Image synthesis of monoenergetic CT image in dual-energy CT using kilovoltage CT with deep convolutional generative adversarial networks

Purpose: To synthesize a dual-energy computed tomography (DECT) image from an equivalent kilovoltage computed tomography (kV-CT) image using a deep convolutional adversarial network. Methods: A total of 18,084 images of 28 patients are categorized into training and test datasets. Monoenergetic CT images at 40, 70, and 140 keV and equivalent kVCT images at 120 kVp are reconstructed via DECT and are defined as the reference images. An image prediction framework is created to generate monoenergetic computed tomography (CT) images from kV-CT images. The accuracy of the images generated by the CNN model is determined by evaluating the mean absolute error (MAE), mean square error (MSE), relative root mean square error (RMSE), peak signal-to-noise ratio (PSNR), structural similarity index (SSIM), and mutual information between the synthesized and reference monochromatic CT images. Moreover, the pixel values between the synthetic and reference images are measured and compared using a manually drawn region of interest (ROI). Results: The difference in the monoenergetic CT numbers of the ROIs between the synthetic and reference monoenergetic CT images is within the standard deviation values. The MAE, MSE, RMSE, and SSIM are the smallest for the image conversion of 120 kVp to 140 keV. The PSNR is the smallest and the MI is the largest for the synthetic 70 keV image. Conclusions: The proposed model can act as a suitable alternative to the existing methods for the reconstruction of monoenergetic CT images in DECT from single-energy CT images

Dose compensation based on biological effectiveness due to interruption time for photon radiation therapy

Objective:To evaluate the biological effectiveness of dose associated with interruption time; and propose the dose compensation method based on biological effectiveness when an interruption occurs during photon radiation therapy. Methods:The lineal energy distribution for human salivary gland tumor was calculated by Monte Carlo simulation using a photon beam. The biological dose (Dbio) was estimated using the microdosimetric kinetic model. The dose compensating factor with the physical dose for the difference of the Dbio with and without interruption (Δ) was derived. The interruption time (τ) was varied to 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, 10, 20, 30, 40, 50, 75, and 120 min. The dose per fraction and dose rate varied from 2 to 8 Gy and 0.1 to 24 Gy/min, respectively. Results:The maximum Δ with 1 Gy/min occurred when the interruption occurred at half the dose. The Δ with 1 Gy/min at half of the dose was over 3% for τ >= 20 min for 2 Gy, τ = 10 min for 5 Gy, and τ = 10 min for 8 Gy. The maximum difference of the Δ due to the dose rate was within 3% for 2 and 5 Gy, and achieving values of 4.0% for 8 Gy. The dose compensating factor was larger with a high dose per fraction and high-dose rate beams. Conclusion:A loss of biological effectiveness occurs due to interruption. Our proposal method could correct for the unexpected decrease of the biological effectiveness caused by interruption time. Advances in knowledge:For photon radiotherapy, the interruption causes the sublethal damage repair. The current study proposed the dose compensation method for the decrease of the biological effect by the interruption

Assessment of biological dosimetric margin for stereotactic body radiation therapy

Purpose: To develop a novel biological dosimetric margin (BDM) and to create a biological conversion factor (BCF) that compensates for the difference between physical dosimetric margin (PDM) and BDM, which provides a novel scheme of a direct estimation of the BDM from the physical dose (PD) distribution. Methods: The offset to isocenter was applied in 1‐mm steps along left‐right (LR), anterior‐posterior (AP), and cranio‐caudal (CC) directions for 10 treatment plans of lung stereotactic body radiation therapy (SBRT) with a prescribed dose of 48 Gy. These plans were recalculated to biological equivalent dose (BED) by the linearquadratic model for the dose per fraction (DPF) of d = 3–20 Gy/fr and α/β= 3 - 10. BDM and PDM were defined so that the region that satisfied that the dose covering 95% (or 98%) of the clinical target volume was greater than or equal to the 90% of the prescribed PD and BED, respectively. An empirical formula of the BCF was created as a function of the DPF. Results: There was no significant difference between LR and AP directions for neither the PDM nor BDM. On the other hand, BDM and PDM in the CC direction were significantly larger than in the other directions. BCFs of D95% and D98% were derived for the transverse (LR and AP) and longitudinal (CC) directions. Conclusions: A novel scheme to directly estimate the BDM using the BCF was developed. This technique is expected to enable the BED‐based SBRT treatment planning using PD‐based treatment planning systems

Synthesized effective atomic numbers for commercially available dual-energy CT

Purpose: The objective of this study was to assess synthesized effective atomic number (Zeff) values with a new developed tissue characteristic phantom and contrast material of varying iodine concentrations using single-source fast kilovoltage switching dual-energy CT (DECT) scanner. Methods: A newly developed multi energy tissue characterisation CT phantom and an acrylic phantom with various iodine concentrations of were scanned using single-source fast kilovoltage switching DECT (GE-DECT) scanner. The difference between the measured and theoretical values of Zeff were evaluated. Additionally, the difference and coefficient of variation (CV) values of the theoretical and measured values were compared with values obtained with the Canon-DECT scanner that was analysed in our previous study. Results: The average Zeff difference in the Multi-energy phantom was within 4.5%. The average difference of the theoretical and measured Zeff values for the acrylic phantom with variation of iodine concentration was within 3.3%. Compared to the results for the single-source Canon-DECT scanner used in our previous study, the average difference and CV of the theoretical and measured Zeff values obtained with the GE-DECT scanner were markedly smaller. Conclusions: The accuracy of the synthesized Zeff values with GE-DECT had a good agreement with the theoretical Zeff values for the Multi-Energy phantom. The GE-DECT could reduce the noise and the accuracy of the Zeff values than that with Canon-DECT for the varying iodine concentrations of contrast medium. Advances in knowledge: The accuracy and precision of the Zeff values of the contrast medium with the GE-DECT could be sufficient with human equivalent materials

Image synthesis of effective atomic number images using a deep convolutional neural network-based generative adversarial network

Background: The effective atomic numbers obtained from dual-energy computed tomography (DECT) can aid in characterization of materials. In this study, an effective atomic number image reconstructed from a DECT image was synthesized using an equivalent single-energy CT image with a deep convolutional neural network (CNN)-based generative adversarial network (GAN). Materials and methods: The image synthesis framework to obtain the effective atomic number images from a single-energy CT image at 120 kVp using a CNN-based GAN was developed. The evaluation metrics were the mean absolute error (MAE), relative root mean square error (RMSE), relative mean square error (MSE), structural similarity index (SSIM), peak signal-to-noise ratio (PSNR), and mutual information (MI). Results: The difference between the reference and synthetic effective atomic numbers was within 9.7% in all regions of interest. The averages of MAE, RMSE, MSE, SSIM, PSNR, and MI of the reference and synthesized images in the test data were 0.09, 0.045, 0.0, 0.89, 54.97, and 1.03, respectively. Conclusions: In this study, an image synthesis framework using single-energy CT images was constructed to obtain atomic number images scanned by DECT. This image synthesis framework can aid in material decomposition without extra scans in DECT.

Multileaf-collimator daily quality assurance of Vero4DRT system: our one-year experience

Purpose: We assessed the daily quality assurance (QA) of multi-leaf collimator (MLC) using the Vero4DRT system. Methods: As part of daily MLC QA, the irradiation field was set to 100 × 150 mm2 with a gantry angle of 0 º. Only the leaf positioning error values only were displayed. We developed an in-house program to easily acquire these values using an open source optical character recognition engine. This test was implemented between 24 August 2015 and 23 August 2016. Results: The maximum leaf positioning error was 0.40 mm in both banks. In addition, the maximum deviation was 0.10 mm in both banks. The average and standard deviation for left and right banks were 0.19 mm ± 0.11 mm and 0.15 mm ± 0.09 mm, respectively. In our one-year measurement, the leaf positioning error was less than 0.50 mm. Therefore, if the leaf position error for daily MLC QA exceeded 0.50 mm, then an external intervention is required.Conclusion: The daily MLC QA of our one-year evaluation of the Vero4DRT system demonstrates an excellent leaf accuracy and reproducibility, thereby giving confidence in the quality of the treatment

Stability assessment of radiation isocenter with the gimbaled linac system

Purpose: We report the results of our year-long radiation isocenter accuracy verification for daily quality assurance (QA) implementation on a Vero4DRT system. Methods: The radiation isocenter was calculated using a cube phantom with a steel ball of diameter 10 mm fixed to the center of the phantom. A single photon beam was set with a field size of 100 × 100 mm2. Coincidence of the centroid of the steel ball at kiloVolt X-ray imaging isocenter and megaVolt beam radiation isocenter at each gantry and ring angle was tested. This procedure was performed for gantry angles of 0°, 90°, 180°, and 270°, and ring angles of 0°, 20°, and 340°. The centroid of the steel ball and the center of the radiation field were calculated to analyze the radiation isocenter error. This analysis was automatically calculated using the Daily Check tool in the Vero4DRT system. This QA was implemented between 24 August 2015 and 23 August 2016.Results: The average and standard deviation for pan and tilt directions were 0.12 ± 0.10 mm and -0.20 ± 0.13 mm, respectively. The maximum radiation isocenter accuracy error was 0.50 mm in both directions. Conclusion: The radiation isocenter alignment for the one year duration of the experiment was performed with high accuracy

Fyn phosphorylates AMPK to inhibit AMPK activity and AMP-dependent activation of autophagy

We previously demonstrated that proto-oncogene Fyn decreased energy expenditure and increased metabolic phenotypes. Also Fyn decreased autophagy-mediated muscle mass by directly inhibiting LKB1 and stimulating STAT3 activities, respectively. AMPK, a downstream target of LKB1, was recently identified as a key molecule controlling autophagy. Here we identified that Fyn phosphorylates the α subunit of AMPK on Y436 and inhibits AMPK enzymatic activity without altering the assembly state of the AMPK heterotrimeric complex. As pro-inflammatory mediators are reported modulators of the autophagy processes, treatment with the pro-inflammatory cytokine TNFα resulted in 1) increased Fyn activity 2) stimulated Fyn-dependent AMPKα tyrosine phosphorylation and 3) decreased AICAR-dependent AMPK activation. Importantly, TNFα induced inhibition of autophagy was not observed when AMPKα was mutated on Y436. 4) These data demonstrate that Fyn plays an important role in relaying the effects of TNFα on autophagy and apoptosis via phosphorylation and inhibition of AMPK

Quality assurance for dynamic tumor tracking using the Vero4DRT system

Purpose: We perform quality assurance (QA) for indirect dynamic tumor tracking (DTT) using four-dimensional radiation therapy (the Vero4DRT™ system).Methods: A single photon beam was set with a 40 × 40 mm2 field size at a gantry angle of zero degrees and a low monitor unit setting of 200. Doses were measured using a 0.016 cm3 ionization chamber inserted in a phantom under stationary, DTT, and non-DTT conditions for sinusoidal (peak-to-peak) amplitude [A] and breathing period [T] (20 mm, 2 s; 20 mm, 4 s; and 40 mm, 4 s). The stationary condition was measured for comparison. Dose profiles were measured using Gafchromic EBT3 films in the phantom under the same conditions.Results: For chamber measurement, the relative doses were as follows: 0.99 with non-DTT and 1.00 with DTT at A = 20 mm and T = 2 s; 0.99 with non-DTT and 1.00 with DTT at A = 20 mm and T = 4 s; and 0.84 with non-DTT and 1.00 with DTT at A = 40 mm and T = 4 s. For film measurement, the spatial distances between the 90% dose of the dose profiles were as follows: 6.53 mm for non-DTT and 0.40 mm for DTT at A = 20 mm and T = 2 s; 6.33 mm for non-DTT and 0.15 mm for DTT at A = 20 mm and T = 4 s; and 10.61 mm for non-DTT and 0.17 mm with DTT at A = 40 mm and T = 4 s.Conclusion: Our results showed high dosimetric and geometric accuracy for DTT using four-dimensional modeling and marked reduction of the blurring effects on dose distribution. We recommend the use of a QA procedure for DTT performed using the Vero4DRT™ system