Calibration and quality assurance for rounded leaf-end MLC systems.

Multileaf collimator (MLC) systems are available on most commercial linear accelerators, and many of these MLC systems utilize a design with rounded leaf ends and linear motion of the leaves. In this kind of system, the agreement between the digital MLC position readouts and the light field or radiation field edges must be achieved with software, since the leaves do not move in a focused motion like that used for most collimator jaw systems. In this work we address a number of the calibration and quality assurance issues associated with the acceptance, commissioning, and routine clinical use of this type of MLC system. These issues are particularly important for MLCs used for various types of intensity modulated radiation therapy (IMRT) and small, conformal fields. For rounded leaf end MLCs, it is generally not possible to make both the light and radiation field edges agree with the digital readout, so differences between the two kinds of calibrations are illustrated in this work using one vendor's MLC system. It is increasingly critical that the MLC leaf calibration be very consistent with the radiation field edges, so in this work a methodology for performing accurate radiation field size calibration is discussed. A system external to the vendor's MLC control system is used to correct or handle limitations in the MLC control system. When such a system of corrections is utilized, it is found that the MLC radiation field size can be defined with an accuracy of approximately 0.3 mm, much more accurate than most vendor's specifications for MLC accuracy. Quality assurance testing for such a calibration correction system is also demonstrated.

Effects of cyclical etidronate combined with calcitriol versus cyclical etidronate alone on spine and femoral neck bone mineral density in postmenopausal osteoporotic women.

OBJECTIVES: Few data are available on the effects of combination therapy for the treatment of osteoporosis. The aim of this study was to compare the effects of intermittent cyclical etidronate (E) therapy alone with a combination of cyclical etidronate and calcitriol (E + C) on spine and femoral neck bone mineral density (BMD) at one year. METHODS: Postmenopausal women with at least one non-traumatic vertebral fracture or z score < -1.5 were randomly allocated to an E group (each cycle = oral etidronate 400 mg daily for 14 days followed by calcium 500 mg daily for 76 days) or an E + C group (as for E plus oral calcitriol 0.5 microgram daily). Lumbar spine and femoral neck BMDs were measured by dual energy x ray absorptiometry at baseline and at one year. The study design did not contain a placebo group. RESULTS: The mean % increase in lumbar spine BMD was 5.2% (95% CI = 3.4 to 7.0) in the E + C group (n = 24), which was significantly greater than the 2.7% (95% CI = 1.3 to 4.1) increase in the E group (n = 23) (p < 0.05). The femoral neck BMD in the E + C group increased by 2.0% (95% CI = 0.8 to 3.2), which was significantly different from the E group where there was a -0.4% (95% CI = -2.4 to 1.6) change (p = 0.046). CONCLUSIONS: These data show that a combination of cyclical etidronate and calcitriol is better than cyclical etidronate alone in terms of changes in BMD at both spine and femoral neck sites. Although further data are needed on fracture efficacy, this study suggests that combination therapies have additive therapeutic potential that may exceed that expected from their theoretical mode of action.

Mechanical and dosimetric quality control for computer controlled radiotherapy treatment equipment.

Modern computer controlled radiotherapy treatment equipment offers the possibility of delivering complex, multiple field treatments with minimal operator intervention, thus making multiple field conformal therapy practical. Conventional quality control programs are inadequate for this new technology, so new quality control procedures are needed. A reasonably fast, sensitive, and complete daily quality control program has been developed in our clinic that includes nearly automated mechanical as well as dosimetric tests. Automated delivery of these quality control fields is performed by the control system of the MM50 racetrack microtron, directed by the CCRS sequence processor [D. L. McShan and B. A. Fraass, Proceedings of the XIth International Conference on the use of computers in Radiation Therapy, 20-24 March 1994, Manchester, U.K. (North Western Medical Physics Department, Manchester, U.K., 1994), pp. 210-211], which controls the treatment process. The mechanical tests involve multiple irradiations of a single film to check the accuracy and reproducibility of the computer controlled setup of gantry and collimator angles, table orientation, collimator jaws, and multileaf collimator shape. The dosimetric tests, which involve multiple irradiations of an array of ionization chambers in a commercial dose detector (Keithly model 90100 Tracker System) rigidly attached to the head of the treatment gantry, check the output and symmetry of the treatment unit as a function of gantry and collimator angle and other parameters. For each of the dosimetric tests, readings from the five ionization chambers are automatically read out, stored, and analyzed by the computer, along with the geometric parameters of the treatment unit for that beam.(ABSTRACT TRUNCATED AT 250 WORDS)

Application of the MRFIT smoking cessation program to a healthy, mixed-sex sample.

The Multiple Risk Factor Intervention Trial (MRFIT) included a smoking cessation program that was highly successful (40.3% abstinence prevalence rate at 48-month follow-up) when used with other interventions for a male, middle-aged population at high risk for coronary heart disease (CHD). Our study employed the MRFIT cessation program alone with a mixed-sex, mixed-age, healthy population. We wished to determine its effectiveness when applied in a manner similar to other smoking cessation programs. Fifty-six subjects participated in a 10-week intervention followed by maintenance or extended intervention programs. The 52% abstinence prevalence rate at the end of the 10-week intervention dropped to 32% after four months, 25% at eight months, 25% at 12 months, and 27% at 16 months. The higher cessation rates of the original MRFIT study may be related to motivation and other characteristics of the high-risk population and to the combination of the smoking component with other interventions for CHD, rather than to the characteristics of the smoking intervention itself. Although the MRFIT program is comprehensive and includes vigorous maintenance activities, it is also expensive and may not be cost-effective or as desirable as programs with slightly lower cessation rates.

Diabetes in the elderly: the Oxford Community Diabetes Study.

Most diabetic patients are elderly but their clinical characteristics remain poorly defined. A population survey identified 259 known diabetic patients aged 60 years or more giving a prevalence of 3% in this age group. A total of 193 patients (75%) were interviewed and examined, 155 (80%) of whom had been diagnosed at under 70 years of age. Forty-two patients (22%) were insulin-treated but clinical characteristics suggested that at least 95% of all elderly patients had Type 2 diabetes. Blood glucose control was poor with median HbA1 9.7% (range 4.9-17.1%, normal reference range 5.0-7.5%), and 55% were either overweight or obese. There was a high morbidity from diabetes and other conditions: the prevalence of hypertension (untreated blood pressure of 160/95 mmHg or more or antihypertensive medication) was 52%, of stroke 5%, of nephropathy (urinary albumin concentration greater than or equal to 300 mg l-1) 3%, of lower limb amputations 4%, and of foot ulcers 7%. The prevalence of symmetrically impaired distal vibration perception was 23%, and 54% of patients either needed or were receiving chiropody. The prevalence of a corrected distant visual acuity of 6/12 or worse was 32% and of retinopathy of any degree was 26%. There was extensive co-morbidity which was not confined to a single subgroup of patients.

Diabetic autonomic neuropathy: the prevalence of impaired heart rate variability in a geographically defined population.

The prevalence of diabetic autonomic neuropathy and its relationship with other diabetic complications were studied in a geographically defined population. Heart rate variability was measured by a computerized technique at rest and in response to both a single deep breath and a Valsalva manoeuvre. Among 43 Type 1 (insulin-dependent) and 202 Type 2 (non-insulin-dependent) patients results below the 2.5 centile for age-related normal ranges occurred in 9 Type 1 and 32 Type 2 patients (16.7, 95% Cl 12.6 to 21.9, %). Symptomatic autonomic neuropathy was uncommon but was significantly more frequent in Type 1 than Type 2 patients (5 Type 1, 1 Type 2, p less than 0.001 Fisher's exact test). In Type 1 diabetes, cardiovascular autonomic dysfunction was significantly associated with impaired vibration perception and a higher logarithmic urinary albumin concentration and, in Type 2 diabetes, it was associated with a significantly higher body mass index, systolic blood pressure, and logarithm of the urinary albumin and fasting insulin concentrations. The aggregation of these factors with cardiovascular autonomic dysfunction suggests that mortality might be increased in Type 2 patients with asymptomatic autonomic neuropathy.

Diabetes mellitus: attitudes, knowledge and glycaemic control in a cross-sectional population.

A questionnaire to households in Oxfordshire identified 431 diabetic patients living in the area and 272 of them completed a questionnaire about their attitudes to and knowledge of diabetes, and were subsequently interviewed. Most did not regard diabetes as a serious disease and had little knowledge of possible complications. Patients found dietary compliance the most difficult part of their treatment. Among non-insulin treated patients there was a significant association between difficulty with diet and body mass index and glycosylated haemoglobin values. The results suggest that there is a need for more effective advice on diet and for better education of patients about the nature of diabetes and its complications.

The Oxford Community Diabetes Study: evidence for an increase in the prevalence of known diabetes in Great Britain.

A prevalence survey for known diabetes was conducted in a geographically defined population of nearly 40,100 in Oxford in April 1982. The age-adjusted prevalence rate was 10.4/1000 which did not differ significantly from age-adjusted rates of 9.5/1000 in Poole and 10.5/1000 in Southall. The prevalence increased with age and was higher in men than women over the age of 30 years. Our results confirm that there has been a change in the male to female sex ratio and suggest that there are about 500,000 diagnosed diabetics in England and Wales including about 190,000 insulin-treated patients. These findings are consistent with a secular increase in the prevalence of diagnosed diabetes over the last two decades which has important implications for the planning and provision of resources for care.

A double-blind, placebo-controlled, crossover trial to investigate the additive hypotensive effect of a diuretic (mefruside) to that produced by nifedipine.

Several reports suggest that when diuretics are added to nifedipine (N), they do not exert any additional hypotensive effect to that produced by N alone. We present the first double-blind, crossover trial to investigate this interaction. Twenty-four black patients with moderate to severe essential hypertension entered the trial. After an initial "open" 4 weeks of therapy with N slow release (SR) 20 mg. b.i.d., those 17 patients whose blood pressures (BP) were not controlled (greater than 160 mm Hg systolic and/or greater than 90 mm Hg diastolic) were randomly allocated (double-blind) to 4 weeks treatment with N SR 20 mg. b.i.d., plus either mefruside 1 q.d. (a thiazide-like diuretic) or matching placebo. Patients then crossed over for a second 4 week treatment period. Blood pressures were measured at 2 weekly intervals under the same conditions using Hawksley random zero sphgymomanometers by one of two standardized observers after patients had been lying for 5 min and standing for 2 min. Analysis (taking account of period effect) of the mean results for the 16 patients completing the trial confirms that, contrary to what previous uncontrolled data suggest, lying and standing systolic and diastolic BPs are significantly lower (8.5/4.5 mm Hg: 2p less than 0.01 and 7.9/5.0 mm Hg: 2p less than 0.05, respectively) with nifedipine plus diuretic than with nifedipine plus placebo.

Blood pressures higher in the home than in the clinic in rural Kenya.

The conditions under which blood pressures (BPs) are recorded are critical, and it has been demonstrated several times that BPs measured in the home are lower than those measured in the clinic. However, these comparisons are based on home BPs measured by the patients or their friends and relatives and clinic BPs measured by doctors and nurses. To our knowledge, no comparison of home and clinic BPs measured by the same observer has been reported, and we present the results of such a study which is the first to demonstrate higher BPs in the home environment, perhaps reflecting the unacculturated nature of the study population.

Allergy to laboratory animals: a retrospective and a prospective study.

Twenty four volunteers who had been allergic to laboratory animals for some years were examined by means of a questionnaire paying particular attention to symptoms associated with rats and by serological and skin tests with extracts of rat urine (retrospective study). Nasal and eye symptoms were reported by 21 and 16 individuals respectively: 13 had asthma. Positive skin tests and high levels of specific IgE antibody to rat urine extract were found in 17 of the more severely affected individuals and this group included 12 of those with asthma. Latent periods of work with animals before symptoms appeared varied from 0.5 to 12 years. Also 148 individuals were studied during their first year of work with animals (prospective study). Symptoms developing during the year were reported by 15%, asthma by 2%. IgE antibody levels to rat urine were raised in 40% of affected and 6% of the unaffected individuals but there was no significant correlation between symptoms and either antibody levels or positive skin tests. Allergic symptoms developing during the first year of postemployment were, on the whole, much milder than those seen in the retrospective study. A tentative conclusion is that most individuals who become allergic to laboratory animals develop the condition in a mild form during their first year of employment but it appears probable that atopic individuals, although having an equal chance of developing allergy as compared with non-atopic individuals, may eventually progress to a more severe form of the disease.

Estimation of airborne rat-derived antigens by ELISA.

Double antibody sandwich ELISA procedures have been devised to estimate the concentrations of airborne rat urinary and epidermal antigens. Both assays were capable of detecting at least 3 ng/ml of antigen protein. Unknown concentrations were estimated in terms of the standard, laboratory-prepared material, as calculated from the linear relationship between absorbance and log concentration. The coefficient of variation of a single assay was 12%, the methods have been applied to extracts of the filter material from static and personal samplers in an animal room.

An animal model for the investigation of adverse responses to i.v. anesthetic agents and their solvents.

In man the number of adverse responses to the Cremophor-containing anaesthetic agents Althesin and propanidid (Epontol) has been reported to be greater than that encountered with thiopentone. The response of the mini-pig to repeated injection of a range of i.v. anaesthetics and their solvents has been investigated in an attempt to ascertain the possible role of Cremophor in the production of these responses. A second injection of Cremophor EL or the Cremophor/Micellophor-containing agents Althesin and propanidid (Epontol), given 7 days after the first, produced a high frequency of adverse responses. On only one occasion, when alphaxalone and alphadolone were given in a mixture of alcohol and propylene glycol, was an abnormal response seen on the first administration of any agent. The second administration of alphaxalone and alphadolone in the same solvent produced abnormal responses in two of four pigs. No such responses were seen when propanidid was administered in alcohol and propylene glycol or when this solvent mixture was given alone. No abnormal responses were seen following the repeated administration of thiopentone. A marked increase in arterial pressure, and an immediate but transient marked decrease in the numbers of circulating polymorphonuclear leucocytes, were consistent findings in animals showing adverse responses. No abnormal responses were found when the interval between two administrations of Althesin was extended to 3 weeks.