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P Graham

Publications and source records attributed to P Graham.

At least 37 records · Page 2Linked to original sources
PubMed2000

Bayesian inference for a generalized population attributable fraction: the impact of early vitamin A levels on chronic lung disease in very low birthweight infants.

In this paper, the population attributable fraction is studied using the potential responses framework of Rubin's causal model. This framework facilitates definition of a general measure of population attributable effect which can accommodate many-valued and multivariate exposures as well as many-valued responses. Inferential issues are considered from the Bayesian perspective. Finite population inference is emphasized with inference in the case of a fully observed population given particular attention. The key inferential issue concerns computation of the posterior distribution of unobserved potential responses, given observed responses, exposures and covariates. A dependency on model parameters about which observed data are uninformative is highlighted and this reflects the unobservable nature of causal effects. In an application to a small cohort study of respiratory problems in very low birthweight infants, posterior inferences were found to be insensitive to assumptions concerning the joint distribution of potential response variables but sensitive to the assumption of weak ignorability, a weaker form of the more familiar assumption of no confounding by omitted covariates. In a model-based set-up, the weak ignorability assumption is identified with setting a model parameter to zero, and consequently uncertainty concerning this assumption can, in principle, be handled via the prior distribution for the model parameters.

Bayes Theorem↗
PubMed2000

Three-dimensional dose distribution of tangential breast irradiation: results of a multicentre phantom dosimetry study.

BACKGROUND AND PURPOSE: One aspect of good radiotherapeutic practice is to achieve dose homogeneity. Dose inhomogeneities occur with breast tangent irradiation, particularly in women with large breasts. MATERIALS AND METHODS: Ten Australian radiation oncology centres agreed to participate in this multicentre phantom dosimetry study. An Alderson radiation therapy anthropomorphic phantom with attachable breasts of two different cup sizes (B and DD) was used. The entire phantom was capable of having thermoluminescent dosimeters (TLD) material inserted at various locations. Nine TLD positions were distributed throughout the left breast phantom including the superior and inferior planes. The ten centres were asked to simulate, plan and treat (with a prescription of 100 cGy) the breast phantoms according to their standard practice. Point doses from resultant computer plans were calculated for each TLD position. Measured and calculated (planning computer) doses were compared. RESULTS: The dose planning predictability between departments did not appear to be significantly different for both the small and large breast phantoms. The median dose deviation (calculated dose minus measured dose) for all centres ranged from 2. 3 to 5.3 cGy on the central axis and from 2.1 to 7.5 cGy for the off-axis planes. The highest absolute dose was measured in the inferior plane of the large breast (128.7 cGy). The greatest dose inhomogeneity occurred in the small breast phantom volume (median range 93.2-105 cGy) compared with the large breast phantom volume (median range, 100.1-107.7 cGy). There was considerable variation in the use (or not) of wedges to obtain optimized dosimetry. No department used 3D compensators. CONCLUSION: The results highlight areas of potential improvement in the delivery of breast tangent radiotherapy. Despite reasonable dose predictability, the greatest dose deviation and highest measured doses occurred in the inferior aspects of both the small and large breast phantoms.

Breast Neoplasms↗
PubMed2000

Meeting the International Conference on Harmonisation's Guidelines on Validation of Analytical Procedures: quantification as exemplified by a near-infrared reflectance assay of paracetamol in intact tablets.

This Perspective explains how the International Conference on Harmonisation's Guidelines on Validation of Analytical Procedures for quantitative methods can be met by near-infrared (NIR) assays of intact pharmaceutical products. Each of the validation characteristics (accuracy, precision, specificity, detection limit, quantification limit, linearity, range, robustness and system suitability testing) is defined, examined for their relevance to quantitative methods and examples given on how they may be used to demonstrate that near-infrared assays are fit for purpose. Methods for preparing samples for calibration are given in detail. The intention is to provide information so that a pharmaceutical manufacturer could validate a method suitable for an application for a variation of a marketing authorisation for an existing product and use a NIR assay instead of the previous method. The perspective is illustrated in detail using a NIR reflectance assay of paracetamol in intact tablets. This proven assay gives results comparable to the British Pharmacopeia ultraviolet assay for paracetamol, the standard errors of calibration and prediction for the NIR method being 0.48% w/w and 0.71% w/w respectively. The method is also precise, the standard deviation and coefficient of variation for six NIR assays on the same day being 0.14% w/w and 0.16% w/w respectively, while measurements over six consecutive days gave 0.31% w/w and 0.36% w/w respectively.

Acetaminophen↗
PubMed2000

Armrest versus vacuum bag immobilization in the treatment of breast cancer by radiation therapy: a randomized comparison.

Thirty patients in randomized sequence were simulated in both an arm-rest and a vacuum bag immobilization device and also randomized to treatment in one of the two devices. Overall patient comfort significantly favoured the use of the arm-rest, although both were acceptable. Lung exposed in the tangential beams was less in the vacuum bag device. Supraclavicular skin folding was greater in the vacuum bag, but this is probably related to the angle of arm abduction. Treatment times and stability of the setups were not significantly different. This is a small study piloting a technical comparison and the findings require confirmation in a larger sample.

Adult↗
PubMed2000

Treatment interventions and findings from research: bridging the chasm in child psychiatry.

BACKGROUND: Along with all other branches of medicine, child and adolescent psychiatry is faced with the need to consider its evidence base and justify its activities accordingly. AIMS: To consider critically the use of the term 'evidence', to suggest limits to the value of conventionally defined evidence and to point to possible ways forward to bridge the gap between research findings and clinical practice. METHOD: A review of the literature relating to the use of evidence-based methods. RESULTS: The term 'evidence' needs to be used more widely than is conventionally the case. Substantial evidence exists from controlled trials, but there are barriers to its use. CONCLUSIONS: A move away from nonvalidated methods of intervention is both desirable and feasible. The use of qualitative methods of enquiry, both in situations where controlled trials are unlikely to be feasible and as adjuncts to quantitative methods, should be considered more seriously.

Child Psychiatry↗
PubMed2000

A comparison of primary and proxy respondent reports of habitual physical activity, using kappa statistics and log-linear models.

BACKGROUND: Many epidemiological studies rely in part on proxy informants. There is little published information on the reliability of proxy-respondent reports of physical activity. METHODS: Self-reported data on vigorous and moderate physical activity, from a representative sub-sample of participants in a community-based case-control study of coronary heart disease, were compared with information collected from their next-of-kin. RESULTS: Relative to primary respondents, proxy respondents under-reported activity by approximately 10 percentage points, for both leisure and work-time activity. On a simple three point scale (inactivity/moderate activity/physical activity), 70% of primary-proxy pairs were in exact agreement with regard to leisure time activity and 67% of pairs were in exact agreement on work-time activity. The corresponding values for the weighted kappa statistic were 0.66 [95% confidence interval (CI) 0.59-0.72] and 0.62 (0.54-0.72). Log-linear modelling provided evidence for superior agreement on worktime activity when the proxy was not the primary respondent's spouse. DISCUSSION: Overall levels of primary-proxy respondent agreement on physical activity seem somewhat lower than has been reported for smoking and alcohol-drinking frequency. There seems little reason to prefer spouse proxies when endeavouring to elicit information on work-time physical activity. Log-linear modelling provides an efficient means of exploring covariate effects in observer-agreement studies.

Adult↗
PubMed1999

Pion conformal radiation of prostate cancer: results of a randomized study.

PURPOSE: To compare the efficacy of pion radiation therapy with conventional external beam photon therapy, for the treatment of locally advanced stage T3/4, N0, M0 adenocarcinoma of the prostate. METHODS AND MATERIALS: Two hundred seventeen eligible patients were randomly allocated to either photon or pion therapy. No adjuvant hormone therapy was used. RESULTS: Median follow-up was 42 months (range 2-90). Acute bladder toxicity was worse in the pion arm, p = 0.2, but other acute toxicity did not differ. Late grade 2 toxicity was significantly less in the pion arm (29% at 5 years versus 48%, p = 0.002), but late grade 3 or 4 toxicity did not differ. Clinical local control was not significantly different between treatment arms (64% after 5 years with photons, 56% with pions, p = 0.6). Cause-specific and overall survival also did not differ (p = 0.7). There was a significant delay in time to first failure in the photon arm, largely as a result of decreased biochemical relapse, p = 0.01. A multivariate analysis is presented. CONCLUSION: Pion therapy was well tolerated, with increased acute toxicity and significantly decreased late tissue injury. This contrasts with the late toxicity observed with higher LET particle therapy such as neutron therapy. No improvement in local control with pion therapy was observed.

Adenocarcinoma↗
PubMed1999

The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.

Journal Article↗
PubMed1999

Uniform molecular analysis using femtosecond laser mass spectrometry

The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd.

Journal Article↗
PubMed1999

Heart or heart-lung transplantation: psychosocial outcome.

The psychosocial outcome of 23 heart and 21 heart-lung transplant recipients, aged 5-17 yrs, was determined and compared with the psychosocial outcome of a group of 46 children and adolescents who underwent conventional cardiac surgery. Preoperatively, and 12 months post-operatively, the patients' physical health status, mental state (ICD-9) and level of psychosocial functioning (GAF scale, DSM-IIIR) were assessed. There was an improvement in physical health in all groups. Preoperatively, psychiatric disorder, including anxiety and phobic states, depression and adjustment reaction, was noted in 6/23 (26%) children assessed for heart transplantation, 6/21 (28.5%) children assessed for heart-lung transplantation, and 12/46 (26%) children undergoing conventional cardiac surgery. The prevalence of psychiatric disorder remained in the transplant group but decreased in the non-transplant comparison group (6.5%). Improvement in overall levels of psychosocial functioning were found in all groups, but over 40% of all the participants were still functioning below normal levels. In summary, children with end-stage cardio-respiratory disease benefit physically and psychologically from heart or heart-lung transplantation treatment but there is a need for systematic psychosocial support both before and after transplantation.

Adolescent↗
PubMed1999

A rapid quantitative assay of intact paracetamol tablets by reflectance near-infrared spectroscopy.

Near-infrared (NIR) reflectance spectroscopy was used to determine rapidly and non-destructively the content of paracetamol in bulk batches of intact Sterwin 500 mg tablets by collecting NIR spectra in the range 1100-2500 nm and using a multiple linear regression calibration method. The developed NIR method gave results comparable to the British Pharmacopoeia 1993 UV assay procedure, the standard errors of calibration and prediction being 0.48% and 0.71% m/m, respectively. The method showed good repeatability, the standard deviation and coefficient of variation for six NIR assays on the same batch on the same day being 0.14 and 0.16% m/m, respectively, while measurements over six consecutive days gave 0.31 and 0.36% m/m, respectively. Applying the calibration to a parallel test set gave a mean bias of -0.22% and a mean accuracy of 0.45%. The developed method illustrates how the full potential of NIR can be utilised and how the ICH guidelines which recommend the validation of linearity, range, accuracy and precision for pharmaceutical registration purposes can be applied. Duplicate determinations on bulk batches could be performed in under 2 min, allowing the potential use of the method on-line for real time monitoring of a running production process.

Acetaminophen↗
PubMed1999

Tattoo allergy in patients receiving adjuvant radiotherapy for breast cancer.

Tattooing is routinely employed prior to radiotherapy treatment but allergies to tattoos are rare. New information on the incidence of tattoo allergy at St George Hospital is presented with details of two clinical cases. The literature on tattoo allergy has been unable to estimate the incidence of allergic reaction to tattoos because the total number of patients treated is unknown and not all patients were followed up. Our radiation oncology population for the first time has provided a known denominator, but wide confidence intervals prevent an accurate estimate of the incidence. Salient issues about tattoo allergy are highlighted based on a review of the published literature from 1966 to 1998.

Adult↗
PubMed1999

Health expectancy in New Zealand, 1981-1991: social variations and trends in a period of rapid social and economic change.

STUDY OBJECTIVE: To assess social variations and trends in health expectancy over a period of rapid social and economic change. DESIGN: Cross sectional survey data on the association between social status--gender, socioeconomic class and ethnic group--and measures of health status at two points in time approximately a decade apart. The Sullivan method of calculating health expectancy was used. SETTING: The adult population of New Zealand in the periods 1980-81 and 1992-93. PARTICIPANTS: Representative samples of the adult civilian non-institutionalised population of 6,891 (1980-81) and 5,873 (1992-93) respectively. MAIN RESULTS: In comparison with life expectancy, adjusting for health status narrowed the gender gap but widened socioeconomic and ethnic differentials. These results were replicated for three measures--self reported health, mobility, and handicap--suggesting a robustness of outcome to specific indicators. Comparable data over the period of study were only available for the mobility measure. Increases in longevity appeared to be fully absorbed by minor disability. Ethnic and socioeconomic disadvantages remained static or widened for the 15-64 age group, suggesting a potential social polarisation in the disability transition. CONCLUSIONS: The operationalization of health expectancy appears to be rather robust to specific indicators. Health expectancy may provide a sensitive health impact assessment of social and economic policy. Existing theories of the disability transition may need to be modified to take account of social variation, at least in the special case of disability free health expectancy over the 15-64 age range.

Adolescent↗