Creation and Implementation of an Interdisciplinary Workflow for CBCT-Based Online Adaptive Radiotherapy

PURPOSE/OBJECTIVE(S)

CBCT-based online adaptive radiotherapy (OART) is an emerging treatment strategy to replan based on the anatomy of the day while the patient remains on the couch. OART is not just an add-on to the current workflow; it necessitates a new approach across the patient's path of care, from CT simulation to treatment delivery. OART requires the addition of duties to clinical personnel, strategies to create auto-plan templates, and monitoring the "black box" adaptation process. Studies have shown that OART implementation is limited by its resource-intensive nature and the risks associated with the treatment approach. We hypothesized that the implementation of an interdisciplinary, streamlined workflow and checklists would enhance the OART treatment efficiency, prevent medical errors from the adaptation, and minimize the burden on clinicians.

MATERIALS/METHODS

An interdisciplinary OART working group comprising radiation oncologists, medical physicists, dosimetrists, and therapists was created to enable weekly knowledge sharing, workflow design, implementation, and continuous process improvement. 213 adaptive sessions from 5 treatment sites (pancreas, bladder, prostate, rectum, anus) were treated on a CBCT-based OART platform in a single institutional study. An evaluation of the treatment safety and workflow time was performed for each adaptive session.

RESULTS

The OART workflow was divided into four sub-workflows: 1) pre-treatment site-specific template preparation, 2) pre-treatment initial planning and verification, 3) on-treatment procedure, and 4) post-treatment evaluation. The sub-processes involved 4, 8, 13, and 4 separate, sequentially tasks, respectively, and a total of 11 task checklists. The template preparation is a new process developed for site-specific, standardized physician template directives, automated planning template development, and testing for its accuracy and robustness. The planning templates generated high-quality initial plans automatically within minutes once structures were segmented on the planning CT. This process was replicated during treatment using the CBCT. The median (interquartile range) online procedure time, defined as the time from initial CBCT to plan approval, of the five treatment sites (pancreas, bladder, prostate, rectum, anus) was 22.1 (19.2-24.8) min, 16.5 (15.3-17.5) min, 14.7 (13.9-17.4) min, 17 (15.3-19.7) min, and 24 (21.4-25.8) min, respectively. Safety assessment determined that no treatment deviations were observed.

CONCLUSION

Creating an interdisciplinary, standardized workflow and checklists allowed the safe delivery of OART with clinically feasible online procedure time and significantly reduced initial planning time compared with traditional EBRT. The unique workflow is essential to minimize the burden on the care team, increase patient safety, and access to OART.

Energetic Electron Precipitation Driven by Electromagnetic Ion Cyclotron Waves from ELFIN's Low Altitude Perspective

We review comprehensive observations of electromagnetic ion cyclotron (EMIC) wave-driven energetic electron precipitation using data collected by the energetic electron detector on the Electron Losses and Fields InvestigatioN (ELFIN) mission, two polar-orbiting low-altitude spinning CubeSats, measuring 50-5000 keV electrons with good pitch-angle and energy resolution. EMIC wave-driven precipitation exhibits a distinct signature in energy-spectrograms of the precipitating-to-trapped flux ratio: peaks at >0.5 MeV which are abrupt (bursty) (lasting ∼17 s, or Δ L ∼ 0.56 ) with significant substructure (occasionally down to sub-second timescale). We attribute the bursty nature of the precipitation to the spatial extent and structuredness of the wave field at the equator. Multiple ELFIN passes over the same MLT sector allow us to study the spatial and temporal evolution of the EMIC wave - electron interaction region. Case studies employing conjugate ground-based or equatorial observations of the EMIC waves reveal that the energy of moderate and strong precipitation at ELFIN approximately agrees with theoretical expectations for cyclotron resonant interactions in a cold plasma. Using multiple years of ELFIN data uniformly distributed in local time, we assemble a statistical database of ∼50 events of strong EMIC wave-driven precipitation. Most reside at L ∼ 5 - 7 at dusk, while a smaller subset exists at L ∼ 8 - 12 at post-midnight. The energies of the peak-precipitation ratio and of the half-peak precipitation ratio (our proxy for the minimum resonance energy) exhibit an L -shell dependence in good agreement with theoretical estimates based on prior statistical observations of EMIC wave power spectra. The precipitation ratio's spectral shape for the most intense events has an exponential falloff away from the peak (i.e., on either side of ∼ 1.45 MeV). It too agrees well with quasi-linear diffusion theory based on prior statistics of wave spectra. It should be noted though that this diffusive treatment likely includes effects from nonlinear resonant interactions (especially at high energies) and nonresonant effects from sharp wave packet edges (at low energies). Sub-MeV electron precipitation observed concurrently with strong EMIC wave-driven >1 MeV precipitation has a spectral shape that is consistent with efficient pitch-angle scattering down to ∼ 200-300 keV by much less intense higher frequency EMIC waves at dusk (where such waves are most frequent). At ∼100 keV, whistler-mode chorus may be implicated in concurrent precipitation. These results confirm the critical role of EMIC waves in driving relativistic electron losses. Nonlinear effects may abound and require further investigation.

Counteracting age-related VEGF signaling insufficiency promotes healthy aging and extends life span

Aging is an established risk factor for vascular diseases, but vascular aging itself may contribute to the progressive deterioration of organ function. Here, we show in aged mice that vascular endothelial growth factor (VEGF) signaling insufficiency, which is caused by increased production of decoy receptors, may drive physiological aging across multiple organ systems. Increasing VEGF signaling prevented age-associated capillary loss, improved organ perfusion and function, and extended life span. Healthier aging was evidenced by favorable metabolism and body composition and amelioration of aging-associated pathologies including hepatic steatosis, sarcopenia, osteoporosis, "inflammaging" (age-related multiorgan chronic inflammation), and increased tumor burden. These results indicate that VEGF signaling insufficiency affects organ aging in mice and suggest that modulating this pathway may result in increased mammalian life span and improved overall health.

Perioperative intravenous contrast administration and the incidence of acute kidney injury after major gastrointestinal surgery: prospective, multicentre cohort study

BACKGROUND

This study aimed to determine the impact of preoperative exposure to intravenous contrast for CT and the risk of developing postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery.

METHODS

This prospective, multicentre cohort study included adults undergoing gastrointestinal resection, stoma reversal or liver resection. Both elective and emergency procedures were included. Preoperative exposure to intravenous contrast was defined as exposure to contrast administered for the purposes of CT up to 7 days before surgery. The primary endpoint was the rate of AKI within 7 days. Propensity score-matched models were adjusted for patient, disease and operative variables. In a sensitivity analysis, a propensity score-matched model explored the association between preoperative exposure to contrast and AKI in the first 48 h after surgery.

RESULTS

A total of 5378 patients were included across 173 centres. Overall, 1249 patients (23·2 per cent) received intravenous contrast. The overall rate of AKI within 7 days of surgery was 13·4 per cent (718 of 5378). In the propensity score-matched model, preoperative exposure to contrast was not associated with AKI within 7 days (odds ratio (OR) 0·95, 95 per cent c.i. 0·73 to 1·21; P = 0·669). The sensitivity analysis showed no association between preoperative contrast administration and AKI within 48 h after operation (OR 1·09, 0·84 to 1·41; P = 0·498).

CONCLUSION

There was no association between preoperative intravenous contrast administered for CT up to 7 days before surgery and postoperative AKI. Risk of contrast-induced nephropathy should not be used as a reason to avoid contrast-enhanced CT.

RapidPlan for Knowledge-Based Planning of Malignant Pleural Mesothelioma

PURPOSE

Treatment planning for malignant pleural mesothelioma is a challenging task due to the relatively large size of the target and the need to spare critical organs that overlap with or are within the target volume. We aimed to develop a knowledge-based model using RapidPlan (RP) for patients with 2 intact lungs.

METHODS AND MATERIALS

Data from 57 patients treated with volumetric modulated arc therapy were chosen for training the dose estimation model at a single dose level. The prescription dose was 50.4 Gy in 1.8 Gy fractions. The model was validated on 23 new patients by comparing the clinical plan to the RP. Time taken to plan the RP was compared with that for the clinical plan.

RESULTS

For similar target coverage and plan inhomogeneity, RP significantly improved the sparing of the contralateral lung, heart, stomach, esophagus, and ipsilateral kidney. On average, the contralateral lung V5 Gy and V10 Gy were reduced by 13.9% (P < .001) and 7.9% (P < .001), respectively. The mean heart dose was reduced by 5 Gy (P < .001) and V30 Gy by 9.1% (P < .001). Mean dose to the stomach and esophagus were both reduced by 5 Gy (P < .001), and the ipsilateral kidney V18 Gy by 4.1% (P < .001). Mean total lung dose was reduced by 0.8 Gy with RP, which enabled an increase in prescription dose by 1 fraction Absolute volume of ipsilateral lung was adequately spared by both techniques, while sparing of all other organs, namely the cord, liver, and bowel, was not compromised with RP. Time taken with RP was 20 minutes, 45 seconds versus at least 4 hours for an experienced treatment planner.

CONCLUSIONS

The RP model for malignant pleural mesothelioma showed improved sparing of critical organs with a reduced treatment planning time and increased prescription dose.

ApoCIII-Lp(a) complexes in conjunction with Lp(a)-OxPL predict rapid progression of aortic stenosis

OBJECTIVE

This study assessed whether apolipoprotein CIII-lipoprotein(a) complexes (ApoCIII-Lp(a)) associate with progression of calcific aortic valve stenosis (AS).

METHODS

Immunostaining for ApoC-III was performed in explanted aortic valve leaflets in 68 patients with leaflet pathological grades of 1-4. Assays measuring circulating levels of ApoCIII-Lp(a) complexes were measured in 218 patients with mild-moderate AS from the AS Progression Observation: Measuring Effects of Rosuvastatin (ASTRONOMER) trial. The progression rate of AS, measured as annualised changes in peak aortic jet velocity (V_peak), and combined rates of aortic valve replacement (AVR) and cardiac death were determined. For further confirmation of the assay data, a proteomic analysis of purified Lp(a) was performed to confirm the presence of apoC-III on Lp(a).

RESULTS

Immunohistochemically detected ApoC-III was prominent in all grades of leaflet lesion severity. Significant interactions were present between ApoCIII-Lp(a) and Lp(a), oxidised phospholipids on apolipoprotein B-100 (OxPL-apoB) or on apolipoprotein (a) (OxPL-apo(a)) with annualised V_peak (all p<0.05). After multivariable adjustment, patients in the top tertile of both apoCIII-Lp(a) and Lp(a) had significantly higher annualised V_peak (p<0.001) and risk of AVR/cardiac death (p=0.03). Similar results were noted with OxPL-apoB and OxPL-apo(a). There was no association between autotaxin (ATX) on ApoB and ATX on Lp(a) with faster progression of AS. Proteomic analysis of purified Lp(a) showed that apoC-III was prominently present on Lp(a).

CONCLUSION

ApoC-III is present on Lp(a) and in aortic valve leaflets. Elevated levels of ApoCIII-Lp(a) complexes in conjunction with Lp(a), OxPL-apoB or OxPL-apo(a) identify patients with pre-existing mild-moderate AS who display rapid progression of AS and higher rates of AVR/cardiac death.

TRIAL REGISTRATION

NCT00800800.

Permanent Pacing in a Patient With Fontan Circulation: Use All You Have at Your Discretion

Patients with Fontan circulation post significant technical challenges at the time of permanent pacemaker implantation, as majority of them are treated with surgically implanted epicardial pacemakers. However, transvenous pacemaker implantation is technically feasible, and the treating physician should be aware of each individual's anatomy and available treatment options.

Revealing the inner workings of the power function algorithm in Charged Aerosol Detection: A simple and effective approach to optimizing power function value for quantitative analysis

In recent years, charged aerosol detection (CAD) has become a valuable tool for fast and efficient quantitative chromatographic analysis of drug substances with weak UV absorption. In analytical method development using CAD, the power function settings available in the instrument software are key for linearization of the signal response with respect to analyte concentration. However, the relatively poor understanding of the power function algorithm has limited a more widespread use of CAD for quantitative assays, especially in the late stage of method validation and GMP laboratories. Herein, we present an approach to understand the inner workings of the power function value (PFV), the PFV optimization algorithm, as well as a method to determine the optimum PFV based on the signals acquired at PFV = 1 (default CAD settings). The exponent and the constant in the PFV equation used for modeling follow a trend as a function of PFV. The CAD signal at any PFV was modeled based on the signal acquired at PFV = 1, the modelling was successful for two analytes at different concentration levels on two different CAD detectors of the same model. This method reveals the functionality of the PFV which substantially simplifies the workflow needed to optimize the detector signal. The accuracy between the experimental and theoretical results showed high correlation and always resulted in the same optimum PFV determined by both ways. The approach described in this investigation simplifies the selection of the optimum PFV at which the signal is more linear, the signal-to-noise is higher, and the area reproducibility is better. The power function algorithm elucidated herein enables determination of optimum PFV from minimal experimental output and excellent overall accuracy. This paper provides an approach that includes no data transformation outside the vendor software, a very important requirement to easily validate and report results in a GMP environment.

Kinetics and Degradation Mechanism of Adrenaline Derivative CpQ in Diluted Aqueous Solutions

The degradation kinetics of an adrenaline (epinephrine) derivative, CpQ, was studied in solution in the pH range of 1-12 at 40-80 °C by high-performance liquid chromatography and ultraviolet-visible spectroscopy. The pH-rate profile exhibits a bell-shaped curve with two sigmoidal regions in the specific acid-catalyzed and specific base-catalyzed regions. The pH range of maximum stability was 2.5-4.5 with the main degradation pathway being the oxidative N-dealkylation of the aliphatic amino moiety followed by fast interconversion of the resulting fragments to stable degradation products. The autoxidation reaction was slower than the reaction of the oxygen reactive species. The chiral center underwent R to S racemization by a polar reaction mechanism under acidic conditions with a rate minimum at pH 4. The rates of degradation of the R and S enantiomers were similar across all pHs. CpQ degradation in the presence of hydrogen peroxide at 40 °C was significantly faster, and the extent of increases with pH. Metal ions bind to CpQ and catalyze its hydrolysis in the order Fe³⁺ > Fe²⁺ > Mg²⁺ > Mn²⁺ > Ti³⁺ > Sr²⁺ > Zn²⁺, with a rate enhancement of ≤1 order of magnitude at the studied pH values of 1 and 5. There was no buffer catalysis observed in the hydrolysis of the studied compound for maleate and phosphate but significant buffer catalysis in the case of citrate and malate.

Attenuating the rate of total body fat accumulation and alleviating liver damage by oral administration of vitamin D-enriched edible mushrooms in a diet-induced obesity murine model is mediated by an anti-inflammatory paradigm shift

Background

Hypovitaminosis D is associated with many features of the metabolic syndrome, including non-alcoholic fatty liver disease. Vitamin D-enriched mushrooms extracts exert a synergistic anti-inflammatory effect. The aim of the present study is to determine the immunomodulatory effect of oral administration of vitamin D-enriched mushrooms extracts on high-fat diet (HFD) animal model of non-alcoholic steatohepatitis (NASH).

Methods

C57BL/6 mice on HFD were orally administered with vitamin D supplement, Lentinula edodes (LE) mushrooms extract, or vitamin D-enriched mushrooms extract for 25 weeks. Mice were studied for the effect of the treatment on the immune system, liver functions and histology, insulin resistance and lipid profile.

Results

Treatment with vitamin D-enriched LE extracts was associated with significant attenuation of the rate of total body fat accumulation, along with a decrease in hepatic fat content as measured by an EchoMRI. Significant alleviation of liver damage manifested by a marked decrease in ALT, and AST serum levels (from 900 and 1021 U/L in the control group to 313 and 340; 294 and 292; and 366 and 321 U/L for ALT and AST, in Vit D, LE and LE + Vit D treated groups, respectively). A corresponding effect on hepatocyte ballooning were also noted. A significant decrease in serum triglycerides (from 103 to 75, 69 and 72 mg/dL), total cholesterol (from 267 to 160, 157 and 184 mg/dL), and LDL cholesterol (from 193 mg/dL to 133, 115 and 124 mg/dL) along with an increase in the HDL/LDL ratio, and improved glucose levels were documented. These beneficial effects were associated with a systemic immunomodulatory effect associated with an increased CD4/CD8 lymphocyte ratio (from 1.38 in the control group to 1.69, 1.71 and 1.63), and a pro- to an anti-inflammatory cytokine shift.

Conclusions

Oral administration of vitamin-D enriched mushrooms extracts exerts an immune modulatory hepato-protective effect in NASH model.

Analysis of Short- and Long-term Outcomes of Patients With Surgically Treated Left-sided Infective Endocarditis: A 5-Year Longitudinal Follow-up Study

This study aims to analyze survival, repeat hospitalization, and risk factors for surgically treated left-sided endocarditis. Retrospective review of all 166 (114 native and 52 prosthetic) patients operated between January 2004 and March 2015 was performed. Long-term survival and repeat hospitalization data for 134 of 166 patients were obtained via linked clinical databases with the Manitoba Centre for Health Policy. Kaplan-Meier estimates of survival and hospital readmission and Cox multivariable regression analysis of factors influencing outcomes were performed. Survival at 1 and 5 years was 91% and 80%, respectively, and major adverse prosthesis-related event repeat hospitalization rates were 12% and 21%, respectively. Repeat hospitalization because of endocarditis was 7% and 11% at 1 and 5 years, respectively. Survival and repeat hospitalization were similar for aortic and mitral valves. Survival after surgically treated endocarditis was similar to survival for age-, sex-, and valve-matched surgical valve replacements for noninfectious indications (P = 0.53). Viridans Streptococci was the most common organism in native valve endocarditis, and culture negative endocarditis was most common in prosthetic valves. Prosthetic valve endocarditis (P < 0.01) and preoperative renal dysfunction (P < 0.01) were risk factors for in-hospital mortality and major postoperative adverse events. Diabetes and renal dysfunction were associated with poor long-term survival, functional survival, and repeat hospitalization. This analysis suggests that surgery remains a very effective tool in management of these complex patients in terms of survival and major adverse prosthesis-related event repeat hospitalization.

Non-invasive bedside assessment of central venous pressure: scanning into the future

BACKGROUND

Noninvasive evaluation of central venous pressure (CVP) can be achieved by assessing the Jugular Venous Pressure (JVP), Peripheral Venous Collapse (PVC), and ultrasound visualization of the inferior vena cava. The relative accuracy of these techniques compared to one another and their application by trainees of varying experience remains uncertain. We compare the application and utility of the JVP, PVC, and handheld Mini Echo amongst trainees of varying experience including a medical student, internal medicine resident, and cardiology fellow. We also introduce and validate a new physical exam technique to assess central venous pressures, the Anthem sign.

METHODS

Patients presenting for their regularly scheduled echocardiograms at the hospital echo department had clinical evaluations of their CVP using these non-invasive bedside techniques. The examiners were blinded to the echo results, each other's assessments, and patient history; their CVP estimates were compared to the gold standard level 3 echo-cardiographer's estimates at the completion of the study.

RESULTS

325 patients combined were examined (mean age 65, s.d. 16 years). When compared to the gold standard of central venous pressure by a level 3 echocardiographer, the JVP was the most sensitive at 86%, improving with clinical experience (p<0.01). The classic PVC technique and Anthem sign had better specificity compared to the JVP. Mini Echo estimates were comparable to physical exam assessments.

CONCLUSIONS

JVP evaluation is the most sensitive physical examination technique in CVP assessments. The PVC techniques along with the newly described Anthem sign may be of value for the early learner who still has not mastered the art of JVP assessment and in obese patients in whom JVP evaluation is problematic. Mini Echo estimates of CVPs are comparable to physical examination by trained clinicians and require less instruction. The use of Mini Echo in medical training should be further evaluated and encouraged.

Hemorrhoidal dearterialization with mucopexy versus hemorrhoidectomy: 3-year follow-up assessment of a randomized controlled trial

BACKGROUND

A randomized controlled trial showed that patients with grade III or IV internal hemorrhoids had similar symptomatic relief of symptoms up to 3 months following dearterialization with mucopexy or hemorrhoidectomy albeit with less postoperative pain after the former. This study aimed to compare hemorrhoidal recurrence and chronic complications at 3-year follow-up.

METHODS

This study was carried out on 40 patients with grade III or IV internal hemorrhoids previously enrolled to a randomized trial comparing dearterialization to hemorrhoidectomy. Recurrence was defined as internal hemorrhoids diagnosed on proctoscopy. Chronic complications were nonresolving adverse events related to surgery. Outcome measures included patient-reported outcomes and quality of life measured by brief pain inventory (BPI), SF-12, and fecal incontinence surveys.

RESULTS

At median follow-up of 36 (27-43) months, 13 patients (32.5 %) were lost to follow-up. Patient-reported outcomes suggested no difference between dearterialization and hemorrhoidectomy in persistent symptoms, occurring in 1 (8.3 %) vs. 2 (13.3 %) patients (p = 0.681) and in symptom recurrence, occurring in 6 (50 %) vs. 4 (26.7 %) patients (p = 0.212). On proctoscopy, recurrence was seen in 2 (13.3 %) vs. 1 (6.7 %) patients (p = 0.411), all with index grade IV disease. One patient in each arm required reoperation (p = 0.869). Chronic complications were not seen in the dearterialization arm while they occurred in 2 (13.3 %) hemorrhoidectomy patients (p = 0.189) and included unhealed wound (n = 1), anal fissure (n = 1) and fecal incontinence (n = 1). There was a trend toward more patient reported than actual recurrence on proctoscopy (10 vs. 3, p = 0.259). There was no difference in BPI, SF-12, and fecal incontinence quality of life scores.

CONCLUSIONS

Recurrence rates did not differ significantly at 3-year follow-up and occurred in patients with index grade IV hemorrhoids. Chronic complications occurred only after hemorrhoidectomy.

The impact of intravenous fluid administration on complication rates in bowel surgery within an enhanced recovery protocol: a randomized controlled trial

AIM

A randomized controlled trial was conducted to test the hypothesis that there is no difference in complications in patients receiving intravenous (iv) water and electrolyte, based on either stroke volume or clinical indicators at bowel surgery.

METHOD

Eligible patients were randomized either to intra-operative iv administration of fluid boluses based on stroke volume measured by oesophageal Doppler (probe arm) or to iv fluid based on clinical indicators (no-probe arm). The end-point was the complication rate, defined as deviation from an uneventful postoperative course. Surgery was defined as elective bowel resection with primary anastomosis. All patients were on an enhanced recovery protocol. A randomized controlled trial suggested a sample size of 91 patients.

RESULTS

Ninety-one patients were randomized. Seventeen were excluded because of withdrawal of consent, failure of the procedure or cancellation of surgery. Patients were comparable for age (P = 0.89), gender (P = 0.14), body mass index (BMI) (P = 0.7), American Society of Anesthesiology (ASA) score (P > 0.9), race (P = 0.55), colorectal POSSUM score (P = 0.11), comorbidity (P = 0.4), previous operations (P = 0.45) and diagnosis (P = 0.50). Physiological and Operative Severity Score for the Enumeration of Morbidity and Mortality (POSSUM)-predicted mortality was higher in the test (probe) arm (P = 0.011). No differences were observed in epidural analgesia (P = 0.16), type of resection (P = 0.43), incision length (P = 0.40), type of incision (P = 0.47), operation time (P = 0.92), estimated blood loss (EBL) (P = 0.56), time to ambulation (P = 0.95), flatus (P = 0.37), diet (P = 0.17), removal of the epidural anaesthesia (P = 0.26) and length of hospital stay (LOS) (P = 0.575). Intra-operative fluids administered were 3.1 (0.7-77) vs 4 (0.9-6.2) liters (P = 0.53). Postoperative fluids administered were 12.5 (5.5-84.6) vs 11.3 (3.4-49.8) (P = 0.42). Overall and septic complication rates were significantly decreased in the test arm (7/32 (22%) vs 19/40 (49%) (P = 0.022) and 2/32 (6.2%) vs 12/40 (30%) (P = 0.05), respectively).

CONCLUSION

Intra-operative administration of iv water and electrolyte during bowel surgery, based on stroke volume measured using oesophageal Doppler, was associated with decreased complication rates.

Search for a vectorlike quark with charge 2/3 in t+Z events from pp collisions at √s=7 TeV

A search for pair-produced heavy vectorlike charge-2/3 quarks, T, in pp collisions at a center-of-mass energy of 7 TeV, is performed with the CMS detector at the LHC. Events consistent with the flavor-changing-neutral-current decay of a T quark to a top quark and a Z boson are selected by requiring two leptons from the Z-boson decay, as well as an additional isolated charged lepton. In a data sample corresponding to an integrated luminosity of 1.14  fb(-1), the number of observed events is found to be consistent with the standard model background prediction. Assuming a branching fraction of 100% for the decay T→tZ, a T quark with a mass less than 475  GeV/c(2) is excluded at the 95% confidence level.