it has proved necessary to develop a dedicated automation system to handle NPL alanine dosimeter pellets. In this paper we describe an automatic sample changer for placing and retrieving alanine pellets into and out of the cavity of a standard research grade EPR spectrometer. Up to 32 pellets can be held in each removable sample tray. The sample changer software has been interfaced into the spectrometer control software to enable complete automation of the measurement process, including the optimization of spectrometer settings and rotation of the sample within the cavity.     

Temperature stabilization of alanine dosimeters used for food processing and sterilization

The International Atomic Energy Agency has established a dose quality audit service for radiation processing facilities. The objective of the service is to provide an independent check on the routine dosimetry system in use at the facility. The audit service is based on the use of alanine EPR dosimetry. Generally, alanine dosimeters are irradiated at the facility together with a product, and the response is then analyzed at the IAEA laboratory. Practice of the audit service has shown that the main uncertainty in alanine dosimetry is due to absence of temperature control at the irradiation facilities. Here, a method for stabilizing the temperature of the dosimeter during irradiation is proposed.     

牙釉质EPR剂量测定方法的主要影响因素分析

EPR(电子顺磁共振)剂量测定方法是回顾性测定个人辐射剂量的主要方法,它能够准确估算出很久以前发生的辐射照射事件的吸收剂量值,其理论基础是在牙釉质中,辐射所致自由基水平随着辐射剂量的增加而增加。目前,将EPR方法用于低剂量测定还存在一些困难,为了降低测量阈值,减小误差,优化方法,需要进一步研究该方法的影响因素。本文重点分析了影响牙釉质EPR剂量方法测量阈值和测量结果不确定度的主要因素,并对解决这些问题的修正方法进行了讨论。     

The extension of the range of NIM alanine/ESR dosimetric system to therapy level

The NIM alanine/ESR dosimetric system, which was designed for industrial radiation processing, has been improved to be suited for applications in therapy dose range. Two different procedures of dose intercomparisons between IAEA and NIM were carried out with the improved system in the range of 2.5 to 100 Gy. In the first procedure, a set of NIM alanine dosimeters were irradiated at IAEA dosimetric laboratory and part of dosimeters marked “for evaluated” were evaluated using the rest of those with “known dose” given by IAEA. Most of evaluated doses agreed with IAEA doses within 1%. In the second procedure, all above dosimeters were evaluated on the base of NIM dosimetry. The results indicated that the doses determined by NIM agreed with those given by IAEA within 3% on the average.     

Use of alanine for dosimetry intercomparisons among Italian radiotherapy centers.

A pilot program of postal dosimetry intercomparison among 16 Italian Radiotherapy Centers was performed using the ISS Alanine/EPR dosimetry as a transfer system. Dosimeters were irradiated at 10 Gy with high-energy photon beams, both in reference condition in a water phantom and in an anthropomorphic phantom during the simulated treatment of rectum cancer. Intercomparison design along with alanine performances analyzing the different contributions to the combined uncertainty in dose assessment are reported. Main results of the pilot intercomparison, terminated in 2002, are also presented.     

Sand for high-dose dosimetry using the EPR technique.

The electronic paramagnetic resonance (EPR) technique was utilized to study sand samples from different Brazilian beaches for high-dose dosimetry. Sand also contains concentrations of heavy minerals. Sand samples were studied in relation to their main dosimetric properties: response reproducibility, reutilization, batch uniformity, detection range and dose response. The EPR signal grows significantly as a function of absorbed dose for g=1.999. All studied sand samples can be used as EPR dosimeters for different applications in medical, agricultural and industrial areas.     

Development of a secondary standard for the absorbed dose to water based on the alanine EPR dosimetry system.

The primary measurand in the dosimetry for radiation therapy is the absorbed dose to water, D(W). An alanine/EPR based secondary standard for D(W) for high-energy photon and electron radiation is presently under construction at the Physikalisch-Technische Bundesanstalt. A technique of transfer dosimetry that makes it possible to reduce the reproducibility to a level below 0.5% in the 5-50 Gy range is presented. It takes advantage of a reference sample. Results of investigations of some effects, such as environmental humidity, are presented.     

In vivo ESR dosimetry in total body irradiation

Total body irradiation (TBI) using high doses (about 10 Gy) with photons in the range between 1 and 10 MV combined with intensive chemotherapy has been used successfully in treatment of acute and chronic leukemia before bone marrow transplantation. One of the principal international guidelines in TBI is to use in vivo dosimetry in order to compare the prescribed dose with that absorbed. The use of in vivo dosimetry is also useful as a retrospective evaluation of any deviation from the prescribed dose greater than +/- 5% for relevant parts of the body, especially in the lung and in other organs at risk. In this paper, Electron Spin Resonance (ESR), using alanine dosimeters, is demonstrated to be a powerful tool for absorbed dose evaluation in TBI by detection of free radicals produced in alanine by ionizing radiation. In this study, we present the results obtained using ESR dosimetry in eleven patients undergoing TBI. The major advantages appear to be: 1. the ESR signal in alanine dosimetry is stable for years without fading: 2. the detection of the ESR signal does not destroy the information and so enables a retrospective judgment of the TBI plan adopted.     

电子顺磁共振在体测量指甲剂量方法的可行性研究

目的 针对核应急医学救援剂量评估的需求,为解决指甲电子顺磁共振（EPR）剂量评估方法中机械诱发信号难以分离的问题,探讨指甲EPR在体测量的可行性。方法 利用自研的指甲在体EPR测量装置,对未剪碎指甲进行整体测量,在无机械诱发信号干扰的条件下研究指甲的本底信号及辐射诱发信号特性,探索通过水处理恢复本底信号的方法;开展指甲实际在体EPR测量实验,评价在体测量条件对EPR波谱的影响。结果 未剪碎指甲的本底信号分布服从正态分布,不同性别志愿者的指甲本底信号差异无统计学意义（P>0.05）;在2~10 Gy范围内建立了剂量响应关系,指甲辐射诱发信号半衰期约为5 d;建立了变温结合水处理的本底信号恢复方法,处理后指甲EPR信号与本底信号差异无统计学意义（P>0.05）;获得了实际在体测量条件下的指甲EPR波谱。结论 利用本方法可以获得不含有机械诱发信号的EPR波谱,初步验证了指甲在体EPR测量用于剂量评估的可行性。     

用电子顺磁共振波谱拟合方法估算牙釉质辐射剂量

目的 探讨运用电子顺磁共振(electron paramagnetic resonance, EPR)波谱拟合技术估算牙釉质EPR辐射剂量的准确性。方法 编制多成分叠加型EPR粉末波谱拟合软件,分别拟合牙齿本底信号(background signal,BS)和辐照诱发信号(radiation-induced signal,RS)的EPR波谱模型,用波谱模型叠加计算方法拟合出实际辐照后牙釉质的EPR波谱,从复合谱中提取出RS成分并计算其相对强度,建立剂量响应曲线,估算样品剂量,并将剂量估算结果与传统的波谱强度测量方法进行比较。结果 拟合获得的BS信号为单峰高斯线形粉末谱,g=2.0035,线宽Hpp=0.650-1.100 mT; RS信号为轴对称多晶粉末谱线形,其g_⊥=2.0018,g_‖＝1.9965,线宽Hpp=0.335-0.400 mT;分离BS与RS后得到的RS相对强度与辐照剂量呈线性相关,剂量响应方程为:y=240.74x+76 724(R²=0.9947),剂量估算结果相对误差期望值为0.13。结论 EPR波谱拟合方法在一定程度上提高了牙釉质辐射剂量估计的准确性和可信度。     

Reference dosimetry and measurement quality assurance

Measurements of absorbed dose made by a reference dosimetry system, such as alanine, have been suggested for achieving quality assurance through traceability to primary standards. Such traceability can assist users of radiation worldwide in enhancing quality control in medicine, agriculture, and industry. International and national standards of absorbed dose are still needed for applications of γ-ray and electron dosimetry at high doses (e.g. radiation therapy, food irradiation and industrial radiation processing). Reference systems, such as ferrous sulfate dosimeters measured by spectrophotometry and alanine measured by electron spin resonance spectrometry are already well established. Another useful reference system for high doses is supplied as dichromate solutions measured by spectrophotometry. Reference dosimetry, particularly for electron beams, can be accomplished with thin alanine or radiochromic dye film dosimeters.     

Electron arc therapy treatment planning verification with alanine/EPR dosimetry.

Alanine/EPR dosimetry was applied to measure dose distributions during electron arc therapy treatments generated by electron beams moving isocentrically over a stated arc. Alanine-polyethylene pellets, prepared at ISS according to the NIST recipe, inserted in a homogeneous cylindrical and anthropomorphic phantoms, were used. Preliminary, alanine response to static electron beams in the (6-20) MeV nominal energy range was studied. Then alanine dosimetry was applied to determine the dose versus the gantry angle at a reference point in a cylindrical homogeneous phantom. Finally, arc therapy treatment planning verification was performed in anthropomorphic phantom.     

Physically-based biodosimetry using in vivo EPR of teeth in patients undergoing total body irradiation

Purpose:?The ability to estimate individual exposures to radiation following a large attack or incident has been identified as a necessity for rational and effective emergency medical response. In vivo electron paramagnetic resonance (EPR) spectroscopy of tooth enamel has been developed to meet this need.

Materials and methods:?A novel transportable EPR spectrometer, developed to facilitate tooth dosimetry in an emergency response setting, was used to measure upper incisors in a model system, in unirradiated subjects, and in patients who had received total body doses of 2 Gy.

Results:?A linear dose response was observed in the model system. A statistically significant increase in the intensity of the radiation-induced EPR signal was observed in irradiated versus unirradiated subjects, with an estimated standard error of dose prediction of 0.9?±?0.3 Gy.

Conclusions:?These results demonstrate the current ability of in vivo EPR tooth dosimetry to distinguish between subjects who have not been irradiated and those who have received exposures that place them at risk for acute radiation syndrome. Procedural and technical developments to further increase the precision of dose estimation and ensure reliable operation in the emergency setting are underway. With these developments EPR tooth dosimetry is likely to be a valuable resource for triage following potential radiation exposure of a large population.     

The dose response of normoxic polymer gel dosimeters measured using X-ray CT

X-ray CT was used to determine the dose response of normoxic polymer gel dosimeters. Normoxic polymer gel dosimeters were manufactured and irradiated up to 150 Gy. Up to 50 CT images were acquired on a Toshiba Aquilion Multislice CT scanner using protocols for 80 kV and 135 kV to determine dose response. HU-dose sensitivity, the linear regression of data for the HU versus dose for the linear part of the curve up to 60 Gy was 0.38+/-0.07 HU Gy(-1) for 135 kV and 0.37+/-0.01 HU Gy(-1) for 80 kV. Dose resolution was found to be < 1.3 Gy for an absorbed dose range up to 70 Gy for 135 kV, similar to that measured previously for polyacrylamide gel (PAG). Although the HU-dose sensitivity was lower than that previously measured for PAG gel dosimeters it had a greater range of absorbed dose indicating that normoxic polymer gel dosimeters have potential in CT gel dosimetry.     

A study of the composite character of the ESR spectrum of alanine

Both L and DL-alanine ESR powder spectra have been studied in the dose range of 1–10⁶ Gy. By using Maximum Likelihood Common Factor Analysis (MLCFA), it has been demonstrated that the ESR spectrum of L-alanine is at least 3-fold composite over the whole dose range considered. For DL-alanine, in certain dose ranges only two ESR components could be detected. Possible consequences for the application and optimization of alanine dosimetry are discussed.     

A unique calibration curve for alanine EPR dosimetry systems

The alanine EPR dose-response curve was proposed to follow a saturating exponential function. In this study the characteristic parameter D₃₇3of the exponential function was estimated for two types of dosimeters and different EPR spectrometer configurations. The results suggest that only below about 0.3 mW the alanine EPR signal is not saturated with microwave power. A unique alanine calibration curve is suggested for measurements with non-saturating microwave power.