Ultra-low dose whole-body CT for attenuation correction in a dual tracer PET/CT protocol for multiple myeloma

PurposeTo investigate within phantoms the minimum CT dose allowed for accurate attenuation correction of PET data and to quantify the effective dose reduction when a CT for this purpose is incorporated in the clinical setting.MethodsThe NEMA image quality phantom was scanned within a large parallelepiped container. Twenty-one different CT images were acquired to correct attenuation of PET raw data. Radiation dose and image quality were evaluated.Thirty-one patients with proven multiple myeloma who underwent a dual tracer PET/CT scan were retrospectively reviewed. ¹⁸F-fluorodeoxyglucose PET/CT included a diagnostic whole-body low dose CT (WBLDCT: 120 kV-80mAs) and ¹¹C-Methionine PET/CT included a whole-body ultra-low dose CT (WBULDCT) for attenuation correction (100 kV-40mAs). Effective dose and image quality were analysed.ResultsOnly the two lowest radiation dose conditions (80 kV-20mAs and 80 kV-10mAs) produced artifacts in CT images that degraded corrected PET images. For all the other conditions (CTDI_vol ≥ 0.43 mGy), PET contrast recovery coefficients varied less than ± 1.2%.Patients received a median dose of 6.4 mSv from diagnostic CT and 2.1 mSv from the attenuation correction CT. Despite the worse image quality of this CT, 94.8% of bone lesions were identifiable.ConclusionPhantom experiments showed that an ultra-low dose CT can be implemented in PET/CT procedures without any noticeable degradation in the attenuation corrected PET scan. The replacement of the standard CT for this ultra-low dose CT in clinical PET/CT scans involves a significant radiation dose reduction.     

Normalized glandular dose coefficients in mammography,digital breast tomosynthesis and dedicated breast CT

PurposeTo provide mean glandular dose (MGD) estimates via Monte Carlo (MC) simulations as a function of the breast models and scan parameters in mammography, digital breast tomosynthesis (DBT) and dedicated breast CT (BCT).MethodsThe MC code was based on GEANT4 toolkit. The simulated compressed breast was either a cylinder with a semi-circular section or ad hoc shaped for oblique view (MLO). In DBT we studied the influence of breast models and exam parameters on the T-factors (i.e. the conversion factor for the calculation of the MGD in DBT from that for a 0-degree projection), and in BCT we investigated the influence on the MGD estimates of the ion chamber volume used for the air kerma measurements.ResultsIn mammography, a model representative of a breast undergoing an MLO view exam did not produce substantial differences (0.4%) in MGD estimates, when compared to a conventional cranio-caudal (CC) view breast model. The beam half value layer did not present a significant influence on T-factors in DBT (<0.8%), while the skin model presented significant influence on MGD estimates (up to 3.3% at 30 degrees scan angle), increasing for larger scan angles. We derived a correction factor for taking into account the different ion chamber volume used in MGD estimates in BCT.ConclusionsA series of MC code modules for MGD estimates in 2D and 3D breast imaging have been developed in order to take into account the most recent advances in breast models.     

Accuracy of target delineation by positron emission tomography-based auto-segmentation methods after deformable image registration: A phantom study

PurposeDiagnostic positron emission tomography and computed tomography (PET/CT) images can be fused to the planning CT images by a deformable image registration (DIR). The aim of this study was to evaluate the standardized uptake value (SUV) and target delineation on deformed PET images.MethodsWe used a cylindrical phantom and removable inserts of four spheres (16–38 mm in diameter) and three ellipsoids with a volume equal to the 38-mm-diameter sphere (S38) in each. S38 was filled with 18F-fluorodeoxyglucose activity, and then PET/CT images were acquired. The contours of S38 were generated using original PET images by PET auto-segmentation (PET-AS) methods of (1) SUV2.5, (2) 40% of maximum SUV (SUV40%max), and (3) gradient-based (GB), and were deformed to the other inserts by DIR. We compared the volumes and the SUV_max with the generated contours using the deformed PET images.ResultsThe SUV_max was slightly decreased by DIR; the mean absolute difference was −0.10 ± 0.04. For SUV2.5 and SUV40%max, the differences in S38 volumes between the original and deformed PET images were less than 5%, regardless of deformation type. For the GB, the contoured volumes obtained from deformed PET images were larger than those of the original PET images for the deformation type of ellipsoids. When the S38 was deformed to the 16-mm-diameter sphere, the maximum volume difference was −22.8%.ConclusionsAlthough SUV fluctuations by DIR were negligible, the target delineation on deformed PET images by the GB should be carefully considered owing to the distortion of intensity profiles.     

Imaging performance of phase-contrast breast computed tomography with synchrotron radiation and a CdTe photon-counting detector

PurposeWithin the SYRMA-CT collaboration based at the ELETTRA synchrotron radiation (SR) facility the authors investigated the imaging performance of the phase-contrast computed tomography (CT) system dedicated to monochromatic in vivo 3D imaging of the female breast, for breast cancer diagnosis.MethodsTest objects were imaged at 38 keV using monochromatic SR and a high-resolution CdTe photon-counting detector. Signal and noise performance were evaluated using modulation transfer function (MTF) and noise power spectrum. The analysis was performed on the images obtained with the application of a phase retrieval algorithm as well as on those obtained without phase retrieval. The contrast to noise ratio (CNR) and the capability of detecting test microcalcification clusters and soft masses were investigated.ResultsFor a voxel size of (60 μm)³, images without phase retrieval showed higher spatial resolution (6.7 mm⁻¹ at 10% MTF) than corresponding images with phase retrieval (2.5 mm⁻¹). Phase retrieval produced a reduction of the noise level and an increase of the CNR by more than one order of magnitude, compared to raw phase-contrast images. Microcalcifications with a diameter down to 130 μm could be detected in both types of images.ConclusionsThe investigation on test objects indicates that breast CT with a monochromatic SR source is technically feasible in terms of spatial resolution, image noise and contrast, for in vivo 3D imaging with a dose comparable to that of two-view mammography. Images obtained with the phase retrieval algorithm showed the best performance in the trade-off between spatial resolution and image noise.     

Radiobiological risks in terms of effective dose and organ dose from 18F-FDG whole-body PET/CT procedures

IntroductionIntegrated Positron Emission Tomography (PET) with Computerized tomography (CT) (PET/CT) are widely used to diagnose, stage and track human diseases during whole body scanning. Multi-modality imaging is an interesting area of research that aims at acquiring united morphological-functional image information for accurate diagnosing and staging of the disease. However, PET/CT procedure accompanied with high radiation dose from CT and administered radioactivity. The aim of the present study was to estimate the patients’ dose from ¹⁸F-fluorodeoxyglucose imaging (18F-FDG) hybrid PET/CT whole body scan.Materials and methodsRADAR (Radiation Dose Assessment Resource) software was used to estimate the effective dose for 156 patients (110 (70.5%)) males and 46 (39.5%) female) examined using Discovery PET/CT 710, GE Medical Systems installed at Kuwait Cancer Control Center (KCCC).ResultsThe effective dose results presented in this PET/CT study ranged from (1.56–9.94 mSv). The effective dose was calculated to be 3.88 mSv in females and 3.71 mSv in males. The overall breast (female), lung, liver, kidney and thyroid were 7.4, 7.2, 5.2, 4, 3 and 2.9, respectively.For females, the body mass index (BMI) was 28.49 kg/m² and for males it was 26.50 kg/m² which showed overweight values for both genders. Conclusions: The findings indicate that the effective dose of 18F-FDG in both male and female patients was not substantially different. The study suggested that the risk–benefit proportions of any ¹⁸F-FDG whole body PET/CT scan should be clarified and carefully weighed. Patient’s doses are lower compared with previous studies.     

Comparison of 68GA-FAPI-04 PET/CT and 18F-FDG PET/CT in detection of metastatic bone disease in various cancers

ObjectiveOur aim in this retrospective study was to compare the diagnostic accuracy of ⁶⁸Ga-FAPI-04 PET/CT and ¹⁸F-FDG PET/CT in detecting bone metastases of various cancers and to evaluate the potential usefulness of ⁶⁸Ga-FAPI-04 PET/CT in detecting metastatic bone disease.Material and methodOur retrospective study included 44 patients diagnosed with bone metastases due to various cancers between January 2021 and February 2022. All patients underwent ⁶⁸Ga-FAPI-04 PET/CT and ¹⁸F-FDG PET/CT imaging within 14 days. In the semi-quantitative analysis of the skeletal system, all regions with higher uptake than background activity were considered pathological. SUVmax and Metastasis-to-background ratio (TBR) values were calculated from metastatic sites.ResultsA total of 827 bone metastases were detected in our study. The diagnostic accuracies of FAPI PET/CT and ¹⁸F-FDG PET/CT were 91.8% and 81.5%, respectively (P < 0.001). When all bone metastases were compared, the SUVmax of ⁶⁸Ga-FAPI-04 PET/CT was statistically significantly higher than that of ¹⁸F-FDG PET/CT (median 6.15 vs. 5.2; P < 0.001). When FDG and FAPI SUVmax values were compared according to metastasis types, FAPI SUVmax and TBR values in osteolytic, medullary and mixed type bone metastases were found to be statistically significantly higher than FDG (P-values: < 0.001, < 0.001, < 0.001, respectively). There was no statistically significant difference between FDG and FAPI SUVmax values in osteoblastic bone metastases (P = 0.26).ConclusionIt has been shown that ⁶⁸Ga-FAPI-04 PET/CT is superior to ¹⁸F-FDG PET/CT in detecting metastatic bone disease and may have more clinical impact on disease management.     

Comparative investigation of the detective quantum efficiency of direct and indirect conversion detector technologies in dedicated breast CT

PurposeTo investigate the dose saving potential of direct-converting CdTe photon-counting detector technology for dedicated breast CT.Materials and methodsWe analyzed the modulation transfer function (MTF), the noise power spectrum (NPS) and the detective quantum efficiency (DQE) of two detector technologies, suitable for breast CT (BCT): a flat-panel energy-integrating detector with a 70 μm and a 208 μm thick gadolinium oxysulfide (GOS) and a 150 μm thick cesium iodide (CsI) scintillator and a photon-counting detector with a 1000 μm thick CdTe sensor.ResultsThe measurements for GOS scintillator thicknesses of 70 μm and 208 μm delivered 10% pre-sampled MTF values of 6.6 mm⁻¹ and 3.2 mm⁻¹, and DQE(0) values of 23% and 61%. The 10% pre-sampled MTF value for the 150 μm thick CsI scintillator 6.9 mm⁻¹, and the DQE(0) value was 49%. The CdTe sensor reached a 10% pre-sampled MTF value of 8.5 mm⁻¹ and a DQE(0) value of 85%.ConclusionThe photon-counting CdTe detector technology allows for significant dose reduction compared to the energy-integrating scintillation detector technology used in BCT today. Our comparative evaluation indicates that a high potential dose saving may be possible for BCT by using CdTe detectors, without loss of spatial resolution.     

Megavoltage 2D topographic imaging: An attractive alternative to megavoltage CT for the localization of breast cancer patients treated with TomoDirect

PurposeTo show the usefulness of topographic 2D megavoltage images (MV2D) for the localization of breast cancer patients treated with TomoDirect (TD), a radiotherapy treatment technique with fixed-angle beams performed on a TomoTherapy system.MethodsA method was developed to quickly localize breast cancer patients treated with TD by registering the MV2D images produced before a TD treatment with reference images reconstructed from a kilovoltage CT simulation scanner and by using the projection of the beam-eye-view TD treatment field. Dose and image quality measurements were performed to determine the optimal parameters for acquiring MV2D images. A TD treatment was simulated on a chest phantom equipped with a breast attachment. MVCT and MV2D images were performed for 7 different shifted positions of the phantom and registered by 10 different operators with the simulation kilovoltage CT images.ResultsCompared to MVCT, MV2D imaging reduces the dose by a factor of up to 45 and the acquisition time by a factor of up to 49. Comparing the registration shift values obtained for the phantom images obtained with MVCT in the coarse mode to those obtained with MV2D, the mean difference is 1.0 ± 1.1 mm, −1.1 mm ± 1.1, and −0.1 ± 2.2 mm, respectively, in the lateral, longitudinal, and vertical directions.ConclusionsWith dual advantages (very fast imaging and a potentially reduced dose to the heart and contralateral organs), MV2D topographic images may be an attractive alternative to MVCT for the localization of breast cancer patients treated with TomoDirect.     

Few-view CT reconstruction via a novel non-local means algorithm

PurposeNon-local means (NLM) based reconstruction method is a promising algorithm for few-view computed tomography (CT) reconstruction, but often suffers from over-smoothed image edges. To address this problem, an adaptive NLM reconstruction method based on rotational invariance (ART-RIANLM) is proposed.MethodsThe method consists of four steps: 1) Initializing parameters; 2) ART reconstruction using raw data; 3) Positivity constraint of the reconstructed image; 4) Image updating by RIANLM filtering. In RIANLM, two kinds of rotational invariance measures which are average gradient (AG) and region homogeneity (RH) are proposed to calculate the distance between two patches and a novel NLM filter is developed to avoid over-smoothed image. Moreover, the parameter h in RIANLM which controls the decay of the weights is adaptive to avoid over-smoothness, while it is constant in NLM during the whole reconstruction process. The proposed method is validated on two digital phantoms and real projection data.ResultsIn our experiments, the searching neighborhood size is set as 15 × 15 and the similarity window is set as 3 × 3. For the simulated case of Shepp-Logan phantom, ART-RIANLM produces higher SNR (36.23 dB > 24.00 dB) and lower MAE (0.0006 < 0.0024) reconstructed images than ART-NLM. The visual inspection demonstrated that the proposed method could suppress artifacts or noises more effectively and recover image edges better. The result of real data case is also consistent with the simulation result.ConclusionsA RIANLM based reconstruction method for few-view CT is presented. Compared to the traditional ART-NLM method, SNR and MAE from ART-RIANLM increases 51% and decreases 75%, respectively.     

Evaluation of a cycle-generative adversarial network-based cone-beam CT to synthetic CT conversion algorithm for adaptive radiation therapy

PurposeImage-guided radiation therapy could benefit from implementing adaptive radiation therapy (ART) techniques. A cycle-generative adversarial network (cycle-GAN)-based cone-beam computed tomography (CBCT)-to-synthetic CT (sCT) conversion algorithm was evaluated regarding image quality, image segmentation and dosimetric accuracy for head and neck (H&N), thoracic and pelvic body regions.MethodsUsing a cycle-GAN, three body site-specific models were priorly trained with independent paired CT and CBCT datasets of a kV imaging system (XVI, Elekta). sCT were generated based on first-fraction CBCT for 15 patients of each body region. Mean errors (ME) and mean absolute errors (MAE) were analyzed for the sCT. On the sCT, manually delineated structures were compared to deformed structures from the planning CT (pCT) and evaluated with standard segmentation metrics. Treatment plans were recalculated on sCT. A comparison of clinically relevant dose-volume parameters (D₉₈, D₅₀ and D₂ of the target volume) and 3D-gamma (3%/3mm) analysis were performed.ResultsThe mean ME and MAE were 1.4, 29.6, 5.4 Hounsfield units (HU) and 77.2, 94.2, 41.8 HU for H&N, thoracic and pelvic region, respectively. Dice similarity coefficients varied between 66.7 ± 8.3% (seminal vesicles) and 94.9 ± 2.0% (lungs). Maximum mean surface distances were 6.3 mm (heart), followed by 3.5 mm (brainstem). The mean dosimetric differences of the target volumes did not exceed 1.7%. Mean 3D gamma pass rates greater than 97.8% were achieved in all cases.ConclusionsThe presented method generates sCT images with a quality close to pCT and yielded clinically acceptable dosimetric deviations. Thus, an important prerequisite towards clinical implementation of CBCT-based ART is fulfilled.     

Geometric inaccuracy and co-registration errors for CT,DynaCT and MRI images used in robotic stereotactic radiosurgery treatment planning

PurposeTo measure the combined errors due to geometric inaccuracy and image co-registration on secondary images (dynamic CT angiography (dCTA), 3D DynaCT angiography (DynaCTA), and magnetic resonance images (MRI)) that are routinely used to aid in target delineation and planning for stereotactic radiosurgery (SRS).MethodsThree phantoms (one commercial and two in-house built) and two different analysis approaches (commercial and MATLAB based) were used to quantify the magnitude of geometric image distortion and co-registration errors for different imaging modalities within CyberKnife’s MultiPlan treatment planning software. For each phantom, the combined errors were reported as a mean target registration error (TRE). The mean TRE’s for different intramodality imaging parameters (e.g., mAs, kVp, and phantom set-ups) and for dCTA, DynaCTA, and MRI systems were measured.ResultsOnly X-ray based imaging can be performed with the commercial phantom, and the mean TRE ± standard deviation values were large compared to the in-house analysis using MATLAB. With the 3D printed phantom, even drastic changes in treatment planning CT imaging protocols did not greatly influence the mean TRE (<0.5 mm for a 1 mm slice thickness CT). For all imaging modalities, the largest mean TRE was found on DynaCT, followed by T2-weighted MR images (albeit all <1 mm).ConclusionsThe user may overestimate the mean TRE if the commercial phantom and MultiPlan were used solely. The 3D printed phantom design is a sensitive and suitable quality assurance tool for measuring 3D geometric inaccuracy and co-registration errors across all imaging modalities.     

Investigation of the dose distribution for a cone beam CT system dedicated to breast imaging

Cone-beam breast Computed Tomography (bCT) is an X-ray imaging technique for breast cancer diagnosis, in principle capable of delivering a much more homogeneous dose spatial pattern to the breast volume than conventional mammography, at dose levels comparable to two-view mammography. We present an investigation of the three-dimensional dose distribution for a cone-beam CT system dedicated to breast imaging. We employed Monte Carlo simulations for estimating the dose deposited within a breast phantom having a hemiellipsoidal shape placed on a cylinder of 3.5 cm thickness that simulates the chest wall. This phantom represents a pendulant breast in a bCT exam with the average diameter at chest wall, assumed to correspond to a 5-cm-thick compressed breast in mammography. The phantom is irradiated in a circular orbit with an X-ray cone beam selected from four different techniques: 50, 60, 70, and 80 kVp from a tube with tungsten anode, 1.8 mm Al inherent filtration and additional filtration of 0.2 mm Cu. Using the Monte Carlo code GEANT4 we simulated a system similar to the experimental apparatus available in our lab. Simulations were performed at a constant free-in-air air kerma at the isocenter (1 μGy); the corresponding total number of photon histories per scan was 288 million at 80 kVp. We found that the more energetic beams provide a more uniform dose distribution than at low energy: the 50 kVp beam presents a frequency distribution of absorbed dose values with a coefficient of variation almost double than that for the 80 kVp beam. This is confirmed by the analysis of the relative dose profiles along the radial (i.e. parallel to the “chest wall”) and longitudinal (i.e. from “chest wall” to “nipple”) directions. Maximum radial deviations are on the order of 25% for the 80 kVp beam, whereas for the 50 kVp beam variations around 43% were observed, with the lowest dose values being found along the central longitudinal axis of the phantom.     

Evaluation of the Block Matching deformable registration algorithm in the field of head-and-neck adaptive radiotherapy

Background and purposeTo compare the accuracy of the Block Matching deformable registration (DIR) against rigid image registration (RIR) for head-and-neck multi-modal images CT to cone-beam CT (CBCT) registration.Material and methodsPlanning-CT and weekly CBCT of 10 patients were used for this study. Several volumes, including medullary canal (MC), thyroid cartilage (TC), hyoid bone (HB) and submandibular gland (SMG) were transposed from CT to CBCT images using either DIR or RIR. Transposed volumes were compared with the manual delineation of these volumes on every CBCT. The parameters of similarity used for analysis were: Dice Similarity Index (DSI), 95%-Hausdorff Distance (95%-HD) and difference of volumes (cc).ResultsWith DIR, the major mean difference of volumes was −1.4 cc for MC, revealing limited under-segmentation. DIR limited variability of DSI and 95%-HD. It significantly improved DSI for TC and HB and 95%-HD for all structures but SMG. With DIR, mean 95%-HD (mm) was 3.01 ± 0.80, 5.33 ± 2.51, 4.99 ± 1.69, 3.07 ± 1.31 for MC, TC, HB and SMG, respectively. With RIR, it was 3.92 ± 1.86, 6.94 ± 3.98, 6.44 ± 3.37 and 3.41 ± 2.25, respectively.ConclusionBlock Matching is a valid algorithm for deformable multi-modal CT to CBCT registration. Values of 95%-HD are useful for ongoing development of its application to the cumulative dose calculation.     

Simultaneous achievement of accurate CT number and image quality improvement for myocardial perfusion CT at 320-MDCT volume scanning

PurposeTo investigate differences in image-to-image variations between full- and half-scan reconstruction on myocardial CT perfusion (CTP) study.MethodsUsing a cardiac phantom we performed ECG-gated myocardial CTP on a second-generation 320-multidetector CT volume scanner. The heart rate was set at 60 bpm; once per second for a total of 24 s were performed. CT images were acquired at 80- and 120 kVp and subjected to full- and half-scan reconstruction. On images acquired at the same slice level we then measured image-to-image variations, coefficients of variance (CV), and image noise.ResultsThe image-to-image variations with full- and half-scan reconstruction were 1.3 HU vs. 27.2 HU at 80 kVp (p < 0.001) and 0.70 HU vs. 9.3 HU at 120 kVp (p < 0.001) even though the mean HU value was almost the same for both reconstruction methods. The CV of 80- and 120-kVp images of the left ventricular cavity decreased by 0.16% and 0.17%, respectively, with full-scan reconstruction; with half-scan reconstruction it decreased by 3.34% and 2.30%, respectively. Compared with half-scan reconstruction, the image noise was reduced by 27.2% at 80 kVp and by 28.0% at 120 kVp with full-scan reconstruction.ConclusionMyocardial CTP with full-scan reconstruction substantially decreased image-to-image variations and provided accurate CT attenuation.     

Valeur pronostique de la TEP/TDM dans le bilan initial du cancer du col utérin : SUVmax de la tumeur primitive et stadification ganglionnaire

PurposeWe investigated the prognostic significance of F-18 fluorodeoxyglucose (FDG) uptake measured as maximum Standardized Uptake Value (SUV_max) in primary tumor by positron emission tomography/computed tomography (PET/CT) in cervical cancer. The secondary objective was to determine the accuracy of the PET/CT for detecting pelvic lymph node (PLN) and para-aortic lymph node (PALN) metastases.MethodsThis retrospective study included 49 consecutive patients with stage IB1 to IVB cervical cancer. Univariate analysis was performed to determine the relationships between SUV_max value and pathological prognostics factors. Survival was estimated by Kaplan-Meier method. The gold standard of LN metastases was histologic.ResultsA significant difference in SUV_max was observed between stage I and stage II, stage I and stage IV and tumor size ≤ 4 cm and > 4 cm (P = 0.0001). There was a significant correlation between the SUV_max and tumor maximal size (r = 0.597) (P < 0.0001). PLN metastasis was found to be predictive of progression-free survival (P = 0.0007). The negative predictive value (NPV) of the PET/CT for PALN was 100% for locally advanced cervical carcinoma in 24 patients. The specificity and NPV of the PET/CT for PLN in eight early-stage cervical cancer were 100% and 87.5% (7/8) respectively. The PET/CT false-negative PLN measured less than 2 mm.ConclusionOur results demonstrate a correlation between SUV_max and tumor maximal size, which represents an indicator of tumor aggressiveness. PET/CT is effective to predict the absence of PALN in locally advanced cervical carcinoma. PET/CT is not sufficient to predict PLN in early-stage cancer without lymphadenectomy.     

Technical Note: Quality assessment of virtual monochromatic spectral images on a dual energy CT scanner

PurposeTo assess the quality of images obtained on a dual energy computed tomography (CT) scanner.MethodsImage quality was assessed on a 64 detector-row fast kVp-switching dual energy CT scanner (Revolution GSI, GE Medical Systems). The Catphan phantom and a low contrast resolution phantom were employed. Acquisitions were performed at eight different radiation dose levels that ranged from 9 mGy to 32 mGy. Virtual monochromatic spectral images (VMI) were reconstructed in the 40–140 keV range using all available kernels and iterative reconstruction (IR) at four different blending levels. Modulation Transfer Function (MTF) curves, image noise, image contrast, noise power spectrum and contrast to noise ratio were assessed.ResultsIn-plane spatial resolution at the 10% of the MTF curve was 0.60 mm⁻¹. In-plane spatial resolution was not modified with VMI energy and IR blending level. Image noise was reduced from 16.6 at 9 mGy to 6.7 at 32 mGy, while peak frequency remained within 0.14 ± 0.01 mm⁻¹. Image noise was reduced from 14.3 at IR 10% to 11.5 at IR 50% at a constant peak frequency. The lowest image noise and maximum peak frequency were recorded at 70 keV.ConclusionsOur results have shown how objective image quality is varied when different levels of radiation dose and different settings in IR are applied. These results provide CT operators an in depth understanding of the imaging performance characteristics in dual energy CT.     

Radiation dosimetry of 18F-flurocholine PET/CT studies in prostate cancer patients

PurposeWe aimed to evaluate the Equivalent Doses (H_Ts) to highly exposed organs as well as the Effective Dose (ED) for ¹⁸F-fluorocholine PET/CT scan in the follow-up of prostate cancer patients.MethodsFifty patients were administered with ¹⁸F-fluorocholine. The activities in organs with the highest uptake were derived by region-of-interest (ROI) analysis. OLINDA/EXM1.0 and Impact software were used to assess ED for the administered ¹⁸F-fluorocholine and CT scan, respectively, and the ¹⁸F-fluorocholine and CT-scan EDs summed to yield the total ED for the PET/CT procedure.ResultsThe calculated ¹⁸F-fluorocholine and CT scans EDs based on ICRP Publication 103 were 5.2 mSv/300 MBq and 6.7 mSv, respectively. The ¹⁸F-fluorocholine H_Ts to the liver, kidneys, spleen and pancreas were about threefold higher than those from the CT, which contributed a greater proportion of the total ED than the ¹⁸F-fluorocholine did.ConclusionsFor ¹⁸F-fluorocholine PET/CT procedures, about 40% of the ED is contributed by administered ¹⁸F-fluorocholine and 60% by the CT scan. The kidneys and liver were the highly exposed organs. Considering the large number of diagnostic procedures oncology patients undergo, radiation dosimetry is important in relation to the stochastic risk of such procedures.     

Can different Catphan phantoms be used in a multi-centre audit of radiotherapy CT image quality?

PurposeTo determine the variation between Catphan image quality CT phantoms, specifically for use in a future multi-centre image quality audit.Method14 Catphan phantoms (models 503, 504 and 604) were scanned on a Canon Aquilion Prime CT scanner using a single scan protocol. Measurements were made of noise in the uniformity section, visibility of low contrast targets and contrast, x-ray attenuation and CT number for 5 materials in the sensitometry section. Scans were also acquired using one phantom and varying reconstruction field of view, image slice thickness, effective tube-current-time product and iterative reconstruction settings to determine how the degree of inter-phantom variability compared with the magnitude of changes from scan parameter alteration.ResultsAcross all phantoms the mean CT value in the uniformity section was 7.0 (SD 0.9) range: 4.9–8.1 HU. For the different materials the CT numbers were air: −1004 ± 5, Polymethylpentene: −190 ± 2, Polystyrene: −42 ± 2, Delrin: 321 ± 5 and Teflon: 898 ± 8 HU. Consistency of low contrast targets through visual scoring was good. Measured contrast was lower (p < 0.001) with more variability for 504 versus 604 models. All phantoms produced identical tube current settings with x-ray tube current modulation, indicating no x-ray attenuation differences. The degree of change in image quality metrics between phantoms was small compared with results when scan parameters were varied.ConclusionCatphan phantoms model 604 showed minimal differences and will be used for multi-centre inter-comparison work, with the consistency between phantoms appropriate for measuring possible variations in image quality.     

Pretreatment CT and PET radiomics predicting rectal cancer patients in response to neoadjuvant chemoradiotherapy

BackgroundThe purpose of this study was to characterize pre-treatment non-contrast computed tomography (CT) and ¹⁸F-fluorodeoxyglucose positron emission tomography (PET) based radiomics signatures predictive of pathological response and clinical outcomes in rectal cancer patients treated with neoadjuvant chemoradiotherapy (NACR T).Materials and methodsAn exploratory analysis was performed using pre-treatment non-contrast CT and PET imaging dataset. The association of tumor regression grade (TRG) and neoadjuvant rectal (NAR) score with pre-treatment CT and PET features was assessed using machine learning algorithms. Three separate predictive models were built for composite features from CT + PET.ResultsThe patterns of pathological response were TRG 0 (n = 13; 19.7%), 1 (n = 34; 51.5%), 2 (n = 16; 24.2%), and 3 (n = 3; 4.5%). There were 20 (30.3%) patients with low, 22 (33.3%) with intermediate and 24 (36.4%) with high NAR scores. Three separate predictive models were built for composite features from CT + PET and analyzed separately for clinical endpoints. Composite features with α = 0.2 resulted in the best predictive power using logistic regression. For pathological response prediction, the signature resulted in 88.1% accuracy in predicting TRG 0 vs. TRG 1–3; 91% accuracy in predicting TRG 0–1 vs. TRG 2–3. For the surrogate of DFS and OS, it resulted in 67.7% accuracy in predicting low vs. intermediate vs. high NAR scores.ConclusionThe pre-treatment composite radiomics signatures were highly predictive of pathological response in rectal cancer treated with NACR T. A larger cohort is warranted for further validation.