Cone-beam-CT guided radiation therapy: technical implementation.

BACKGROUND AND PURPOSE: X-ray volumetric imaging system (XVI) mounted on a linear accelerator is available for image guidance applications. In preparation for clinical implementation, phantom and patient imaging studies were conducted to determine the irradiation parameters that would trade-off image quality, patient dose and scanning time. PATIENTS AND METHODS: The XVI image quality and imaging dose were benchmarked against those obtained with a helical CT scanner for a head and body phantom. The irradiation parameters were varied including the total imaging dose, number of projections, field of view, reconstruction resolution and use of a scatter rejection grid. We characterized the image quality based on relative contrast, noise, contrast to noise ratio (CNR) and point spread function (PSF). XVI scans of pelvis, head and neck and lung patients were acquired and submitted to a range of observers to identify the favorable reconstruction parameters. RESULTS: Phantom studies have demonstrated that a scatter rejection grid reduces photon scattering and improves the image uniformity. For the body phantom, the helical CT and the wide field XVI technique produce similar image quality, with surface doses of 0.025 and 0.044 Gy respectively. We have demonstrated that the local tomography technique improves the image contrast and the CNR while reducing the skin dose by 40-50% compared to the wide field technique. Clinical scans of head and neck, lung and prostate patients present good soft tissue contrast and excellent bone definition. CONCLUSIONS: With adjustment of irradiation parameters and an imaging surface dose of less than 0.05 Gy, high quality XVI images can be obtained for a phantom simulating the body thickness. XVI is currently feasible for image-guided treatments of head and neck, torso and pelvic areas using soft tissue and bony structures.     

Diagnostic imaging of lung cancer on multislice CT (MDCT)

Helical CT, and the newest technological development, multislice CT (multidetector CT: MDCT), have revolutionized the diagnostic approach to diseases of the chest including lung cancer. There are several factors that contribute to the important role of multislice CT scanning of the chest: (1) data acquisition is so rapid that the scanning of the entire lung can be performed during a single breath-hold period; (2) continuous acquisition of thin slices allows the improvement of the image quality of multiplanar reconstruction of thoracic abnormalities; (3) MDCT may help reduce the radiation dose, so that, compared to conventional or single-slice helical CT, the radiation dose is lowered with comparable image quality. The advantages of MDCT include both improved nodule detection and nodule characterization on lung cancer screening programs, because the entire lung can be scanned with thin slice in a single breath-hold without an intersection gap. In the evaluation of lung cancer, MDCT will allow improved detection of pleural dissemination and hilar lymph node adenopathy because of the continuous and narrow scan collimation.     

Abdominal pediatric cancer surveillance using serial computed tomography: evaluation of organ absorbed dose and effective dose

Computed tomography (CT) is used extensively in cancer diagnosis, staging, evaluation of response to treatment, and in active surveillance for cancer reoccurrence. A review of CT technology is provided, at a level of detail appropriate for a busy clinician to review. The basis of x-ray CT dosimetry is also discussed, and concepts of absorbed dose and effective dose (ED) are distinguished. Absorbed dose is a physical quantity (measured in milligray [mGy]) equal to the x-ray energy deposited in a mass of tissue, whereas ED uses an organ-specific weighting method that converts organ doses to ED measured in millisieverts (mSv). The organ weighting values carry with them a measure of radiation risk, and so ED (in mSv) is not a physical dose metric but rather is one that conveys radiation risk. The use of CT in a cancer surveillance protocol was used as an example of a pediatric patient who had kidney cancer, with surgery and radiation therapy. The active use of CT for cancer surveillance along with diagnostic CT scans led to a total of 50 CT scans performed on this child in a 7-year period. It was estimated that the patient received an average organ dose of 431 mGy from these CT scans. By comparison, the radiation therapy was performed and delivered 50.4 Gy to the patient's abdomen. Thus, the total dose from CT represented only 0.8% of the patient's radiation dose.     

CT扫描/重建参数对三维治疗计划系统影像的影响

[目的]研究CT模拟定位中,CT扫描/重建参数对三维治疗计划重建的三维假体的几何精确度的影响.[方法]在西门子CT模拟机（Somatom plus 4）上扫描自制模体,扫描所得图像登记到ADAC三维治疗计划系统重建成三维假体,测量假体的相关坐标数据并与模体的实际数据相比较;对Catphan 412模体扫描并测量各组图像的实际层厚,讨论实际层厚的变化对计划系统中登记影像的几何精度影响.[结果]（1）CT扫描所采用的不同扫描/重建参数对三维计划系统中重建的三维假体的左右及上下方向的几何精度影响不大,但对重建假体的前后方向（即模体扫描的步进方向）的几何精度有一定的影响.（2）CT扫描所采用的螺距及重建模式会对层厚敏感度曲线（SSP）半高宽值产生影响,该变化对重建假体的前后方向几何精度同样有一定的影响.[结论]重建CT图像的前后方向的几何误差是随着扫描层厚增加而增加,主要是由于CT扫描的部分容积效应影响.单纯增加螺距或使用360度线性内插（Wide）重建模式,都会引起CT图像实际层厚的增加,引起更大的容积效应影响.同时部分容积效应也会导致三维治疗计划系统中数字重建影像（DRR）分辨率的降低.     

A simplified shielding approach for limiting fetal dose during radiation therapy of pregnant patients

Purpose: To investigate the effectiveness of a simple and practical shielding device to reduce fetal dose for a patient undergoing radiation therapy of nasopharyngeal carcinoma.

Methods and Materials: Using 5-cm-thick lead bricks and a heavy-duty steel cart, a 50 × 50-cm portable shield was designed and fabricated to reduce fetal dose due to collimator scatter and head leakage radiation. With the gantry at 90°/270° the shield can be easily positioned between the machine head and the fetus to reduce peripheral dose. Dose measurements for 6-MV X-rays and 9-MeV electrons have been made, utilizing a Rando phantom, to quantify the effect of the shield.

Results: Measurements show that the peripheral dose to the fetus can be reduced by 60% when the simple shielding device is used.     

A systematic review of radiation dose associated with different generations of multidetector CT coronary angiography

The purpose of this paper is to perform a systematic review on radiation dose reduction in coronary computed tomography (CT) angiography that is done using different generations of multidetector CT (MDCT) scanners ranging from four-slice to 320-slice CTs, and have different dose-saving techniques. The method followed was to search for references on coronary CT angiography (CTA) that had been published in English between 1998 and February 2011. The effective radiation dose reported in each study based on different generations of MDCT scanners was analysed and compared between the types of scanners, gender, exposure factors and scanning protocols. Sixty-six studies were eligible for inclusion in this analysis. The mean effective dose (ED) for MDCT angiography with retrospective electrocardiogram (ECG) gating without use of any dose-saving protocol was 6.0 ± 2.8, 10.4 ± 4.90 and 11.8 ± 5.9 mSv for four-slice, 16-slice and 64-slice CTs, respectively. More dose-saving strategies were applied in recent CT generations including prospective ECG-gating protocols, application of lower tube voltage and tube current modulation to achieve a noteworthy dose reduction. Prospective ECG-gating protocol was increasingly used in 64, 125, 256 and 320 slices with corresponding ED of 4.1 ± 1.7, 3.6 ± 0.4, 3.0 ± 1.9 and 7.6 ± 1.6 mSv, respectively. Lower tube voltage and tube current modulation were widely applied in 64-slice CT and resulted in significant dose reduction (P < 0.05). This analysis has shown that dose-saving strategies can substantially reduce the radiation dose in CT coronary angiography. The fact that more and more clinicians are opting for dose-saving strategies in CT coronary angiography indicates an increased awareness of risks associated with high radiation doses among them.     

1200例肿瘤患者CT检查辐射剂量的调查研究

目的 调查当前肿瘤患者CT检查的辐射剂量,与国家新标准给出的诊断学参考水平进行对比分析.方法 应用标准模体测量5台不同类型CT在典型扫描条件下的加权CT剂量指数（CTDIw）,并回顾统计900例成年肿瘤患者及300例儿童肿瘤患者的CT检查剂量参数,包括平均容积CT剂量指数（CTDIvol）、剂量长度乘积（DLP）、75％分位DLP值,估算有效剂量.结果 成人头部的CTDIw测量值与参考值处于同一水平,腰椎及腹部的CTDIw测量值小于参考值.对于成年患者,脑血管增强扫描的DLP最高,而腹部增强扫描的有效剂量最大.对于儿童患者,不同年龄段的DLP无明显差别.结论 CTDI虽然可以反映CT断层平面的剂量状况,但不能反映患者检查的总剂量水平.对于需要多次重复扫描的检查,因为有可能造成患者个体的高辐射剂量,国家标准应给出以DLP为单位的诊断学参考水平作为对照.应用个体化的扫描方案是降低儿童剂量的有效手段.     

Radiation exposure to personnel in cardiac catheterization laboratories

Radiation exposure in personnel of cardiac catheterization units is based on local dosimetry during patient investigations. In the present study, dose rates were measured at various heights in representative locations, with and without fixed radiation protection shields in place. To determine the effective dose values, TLD measurements were performed using on Alderson phantom to generate radiation scatter and a second phantom in the position of the cardiologist performing the catheterization. Various types of personal radiation protection garment and fixed shields were considered in the calculations. Our results indicate on one hand that good protective standards can be achieved with effective doses below 1 mSv/year under optimized conditions. On the other hand, inappropriate radiation protection equipment can cause substantial increase of radiation doses. Alone the lack of a thyroid shield increases the effective dose of the cardiologist by a factor of 3. For the personnel, effective doses were generally higher than personal doses by a factor between 1.5 and 4.8 depending on the radiation protection situation.     

A feasibility study for image guided radiotherapy using low dose, high speed, cone beam X-ray volumetric imaging.

BACKGROUND AND PURPOSE: Image Guidance of patient set-up for radiotherapy can be achieved by acquiring X-ray volumetric images (XVI) with Elekta Synergy and registering these to the planning CT scan. This enables full 3D registration of structures from similar 3D imaging modalities and offers superior image quality, rotational set-up information and a large field of view. This study uses the head section of the Rando phantom to demonstrate a new paradigm of faster, lower dose XVI that still allows registration to high precision. MATERIALS AND METHODS: One high exposure XVI scan and one low exposure XVI scan were performed with a Rando Head Phantom. The second scan was used to simulate ultra low dose, fast acquisition, full and half scans by discarding a large number of projections before reconstruction. Dose measurements were performed using Thermo Luminescent Dosimeters (TLD) and an ion chamber. The reconstructed XVI scans were automatically registered with a helical CT scan of the Rando Head using the volumetric, grey-level, cross-correlation algorithm implemented in the Syntegra software package (Philips Medical Systems). Reproducibility of the registration process was investigated. RESULTS: In both XVI scans the body surface, bone-tissue and tissue air interfaces were clearly visible. Although the subjective image quality of the low dose cone beam scan was reduced, registration of both cone beam scans with the planning CT scan agreed within 0.1 mm and 0.1 degrees . Dose to the patient was reduced from 28mGy to less than 1mGy and the equivalent scan speed reduced to one minute or less. CONCLUSIONS: Automatic 3D registration of high speed, ultra low dose XVI scans with the planning CT scan can be used for precision 3D patient set-up verification/image guidance on a daily basis with out loss of accuracy when compared to higher dose XVI scans.     

Evaluation of image-guided helical tomotherapy for the retreatment of spinal metastasis

INTRODUCTION: Patients with vertebral metastasis that receive radiation therapy are typically treated to the spinal cord tolerance dose. As such, it is difficult to successfully deliver a second course of radiation therapy for patients with overlapping treatment volumes. In this study, an image-guided helical tomotherapy system was evaluated for the retreatment of previously irradiated vertebral metastasis. METHODS AND MATERIALS: Helical tomotherapy dose gradients and maximum cord doses were measured in a cylindrical phantom for geometric test cases with separations between the planning target volume (PTV) and the spinal cord organ at risk (OAR) of 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm. Megavoltage computed tomography (CT) images were examined for their ability to localize spinal anatomy for positioning purposes by repeat imaging of the cervical spine in an anthropomorphic phantom. In addition to the phantom studies, 8 patients with cord compressions that had received previous radiation therapy were retreated to a mean dose of 28 Gy using conventional fractionation. RESULTS AND DISCUSSION: Megavoltage CT images were capable of positioning an anthropomorphic phantom to within +/-1.2 mm (2sigma) superior-inferiorly and within +/-0.6 mm (2sigma) anterior-posteriorly and laterally. Dose gradients of 10% per mm were measured in phantom while PTV uniformity indices of less than 11% were maintained. The calculated maximum cord dose was 25% of the prescribed dose for a 10-mm PTV-to-OAR separation and 71% of the prescribed dose for a PTV-to-OAR separation of 2 mm. Eight patients total have been treated without radiation-induced myelopathy or any other adverse effects from treatment. CONCLUSIONS: A technique has been evaluated for the retreatment of vertebral metastasis using image-guided helical tomotherapy. Phantom and patient studies indicated that a tomotherapy system is capable of delivering dose gradients of 10% per mm and positioning the patient within 1.2 mm without the use of special stereotactic immobilization.     

Radiation Doses to the Lens of the Eye During Computerised Tomography of the Orbit; A Comparison of Four Modern Computerised Tomography Units

A previous study has looked at the estimated radiation dose to the lens of the eye during CT scanning of the orbit, pituitary fossa and brain with a recently installed GE 9800 Quick CT using a phantom simulating the lens of the eye. In this study the same phantom was used to compare the estimated radiation dose delivered to the lens of the eye by three other newly installed CT units of different manufacture. There was significant variation between the doses measured from the four machines when operated with the parameters commonly used in clinical practice. However, in all cases scanning of the phantom using routine techniques delivered a dose to the simulated lens which was much lower than the threshold dose for cataracts. There is, never-the-less, a potential for delivery of much higher doses.     

CBCT图像质量质控体系建立及结果分析

目的 通过建立完善的图像质控体系来保证设备满足临床需要。方法 对Catphan₅₀₄模体进行高质量头部、标准剂量头部、盆腔扫描并分析各自CBCT图像,检测CT值线性、CT值均匀性、空间分辨力、密度分辨力是否满足要求。采用成组t检验比较不同扫描条件的结果差异。结果采用标准剂量头部扫描条件得到的CT值更接近标准CT值,优于盆腔扫描条件得到的结果。CT值均匀性检测结果显示标准剂量头部优于高质量头部和盆腔(9.7±3.9∶17.9±5.3,P=0.00和9.5±4.0∶31.1±5.7,P=0.00)。密度分辨力高质量头部、盆腔扫描方式优于标准剂量头部(5.6±0.1∶1.3±0.5,P=0.00和6.0±1.0∶1.3±0.5,P=0.00)。空间线性距离结果十分准确,范围为4.98~5.06 cm。结论 设备空间线性距离准确、稳定,而CT值线性、CT值均匀性受扫描条件影响较大。对空间分辨力、密度分辨力则要做到因设备不同而设定标准与误差范围。     

Performance evaluation of an 85-cm-bore X-ray computed tomography scanner designed for radiation oncology and comparison with current diagnostic CT scanners

INTRODUCTION: The demand for computed tomography (CT) virtual simulation is constantly increasing with the wider adoption of three-dimensional conformal and intensity-modulated radiation therapy. Virtual simulation CT studies are typically acquired on conventional diagnostic scanners equipped with an external patient positioning laser system and specialized planning and visualization software. Virtual simulation technology has matured to a point where conventional simulators may be replaced with CT scanners. However, diagnostic CT scanner gantry bores (typically 65-70 cm) can present an obstacle to the CT simulation process by limiting patient positions, compared to those that can be attained in a conventional simulator. For example, breast cancer patients cannot always be scanned in the treatment position without compromising reproducibility and appropriateness of setup. Extremely large patients or patients requiring special immobilization or large setup devices are often unable to enter the limited-bore gantry. A dedicated 85-cm-bore radiation oncology CT scanner has the potential to eliminate these problems. The scanner should provide diagnostic-quality images at diagnostic-comparable dose levels. The purpose of this study was to independently evaluate the performance of a novel 85-cm-bore CT X-ray scanner designed specifically for radiation oncology and compare it against diagnostic-type, 70-cm-bore scanners that may be used in the same setting. MATERIALS AND METHODS: We performed image quality and dosimetric measurements on an 85-cm-bore CT scanner (AcQSim CT, Marconi Medical Systems, Inc., Cleveland, OH) and a 70-cm-bore, diagnostic-type scanner (UltraZ CT, Marconi Medical Systems, Inc.). Image quality measurements were performed using a manufacturer-supplied phantom (Performance Phantom, Marconi Medical Systems, Inc.), following the manufacturer's suggested testing procedures, and an independent image quality phantom (CATPHAN 500, The Phantom Laboratory, New York, NY). The standard image quality parameters evaluated for the purpose of comparison were as follows: slice thickness accuracy, high-contrast resolution (limiting spatial resolution), low-contrast resolution, uniformity and noise, and CT number accuracy and linearity. Standard head and body protocols were employed throughout most of our measurements and were kept equal between the two scanners. The computed tomography dose index was measured for standard head and body imaging protocols using accepted methods and procedures. For comparison purposes, data for a diagnostic-type, 70-cm-bore scanner (GE HighSpeed CT/i) were extracted from the literature. The results obtained for the 85-cm-bore scanner are compared with the following: (1) manufacturer-provided autoperformance phantom test results (validating its use for routine quality assurance), (2) a similar set of measurements performed on a conventional 70-cm-bore, diagnostic-type CT scanner (UltraZ CT, Marconi Medical Systems, Inc.), and (3) current available data on other diagnostic-type CT scanners (GE HighSpeed CT/i). RESULTS: Head and body doses seem on average to be slightly (1-2 cGy) higher for the 85-cm-bore unit than for conventional 70-cm units. Measured slice thickness was within acceptable criteria, +/-0.5 mm. There does not seem to be any significant difference in high-contrast resolution. Both units render a limiting value of approximately 7-8 lp/cm for slice thickness 8-10 mm. Both units exhibit comparable CT number uniformity, accuracy, and linearity. Noise levels seem to be slightly increased (by approximately 0.05-0.2%) for the large-bore geometry. Low-contrast resolution for both units was comparable (4.5-5.5 mm @ 0.35%). All image quality parameters are well within diagnostic acceptable levels. CONCLUSION: The overall imaging performance and mechanical integrity of the 85-cm-bore scanner are comparable to those of conventional diagnostic scanners that may be employed in a radiation oncology setting.     

Investigations of peripheral dose for helical tomotherapy

PurposeWhenever treating a patient with percutaneous radiotherapy, a certain amount of dose is inevitably delivered to healthy tissue. This is mainly due to beam's entry and exit in the region of the target volume. In regions distant from the target volume, dose is delivered by leakage from the MLC and head scatter from the accelerator head and phantom scatter from the target volume (peripheral dose). Helical tomotherapy is a form of radiation therapy with a uniquely designed machine and delivery pattern which influence the peripheral dose. The goal of this work was to investigate peripheral dose in helical tomotherapy. The experiments were used to establish a complex characterization of the peripheral dose.Materials and methodsA 30*30*60cm³ slab phantom and TLD-100 (Lithium fluoride) were used for the experiments. Treatment procedures were generated with the tomotherapy planning system (TPS). Additionally, procedures were created on the Operator Station of the tomotherapy system without a calculation of the dose distribution. The peripheral dose which was produced by a typical tomotherapy treatment plan was measured. Furthermore, these procedures were used to differentiate the parts of the peripheral dose in phantom scatter dose and head scatter and leakage dose. Additionally, the relation between peripheral dose and treatment time and between peripheral dose and delivered dose was investigated. Additionally, the peripheral dose was measured in an Alderson phantom.ResultsDistances of 30cm or more resulted in a decrease of the peripheral dose to less than 0.1% of the target dose. The measured doses have an offset of approximately 1cGy in comparison to the calculated doses from the TPS. The separated head scatter and leakage dose was measured in the range of 1cGy for typical treatments. Furthermore, the investigations show a linear correlation between head scatter leakage dose and treatment time and between scatter dose parts and delivered dose. A peripheral dose of 0.28% of the target dose was measured in the Alderson phantom at a distance of 17.5cm from the edge of the target volume.ConclusionsThe peripheral dose delivered by a tomotherapy treatment is clinically unobjectionable. The measurements confirmed a linear correlation between head scatter and leakage and treatment time and between scatter dose and delivered dose.     

螺旋断层放疗系统调强放疗验证

目的 通过螺旋断层放疗系统一系列调强放疗验证方法的研究,探讨其调强放疗的质量保证验证方法是否可行.方法 采用断层放疗计划系统进行调强放疗计划设计.为实现其剂量验证,笔者采用圆柱形固体水模体、0.056cm3 AISL电离室及EDR2胶片来实现对计划进行绝对剂量及相对剂量验证.将剂最胶片和电离室分别置于模体中,调用患者治疗计划束流数据对模体进行模拟照射;由此得出轴向截面上的等剂量分布和点绝对剂量,与计划模体的等剂量曲线及计算剂量结果进行比对.束流照射前,利用调强放疗兆伏特CT对摆位模体实行图像引导,与计划系统中模体千伏特CT图像进行配准比较,实现验证模体摆位准确性.结果 轴向测得注量分布与断层放疗计划系统计算结果相一致,测量点绝对剂量测量的结果与计划系统的计算误差均在±3%以内.测量模体的摆位误差基本可保持在1mm以内,但由于床从摆位虚拟中心到束流中心之间存在垂直下降2mm的系统误差,需要在模体或患者摆位中予以考虑.结论 3个月临床实践证明断层放疗的调强放疗所采用上述质量保证措施是切实可行的,建立了其质最保证体系.     

Computed tomography pelvimetry: Accuracy and radiation dose compared with conventional pelvimetry

Several publications in the past few years have indicated that computed tomography (CT) pelvimetry is preferable to conventional pelvimetry when considering accuracy and radiation dose. Many of the previous publications have, however, compared state of the art CT pelvimetry with outmoded conventional pelvimetry techniques. This study compared both the accuracy and the radiation dose of CT pelvimetry with conventional pelvimetry as practised in two large teaching obstetric hospitals in Melbourne. The study did not demonstrate any significant difference in the accuracy between the two methods. The radiation dose to the fetal gonads was also similar. The radiation dose using CT pelvimetry could be significantly lowered if the axial CT section through the ischial spines were excluded from the CT technique.     

Whole-body dose from tomotherapy delivery

Purpose: To measure whole-body dose in tomotherapy of the head and neck region resulting from internal patient scatter and linear accelerator leakage.Methods and Materials: Treatments are performed using a commercial computer-controlled intensity modulated radiation therapy planning and delivery system (Peacock, NOMOS Corp.) and a 6-MV linear accelerator (Clinac 6/100, Varian Corp.). The patient dose outside the treatment field is measured in a water-equivalent phantom using thermoluminescent dosimetry. The whole-body dose components from internal scatter and leakage are separately determined. The use of fixed-portal leakage and scattered radiation measurements to estimate the whole-body dose from tomotherapy is evaluated.Results: The internally scattered dose is significant near the target, but becomes negligible relative to the leakage dose beyond 15 cm from the target. Dose at 10 cm from the target volume, due to internal scatter and leakage, is approximately 2.5% of the total target dose, reducing to 0.5% at 30 cm. The measured dose is relatively uniform throughout the phantom.Conclusion: The whole-body dose equivalent from a tomotherapy treatment is greater than that from conventional radiation therapy. Further studies are required to assess the trade-off between improved dose distribution conformality and a possible slight increase in radiation-induced fatal malignancies. The accuracy of using fixed-portal leakage and scattered dose measurements to estimate the whole-body dose from tomotherapy treatments is adequate, if the appropriate fixed-portal field size equivalent is used.     

CT值-相对电子密度转换曲线的影响因素分析

目的 探讨本院使用不同扫描参数、电子密度体模和CT机对CT值-相对电子密度(CT-RED)转换曲线的影响因素。方法 在不同扫描电压、层厚下测量TM164CT性能模体和CIRS-062电子密度模体不同电子密度插件在东芝AQUILION^TM型、西门子SOMATOM^TMSENSATION^TM 64型CT和西门子SOMATOM^TMSENSATION^TM OPEN型CT机扫描的CT值,建立相应的CT-RED转换曲线并进行比较。结果 1、2、3 mm扫描层厚及不同扫描电流对CT值影响可忽略,低原子序数材料在不同型号CT、不同扫描电压下的CT值差异可忽略;不同扫描电压对高原子序数材料CT值有明显差异,同台CT机出现的最大差异约为400 HU;两种模体在软组织-致密骨范围内所提供的CT值有明显差异,最大可达约500 HU。结论 不同电子密度模体、CT机及扫描电压对CT-RED转换曲线高原子序数材料部分有影响,因此在治疗计划系统使用前必须根据临床使用条件选用合适的电子密度模体对该曲线进行测量,以保证治疗计划剂量计算的精确度。     

Randomized prospective comparison of non‐contrast enhanced helical computed tomography and intravenous urography in the diagnosis of acute ureteric colic

Non‐contrast enhanced helical CT has become an accepted technique for evaluating acute ureteric colic. The results of a randomized prospective comparison of the accuracy, cost and radiation dose of CT and intravenous urography (IVU) are presented. All patients presenting to the Emergency Department with symptoms and signs suggestive of ureteric colic over a 16‐month period (n = 242) were randomized to CT or IVU. Follow up was obtained for 228 patients (94%), with 14 patients (6%) lost to follow up. One hundred and twenty‐three patients (54%) underwent CT and 105 (46%) had an IVU. At follow up the sensitivity and specificity of CT were each 100%, while those of IVU were 99% and 100%, respectively. Computed tomography demonstrated seven of 26 (27%) potential alternative diagnoses, whereas IVU suggested one of 23 (4%). Estimates of the average effective dose were calculated for CT (4.95 mSv) and IVU (1.48 mSv, 95% confidence interval (CI) 0.7–2.27). Radiation dose and intravenous contrast material safety are discussed and the relative costs are considered. Computed tomography is as accurate as IVU in the diagnosis of acute ureteric colic. It confers certain major diagnostic benefits, and is a fast, well‐tolerated technique. Its accompanying higher effective radiation dose is recognized.