Intracellular oxygen transient quantification in vivo during Ultra-High Dose Rate (UHDR) FLASH radiotherapy

PURPOSE

Large, rapid extracellular oxygen transients (ΔpO2) have been measured in vivo during Ultra-High Dose Rate (UHDR) radiotherapy; however, it has been unclear if this matches intracellular oxygen levels. Here, the endogenously produced Protoporphyrin IX (PpIX) delayed fluorescence (DF) signal was measured as an intracellular in vivo oxygen sensor to quantify these transients, with direct comparison to extracellular pO2. Intracellular ΔpO2 is closer to the cellular DNA, the site of major radiobiological damage and therefore should help elucidate radiochemical mechanisms of the FLASH effect and potentially be translated to human tissue measurement.

METHODS & MATERIALS

Protoporphyrin IX (PpIX) was induced in mouse skin through intraperitoneal injection of 250mg/kg of aminolevulinic acid. The animals were also administered a 50 µL intradermal injection of 10 µM Oxyphor G4 (PdG4) for phosphorescence lifetime pO2 measurement. Paired oxygen transients were quantified on leg or flank tissues, while delivering 10 MeV electrons in 3 µs pulses at 360 Hz for a total dose of 10-28Gy.

RESULTS

Transient reductions in pO2 were quantifiable in both PpIX delayed fluorescence and Oxyphor phosphorescence, corresponding to intracellular and extracellular pO2 values, respectively. Reponses were quantified for 10, 22, and 28 Gy doses, with ΔpO2 being proportional to dose on average. The ΔpO2 values were dependent upon initial pO2 in a logistic function. The average and standard deviations in ΔpO2 per dose were 0.56±0.18 mmHg/Gy and 0.43±0.06 mmHg/Gy for PpIX and Oxyphor, respectively, for initial pO2>20 mmHg. While there was large variability in the individual animal measurements of ΔpO2, the average values demonstrated a direct and proportional correlation between intracellular and extracellular pO2 changes, following a linear 1:1 relationship.

CONCLUSIONS

A fundamentally new approach to measure intracellular oxygen depletion in living tissue showed that ΔpO2 transients seen during UHDR-RT matched those taken using extracellular oxygen measurement. This approach could be translated to humans to quantify intracellular ΔpO2. The measurement of these transients could potentially allow estimation of intracellular reactive oxygen species production.

Clinical Features, Non-Contrast CT Radiomic and Radiological Signs in Models for the Prediction of Hematoma Expansion in Intracerebral Hemorrhage

PURPOSE

Rapid identification of hematoma expansion (HE) risk at baseline is a priority in intracerebral hemorrhage (ICH) patients and may impact clinical decision making. Predictive scores using clinical features and Non-Contract Computed Tomography (NCCT)-based features exist, however, the extent to which each feature set contributes to identification is limited. This paper aims to investigate the relative value of clinical, radiological, and radiomics features in HE prediction.

METHODS

Original data was retrospectively obtained from three major prospective clinical trials ["Spot Sign" Selection of Intracerebral Hemorrhage to Guide Hemostatic Therapy (SPOTLIGHT)NCT01359202; The Spot Sign for Predicting and Treating ICH Growth Study (STOP-IT)NCT00810888] Patients baseline and follow-up scans following ICH were included. Clinical, NCCT radiological, and radiomics features were extracted, and multivariate modeling was conducted on each feature set.

RESULTS

317 patients from 38 sites met inclusion criteria. Warfarin use (p=0.001) and GCS score (p=0.046) were significant clinical predictors of HE. The best performing model for HE prediction included clinical, radiological, and radiomic features with an area under the curve (AUC) of 87.7%. NCCT radiological features improved upon clinical benchmark model AUC by 6.5% and a clinical & radiomic combination model by 6.4%. Addition of radiomics features improved goodness of fit of both clinical (p=0.012) and clinical & NCCT radiological (p=0.007) models, with marginal improvements on AUC. Inclusion of NCCT radiological signs was best for ruling out HE whereas the radiomic features were best for ruling in HE.

CONCLUSION

NCCT-based radiological and radiomics features can improve HE prediction when added to clinical features.

Effects of UHDR and Conventional Irradiation on Behavioral and Cognitive Performance and the Percentage of Ly6G+ CD45+ Cells in the Hippocampus

We assessed the effects of conventional and ultra-high dose rate (UHDR) electron irradiation on behavioral and cognitive performance one month following exposure and assessed whether these effects were associated with alterations in the number of immune cells in the hippocampus using flow cytometry. Two-month-old female and male C57BL/6J mice received whole-brain conventional or UHDR irradiation. UHDR mice were irradiated with 9 MeV electrons, delivered by the Linac-based/modified beam control. The mice were irradiated or sham-irradiated at Dartmouth, the following week shipped to OHSU, and behaviorally and cognitively tested between 27 and 41 days after exposure. Conventional- and UHDR-irradiated mice showed impaired novel object recognition. During fear learning, conventional- and UHDR-irradiated mice moved less during the inter-stimulus interval (ISI) and UHDR-irradiated mice also moved less during the baseline period (prior to the first tone). In irradiated mice, reduced activity levels were also seen in the home cage: conventional- and UHDR-irradiated mice moved less during the light period and UHDR-irradiated mice moved less during the dark period. Following behavioral and cognitive testing, infiltrating immune cells in the hippocampus were analyzed by flow cytometry. The percentage of Ly6G+ CD45+ cells in the hippocampus was lower in conventional- and UHDR-irradiated than sham-irradiated mice, suggesting that neutrophils might be particularly sensitive to radiation. The percentage of Ly6G+ CD45+ cells in the hippocampus was positively correlated with the time spent exploring the novel object in the object recognition test. Under the experimental conditions used, cognitive injury was comparable in conventional and UHDR mice. However, the percentage of CD45+ CD11b+ Ly6+ and CD45+ CD11b+ Ly6G- cells in the hippocampus cells in the hippocampus was altered in conventional- but not UHDR-irradiated mice and the reduced percentage of Ly6G+ CD45+ cells in the hippocampus might mediate some of the detrimental radiation-induced cognitive effects.

Ultra-fast, high spatial resolution single-pulse scintillation imaging of synchrocyclotron pencil beam scanning proton delivery

Objective.To demonstrates the ability of an ultra-fast imaging system to measure high resolution spatial and temporal beam characteristics of a synchrocyclotron proton pencil beam scanning (PBS) system.Approach.An ultra-fast (1 kHz frame rate), intensified CMOS camera was triggered by a scintillation sheet coupled to a remote trigger unit for beam on detection. The camera was calibrated using the linear (R2> 0.9922) dose response of a single spot beam to varying currents. Film taken for the single spot beam was used to produce a scintillation intensity to absolute dose calibration.Main results. Spatial alignment was confirmed with the film, where thexandy-profiles of the single spot cumulative image agreed within 1 mm. A sample brain patient plan was analyzed to demonstrate dose and temporal accuracy for a clinically-relevant plan, through agreement within 1 mm to the planned and delivered spot locations. The cumulative dose agreed with the planned dose with a gamma passing rate of 97.5% (2 mm/3%, 10% dose threshold).Significance. This is the first system able to capture single-pulse spatial and temporal information for the unique pulse structure of a synchrocyclotron PBS systems at conventional dose rates, enabled by the ultra-fast sampling frame rate of this camera. This study indicates that, with continued camera development and testing, target applications in clinical and FLASH proton beam characterization and validation are possible.

Original and Modified Graeb Score Correlation With Intraventricular Hemorrhage and Clinical Outcome Prediction in Hyperacute Intracranial Hemorrhage

Background and Purpose- The Graeb score is a visual rating scale of intraventricular hemorrhage (IVH) on noncontrast head CT. Little data exist in the hyperacute (<6 hour) period for reliability and predictive value of the modified Graeb Score (mGS) or the original Graeb Score (oGS) for clinical outcomes or their correlation with quantitative IVH volumes. Methods- A retrospective analysis of multicenter prospective intracranial hemorrhage study was performed. oGS and mGS inter-observer agreement and IVH volume correlation on the baseline noncontrast head CT were calculated by intraclass correlation coefficient and Pearson coefficient respectively. Predictors of poor outcome (modified Rankin Scale scores ≥4) at 3 months were identified using a backward stepwise selection multivariable analysis. oGS and mGS performance for modified Rankin Scale scores ≥4 was determined by receiver operating characteristic analysis. Results- One hundred forty-one patients (65±12 years) with median (interquartile range) time to CT of 82.5 (70.3-157.5) minutes were included. IVH was observed in 43 (30%) patients. Inter-observer agreement was excellent for both oGS (intraclass correlation coefficient, 0.90 [95% CI, 0.80-0.95]) and mGS (intraclass correlation coefficient, 0.97 [95% CI, 0.84-0.99]). mGS (R=0.79; P<0.01) correlated better than oGS (R=0.71; P<0.01) with IVH volumes (P=0.02). Models of thresholded oGS and mGS were not different from a model of planimetric baseline intracranial hemorrhage and IVH volume for poor outcome prediction. Area under the curves were 0.70, 0.73, and 0.72, respectively. Conclusions- Excellent correlation for oGS and mGS with IVH volume was seen. Thresholded oGS and mGS are reasonable surrogates for planimetric IVH volume for hyperacute intracranial hemorrhage studies.

Reinitiation of Anticoagulation After Surgical Evacuation of Subdural Hematomas

BACKGROUND

Chronic subdural hematoma (cSDH) is an increasingly common condition due to the growing use of anticoagulation. Currently, there remains a lack of evidence to guide the optimal timing of anticoagulant reinitiation for stroke prevention in atrial fibrillation after cSDH evacuation. We aimed to better understand the perceived risks of hemorrhagic and embolic complications along with current practice patterns on restarting anticoagulation after surgical evacuation of cSDH.

METHODS

We conducted a survey of Canadian neurosurgeons and stroke neurologists using a novel self-administered questionnaire using clinical cases that included questions on clinical experience, practice setting, practice patterns, and perceptions on stroke/bleeding risk with anticoagulation reinitiation after cSDH evacuation. The instrument was evaluated for clinical sensibility by 5 neurosurgeons, neurologists, and intensivists.

RESULTS

The response rate after 4 mailings was 40% for neurosurgeons (55/136) and 21% for stroke neurologists (26/122). Almost all participants would restart anticoagulation for stroke prevention in atrial fibrillation after cSDH evacuation (91.8% in low-risk patients, 98.6% in high-risk patients). Time to reinitiation of anticoagulation varied considerably, particularly for high-risk patients where 36% of participants would restart anticoagulation within 1 week of surgery, 44% between 1 and 4 weeks after surgery, and 19% after 4 weeks postoperatively. The perceived risk of stroke and SDH reaccumulation varied considerably among participants and was dependent on timing of anticoagulation reinitiation.

CONCLUSIONS

There is considerable variation in current practice patterns and perceived risks of embolic and hemorrhagic complications with anticoagulation reinitiation after cSDH evacuation. These results demonstrate clinical equipoise that warrant further targeted investigation in large-scale randomized controlled trials.

2018 Focused Update of the Canadian Cardiovascular Society Guidelines for the Management of Atrial Fibrillation

The Canadian Cardiovascular Society (CCS) Atrial Fibrillation Guidelines Committee provides periodic reviews of new data to produce focused updates that address clinically important advances in atrial fibrillation (AF) management. This 2018 Focused Update addresses: (1) anticoagulation in the context of cardioversion of AF; (2) the management of antithrombotic therapy for patients with AF in the context of coronary artery disease; (3) investigation and management of subclinical AF; (4) the use of antidotes for the reversal of non-vitamin K antagonist oral anticoagulants; (5) acute pharmacological cardioversion of AF; (6) catheter ablation for AF, including patients with concomitant AF and heart failure; and (7) an integrated approach to the patient with AF and modifiable cardiovascular risk factors. The recommendations were developed using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) standards. Individual studies and literature were reviewed for quality and bias; the literature review process and evidence tables are included as Supplementary Material and are available on the CCS Web site. Details of the updated recommendations are presented, along with their background and rationale. This document is linked to an updated summary of all CCS AF guidelines recommendations, from 2010 to the present 2018 Focused Update, which is provided in the Supplementary Material.

Correcting Cherenkov light attenuation in tissue using spatial frequency domain imaging for quantitative surface dosimetry during whole breast radiation therapy

Imaging Cherenkov emission during radiotherapy permits real-time visualization of external beam delivery on superficial tissue. This signal is linear with absorbed dose in homogeneous media, indicating potential for quantitative dosimetry. In humans, the inherent heterogeneity of tissue optical properties (primarily from blood and skin pigment) distorts the linearity between detected Cherenkov signal and absorbed dose. We examine the potential to correct for superficial vasculature using spatial frequency domain imaging (SFDI) to map tissue optical properties for large fields of view. In phantoms, applying intensity corrections to simulate blood vessels improves Cherenkov image (CI) negative contrast by 24% for a vessel 1.9-mm-in diameter. In human trials, SFDI and CI are acquired for women undergoing whole breast radiotherapy. Applied corrections reduce heterogeneity due to vasculature within the sampling limits of the SFDI from a 22% difference as compared to the treatment plan, down to 6% in one region and from 14% down to 4% in another region. The optimal use for this combined imaging system approach is to correct for small heterogeneities such as superficial blood vessels or for interpatient variations in blood/melanin content such that the corrected CI more closely represents the surface dose delivered.

High prevalence of modifiable stroke risk factors identified in a pharmacy-based screening programme

Background

Population-based screening for atrial fibrillation (AF) is a promising public health strategy to prevent stroke. However, none of the published reports have evaluated comprehensive screening for additional stroke risk factors such as hypertension and diabetes in a pharmacy setting.

Methods

The Program for the Identification of ‘Actionable’ Atrial Fibrillation in the Pharmacy Setting (PIAAF-Pharmacy) screened individuals aged ≥65 years, attending community pharmacies in Canada, who were not receiving oral anticoagulation (OAC). Participants were screened for AF using a hand-held ECG device, had blood pressure (BP) measured, and diabetes risk estimated using the Canadian Diabetes Risk Assessment Questionnaire (CANRISK) questionnaire. ‘Actionable’ AF was defined as unrecognised or undertreated AF. A 6-week follow-up visit with the family physician was suggested for participants with ‘actionable’ AF and a scheduled 3-month visit occurred at an AF clinic.

Results

During 6 months, 1145 participants were screened at 30 pharmacies. ‘Actionable’ AF was identified in 2.5% (95% CI 1.7 to 3.6; n=29); of these, 96% were newly diagnosed. Participants with ‘actionable AF’ had a mean age of 77.2±6.8 years, 58.6% were male and 93.1% had a CHA₂DS₂-VASc score ≥2. A BP>140/90 was found in 54.9% (616/1122) of participants and 44.4% (214/492) were found to be at high risk of diabetes. At 3 months, only 17% of participants were started on OAC, 50% had improved BP and 71% had confirmatory diabetes testing.

Conclusions

Integrated stroke screening identifies a high prevalence of individuals who could benefit from stroke prevention therapies but must be coupled with a defined care pathway.

Abstract 210: Association between Paroxysmal Supraventricular Tachycardia and Ischemic Stroke in Patients Without Atrial Fibrillation

Introduction: Paroxysmal supraventricular tachycardia (PSVT) is viewed as a benign heart-rhythm disorder. However, recent studies suggest that atrial dysrhythmias other than atrial fibrillation/flutter (AF) may signify an increased stroke risk.

Hypothesis: PSVT is associated with subsequent ischemic stroke in patients without documented AF.

Methods: We obtained inpatient and outpatient claims data from 2010-2011 in a 5% sample of Medicare beneficiaries ≥66 years of age. We included only patients with a pacemaker or defibrillator, since such patients often undergo interrogation of heart rhythm. Patients with AF or stroke before or at the time of device implantation were excluded. Our predictor variable was PSVT. The primary outcome was ischemic stroke and the secondary outcome was embolic stroke. All diagnoses were ascertained from ICD-9-CM codes using previously validated algorithms. We used Kaplan-Meier survival analysis and the log-rank test to compare outcomes in patients with and without PSVT, which was modeled as a time-varying covariate. Patients were censored at the time of incident AF, stroke, death, or on December 31, 2011. Cox proportional hazards analysis was used to assess the relationship between PSVT and stroke while adjusting for demographic characteristics and vascular risk factors.

Results: Among 42,152 eligible patients with a median 1.8 years of follow-up, 2,245 (5.3%) had PSVT and 1,007 (2.4%) developed a stroke. The incidence of stroke after a PSVT diagnosis (2.17% per year; 95% confidence interval [CI], 1.45-3.24%) was significantly higher than in patients without PSVT (0.95% per year; 95% CI, 0.87-1.03%; P < 0.001). After adjustment for demographic characteristics and vascular risk factors, PSVT was associated with a higher hazard of stroke (hazard ratio [HR], 2.0; 95% CI, 1.3-3.0). This association appeared stronger for embolic stroke (HR, 3.6; 95% CI, 1.1-11.8).

Conclusions: In Medicare beneficiaries with implantable pacemakers or defibrillators, PSVT was associated with ischemic stroke, especially embolic stroke, in the absence of documented AF. These results build on recent findings that disturbances of atrial rhythm and function other than AF may be a previously unrecognized stroke risk factor.

2014 focused update of the Canadian Cardiovascular Society Guidelines for the management of atrial fibrillation

Atrial fibrillation (AF) is an extremely common clinical problem with an important population morbidity and mortality burden. The management of AF is complex and fraught with many uncertain and contentious issues, which are being addressed by extensive ongoing basic and clinical research. The Canadian Cardiovascular Society AF Guidelines Committee produced an extensive set of evidence-based AF management guidelines in 2010 and updated them in the areas of anticoagulation and rate/rhythm control in 2012. In late 2013, the committee judged that sufficient new information regarding AF management had become available since 2012 to warrant an update to the Canadian Cardiovascular Society AF Guidelines. After extensive evaluation of the new evidence, the committee has updated the guidelines for: (1) stroke prevention principles; (2) anticoagulation of AF patients with chronic kidney disease; (3) detection of AF in patients with stroke; (4) investigation and management of subclinical AF; (5) left atrial appendage closure in stroke prevention; (6) emergency department management of AF; (7) periprocedural anticoagulation management; and (8) rate and rhythm control including catheter ablation. This report presents the details of the updated recommendations, along with their background and rationale. In addition, a complete set of presently applicable recommendations, those that have been updated and those that remain in force from previous guideline versions, is provided in the Supplementary Material.

iPad technology for home rehabilitation after stroke (iHOME): a proof-of-concept randomized trial

BACKGROUND

Tablets are a novel line of computers controlled by a multitouch screen. Fine motor movements are captured on the tablet computer through electrical fields and can be qualitatively and quantitatively assessed. Evidence is limited on tablet use for stroke rehabilitation.

METHODS

iHOME is an investigator-initiated randomized controlled pilot trial with a single-blinded outcome assessment. The intervention consists of iPad use (investigational group) vs. usual care (control group) among patients receiving conventional outpatient rehabilitation. Eligibility includes aged 18-85 years who experienced a mild ischemic or hemorrhagic stroke (as diagnosed on neuroimaging and determined by the Chedoke-McMaster score ≥3. The STROKE REHAB® software for the iPad was specifically designed for patients with fine motor weakness and/or neglect. Of the total 30 patients, 20 will be in iHOME Acute (enrolled within three-months of stroke onset) and 10 patients in iHOME Chronic (enrolled more than six-months from onset).

OUTCOME MEASURES

The primary feasibility outcome is the proportion of the scheduled iPad time used (more than 70% (≥140 mins) of the total 'dose' of intervention intended will be considered successful). Efficacy in fine motor movements will be assessed using the nine-hole peg test; time to magnify and pop the balloons in the iPad software application, and improvement in Wolf Motor Function Test.

CONCLUSIONS

iHOME is a randomized controlled trial assessing the feasibility, safety, and efficacy of tablet technology for home use in stroke rehabilitation. The results of this study will serve as the basis for a larger multicenter trial.