Organ and effective dose reduction in adult chest CT using abdominal lead shielding

Objectives

The purpose of this study was to evaluate and compare organ and effective dose savings that could be achieved using conventional lead aprons and a new, custom-designed shield as out-of-plane shielding devices during chest CT scans.

Methods

Thermoluminescent dosimeters were used to measure doses throughout the abdomen and pelvis during CT scans of the chest of a RANDO phantom. Dose measurements were made with no shielding, with lead aprons and with the new shield around the abdomen and pelvis in order to quantify the achievable organ and effective dose reductions.

Results

Average dose savings in the 10 phantom sections ranged from 5% to 78% with the highest point dose saving of 93% being found in the mid-pelvis. When shielding was used, the maximum measured organ dose reduction was a 72% dose saving to the testes. Significant dose savings were found throughout the abdomen and pelvis, which contributed to an effective dose saving of 4% that was achieved over and above the dose savings obtained through conventional optimisation strategies. This could yield significant population dose savings and reductions in collective radiation risk.

Conclusion

In this study significant organ and effective dose reductions have been achieved through the use of abdominal shielding during chest CT examinations and it is therefore recommended that out-of-plane patient shielding devices should be used for all chest CT scans and potentially for every CT scan, irrespective of body part.Good radiographic practice aims to ensure that patient radiation dose from any examination is kept as low as reasonably practicable (ALARP) [1] as long as the image quality is consistent with the intended purpose of the examination. There are many steps that can be taken in order to reduce the radiation dose on a patient-by-patient basis. One such method is to place radiation-absorbing material, usually in the form of lead rubber shielding, onto the patient surface, outside of the anatomy of interest. Shielding in this manner has been used in dental and conventional radiology as well as fluoroscopy and has been shown to yield significant dose savings [2-7]. This technique, referred to as “out-of-plane” shielding, has also been advocated in CT for protection of the breast and thyroid [8-12]. However, the main use of such shielding has been in protecting the foetus of pregnant patients undergoing head, neck, chest or extremity CT scans. There has been uncertainty whether or not such shielding results in a decrease or increase in the foetal radiation dose due to the potential for increased internal scatter from the shields. Hidajat et al [10] reported no reduction in the dose to the uterus and ovaries when a thin lead shield was used during a scan of the upper abdomen. This, along with further anecdotal evidence, has caused debate over the effectiveness of out-of-plane shielding in CT.In recent years a number of papers have shown that abdominal shielding yields foetal dose reductions of approximately 35% in both early and late stage pregnancy when patients undergo chest CT [13-15]. Despite this evidence, out-of-plane shielding has not been used regularly in CT scanning even though the use of such shielding has no effect on the quality of the images produced.Recent publications have brought the issue of radiation dose in CT to the forefront of thinking in the radiology community. In late 2009 Smith-Bindman et al [16] showed that for each examination type there was an average 13-fold variation between the highest and lowest radiation doses from standard CT scans in four hospitals in the San Francisco Bay Area, CA. Further analysis showed that the risk of cancer induction from CT scans was highest for coronary angiography scans of 20-year-old women where 1 cancer could potentially be induced per 150 patient examinations.Concern was also expressed following the publication of Berrington de Gonzalez et al [17], who sought to quantify the number of cases of cancer that could be attributed to CT scanning in the United States during 2007. It was estimated that 29 000 cancers could be related to CT scans of which 14 000 resulted from abdomen/pelvis scans, 4100 resulted from chest scans, 4000 resulted from head CT and a further 2700 from chest CT angiography. Given the rapid development in scanning technology it is likely that the number of scans performed in 2008 and 2009 is higher than the reported figures of 70 million CT scans for 2007 and, as such, the number of cancers induced could be greater than the 29 000 figure for 2007.The advent of multislice CT (MSCT) has increased the range of examinations that can be performed, and as such Fazer et al [18] now estimate that in the United States approximately 50% of the collective effective dose resulting from medical procedures is attributable to CT scanning. Similarly in the UK approximately 47% of the collective dose from medical procedures is attributable to CT scanning [19].     

Dose reduction in maxillofacial imaging using low dose Cone Beam CT

Objectives(a) To measure the absorbed dose at certain anatomical sites of a RANDO phantom and to estimate the effective dose in radiographic imaging of the jaws using low dose Cone Beam computed tomography (CBCT) and (b) to compare the absorbed and the effective doses between thyroid and cervical spine shielding and non-shielding techniques.Study designThermoluminescent dosimeters (TLD-100) were placed at 14 sites in a RANDO phantom, using a Cone Beam CT device (Newtom, Model QR-DVT 9000, Verona, Italy). Dosimetry was carried out applying two techniques: in the first, there was no shielding device used while in the second one, a shielding device (EUREKA!, TRIX) was applied for protection of the thyroid gland and the cervical spine. Effective dose was estimated according to ICRP₆₀ report (E_ICRP). An additional estimation of the effective dose was accomplished including the doses of the salivary glands (E_SAL). A Wilcoxon Signed Ranks Test was used for statistical analysis.ResultsIn the non-shielding technique the absorbed doses ranged from 0.16 to 1.67 mGy, while 0.32 and 1.28 mGy were the doses to the thyroid and the cervical spine, respectively. The effective dose, E_ICRP, was 0.035 mSv and the E_SAL was 0.064 mSv. In the shielding technique, the absorbed doses ranged from 0.09 to 1.64 mGy, while 0.18 and 0.95 mGy were the respective values for the thyroid and the cervical spine. The effective dose, E_ICRP, was 0.023 mSv and E_SAL was 0.052 mSv.ConclusionsThe use of CBCT for maxillofacial imaging results in a reduced absorbed and effective dose. The use of lead shielding leads to a further reduction of the absorbed doses of thyroid and cervical spine, as well as the effective dose.     

Entrance skin dosimetry and size-specific dose estimate from pediatric chest CTA

BackgroundSize-specific dose estimate (SSDE), which corrects CT dose index (CTDI) for body diameter and is a better measure of organ dose than is CTDI, has not yet been validated in vivo.ObjectiveThe purpose was to determine the correlation between SSDE and measured breast entrance skin dose (ESD) for pediatric chest CT angiography across a variety of techniques, scanner models, and patient sizes.MethodsDuring 42 examinations done on 4 different scanners over 7 years, we measured mid-sternal ESD as an approximation of breast dose with skin dosimeters. We recorded age, weight, effective tube current, kilovoltage potential, console CTDI, and dose-length product, from which we calculated effective dose. We measured effective chest diameter to convert CTDI to SSDE, and we correlated SSDE with measured ESD, using linear regression. We evaluated image quality to answer the clinical question.ResultsPatient mean (±SD) age was 8.4 ± 6.1 years (median, 7.9 years; range, 0.02–19.5 years); mean weight was 35 ± 27 kg (median, 26 kg; range, 3.5–115 kg); effective chest diameter was 20 ± 7 cm (median, 19 cm; range, 10–35 cm). Mean effective dose was 2.9 ± 2.8 mSv (median, 2.2 mSv; range, 0.1–14.4 mSv). We observed a linear correlation (R² = 0.98, P < .005) between SSDE (mean, 11 ± 11mGy; median, 7 mGy; range, 0.5–40 mGy) and breast ESD (mean, 12 ± 11 mGy; median, 7 mGy; range, 0.3–44 mGy). Our doses, which compared favorably with those previously reported, decreased significantly (P < .05) during the course of our study, because of the introduction of automatic exposure control, low kilovoltage, and high pitch techniques. All studies were of diagnostic quality.ConclusionSSDE is a valid dose measure in children undergoing chest CT angiography over a wide range of scanner platforms, techniques, and patient sizes, and it may be used to model breast dose and to document the results of dose reduction strategies.     

CT扫描所致受检者器官剂量的体模实验研究

目的 了解不同部位X射线CT扫描所致受检者器官或组织的吸收剂量及其分布。方法 实测体模中重要组织器官的CT值,并转换成线性吸收系数与人体正常值进行比较;在体模中 布放光致辐射发光玻璃剂量计,分别模拟测量头部、胸部、腹部和盆腔CT扫描所致受检者主要器官或组织的吸收剂量。结果 实验用仿真人体模具有良好的组织等效性。头部扫描吸收剂量最大的器官是大脑,胸部扫描吸收剂量较大的器官是甲状腺、乳腺、肺和食道,腹部扫描吸收剂量较大的器官是肝、胃、结肠和肺,单次盆腔扫描体所致骨表面和结肠的吸收剂量可达50 mGy以上。结论 X射线CT扫描所致受检者的器官剂量及其分布随扫描部位的不同而异。盆腔扫描时结肠、红骨髓、性腺和膀胱等主要器官的吸收剂量较大,应引起注意。     

Radiation dose differences between thoracic radiotherapy planning CT and thoracic diagnostic CT scans

PurposeTo compare the absorbed dose from computed tomography (CT) in radiotherapy planning (RP-CT) against those from diagnostic CT (DG-CT) examinations and to explore the possible reasons for any dose differences.MethodTwo groups of patients underwent CT-scans of the thorax with either DG-CT (n = 55) or RP-CT (n = 55). Patients from each group had similar weight and body mass index (BMI) and were divided into low (<25) and high BMI (>25). Parameters including CTDIvol, DLP and scan-length were compared.ResultsThe mean CTDIvol and DLP values from RP-CT (38.1 mGy, 1472 mGy cm) are approximately four times higher than for DG-CT (9.63 mGy, 376.5 mGy cm). For low BMI group, the CTDIvol in the RP-CT scans (36.4 mGy) is 6.3 times higher than the one in the DG-CT scans (5.8 mGy). For the high BMI group, the CTDIvol in the RP-CT (39.6 mGy) is 2.5 times higher than the one in the DG-CT scans (15.8 mGy). In the DG-CT scans a strong negative linear correlation between noise index (NI) and mean CTDIvol was observed (r = −0.954, p = 0.004); the higher NI, the lower CTDIvol. This was not the case in the RP-CT scans.ConclusionThe absorbed radiation dose is significantly higher and less BMI dependent for RP-CT scans compared to DG-CT. Image quality requirements of the examinations should be researched to ensure that radiation doses are not unnecessarily high.     

The effect of different exposure parameters on radiation dose in digital mammography and digital breast tomosynthesis: A phantom study

IntroductionThere are concerns regarding the increase in radiation dose among women undergoing both digital mammography (DM) and digital breast tomosynthesis (DBT). The aim of this study was to evaluate the effect of different exposure parameters on entrance skin dose (ESD) and average glandular dose (AGD) for DM and DBT using a phantom.MethodsThe ESD and AGD of 30 DM and DBT (cranio-caudal projection) examinations using a tissue equivalent phantom where acquired using a GE Senographe Essential DM unit. Commercial phantoms were used to simulate three different breast thicknesses and compositions. Tube potential, tube load, and target/filter combinations were also varied with ESD and AGD recorded directly from the DM unit. Comparisons were made using the non-parametric Kruskal Wallis, Mann–Whitney, and Wilcoxon signed rank tests.ResultsThe individual ESD values for 4 cm, 5 cm, and 6 cm thick phantoms for DM and DBT at Rh/Rh target/filter combination and 30–32 kV/56 mAs levels were 5.06 and 4.18 mGy; 5.82 and 5.08 mGy; and 7.26 and 11.4 mGy, respectively; while AGDs were 1.57 and 1.30 mGy, 1.33 and 1.39 mGy; and 1.29 and 3.60 mGy, respectively. The Kruskal–Wallis test showed a statistically significant difference in AGD for DM (P = .029) but not for DBT (P = 0.368). The Mann–Whitney and Wilcoxon signed rank tests showed no statistically significant difference for ESD or AGD between both DM and DBT techniques (P = .827 and .513). The percentage differences in ESD for phantom thicknesses of 4 cm, 5 cm, and 6 cm between DBT and DM ranged between −21% and 36%; while for AGD between −21% and 64.2%.ConclusionsThe ESD and AGD for single view projection in DM and DBT showed differences at 4 and 6 cm breast thicknesses and compositions but not at 5 cm thickness with 30–32 kV and a Rh/Rh target/filter combination.Implications for practiceA fibro-fatty breast results in less radiation dose variations in terms of ESD and AGD between DM and DBT techniques.     

Patient dose increase caused by posteroanterior CT localizer radiographs

IntroductionThe aim of this study was to compare the output dose (volume CT dose index [ CTDI_vol], and dose length product [DLP]) of automatic tube current modulation (ATCM) determined by localizer radiographs obtained in the anteroposterior (AP) and posteroanterior (PA) directions.MethodsOne hundred and twenty-four patients who underwent upper abdomen and/or chest–to–pelvis computed tomography (CT) were included. Patients underwent two series of CT examinations, and localizer radiographs were obtained in the AP and PA directions. The horizontal diameter of the localizer radiograph, scan length, CTDI_vol, and DLP were measured.ResultsThere was no significant difference in the scan length; however, all the other values were significantly higher in the PA direction. The mean horizontal diameter was 33.1 ± 2.6 cm and 35.4 ± 2.9 cm in the AP and PA directions of the localizer radiographs, respectively. The CTDI_vol and DLP in the PA direction increased by approximately 7–8%.Bland-Altman plots between AP and PA localizer directions in upper abdominal CT showed a positive bias of 1.1 mGy and 30.0 mGy cm for CTDI_vol and DLP, respectively. Correspondingly, chest–to–pelvic CT showed a positive bias of 0.93 mGy and 69.3 mGy cm for CTDI_vol and DLP, respectively.ConclusionThe output dose of ATCM determined by localizer radiographs obtained in the PA direction was increased compared to the AP direction. Localizer radiographs obtained in the AP direction should be preferred for optimizing the output dose using ATCM.Implications for practiceBased on the evidence of this study, localizer radiographs obtained in the AP direction should be preferred for optimizing the output dose in CT examinations.     

双能量扫描对正常成人甲状腺能谱及辐射剂量的影响

目的 应用双源CT研究正常成人甲状腺能谱曲线及碘图特点,为甲状腺占位性病变的鉴别诊断提供依据。方法 选取70例受试者均经超声检查排除甲状腺疾病,男32例,女38例,进行双源CT颈部扫描。分别利用Liver VNC和Monoenergetic软件得到碘图及能谱曲线,分析甲状腺能谱曲线及碘含量。结果 甲状腺平扫碘含量为(1.35±0.19)mg/ml,其中左叶为(1.35±0.23) mg/ml,右叶为(1.35±0.21) mg/ml,二者比较差异无统计学意义(P>0.05)。男、女两组甲状腺碘含量比较差异无统计学意义(P>0.05)。甲状腺左、右叶的能谱曲线斜率分别为9.98±2.43和9.74±1.63,男、女组分别为9.88±1.74和9.74±0.09,差异均无统计学意义(P>0.05)。双能量扫描剂量长度乘积(DLP)为(208.29±21.80)mGy ·cm,平均有效剂量为(1.23±0.13)mSv。结论 正常成人甲状腺双能量扫描获得能谱曲线有一定特征性,且可以测量甲状腺碘浓度,对于诊断甲状腺占位有指导价值。     

A pilot study investigating two dose reduction techniques for AP lumbar spine radiography using direct dosimetry and Projection VR

IntroductionThe purpose of this study was to compare radiation dose measurements generated using a virtual radiography simulation with experimental dosimeter measurements for two radiation dose reduction techniques in digital radiography.MethodsEntrance Surface Dose (ESD) measurements were generated for an antero-posterior lumbar spine radiograph experimentally using NanoDOT™, single point dosimeters, for two radiographic systems (systems 1 and 2) and using Projection VR™, a virtual radiography simulation (system 3). Two dose reduction methods were tested, application of the 15% kVp rule, or simplified 10 kVp rule, and the exposure maintenance formula. The 15% or 10 kVp rules use a specified increase in kVp and halving of the mAs to reduce patient ESD. The exposure maintenance formula uses the increase in source-to-object distance to reduce ESD.ResultsIncreasing kVp from 75 to 96 kVp, with the concomitant decrease in mAs, resulted in percent ESD reduction of 59.5% (4.02–1.63 mGy), 60.8% (3.55–1.39 mGy), and 60.3% (6.65–2.64 mGy), for experimental systems 1 and 2, and virtual simulation (system 3), respectively. Increasing the SID (with the appropriate increase in mAs) from 100 to 140 cm reduced ESD by 22.3% 18.8%, and 23.5%, for experimental systems 1 and 2, and virtual simulation (system 3), respectively.ConclusionPercent dose reduction measurements were similar between the experimental and virtual measurement systems investigated. For the dose reduction practices tested, Projection VR™ provides a realistic alternate of percent dose reduction to direct dosimetry.     

Computed tomography of the head: An experimental study to investigate the effectiveness of lead shielding during three scanning protocols

PurposeThe purpose of this experimental study, carried out in 2002, was to investigate the effectiveness of lead shielding during three scanning protocols for Computed Tomography (CT) head examinations.During CT, the thyroid is irradiated via scattered radiation outside the primary beam. Scientists have proved a definite link between thyroid cancer and radiation but have struggled to quantify the risks from low doses such as those in medical exposures. Children are known to be at higher risks from the effects of radiation than adults.MethodAn anthropomorphic phantom was used to simulate the patient. Shielding in the form of a standard lead thyroid shield was used due to the nature of the rotating X-ray beam involved with CT. Thermoluminescent detector chips were used to measure the approximate dose to the thyroid with and without the application of the shield.ResultsThe effectiveness of shielding varied with scanning technique, as did the thyroid dose due to scattered radiation. The lead shield significantly reduced the dose to the thyroid by 46–58% at the surface of the thyroid and by 37–44% within the thyroid tissue at 1 cm depth.ConclusionIn light of the increasing number of CT scanners, and the fact that head scans account for 50% of all CT examinations and 25% of the collective dose from CT to the UK population, it is important that all methods of dose reduction are considered. The use of shielding is a simple yet effective method of dose optimisation that has not been extensively investigated.     

Comparison of scattered entrance skin dose burden in MSCT,CBCT, and X-ray for suspected scaphoid injury: Regional dose measurements in a phantom model

IntroductionScaphoid radiography has poor sensitivity for acute fracture detection and often requires repeat delayed imaging. Although magnetic resonance (MR) imaging is considered the gold standard, computed tomography (CT) is often used as an alternative due to ease of access. Cone-Beam CT (CBCT) offers equivalent diagnostic efficacy to Multi Slice CT (MSCT) at reduced dose. We aimed to establish the difference in scattered dose between modalities for scaphoid imaging.MethodsAnatomical regional entrance surface dose measurements were taken at 3 regions on an anthropomorphic torso phantom positioned as a patient to a wrist phantom undergoing scaphoid imaging for three modalities (CBCT, MSCT, four-view projection radiography). Exposure factors were based on audit of clinical exposures. Each dose measurement was repeated three times per anatomical region, modality, exposure setting and projection.ResultsUnder unpaired T-test CBCT gave significantly lower mean dose at the neck (1.64 vs 18 mGy), chest (2.78 vs 8.01) and abdomen (1.288 vs 2.93) than MSCT (p < .0001). However CBCT had significantly higher mean dose than four-view radiography at the neck, chest and abdomen (0.031, 0.035, and 0.021 mGy) (p < .0001).ConclusionCBCT of the wrist carries a significantly higher scattered radiation dose to the neck, chest and abdomen than four view scaphoid radiography, but significantly lower scattered dose than MSCT of the wrist of equivalent diagnostic value.Implications for practiceThe use of CBCT for scaphoid injury carries significantly lower scattered dose to radio-sensitive structures investigated here than equivalent MSCT, and may be of greater use as an early cross-sectional investigation for suspected scaphoid fracture.     

双源CT扫描模式对头颈部辐射剂量和影像质量的影响

目的 探讨头颈部CT扫描中,不同扫描模式对辐射剂量和影像质量的影响程度。方法 利用头颈部仿真模体和双源CT,分别使用固定扫描条件120 kV和200 mAs,以及自动管电流调制技术（CARE Dose 4D）、自动管电压调制技术（CARE kV）和部分角度扫描模式（X-CARE）的组合进行成像,分别为120 kV+200 mAs、120 kV+200 mAs+X-CARE、CARE Dose 4D+120 kV、CARE Dose 4D+120 kV+X-CARE、CARE Dose 4D+CARE kV、CARE Dose 4D+CARE kV+X-CARE 6种扫描模式。每次扫描均使用两片热释光剂量片（TLD）分别测量眼晶状体和甲状腺的剂量,两片TLD所测数值取均值。记录以上各种扫描时的容积CT剂量指数（CTDI_vol）和剂量长度乘积（DLP）,测量眼晶状体层面和甲状腺层面影像的对比度噪声比（CNR）。结果 120 kV+200 mAs扫描时,眼晶状体和甲状腺的器官剂量分别为19.8和26.0 mGy,使用120 kV+200 mAs+X-CARE可降低剂量至13.3和22.2 mGy;与CARE Dose 4D+120 kV相比,CARE Dose 4D+CARE kV可使CTDI_vol由13.1降至10.1 mGy,眼晶状体剂量和甲状腺剂量由20.8和23.7 mGy分别降至16.6和19.9 mGy,而使用CARE Dose 4D+CARE kV+X-CARE时,器官剂量又进一步分别降至6.3和11.0 mGy,但影像质量显著降低;与CARE Dose 4D+120 kV相比,使用CARE Dose 4D+120 kV+X-CARE,眼晶状体和甲状腺剂量分别由20.8和23.7 mGy降至9.6和15.1 mGy,同时CTDI_vol由13.1 mGy降至9.3 mGy。使用CARE Dose 4D+CARE kV+X-CARE时,CTDI_vol和器官剂量降至最低,但头颅和颈部CNR也降至最低。结论 颅脑扫描时CARE Dose 4D+120 kV+X-CARE模式、颈部扫描时CARE Dose 4D+CARE kV模式在保持影像质量较好的同时可有效降低辐射剂量。当对影像质量要求不高时可选用CARE Dose 4D+CARE kV+X-CARE模式,从而显著降低辐射剂量。     

Radiation dose and cancer risk from pediatric CT examinations on 64-slice CT: A phantom study

Objective

To measure the radiation dose from CT scans in an anthropomorphic phantom using a 64-slice MDCT, and to estimate the associated cancer risk.

Materials and methods

Organ doses were measured with a 5-year-old phantom and thermoluminescent dosimeters. Four protocols; head CT, thorax CT, abdomen CT and pelvis CT were studied. Cancer risks, in the form of lifetime attributable risk (LAR) of cancer incidence, were estimated by linear extrapolation using the organ radiation doses and the LAR data.

Results

The effective doses for head, thorax, abdomen and pelvis CT, were 0.7 mSv, 3.5 mSv, 3.0 mSv, 1.3 mSv respectively. The organs with the highest dose were; for head CT, salivary gland (22.33 mGy); for thorax CT, breast (7.89 mGy); for abdomen CT, colon (6.62 mGy); for pelvis CT, bladder (4.28 mGy). The corresponding LARs for boys and girls were 0.015-0.053% and 0.034-0.155% respectively. The organs with highest LARs were; for head CT, thyroid gland (0.003% for boys, 0.015% for girls); for thorax CT, lung for boys (0.014%) and breast for girls (0.069%); for abdomen CT, colon for boys (0.017%) and lung for girls (0.016%); for pelvis CT, bladder for both boys and girls (0.008%).

Conclusion

The effective doses from these common pediatric CT examinations ranged from 0.7 mSv to 3.5 mSv and the associated lifetime cancer risks were found to be up to 0.16%, with some organs of higher radiosensitivity including breast, thyroid gland, colon and lungs.     

Dose reduction to radiosensitive tissues in CT. Do commercially available shields meet the users' needs?

AIM: To assess the effectiveness and economy of routinely using commercially available in-plane bismuth shielding during CT scanning of the chest and brain. METHODS AND MATERIALS: Forty patients were scanned with thermoluminescent dosemeters (TLDs) in situ to measure the radiation dose to the thyroid and eye during CT scanning of the brain and chest. Half of the patients had the "AttenuRad" shield in place during scanning. RESULTS: Use of the shielding reduced the mean dose to the eye from 6.0 +/- 0.3 mGy to 4.9 mGy +/- 0.2 mGy and the thyroid dose from 16.4 mGy +/- 1.2 mGy to 7.1 mGy +/- 0.5 mGy. CONCLUSION: Use of the thyroid shield is recommended for all CT scanning of the chest. The eye shield does not produce as marked a reduction in radiation dose to the lens of the eye, when an angled gantry is used, since the eyes are not in the primary beam. Use of the eyeshield is justifiable where irradiation of the orbit is unavoidable, although whether artifacts would be a problem if the shield was used in this way was not assessed.     

Brain radiotherapy during pregnancy: an analysis of conceptus dose using anthropomorphic phantoms.

The aims of this study were: (a) to determine conceptus dose resulting from brain radiotherapy; (b) to investigate the necessity of using shielding devices over patient's abdomen during treatment; and (c) to estimate the components of conceptus dose. Radiation doses received by conceptus were measured using anthropomorphic phantoms simulating pregnancy at 4, 12 and 24 weeks gestation and thermoluminescent dosemeters. All irradiations were performed with two lateral and opposed fields approximating the minimum, medium and maximum field size used during treatment of brain malignancies. For a treatment course delivering 65 Gy to tumour without using shielding equipment, conceptus dose never exceeded 100 mGy. Appropriate positioning of 5.1 cm of lead over the phantom's abdomen provided reduction of conceptus dose from 26% to 71%, depending upon gestational age, field size and distance from the field isocentre. The contribution of scatter arising from within the phantom to the conceptus dose was small compared with that from head leakage and collimator scatter. Our dosimetric results indicate that the construction of special shielding equipment is not a prerequisite for treating brain malignancies during pregnancy. However, based on the concept that exposures in women of childbearing age should be kept as low as reasonably achievable, we suggest that shielding devices should be used whenever possible.     

Radiation dose in 320-slice multidetector cardiac CT: A single center experience of evolving dose minimization

BackgroundMinimization of radiation exposure remains an important subject that occurs in parallel with advances in scanner technology.ObjectiveWe report our experience of evolving radiation dose and its determinants after the introduction of 320-multidetector row cardiac CT within a single tertiary cardiology referral service.MethodsFour cohorts of consecutive patients (total 525 scans), who underwent cardiac CT at defined time points as early as 2008, are described. These include a cohort just after scanner installation, after 2 upgrades of the operating system, and after introduction of an adaptive iterative image reconstruction algorithm. The proportions of nondiagnostic coronary artery segments and studies with nondiagnostic segments were compared between cohorts.ResultsSignificant reductions were observed in median radiation doses in all cohorts compared with the initial cohort (P < .001). Median dose-length product fell from 944 mGy · cm (interquartile range [IQR], 567.3–1426.5 mGy · cm) to 156 mGy · cm (IQR, 99.2–265.0 mGy · cm). Although the proportion of prospectively triggered scans has increased, reductions in radiation dose have occurred independently of distribution of scan formats. In multiple regression that combined all groups, determinants of dose-length product were tube output, the number of cardiac cycles scanned, tube voltage, scan length, scan format, body mass index, phase width, and heart rate (adjusted R² = 0.85, P < .001). The proportion of nondiagnostic coronary artery segments was slightly increased in group 4 (2.9%; P < .01).ConclusionWhile maintaining diagnostic quality in 320-multidetector row cardiac CT, the radiation dose has decreased substantially because of a combination of dose-reduction protocols and technical improvements. Continued minimization of radiation dose will increase the potential for cardiac CT to expand as a cardiac imaging modality.     

心血管病介入操作时患者受照剂量研究

目的 对心血管介入手术中患者所受辐射剂量及与辐射剂量相关的指标进行采集和分析,为改善患者的辐射防护提供依据.方法 对在省属三级甲等医院进行的26例完整的心血管介入手术的患者进行临床数据采集,按手术类别分成冠状动脉血管造影术(CA)及行冠状动脉血管造影术(CA)后继续行经皮穿刺腔内冠状动脉成形术(PTCA)两组,采用TLD个人剂量计照射野矩阵测量法,检测患者荧光照射时间、入射皮肤剂量(ESD)、最高皮肤剂量(PSD)、剂量-面积乘积(DAP)等指标,用TLD测量在模拟心血管手术条件下体模器官剂量.结果 荧光透视时间为(17.7±15.6)min,范围为0.80～42.4 min;ESD范围为(159±138)mGy,4.40～459 mGy;PSD范围为(769±705)mGy,22.6～2.43×103mGy.CA+PTCA组的荧光照射时间、ESD、PSD均大于CA组,差异有统计学意义.最大皮肤受照剂量与透视时间有较好的相关性(r=0.84,P＜0.01).结论 心血管病放射性介入操作时,可通过透视时间来估算最大皮肤受照剂量.

Abstract：

Objective To collect and analyze the radiation dose to patients in cardiovascular interventional procedures and the radiation dose-related indicators,in order to provide a basis for improving radiation protection of patients.MethodsThe clinical data of 26 cases of complete cardiovascular interventional procedures was collected in the municipal Grade A Class Three hospitals,including coronary angiography (CA) and percutaneous transluminal coronary angioplasty (PTCA),and the patient-received radiation doses and other related factors was studied.TLD personal dosimeter radiation field matrix method was used to measure fluorescence time,the entrance skin dose (ESD),the peak skin dose (PSD),dosearea product (DAP) and other indicators.TLD was used to measure the organ dose of the phantom under the cardiovascular interventional procedure condition.ResultsThe fluoroscopy time was (17.7 ±15.6) min during the range of 0.80-42.4 min.The average entrance skin dose (ESD) was (159 ± 138)mGy during the range of 4.40-459 mGy.The peak skin dose (PSD) was (769 ± 705) mGy during the range of 22.6 - 2.43 × 103mGy.The fluorescence time,entrance skin dose (ESD) ,peak skin dose (PSD) of the group CA + PTCA are greater than the group CA and the difference has statistical significan.The peak skin dose and the fluoroscopy time have good linear correlation (r = 0.84,P ＜ 0.01 ).Conclusion The peak skin dose the patient received in cardiovascular interventional radiological operation can be estimated through the fluoroscopy time.     

Radiation dose from volumetric helical perfusion CT of the thorax, abdomen or pelvis

Purpose

To evaluate the radiation doses delivered during volumetric helical perfusion CT of the thorax, abdomen or pelvis.

Materials and methods

The dose-length product (DLP) and CT dose index (CTDIvol) were recorded and effective dose (E) determined for patients undergoing CT (4D adaptive spiral) for tumour evaluation. Image noise and contrast to noise (CNR) at peak enhancement were also assessed for quality.

Results

Forty two consecutive examinations were included: thorax (16), abdomen (10), pelvis (16). Z-axis coverage ranged from 11.4 to 15.7?cm. Mean DLP was 1288.8?mGy.cm (range: 648 to 2456?mGy.cm). Mean CTDIvol was 96.2?mGy (range: 32.3 to 169.4?mGy). Mean effective dose was 19.6?mSv (range: 12.3?mSv to 36.7?mSv). In comparison mean DLP and effective dose was 885.2?mGy.cm (range: 504 to 1633?mGy.cm) and 13.3 mSV (range: 7.8 to 24.5?mSv) respectively for the standard staging CT thorax, abdomen and pelvis. Mean tumour CNR at peak enhancement was 1.87.

Conclusion

The radiation dose imposed by perfusion CT was on average 1.5 times that of a CT thorax, abdomen and pelvis. The dose is not insubstantial, and must be balanced by the potential clinical utility of additional physiologic data. Further efforts towards dose reduction should be encouraged.     

Effect of high- and low-energy entrance surface dose allocation ratio for two-shot dual-energy subtraction imaging on low-contrast resolution

IntroductionDual-energy subtraction (DES) imaging can obtain chest radiographs with high contrast between nodules and healthy lung tissue, and evaluating of chest radiography and evaluating exposure conditions is crucial to obtain a high-quality diagnostic image. This study aimed to investigate the effect of the dose allocation ratio of entrance surface dose (ESD) between high- and low-energy projection in low-contrast resolution of soft-tissue images for two-shot DES imaging in digital radiography using a contrast-detail phantom (CD phantom).MethodsA custom-made phantom mimicking a human chest that combined a CD phantom, polymethylmethacrylate square plate, and an aluminum plate (1–3 mm) was used. The tube voltage was 120 kVp (high-energy) and 60 kVp (low-energy). The ESD was changed from 0.1 to 0.5 mGy in 0.1 mGy increments. Dose allocation ratio of ESD between 120 kVp and 60 kVp projection was set at 1:1, 1:2, 1:3, and 2:1. Inverse image quality figure (IQF_inv) was calculated from the custom-made phantom images.ResultsWhen the total ESD and aluminum thickness were constant, no significant difference in IQF_inv was observed under most conditions of varied dose allocation ratio. Similarly, when the total ESD and the dose allocation ratio were constant, there was no significant difference in IQF_inv based on the aluminum plate thickness.ConclusionUsing IQF_inv to evaluate the quality of the two-shot DES image suggested that dose allocation ratio did not have a significant effect on low-contrast resolution of soft-tissue images.Implications for practiceThe present results provide useful information for determining exposure conditions for two-shot DES imaging.     

Effect of leaded glasses and thyroid shielding on cone beam CT radiation dose in an adult female phantom

Objectives:

This study aims to demonstrate the effectiveness of leaded glasses in reducing the lens of eye dose and of lead thyroid collars in reducing the dose to the thyroid gland of an adult female from dental cone beam CT (CBCT). The effect of collimation on the radiation dose in head organs is also examined.

Methods:

Dose measurements were conducted by placing optically stimulated luminescent dosemeters in an anthropomorphic female phantom. Eye lens dose was measured by placing a dosemeter on the anterior surface of the phantom eye location. All exposures were performed on one commercially available dental CBCT machine, using selected collimation and exposure techniques. Each scan technique was performed without any lead shielding and then repeated with lead shielding in place. To calculate the percent reduction from lead shielding, the dose measured with lead shielding was divided by the dose measured without lead shielding. The percent reduction from collimation was calculated by comparing the dose measured with collimation to the dose measured without collimation.

Results:

The dose to the internal eye for one of the scans without leaded glasses or thyroid shield was 0.450 cGy and with glasses and thyroid shield was 0.116 cGy (a 74% reduction). The reduction to the lens of the eye was from 0.396 cGy to 0.153 cGy (a 61% reduction). Without glasses or thyroid shield, the thyroid dose was 0.158 cGy; and when both glasses and shield were used, the thyroid dose was reduced to 0.091 cGy (a 42% reduction).

Conclusions:

Collimation alone reduced the dose to the brain by up to 91%, with a similar reduction in other organs. Based on these data, leaded glasses, thyroid collars and collimation minimize the dose to organs outside the field of view.