Investigating centering,scan length,and arm position impact on radiation dose across 4 countries from 4 continents during pandemic: Mitigating key radioprotection issues

PurposeOptimization of CT scan practices can help achieve and maintain optimal radiation protection. The aim was to assess centering, scan length, and positioning of patients undergoing chest CT for suspected or known COVID-19 pneumonia and to investigate their effect on associated radiation doses.MethodsWith respective approvals from institutional review boards, we compiled CT imaging and radiation dose data from four hospitals belonging to four countries (Brazil, Iran, Italy, and USA) on 400 adult patients who underwent chest CT for suspected or known COVID-19 pneumonia between April 2020 and August 2020. We recorded patient demographics and volume CT dose index (CTDI_vol) and dose length product (DLP). From thin-section CT images of each patient, we estimated the scan length and recorded the first and last vertebral bodies at the scan start and end locations. Patient mis-centering and arm position were recorded. Data were analyzed with analysis of variance (ANOVA).ResultsThe extent and frequency of patient mis-centering did not differ across the four CT facilities (>0.09). The frequency of patients scanned with arms by their side (11–40% relative to those with arms up) had greater mis-centering and higher CTDI_vol and DLP at 2/4 facilities (p = 0.027–0.05). Despite lack of variations in effective diameters (p = 0.14), there were significantly variations in scan lengths, CTDI_vol and DLP across the four facilities (p < 0.001).ConclusionsMis-centering, over-scanning, and arms by the side are frequent issues with use of chest CT in COVID-19 pneumonia and are associated with higher radiation doses.     

How Much Is the Dose Varying between Follow-Up CT-Examinations Performed on the Same Scanner with the Same Imaging Protocol?

PurposeTo investigate the dose variation between follow-up CT examinations, when a patient is examined several times on the same scanner with the identical scan protocol which comprised automated exposure control.ResultsThe median percentage difference in DLP between follow-up examinations was 9.6% for CH-CT, 10.3% for LI-CT, and 10.1% for AB-CT; the median percentage difference in CTDI_vol 8.3% for CH-CT, 7.4% for LI-CT and 7.7% for AB-CT (p<0.0001 for all values). The maximum difference in DLP between follow-up examinations was 67.5% for CH-CT, 50.8% for LI-CT and 74.3% for AB-CT; the maximum difference in CTDI_vol 62.9% for CH-CT, 47.2% for LI-CT, and 49% for AB-CT.ConclusionA significant variance in the radiation dose occurs between follow-up CT examinations when the same CT scanner and the identical imaging protocol are used in combination with automated exposure control.     

Apport du TDM en imagerie multimodalité : le point de vue du physicien médical

The recent introduction of hybrid systems SPECT/CT and PET/CT in nuclear medicine, greatly improved the diagnostic accuracy for particular clinical indications, due to the possible attenuation correction of functional images and the availability of helpful anatomic information. The introduction of CT in the nuclear diagnostic process results in a significant increase of the patient dose. This increase should be justified and optimized considering both the clinical question and the CT settings available on these systems. The choice of CT settings directly affects the effective dose. It varies basically as the square of the tube voltage, linearly with the length of the scan and the product of the current by the rotation time of the tube. It is also inversely proportional to the pitch. For attenuation correction, the literature shows that it is possible to use a low CT tube current without significant effect on tumor FDG uptake or lesion size. Conversely low CT voltage must be used with caution, depending on the algorithm implemented in the CT hybrid device to transform CT Hounsfield units to the attenuation map at the appropriate energy. The radiation dose for anatomic correlation can be substantially lower than for diagnostic-quality CT. It is possible to reduce the patient's radiation dose by a factor of 2 or 3 by acquiring a low-dose PET/CT scan for anatomic correlation of adequate image quality if compared with diagnostic ¹⁸FDG PET/CT. Using specific CT settings, the effective dose can range 7.3–11.3 mSv depending on the patient weight and age.     

64层螺旋CT不同剂量扫描对活动性继发性肺结核患者诊断价值、图像质量和辐射剂量的影响

目的:研究64层螺旋CT不同剂量扫描对活动性继发性肺结核患者诊断价值、图像质量和辐射剂量的影响,旨在为临床活动性继发性肺结核患者提供更为安全有效的检查方案。方法:将我院从2018年1月2020年1月收治的100例活动性继发性肺结核患者纳入研究。对所有患者分别进行低剂量(40 m A)以及常规剂量(120 m A)扫描和薄层重建。比较不同剂量扫描的诊断准确率、影像学表现、图像质量以及辐射参数、患者满意度。结果:64层螺旋CT低剂量扫描与常规剂量扫描诊断活动性继发性肺结核的准确率分别为92.00%、93.00%,两者比较差异无统计学意义(P>0.05)。低剂量扫描及常规剂量扫描在空洞、钙化灶、实变、磨玻璃密度影及树芽征发生率方面对比差异均无统计学意义(P>0.05)。低剂量扫描及常规剂量扫描在扫描图像质量、薄层重建图像质量方面对比差异均无统计学意义(P>0.05)。低剂量扫描各项扫描辐射参数均低于常规剂量扫描,差异有统计学意义(P<0.05)。低剂量扫描的患者满意度高于常规剂量扫描的患者(P<0.05)。结论:64层螺旋CT不同剂量扫描对活动性继发性肺结核患者的诊断价值及生成的图像质量相近,但低剂量扫描可有效降低辐射剂量,从而在一定程度上增加扫描的安全性,使患者满意度提升。     

A model-based approach of scatter dose contributions and efficiency of apron shielding for radiation protection in CT

Given the contribution of scattered radiations to patient dose in CT, apron shielding is often used for radiation protection. In this study the efficiency of apron was assessed with a model-based approach of the contributions of the four scatter sources in CT, i.e. external scattered radiations from the tube and table, internal scatter from the patient and backscatter from the shielding. For this purpose, CTDI phantoms filled with thermoluminescent dosimeters were scanned without apron, and then with an apron at 0, 2.5 and 5 cm from the primary field. Scatter from the tube was measured separately in air. The scatter contributions were separated and mathematically modelled. The protective efficiency of the apron was low, only 1.5% in scatter dose reduction on average. The apron at 0 cm from the beam lowered the dose by 7.5% at the phantom bottom but increased the dose by 2% at the top (backscatter) and did not affect the centre. When the apron was placed at 2.5 or 5 cm, the results were intermediate to the one obtained with the shielding at 0 cm and without shielding. The apron effectiveness is finally limited to the small fraction of external scattered radiation.     

Effects of X-Ray Dose On Rhizosphere Studies Using X-Ray Computed Tomography

X-ray Computed Tomography (CT) is a non-destructive imaging technique originally designed for diagnostic medicine, which was adopted for rhizosphere and soil science applications in the early 1980s. X-ray CT enables researchers to simultaneously visualise and quantify the heterogeneous soil matrix of mineral grains, organic matter, air-filled pores and water-filled pores. Additionally, X-ray CT allows visualisation of plant roots in situ without the need for traditional invasive methods such as root washing. However, one routinely unreported aspect of X-ray CT is the potential effect of X-ray dose on the soil-borne microorganisms and plants in rhizosphere investigations. Here we aimed to i) highlight the need for more consistent reporting of X-ray CT parameters for dose to sample, ii) to provide an overview of previously reported impacts of X-rays on soil microorganisms and plant roots and iii) present new data investigating the response of plant roots and microbial communities to X-ray exposure. Fewer than 5% of the 126 publications included in the literature review contained sufficient information to calculate dose and only 2.4% of the publications explicitly state an estimate of dose received by each sample. We conducted a study involving rice roots growing in soil, observing no significant difference between the numbers of root tips, root volume and total root length in scanned versus unscanned samples. In parallel, a soil microbe experiment scanning samples over a total of 24 weeks observed no significant difference between the scanned and unscanned microbial biomass values. We conclude from the literature review and our own experiments that X-ray CT does not impact plant growth or soil microbial populations when employing a low level of dose (<30 Gy). However, the call for higher throughput X-ray CT means that doses that biological samples receive are likely to increase and thus should be closely monitored.     

Comparative dose levels between CT-scanner and slot-scanning device (EOS system) in pregnant women pelvimetry

PurposeTo estimate fetal absorbed doses for pregnant women pelvimetry, a comparative study between EOS imaging system and low-dose spiral CT-scanner was carried out. For this purpose three different studies were investigated: in vivo, in vitro and Monte Carlo calculations.MethodsIn vivo dosimetry was performed, using OSL NanoDot dosimeters, to determine the dose to the skin of twenty pregnant women. In vitro studies were established by using a cubic phantom of water, in order to estimate the out of field doses. In the latter study, OSLDs were placed at depths corresponding to the lowest, average and highest position of the uterus. Monte Carlo calculations of effective doses to high radio-sensitive organs were established, using PCXMC and CTExpo software suites for EOS imaging system and CT-scanner, respectively.ResultsThe EOS imaging system reduces radiation exposure 4 to 8 times compared to the CT-scanner. The entrance skin doses were 74% (p-values <0.01) higher with the CT-scanner than with the EOS system. In the out of field region, the measured doses of the EOS system were reduced by 80% (p-values <0.02).Monte Carlo calculations confirmed that effective doses to organs are less accentuated for EOS than for CT pelvimetry.ConclusionsThe EOS system is less irradiating than the CT exam. The out-of-field dose which is significant, is lower in the EOS than in the CT-scanner and could be reduced even further by optimizing the time used for image acquisition.     

Infant Cardiac CT Angiography with 64-Slice and 256-Slice CT: Comparison of Radiation Dose and Image Quality Using a Pediatric Phantom

Background

The aims of this study were to investigate the image quality and radiation exposure of pediatric protocols for cardiac CT angiography (CTA) in infants under one year of age.

Methodology/Principal Findings

Cardiac CTA examinations were performed using an anthropomorphic phantom representing a 1-year-old child scanned with non-electrocardiogram-gated (NG), retrospectively electrocardiogram-gated helical (RGH) and prospectively electrocardiogram-gated axial (PGA) techniques in 64-slice and 256-slice CT scanners. The thermoluminescent dosimeters (TLD) were used for direct organ dose measurement, while dose-length product and effective mAs were also used to estimate the patient dose. For image quality, noise and signal-to-noise-ratio (SNR) were assessed based on regions-of-interest drawn on the reconstructed CT images, and were compared with the proposed cardiac image quantum index (CIQI). Estimated dose results were in accordant to the measured doses. The NG scan showed the best image quality in terms of noise and SNR. The PGA scan had better image quality than the RGH scan with 83.70% dose reduction. Noise and SNR were also corresponded to the proposed CIQI.

Conclusions/Significance

The PGA scan protocol was a good choice in balancing radiation exposure and image quality for infant cardiac CTA. We also suggested that the effective mAs and the CIQI were suitable in assessing the tradeoffs between radiation dose and image quality for cardiac CTA in infants. These results are useful for future implementation of dose reduction strategies in pediatric cardiac CTA protocols.     

Generating and using patient-specific whole-body models for organ dose estimates in CT with increased accuracy: Feasibility and validation

The estimation of patient dose using Monte Carlo (MC) simulations based on the available patient CT images is limited to the length of the scan. Software tools for dose estimation based on standard computational phantoms overcome this problem; however, they are limited with respect to taking individual patient anatomy into account. The purpose of this study was to generate whole-body patient models in order to take scattered radiation and over-scanning effects into account. Thorax examinations were performed on three physical anthropomorphic phantoms at tube voltages of 80 kV and 120 kV; absorbed dose was measured using thermoluminescence dosimeters (TLD). Whole-body voxel models were built as a combination of the acquired CT images appended by data taken from widely used anthropomorphic voxel phantoms. MC simulations were performed both for the CT image volumes alone and for the whole-body models. Measured and calculated dose distributions were compared for each TLD chip position; additionally, organ doses were determined.MC simulations based only on CT data underestimated dose by 8%–15% on average depending on patient size with highest underestimation values of 37% for the adult phantom at the caudal border of the image volume. The use of whole-body models substantially reduced these errors; measured and simulated results consistently agreed to better than 10%.This study demonstrates that combined whole-body models can provide three-dimensional dose distributions with improved accuracy. Using the presented concept should be of high interest for research studies which demand high accuracy, e.g. for dose optimization efforts.     

Dual-energy CT imaging of orbits during episcleral brachytherapy with Ru-106 plaques: A phantom study on its potential for plaque position verification

PurposeTo investigate the potential of dual energy CT (DECT) to suppress metal artifacts and accurately depict episcleral brachytherapy Ru-106 plaques after surgical placement.MethodsAn anthropomorphic phantom simulating the adult head after surgical placement of a Ru-106 plaque was employed. Nine DECT acquisition protocols for orbital imaging were applied. Monochromatic 140 keV images were generated using iterative reconstruction and an available metal artifact reduction algorithm. Generated image datasets were graded by four observers regarding the ability to accurate demarcate the Ru-106 plaque. Objective image quality and visual grading analysis (VGA) was performed to compare different acquisition protocols. The DECT imaging protocol which allowed accurate plaque demarcation at minimum exposure was identified. The eye-lens dose from orbital DECT, with and without the use of radioprotective bismuth eye-shields, was determined using Monte Carlo methods.ResultsAll DECT acquisition protocols were judged to allow clear demarcation of the plaque borders despite some moderate streaking/shading artifacts. The differences between mean observers’ VGA scores for the 9 DECT imaging protocols were not statistically significant (p > 0.05). The eye-lens dose from the proposed low-exposure DECT protocol was found to be 20.1 and 22.8 mGy for the treated and the healthy eye, respectively. Bismuth shielding was found to accomplish >40% reduction in eye-lens dose without inducing shielding-related artifacts that obscure plaque delineation.ConclusionsDECT imaging of orbits after Ru-106 plaque positioning for ocular brachytherapy was found to allow artifact-free delineation of plaque margins at relatively low patient exposure, providing the potential for post-surgery plaque position verification.     

Data and methods to assess occupational exposure to personnel involved in cardiac catheterization procedures

PurposeTo provide normalized scatter exposure data and methods for reliable estimation of cumulative effective dose and eye-lens equivalent dose to personnel involved in fluoroscopically guided cardiac catheterization (FGCC) procedures.MethodsAn anthropomorphic phantom was placed supine on the table of a modern digital C-arm angiographic system and 17 different fluoroscopic projections commonly employed during FGCC procedures were represented. Scatter exposure rates at the waist and eye level were measured for varying exposure parameters and position in the operating room. The effect of beam field size, patient size, use of radioprotective garments and small variations in projection angulation and table height on scatter radiation was investigated.ResultsApart from the position and use of radio-protective garments, radiation burden to operators during fluoroscopic guidance was found to remarkably depend beam field size (>45% reduction if a 10 × 10 cm² instead of 15 × 15 cm² fluoroscopy beam is used) and patient size (>25% increased scatter for obese patients). In contrast, the variation of measured scatter exposure from a given projection was found to be <10% when the source to skin distance was altered by ±10 cm or beam angulation of a specific projection was altered by ±10°.ConclusionPresented scatter exposure data charts and methods allow for prospective and retrospective estimation of effective dose and eye-lens equivalent dose to personnel involved in any FGCC procedure. Projection specific maps of scatter exposure produced may enhance familiarization of involved medical staff to good radiation protection practice and optimization of working habits in the cardiac catheterization lab.     

光耦功率放大技术在CT超低剂量扫描的研究

目的将全新的光电耦合高电压强电流放大处理技术用于CT机的前置放大处理中,隔离噪声和高电压大电流放大图像信号,实现超低剂量扫描,高清晰成像。方法将光电耦合放大器制作成射线剂量仪,并用CT机等超低剂量120KV、3-6mA…对其曝光,并与标准射线剂量仪校准,使其输出值不仅为射线剂量值,更能显示为高电压和大电流的优质图像信噪比。结果超小电流扫描经探测和光耦放大后最大值为87.5V和0.96A,而噪声电压为0.13μV、电流仅为0.02μA,给超低剂量扫描和传输处理时的功耗及高电压的宽动态范围显示留了很大空间。结论 CT超低剂量扫描时光耦放大器可在源头彻底隔离各种噪声并超高倍放大、高电压大电流输出图像信号,可保证高清晰高分辨率成像。     

Scintigraphie des parathyroïdes double isotope Tc-MIBI/I dans l’hyperparathyroïdisme primaire : comparaison entre un protocole d’acquisition planaire et une TEMP de soustraction couplée à la TDM

In patient with primary hyperparathyroidism, preoperative imaging first objective is to determine accurately and reliably position and anatomic localization of enlarged parathyroid gland in order to guide surgeon for gland removal and to permit minimally invasive surgery. Although subtraction planar scintigraphy is an efficient imaging to diagnose hyperfunctioning parathyroid, the lack of anatomical reference for this single imaging technique could be obviated by hybrid imaging. We compared, in 23 patients with primary hyperparathyroidism, a planar scan of neck and mediastinum associated with a cervical anterior pinhole scan to a subtraction (¹²³I/^99mTc-MIBI) SPECT scan of neck and mediastinum fused with CT. Surgical and histopathologic findings were used as the standard of truth. Subtraction SPECT/CT appeared to be more sensitive and specific than planar protocol to diagnose and to accurately localize pathologic parathyroid. Sensitivity was 76 and 56 %, specificity was 100 and 80 % for hybrid SPECT/CT and planar protocol respectively. SPECT protocol was typically more efficient to diagnose pathologic parathyroid derived from upper gland and for patient with concomitant nodular goiter.     

On the need for massive additional shielding of a catheterization laboratory for the implementation of high dose rate 192Ir intravascular brachytherapy

Purpose: There is a widespread belief in the cardiology and radiation oncology community that high dose rate 192Ir intravascular brachytherapy cannot be implemented without massive additional shielding of the conventional catheterization labs. The purpose of this work is to show that this is a myth, which is not based on sound radiation protection principles.Methods: Exposure rates in air were calculated for a variety of point and line sources of 192Ir. Exposures per treatment at different distances from the source were calculated for a typical intravascular brachytherapy treatment of a 15-Gy dose at a radial distance of 2 mm from the source and for source lengths in the range of 0 to 10 cm. Additionally, exposure rates outside the catheterization lab were calculated for various lead shielding thicknesses typical of conventional X-ray facilities. These rates were used along with the NCRP recommendations on radiation facility design to assess shielding requirements.Results: For a treatment dose of 15 Gy at 2 mm, the occupational exposure per treatment at 2 m in air without any tissue attenuation or shielding was 7.8 mR for a lesion length of 3.0 cm. This exposure/treatment is independent of the dose rate or the activity of the source. However, it increases as lesion length is increased, increasing from 5.4 to 24.9 mR as lesion length increased from 2 to 10 cm. Exposures in unrestricted areas outside the catheterization lab using the NCRP shielding rationale can be kept below 2 mR per treatment and using appropriate workload, use, and occupancy factors below 2 mR per week.Conclusions: The feasibility of implementing a high dose rate 192Ir intravascular brachytherapy program in a catheterization laboratory is totally independent of the dose rate or the activity of the source. If it is feasible to implement 192Ir brachytherapy in a conventional catheterization lab using low activity 192Ir seeds, then it is also feasible to do so with a high activity 192Ir afterloader.     

Shielding disk position in intra-operative electron radiotherapy (IOERT): A Monte Carlo study

PurposeIn IOERT breast treatments, a shielding disk is frequently used to protect the underlying healthy structures. The disk is usually composed of two materials, a low-Z material intended to be oriented towards the beam and a high-Z material. As tissues are repositioned around the shield before treatment, the disk is no longer visible and its correct alignment with respect to the beam is guaranteed. This paper studies the dosimetric characteristics of four possible clinical positioning scenarios of the shielding disk. A new alignment method for the shielding disk in the beam is introduced. Finally, it suggests a new design for the shielding disk.MethodsAs the first step, the IOERT machine “Mobetron 1000” was modeled by using Monte Carlo simulation, tuning the MC model until an excellent match with the measured PDDs and profiles was achieved. Four possible shielding disk positioning scenarios were considered, determining the dosimetric impact. Furthermore, in our center, to prevent beam misalignment, we have developed a shielding disk equipped with guiding rods. Having ascertained a correct alignment between the disk and the beam, we can propose a new internal design of the shielding disk that can improve the dose distribution with a better coverage of the treated area.ResultsAll MC simulations were performed with a 12 MeV beam, the maximum energy of Mobetron 1000 and a 5.5 cm diameter flat tip applicator, this applicator being the most clinically used. The simulations were compared with measurements performed in a water phantom and showed good results within 2.2% of root mean square difference (RMSD). The misplacement positions of the shielding disk have dosimetric impacts in the treatment volume and a small translation could have a significant influence on healthy tissues. The D-scenario is the worst which could happens when the shielding disk is flipped upside down, giving up to 144% dose instead of 90% at the surface of the Pb/Al shielding disk. A new shielding design used, together with our alignment tool, is able to give a more homogeneous dose in the target area.ConclusionsThe accuracy of shielding disk position can still be problematic in IOERT dosimetry. Any method that can ascertain the good alignment between the shielding disk and the beam is beneficial for the dose distribution and is a prerequisite for an optimized shield internal design that could improve the coverage of the treated area and the protection of healthy tissues.     

The Impact of Iterative Reconstruction on Computed Tomography Radiation Dosimetry: Evaluation in a Routine Clinical Setting

Purpose

To evaluate the effect of introduction of iterative reconstruction as a mandated software upgrade on radiation dosimetry in routine clinical practice over a range of computed tomography examinations.

Methods

Random samples of scanning data were extracted from a centralised Picture Archiving Communication System pertaining to 10 commonly performed computed tomography examination types undertaken at two hospitals in Western Australia, before and after the introduction of iterative reconstruction. Changes in the mean dose length product and effective dose were evaluated along with estimations of associated changes to annual cancer incidence.

Results

We observed statistically significant reductions in the effective radiation dose for head computed tomography (22–27%) consistent with those reported in the literature. In contrast the reductions observed for non-contrast chest (37–47%); chest pulmonary embolism study (28%), chest/abdominal/pelvic study (16%) and thoracic spine (39%) computed tomography. Statistically significant reductions in radiation dose were not identified in angiographic computed tomography. Dose reductions translated to substantial lowering of the lifetime attributable risk, especially for younger females, and estimated numbers of incident cancers.

Conclusion

Reduction of CT dose is a priority Iterative reconstruction algorithms have the potential to significantly assist with dose reduction across a range of protocols. However, this reduction in dose is achieved via reductions in image noise. Fully realising the potential dose reduction of iterative reconstruction requires the adjustment of image factors and forgoing the noise reduction potential of the iterative algorithm. Our study has demonstrated a reduction in radiation dose for some scanning protocols, but not to the extent experimental studies had previously shown or in all protocols expected, raising questions about the extent to which iterative reconstruction achieves dose reduction in real world clinical practice.     

Imaging Non-Specific Wrist Pain: Interobserver Agreement and Diagnostic Accuracy of SPECT/CT,MRI, CT,Bone Scan and Plain Radiographs

Purpose

Chronic hand and wrist pain is a common clinical issue for orthopaedic surgeons and rheumatologists. The purpose of this study was 1. To analyze the interobserver agreement of SPECT/CT, MRI, CT, bone scan and plain radiographs in patients with non-specific pain of the hand and wrist, and 2. to assess the diagnostic accuracy of these imaging methods in this selected patient population.

Materials and Methods

Thirty-two consecutive patients with non-specific pain of the hand or wrist were evaluated retrospectively. All patients had been imaged by plain radiographs, planar early-phase imaging (bone scan), late-phase imaging (SPECT/CT including bone scan and CT), and MRI. Two experienced and two inexperienced readers analyzed the images with a standardized read-out protocol. Reading criteria were lesion detection and localisation, type and etiology of the underlying pathology. Diagnostic accuracy and interobserver agreement were determined for all readers and imaging modalities.

Results

The most accurate modality for experienced readers was SPECT/CT (accuracy 77%), followed by MRI (56%). The best performing, though little accurate modality for inexperienced readers was also SPECT/CT (44%), followed by MRI and bone scan (38% each). The interobserver agreement of experienced readers was generally high in SPECT/CT concerning lesion detection (kappa 0.93, MRI 0.72), localisation (kappa 0.91, MRI 0.75) and etiology (kappa 0.85, MRI 0.74), while MRI yielded better results on typification of lesions (kappa 0.75, SPECT/CT 0.69). There was poor agreement between experienced and inexperienced readers in SPECT/CT and MRI.

Conclusions

SPECT/CT proved to be the most helpful imaging modality in patients with non-specific wrist pain. The method was found reliable, providing high interobserver agreement, being outperformed by MRI only concerning the typification of lesions. We believe it is beneficial to integrate SPECT/CT into the diagnostic imaging algorithm of chronic wrist pain.     

不同剂量多排螺旋CT扫描对儿童肺结核的诊断价值比较研究

目的:探讨不同剂量多排螺旋CT扫描对儿童肺结核(PTB)的诊断价值。方法:以我院于2016年5月～2018年11月收治的156例PTB患儿为研究对象,根据患儿年龄分为A组52例(0～5岁)、B组52例(6～9岁)、C组52例(10～14岁)。三组患儿均进行低剂量64排螺旋CT扫描,其中A组剂量为20 MA,B组剂量为30 MA,C组剂量为40 MA,2 d后,三组患儿均进行常规剂量64排螺旋CT扫描,其中A组剂量为100 MA,B组和C组剂量均为150 MA。分别对比A组、B组、C组患儿低剂量与常规剂量CT扫描的扫描效果、图像优良率及辐射剂量。结果:A组、B组、C组患儿低剂量与常规剂量CT扫描对病灶数量、结节、空洞、胸膜粘连、钙化灶的显像率比较差异无统计学意义(P0.05),但A组、B组、C组患儿低剂量CT扫描对毛刺、磨玻璃影的显像率明显低于常规剂量CT扫描(P0.05);A组、B组、C组患儿低剂量与常规剂量CT扫描的图像优良率比较差异无统计学意义(P0.05);与常规剂量CT扫描相比,A组、B组、C组患儿低剂量CT扫描的剂量长度乘积(DLP)、CT剂量指数(CTDIvoI)、CT加权剂量指数(CTDIw)、放射剂量明显更低(P0.05)。结论:使用常规剂量多排螺旋CT扫描对PTB儿童毛刺、磨玻璃影的显像效果较好,但是使用低剂量多排螺旋CT扫描同样能够确保图像的质量,达到诊断要求,并且能够降低对患儿的辐射剂量,在考虑人体健康的前提下,建议使用低剂量多排螺旋CT扫描。     

A study to determine the impact of IMPT optimization techniques on prostate synthetic CT image sets dose comparison against CT image sets

BackgroundThe objective of this study is to determine the impact of intensity modulated proton therapty (IMPT) optimization techniques on the proton dose comparison of commercially available magnetic resonance for calculating attenuation (MRCA T) images, a synthetic computed tomography CT (sCT) based on magnetic resonance imaging (MRI) scan against the CT images and find out the optimization technique which creates plans with the least dose differences against the regular CT image sets.Material and methodsRegular CT data sets and sCT image sets were obtained for 10 prostate patients for the study. Six plans were created using six distinct IMPT optimization techniques including multi-field optimization (MFO), single field uniform dose (SFUD) optimization, and robust optimization (RO) in CT image sets. These plans were copied to MRCA T, sCT datasets and doses were computed. Doses from CT and MRCA T data sets were compared for each patient using 2D dose distribution display, dose volume histograms (DVH), homogeneity index (HI), conformation number (CN) and 3D gamma analysis. A two tailed t-test was conducted on HI and CN with 5% significance level with a null hypothesis for CT and sCT image sets.ResultsAnalysis of ten CT and sCT image sets with different IMPT optimization techniques shows that a few of the techniques show significant differences between plans for a few evaluation parameters. Isodose lines, DVH, HI, CN and t-test analysis shows that robust optimizations with 2% range error incorporated results in plans, when re-computed in sCT image sets results in the least dose differences against CT plans compared to other optimization techniques. The second best optimization technique with the least dose differences was robust optimization with 5% range error.ConclusionThis study affirmatively demonstrates the impact of IMPT optimization techniques on synthetic CT image sets dose comparison against CT images and determines the robust optimization with 2% range error as the optimization technique which gives the least dose difference when compared to CT plans.