Patient and personnel exposure during CT fluoroscopy-guided interventional procedures

PURPOSE: To estimate patient dose and personnel exposure from phantom measurements during computed tomographic (CT) fluoroscopy, to use the estimates to provide users with dose information, and to recommend methods to reduce exposure. MATERIALS AND METHODS: Surface dose was estimated on a CT dosimetric phantom by using thermoluminescent dosimetric (TLD) and CT pencil chamber measurements. Scatter exposure was estimated from scattered radiation measured at distances of 10 cm to 1 m from the phantom. Scatter exposures measured with and without placement of a lead drape on the phantom surface adjacent to the scanning plane were compared. RESULTS: Phantom surface dose rates ranged from 2.3 to 10. 4 mGy/sec. Scattered exposure rates for a commonly used CT fluoroscopic technique (120 kVp, 50 mA, 10-mm section thickness) were 27 and 1.2 microGy/sec at 10 cm and 1 m, respectively, from the phantom. Lead drapes reduced the scattered exposure by approximately 71% and 14% at distances of 10 and 60 cm from the scanning plane, respectively. CONCLUSION: High exposures to patients and personnel may occur during CT fluoroscopy-guided interventions. Radiation exposure to patients and personnel may be reduced by modifying CT scanning techniques and by limiting fluoroscopic time. In addition, scatter exposure to personnel may be substantially reduced by placing a lead drape adjacent to the scanning plane.     

Radiation protection system for interventional procedures of the upper extremity: evaluation in a phantom model

PURPOSE: To design a radiation protection system for interventional procedures of the upper extremity and to evaluate the effectiveness of the system. MATERIALS AND METHODS: The radiation protection system consisted of an image intensifier (I-I) hood and x-ray tube cover. The I-I hood encircled the I-I to protect against scattered radiation from the patient's upper extremity and the table. The I-I hood consisted of four components: a device for attaching the hoods, two acrylate hoods with an 0.50-mm Pb equivalent, and a lead curtain hood with a 0.35-mm Pb equivalent. The x-ray tube cover was constructed of lead curtain to protect against backscattering radiation from the catheter table. An extremity phantom was used to measure the scattered radiation around the angiographic apparatus. The scattering dose rates were measured with an ionization dosimeter with and without a radiation protection system. The heights of the measuring points from the floor were 50 cm (operator's lower limbs), 100 cm (operator's abdomen), and 150 cm (operator's head/neck). RESULTS: The dose rates were reduced most with the combination of the I-I hood and the x-ray tube cover. The x-ray tube cover was effective in reducing scattering when it was set close to the table and the phantom. The maximum percentage decreases in dose rates by the radiation protection system were 99% at 50 cm, 73% at 100 cm, and 100% at 150 cm. Therefore, at 50 cm and 150 cm, the high-dose-rate area around the angiographic apparatus was reduced almost completely by the radiation protection system. CONCLUSION: The radiation protection system for interventional procedures of the upper extremity was effective in reducing scattered radiation around the angiographic apparatus.     

Using a sterile disposable protective surgical drape for reduction of radiation exposure to interventionalists.

OBJECTIVE: The purpose of this paper is to show the effectiveness of a new radiation protection method designed to decrease the amount of scatter radiation received by practitioners performing procedures under fluoroscopic guidance. MATERIALS AND METHODS: A sterile, disposable, lead-free surgical drape containing radiation protection material composed primarily of bismuth was evaluated for effectiveness in reducing radiation doses to health care personnel. Measurements of phantom scatter, patient scatter, skin entrance, and the effects of collimation, together with comparative monthly thermoluminescent dosimeter recordings, were taken to determine the effectiveness of X-ray beam attenuation using the bismuth drapes. RESULTS: Scatter radiation to physicians, as measured by thermoluminescent dosimeters placed on each eye, the thyroid, and the wrist, was reduced by 12-fold for the eyes, 25-fold for the thyroid, and 29-fold for the hands when the radiation-attenuating surgical drape was used when compared with control studies performed with a standard nonattenuating surgical drape alone. Monthly thermoluminescent dosimeter measurements decreased fourfold in one physician. Using the protective drape reduced exposure to the assistant in each case to negligible levels. Skin entrance dose was not increased unless the protective drape was placed directly in the X-ray beam. An X-ray attenuation factor equivalent to 0.1 mm of lead with 8 x 8 cm collimation reduced the scatter rates from five- to ninefold despite a 30-40% increase in entrance exposure rate as the lead equivalence increased. CONCLUSION: Depending on the procedure, the height of the practitioner, and the positioning of the radiation-attenuating surgical drape, use of this drape can substantially reduce the radiation dose to personnel with minimal or no additional radiation exposure to the patient.     

Analysis of radiation scatter during angiographic procedures: evaluation of a phantom model and a modified radiation protection system

PURPOSE: To study the radiation scattering associated with the digital subtraction angiography (DSA) unit in angiographic procedures and to design an effective radiation protection shield based on these data. MATERIALS AND METHODS: The number of scattered photons was measured at three points relative to the operator's position. Anteroposterior abdominal and lateral cranial fluoroscopy were evaluated. As protective devices, a lead curtain, sliding shields, and a brim-shaped image intensifier (II) hood were designed. RESULTS: In abdominal fluoroscopy, radiation was found to scatter to the operator's lower limbs from the underside of the catheter table, to the abdomen from the side of the patient's body, and to the head and neck from the table surface adjacent to the patient. The use of protective devices reduced exposure from 2.89 to 0.058 mR/min for the operator's lower limbs, from 0.987 to 0.069 mR/min for the operator's abdomen, and from 0.696 to 0.139 mR/ min for the operator's head and neck area. With lateral cranial fluoroscopy, radiation was detected to scatter to the operator's lower limbs from the underside of the catheter table, to the abdomen from the patient's temporal area, and to the head and neck from the patient's face. The use of protective devices reduced exposure from 0.248 to 0.010 mR/min for the operator's lower limbs, from 0.129 to 0.010 mR/min for the operator's abdomen, and from 0.162 to 0.018 mR/min for the operator's head and neck area. CONCLUSIONS: The characteristic directions of scattering to the operator were identified. An effective modified radiation protection system was designed based on this information.     

Evaluation of additional lead shielding in protecting the physician from radiation during cardiac interventional procedures

Since cardiac interventional procedures deliver high doses of radiation to the physician, radiation protection for the physician in cardiac catheterization laboratories is very important. One of the most important means of protecting the physician from scatter radiation is to use additional lead shielding devices, such as tableside lead drapes and ceiling-mounted lead acrylic protection. During cardiac interventional procedures (cardiac IVR), however, it is not clear how much lead shielding reduces the physician dose. This study compared the physician dose [effective dose equivalent (EDE) and dose equivalent (DE)] with and without additional shielding during cardiac IVR. Fluoroscopy scatter radiation was measured using a human phantom, with an ionization chamber survey meter, with and without additional shielding. With the additional shielding, fluoroscopy scatter radiation measured with the human phantom was reduced by up to 98%, as compared with that without. The mean EDE (whole body, mean+/-SD) dose to the operator, determined using a Luxel badge, was 2.55+/-1.65 and 4.65+/-1.21 mSv/year with and without the additional shielding, respectively (p=0.086). Similarly, the mean DE (lens of the eye) to the operator was 15.0+/-9.3 and 25.73+/-5.28 mSv/year, respectively (p=0.092). In conclusion, although tableside drapes and lead acrylic shields suspended from the ceiling provided extra protection to the physician during cardiac IVR, the reduction in the estimated physician dose (EDE and DE) during cardiac catheterization with additional shielding was lower than we expected. Therefore, there is a need to develop more ergonomically useful protection devices for cardiac IVR.     

CT引导下125I粒子植入对相关医务人员的辐射剂量评估

目的评估CT引导下125I粒子植入过程中相关医务人员在不同距离及有无辐射防护措施下的周围剂量当量率。方法125I粒子植入后立即使用多功能射线检测仪测量50例125I粒子植入患者距粒子植入部位体表不同垂直距离（5 cm、10 cm、1 m、2 m和3 m）及有无防护措施条件下的周围剂量当量率,评估医务人员受到的辐射剂量。组间比较采用单因素方差分析。结果距离粒子植入部位体表垂直距离为5 cm、10 cm、1 m、2 m和3 m处的周围剂量当量率分别为（1091.75±10.53）、（1055.50±31.68）、（123.45±20.83）、（20.95±6.10）和（7.78±3.24）μSv/h。0.5 mm铅当量铅衣屏蔽后5 cm、10 cm、1 m、2 m和3 m处的周围剂量当量率分别为（1.36±2.03）、（0.97±1.48）、（0.46±0.63）、（0.29±0.34）和（0.14±0.12）μSv/h。屏蔽前后周围剂量当量率的差异均有统计学意义（F=183.718、71.202、217.411、184.169、108.222,均P < 0.05）。结论CT引导下125I粒子植入过程中相关医务人员采取适当的距离防护及穿戴个人防护用品可以大大降低125I粒子带来的辐射影响。     

Evaluation of surface dose and image quality using the half-scan mode in chest computed tomography-guided interventional radiology: a phantom study

The authors aimed to evaluate the effects of the half-scan mode on image quality and physician exposure to radiation in computed tomography (CT)-guided interventional radiology (IVR) to the right lung using an intermittent CT fluoroscopy technique for measuring phantom surface dose distribution and image noise. For the half-scan mode, settings at 0°, 90°, 180°, and 270° were used as the central axis of the X-ray exposure range on the chest phantom. With the center of the ventral side in the chest phantom defined as 0°, optically stimulated luminescent dosimeters were attached at five positions at 30° intervals on the right side of the phantom surface. Securing a space for device operation during the procedure is necessary. The couch was shifted downward by 50 mm to reproduce the conditions used for measurement in clinical settings. Image noise and contrast-to-noise ratio were measured to assess image quality; subjective evaluation was performed using simulated lung nodules placed in the phantom. The phantom surface dose distribution in the measured half-scan mode depended on the angle setting. Additionally, the phantom surface dose in the half-scan mode at the 90° setting was reduced by approximately 50%; however, image quality was clearly decreased. In CT-guided IVR to the right lung, using a lead drape and half-scan mode according to the procedural situation is important.     

降低儿童16层螺旋CT检查辐射剂量的研究

目的论证CT扫描参数kVp和mAs与剂量和图像噪声的关系,在不影响临床诊断的基础上,修正并验证一种基于成人扫描参数的安全可行的儿童16层螺旋CT检查的扫描参数。方法利用16层螺旋CT,采用标准CT剂量指数(CTDI)测试仪、100mm笔型电离室,分别测量16cm和32cm直径模体在2mm×5mm准直宽度时不同kVp和mAs的CTDI;采用20cm标准水模,测量单一感兴趣区域(ROI)标准偏差值SD代表噪声水平。以成人扫描参数的不同百分比修正为不同年龄段儿童CT扫描的参数供临床验证。结果随着kVp和mAs的增加,CTDI随之增加,并与mAs呈线性关系;16cm直径模体的表面CTDI要高于32cm模体58%;实际的加权CTDIw值高于CT扫描仪显示的CTDIw;mAs相同时,kVp越高,图像噪声SD值越低,在kVp固定时,随着mAs的增加,图像噪声SD随之减少,当mAs增加到一定程度后,图像噪声趋向平稳。结论在不影响临床诊断的图像噪声水平下,根据年龄和体型特点,儿童16层CT检查mAs可以比成人降低10%～85%。     

Dose reduction during CT scanning in an anthropomorphic phantom by the use of a male gonad shield.

Shielding the radiosensitive gonads during X-ray exposure has been advocated for plain film radiography for many years. In the UK, gonad shields are not widely employed in routine CT scanning, possibly owing to a perceived difficulty in protecting the gonads from a multidirectional X-ray source. The increasing numbers of CT scanners in the UK, with the large doses they deliver to patients, make potential dose reduction methods an important issue. This study measures the dose reduction achievable by shielding the male gonads with a lead wrap-around protection device. The reductions in dose when shielded both from direct radiation and from indirect radiation scattered from local tissues were studied. The use of the device resulted in a statistically significant reduction in the absorbed testicular dose from both direct and scattered radiation, with no increase in the dose measured in surrounding tissues. In three clinically relevant experimental protocols where the testes were not irradiated directly, the testicular absorbed dose from indirect scatter was reduced by 77-93% of the corresponding non-shielded figure. In these three experiments, image quality was unaltered by the use of the shield. A larger dose reduction was obtained when the shield was used to protect the testes from direct irradiation. However, this was achieved at the expense of considerable image degradation from streak artefact that would effectively prevent the clinical use of the device in this setting.     

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.     

Scattered radiation level during videofluoroscopy for swallowing study

AIM: To evaluate the scattered radiation exposure to the surroundings during videofluoroscopy for swallowing study (VFSS). MATERIALS AND METHODS: Scattered radiation exposure was measured using an ion chamber survey meter for 17 adult patients undergoing videofluoroscopy for swallowing study. The cumulative dose area product of each case was also recorded. Data were presented as mean +/- standard deviation. RESULTS: The scattered radiation exposure at a distance of 150 cm from the patient and the dose area product recorded were 149 +/- 78 microR (range 42-308 microR) and 842 +/- 544 cGy.cm(2) (range 258-2151 cGy.cm(2)), respectively, for a single study of 18 +/- 6 minutes. A formula was then derived for estimating the scattered radiation dose to muscle tissue at an arbitrary distance based on the accumulated dose area product. With this formula, the mean scattered radiation dose to naked muscle tissue of the surrounding people at a distance of 30-100 cm from the patient were estimated to be 33.68-3.03 microSv respectively. CONCLUSION: The scattered radiation detriment associated with videofluoroscopy for swallowing study was well within acceptable levels.     

Occupational exposure in the electrophysiology laboratory: quantifying and minimizing radiation burden

Fluoroscopically guided procedures in the electrophysiology room, such as radiofrequency catheter ablation and implantation of cardiac resynchronization devices, may result in high radiation exposure of electrophysiologists and assisting staff. Our aim was to provide accurate and applicable data on occupational doses to the electrophysiology laboratory personnel. We exposed fluoroscopically an anthropomorphic phantom at three projections common in electrophysiology studies. For each exposure, scattered radiation was measured at 182 sites of the cardiology room at four body levels. Effective dose values, eye lens, skin and gonadal doses to the laboratory staff were calculated. Our study has shown that a procedure requiring 40 min of fluoroscopy yields a maximum effective dose of 129 microSv and a maximum value of gonadal dose of 56.8 microSv to staff using a 0.35 mm lead-equivalent apron. A conservative estimate of the electrophysiologist's annual maximum permissible workload is 155 procedures. Staff effective dose values vary by a factor of 40 due to positioning during fluoroscopy and by a factor of 11 due to radiation protection equipment. Undercouch protective shields may reduce gonadal doses up to 98% and effective dose up to 25%. Consequently, radiation levels in the electrophysiology room are not negligible. Mitigation of occupational exposure is feasible through good fluoroscopy and working practices.     

铋屏蔽对头颈部多层螺旋CT中眼晶状体辐射剂量的降低作用

目的 探讨扫描平面内铋屏蔽在头颈部多层螺旋CT(MSCT)扫描中对影像质量的影响和眼晶状体辐射剂量的降低作用.方法 分别使用颅脑、颞骨和鼻窦临床扫描条件,在无屏蔽、1层、2层和3层铋屏蔽覆盖眼部区域时,对标准水模和离体头颅标本进行扫描,用热释光剂量片测量头颅标本每次扫描时的眼晶状体器官剂量.在屏蔽材料和被扫描体间放置5、10、15和20 mm厚的海绵时,使用鼻窦扫描条件采集影像,并测量眼晶状体的剂量.测量水模影像中与屏蔽物为2、4、6和8 cm距离处的CT值,主观评价头颅标本影像中伪影对解剖结构的影响.结果 颅脑、颞骨和鼻窦CT临床扫描中眼晶状体的器官剂量分别为24.31、27.60和20.01 mGy.使用铋屏蔽时,均使得眼晶状体剂量有显著下降,但下降幅度随着铋屏蔽物的增加而降低.在各种厚度的屏蔽物时,屏蔽物间隙越大,眼晶状体剂量的降低程度越小,测量兴趣区CT值的增加程度也显著降低.颅脑和颞骨CT扫描分别使用2层和3层铋屏蔽,在不影响诊断的前提下,可有效降低眼晶状体剂量分别为47.1%和59.1%;鼻窦CT扫描时,1层屏蔽无间隙、2层屏蔽1.5 cm间隙不影响诊断,可降低眼晶状体剂量分别为31.5%和34.5%.结论 扫描平面内铋屏蔽材料的合理应用,可有效降低头颈部CT扫描中眼晶状体的辐射剂量.     

Single versus multi-detector row CT: comparison of radiation doses and dose profiles

RATIONALE AND OBJECTIVES: The purpose of this study was twofold: (a) to compare the radiation dose profile between computed tomography (CT) with a single detector row (SD) and with a multi-detector row (MD) and (b) to compare specific organ doses between SD CT and MD CT. MATERIALS AND METHODS: Thermoluminescent dosimeters placed within a 32-cm-diameter cylindrical phantom were used to measure and compare dose profiles from one SD CT scanner and from one MD CT scanner. SD CT scanning parameters were 210 mA, 140 kVp, pitch of 1.0, 5-mm section thickness, and 0.8-second gantry rotation speed. MD CT scanning parameters were 130 mA, 140 kVp, pitch of 0.75, 4 x 5-mm section thickness, 15-mm table feed, and 0.8-second gantry rotation speed. To plot radiation dose profile, doses were measured both in the imaging plane and in the area adjacent to the imaging plane. The resultant data were normalized to achieve constant image noise between MD CT and SD CT. Direct doses to individual organs from primary and scattered radiation were measured with an anthropomorphic phantom containing thermoluminescent dosimeters and with a standard pelvic imaging protocol for both MD CT and SD CT. RESULTS: MD CT resulted in a dose profile approximately 27% higher than that from SD CT in the plane of imaging (8.0 vs 6.3 mGy) and 69% higher adjacent to the plane of imaging (6.8 vs 4.0 mGy). The individual doses to the kidneys, uterus, ovaries, and pelvic bone marrow were 92%-180% higher with MD CT than with SD CT. CONCLUSION: With image noise constant between SD CT and MD CT, the radiation dose profile both inside and outside the plane of imaging was higher with MD CT than with SD CT. Organ dose also was higher with MD CT than with SD CT. This difference should be accounted for in the design of MD CT protocols, especially as MD CT technology becomes more widely available for clinical use.     

A comparative study of thoracic radiation doses from 64-slice cardiac CT

The goal of this study was to measure radiation doses for 64-slice cardiac CT angiography studies and to study the dose-savings features of these CT scanners. This was done using various phantoms. These radiation doses were compared with those from typical helical body CT scans, fluoroscopy cardiac catheterization studies and mammography examinations. Radiation measurements were made with a CT ionization detector and a solid state dosimeter. A GE 64-slice Lightspeed VCT and a Siemens Somatom Sensation 64 CT were used to scan a standard 32 cm acrylic phantom and an anthropomorphic phantom. Data were collected in axial and various gated cardiac helical modes. Organ doses and the effective doses were calculated from the measurements. In gated CT cardiac mode with the 32 cm acrylic phantom, the measured radiation doses per study were generally three to seven times greater than those from typical body helical CT examinations; the range depended upon selectable scan parameters. With the anatomical phantom, the surface doses in the anteroposterior (AP) plane were typically 20-60% higher than those measured using the 32 cm phantom. The lateral surface doses were -4% to +15%. These results can be attributed to the shorter AP dimension and the air in the lungs. The CT skin entrance radiation doses were 80-90% less than diagnostic cardiac catheterization studies, and organ doses were similar. Because 64-slice cardiac gated CT uses pitches equal to 0.20-0.27 and high mAs values, the patient radiation doses are appreciably higher than in routine body CT examinations. The female breast, which could receive a radiation dose 10-30 times that received from mammography screening, is an organ of particular concern.     

Internal barium shielding to minimize fetal irradiation in spiral chest CT: a phantom simulation experiment

PURPOSE: To use a phantom to prospectively examine the attenuating effect of barium sulfate as an internal shield to protect the fetus. MATERIALS AND METHODS: In an adult-size phantom, 1- and 2-cm-thick acrylic slabs containing 315 or 630 mL of water, 2% or 40% barium sulfate suspension, and a 1-mm lead sheet were placed under the diaphragm. In 17 experiments, fetal dose was measured by using thermoluminescent dosimeters that were placed immediately under (near field) and 10 cm below (far field) the water slab (eight experiments), barium sulfate slab (eight experiments), and lead sheet (one experiment). In a pulmonary embolism protocol, the phantom was scanned with single-detector spiral computed tomography (CT) at 130 kVp and 230 mAs. RESULTS: The control radiation dose was 3.60 mSv+/-0.54 (standard deviation) with the water slab at near field, where the uterus dome is at near term, and 0.507 mSv+/-0.07 with the water slab at far field, the uterus position during early gestation. Scattered radiation was attenuated 13% and 21% with 2% barium sulfate and 87% and 96% with 40% barium sulfate, as calculated in the near and far fields, respectively, and 99% with the 1-mm lead sheet. The extrapolated attenuations for 5%-40% barium sulfate suspensions indicated that beyond a 30% suspension, attenuation increased further only slightly. CONCLUSION: Study results in the phantom experiment suggest that fetal irradiation during maternal chest CT can be reduced substantially with barium shielding.     

Measurement of background signals due to scattered and off-focal radiation on CT scanners

The magnitude of scattered and off-focal radiation in relation to the primary radiation has been measured for 4 commercial CT scanners of third generation (only rotation). The measurement has been done by placing a lead beam stop in front of a scattering phantom as well as without a phantom and registering the detector signal behind and outside the lead beam stop. The off-focal radiation has been found to be very similar in magnitude for 3 of the scanners compared, while the scattered radiation from the phantom was found to vary with parameters like distance between phantom and detector, grid in front of the detector and self collimation of the detector.     

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.     

单纯CT伪影对放疗剂量计算的影响

目的 通过人为制造CT伪影,来研究实际临床操作中单纯伪影对放疗剂量计算的影响。方法 对替换钛合金组件前后的模体进行CT扫描,统计替换前后不同位置的CT值;将钛合金区域的CT值修正为水模体的CT值,并采用Varian的各向异性分析算法（AAA）、Acuros XB （AXB）算法和Pinnacle系统的筒串卷积算法（CCC）3种算法,对替换钛合金组件前后的模体进行剂量计算,统计替换前后不同位置的绝对剂量值,并进行分析。结果 Varian和Pinnacle系统对评价CT值大小比较一致。对于均匀模体,CT值偏差30 HU以下时,3种不同的算法在距离体表0.5 cm时,剂量偏差最大达到12.0%,最小为6.0%;1.5 cm以上偏差的绝对值均<1.0%。对于肺部模体来说,Varian的AAA算法和AXB算法在CT值相差15 HU的情况下,剂量值相差在1.0%左右;但Pinnacle系统的CCC算法在同样情况下剂量值相差较大,相差5.0%左右。结论 CT伪影对放疗剂量计算存在明显影响,导致组织剂量分布发生变化,可能造成浅部肿瘤照射剂量不足,深部肿瘤过量照射。     

Radiation Protection in Interventional Radiology: Survey Results of Attitudes and Use

PurposeTo assess attitudes of interventional radiologists toward personal radiation protection and the use of radiation protection devices.Materials and MethodsInvitations to an anonymous online survey that comprised eight questions focused on operator attitudes toward radiation protection devices were sent via e-mail to the active membership of the Society of Interventional Radiology (SIR): a total of 3,158 e-mail invitations. A single reminder e-mail was sent.ResultsThere were 504 survey responders (16% response rate). Reported radiation safety device use included lead apron (99%), thyroid shield (94%), leaded eyeglasses (54%), ceiling-suspended leaded shield (44%), rolling leaded shields (12%), ceiling-suspended/rolling lead-equivalent apron (4%), radiation-attenuating sterile surgical gloves (1%), and sterile lead-equivalent patient-mounted drape (4%). Reasons commonly cited for not using certain devices were comfort (eyewear), ease of use (mounted shields), and lack of availability (rolling/hanging shields and patient-mounted shields).ConclusionsInterventionalists have an array of tools from which to choose for personal radiation protection; however, for a variety of reasons related to lack of availability or choice, these tools are not universally employed. Further study may be of value to clarify why comfort was cited most often as the primary barrier to the use of protective eyewear and difficulty of use was cited as the primary barrier to use of mounted shields (despite reporting that concern for radiation-induced injury to the eye is paramount). It may also be of interest to further study why certain devices with demonstrable protection effects are not readily available, such as rolling/hanging and patient-mounted shields.