A new incomplete-repair model based on a 'reciprocal-time' pattern of sublethal damage repair

A radiobiological model for closely spaced non-instantaneous radiation fractions is presented, based on the premise that the time process of sublethal damage (SLD) repair is 'reciprocal-time' (second order), rather than exponential (first order), in form. The initial clinical implications of such an incomplete-repair model are assessed. A previously derived linear-quadratic-based model was revised to take account of the possibility that SLD may repair with time such that the fraction of an element of initial damage remaining at time t is given as 1/(1 + zt), where z is an appropriate rate constant; z is the reciprocal of the first half-time (tau) of repair. The general equation so derived for incomplete repair is applicable to all types of radiotherapy delivered at high, low and medium dose-rate in fractions delivered at regular time intervals. The model allows both the fraction duration and interfraction intervals to vary between zero and infinity. For any given value of z, reciprocal repair is associated with an apparent 'slowing-down' in the SLD repair rate as treatment proceeds. The instantaneous repair rates are not directly governed by total dose or dose per fraction, but are influenced by the treatment duration and individual fraction duration. Instantaneous repair rates of SLD appear to be slower towards the end of a continuous treatment, and are also slower following 'long' fractions than they are following 'short' fractions. The new model, with its single repair-rate parameter, is shown to be capable of providing a degree of quantitative explanation for some enigmas that have been encountered in clinical studies. A single-component reciprocal repair process provides an alternative explanation for the apparent existence of a range of repair rates in human tissues, and which have hitherto been explained by postulating the existence of a multi-exponential repair process. The build-up of SLD over extended treatments is greater than would be inferred using a single-exponential repair model and this has important implications in several areas of radiotherapy.

Contrast enhanced dynamic MRI of cervical carcinoma during radiotherapy: early prediction of tumour regression rate

This prospective study investigated the relationship between changes in the MRI dynamic enhancement of cervical carcinoma early during radiotherapy, and tumour regression rate throughout radiotherapy. A total of 36 MRI examinations was performed in seven patients with cervical carcinoma, including a T2 weighted sequence weekly during radiotherapy and also a multislice dynamic Gd-DTPA enhanced sequence before and after the first 2 weeks of radiotherapy. Tumour enhancement was determined on dynamic images using a region of interest and signal-to-noise ratio method. Serial tumour volumes over time on T2 weighted images were estimated using the Cavalieri method of modern design-based stereology to obtain tumour regression rate. It was found that peak and mean enhancement prior to radiotherapy ranged from 3.0 to 13.3, and from 1.9 to 12.2, respectively. After 2 weeks of radiotherapy, peak and mean enhancement ranged from 7.5 to 13.0, and from 6.3 to 10.6, respectively. The change in peak and mean tumour enhancement between dynamic scans ranged, respectively, from -2.0 to 8.4 and from -4.5 to 8.5. Tumour volume decreased exponentially with time (p < 0.01). Tumour regression rates ranged from 2.0% to 15.2% per day, and correlated positively with changes of both peak and mean tumour enhancement (p < 0.01). It is concluded that MRI dynamic enhancement during the first 2 weeks of radiotherapy may provide early prediction of tumour regression rate, and therefore be of value in designing treatment schedules for cervical carcinoma.

Frontonasal dysostosis in two successive generations

Frontonasal dysostosis (also called frontonasal "dysplasia") comprises ocular hypertelorism, median facial cleft affecting nose and/or upper lip, unilateral or bilateral cleft of the alae nasi, anterior cranium bifidum occultum, or a widow's peak. Usually it is a sporadic disorder, although a few familial cases have been reported. We describe a 2-year-old girl with anterior cranium bifidum occultum, lipoma of genu and anterior part of the corpus callosum, and hypertelorism. Her mother had a history of a nasal drip at birth caused by a defect in the cribriform plate and phenotypically, a widow's peak. This observation suggests either autosomal dominant or X-linked dominant inheritance. The family illustrates the importance of identifying mild expression of frontonasal dysostosis before genetic counseling.

Neonatal nurse practitioners--a model for expanding the boundaries of nursing culture in New Zealand

The development and terminology of what constitutes advanced practice nursing roles in New Zealand has been the subject of recent debate within nursing. This article outlines the development of the neonatal nurse practitioner role in New Zealand as an example of one advanced practice nursing role. A model of how nursing culture changes to include roles that incorporate components that historically have been considered the domain of other health professionals is proposed. This article outlines some of the issues surrounding the neonatal nurse practitioner role, including the educational requirements for this role in New Zealand.

Inclusion of molecular biotherapies with radical radiotherapy: modeling of combined modality treatment schedules

PURPOSE

The use of molecular biology based therapies concurrently with radical radiotherapy is likely to offer potential benefits, but there is relatively little use of classical radiobiology in the rationale for such applications. The biological mechanisms that govern the outcomes of radiotherapy need to be completely understood before rational application and optimization of such adjuvant biotherapies with radiotherapy.

METHODS AND MATERIALS

Existing biomathematical models of radiotherapy can be used to explore the possible impact of biotherapies that modify tumor proliferation rates and/or radiosensitivity parameters during radiotherapy. Equations that show how to incorporate biotherapies with the linear-quadratic model of radiation cell kill are presented. Also considered are changes in tumor physiology, such as improved blood flow with enhanced delivery of biotherapy to the tumor cells and accelerated clonogen repopulation during radiotherapy. Monte Carlo random sampling methods are used to simulate these effects in heterogenous tumor populations with variation in radiosensitivities, clonogen numbers, and doubling times, as well as variations in repopulation onset rates and in vascular perfusion rates with time.

RESULTS

The time onset and duration of exposure of each type of biotherapy during radical radiotherapy can influence the predicted tumor cure probabilities in subtle ways. In general, the efficacy of biotherapies that radiosensitize will depend upon the number of radiotherapy fractions that are sensitized and the change in blood flow with time during radiotherapy. Biotherapies that control repopulation will depend not only on the duration of exposure but also, where accelerated repopulation occurs, on the time at which biotherapy is initiated during radiotherapy. From the ranges of radiobiological parameters and biotherapy efficacies assumed for exploratory examples, large changes of tumor control probability (TCP) are encountered in individual tumors from the application of cytostatic therapy. There are predictions of smaller increments in TCP in heterogenous tumor populations from the application of cytostatic and radiosensitizing biotherapies in combination.

CONCLUSIONS

The exercises show how the scheduling of biotherapies may critically influence tumor cure probabilities in subtle ways and give considerable insight into the interacting biological mechanisms that influence these changes. Future therapeutic developments should be guided by these principles.

Autobiographical memory and dissociation in borderline personality disorder

BACKGROUND

This study investigated whether individuals with borderline personality disorder (BPD) tend to be overgeneral in their autobiographical recall and whether the extent of their overgeneral recall covaries with their susceptibilities to dissociative experiences, as expected on theoretical grounds.

METHODS

Twenty-three patients with BPD and 23 matched controls completed the Autobiographical Memory Test (AMT) and self-report measures of depression, anxiety, trait anger and dissociative experiences.

RESULTS

Participants with BPD scored significantly higher than the control group on the measures of depression, anxiety, trait anger, and dissociative experiences and also retrieved significantly more general memories on the AMT. The number of general memories retrieved by the BPD group correlated significantly with their dissociation scores but not with their scores on mood measures.

CONCLUSIONS

Patients with BPD have difficulties in recalling specific autobiographical memories. These difficulties are related to their tendency to dissociate and may help them to avoid episodic information that would evoke acutely negative affect.

Experimental approaches to the development of a recombinant hookworm vaccine

Hookworm infection is a major parasitic cause of morbidity in the developing nations of the tropics. Development of a genetically engineered vaccine would be a useful tool in the control of this infection in highly endemic areas. Recombinant polypeptides belonging to the Ancylostoma secreted protein (ASP)-1 family have shown promise for reducing hookworm burdens after larval challenge infections in mice. Typically, these polypeptides are expressed in Escherichia coli and administered as an alum precipitate. Vaccine protection is antibody dependent. It is anticipated that a cocktail of different recombinant hookworm antigens may be required in order to effectively prevent heavy hookworm infections and disease. The progress of this work has been hampered by the absence of both a convenient laboratory animal with which to study hookworm infections resembling human infection, as well as the lack of easy availability of native hookworm antigens. In addition, useful human serologic correlates of antihookworm immunity are still poorly defined.

The epidemiology of surgically repaired aneurysms in the United States

OBJECTIVE

The purpose of this study was to determine the results of surgery for hospitalized cases of aneurysms in the United States, thereby providing a standard of comparison for new techniques proposed to treat aneurysms.

METHODS

Data on hospitalized aneurysm cases were collected from the National Hospital Discharge Survey, a comprehensive database of patients hospitalized in the United States for treatment from the years 1984 to 1994. The National Hospital Discharge Survey samples non-federal, acute-care hospitals with an average length of stay of less than 30 days. All the cases had a diagnosis of or a surgical procedure for a non-cerebral aneurysm.

RESULTS

In the year 1994, 51,949 non-cerebral aneurysms were repaired in the United States, and 75% of these procedures were abdominal aortic aneurysm (AAA) surgeries. The operative mortality rates for AAA were higher than previously reported from multi-institutional studies and were found to be 8.4% for elective repair and 68% for emergency AAA repair. The number of aneurysm surgeries per thousand population varied by region: surgery rates were more frequent in the Northeast and less frequent in the West. Surgical volume appeared to decrease for smaller hospitals and increase for larger hospitals for the period between 1990 and 1994. The overall mortality rates for all aneurysm surgeries diminished with hospital size. However, no significant difference was found for the rates of elective AAA repair between hospital sizes. The percentage of men with aneurysms who underwent surgery for repair was significantly higher than for women with aneurysms. In addition, the AAA repair rates increased for men from 1985 to 1994, and the number of women reported with repaired AAAs remained constant.

CONCLUSION

The location of aneurysm, urgency of repair, region, sex, and hospital size are important factors related to patient treatment and outcome. These data provide a standard of comparison against which surgeons can compare their own results, and they provide a benchmark for the evaluation of interventional techniques proposed to treat aneurysms.

Use of the NAL-AB wordlists as a South African English speech discrimination test

South Africa still lacks a South African English specific speech discrimination test. As an alternative, this study investigated the use of the Australian English, National Acoustic Laboratories Arthur Boothroyd (NAL-AB) wordlists to assess the speech discrimination of South African English speakers. Thirty South African English speakers were tested at 0, 5, 10, 20 and 25 dBHL (audiometer dial reading) and their performance-intensity functions were compared qualitatively to the NAL-AB wordlist normative data. Results showed three general patterns; similar performance for both groups; poorer performance by the South African English speakers at the low to mid presentation intensities only; and poorer performance by the South African English speakers across most presentation intensities. Use of the NAL-AB wordlists at threshold levels or for site of lesion assessment was therefore concluded to be unwise. Use of these wordlists at supra-threshold levels, however, would provide a valid and reliable option for the speech discrimination assessment of South African English speakers.

Familial advanced sleep-phase syndrome: A short-period circadian rhythm variant in humans

Biological circadian clocks oscillate with an approximately 24-hour period, are ubiquitous, and presumably confer a selective advantage by anticipating the transitions between day and night. The circadian rhythms of sleep, melatonin secretion and body core temperature are thought to be generated by the suprachiasmatic nucleus of the hypothalamus, the anatomic locus of the mammalian circadian clock. Autosomal semi-dominant mutations in rodents with fast or slow biological clocks (that is, short or long endogenous period lengths; tau) are associated with phase-advanced or delayed sleep-wake rhythms, respectively. These models predict the existence of familial human circadian rhythm variants but none of the human circadian rhythm disorders are known to have a familial tendency. Although a slight 'morning lark' tendency is common, individuals with a large and disabling sleep phase-advance are rare. This disorder, advanced sleep-phase syndrome, is characterized by very early sleep onset and offset; only two cases are reported in young adults. Here we describe three kindreds with a profound phase advance of the sleep-wake, melatonin and temperature rhythms associated with a very short tau. The trait segregates as an autosomal dominant with high penetrance. These kindreds represent a well-characterized familial circadian rhythm variant in humans and provide a unique opportunity for genetic analysis of human circadian physiology.

Modeling the covariance structure in pharmacokinetic crossover trials

Pharmacokinetic studies of drug and metabolite concentrations in the blood are usually conducted as crossover trials, especially in phases I and II. A longitudinal series of measurements is collected on each subject within each period. However, much of the dependence among such observations, within and between periods, is generally ignored in analyzing this type of data. Usually, only a random coefficient model is fitted for the parameters in the nonlinear mean function, along with allowing the variance to depend on the mean so that it changes over time. Here, we develop models to allow more fully for the structure of the crossover study. We introduce two levels of variance components, for the subjects and for the periods within subjects, and also an autocorrelation within periods. We also retain the time-varying variance, using a separate variance function for this, different from that for the mean. We apply this model to a phase I study of the drug flosequinan and its metabolite. This drug was developed for the treatment of heart failure. Because the metabolite also exhibits an active pharmacologic effect, study of both the parent drug and the metabolite is of interest. We find that the autocorrelation is the element in the covariance structure that most improves the fit of the model but that two levels of variance components can also be necessary.

Ethylene-regulated gene expression in tomato fruit: characterization of novel ethylene-responsive and ripening-related genes isolated by differential display

Differential display was used to isolate early ethylene-regulated genes from late immature green tomato fruit in order to obtain a broader understanding of the molecular basis by which ethylene coordinates the ripening process. Nineteen novel ethylene-responsive (ER) cDNA clones were isolated that fell into three classes: (i) ethylene up-regulated (ii) ethylene down-regulated, and (iii) transiently induced. Expression analysis revealed that ethylene-dependent changes in mRNA accumulation occurred rapidly (15 min) for most of the ER clones. The predicted proteins encoded by the ER genes are putatively involved in processes as diverse as primary metabolism, hormone signalling and stress responses. Although a number of the isolated ER clones correspond to genes already documented in other species, their responsiveness to ethylene is described here for the first time. Among the ER clones sharing high homology with regulatory genes, ER43, a putative GTP-binding protein, and ER50, a CTR1-like clone, are potentially involved in signal transduction. ER24 is homologous to the multi-protein bridging factor MBF1 involved in transcriptional activation, and finally, two clones are homologous to genes involved in post-transcriptional regulation: ER49, a putative translational elongation factor, and ER68, a mRNA helicase-like gene. Six ER clones correspond to as yet unidentified genes. The expression studies indicated that all the ER genes are ripening-regulated, and, depending on the clone, show changes in transcript accumulation either at the breaker, turning, or red stage. Analysis of transcript accumulation in different organs indicated a strong bias towards expression in the fruit for many of the clones. The potential roles for some of the ER clones in propagating the ethylene response and regulating fruit ripening are discussed.

Further evidence from two families that craniofrontonasal dysplasia maps to Xp22

Craniofrontonasal dysplasia (CFND) is a rare X-linked disorder that maps to a 13-cM region on Xp22. Phenotypic features include craniosynostosis, hypertelorism and a broad nasal root with or without a bifid nasal tip. Multiple examples have been reported of males having a less severe phenotype than females. We report haplotype analyses in two CFND families over the critical region to which the gene has been mapped. In pedigree 1, a clinically unaffected male inherited the affected marker haplotype spanning the critical region. We suggest that this individual does have the CFND mutation, but has an extremely mild phenotype that is not detectable with clinical examination. Under the assumption that he is an unknown phenotype, a combined two-point LOD score of 1.68 at zero recombination was obtained, increasing the previously reported total to 5.61 (DXS8022). The data do not narrow down the critical region. This result stresses the importance of subjecting fathers of apparently sporadic cases to a highly critical medical examination and may also explain the unequal ratio of reported female-to-male cases.

Enhanced normal tissue doses caused by tumour shrinkage during brachytherapy

Published data concerning shrinkage rates of low-grade gliomas implanted with 125I seeds have been used to determine the likely influence of such shrinkage on normal tissue doses. It is demonstrated that a tumour volume shrinkage of 50% over 6 months can bring about a 30% increase in the dose delivered to tissues which shrink centripetally towards the implanted volume. The use of radionuclides with a half-life shorter than that of 125I would substantially reduce shrinkage-induced dose increments.

Overcoming multidrug resistance: valspodar as a paradigm for nursing care

PURPOSE/OBJECTIVES

To review the mechanisms of multidrug resistance (MDR) in human cancer and the clinical use of MDR modulators to overcome or reverse P-glycoprotein (P-gp)-mediated MDR.

DATA SOURCES

Current literature, ongoing clinical trials, and clinical experience.

DATA SYNTHESIS

Agents, such as valspodar, that block the activity of P-gp can reverse or overcome MDR caused by overexpression of P-gp. The MDR modulator valspodar (PSC 833; Novartis Pharmaceuticals Corporation, East Hanover, NJ) is examined as a model for establishing nursing guidelines for this new class of therapeutic agents.

CONCLUSIONS

The dose of some chemotherapy agents must be modified with concurrent valspodar administration. Studies examining the safety and efficacy of valspodar as a prototype of MDR modulators provide the basis for establishing nursing care guidelines.

IMPLICATIONS FOR NURSING PRACTICE

Nursing care for the administration of valspodar includes understanding patient selection, criteria, dosing, and administration; side-effect management; patient monitoring and follow-up; and patient education.

Primary care physicians' training and their community involvement

BACKGROUND AND OBJECTIVES

Physicians who incorporate a community perspective into their clinical practice can provide more effective care, but little is known about the type of training that helps physicians include this perspective. This study examines associations between physicians' current level of involvement in their communities and a range of prior educational experiences.

METHODS

We obtained data from 247 recently graduated primary care physicians through a nationwide mail survey. Physicians described their community-related training experiences during medical school and residency. They also described their current involvement in each of 4 domains of community work. Associations between different training experiences and physicians' current community involvement were examined.

RESULTS

Subjects generally reported limited community-related training. Physicians who did receive training in content relevant to a given community domain were significantly more involved in that domain as practicing physicians. Rotating in rural locations and having a mentor active in the community also were associated with greater current community involvement.

CONCLUSIONS

These data provide evidence that formal training experiences can influence how actively physicians will later interact with their communities. We should provide medical students and residents with educational content in all 4 domains of community work, place them in carefully selected locations, and arrange mentor relationships.

High dose rate brachytherapy practice for the treatment of gynaecological cancers in the UK

A summary of UK high dose rate brachytherapy practice in gynaecological cancer is presented. There appears to be relatively good uniformity in dose prescription and biological effective doses, which represents a considerable improvement from the findings of a previous report of UK low dose rate brachytherapy practice in 1991. Individual details of the dose schedules used at each treatment centre are presented.