Jingzhi Li

Arterial occlusions increase the risk of in-stent restenosis after vertebral artery ostium stenting

Objective The study was designed to investigate if vascular occlusion in the internal carotid artery (ICA) or the contralateral vertebral artery (VA) contribute to developing in-stent restenosis (ISR) in patients with vertebral artery ostium stenosis (VAOS). Methods 420 consecutive patients treated with VAOS stents (from a population of 8145 patients with VAOS) from January 2013 to December 2014 were analyzed in this retrospective study; 216 with drug eluted stents and 204 with bare metal stents. Based on pre-stent DSA findings, patients were divided into four groups: both carotid and vertebral arteries patent (PAT), ICA occlusion (ICA-OCC), contralateral VA occlusion (CVA-OCC), and combined occlusions (C-OCC). The incidence of ISR (stenosis >50%) was compared between groups using Cox regression analysis. Results Of the 420 patients, the mean incidence of ISR was 36.4%, with a median 12 months of follow-up (IQR 3–12). Logistic regression analysis showed that drug eluting stent had less ISR than bare metal stent (OR=0.38, 95%u2009CI 0.19 to 0.75, P=0.01). Cox regression analysis showed that CVA-OCC (HR=1.63, P=0.02) and C-OCC (HR=3.30, P=0.001) were risk factors for ISR but not ICA-OCC (P=0.31). In the CVA-OCC and C-OCC groups, in-stent peak systolic velocity (PSV) ≥140 cm/s, 1u2009day after successful stenting, was associated with subsequent development of ISR (OR=2.81, 95%u2009CI 1.06 to 7.43, P=0.04). Conclusion Contralateral VA occlusion at the time of stenting increased the risk of ISR, especially if stent PSV on day 1 was >140 cm/s. Bare metal stents had more ISR than drug eluting stents.

Sensitization of Hypoxic Tumors to Radiation Therapy Using Ultrasound-Sensitive Oxygen Microbubbles

Tumor hypoxia has been shown to decrease the sensitivity of solid tumors to radiation. Systemic efforts to increase tumor oxygenation levels immediately prior to therapy, however, have largely proven unsuccessful. The objective of this work was to determine the utility of oxygen-filled, ultrasound sensitive microbubbles for locally delivering oxygen and sensitizing tissue to radiation in a breast cancer model.

Influence of Data Parsing on Contrast Enhanced Ultrasound Exams

RATIONALE AND OBJECTIVESnTo explore the influence of data parsing (either selection of frames at set time intervals or by an experienced sonographer) of contrast-enhanced ultrasound (CEUS) exams on physician diagnoses and confidence levels.nnnMATERIALS AND METHODSnForty consecutive CEUS exams consisting of 10 cases each of indeterminate liver lesions, indeterminate renal lesions, renal cell carcinoma postablation follow-up, and hepatocellular carcinoma postchemoembolization follow-up were selected for analysis. Exams were parsed into sets consisting of five images selected by the performing sonographer and sets containing systematically stored frames every 10, 30, and 60 seconds. Three blinded physicians then reviewed the cine loop and each set of images in randomized order and provided a diagnosis and confidence level.nnnRESULTSnFor all clinical applications investigated, no statistically significant differences in diagnostic performance measures or reader confidence were observed between review of the entire cine loop and images selected by the performing sonographer (p > 0.42). Diagnostic performance at 10-second intervals did not show statically significant changes compared to the full cine loop review for all applications (p > 0.18), although reader confidence decreased. At 30-60-second intervals, both diagnostic performance and reader confidence showed statistically significant reduction compared to review of the full cine loop (p < 0.045).nnnCONCLUSIONSnTransfer and review of large cine loops from CEUS exams represent a potential barrier to adoption within the United States workflows. This study demonstrates that images selected by a performing trained sonographer may provide the same value without the review time and data storage costs needed for full cine loop review. Parsing by time points reduced reader confidence and diagnostic performance.

Sensitization of hypoxic tumors to radiation therapy using ultrasound sensitive oxygen microbubbles

Tumor hypoxia has been shown to decrease the sensitivity of solid tumors to radiation. Systemic efforts to increase tumor oxygenation levels immediately prior to therapy, however, have largely proven unsuccessful. The objective of this work was to determine the utility of oxygen-filled, ultrasound sensitive microbubbles for locally delivering oxygen and sensitizing tissue to radiation in a breast cancer model.

Time intensity curve analysis of subharmonic transabdominal and harmonic endoscopic contrast-enhanced ultrasound of pancreatic masses

Pancreatic cancer is associated with poor clinical outcomes primarily, due to the advanced stage of disease at diagnosis. Harmonic contrast-enhanced endoscopic ultrasound has been proposed as an imaging approach for characterizing pancreatic masses. As an alternative, transabdominal subharmonic imaging has been proposed to limit invasiveness and better suppress nonlinear tissue echoes. In both of these approaches, time-intensity curve (TIC) analysis can be performed to quantify blood flow dynamics. The purpose of this study was to compare time TICs from both harmonic endoscopic ultrasound and subharmonic transabdominal ultrasound in pancreatic masses.

SU-E-J-47: Comparison of Online Image Registrations of Varian TrueBeam Cone-Beam CT and BrainLab ExacTrac Imaging Systems

Purpose To compare online image registrations of TrueBeam cone-beam CT (CBCT) and BrainLab ExacTrac imaging systems. Methods Tests were performed on a Varian TrueBeam STx linear accelerator (Version 2.0), which is integrated with a BrainLab ExacTrac imaging system (Version 6.0.5). The study was focused on comparing the online image registrations for translational shifts. A Rando head phantom was placed on treatment couch and immobilized with a BrainLab mask. The phantom was shifted by moving the couch translationally for 8 mm with a step size of 1 mm, in vertical, longitudinal, and lateral directions, respectively. At each location, the phantom was imaged with CBCT and ExacTrac x-ray. CBCT images were registered with TrueBeam and ExacTrac online registration algorithms, respectively. And ExacTrac x-ray image registrations were performed. Shifts calculated from different registrations were compared with nominal couch shifts. Results The averages and ranges of absolute differences between couch shifts and calculated phantom shifts obtained from ExacTrac x-ray registration, ExacTrac CBCT registration with default window, ExaxTrac CBCT registration with adjusted window (bone), Truebeam CBCT registration with bone window, and Truebeam CBCT registration with soft tissue window, were: 0.07 (0.02–0.14), 0.14 (0.01–0.35), 0.12 (0.02–0.28), 0.09 (0–0.20), and 0.06 (0–0.10) mm, in vertical direction; 0.06 (0.01–0.12), 0.27 (0.07–0.57), 0.23 (0.02–0.48), 0.04 (0–0.10), and 0.08 (0– 0.20) mm, in longitudinal direction; 0.05 (0.01–0.21), 0.35 (0.14–0.80), 0.25 (0.01–0.56), 0.19 (0–0.40), and 0.20 (0–0.40) mm, in lateral direction. Conclusion The shifts calculated from ExacTrac x-ray and TrueBeam CBCT registrations were close to each other (the differences between were less than 0.40 mm in any direction), and had better agreements with couch shifts than those from ExacTrac CBCT registrations. There were no significant differences between TrueBeam CBCT registrations using different windows. In ExacTrac CBCT registrations, using bone window led to better agreements than using default window.

SU‐E‐T‐540: Evaluation of Forced‐Density Corrected Dose Calculation for Lung Cancer Treatment

PURPOSEnThe study was aimed to evaluate the accuracy of lung cancer treatment dose calculations using a bulk electron density for forced-density correction, in situations where CT images are acquired in other institutions and the information of CT number to electron density (CT-to-ED) conversion is unavailable for conducting pixel density correction.nnnMETHODSnEleven 3D SBRT lung cases were studied. Treatment plans were generated initially with pixel-density correction using a known CT-to-ED conversion, in a CMS XIO treatment planning system using superposition algorithm. The plans were re-calculated with contour-based density correction, i.e., forced-density correction: a density of 0.26 g/cm3 was assigned to lung structures, which was a population average taken from a literature, and unit density was assigned to other structures. Monitor units were kept the same in both plans.nnnRESULTSnThe doses calculated using forced-density correction were compared against those calculated using pixel-density correction. The absolute percentage differences of PTV D95, PTV mean dose, and V20, among the 11 cases, were 2.49±1.69%, 1.69±1.5%, and 1.88±2.36%, respectively.nnnCONCLUSIONSnThe results showed that the dose calculation using the bulk density and forced density correction generated dose distributions close to those calculated using pixel-density correction and actual CT-to-ED conversion. None.

SU‐E‐T‐709: Monte Carlo Evaluation of Superposition‐Algorithm Skin Dose Calculation for Brain Radiotherapy

Purpose: Skindose is one of the concerns in brainradiotherapy: over dose will cause patient hair loss. It is important to predict accurate skindose in treatment planning. Inaccuracy of skindose calculations using some treatment planning systems has been reported in literatures. Monte Carlo calculation is recognized as the gold standard in radiationdose calculation. The study was aimed to apply Monte Carlo calculation to evaluate the accuracy of skindose calculation performed with our clinic treatment planning system (CMS XIO), which is based on a superposition algorithm. Methods: A conformal treatment plan for braintumortreatment was generated in a CMS XIO treatment planning system and the plan was recalculated using a Monte Carlo calculation algorithm for the same linear accelerator with the same beam settings (beam energy, angles, field sizes, and monitor units). The Monte Carlo calculation was performed in a CMS Monaco treatment planning system in the QA mode, with variance of 1%. The treatment plans used 4 photon conformal beams (6 MV). The skin structure was ∼5 mm thick, which represented the thickness of clinic concern. The skindoses calculated using the XIO superposition algorithm were compared against those calculated using the Monte Carlo algorithm. Results: For each individual beam, the differences of the mean skindoses were 0.4%, 0.9%, 1.9%, and –1.4%, respectively, and the differences of the maximum skindoses were –2.6%, –3.1%, 2.9%, and –3.7%, respectively. For the composite beams (4 beams were on), the differences of the mean doses and the maximum doses were 0.6% and –1.4%, respectively. Conclusions: There were no clear trends in the dose differences. The differences in skindose between the superposition calculation and the Monte Carlo calculation were not significant: < 2% in mean dose and < 4% in maximum dose.

SU‐FF‐T‐125: Commissioning of Monaco Monte Carlo IMRT Treatment Planning System

Purpose: To commission CMS Monaco IMRTtreatment planning system for clinical applications using a standard test suite. Methods and Materials: A system test including IMRT planning and plan delivery was performed for CMS Monaco IMRTtreatment planning system, version 1.0.2. Four cases from TG‐119 were studied: one head and neck case, one prostate case, and two C shape cases. IMRT plans were generated with the dose goals set by TG‐119 and were compared with the plans generated using CMS XiO treatment planning system. Analysis metrics were for dose coverage, number of segments, total MU, MU efficiency, number of segments per beam, and delivery time. The IMRT plans were delivered on an Elekta Synergy linear accelerator with step‐and‐shoot technique. This linac has 4‐mm MLC.IMRT QA was performed with field by field review using a diode array device Mapcheck. Results: Monaco plans showed similar target dose coverage as XiO plans and improved organ sparing in some cases. The ratios (Monaco/XiO) of number of total segments, total MU, number of segments per beam, and MU efficiency (Dose/MU) were 0.21–0.76, 0.56–0.77, 0.21–0.50, and 1.31–1.86, respectively. The delivery time of a Monaco plan was shorter than the XiO plan having the same number of beams by approximately 33%. IMRT QA pass rates of the Monaco plans were 93.8%–97.6% for the criteria of 3‐mm, 3%, and 10% threshold, which in three cases were higher than the XiO plans (93.1%–96.6%). Conclusion: The IMRT plans from the Monaco treatment planning system showed advantages over XiO plans. These advantages include smaller number of segments, smaller MU, smaller number of segments per beam, and higher MU efficiency. Additionally, the delivery time was shorter. The QA pass rates were similar to or higher than the XiO plans.