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.     

Phase I/II 90Y-Zevalin (yttrium-90 ibritumomab tiuxetan, IDEC-Y2B8) radioimmunotherapy dosimetry results in relapsed or refractory non-Hodgkin’s lymphoma

Dosimetry studies in patients with non-Hodgkin’s lymphoma were performed to estimate the radiation absorbed dose to normal organs and bone marrow from ⁹⁰Y-Zevalin (yttrium-90 ibritumomab tiuxetan, IDEC-Y2B8) treatment in this phase I/II, multicenter trial. The trial was designed to determine the dose of Rituximab (chimeric anti-CD20, Rituxan, IDEC-C2B8, MabThera), the unlabeled antibody given prior to the radioconjugate to clear peripheral blood B cells and optimize distribution, and to determine the maximum tolerated dose of ⁹⁰Y-Zevalin [7.4, 11, or 15 MBq/kg (0.2, 0.3, or 0.4 mCi/kg)]. Patients received ¹¹¹In-Zevalin (indium-111 ibritumomab tiuxetan, IDEC-In2B8 ) on day 0 followed by a therapeutic dose of ⁹⁰Y-Zevalin on day 7. Both doses were preceded by an infusion of the chimeric, unlabeled antibody Rituximab. Following administration of ¹¹¹In-Zevalin, serial anterior/posterior whole-body scans were acquired. Major-organ radioactivity versus time estimates were calculated using regions of interest. Residence times were computed and entered into the MIRDOSE3 computer software program to calculate estimated radiation absorbed dose to each organ. Initial analyses of estimated radiation absorbed dose were completed at the clinical site. An additional, centralized dosimetry analysis was performed subsequently to provide a consistent analysis of data collected from the seven clinical sites. In all patients with dosimetry data (n =56), normal organ and red marrow radiation absorbed doses were estimated to be well under the protocol-defined upper limit of 20 Gy and 3 Gy, respectively. Median estimated radiation absorbed dose was 3.4 Gy to liver (range 1.2–7.8 Gy), 2.6 Gy to lungs (range 0.72–4.4 Gy), and 0.38 Gy to kidneys (range 0.07–0.61 Gy). Median estimated tumor radiation absorbed dose was 17 Gy (range 5.8–67 Gy). No correlation was noted between hematologic toxicity and the following variables: red marrow radiation absorbed dose, blood T _1/2, blood AUC, plasma T _1/2, and plasma AUC. It is concluded that ⁹⁰Y-Zevalin administered at nonmyeloablative maximum tolerated doses results in acceptable radiation absorbed doses to normal organs. The only toxicity of note is hematologic and is not correlated to red marrow radiation absorbed dose estimates or T _1/2, reflecting that hematologic toxicity is dependent on bone marrow reserve in this heavily pretreated population. Received 24 January and in revised form 20 March 2000     

ESR and TL dosimetry systems: comparative measurements for human phantom

Mixtures of small fragments on tooth enamel as well as thermoluminescence (TL) dosimeters were placed into the tissue-equivalent phantom of the human head with skeleton (approximately at the level of the jaws) and irradiated using ¹³⁷Cs low dose-rate gamma therapeutic sources (‘SELEKTRON’ LDR ¹³⁷Cs). Phantom, samples of teeth and TL detectors were irradiated behind water tank to produce scattered irradiation. The same irradiation with the same geometry was performed in air too. For gamma-spectrometry ¹³⁷Cs sources with very low activity were used but with the same geometry as therapeutic sources. The absorbed dose in enamel was estimated with the help of ESR spectrometer ‘ESP-300 E’ (Brucker). The samples of tooth enamel were partially used for preliminary dose evaluation by ESR signal before starting of experiment. TL dosimetry was performed by TL reader model 8800 (HARSHAW) using TL dosimeters calibrated with ¹³⁷Cs. The paper presents data obtained in comparative aspects.     

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.     

Atomic bomb and accident dosimetry with ESR: Natural rocks and human tooth in-vivo spectrometer

ESR dosimetry of some construction materials at Hiroshima and Nagasaki was carried out to determine the A-bomb radiation dose. Some minerals exposed to low-level natural radiation over a given geological time period can be also used to determine the intense A-bomb radiation dose. Finally, an ESR cavity and a special NdBFe (Neomax) magnet system for in-vivo measurement of radiation dose of a human tooth without extraction is designed and manufactured.     

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.     

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.     

山羊牙釉质电子自旋共振的剂量学特性

目的 探讨山羊牙釉质电子自旋共振(ESR)的剂量学的特性.方法 采用机械和化学处理相结合的方法,制备5组不同年龄的山羊牙釉质样品.用137 Cs γ射线照射山羊牙釉质样品,使用ESR波谱仪测量辐射前和不同辐射剂量后不同牙釉质样品的ESR信号.结果 137Cs γ射线照射前,山羊牙釉质所固有的ESR本底信号平均值为21.5,明显低于人的平均本底强度水平39.5;与人牙釉质相同,山羊牙釉质照射后产生的剂量学信号的强度与照射剂量线性相关,5组100 mg山羊牙釉质样品,其剂量学峰的辐射灵敏度的平均值为(34.3±1.9)/Gy,与人牙釉质样品的辐射响应平均值36.3/Gy非常接近.结论 人类牙釉质样品缺乏时,可以用相同辐射环境中的山羊牙釉质作为替代品进行剂量重建,为正确地评价辐射事故剂量提供科学依据.

Abstract：

Objectlve To study the properties of goat tooth enamel electron spin resonance (ESR)dosimetry.Methods Tootll enamel samples of goats were achieved by combined mechanical and chemical treatment at the ages of l,2,3,5,and 6 years.respectively and 9 enamel samples of adult molar were obtained.These enamel samples were exposed to 137Cs γ-rays at the cumulative doses of 0,0.5,1.0,2.0,and 5.0 Gy,respectively.ESR spectra Was measured before and after exposure.Results The background signal of goat tooth samples W88 21.5,significantly lower than that of the adult molar samples(39.5).The dusimetric signal intensity of the goat enamel increased with the radiation dose in a linear manner just as that of the human molars.The average radiation sensitivity of the goat tooth samples was(34.3±1.9)/Gy,close to that of the human tooth samples.Conclusions Goat teeth can be used for retrospective radiation dose reconstruction when human teeth are unavailable,in order to previde scientific data for dose reconstruction accurately.     

Lactose and “Tris” Lyoluminescence dosimetry systems and ESR correlation studies

Lyoluminescence (LL) dosimeters have been developed using lactose monohydrate (disaccharide) and tris(hydroxymethyl)aminomethane (“Tris”) systems and attempts have been made to understand the LL mechanism through ESR correlation studies. Tris LL dosimeter has a γ-ray sensitivity with a linear response in the absorbed-dose range 0.05–200 Gy (5 −2 × 10⁴ rad), while the lactose response extends to a higher range from 1 to 10⁴ Gy (10²–10⁶ rad). The LL output of lactose and Tris did not show any appreciable decay for a period of 6 months after irradiation. ESR measurements show that free-radical concentration in both the systems increases with γ-ray dose in the range 10²–10⁵ Gy. The minimum dose required to measure the radiation-induced ESR signal for Tris is ∼ 500 Gy, the dose at which the LL output saturates, while lactose shows a radiation-induced ESR signal right at the minimum dose where LL could be detected. The estimated value of free-radical concentration for lactose was 10¹⁴–10¹⁷ spins/g in the dose range 10²–10⁵ Gy, while for Tris it is 10¹⁶–10¹⁷ spins/g in the dose range 10³–10⁵ Gy. ESR spectral features of the irradiated Tris show the presence of two distinct radical species and one of these species is found to decay with time. This species has been assigned to a R-cHOH radical on the basis of a detailed single-crystal ESR study. The principal g factors of the radicals are g_x = 2.0021, _y = 2.0041, g_z = 2.0024 and the principal hyperfine couplings are found to be A_x = 15.8 G, A_y = 23.4 G and A_z = 13.8 G. The estimated spin density on the radical carbon atom is 0.7. ESR signal stabilities of lactose and Tris were also studied. Lactose did not show any appreciable ESR decay for a period of 3 months after irradiation, while, for Tris, one of the radicals showed a decay of 45% for the same period.     

Dose estimation by chromosome aberration analysis and micronucleus assays in victims accidentally exposed to 60Co radiation

The objective of this study was to assess the radiation exposure levels in victims of a ⁶⁰Co radiation accident using chromosome aberration analysis and the micronucleus assay. Peripheral blood samples were collected from three victims exposed to ⁶⁰Co 10 days after the accident and were used for the chromosome aberration and micronucleus assays. After in vitro culture of the lymphocytes, the frequencies of dicentric chromosomes and rings (dic+r) and the numbers of cytokinesis blocking micronuclei (CBMN) in the first mitotic division were determined and used to estimate radiation dosimetry. The Poisson distribution of the frequency of dic+r in lymphocytes was used to assess the uniformity of the exposure to ⁶⁰Co radiation. Based on the frequency of dic+r in lymphocytes, estimates of radiation exposure of the three victims were 5.61 Gy (A), 2.48 Gy (B) and 2.68 Gy (C). The values were estimated based on the frequencies of CBMN, which were 5.45 Gy (A), 2.78 Gy (B) and 2.84 Gy (C). The estimated radiation dosimetry demonstrated a critical role in estimating the radiation dose and facilitating an accurate clinical diagnosis. Furthermore, the frequencies of dir+r in victims A and B deviated significantly from a normal Poisson distribution. Chromosome aberration analysis offers a reliable means for estimating biological exposure to radiation. In the present study, the micronucleus assay demonstrated a high correlation with the chromosome aberration analysis in determining the radiation dosimetry 10 days after radiation exposure.As early as the mid-1960s, ionising radiation was known to be capable of inducing chromosome aberrations in the metaphase of human peripheral lymphocytes [1, 2]. Since then, the chromosome aberration assay has been widely used as a sensitive biomarker for dose reconstruction following radiation exposure [3–6]. In particular, the analysis of dicentric chromosomes and rings (dic+r), two aberrations exemplifying inter- and intrachromosomal exchanges, respectively, has been generally considered to be the standard means for estimating biodosimetry based on its well-established dose–response relationship with radiation exposure and its low baseline levels in the general population [7, 8]. However, the utility of the chromosome aberration assay relies heavily on the expertise and experience of individual investigators. As an alternative method for determining radiation biodosimetry, the cytokinesis blocking micronucleus (CBMN) assay is easy to perform and less time-consuming, but its drawbacks include large individual variations in baseline values in the general population [7] and a markedly lower sensitivity when used for estimating low dose exposure compared with the chromosome aberration assay. Therefore, the micronucleus assay is widely used as a supplement to the chromosome aberration analysis [9]. In the present study, we made a comparative estimate of the radiation exposure in three victims of a ⁶⁰Co radiation accident that occurred in 1999 using dose–response curves of γ-ray-induced chromosome aberration and micronuclei, which were previously established in our laboratory. The results provide evidence of the utility of both methods in estimating biological doses of radiation exposure in humans.     

Formation and decay of the E1′ center and of its precursor

The E₁′ center has been used for ESR dating of quartz with assuming that the signal intensity increases with natural radiation dose as those of other ESR signals do. However, this simple assumption is not necessarily correct. Formation and decay of the E₁′ center are closely related with its precursor, diamagnetic oxygen vacancies. Gamma ray of large dose (>100 kGy) creates oxygen vacancies giving little dose rate effect, which, therefore, might be useful for dating of granites and high dose dosimetry.     

125I粒子治疗舌下腺恶性肿瘤的靶区剂量分布研究

目的 测量并计算¹²⁵I放射性粒子治疗舌下腺恶性肿瘤的放射剂量在口底靶区及靶区周缘黏膜、颌骨、皮肤等组织器官的分布,为临床治疗提供客观依据.方法 利用仿生物人体模型进行实验,分别使用活度为29.6、25.9 MBq/粒的¹²⁵I放射性粒子31粒,处方剂量(即周缘匹配剂量)120 Gy,模拟对单侧舌下腺恶性肿瘤进行组织间植入近距离放疗,采用热释光剂量计测量并计算口底靶区及周围组织器官的剂量值,采用辐射自显影胶片绘制剂量分布曲线.结果 靶区中心剂量达到390~500 Gy,靶区边缘剂量达到160~480 Gy,靶区边缘外1 cm剂量达到90~170 Gy.皮肤的接受剂量为25~81 Gy,下颌骨靶区外的接受剂量为7.9~67 Gy.靶区内剂量分布无明显冷区.结论 ¹²⁵I放射性粒子治疗口底区舌下腺恶性肿瘤,可以达到有效的靶区内治疗剂量分布.对周围组织的放射剂量在安全限值以下.对下颌骨的放射剂量较小,减少了放射性骨损伤的可能.     

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.     

Helical Tomotherapy-Based STAT RT: Dosimetric Evaluation for Clinical Implementation of a Rapid Radiation Palliation Program

Helical tomotherapy–based STAT radiation therapy (RT) uses an efficient software algorithm for rapid intensity-modulated treatment planning, enabling conformal radiation treatment plans to be generated on megavoltage computed tomography (MVCT) scans for CT simulation, treatment planning, and treatment delivery in one session. We compared helical tomotherapy–based STAT RT dosimetry with standard linac-based 3D conformal plans and standard helical tomotherapy–based intensity-modulated radiation therapy (IMRT) dosimetry for palliative treatments of whole brain, a central obstructive lung mass, multilevel spine disease, and a hip metastasis. Specifically, we compared the conformality, homogeneity, and dose with regional organs at risk (OARs) for each plan as an initial step in the clinical implementation of a STAT RT rapid radiation palliation program. Hypothetical planning target volumes (PTVs) were contoured on an anthropomorphic phantom in the lung, spine, brain, and hip. Treatment plans were created using three planning techniques: 3D conformal on Pinnacle³, helical tomotherapy, and helical tomotherapy–based STAT RT. Plan homogeneity, conformality, and dose to OARs were analyzed and compared. STAT RT and tomotherapy improved conformality indices for spine and lung plans (CI spine = 1.21, 1.17; CI lung = 1.20, 1.07, respectively) in comparison with standard palliative anteroposterior/posteroanterior (AP/PA) treatment plans (CI spine = 7.01, CI lung = 7.30), with better sparing of heart, esophagus, and spinal cord. For palliative whole-brain radiotherapy, STAT RT and tomotherapy reduced maximum and mean doses to the orbits and lens (maximum/mean lens dose: STAT RT = 2.94/2.65 Gy, tomotherapy = 3.13/2.80 Gy, Lateral opposed fields = 7.02/3.65 Gy), with an increased dose to the scalp (mean scalp dose: STAT RT = 16.19 Gy, tomotherapy = 15.61 Gy, lateral opposed fields = 14.01 Gy). For bony metastatic hip lesions, conformality with both tomotherapy techniques (CI = 1.01 each) is superior to AP/PA treatments (CI = 1.21), as expected. Helical tomotherapy–based STAT RT treatment planning provides clinically acceptable dosimetry, with conformality and homogeneity that is superior to standard linac-based 3D conformal planning and is only slightly inferior to standard helical tomotherapy IMRT dosimetry. STAT RT facilitates rapid treatment planning and delivery for palliative radiation of patients with metastatic disease, with relative sparing of adjacent OARs compared with standard 3D conformal plans.     

Thermoluminescence characteristics of Nd-doped SiO2 optical fibers irradiated with the 60Co gamma rays

Thermoluminescence (TL) properties (radiation sensitivity, dose response, signal fading) of Nd-doped SiO₂ optical fibers irradiated with 1.25 MeV photons to 1–50 Gy were studied. The peak of the glow curve is around 190 °C regardless of the dose. The dose response is linear up to 50 Gy. The radiation sensitivity is 219 nC mg⁻¹ Gy⁻¹. The fiber can be a potential candidate for photon radiotherapy dosimetry due to its high radiation sensitivity, linear dose response in a wide range, slow fading, and high spatial resolution due to the small size of the fiber.     

Dosimetric benefits of hemigland stereotactic body radiotherapy for prostate cancer: implications for focal therapy

Objective:

Compared with standard, whole-gland (WG) therapies for prostate cancer, focal approaches may provide equivalent oncologic outcomes with fewer adverse effects. The purpose of this study was to compare organ-at-risk (OAR) dosimetry between hemigland (HG) and WG stereotactic body radiotherapy (SBRT) plans.

Methods:

Volumetric-modulated arc radiotherapy-based SBRT plans were designed to treat the left HG, right HG and WG in eight patients, using five fractions of 8 Gy. OARs of interest included the contralateral HG, rectum, urinary bladder, urethra, penile bulb and contralateral neurovascular bundle.

Results:

Rectal V_80% (the percentage of a normal structure receiving a dose of 80%) and V_90% were significantly lower with HG plans than with WG plans (median values of 4.4 vs 2.5 cm³ and 2.1 vs 1.1 cm³, respectively, p < 0.05 by Student''s t-test). Bladder V_50% was also reduced significantly in HG plans (32.3 vs 17.4 cm³, p < 0.05), with a trend towards reduction of V_100% (3.4 vs 1.3 cm³, p = 0.09). Urethral maximum dose and mean doses to the penile bulb and contralateral neurovascular bundle were also reduced significantly (42.0 vs 39.7 Gy, p < 0.00001; 13.3 vs 9.2 Gy, p < 0.05; and 40.2 vs 19.3 Gy, p < 0.00001, respectively).

Conclusion:

Targeting an HG volume rather than a WG volume when delivering SBRT can offer statistically significant reductions for all OARs. Given the large magnitude of the reduction in dose to these OARs, it is anticipated that HG SBRT could offer a superior toxicity profile when compared with WG SBRT. This is likely to be most relevant in the context of salvaging a local failure after radiation therapy.

Advances in knowledge:

The dosimetric feasibility of HG SBRT is demonstrated. When compared with WG SBRT plans, the HG plans demonstrate statistically significant and large magnitude reduction in doses to the rectum, bladder, urethra, penile bulb and contralateral neurovascular bundle, suggesting the possibility of improved toxicity outcomes with HG SBRT. This is likely to be most relevant in the context of salvaging a local failure after radiation therapy.     

3D dosimetry in patients with early breast cancer undergoing Intraoperative Avidination for Radionuclide Therapy (IART?) combined with external beam radiation therapy

Purpose

Intraoperative Avidination for Radionuclide Therapy (IART?) is a novel targeted radionuclide therapy recently used in patients with early breast cancer. It is a radionuclide approach with ⁹⁰Y-biotin combined with external beam radiotherapy (EBRT) to release a boost of radiation in the tumour bed. Two previous clinical trials using dosimetry based on the calculation of mean absorbed dose values with the hypothesis of uniform activity distribution (MIRD 16 method) assessed the feasibility and safety of IART?. In the present retrospective study, a voxel dosimetry analysis was performed to investigate heterogeneity in distribution of the absorbed dose. The aim of this work was to compare dosimetric and radiobiological evaluations derived from average absorbed dose vs. voxel absorbed dose approaches.

Methods

We evaluated 14 patients who were injected with avidin into the tumour bed after conservative surgery and 1?day later received an intravenous injection of 3.7?GBq of ⁹⁰Y-biotin (together with 185?MBq ¹¹¹In-biotin for imaging). Sequential images were used to estimate the absorbed dose in the target region according to the standard dosimetry method (SDM) and the voxel dosimetry method (VDM). The biologically effective dose (BED) distribution was also evaluated. Dose/volume and BED volume histograms were generated to derive equivalent uniform BED (EUBED) and equivalent uniform dose (EUD) values.

Results

No “cold spots” were highlighted by voxel dosimetry. The median absorbed-dose in the target region was 20?Gy (range 15–27?Gy) by SDM, and the median EUD was 20.4?Gy (range 16.5–29.4?Gy) by the VDM; SDM and VDM estimates differed by about 6?%. The EUD/mean voxel absorbed dose ratio was >0.9 in all patients, indicative of acceptable uniformity in the target. The median BED and EUBED values were 21.8?Gy (range 15.9–29.3?Gy) and 22.8?Gy (range 17.3–31.8?Gy), respectively.

Conclusion

VDM highlighted the absence of significant heterogeneity in absorbed dose in the target. The EUD/mean absorbed dose ratio indicated a biological efficacy comparable to that of uniform distribution of absorbed dose. The VDM is recommended for improving accuracy, taking into account actual activity distribution in the target region. The radiobiological model applied allowed us to compare the effects of IART? with those of EBRT and to match the two irradiation modalities.     

Ammonium tartrate as an ESR dosimeter material

This study is one step in the search for an ESR dosimeter material with a higher signal intensity than the commonly used l-α-alanine, to be useful in the clinical dose range (approximately 0.1–20 Gy). The substance ammonium tartrate was found and investigated regarding signal intensity, radical stability, dose response and dose resolution. The ESR signal intensity of ammonium tartrate was shown to be more than twice the intensity of the alanine signal. The data indicate that an unstable radiation induced radical contributes to the ESR signal initially; after a couple of hours it has converted to a secondary radical which has a decay slow enough to be considered stable during the first two weeks after irradiation. Ammonium tartrate has a linear dose response in the investigated range of 0.5–4000 Gy and a dose resolution of 0.1 Gy at the 0.5 Gy level where, as a comparison, the corresponding value for alanine is 0.3 Gy. We thus find the substance suitable for clinical dosimetry.     

Reduction of radiation exposure by lead curtain shielding in dedicated extremity cone beam CT

Objective:

A dedicated extremity cone beam CT (CBCT) was introduced recently, and is rapidly becoming an attractive modality for extremity imaging. This study aimed to evaluate the effectiveness of a curtain-shaped lead shielding in reducing the exposure of patients to scattered radiation in dedicated extremity CBCT.

Methods:

A dedicated extremity CBCT scanner was used. The lead shielding curtain was 42 × 60 cm with 0.5-mm lead equivalent. Scattered radiation dose from CBCT was measured using thermoluminescence dosimetry chips at 20 points, at different distances and directions from the CT gantry. Two sets of scattered radiation dose measurements were performed before and after installation of curtain-shaped lead shield, and the percentage reduction in dose in air was calculated.

Results:

Mean radiation exposure dose at measured points was 34.46 ± 48.40 μGy without curtains and 9.67 ± 4.53 μGy with curtains, exhibiting 71.94% reduction (p = 0.000). The use of lead shielding curtains significantly reduced scattered radiation at 0.5, 1.0 and 1.5 m from the CT gantry, with percent reductions of 84.8%, 58.0% and 35.5%, respectively (p = 0.000, 0.000 and 0.002). The percent reduction in the diagonal (+45°, −45°) and vertical forward (0°) directions were 86.3%, 83.1% and 77.7%, respectively, and were statistically significant (p = 0.029, 0.020 and 0.041).

Conclusion:

Shielding with lead curtains suggests an easy and effective method for reducing patient exposure to radiation in extremity CBCT imaging.

Advances in knowledge:

Lead shielding curtains are an effective technique to reduce scattered radiation dose in dedicated extremity CBCT, with higher dose reduction closer to the gantry opening.Plain radiographic examinations are routinely used in initial evaluation of bony injuries, but superimposition of structures and other inherent problems associated with this technique cause misdiagnosis.¹ CT is widely used for more detailed evaluation of suspected injuries in extremities. Multidetector CT (MDCT) can provide medical practitioners with detailed morphological information on osseous and soft-tissue structures.More recently, cone beam CT (CBCT) has been introduced for extremity imaging.² This application offers an attractive alternative with high spatial resolution, which enables detailed visualization of osseous structures, easy installation owing to its smaller size, and relatively low radiation dose compared with conventional MDCT scanners.^3–7 There are an increasing number of papers reporting various clinical applications of CBCT, such as in CT angiography and in weight-bearing imaging.^8,9 Like other imaging modalities using ionizing radiation, reducing patient radiation dose is an important issue.¹⁰ Patient radiation exposure can be largely categorized into the following two categories: (1) radiation dose within the field of view (FOV) and (2) scattered radiation extending beyond the FOV area. Although radiation dose within FOV has been a major concern regarding patient dose, we cannot neglect the out-of-field radiation that can affect radiosensitive organs such as the gonads and the thyroid gland in extremities imaging.Several approaches exist for reducing scattered radiation, including decreasing the overall radiation dose by adjusting the radiation source and shielding. Decreasing radiation exposure dose within FOV results in reduced out-of-FOV radiation because scattered radiation is positively correlated to the entrance surface dose.¹¹ However, a certain amount of radiation dose is necessary within the FOV for maintaining image quality. Therefore, there are limitations on reducing the scattered radiation by adjusting the radiation source. Shielding materials can be placed between the radiation source and the areas where protection is needed for further reducing the out-of-field radiation. Various methods have been developed for reducing the scattered radiation, for example, lead apron, lead shield and radio-absorbable drape in the setting of fluoroscopy-guided procedures.^12,13 However, there are no standardized methods for reducing the scattered radiation to patients in extremity scanning using mobile dedicated extremity CBCT.Therefore, we proposed a curtain-shaped radiation-absorbing material hung at the gantry outlet. The goal of this study was to evaluate the effectiveness of curtain-shaped lead shielding technique for reducing the radiation exposure in dedicated extremity CBCT.     

Microsphere Localization and Dose Quantification Using Positron Emission Tomography/CT following Hepatic Intraarterial Radioembolization with Yttrium-90 in Patients with Advanced Hepatocellular Carcinoma

PurposeTo characterize the distribution of absorbed radiation dose after glass microsphere radioembolization for hepatocellular carcinoma (HCC) using yttrium-90 (⁹⁰Y) positron emission tomography/computed tomography (PET/CT).Materials and MethodsIn this retrospective study, 64 ⁹⁰Y PET/CT scans performed after treatment were evaluated following ⁹⁰Y glass-bead radioembolization in patients with advanced HCC. The intended dose to the target volume ranged from 83–129 Gy. Three-dimensional “dose maps” were created from reconstructed PET images using a voxel-based S-value transformation. Liver parenchyma and liver tumors were contoured on cross-sectional imaging and aligned with the created dose maps.ResultsThere were 113 tumors examined as part of 64 lobar treatments. The average tumor size was 4.8 cm ± 4.0 with an average tumor dose of 173 Gy ± 109. The average dose to the nontumor parenchyma within the target volume was 93.4 Gy ± 32.6, with on average 50% of the parenchymal voxels receiving > 79 Gy ± 23 and 10% receiving > 173 Gy ± 55. The average and median tumor-to-parenchymal weighted dose ratios were 2.2 and 1.9, respectively.ConclusionsUsing recommended dosimetry and administration techniques for lobar glass microsphere radioembolization, high doses to target tumors as well as background parenchyma were achieved on average with modest preferential uptake within tumors. There was wide variation in measured tumor and parenchymal doses after hepatic radioembolization for HCC, suggesting the need for continued development of patient-specific dosimetry.