Hui-Yu Tsai

Prediction of Nodal Metastasis in Head and Neck Cancer Using a 3T MRI ADC Map

BACKGROUND AND PURPOSE: The detection of cervical nodal metastases is important for the prognosis and treatment of head and neck tumors. The purpose of this study was to assess the ability of ADC values at 3T to distinguish malignant from benign lymph nodes. MATERIALS AND METHODS: From July 2009 to June 2010, twenty-two patients (21 men and 1 woman; mean age, 49.8 ± 9.5 years; age range, 28–66 years) scheduled for surgical treatment of biopsy-proved head and neck cancer were prospectively and consecutively enrolled in this study. All patients were scanned on a 3T imaging unit (Verio) by using a 12-channel head coil combined with a 4-channel neck coil. Histologic findings were the reference standard for the diagnosis of lymph node metastasis. RESULTS: The ADC values derived from the signal intensity averaged across images obtained with b-values of 0 and 800 s/mm2 were 1.086 ± 0.222 × 10−3 mm2/s for benign lymph nodes and 0.705 ± 0.118 × 10−3 mm2/s for malignant lymph nodes (P < .0001). When an ADC value of 0.851 × 10−3 mm2/s was used as a threshold value for differentiating benign from malignant lymph nodes, the best results were obtained with an accuracy of 91.0%, sensitivity of 91.3%, and specificity of 91.1%. CONCLUSIONS: The ADC value is a sensitive and specific parameter that can help to differentiate malignant from benign lymph nodes.

Fuzzy C-means clustering of magnetic resonance imaging on apparent diffusion coefficient maps for predicting nodal metastasis in head and neck cancer

OBJECTIVE The present study evaluated and analyzed apparent diffusion coefficients (ADCs) from partitions through a fuzzy C-means (FCM) technique for distinguishing nodal metastasis in head and neck cancer. METHODS MRI studies of 169 lymph node lesions, dissected from 22 patients with a histopathologically confirmed lymph node status, were analyzed using in-house software developed using MATLAB(®) (The MathWorks(®) Inc., Natick, MA). A radiologist manually contoured the lesions, and ADCs for each lesion were divided into two (low and high) and three (low, intermediate and high) partitions by using the FCM clustering algorithm. RESULTS The results showed that the low-value ADC clusters were more sensitive (95.7%) in distinguishing malignant from benign lesions than the whole-lesion mean ADC values (78.3%), while retaining a high specificity (approximately 90%). Moreover, receiver-operating characteristic curves demonstrated that the low-value ADC clusters used as a predictor of malignancy for lymph nodes could achieve a higher area under the curve (0.949 and 0.944 for two and three partitions, respectively). CONCLUSION The segmentation by ADC values of lesions through the FCM technique enables the efficient characterization of the lymph node pathology and can help distinguish malignant from benign lymph nodes. ADVANCES IN KNOWLEDGE Tumour heterogeneity may degrade the prediction of metastatic lymph nodes that involves using mean region-of-interest ADC values. The clustering of ADC values in lesions by using FCM can improve the diagnostic accuracy of nodal metastasis and reduce interreader variance.

SU‐GG‐I‐73: CT Image Quality and Radiation Dose Survey in Taiwan

Introduction: The Standards for Medical Exposure Quality Assurance, derived from Ionizing Radiation Protection Act, was enforced in Taiwan since July 1, 2005. The first diagnostic facility, mammography, was included in the regulation since July 1, 2008. The Atomic Energy Council plans to include computed tomography(CT) in the next stage. Before that, the national survey for realizing the current level of CTquality assurance is necessary. The purpose of this study is to survey the image quality and patient doses for CT in Taiwan. Methods and Materials: Trained investigators conducted on‐site measurements, started from March 2009. An ACR CT accreditation phantom (Model 464, Gammex) was used to evaluate CTimage quality, including slice thickness accuracy, CT number accuracy, image uniformity, artifact, spatial resolution, and low contrast detectability. Computed tomography dose indexs(CTDI) in head and body phantoms were measured by a pencil‐type ionization chamber (10X6‐3CT, Radcal). Radiation beam width was assessed by chromic films (XR‐CT Dosimetry film, Gafchromic). Representative patient doses for adult head, adult abdomen, and 5‐years pediatric abdomen examinations were evaluated, including volume CTDI(CTDIvol). Results: There are 425 CT scanners, including CT, PET/CT, SPECT/CT, and CT simulator, in 241 hospitals in Taiwan. The preliminary results, obtained from March to December 2009, included 222 units in 142 hospitals. The fail rates of image quality items are low. The CTDIvol for adult head, adult abdomen, and 5‐years pediatric abdomen examinations are 58, 18, and 26 mGy. The rates of CTDIvol for adult head, adult abdomen, and 5‐years pediatric abdomen examinations over the ACR limits are 10%, 25%, and 32%. Conclusion: The preliminary results give us a view of current level in miniature of CTimage quality and patient doses in Taiwan. Once the survey is complete, final results will be useful and helpful references for the Atomic Energy Council.

Survey of Radiation Dose, Image Quality and Equipment Performance of Mammography Units in Taiwan

This paper describes the results of national survey of mammography systems in Taiwan during the period of February to December 2008. Purpose of the survey was to help understanding the equipment performance, radiation dose, image quality and current status of quality assurance programs of each mammography facility, which served as references for the new regulation of mammography quality assurance and standards started on July 1, 2008 in Taiwan. The scope of the survey covered all mammography units in Taiwan, which included 214 units at 205 sites. Among them, 127 were screen/film units and 87 were digital units (25 CR). The measurements included sensitometry for the screen/film units, signal-difference-to-noise ratio (SDNR) for the digital units, and phantom scores (using the American College of Radiology (ACR) phantom), radiation output, half-value layer (HVL), and average glandular dose (AGD) for all units. The results showed varied sensitometric curves, with a mean base + fog, mid-density (MD) and density difference (DD) of 0.22 ± 0.02, 1.49 ± 0.19 and 1.67 ± 0.23 respectively. Phantom image total scores for screen / film and digital units were 11.09 ± 1.28 and 12.16 ± 0.91, respectively, and were significantly higher (p<0.001) for digital units. The mean SDNR obtained from digital systems ranged from 1.85 to 1.26, a 38% difference, among vendors. The mean AGD was 1.48 ± 0.47 mGy, with the median and third quartile equaled to 1.53 and 1.75 mGy, respectively. There was no significant difference in AGD between the digital and the screen/film systems, except for the CR systems which exhibited significant higher AGD then the screen/film (p<0.001).

MO-F-CAMPUS-I-04: Patient Eye-Lens Dose Reduction in Routine Brain CT Examinations Using Organ-Based Tube Current Modulation and In-Plane Bismuth Shielding

Purpose: The purpose of this study is to assess eye-lens dose for patients who underwent brain CT examinations using two dose reduction Methods: organ-based tube current modulation (OBTCM) and in-plane bismuth shielding method. Methods: This study received institutional review board approval; written informed consent to participate was obtained from all patients. Ninety patients who underwent the routine brain CT examination were randomly assigned to three groups, ie. routine, OBTCM, and bismuth shield. The OBTCM technique reduced the tube current when the X-ray tube rotates in front of patients’ eye-lens region. The patients in the bismuth shield group were covered one-ply bismuth shield in the eyes’ region. Eye-lens doses were measured using TLD-100H chips and the total effective doses were calculated using CT-Expo according to the CT scanning parameters. The surface doses for patients at off-center positions were assessed to evaluate the off-centering effect. Results: Phantom measurements indicates that OBTCM technique could reduced by 26% to 28% of the surface dose to the eye lens, and increased by 25% of the surface dose at the opposed incident direction at the angle of 180°. Patients’ eye-lens doses were reduced 16.9% and 30.5% dose of bismuth shield scan and OBTCM scan, respectively compared to the routine scan. The eye-lens doses were apparently increased when the table position was lower than isocenter. Conclusion: Reducing the dose to the radiosensitive organs, such as eye lens, during routine brain CT examinations could lower the radiation risks. The OBTCM technique and in-plane bismuth shielding could be used to reduce the eye-lens dose. The eye-lens dose could be effectively reduced using OBTCM scan without interfering the diagnostic image quality. Patient position relative the CT gantry also affects the dose level of the eye lens. This study was supported by the grants from the Ministry of Science and Technology of Taiwan (MOST103-2314-B-182-009-MY2), and Chang Gung Memorial Hospital (CMRPD1C0682).

SU‐E‐I‐59: Patient‐Based Average Glandular Dose Estimations in Taiwan

PURPOSE The objective of the study was to investigate the average glandular dose (AGD) distributions based on the patients with average-sized breasts in Taiwan. METHODS Patient data were collected from 199 mammography units of 167 facilities (76% of the units in Taiwan) during 2012 in Taiwan. For each unit, exposure parameters including target/filter, kVp and tube loadings of 15 patients with average-compressed breast size of 4.2±0.5 cm in craniocaudal (CC) views were recorded by the technologists. Half value layer (HVL) and radiation exposure per mAs were measured at specific beam quality during the annual on-site inspection. Entrance skin exposure for each patient was thus estimated based on the radiation output data, patient exposure techniques and compressed breast thickness. Both the conversion factors calculated by Dance and Wu were used for further AGD calculations for comparisons. Average of the AGDs of the 15 patients may served as the represented mean AGD for each mammographic unit, and dose distributions could also be obtained for further evaluations. RESULTS Based on the conversion factors calculated by Dance, AGDs ranged from 95.8 to 505.7 mrad, and the mean, median and 3rd quartile of the estimated AGD of the 199 mammographic units was 191.9 mrad, 172.2 mrad, and 228.0 mrad, respectively. By calculating AGDs using Wus conversion factors, AGDs ranged from 73.3 to 390.4 mrad, and the mean, median and 3rd quartile of the estimated AGD of the 199 mammographic units was 156.1 mrad, 143.5 mrad, and 186.2 mrad, respectively. Estimated AGDs using Wus correction factors got the lower AGD values compared to the AGDs estimated by Dance method. CONCLUSION AGD distributions based on nationwide represented patient data may serve as a baseline dose database for future diagnostic reference level (DRL) establishment in mammography in Taiwan. This work was supported by grants from Atomic Energy Council of Taiwan(AEC10101003L).

SU‐E‐I‐93: Comparison of the AEC Thickness Tracking Using the Signal‐ Difference‐To‐Noise Ratio in 113 Flat‐Panel Digital Mammography Units

Purpose: Signal‐difference‐to‐noise ratio (SDNR) can be served as an indicator representing the sensitivity of an x‐ray system. This study aimed to evaluate the automatic exposure control (AEC) performance using the SDNR based on the national survey data in Taiwan. Methods: Measurements were made on all the 113 flat‐panel digital mammography units in Taiwan during our 2010 national survey. They included GE Senographe 2000D (38), DS (15) and Essential (3), Hologic Selenia with Mo (20) and W (24) targets, Siemens Mammomat NovationDR(8) and Inspiration (4), and IMS Giotto Image3D (1). A disk was placed on top of the 2, 4 and 6‐cm thick acrylic blocks to simulate the contrast. Clinical AEC modes were selected to acquire images and SDNR were then measured as the mean pixel value differences between the disk and the background divided by the noise using the equation defined in ACRIN DMIST recommendations. Results: AEC systems of different manufacturers/models, or even different units with the same models resulted in different target/filter combinations and techniques when performing the thickness tracking. For example, 6‐cm thickness led to 40% Mo/Mo and 60% Mo/Rh in Hologic Selenia systems with Mo target and 4‐cm thickness led to 26% for Mo/Mo and 74% for Mo/Rh in GE 2000D systems. Decreasing SDNRs were observed when thickness increased in all the eight digital models. When normalized the mean SDNR of each model to their 4‐cm‐thickness data, large deviations between 2 cm and 6 cm were observed in the GE systems (94.7%, 87.1% and 63.0% for DS, Essential and 2000D, respectively). Deviations of the other five models ranged from 36.9% to 59.6%. Conclusions: Evaluating AEC performance using SDNR showed the decreasing trend with increasing thickness in all the eight digital models. Considering the average glandular dose together, Figure of Merit will be further investigated in the future.

SU‐GG‐I‐97: Evaluating Skin Dose and Dose Distribution for the Transcatheter Arterial Embolization

Purpose: The purpose of this study is to evaluate the entrance surface doses and dose distribution using Gafchromic films for patients who underwent the transarterial embolisation (TAE) for hepatocellulaer (HCC) by a flat‐panel angiographic system. Methods and Materials: Interventional fluoroscopy procedures may present deterministic and stochastic risk. The ICRP report No. 85 determined that patient doses for tumor embolisation belong to medium dose level. The FDA also suggested that the threshold absorbed dose in skin of 1 Gy should be recorded. In this study, three cases were performed on a digital flat‐panel angiographic system (Siemens Axiom dBA system software version VB31). The cumulative skin dose, frames of digital subtraction angiography, and fluoroscopy time were recorded, whereas the dose‐area product (DAP) was measured by the build‐in transmission chamber. The skin dose distribution was measured with Gafchromic XR‐RV2 films. According to the skin dose limit of ICRP and US Nuclear Regulatory Commission, averaged doses of hot‐spot areas with 10 and 100 cm2 were also evaluated. Results: The measured peak surface dose (PSD), mean dose, 10‐ and 100‐ cm2 area dose were 1538±1214, 153±104, 1404±1047, 1030±761 mGy, respectively. The mean DAP values, cumulative skin dose, fluoroscopy time, and frames of DSA were 230±167 Gy‐cm2, 40±22 minutes, 1991±1572 mGy and 105±91 frames, respectively. Only one case had the ESD over 1 Gy with 129‐cm2skin area, and received over 2Gy with 41‐cm2skin area. Conclusions: The Gafchromic XR‐RV2 films are easy‐to‐use for measuring the entrance surface dose and have advantages to provide the dose distribution of skin. This study indicated that the patient doses are in the range of hundreds of mGy, which might cause deterministic effect and further dose reducing techniques are needed.

SU‐FF‐I‐72: Evaluation and Comparison of Image Quality Figures for Digital Mammography

Purpose: To survey the image quality of digital mammographic units in Taiwan using a mammographic contrast‐detail phantom and an ACR accreditation phantom, and to compare image quality figures from those two phantoms. Method and Materials: The scope of the survey covered most digital mammographic units in Taiwan. On‐site measurements included phantom image acquisitions and entrance surface doses (ESD).Image acquisitions of an ACR accreditation phantom (Victoreen N‐566 18‐220) and ESD measurements were following the protocols of the ACR MammographyQuality Control Manual. A mammographic contrast‐detail phantom (CDMAM type 3.4, Artinis) with 1‐cm PMMA‐equivalent thickness was placed on the PMMA of 3 cm. The CDMAM assembling was exposed using the same technical factors as the ACR accreditation phantom. Signal‐difference‐to‐noise Ratios (SDNR) of the largest mass inside the ACR phantom were calculated by the equation, SDNR = (Mean background − Mean mass )/ (SD background 2 + SD mass 2 ) . Inverse Image quality figures (IQFinv) were calculated according to the threshold diameter (D i,min) at each contrast‐column (Ci ), IQF inv = n/Σ(D i,min ⋅C i ) . Results: Fifty‐seven digital units were surveyed, including 44 DR units and 13 CR units. The tube voltage, tube current‐time product, and ESD range from 23 to 29 kV, 36 to 182 mAs, and 3.22 to 12.4 mGy for imaging the ACR phantom. The mean values and standard deviation of SDNR are 1.97±0.31 for GE 2000D, 1.50±0.91 for GE DS, and 1.76±0.20 for Hologic Lorad Selenia. The mean values and standard deviation of IQFinv are 127±10 for GE 2000D, 120±11 for GE DS, 135±28 for Hologic Lorad Selenia, and 101±0 for Siemens Novation DR. The correlation between SNDR and IQF are mild (R 2=0.414 for GE 2000D; 0.520, GE DS; 0.446, Hologic Lorad Selenia). Conclusion: The SNDR obtained from the ACR phantom mildly correlates with the IQFinv evaluated from the CDMAM phantom.

SU‐FF‐I‐85: Effects of Automatic Dose Rate Control On Patient Dose in a Digital Flat‐Panel Detector System

Purpose: The purpose of this study is to demonstrate how automatic dosecontrol logics, which controldose rate depending on the body thickness, affect radiationdoses of patients undergoing therapeutic and diagnosticliver interventional angiography using a modern angiographic unit with a digital flat‐panel system. Method and Materials: Seventy procedures of transarterial embolization (therapy) and hepatic angiography(diagnosis) were considered in this study. All procedures were performed on a digital flat‐panel angiographic system (Siemens Axiom dBA Twin system software version VB31). Dose‐area products (DAP) were measured by build‐in transmission ion chambers. The DAPs, fluoroscopy time and skindoses (total calculated skindose of acquisitions in one plane) for each examination were recorded. The organ doses and effective doses were calculated by WinODS (v1.0a; Rados Technology Oy, Turku, Finland). Moreover, the relationship between dose rates, weight, height and body mass index (BMI) were analyzed. Results: The median DAP values were 105.5 and 117.2 Gy cm2 for therapeutic and diagnosticliver interventional angiography, respectively. The dose rates were highly correlated with body thickness (R2=0.888 and 0.866 for DSA and fluoroscopy, respectively) and BMI (R2=0.773 and 0.840 for DSA and fluoroscopy, respectively) in one complete procedure. The dose rates were nearly the same for the patients with similar heights, weights, or BMIs. For patients with equal abdomen thickness, the dose rate increases with the BMI. Conclusion: The results of this study indicated the dose varies according to patient sizes. It should be further investigated whether patient doses could be reduced without degradation of the diagnostic and therapeuticliver interventional angiography outcome.