CT Number Changes Research Articles

Effect of Patient Positioning on CT Number Accuracy: A Phantom Study Comparing Energy Integrating and Deep Silicon Photon Counting Detector CT.

Patient positioning during clinical practice can be challenging, and mispositioning leads to a change in CT number. CT number fluctuation was assessed in single-energy (SE) EID, dual-energy (DE) EID, and deep silicon photon-counting detector (PCD) CT over water-equivalent diameter (WED) with different mispositions. A phantom containing five clinically relevant inserts (Mercury Phantom, Gammex) was scanned on a clinical EID CT and a deep silicon PCD CT prototype at vertical positions of 0, 4, 8, and 12 cm. EID scans used 120 kV and rapid kV-switching DE techniques. CT number was calculated for air, water, polystyrene, iodine 10 mg/mL, and bone. Ideal CT numbers were calculated using the NIST XCOM database toolkit. Comparison of measured to ideal CT number utilized relative root mean square error (RMSE). Trends in CT number versus WED were compared using linear regression and statistical comparisons to test for differences in slope. No statistical difference of CT number with mispositioning was seen between acquisition modes. CT number fluctuation was larger due to WED than mispositioning for all material inserts. Water, iodine, and bone, for deep silicon PCD CT had statistically significant (P < 0.05) smaller slopes compared to EIDof CT number over WED for all tested mispositions. The accuracy of deep silicon PCD CT was higher than either SE or DE EID CT for all materials at all mispositions except for polystyrene. WED (ie, patient size) contributes to CT number fluctuation more than mispositioning. The change in CT number was significantly smaller, and CT number accuracy was higher for deep silicon PCD CT in this phantom study.

Needle artifact reduction during interventional CT procedures using a silver filter

BackgroundMAR algorithms have not been productized in interventional imaging because they are too time-consuming. Application of a beam hardening filter can mitigate metal artifacts and doesn’t increase computational burden. We evaluate the ability to reduce metal artifacts of a 0.5 mm silver (Ag) additional filter in a Multidetector Computed Tomography (MDCT) scanner during CT-guided biopsy procedures.MethodsA biopsy needle was positioned inside the lung field of an anthropomorphic phantom (Lungman, Kyoto Kagaku, Kyoto, Japan). CT acquisitions were performed with beam energies of 100 kV, 120 kV, 135 kV, and 120 kV with the Ag filter and reconstructed using a filtered back projection algorithm. For each measurement, the CTDIvol was kept constant at 1 mGy. Quantitative profiles placed in three regions of the artifact (needle, needle tip, and trajectory artifacts) were used to obtain metrics (FWHM, FWTM, width at − 100 HU, and absolute error in HU) to evaluate the blooming artifact, artifact width, change in CT number, and artifact range. An image quality analysis was carried out through image noise measurement. A one-way analysis of variance (ANOVA) test was used to find significant differences between the conventional CT beam energies and the Ag filtered 120 kV beam.ResultsThe 120 kV-Ag is shown to have the shortest range of artifacts compared to the other beam energies. For needle tip and trajectory artifacts, a significant reduction of − 53.6% (p < 0.001) and − 48.7% (p < 0.001) in the drop of the CT number was found, respectively, in comparison with the reference beam of 120 kV as well as a significant decrease of up to − 34.7% in the artifact width (width at − 100 HU, p < 0.001). Also, a significant reduction in the blooming artifact of − 14.2% (FWHM, p < 0.001) and − 53.3% (FWTM, p < 0.001) was found in the needle artifact. No significant changes (p > 0.05) in image noise between the conventional energies and the 120 kV-Ag were found.ConclusionsA 0.5 mm Ag additional MDCT filter demonstrated consistent metal artifact reduction generated by the biopsy needle. This reduction may lead to a better depiction of the target and surrounding structures while maintaining image quality.

Treatment Response Assessment Using Daily Dual-Energy CT during Pre-Operative Radiation Therapy for Early-Stage Breast Cancer

<h3>Purpose/Objective(s)</h3> We have previously reported that the low energy mono-energetic images (MEI) derived from dual-energy CT (DECT) can amplify the detection of radiation-induced changes in tissue. This work aims to investigate the use of low energy MEI derived from daily DECT to assess tumor response during radiation therapy (RT) of early-stage breast cancer. <h3>Materials/Methods</h3> Daily DECT data acquired during routine CT-guided RT delivery for 35 early-stage breast cancer patients enrolled in an institutional prospective pre-operative accelerated partial breast irradiation trial, along with tumor pathological data collected from the biopsy before RT and the excised tissue from the surgery post RT, were analyzed. All patients were treated with 30 Gy in 5 fractions in two weeks. The DECTs were acquired immediately before the fractional dose delivery using an in-room CT scanner equipped with a sequential DE protocol. MEI images across a range of x-ray energies were reconstructed using an image-based material decomposition. Fractional changes in mean CT number (mCTN) in gross tumor volume (GTV) on MEIs were extracted and the changes from the first to the last fraction were correlated to the tumor cellularity changes from the pathological data collected before and after RT using the Student's T-Test. As a control, the mCTN changes on MEIs in a region far from irradiated volumes were calculated. The results from the MEI data were compared to those obtained from the standard 120 kVp CTs of the same subjects. <h3>Results</h3> The data from 20 out of 35 patients were found to be suitable for this analysis. The greatest enhancement in GTV mCTN change was observed for MEI at 40 keV, the lowest available energy. The average change in GTV mCTN between the first and last fractions of treatments was 2.9 times larger for 40 keV MEIs than that for the standard 120 kVp CTs. For 11 out of the 20 patients, the GTV mCTN changes were greater than 15 HU on the 40 keV MEI and their average change in cellularity was 36.5 ± 10.3%. For the remaining 9 patients, the GTV mCTN changes were less than 15 HU on the 40 keV MEI and the average change in cellularity was 14.4 ± 9.8%. The correlation between change in GTV mCTN and change in cellularity was found to be significant (p=0.02). The average mCTN change in the control region was of 0.2 ± 2.0 HU on the 40 keV for all 20 patients. <h3>Conclusion</h3> Tumor pathological response for early-stage breast cancer treated with pre-operative accelerated partial breast irradiation can be predicted by the change of quantitative features, such as mean CT number, on low energy MEI derived from DECT acquired during the radiation treatment. Compared to the standard CT, the low energy MEIs substantially amplify the changes of mCTN, enhancing the viability of using quantitative CT features as a biomarker for early RT response assessment.

The Impacts of Vertical Off-Centring, Localiser Direction, Phantom Positioning and Tube Voltage on CT Number Accuracy: An Experimental Study.

Background: This study investigates the effects of vertical off-centring, localiser direction, tube voltage, and phantom positioning (supine and prone) on computed tomography (CT) numbers and radiation dose. Methods: An anthropomorphic phantom was scanned using a Discovery CT750 HD—128 slice (GE Healthcare) scanner at different tube voltages (80, 120, and 140 kVp). Images employing 0° and 180° localisers were acquired in supine and prone positions for each vertical off-centring (±100, ±60, and ±30 mm from the iso-centre). CT numbers and displayed volume CT dose index (CTDIvol) were recorded. The relationship between dose variation and CT number was investigated. Results: The maximum changes in CT number between the two phantom positions as a function of vertical-off-centring were for the upper thorax 34 HU (0° localiser, 120 kVp), mid thorax 43 HU (180° localiser, 80 kVp), and for the abdominal section 31 HU (0° localiser, 80 kVp) in the prone position. A strong positive correlation was reported between the variation in dose and CT number (r = 0.969, p < 0.001); 95% CI (0.93, 0.99). Conclusions: Patient positioning demands an approach with a high degree of accuracy, especially in cases where clinical decisions depend on CT number accuracy for tissue lesion characterisation.

Exploring Correlation Between CT Number and ADC Value for Understanding Radiation Response

Radiation induced changes in CT number (CTN) have been observed during/after radiation therapy (RT) in various tumors and healthy tissues and have been shown to correlate with radiation response. As CTN is related to the combined radiation attenuations of the intracellular volume (ICV) and the extracellular volume (ECV), the observed CTN changes may be contributed by the radiation induced variations in ICV and ECV, e.g., the ratio of ICV and ECV, in the tumor/tissue. The apparent diffusion coefficient (ADC), derived from diffusion-weighted MRI (DWI) is known to represent cellularity, i.e., the IVC/ECV ratio. The ADC or its change during/after RT has been shown to predict radiation response. CT and ADC images are commonly used in RT, offering necessary and complimentary data, one for anatomic and another for functional information. Based on these observations, we hypothesize that CTN correlates with ADC and this correlation can help understand radiation response in RT. The purpose of this study is to verify this hypothesis by analyzing selected CT and ADC data collected in our clinic.Spleen and kidney were selected as the target organs for this study as they have no fat tissue that can interfere with and add complexity to the analysis. Data for a total of 20 and 15 patients with abdominal/pelvic cancers were used for the spleen and kidney analyses, respectively. The image data included the CT acquired during the standard CT simulation using the same CT scanner at 120 kVp and the ADC maps derived from the DWI acquired immediately before the first fraction using a 1.5T MR-Linac. The time gap between the CT and ADC acquisitions were approximately 3 weeks. Spleen and kidneys (left and right) were contoured on both the ADC and the CT images. The mean values of the ADC and CTN from the voxels within the contours were analyzed using a linear regression method.The CTNs over the patient cohort have a median of 44.7 HU (range 31.5 ∼ 56.9 HU) for spleen, and 29.7 HU (range 23.0 ∼ 38.2 HU) for kidney. Both spleen and kidney data show a strong correlation between CTN and ADC (r = -0.80 for spleen and -0.83 for kidney, P < 0.001 for both). The linear regression lines were ADC = -0.0212 x CTN + 1.86 for the spleen and ADC = -0.0220 x CTN + 2.64 for the kidney. The difference between the y-intercepts may be interpreted as the additional water flow related to the renal filtration. With such an adjustment the data for the two organs can be fitted into one regression line same as that for the spleen.There is a strong correlation between CTN and ADC in kidneys and spleen, suggesting that CTN is related to the ICV/ECV ratio (measured by ADC) and the radiation-induced changes in CTN during RT is related to the ADC changes. Further studies are needed to confirm the CTN and ADC correlation and to use the correlation for understanding radiation response.

Prospective multicenter study on personalized and optimized MDCT contrast protocols: results on liver enhancement.

To determine a personalized and optimized contrast injection protocol for a uniform and optimal diagnostic level of liver parenchymal enhancement, in a large patient population enrolled in a multicenter study. Six hundred ninety-two patients who underwent a standardized multi-phase liver CT examination were prospectively assigned to one contrast media (CM) protocol group: G1 (100 mL fixed volume, 37 gI); G2 (600 mgI/kg of total body weight (TBW)); G3 (750 mgI/kg of fat-free mass (FFM)), and G4 (600 mgI/kg of FFM). Change in liver parenchyma CT number between unenhanced and contrast-enhanced images was measured by two radiologists, on 3-mm pre-contrast and portal phase axial reconstructions. The enhancement histograms were compared across CM protocols, specifically according to a target diagnostic value of 50 HU. The total amount of iodine dose was also compared among protocols by median and interquartile range (IQR). The Kruskal-Wallis and Mann-Whitney U tests were used to assess significant differences (p < 0.005), as appropriate. A significant difference (p < 0.001) was found across the groups with liver enhancement decreasing from median over-enhanced values of 77.0 (G1), 71.3 (G2), and 65.1 (G3) to a target enhancement of 53.2 HU for G4. Enhancement IQR was progressively reduced from 26.5 HU (G1), 26.0 HU (G2), and 17.8 HU (G3) to 14.5 HU (G4). G4 showed a median iodine dose of 26.0 gI, significantly lower (p < 0.001) than G3 (33.9 gI), G2 (38.8 gI), and G1 (37 gI). The 600 mgI/kg FFM-based protocol enabled a diagnostically optimized liver enhancement and improved patient-to-patient enhancement uniformity, while significantly reducing iodine load. • Consistent and clinically adequate liver enhancement is observed with personalized and optimized contrast injection protocol. • Fat-free mass is an appropriate body size parameter for correlation with liver parenchymal enhancement. • Diagnostic oncology follow-up liver CT examinations may be obtained using 600 mgI/kg of FFM.

Effect of X-ray beam energy and image reconstruction technique on computed tomography numbers of various tissue equivalent materials

IntroductionComputed tomography (CT) numbers are used in radiological diagnosis, attenuation correction and radiotherapy treatment planning. Modern CT scanners use iterative reconstruction methods instead of the traditional filtered back projection (FBP). Hence, the investigation of CT number accuracy with image reconstruction techniques and X-ray tube potential (kVp) used in CT is warranted. The aim of this study is to evaluate the effect of Sinogram Affirmed Iterative Reconstruction (SAFIRE) Technique and image acquisition at different tube potentials on CT numbers of different tissue equivalent materials. MethodsImages of the Computerised Imaging Reference System Model 062M Electron Density Phantom were acquired at different tube potentials and reconstructed using FBP and different strengths of SAFIRE. Average CT numbers, in circular regions of interest, and their standard deviations were used to investigate any dependence of CT numbers on tube potentials and/or image reconstruction technique using non-parametric statistical tests with p-values set at 0.05. ResultsStatistically significant differences in CT numbers were not observed (p > 0.091) between the different image reconstruction techniques. CT number of bone equivalent materials increased significantly (p < 0.015), by up to 400 Hounsfield Units, when tube potential was decreased. Such extent of CT number change over the tube potentials range used in this study may influence diagnostic outcomes in lung nodule, contrast enhanced and calcium score studies. For all other tissue equivalent materials, the CT number did not change significantly for different tube potentials. Linear relationship was observed between CT numbers and electron densities. ConclusionThe study concludes that the CT numbers of all tissues did not change significantly with image reconstruction methods. However, the CT numbers of bone equivalent materials increased with decreasing tube potentials, which may result in misrepresentation of clinical information obtained. Implications for practiceWhen CT images are used to extract quantitative parameters such as calcium score, to characterise lung nodules and contrast enhanced structures, the kVp used for image acquisition should be carefully selected to avoid any misrepresentation of clinical information.

Improvement of Beam Hardening Effects of Virtual Monochromatic Image in Dual-energy CT: A Electron Density Phantom Study

A virtual monochromatic image (VMI) is acquired from two different types of polychromatic energy X-rays, not a monochromatic X-ray. The effective energy of monochromatic X-ray does not vary in passing through the patient's body. On the other hand, beam hardening effects are seen in images because of the change of polychromatic X-ray energy. The purpose of the present study was to evaluate the beam hardening improvement effect of VMI using a phantom with a bone mimicking ring. We used a water equivalent electron density phantom with a hole in the center for inserting various measurement materials (i.e. fat, two types of bone with differing densities, contrast medium, blood, and water). Then, the CT numbers of each measurement materials were obtained from single energy CT (SECT) images and VMIs, respectively. Also, an additional bone-mimetic ring was used to obtain the CT numbers for evaluation of beam hardening effect. The CT number change rates were calculated from the obtained CT numbers with and without beam hardening effect. The rate of CT number, change of VMI was significantly lower than that of SECT for all measured materials. In this study, VMI minimized changes in CT numbers due to the beam hardening effect and showed a higher beam hardening reduction effect.

PENGARUH PERUBAHAN SUDUT GANTRY TERHADAP NOISE PADA PEMERIKSAAN CT SCAN DENGAN TEKNIK SEQUENCE

Background: Noise is a fluctuation in the value of CT number and Standard Deviation which is one parameter in the assessment of CT Scan image quality. This study aims to see the effect of changes in the angle of the gantry on noise and conformity with the BAPETEN standard of the value of the CT Number and Standard Deviation fluctuations produced.&#x0D; Methods: This type of research is quantitative with an experimental approach. The research subjects used water phantom to assess the value of CT Number and Standard Deviation by placing ROI on the resulting image. The SPSS test is used to see the relationship between changes in noise and noise. CT Number, Uniformity and Noise Uniformity tests are performed to assess CT Number and Standard Deviation in accordance with BAPETEN regulations.&#x0D; Results: An increase in noise is indicated by fluctuations in the value of CT Number and Standard Deviation resulting from the placement of the ROI at the center of each image produced by each change in the angle of the gantry. The average value of CT Number at the gantry angle 00 (-1.43), 50 (-1.48), 100 (-1.47), 150 (-1.58), 200 (-1.62), 250 (-1.68), 300 (-1.7). The average value of the Standard Deviation at the 00 gantry angle (2.36), 50 (2.35), 100 (2,3), 150 (2,33), 200 (2,42), 250 (2,57), 300 (2.62). There is a significant relationship to the Pearson correlation test between changes in gantry angle and CT Number and Standard Deviation values. CT Number, Uniformity, and Noise Uniformity Test results were used to assess the fluctuations of CT Number and Standard Deviation due to changes in the angle of the gantry in accordance with the standard BAPETEN No. 2 of 2018 on all changes in the 00 gantry angle to -300 with a range of 50.&#x0D; Conclution:. Noise fluctuations are caused by changes in the thickness of the scanning area object from changes in the gantry angle. The greater the change in angle of the gantry, the greater the thickness of the scanning area object. Changing the gantry angle causes the scanning area to change from the circle to the ellipse.&#x0D;

Bismuth shield affecting CT image quality and radiation dose in adjacent and distant zones relative to shielding surface: A phantom study

BackgroundTo quantify image quality and radiation doses in regions adjacent to and distant from bismuth shields in computed tomography (CT). MethodsAn American College of Radiology accreditation phantom with four solid rods embedded in a water-like background was scanned to verify CT number (CTN) accuracy when using bismuth shields. CTNs, image noise, and contrast-to-noise ratios (CNRs) were determined in the phantom at 80–140 kVp. Image quality was investigated on image portions in the zones adjacent (A zone) to and distant (D zone) from a bismuth shield. Surface radiation doses were measured using thermoluminescent dosimeters. Streak artefacts were graded on a 3-point-scale. ResultsChanges in CTN caused by a bismuth shield resulted in changes in X-ray spectra. CTN changes were more apparent in the A zone than in the D zone, particularly for a low tube voltage. The degrees of CTN changes and image noise were proportional to the thickness of the bismuth shields. A 1-ply bismuth shield reduced surface radiation doses by 7.2%–15.5%. The overall CNRs were slightly degraded, and streak artefacts were acceptable. ConclusionsUsing a bismuth shield could result in significant CTN changes and perceivable artefacts, particularly for a superficial organ close to the shield, and is not recommended for quantification CT examinations or follow-up CT examinations.

EP-1145 Xerostomia and volume and CT number changes of parotid glands during IMRT for head and neck cancer

EP-1145 Xerostomia and volume and CT number changes of parotid glands during IMRT for head and neck cancer

Experimental Evaluation of CT Number Changes in 320-Row CBCT Volume Scan for Proton Range Calculation

We investigated the longitudinal positional dependence of CT number in 320-row Cone Beam Computed Tomography (CBCT) volume scan (320-row volume scan) using a simple geometric phantom (SGP) and a chest simulation phantom (CSP) in order to evaluate its effect on proton range calculation. The SGP consisted of lung substitute material (LSM) and a cylindrical phantom (CP) made of high-density polyethylene. The CSP was an anthropomorphic phantom similar to the human chest. The two phantoms were scanned using 320-row volume scan in various longitudinal positions from the central beam axis. In experiments using the SGP, an image blur at the boundary of the two materials became gradually evident when the LSM was placed far away from the beam central axis. The image blur of the phantom was consistent with the gradation in CT number. The maximum difference in CT numbers between the 64-row helical scan and 320-row volume scan at the boundary of the two materials was consistent with approximately 50% of the relative proton stopping power. In contrast, the CT number profile in each longitudinal position was fairly consistent and longitudinal positional dependence rarely occurred in the CSP experiments. Pass lengths of CT beams through areas with widely different electron densities were shorter, and thus did not significantly impact CT numbers. Based on findings from the CSP experiments, we considered 320-row volume scan to be feasible for proton range calculation in clinical settings, although the relatively large longitudinal positional dependence of CT number should be accounted for when doing so.

79P - Evaluation of tissue computed tomography number changes and dosimetric shifts after conventionally fractionated irradiation in patients undergoing breast conserving surgery

79P - Evaluation of tissue computed tomography number changes and dosimetric shifts after conventionally fractionated irradiation in patients undergoing breast conserving surgery

Computed Tomography Number Changes of Gross Tumor Volume with MVCT Scans in Tomotherapy May Detect Early the Radiosensitivity of Non–small Cell Lung Cancer Patients

Evidences have showed that the computed tomography number (CTN) for tumor and certain normal structures can change after irradiation. We explored whether CTN changes of gross tumor volume with MVCT scans in Tomotherapy may be an early indicator for the radiosensitivity of NSCLC patients. Patients with stage I to III non-small cell lung cancer were eligible in this prospective study. MVCT scans were acquired during tomotherapy. The distribution of CTN and the mean values from the first treatment to the 15th treatment were collected based on the GTV generated on daily MVCT. The dose-response curve for decreased CTN of patients was quantified using the slope of a linear regression. The CTN decreased per Gy ( ΔHU/Gy ) for each patient was calculated after the 15th tomotherapy. Follow-up CT was taken after the whole radiation therapy completed, based on which the post-treatment tumor responses were assessed by two thoracic radiologists. According to the tumor responses, a cut-off value for ΔHU/Gy was calculated by SPSS software. From Jun. 2015 to Dec. 2016, 32 eligible patients were enrolled in this study. Males: 19 (60%), Females: 13 (40%), median age: 61.7 years (range 43.3-70.9). The median radiation dose was 60Gy (range 54-63Gy). In the whole group, the mean CTN was decreased by 37.35 ± 27.07 HU from the first treatment to the 15th treatment. The mean GTV was reduced by 10.26 ± 10.15 cm3. The CTN decreased per Gy (ΔHU/Gy) was ranged from 0.37 to 2.37 among all patients. Seven patients (21.9%) reached CR, 18 patients (56.2%) reached PR, and 7 patients (21.9%) reached SD after the complete tomotherapy. The mean CTN reduction ranged from 28.1 HU to 64.0 HU in patients whose post-treatment tumor responses were CR or PR and the CTN changes were linearly correlated with the radiation dose (R2= 0.87，p＜0.001). The mean CTN changes in the left 7 patients were ranged from 9.9 HU to 26.2 HU. The cut off value for ΔHU/Gy was 0.97, above which patients could have a better radiosensitivity and a further favorable post-treatment tumor response. On an early and quantitative scale, the CTN changes of MVCT in tomotherapy may early detect the radiosensitivity of NSCLC patients. Further studies included larger numbers of patients are expected to validate such a finding and explore whether CTN changes of MVCT hold the potential to optimize treatment by adjusting radiation intensity or modifying the therapeutic regimen, based on the observed radiosensitivity of patients.

Corneal Dose Reduction Using a Bismuth-Coated Latex Shield over the Eyes During Brain SPECT/CT.

This study aimed to determine whether a bismuth-coated latex shield (B-shield) could protect the eyes during brain SPECT/CT. Methods: A shield containing the heavy metal bismuth (equivalent to a 0.15-mm-thick lead shield) was placed over a cylindric phantom and the eyes of a 3-dimensional brain phantom filled with 99mTc solution. Subsequently, phantoms with and without the B-shield were compared using SPECT/CT. The CT parameters were 30-200 mA and 130 kV. The dose reduction achieved by the B-shield was measured using a pencil-shaped ionization chamber. The protective effects of the B-shield were determined by evaluating relative radioactivity concentration as well as artifacts (changes in CT number), linear attenuation coefficients, and coefficients of variation on SPECT images. Results: The radiation doses with and without the B-shield were 0.14-0.77 and 0.36-1.93 mGy, respectively, and the B-shield decreased the average radiation dose by about 60%. The B-shield also increased the mean CT number, but only at locations just beneath the surface of the phantom. Streaks of higher density near the underside of the B-shield indicated beam hardening. Linear attenuation coefficients and the coefficients of variation did not significantly differ between phantoms with and without the B-shield, and the relative 99mTc radioactivity concentrations were not affected. Conclusion: The B-shield decreased the radiation dose without affecting estimated attenuation correction or radioactivity concentrations. Although surface artifacts increased with the B-shield, the quality of the SPECT images was acceptable. B-shields can help protect pediatric patients and patients with eye diseases who undergo SPECT imaging.

Prediction of Early Response to Chemoradiation Therapy in Non–Small Cell Lung Cancer by Using Cone Beam Computed Tomography–Based Tumor Volume and Density Changes

Response evaluation is critical in assessing effectiveness of anti-cancer treatment; however, the Response Evaluation Criteria in Solid Tumor (RECIST) may underestimate the efficacy of non–small cell lung cancer (NSCLC) treatment. We sought to investigate the correlations between treatment response and changes in primary tumor volume (TV) and CT number (CTN) using kilovoltage cone-beam computed tomography (KV-CBCT) to assess whether these could be valuable in predicting chemoradiation therapy (CRT) response in NSCLC patients. Patients with inoperable and locally advanced NSCLC who received CRT and had daily CBCT during the course of radiation therapy were involved in this study. The contours of TV were manually delineated by the radiation oncologist from CBCT images on days 1, 6, 11, 16, 21, 26, and 32. The changes in TV (cm3) and the mean CTN (Hu, Hounsfield Units) during the course of radiation therapy delivery were analyzed and correlated with clinical outcomes, based on a clinical examination and serial CT scans. A computer software was used to perform Pearson and t-test analysis of the data, and logistic regression was applied to assess prediction abilities of CTN and TV. CTN reduction was observed in primary tumors for all 56 patients from Day 1 (D1) to Day 32 (D32) CBCTs with a mean value of 24.91±12.34 Hu, and the TV reduced by 30.11 ±23.80 cm3. The lung tumor CTN change was linearly correlated with radiation dose received. The changes in CTN and TV obtained from CBCT images had the potential to be early predictors of response, which could identify NSCLC patients who can benefit from CRT. Prediction value could be improved by a combination of the CTN and TV changes.

Variation in CT Number and Image Noise Uniformity According to Patient Positioning in MDCT.

Many algorithms for clinical decision making rely on assessment of the CT number (expressed as Hounsfield units); however, to our knowledge, few, if any, studies have addressed how CT numbers change as a function of patient positioning within the scanner. An anthropomorphic phantom underwent imaging with varying amounts of vertical orientation misalignment with respect to isocenter. CT number and noise were measured using ROIs in the upper thorax, mid thorax, and abdomen. The degree of noise nonuniformity and changes in the CT number were assessed by comparing values obtained in the anterior versus posterior ROIs. To add clinical relevance, data on vertical mispositioning were collected from 20,316 clinical abdominal CT scans. Box-and-whisker plot analysis was used to identify the range of patient positioning. Absolute CT number changes of more than 20 HU were observed for some ROIs at phantom positions of 10 cm from isocenter, with important differences noted between the thoracic and abdominal regions. Noise uniformity varied by more than twofold for all regions at 10 cm below isocenter. On clinical CT examinations, off-centering of more than 1, 2, 4, and 6 cm occurred for 41%, 19%, 1.9%, and 0.3% of patients, respectively. Radiologists should treat CT number measurements with caution when patients are grossly mispositioned in the scanner. The substantial changes in attenuation values shown in the present study are large enough to warrant further investigation.

Radiation-induced changes in volume and CT number of gross tumour volume and parotid glands during the course of IMRT for head and neck cancers

Introduction. The CT number (CTN) for tumours and organs at risk can change with radiation therapy, which can be an early indicator for radiation response. This study investigates the correlation of radiation-induced changes in volume and CTN in gross tumour volume (GTV) and parotid glands (PG) during the course of intensity-modulated radiation therapy (IMRT) in head and neck cancers (HNC). Materials and methods. Re-CT scans were acquired at four weeks for 71 patients with stage II IVb HNC treated with chemoradiation. The changes in volumes and CTN of the GTV primary, GTV node, and PG at four weeks of radiation were analysed. Pearson’s correlation was used to assess any association between CTN change and volume reduction of the GTVs and PGs. Results. The volumes of the GTVs and the ipsilateral PG and contralateral PG were reduced during the course of the radiation therapy after four weeks with mean volume shrinkage of 26.30 ± 7.66 (p < 0.0001), 32.09 ± 37.2 (p < 0.04), 8.38 ± 1.61 (p < 0.0001), and 9.10 ± 1.81 cm3 (p < 0.0001), respectively, and the mean CTN reduced by 2.50 ± 5.4, 1.79 ± 4.12, 1.90 ± 3.57, and 1.99 ± 3.54 HUs, respectively. For GTVs, the CTN and GTV volume decreases were found to be positively correlated, but the relationship was weak. However, no noticeable correlation was observed between the CTN change and the volume change in both PGs. Conclusions. The CTN changes in GTVs and PGs during delivery of radiation for HNC are measurable and patient specific. The CTN can be reduced in GTVs and PGs with a reasonable correlation between the mean CTN and volume reductions in GTVs, but with no correlation with PGs.

PUB037 Computed Tomography Number Changes of Gross Tumor Volume with MVCT Scans in Tomotherapy May Early Detect the Radiosensitivity of NSCLC Patients

Evidences have showed that the CT number (CTN) for tumor and certain normal tissues can change after irradiation, and the CTN change may be an early indicator for radiosensitivity of NSCLC patients. Patients with stage I to III non-small cell lung cancer were eligible in this prospective study. MVCT scans were acquired during tomotherapy. The distribution of CTN and the mean values from the first treatment to the 15th treatment were collected based on the GTV generated on daily MVCT. The dose-response curve for decreased CTN of patients was quantified using the slope of a linear regression. The CTN decreased per Gy (ΔHU/Gy) for each patient was calculated after the 15th tomotherapy. Follow-up CT was taken after the whole radiation therapy completed, based on which the post-treatment tumor responses were assessed by two thoracic radiologists. According to the tumor responses, a cut-off value for ΔHU/Gy was calculated by SPSS software. From Jun. 2015 to Dec. 2015, 32 eligible patients were enrolled in this study. Males: 19 (60%), Females: 13 (40%), median age: 61.7 years (range 43.3-70.9). The median radiation dose was 60Gy (range 54-63Gy). In the whole group, the mean CTN was decreased by 37.35 ± 27.07 HU from the first treatment to the 15th treatment. The mean GTV was reduced by 10.26 ± 10.15 cm3. The CTN decreased per Gy (ΔHU/Gy) was ranged from 0.37 to 2.37 among all patients. Seven patients (21.9%) reached CR, 18 patients (56.2%) reached PR, and 7 patients (21.9%) reached SD after the complete tomotherapy. The mean CTN reduction ranged from 28.1 HU to 64.0 HU in patients whose post-treatment tumor responses were CR or PR and the CTN changes were linearly correlated with the radiation dose (R2= 0.87, p＜0.001). The mean CTN changes in the left 7 patients were ranged from 9.9 HU to 26.2 HU. The cut off value for ΔHU/Gy was 0.97, above which patients could have a better radiosensitivity and a further favorable post-treatment tumor response. On an early and quantitative scale, the CTN changes of MVCT in tomotherapy may early detect the radiosensitivity of NSCLC patients. Further studies included larger numbers of patients are expected to validate such a finding and explore whether CTN changes of MVCT hold the potential to optimize treatment by adjusting radiation intensity or modifying the therapeutic regimen, based on the observed radiosensitivity of patients.

TU‐H‐207A‐04: How Patient Positioning in CT Affects More Than the AEC: Image Noise Uniformity and CT Number Changes as a Function of Positioning

Purpose:Studies dealing with patient positioning in CT have mainly dealt with dose and image noise changes. For diagnosis, only dose decreases can negatively affect the diagnostic utility of the exam via an increase in image noise. However, a little studied consequence of poor positioning is CT number and noise uniformity changes.Methods:An anthropomorphic phantom was imaged in 2 cm vertical steps between the highest and lowest couch positions. CT number and noise were measured using regions of interest (ROI) in the upper‐thorax, mid‐thorax, and abdomen. The degree of noise non‐uniformity and CT number change was assessed by comparing values obtained in the anterior vs. posterior regions. Additionally, to add clinical support for the study, we analyzed 5,746 abdominal patients at our institution and obtained their lateral and vertical mis‐positioning from iso‐center. The patients ranged in size from teens to large adults. Box and whisker plots were used to identify the range of patient poisonings seen in our clinic.Results:Absolute CT number changes between anterior and posterior ROIs over 10 HU were measured for ROIs at 4 cm off‐centering. Noise uniformity varied by greater than 2 times for all regions at an offset of −10 cm. The 25–75 percentile ranges for patient positioning was −.91 – 1.4, −.87 – .88, −1.3 – .93, −1.8 – .60 cm for pediatrics, small adults, medium adults, and large adults respectively. However, 1.4% of our patients had mis‐positioning errors outside of 4 cm.Conclusion:The CT number changes shown here are large enough to warrant further investigation on how positioning might affect clinical decision making that relies on CT number for pathology characterization, especially due to the fact our clinical positioning data demonstrates we will have HU differences on the order of 10–20 HU.Research support GE Healthcare. TPS supplies CT protocols to GE under a licensing agreement.