Determining optimal eluter design by modeling physical dose enhancement in brachytherapy

PURPOSE

In situ drug release concurrent with radiation therapy has been proposed to enhance the therapeutic ratio of permanent prostate brachytherapy. Both brachytherapy sources and brachytherapy spacers have been proposed as potential eluters to release compounds, such as nanoparticles or chemotherapeutic agents. The relative effectiveness of the approaches has not been compared yet. This work models the physical dose enhancement of implantable eluters in conjunction with brachytherapy to determine which delivery mechanism provides greatest opportunity to enhance the therapeutic ratio.

MATERIALS AND METHODS

The combined effect of implanted eluters and radioactive sources were modeled in a manner that allowed the comparison of the relative effectiveness of different types of implantable eluters over a range of parameters. Prostate geometry, source, and spacer positions were extracted from treatment plans used for 125 I permanent prostate implants. Compound concentrations were calculated using steady-state solution to the diffusion equation including an elimination term characterized by the diffusion-elimination modulus (ϕb ). Does enhancement was assumed to be dependent on compound concentration up to a saturation concentration (csat ). Equivalent uniform dose (EUD) was used as an objective to determine the optimal configuration of eluters for a range of diffusion-elimination moduli, concentrations, and number of eluters. The compound delivery vehicle that produced the greatest enhanced dose was tallied for points in parameter space mentioned to determine the conditions under whether there are situations where one approach is preferable to the other.

RESULTS

The enhanced effect of implanted eluters was calculated for prostate volumes from 14 to 45 cm3 , ϕb from 0.01 to 4 mm-1 , csat from 0.05 to 7.5 times the steady-state compound concentration released from the surface of the eluter. The number of used eluters (ne ) was simulated from 10 to 60 eluters. For the region of (csat , Φ)-space that results in a large fraction of the gland being maximally sensitized, compound eluting spacers or sources produce equal increase in EUD. In the majority of the remaining (csat , Φ)-space, eluting spacers result in a greater EUD than sources even where sources often produce greater maximal physical dose enhancement. Placing eluting implants in planned locations throughout the prostate results in even greater enhancement than using only source or spacer locations.

CONCLUSIONS

Eluting brachytherapy spacers offer an opportunity to increase EUD during the routine brachytherapy process. Incorporating additional needle placements permits compound eluting spacer placement independent of source placement and thereby allowing a further increase in the therapeutic ratio. Additional work is needed to understand the in vivo spatial distribution of compound around eluters, and to incorporate time dependence of both compound release and radiation dose.

Electric field encephalography for brain activity monitoring

OBJECTIVE

We describe an early-stage prototype of a new wireless electrophysiological sensor system, called NeuroDot, which can measure neuroelectric potentials and fields at the scalp in a new modality called Electric Field Encephalography (EFEG). We aim to establish the physical validity of the EFEG modality, and examine some of its properties and relative merits compared to EEG.

APPROACH

We designed a wireless neuroelectric measurement device based on the Texas Instrument ADS1299 Analog Front End platform and a sensor montage, using custom electrodes, to simultaneously measure EFEG and spatially averaged EEG over a localized patch of the scalp (2 cm  ×  2 cm). The signal properties of each modality were compared across tests of noise floor, Berger effect, steady-state visually evoked potential (ssVEP), signal-to-noise ratio (SNR), and others. In order to compare EFEG to EEG modalities in the frequency domain, we use a novel technique to compute spectral power densities and derive narrow-band SNR estimates for ssVEP signals. A simple binary choice brain-computer-interface (BCI) concept based on ssVEP is evaluated. Also, we present examples of high quality recording of transient Visually Evoked Potentials and Fields (tVEPF) that could be used for neurological studies.

MAIN RESULTS

We demonstrate the capability of the NeuroDot system to record high quality EEG signals comparable to some recent clinical and research grade systems on the market. We show that the locally-referenced EFEG metric is resistant to certain types of movement artifacts. In some ssVEP based measurements, the EFEG modality shows promising results, demonstrating superior signal to noise ratios than the same recording processed as an analogous EEG signal. We show that by using EFEG based ssVEP SNR estimates to perform a binary classification in a model BCI, the optimal information transfer rate (ITR) can be raised from 15 to 30 bits per minute-though these preliminary results are likely sensitive to inter-subject variations and choice of scalp locations, so require further investigation.

SIGNIFICANCE

Enhancement of ssVEP SNR using EFEG has the potential to improve visually based BCIs and diagnostic paradigms. The time domain analysis of tVEPF signals shows robust features in the electric field components that might have clinical relevance beyond classical VEP approaches.

Facile Synthesis of Mesoporous MnCO₃ for Supercapacitor Applications

We report a rapid and facile synthesis of MnCO3 with uniform mesopores for supercapacitor applications. Mesoporous MnCO3 was synthesised by a co-precipitation method using MnSO4 and (NH4)HCO3 as manganese and carbonate source, respectively. Powder X-ray diffraction study confirmed the formation of rhodochrosite phase of MnCO3. X-ray photoelectron spectroscopic study ascertained the oxidation state of Mn as 2+ in MnCO3. Scanning and Transmission electron microscopic studies revealed that nanograins of size less than 10 nm agglomerated into submicron sized spherical particles of MnCO3. N2 sorption studies displayed a typical type-IV isotherm with H2 hysteresis, demonstrating mesoporosity of as-prepared MnCO3. Furthermore, the mesoporous MnCO3 particles were evaluated for their capacitance properties by cyclic voltammetry and galvanostatic charge-discharge cycling in aqueous 0.1 M Mg(ClO4)2 electrolyte. The fabricated mesoporous MnCO3 electrodes delivered a specific capacitance of 144 F g-1 at a current density of 0.34 A g-1. It also exhibited good rate capability, high reversibility and cyclic stability over 1000 cycles.

Evaluation of single and two stage anaerobic digestion of landfill leachate: Effect of pH and initial organic loading rate on volatile fatty acid (VFA) and biogas production

This work aims to evaluate the impact of pH and initial organic load (IOL) in terms of Chemical Oxygen Demand (COD) of landfill leachate for the production of value added products during single and two stage anaerobic digestion (AD). It was observed that at an optimal IOL of 48 g/L, acetic acid was dominant at pH 5.5 whereas it was butyric acid at pH of 5.5-6.0 and 10-11. The yield of Volatile Fatty Acids (VFA) was dependent on IOL and it was in the range of 0.26 to 0.36 g VFA/(g COD removed). Methane was also harvested during single and two stage AD and found that it was varying in the range of 0.21-0.34 L CH₄/(g COD removed) and 0.2-0.32 L CH₄/(g COD removed) respectively. An overall increase of 21% COD removal was noticed in two stage AD in comparison to single stage.

Evaluation of serum inflammatory biomarkers as predictors of treatment outcome in pulmonary tuberculosis

OBJECTIVE

To evaluate C-reactive protein (CRP), globulin and white blood cell (WBC) count as predictors of treatment outcome in pulmonary tuberculosis (PTB).

METHODS

An observational study of patients with active PTB was conducted at a tertiary centre. All patients had serum CRP, globulin and WBC measured at baseline and at 2 months following commencement of treatment. The outcome of interest was requirement for extension of treatment beyond 6 months.

RESULTS

There were 226 patients included in the study. Serum globulin 45 g/l was the only baseline biomarker evaluated that independently predicted requirement for treatment extension (OR 3.42, 95%CI 1.597.32, P 0.001). An elevated globulin level that failed to normalise at 2 months was also associated with increased requirement for treatment extension (63.9% vs. 5.1%, P 0.001), and had a low negative likelihood ratio (0.07) for exclusion of requirement for treatment extension. On multivariable analysis, an elevated globulin that failed to normalise at 2 months was independently associated with requirement for treatment extension (OR 6.13, 95%CI 2.2316.80, P 0.001).

CONCLUSIONS

Serum globulin independently predicts requirement for treatment extension in PTB and outperforms CRP and WBC as a predictive biomarker. Normalisation of globulin at 2 months following treatment commencement is associated with low risk of requirement for treatment extension.

Ovarian function after chemotherapy in young breast cancer survivors

Background

As cure rates for breast cancer improve, there is increasing evidence that late effects of treatment-and impaired fertility in particular-are emerging as important concerns among young breast cancer survivors. Older reports have evaluated the occurrence of amenorrhea after treatment, but few data have been reported about the incidence of biochemical evidence for impaired ovarian function in patients who do not become overtly menopausal.

Methods

We conducted a cross-sectional study evaluating anti-Müllerian hormone (amh) in premenopausal chemotherapy-treated breast cancer survivors and control patients. Random serum levels of amh and other relevant clinical data were collected for 100 premenopausal chemotherapy-treated breast cancer survivors and 76 control subjects. Subgroup analyses were performed for women with regular menstrual cycles at the time of amh testing.

Results

After adjustment for age, amh was significantly lower in the overall group of patients receiving chemotherapy (p = 0.002) and in the subgroup reporting normal cycles (p = 0.03). Cyclophosphamide produced a significant dose-dependent reduction in amh (p < 0.001); trastuzumab was associated with increased amh in survivors with normal cycles. Overall, serum amh in survivors was roughly equivalent to that measured in control patients 12 years older.

Conclusions

Young breast cancer survivors often experience significant impairment of ovarian function despite having normal menstrual cycles after treatment. Those results have important implications for patient counselling and the timing of possible referral to a fertility specialist.

Evaluation of the molecular Xpert Xpress Flu/RSV assay vs. Alere i Influenza A & B assay for rapid detection of influenza viruses

A new FDA-approved Xpert Xpress Flu/RSV assay has been released for rapid influenza virus detection. We collected 134 nasopharyngeal specimens to compare the diagnostic performance of the Xpert assay and the Alere i Influenza A & B assay for influenza A and B virus detection. The Xpert assay demonstrated 100% and 96.3% sensitivity to influenza A and influenza B virus respectively. Its specificity was 100% for both viruses. The Alere i assay demonstrated slightly lower sensitivity but similar specificity to the Xpert Xpress assay. Although the Xpert assay (30 min) required longer processing time than the Alere assay (15 min), the handling procedure of the Alere assay was more complicated than the Xpert assay. As the GenXpert system has higher throughput than the Alere system, it is more suitable for hospital clinical laboratories. Overall, the new Xpert Xpress Flu/RSV assay is a reliable and useful tool for rapid influenza detection.

Effect of myocyte-fibroblast coupling on the onset of pathological dynamics in a model of ventricular tissue

Managing lethal cardiac arrhythmias is one of the biggest challenges in modern cardiology, and hence it is very important to understand the factors underlying such arrhythmias. While early afterdepolarizations (EAD) of cardiac cells is known to be one such arrhythmogenic factor, the mechanisms underlying the emergence of tissue level arrhythmias from cellular level EADs is not fully understood. Another known arrhythmogenic condition is fibrosis of cardiac tissue that occurs both due to aging and in many types of heart diseases. In this paper we describe the results of a systematic in-silico study, using the TNNP model of human cardiac cells and MacCannell model for (myo)fibroblasts, on the possible effects of diffuse fibrosis on arrhythmias occurring via EADs. We find that depending on the resting potential of fibroblasts (VFR), M-F coupling can either increase or decrease the region of parameters showing EADs. Fibrosis increases the probability of occurrence of arrhythmias after a single focal stimulation and this effect increases with the strength of the M-F coupling. While in our simulations, arrhythmias occur due to fibrosis induced ectopic activity, we do not observe any specific fibrotic pattern that promotes the occurrence of these ectopic sources.

Modelling of pretreatment and saccharification with different feedstocks and kinetic modeling of sorghum saccharification

Experiments have been performed for pretreatment of sorghum, wheat straw and bamboo through high temperature alkali pretreatment with different alkaline loading and temperatures, and the data on extent of delignification in terms of the final compositions of cellulose, hemicellulose and lignin have been generated. Further, enzymatic saccharification has been carried out in all the cases to find the extent of conversion possible after 72h. The effect of different operating parameters on the extent of delignification and cellulose conversion are evaluated. This data is employed to develop a generalized multi-feedstock and individual feedstock based models which can be used to determine the extent of delignification and cellulose conversion for any and specific biomass respectively with alkaline pretreatment and similar enzyme conditions as considered in the present study. Also, a kinetic model is developed and validated for sorghum for cellulosic conversion.