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M Lovelock

Publications and source records attributed to M Lovelock.

17 recordsLinked to original sources
PubMed2001

Stereotactic intensity-modulation radiation therapy for vertebral body and paraspinal tumors.

Therapeutic doses of radiation for paraspinal tumors are often limited by the dose-related tolerance of the spinal cord. Intensity-modulated radiation therapy (IMRT) is an advanced form of three-dimensional conformal radiation therapy that provides improved coverage of tumor volumes while reducing the radiation dose to the spinal cord. Computer-controlled multileaf collimation provides high conformality, which makes it feasible to treat tumors of any shape, even those that are wrapped around the spinal cord. The use of a newly developed, noninvasive body frame, the capability of fusing computerized tomography and magnetic resonance images, and on-line portal films provide precise target immobilization and target identification. In this paper the authors discuss their preliminary experience in six cases in which IMRT was used to treat paraspinal lesions in patients who harbored locally recurrent tumors and/or tumors that previously received the maximum doses of radiation that could be tolerated by the spinal cord.

Aged↗
PubMed2000

Early carotid endarterectomy after stroke.

The authors sought to determine if patients with stroke and a high-grade carotid stenosis benefited from a delay before carotid endarterectomy. A retrospective study of 45 patients undergoing carotid endarterectomy after stroke is presented. The patients were divided into two groups: group I (early group, n = 20), composed of patients who had carotid endarterectomy less than 6 weeks after stroke, and group II (late group, n = 25), comprised of patients who had carotid endarterectomy more than 6 weeks after stroke. As assessed by cerebral angiography, 100% of patients in group I and 64% of patients in group II had carotid artery stenoses > 76% (P < 0.001). The median interval from stroke to carotid endarterectomy was 14 days in group I and 129 days in group II. There was no mortality in either group. No patients in either group demonstrated any neurological deterioration. The authors conclude that, in select patients, carotid endarterectomy may be done safely less than 6 weeks after stroke in order to avoid new events or carotid occlusion while awaiting surgery.

Aged↗
PubMed1999

Experimental verification of a CT-based Monte Carlo dose-calculation method in heterogeneous phantoms.

To further validate the Monte Carlo dose-calculation method [Med. Phys. 25, 867-878 (1998)] developed at the Memorial Sloan-Kettering Cancer Center, we have performed experimental verification in various inhomogeneous phantoms. The phantom geometries included simple layered slabs, a simulated bone column, a simulated missing-tissue hemisphere, and an anthropomorphic head geometry (Alderson Rando Phantom). The densities of the inhomogeneity range from 0.14 to 1.86 g/cm3, simulating both clinically relevant lunglike and bonelike materials. The data are reported as central axis depth doses, dose profiles, dose values at points of interest, such as points at the interface of two different media and in the "nasopharynx" region of the Rando head. The dosimeters used in the measurement included dosimetry film, TLD chips, and rods. The measured data were compared to that of Monte Carlo calculations for the same geometrical configurations. In the case of the Rando head phantom, a CT scan of the phantom was used to define the calculation geometry and to locate the points of interest. The agreement between the calculation and measurement is generally within 2.5%. This work validates the accuracy of the Monte Carlo method. While Monte Carlo, at present, is still too slow for routine treatment planning, it can be used as a benchmark against which other dose calculation methods can be compared.

Electrons↗
PubMed1999

Endovascular repair of an aortoenteric fistula in a high-risk patient.

PURPOSE: To describe the endovascular repair of an aortoenteric fistula in a high-risk patient. METHODS AND RESULTS: A Vanguard tube stent-graft was deployed at the upper anastomotic suture line of a secondary aortoenteric fistula, successfully sealing the communication between the aorta and the third part of the duodenum without occlusion of the renal arteries. CONCLUSIONS: Endovascular stent-graft repair of aortoenteric fistulae is possible, but further evaluation of this technique will determine its role in the management of this complication.

Aged↗
PubMed1998

A patient-specific Monte Carlo dose-calculation method for photon beams.

A patient-specific, CT-based, Monte Carlo dose-calculation method for photon beams has been developed to correctly account for inhomogeneity in the patient. The method employs the EGS4 system to sample the interaction of radiation in the medium. CT images are used to describe the patient geometry and to determine the density and atomic number in each voxel. The user code (MCPAT) provides the data describing the incident beams, and performs geometry checking and energy scoring in patient CT images. Several variance reduction techniques have been implemented to improve the computation efficiency. The method was verified with measured data and other calculations, both in homogeneous and inhomogeneous media. The method was also applied to a lung treatment, where significant differences in dose distributions, especially in the low-density region, were observed when compared with the results using an equivalent pathlength method. Comparison of the DVHs showed that the Monte Carlo calculated plan predicted an underdose of nearly 20% to the target, while the maximum doses to the cord and the heart were increased by 25% and 33%, respectively. These results suggested that the Monte Carlo method may have an impact on treatment designs, and also that it can be used as a benchmark to assess the accuracy of other dose calculation algorithms. The computation time for the lung case employing five 15-MV wedged beams, with an approximate field size of 13 X 13 cm and the dose grid size of 0.375 cm, was less than 14 h on a 175-MHz computer with a standard deviation of 1.5% in the high-dose region.

Algorithms↗
PubMed1995

Mean mass energy absorption coefficient ratios for megavoltage x-ray beams.

Mean mass energy absorption coefficient ratios of acrylic, polystyrene, and water to air, were calculated using Monte Carlo generated energy spectra. The energy spectra were calculated for 4- to 50-MV x-ray beams, from machines using flattening filters and scanning beams. The validity of these spectra was verified by comparing the measured ionization ratios with the calculated values. The agreement was found to be within 1.9%. For beams of energy below 6 MV, our estimates of the mean mass energy absorption coefficient ratios agree well with those recommended by the TG-21 protocol. For higher energy beams, the discrepancy increases to about 3%. It was found that the discrepancy is attributable to the different spectra used in these calculations.

Humans↗
PubMed1990

Mood changes, obstetric experience and alterations in plasma cortisol, beta-endorphin and corticotrophin releasing hormone during pregnancy and the puerperium.

The relationships between mood change, obstetric experience and alterations in plasma cortisol, beta-endorphin (beta-EP) and corticotrophin-releasing hormone (CRH) were examined in a prospective study of 97 primiparous Australian women. Psychological measures were administered between the 28th week of pregnancy and the 3rd postnatal month, including the Profile of Mood States (POMS) and the Montgomery Asberg Depressive Rating Scale (MADRS). Blood samples were collected for cortisol, beta-EP and CRH assay on most of these occasions and during labour. Factor analysis was used to identify key subsets of psychological variables for use in the subsequent analyses. 'Mood disturbance' and 'tiredness' factors peaked at 38 weeks' gestation, while 'difficulty falling asleep' was greatest around the time of birth. Cortisol, beta-EP and CRH concentrations rose significantly as pregnancy advanced and peaked at birth; plasma CRH correlated with plasma cortisol (r = 0.54) and beta-EP (r = 0.32). Women with the highest 'mood disturbance' and MADRS depression scores at 28 weeks' gestation received significantly more pain relief during labour. Those women whose mood deteriorated from 38 weeks' gestation to postnatal day 2 had larger falls in plasma beta-EP after delivery (p less than 0.01) than those women whose mood improved or remained constant. Women in this mood-deteriorated subgroup also had significantly higher MADRS depression scores at 3 months (p less than 0.01). Mild antenatal depression (MADRS greater than 13) occurred in 5.2% of women and mild postnatal depression in 4.7%. Overall, these data suggest a role for circulating CRH in the regulation of maternal cortisol secretion and significant relationships between maternal postnatal mood states and beta-EP and between antenatal mood states and obstetric events.

Adult↗
PubMed1989

Relation between plasma beta-endorphin and the ventilatory response to hypercapnia in humans.

1. Endogenous opioids have been implicated in the control of breathing in neonates, but their role in ventilatory control in adults remains unclear. 2. We studied the relationship between circulating immunoreactive beta-endorphin and the ventilatory and mouth occlusion pressure responses to hypercapnia in 12 healthy male subjects. In addition, we examined the effect of repetitive hypercapnia on plasma beta-endorphin and cortisol levels. 3. A weak but significant negative relationship between the ventilatory response to hypercapnia and basal plasma beta-endorphin levels was observed (r = -0.35, P less than 0.01). A similar negative relationship was noted between mouth occlusion pressure response to hypercapnia and basal plasma beta-endorphin levels (r = -0.36, P less than 0.01). 4. Repetitive hypercapnia prevented the fall in plasma cortisol that occurred under control conditions (P less than 0.02) but had no effect on plasma beta-endorphin. 5. We conclude that plasma beta-endorphin may play a role in the central chemical control of breathing in man.

Adult↗
PubMed1989

Restriction of placental growth in sheep enhances placental metabolism of fetal beta-endorphin-like immunoreactivity.

The opioid polypeptide beta-endorphin is present in fetal blood but it is not clear whether its source is the fetus or the placenta. We therefore measured beta-endorphin in extracts of fetal femoral arterial and umbilical venous blood plasma in sheep by radioimmunoassay to determine whether the fetus or the placenta is the major source of beta-endorphin in the fetal circulation. Chromatographic analysis of extracts of fetal arterial plasma showed that beta-lipotropin and other precursors of beta-endorphin made only a minor contribution to the immunoreactivity detected. Concentrations of immunoreactive beta-endorphin were higher in the femoral artery than in the umbilical vein in fetal sheep between 113 and 128 days of pregnancy. Therefore the placenta removes beta-endorphin or a closely related polypeptide of fetal origin from the umbilical circulation in sheep at this stage of gestation. Acute hypoxaemia and hypoglycaemia increase the concentrations of immunoassayable beta-endorphin in blood plasma of adult and fetal sheep, but little is known about the effects of chronic hypoxaemia or hypoglycaemia on the circulating levels of beta-endorphin and related polypeptides in the fetus. Therefore we also measured immunoreactive beta-endorphin in blood plasma from fetal sheep in which growth retardation in association with restricted placental growth was produced by removal of endometrial caruncles before mating. Intra-uterine growth retardation was accompanied by chronic hypoglycaemia and chronic hypoxaemia in the fetuses. This was not associated with higher concentrations of beta-endorphin-like immunoreactivity in fetal arterial or umbilical venous plasma, but was accompanied by significantly increased placental extraction of fetal immunoreactive beta-endorphin from the umbilical circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

The effect of repetitive haemorrhage on plasma cortisol, beta-endorphin and N-terminal pro-opiomelanocortin in conscious sheep.

We measured the effect of repeated haemorrhagic stress, performed on four consecutive days in conscious adult sheep, on the plasma concentrations of cortisol and ACTH-related peptides to determine whether the pituitary-adrenal response was altered by stress repetition. Peptides from the C-terminus of the ACTH pro-hormone was measured by beta-endorphin RIA. Glycopeptides derived from the N-terminus of the ACTH pro-hormone were measured by tau 3-MSH RIA. The immunoreactive tau 3-MSH in sheep plasma was found to have an apparent molecular weight of approximately 10,000 by gel chromatography through Sephadex G-75, which is similar to the size of the major circulating form of pro-tau-MSH found in human and rat plasma. Daily haemorrhage consistently elevated plasma concentrations of cortisol and pro-tau-MSH. There was no significant difference in the daily responses of either cortisol or pro-tau-MSH when considered individually. However, there was a significant change over the four days in the relationship between the cortisol and pro-tau-MSH responses, as judged by analysis of variance of the difference in daily z-scores of cortisol and pro-tau-MSH. This trend indicated a relative increase in the secretion of pro-tau-MSH from the pituitary compared to the cortisol response, and suggested that repeated exposure to stressful stimuli may alter the pituitary-adrenal-axis.

Animals↗
PubMed1988

Immunoreactive methionine-enkephalin in cerebrospinal fluid and blood plasma during acute stress in conscious sheep.

The opioid peptide methionine-enkephalin (Met-enkephalin) was measured in plasma and cerebrospinal fluid (CSF) of sheep in which the cisterna magna, carotid artery, and jugular vein were chronically cannulated. Venous blood plasma and CSF were collected before and after stress treatment and in control studies in conscious animals. Plasma and CSF were extracted with octadecylsilica and oxidized, and Met-enkephalin was measured as its Met-sulfoxide derivative by specific RIA. The molecular form of immunoreactive Met-enkephalin was characterized by peptide size exclusion chromatography of an octadecylsilica extract of sheep plasma through Bio-Gel P2, followed by reverse phase liquid chromatography, and was identical to Met-enkephalin and Met-sulfoxide-enkephalin. Insulin-induced hypoglycemia produced an elevation of plasma cortisol and an increase in the plasma concentration of Met-enkephalin. Acute hemorrhage led to an earlier and greater rise in plasma cortisol than that associated with insulin-induced hypoglycemia, but did not increase the concentration of Met-enkephalin in plasma. Neither form of acute stress increased the concentration of Met-enkephalin in CSF. These studies confirm that secretion of Met-enkephalin into blood can be dissociated from stimulation of the pituitary-adrenocortical system. They also show that circulating Met-enkephalin is elevated in conscious sheep during acute hypoglycemic stress, but plasma Met-enkephalin is unlikely to exert effects on the opiate receptors of periaqueductal or spinal nociceptive neurons under these conditions, since it does not enter cerebrospinal fluid in significant amounts.

Animals↗
PubMed1987

Postnatal disappearance of the pregnancy-associated reduced sensitivity of plasma cortisol to feedback inhibition.

We recently observed that the characteristic insensitivity of the pituitary-adrenal system in women to feedback inhibition during pregnancy persists for at least four days postnatally. We therefore examined women during the first five weeks after delivery to assess when the sensitivity of plasma cortisol to glucocorticoid inhibition returns to normal. Dexamethasone (DEXA, 1 mg) was ingested at 11 pm by normal healthy women, once between the 3rd and 27th postnatal days, and again on day 35. Blood plasma was collected at 4 pm on the following day for cortisol assay. Plasma cortisol levels (nmol/L, mean +/- sem [n]) after DEXA in the first two weeks (216 +/- 28, [47]) were higher (p less than 0.001) than in nonmedicated nonpregnant women (47.4 +/- 8.9 [12]) and were normal by the 35th day after delivery (41.7 +/- 4.8 [74]). A negative association was found between post-DEXA cortisol and time after delivery in the first 4 post-partum weeks (r = -0.46, p less than 0.001). The study confirms that insensitivity of plasma cortisol to feedback inhibition persists beyond normal pregnancy in a significant proportion of healthy women for two to three weeks, and is absent by the 5th postnatal week.

Dexamethasone↗
PubMed1986

Acute hemorrhagic stress in conscious sheep elevates immunoreactive beta-endorphin in plasma but not in cerebrospinal fluid.

The effects of acute hemorrhagic stress on the concentrations of immunoreactive beta-endorphin (IR beta EP) in cerebrospinal fluid (CSF) and blood plasma were investigated in conscious sheep in which the cisterna magna, a carotid artery, and a jugular vein were chronically cannulated. Serial samples of CSF and jugular venous blood were collected before and after acute arterial hemorrhage and in control experiments. Basal concentrations of IR beta EP were higher in plasma than in CSF. Plasma concentrations of cortisol and IR beta EP increased within 45 min of the commencement of hemorrhage and returned to near baseline levels within 2.25 h. The concentrations of cortisol and IR beta EP in plasma observed after hemorrhage were significantly different from those observed in controls (analysis of variance). Neither the molar nor the relative changes from initial concentrations of IR beta EP in CSF were significantly different between hemorrhage-stressed and controls by analysis of variance. These results show that hemorrhagic stress in conscious sheep elevates concentrations of IR beta EP in plasma but not in CSF, indicating that pituitary beta EP secreted into blood does not enter CSF in significant amounts.

Animals↗
PubMed1985

Secretion of N-terminal pro-opiomelanocortin-derived peptides in response to acute haemorrhagic stress in conscious sheep.

To determine whether peptides derived from the N-terminus of the corticotropin/melanotropin/endorphin precursor, pro-opiomelanocortin, are released into blood in response to acute haemorrhagic stress, we examined the effect of haemorrhage on plasma concentrations of immunoreactive gamma 3-melanotropin, beta-endorphin and cortisol. Plasma concentrations of immunoreactive gamma 3-melanotropin (mean +/- SEM) increased within 30 min of haemorrhage from 71.1 +/- 10.4 to 106.8 +/- 6.3 fmol/mL (p less than 0.01) and plasma cortisol increased from 16.2 +/- 3.8 to 85.9 +/- 22.4 pmol/mL (p less than 0.025). The changes in plasma immunoreactive gamma 3-melanotropin and beta-endorphin were positively correlated (p less than 0.025). This study shows that peptides derived from the N-terminus of pro-opiomelanocortin are co-secreted with the C-terminal peptide beta-endorphin during acute haemorrhagic stress in sheep.

Animals↗