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Biomedical subjects

R Mohan

Publications and source records attributed to R Mohan.

At least 19 recordsLinked to original sources
PubMed2006

Sustainable waste management in the UK: the public health role.

This paper discusses waste management in the UK and its relationship with health. It aims to outline the role of health professionals in the promotion of waste management, and argues for a change in their role in waste management regulation to help make the process more sustainable. The most common definition of sustainable development is that by the Brundtland commission, i.e. "development that meets the needs of the present without compromising the ability of future generations to meet their own needs". Managing waste sites in a manner that minimises toxic impacts on the current and future generations is obviously a crucial part of this. Although the management of waste facilities is extremely complex, the Integrated Pollution Prevention and Control regime, which requires the input of public health professionals on the regulation of such sites, means that all waste management installations should now be operating in a fashion that minimises any toxicological risks to human health. However, the impacts upon climate change, resource use and health inequalities, as well as the effects of waste transportation, are currently not considered to be part of public health professionals' responsibilities when dealing with these sites. There is also no requirement for public health professionals to become involved in waste management planning issues. The fact that public health professionals are not involved in any of these issues makes it unlikely that the potential impacts upon health are being considered fully, and even more unlikely that waste management will become more sustainable. This paper aims to show that by only considering direct toxicological impacts, public health professionals are not fully addressing all the health issues and are not contributing towards sustainability. There is a need for a change in the way that health professionals deal with waste management issues.

Community Health Planning↗
PubMed2006

The evidence base of complementary and alternative therapies in depression.

BACKGROUND: Depression is one of the leading indications for using Complementary and Alternative Medicine (CAM). This paper reviews the evidence of efficacy of different types of CAM in depression with the aim of identifying the highest level of evidence. METHODS: We conducted literature searches restricted to the English language for studies on CAM as monotherapy in depression. All papers were reviewed by two researchers and the evidence was ranked according to a widely referenced hierarchy of evidence. RESULTS: 19 papers formed the final review. We found Grade 1 evidence on the use of St. John's wort, Tryptophan/5-Hydroxytryptophan, S-adenosyl methionine, Folate, Inositol, Acupuncture and Exercise in Depressive disorders, none of which was conclusively positive. We found RCTs at the Grade 2 level on the use of Saffron (Herbal medicine), Complex Homoeopathy and Relaxation training in Depressive disorders, all of which showed inconclusive results. Other RCTs yielded unequivocally negative results. Studies below this level yielded inconclusive or negative results. LIMITATIONS: Searches were restricted to the English language. Our list of CAM approaches may not have been comprehensive. We excluded studies on the use of CAM as an adjunctive treatment and this review aimed to identify only the highest level of evidence. CONCLUSIONS: None of the CAM studies show evidence of efficacy in depression according to the hierarchy of evidence. The RCT model and the principles underlying many types of CAM are dissonant, making its application in the evaluation of those types of CAM difficult. The hierarchy of evidence we used has limited utility in grading trials of CAM.

Complementary Therapies↗
PubMed2006

mTOR inhibition induces endothelial progenitor cell death.

Immunosuppressants are necessary to prevent graft rejection after solid organ transplantation. However, they are also known to have significant side effects, including endothelial toxicity. Endothelial progenitor cells originate in the bone marrow and are recognized by their angiogenic and endothelial reparative properties. The effects of the immunosuppressants cyclosporine A (CyA), tacrolimus and rapamycin were analyzed on endothelial progenitor-like cells. Rapamycin induced rapid cell death, even at concentrations much lower than those used clinically, in peripheral blood mononuclear cells (PBMC) cultured to favor outgrowth of endothelial progenitors. Cyclosporine A and tacrolimus had no significant effects at clinical concentrations. The effect of rapamycin was specific to endothelial progenitor cells, in particular to the early stages of differentiation, as a lesser effect was observed in late outgrowth endothelial progenitors, mature aortic endothelial cells, and macrophages derived from the same PBMCs. The mechanism of cell death appeared to be apoptosis; however, its induction was probably multifactorial and did not depend on caspase or cathepsin activation. In conclusion, rapamycin induces endothelial progenitor cell death, possibly because it blocks survival signals given by growth factors critically required by these cells.

Apoptosis↗
PubMed2006

Structural, spectral, linear and nonlinear optical properties of new nonlinear optical L-histidinium trichloroacetate crystals.

Single crystals of a new histidinium salt: L-histidinium trichloroacetate {abbreviated as LHTCA; [(C(3)N(2)H(4))CH(2)CH(NH(3))(CO(2))](+)CCl(3)COO(-)} were grown by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in a non-centrosymmetric space group P2(1) of monoclinic system with cell parameters a=5.4505(18) A, b=25.769(8) A, c=9.210(2) A and beta=99.98(2) degrees. The vibrational structure of the compound confirms the presence of various functional groups in the molecule. The UV-vis-NIR spectrum shows a good transparency in the whole of the region from ultraviolet to near IR. The Kurtz powder SHG measurement confirms the frequency doubling of the crystal. Thermal behaviour of the crystals has been investigated by DSC analysis. These preliminary results suggest that LHTCA crystal can act as a potential and promising candidate for frequency doubling applications even from the near UV region to the near IR.

Crystallization↗
PubMed2006

Characteristics of high intent suicide attempters admitted to a general hospital.

BACKGROUND: Suicide intent is a strong predictor of repetition of attempts and subsequent suicide. This study aimed to compare socio-demographics, clinical factors and method of attempt in high and low intent suicide attempters. METHOD: All patients admitted following attempted suicide to a teaching hospital were interviewed. Socio-demographic information, details of the attempt and psychiatric diagnosis were recorded. Scales for assessing suicide intent, lethality, recent life-events and depression were administered. Comparison between high intent and low intent groups were done to identify the characteristics of patients who had high suicidal intent. RESULTS: The sample comprised 203 patients, 84 of whom were classified as high intent attempters using the Suicide Intent Scale. The high intent group were significantly more likely to be male (p = 0.01), of single marital status (p = 0.04), have a psychiatric diagnosis, especially depression (p = 0.001) and use self immolation to attempt suicide (p = 0.001). Patients with high intent had significantly higher lethality (p = 0.001) and recent stressful life-event scores (p = 0.001). CONCLUSIONS: High intent suicide attempts are associated with distinct socio-demographic profiles and psychiatric morbidity. Routine assessment of intent may help to identify individuals with high risk, who can be offered targeted interventions.

Adolescent↗
PubMed2006

A flattening filter free photon treatment concept evaluation with Monte Carlo.

In principle, the concept of flat initial radiation-dose distribution across the beam is unnecessary for intensity modulated radiation therapy. Dynamic leaf positioning during irradiation could appropriately adjust the fluence distribution of an unflattened beam that is peaked in the center and deliver the desired uniform or nonuniform dose distribution. Removing the flattening filter could lead to reduced treatment time through higher dose rates and reduced scatter, because there would be substantially less material in the beam; and possibly other dosimetric and clinical advantages. This work aims to evaluate the properties of a flattening filter free clinical accelerator and to investigate its possible advantages in clinical intensity modulated radiation therapy applications by simulating a Varian 2100-based treatment delivery system with Monte Carlo techniques. Several depth-dose curves and lateral dose distribution profiles have been created for various field sizes, with and without the flattening filter. Data computed with this model were used to evaluate the overall quality of such a system in terms of changes in dose rate, photon and electron fluence, and reduction in out-of-field stray dose from the scattered components and were compared to the corresponding data for a standard treatment head with a flattening filter. The results of the simulations of the flattening filter free system show that a substantial increase in dose rate can be achieved, which would reduce the beam on time and decrease the out-of-field dose for patients due to reduced head-leakage dose. Also close to the treatment field edge, a significant improvement in out-of-field dose could be observed for small fields, which can be attributed to the change in the photon spectra, when the flattening filter is removed from the beamline.

Journal Article↗
PubMed2006

Monte Carlo study of backscatter in a flattening filter free clinical accelerator.

In conventional linear accelerators, the flattening filter provides a uniform lateral dose profile. In intensity modulated radiation therapy applications, however, the flatness of the photon field and hence the presence of a flattening filter, is not necessary. Removing the filter may provide some advantages, such as faster treatments and smaller out-of-field doses to the patients. In clinical accelerators the backscattered radiation dose from the collimators must be taken into account when the dose to the target volume in the patient is being determined. In the case of a conventional machine, this backscatter is known to great precision. In a flattening filter free accelerator, however, the amount of backscatter may be different. In this study we determined the backscatter contribution to the monitor chamber signal in a flattening filter free clinical accelerator (Varian Clinac 21EX) with Monte Carlo simulations. We found that with the exception of very small fields in the 18-MV photon mode, the contribution of backscattered radiation to the monitor signal did not differ from that of conventional machines with a flattening filter. Hence, a flattening filter free clinical accelerator would not necessitate a different backscatter correction.

Computer Simulation↗
PubMed2005

Evacuation decisions in a chemical air pollution incident: cross sectional survey.

OBJECTIVE: To compare the health outcomes in sheltered and evacuated populations after a chemical incident in a plastics factory. DESIGN: Cross sectional survey. SETTING: Urban area in southwest England. PARTICIPANTS: 1750 residents from the area exposed to the chemical smoke, of which 472 were evacuated and the remaining 1278 were advised to shelter indoors. MAIN OUTCOME MEASURE: Number of adverse health symptoms. A case was defined by the presence of four or more symptoms. MAIN RESULTS: 1096 residents (63%; 299 evacuated, 797 sheltered) provided data for analyses. The mean symptom score and proportion of cases were higher in evacuated people than in the sheltered population (evacuated: symptom score 1.9, cases 19.7% (n = 59); sheltered: symptom score 1.0, cases 9.5% (n = 76); P < 0.001 for both). The difference between the two groups attenuated markedly at the end of two weeks from the start of the incident. The two main modifiable risk factors for the odds of becoming a case were evacuation (odds ratio 2.5, 95% confidence interval 1.7 to 3.8) and direct exposure to smoke for more than two hours on the first day of the incident (2.0, 1.7 to 2.3). The distance of residence from the factory or level of exposure before intervention (first six hours) had little effect on the odds of a person becoming a case. CONCLUSIONS: Sheltering may have been a better protective action than evacuation in this chemical incident, which is consistent with the prevailing expert view. Although this study has limitations, it is based on a real event. Evacuations carry their own risks and resource implications; increased awareness may help to reduce unnecessary evacuations in the future.

Air Pollutants↗
PubMed2005

Is the diaphragm motion probability density function normally distributed?

During radiotherapy treatment planning, the margins given to the clinical target volume to form the planning target volume accounts for internal motion and set-up error. Most margin formulas assume that the underlying distributions are independent and normal. Clinical data suggests that the set-up error probability density function (pdf) can be considered to have an approximately normal distribution. However, there is evidence that internal motion does not have a normal distribution. Thus, in general, a convolution of the two pdfs should be performed to determine the total geometric error. The goals of this article were to (1) determine if the internal motion pdf due to respiration can be characterized using a normal distribution, and (2) if not, determine if the total geometric uncertainty for combining internal motion and set-up error can be characterized by a normal distribution. Sixty fluoroscopy diaphragm motion data sets were obtained using three breathing training types: free breathing, audio instruction, and visual feedback. Diaphragm motion was used as a surrogate for liver and lung cancer motion. The data were analyzed with normality tests in the following groups: (1) single motion measurements, (2) combined motion measurements for each patient, and (3) combined motion measurements for all patients. Following this analysis, the diaphragm motion pdfs were convolved with a set-up error pdf, and the standard deviation of the set-up error pdf at which the total geometric error pdf became normal was determined. At set-up error standard deviation values of at least 0.27 and 0.1 cm for free breathing, 0.57 and 0.42 cm for audio instruction, and 0.55 and 0 cm for visual feedback, for single motion measurements and combined motion measurements for each patient, respectively, total geometric error pdfs became approximately normal. When the motion measurements for all the patients were combined, diaphragm motion pdfs were approximately normal for all feedback types. Therefore, for treatment planning purposes in the absence of individual patient measurements, the diaphragm motion pdf can be considered an approximately normal distribution. However, care should be taken when determining a margin based on individual patients measurements as the total geometric error will, in general, not be normally distributed.

Artifacts↗
PubMed2004

Monte Carlo as a four-dimensional radiotherapy treatment-planning tool to account for respiratory motion.

Four-dimensional (4D) radiotherapy is the explicit inclusion of the temporal changes in anatomy during the imaging, planning and delivery of radiotherapy. Temporal anatomic changes can occur for many reasons, though the focus of the current investigation was respiration motion for lung tumours. The aims of the current research were first to develop a 4D Monte Carlo methodology and second to apply this technique to an existing 4D treatment plan. A 4D CT scan consisting of a series of 3D CT image sets acquired at different respiratory phases was used. Deformable image registration was performed to map each CT set from the end-inhale respiration phase to the CT image sets corresponding with subsequent respiration phases. This deformable registration allowed the contours drawn on the end-inhale CT to be automatically drawn on the other respiratory phase CT image sets. A treatment plan was created on the end-inhale CT image set and then automatically created on each of the 3D CT image sets corresponding with subsequent respiration phases, based on the beam arrangement and dose prescription in the end-inhale plan. Dose calculation using Monte Carlo was simultaneously performed on each of the N (=8) 3D image sets with 1/N fewer particles per calculation than for a 3D plan. The dose distribution from each respiratory phase CT image set was mapped back to the end-inhale CT image set for analysis. This use of deformable image registration to merge all the statistically noisy dose distributions back onto one CT image set effectively yielded a 4D Monte Carlo calculation with a statistical uncertainty equivalent to a 3D calculation, with a similar calculation time for the 3D and 4D methods. Monte Carlo as a dose calculation tool for 4D radiotherapy planning has two advantages: (1) higher accuracy for calculation in electronic disequilibrium conditions, such as those encountered during lung radiotherapy, and (2) if deformable image registration is used, the calculation time for Monte Carlo is independent of the number of 3D CT image sets constituting a 4D CT, unlike other algorithms for which the calculation time scales linearly with the number of 3D CT image sets constituting a 4D CT.

Algorithms↗
PubMed2004

Acquiring 4D thoracic CT scans using a multislice helical method.

Respiratory motion degrades anatomic position reproducibility during imaging, necessitates larger margins during radiotherapy planning and causes errors during radiation delivery. Computed tomography (CT) scans acquired synchronously with the respiratory signal can be used to reconstruct 4D CT scans, which can be employed for 4D treatment planning to explicitly account for respiratory motion. The aim of this research was to develop, test and clinically implement a method to acquire 4D thoracic CT scans using a multislice helical method. A commercial position-monitoring system used for respiratory-gated radiotherapy was interfaced with a third generation multislice scanner. 4D cardiac reconstruction methods were modified to allow 4D thoracic CT acquisition. The technique was tested on a phantom under different conditions: stationary, periodic motion and non-periodic motion. 4D CT was also implemented for a lung cancer patient with audio-visual breathing coaching. For all cases, 4D CT images were successfully acquired from eight discrete breathing phases, however, some limitations of the system in terms of respiration reproducibility and breathing period relative to scanner settings were evident. Lung mass for the 4D CT patient scan was reproducible to within 2.1% over the eight phases, though the lung volume changed by 20% between end inspiration and end expiration (870 cm3). 4D CT can be used for 4D radiotherapy, respiration-gated radiotherapy, 'slow' CT acquisition and tumour motion studies.

Humans↗
PubMed2004

Predicting respiratory motion for four-dimensional radiotherapy.

Adapting radiation delivery to respiratory motion is made possible through corrective action based on real-time feedback of target position during respiration. The advantage of this approach lies with its ability to allow tighter margins around the target while simultaneously following its motion. A significant hurdle to the successful implementation of real-time target-tracking-based radiation delivery is the existence of a finite time delay between the acquisition of target position and the mechanical response of the system to the change in position. Target motion during the time delay leads to a resultant lag in the system's response to a change in tumor position. Predicting target position in advance is one approach to ensure accurate delivery. The aim of this manuscript is to estimate the predictive ability of sinusoidal and adaptive filter-based prediction algorithms on multiple sessions of patient respiratory patterns. Respiratory motion information was obtained from recordings of diaphragm motion for five patients over 60 sessions. A prediction algorithm that employed both prediction models-the sinusoidal model and the adaptive filter model-was developed to estimate prediction accuracy over all the sessions. For each session, prediction error was computed for several time instants (response time) in the future (0-1.8 seconds at 0.2-second intervals), based on position data collected over several signal-history lengths (1-7 seconds at 1-second intervals). Based on patient data included in this study, the following observations are made. Qualitative comparison of predicted and actual position indicated a progressive increase in prediction error with an increase in response time. A signal-history length of 5 seconds was found to be the optimal signal history length for prediction using the sinusoidal model for all breathing training modalities. In terms of overall error in predicting respiratory motion, the adaptive filter model performed better than the sinusoidal model. With the adaptive filter, average prediction errors of less than 0.2 cm (1sigma) are possible for response times less than 0.4 seconds. In comparing prediction error with system latency error (no prediction), the adaptive filter model exhibited lesser prediction errors as compared to the sinusoidal model, especially for longer response time values (>0.4 seconds). At smaller response time values (<0.4 seconds), improvements in prediction error reduction are required for both predictive models in order to maximize gains in position accuracy due to prediction. Respiratory motion patterns are inherently complex in nature. While linear prediction-based prediction models perform satisfactorily for shorter response times, their prediction accuracy significantly deteriorates for longer response times. Successful implementation of real-time target-tracking-based radiotherapy requires response times less than 0.4 seconds or improved prediction algorithms.

Algorithms↗
PubMed2004

On the use of EPID-based implanted marker tracking for 4D radiotherapy.

Four-dimensional (4D) radiotherapy delivery to dynamically moving tumors requires a real-time signal of the tumor position as a function of time so that the radiation beam can continuously track the tumor during the respiration cycle. The aim of this study was to develop and evaluate an electronic portal imaging device (EPID)-based marker-tracking system that can be used for real-time tumor targeting, or 4D radiotherapy. Three gold cylinders, 3 mm in length and 1 mm in diameter, were implanted in a dynamic lung phantom. The phantom range of motion was 4 cm with a 3-s "breathing" period. EPID image acquisition parameters were modified, allowing image acquisition in 0.1 s. Images of the stationary and moving phantom were acquired. Software was developed to segment automatically the marker positions from the EPID images. Images acquired in 0.1 s displayed higher noise and a lower signal-noise ratio than those obtained using regular (> 1 s) acquisition settings. However, the markers were still clearly visible on the 0.1-s images. The motion of the phantom blurred the images of the markers and further reduced the signal-noise ratio, though they could still be successfully segmented from the images in 10-30 ms of computation time. The positions of gold markers placed in the lung phantom were detected successfully, even for phantom velocities substantially higher than those observed for typical lung tumors. This study shows that using EPID-based marker tracking for 4D radiotherapy is feasible, however, changes in linear accelerator technology and EPID-based image acquisition as well as patient studies are required before this method can be implemented clinically.

Artifacts↗
PubMed2003

Acquiring a four-dimensional computed tomography dataset using an external respiratory signal.

Four-dimensional (4D) methods strive to achieve highly conformal radiotherapy, particularly for lung and breast tumours, in the presence of respiratory-induced motion of tumours and normal tissues. Four-dimensional radiotherapy accounts for respiratory motion during imaging, planning and radiation delivery, and requires a 4D CT image in which the internal anatomy motion as a function of the respiratory cycle can be quantified. The aims of our research were (a) to develop a method to acquire 4D CT images from a spiral CT scan using an external respiratory signal and (b) to examine the potential utility of 4D CT imaging. A commercially available respiratory motion monitoring system provided an 'external' tracking signal of the patient's breathing. Simultaneous recording of a TTL 'X-Ray ON' signal from the CT scanner indicated the start time of CT image acquisition, thus facilitating time stamping of all subsequent images. An over-sampled spiral CT scan was acquired using a pitch of 0.5 and scanner rotation time of 1.5 s. Each image from such a scan was sorted into an image bin that corresponded with the phase of the respiratory cycle in which the image was acquired. The complete set of such image bins accumulated over a respiratory cycle constitutes a 4D CT dataset. Four-dimensional CT datasets of a mechanical oscillator phantom and a patient undergoing lung radiotherapy were acquired. Motion artefacts were significantly reduced in the images in the 4D CT dataset compared to the three-dimensional (3D) images, for which respiratory motion was not accounted. Accounting for respiratory motion using 4D CT imaging is feasible and yields images with less distortion than 3D images. 4D images also contain respiratory motion information not available in a 3D CT image.

Algorithms↗
PubMed2003

Quantifying the effect of intrafraction motion during breast IMRT planning and dose delivery.

Respiratory motion during intensity modulated radiation therapy (IMRT) causes two types of problems. First, the clinical target volume (CTV) to planning target volume (PTV) margin needed to account for respiratory motion means that the lung and heart dose is higher than would occur in the absence of such motion. Second, because respiratory motion is not synchronized with multileaf collimator (MLC) motion, the delivered dose is not the same as the planned dose. The aims of this work were to evaluate these problems to determine (a) the effects of respiratory motion and setup error during breast IMRT treatment planning, (b) the effects of the interplay between respiratory motion and multileaf collimator (MLC) motion during breast IMRT delivery, and (c) the potential benefits of breast IMRT using breath-hold, respiratory gated, and 4D techniques. Seven early stage breast cancer patient data sets were planned for IMRT delivered with a dynamic MLC (DMLC). For each patient case, eight IMRT plans with varying respiratory motion magnitudes and setup errors (and hence CTV to PTV margins) were created. The effects of respiratory motion and setup error on the treatment plan were determined by comparing the eight dose distributions. For each fraction of these plans, the effect of the interplay between respiratory motion and MLC motion during IMRT delivery was simulated by superimposing the respiratory trace on the planned DMLC leaf motion, facilitating comparisons between the planned and expected dose distributions. When considering respiratory motion in the CTV-PTV expansion during breast IMRT planning, our results show that PTV dose heterogeneity increases with respiratory motion. Lung and heart doses also increase with respiratory motion. Due to the interplay between respiratory motion and MLC motion during IMRT delivery, the planned and expected dose distributions differ. This difference increases with respiratory motion. The expected dose varies from fraction to fraction. However, for the seven patients studied and respiratory trace used, for no breathing, shallow breathing, and normal breathing, there were no statistically significant differences between the planned and expected dose distributions. Thus, for breast IMRT, intrafraction motion degrades treatment plans predominantly by the necessary addition of a larger CTV to PTV margin than would be required in the absence of such motion. This motion can be limited by breath-hold, respiratory gated, or 4D techniques.

Algorithms↗