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Biomedical subjects

M D Evans

Publications and source records attributed to M D Evans.

At least 73 records · Page 4Linked to original sources
PubMed1993

A technique using parallel-opposed high energy electron beams for reirradiation of tumors near the spinal cord.

PURPOSE: Previous radiation treatment of patients with recurrent Hodgkin's lymphoma hampers attempts to give these patients further radiation treatment for their recurrence, because of the potential for serious radiation damage to critical normal structures within the treatment volume. The purpose of this paper is to present a technique we developed for treatment of recurrent Hodgkin's lymphoma in mediastinum and hilum. The technique is based on parallel-opposed electron beams with a spinal cord shield in the posterior electron beam. METHODS AND MATERIALS: The patient was treated with parallel-opposed 20 MeV electron beams and the spinal cord shield was shaped in such a way that the total dose from both the anterior and posterior electron beams did not exceed 33% of the prescribed tumor dose. Wax bolus was used to obtain the desired separation for the electron beams. RESULTS: In an electron beam, the dose under the spinal cord shield depends not only on the depth of the spinal cord but also on the width of the shield. For a given shield width, as the cord depth increases the relative dose under the shield first increases, reaches a maximum, and then decreases to approach the open field depth dose data at large depths. The depth at which the relative dose maximum occurs increases slowly with the shielded width. At a given depth, the relative dose decreases with an increasing shield width. CONCLUSION: Parallel-opposed electron beams with a spinal cord shield in the posterior electron beam provide a viable option in treatment of tumors enveloping the spinal cord. A high tumor dose may be prescribed with a concurrent low dose to the spinal cord obtained with an appropriately shaped spinal cord shield.

Adult↗
PubMed1993

Treatment results of high dose rate brachytherapy in patients with carcinoma of the cervix.

PURPOSE: The combination of external beam irradiation and low-dose-rate brachytherapy is known to be an effective form of treatment in carcinoma of the cervix and any change from this well-established therapeutic combination must be able to equal or improve the treatment results. Since 1984 we have been using high dose rate brachytherapy in conjunction with external beam irradiation for patients with carcinoma of the cervix. This paper reports our long term treatment results in terms of local disease control, survival, and complications. METHODS AND MATERIALS: Between January 1984 and December 1989, 187 previously untreated patients with carcinoma of the cervix underwent combined external beam irradiation and high dose rate brachytherapy. The International Federation of Gynecology and Obstetrics stage distribution of patients was as follows: I B = 15, II A = 35, II B = 68, III A = 9, III B = 54, IV A = 6. External beam irradiation to the whole pelvis was delivered by megavoltage irradiation with once-a-day fractionation, to a median dose of 4600 cGy. High dose rate brachytherapy was delivered by a high-dose-rate remote controlled afterloading unit, containing 20 spherical Cobalt 60 sources with a nominal activity of 19 GBq (0.5 Ci) at the time of installation, giving a typical dose rate to point A of 160 cGy/min, decreasing to about 80 cGy/min at the end of the 5-year study. One to 3 high dose rate brachytherapy treatments delivering 800 to 1000 cGy to point A were given weekly concurrently with the last 2 to 3 weeks of radiation therapy, or following its completion. Maximum rectal and bladder doses were routinely measured for each treatment. RESULTS: Overall 5-year actuarial survivals were as follows: I B = 72%, II A = 65%, II B = 66%, III A = 66%, III B = 45%. Five-year actuarial pelvic control rates were as follows: I B = 66%, II A = 83%, II B = 78%, III A = 88%, III B = 40%. At a median follow-up time of 54 months for patients at risk, 23 patients developed 25 complications attributable to radiotherapy (13 rectal, 3 bladder, 8 small bowel, 1 fistula) at a median time of 18 months following completion of treatment. Thirteen complications (7.6%) were grades 3 or 4. Patients with Stage II disease had a higher incidence of complications than patients with Stages I and III disease (p < 0.05). Rectal complications were significantly higher in patients who received a total rectal dose > 5400 cGy (p = 0.045). CONCLUSION: High-dose-rate brachytherapy treatment results are comparable to those obtained with low dose rate brachytherapy techniques. The use of three high dose rate brachytherapy insertions is a practical, economical, and safe treatment for patients with carcinoma of the cervix.

Adult↗
PubMed1993

The effect of ion implantation on cellular adhesion.

As there are only a finite number of materials suitable for orthopaedic reconstruction, considerable effort has been devoted recently to investigating ways of altering the surface chemistry of prosthetic materials without altering their bulk properties. Ion beam implantation is one such technique which is appropriate for orthopaedic reconstructive materials. This paper investigates the early effect of ion beam modification on cellular attachment of bone derived cells using a prototype device which measures the strength of attachment of individual cells to a silicon substratum. The results point to several conclusions. (1) There is no evidence that ion beam implantation with nitrogen, phosphorus, manganese or magnesium produces increased adhesion of human bone derived cells. (2) Surface etching with hydrofluoric acid, electron bombardment and thermal oxidation increases the strength of attachment between cells and substrata. (3) There is a correlation between wettability and rate of cellular attachment to oxygen implanted substrata during the first 2 h after cellular seeding. However, the increase in cellular attachment cannot be entirely explained by the change in critical surface tension or via increased fibronectin attachment to the substrata.

Bone Transplantation↗
PubMed1993

The design of an adjustable half block for nonasymmetric linear accelerators.

Half-block techniques in radiotherapy may be used to junction two abutting radiation fields. Removable half blocks for linear accelerators not equipped with asymmetrical jaws can accomplish this technique providing the block edge is properly secured with respect to the beam central axis to achieve a smooth beam junction. Successive block edge cuts with a milling machine are, however, required to achieve an acceptable junction of the fields. The design of a half-block device that allows secure adjustment of the block edge on the linac thus alleviating the need for successive milling procedures is presented.

Equipment Design↗
PubMed1993

The use of integral activity to assess scheduled radioactive source changes for brachytherapy.

The development of afterloading brachytherapy devices using radioactive sources with relatively short half-lives has meant that several source changes are required per year. We present here a simple method to evaluate the ability of the supplier to deliver the scheduled amount of activity. Using the integrated activity of the source during the period of its clinical use, a comparison between the scheduled and delivered activity can be quantified.

Brachytherapy↗
PubMed1993

Attachment of human bone cells to tissue culture polystyrene and to unmodified polystyrene: the effect of surface chemistry upon initial cell attachment.

Cell culture studies have often been used in the determination of the suitability of biomaterials as surfaces for the attachment and growth of cells. For such studies of surfaces for potential use in bone implants, cells derived from bone may be maintained in culture on tissue culture polystyrene (TCPS). We have determined the contribution that serum fibronectin (FN) or vitronectin (VN) make to the attachment and spreading of cells cultured from explanted human bone (bone-derived cells) during the first 90 min following seeding on culture surfaces. The attachment of bone-derived cells to TCPS was simulated two-fold by the addition of 10% (v/v) fetal bovine serum (FBS) to the seeding culture medium. The roles of FN and VN were determined by selective removal of the FN or VN from the FBS prior to addition to the culture medium. FBS from which the VN had been removed did not have this stimulatory activity. In contrast, the attachment of bone-derived cells onto TCPS from medium containing FN-depleted serum (which contained VN) was the same as when intact FBS was used. There was incomplete attachment of bone-derived cells (27% of cells) when seeded in medium containing FBS depleted of both VN and FN. Our results show that for human bone-derived cells, the attachment onto TCPS of cells planted in medium containing FBS during the first 90 min of culture is principally as a result of adsorption onto the surface of serum VN. As unmodified polystyrene (PS) has also been used previously as a model biomaterial surface, PS was compared to TCPS for attachment of the bone-derived cells. Attachment of bone-derived cells to TCPS was twice that onto PS, both when the medium was serum-free and when it contained FBS. Bone-derived cells attached to TCPS or PS onto which purified VN or FN had been precoated, with VN adsorbed onto PS being as effective as was VN adsorbed onto TCPS. With FN, there was an effect of the polystyrene surface chemistry which was evident in that suboptimal concentrations of FN had a slightly higher potency when adsorbed onto TCPS than did the same concentrations of FN coated onto PS. When preadsorbed onto TCPS, the potency of FN for attachment of bone-derived cells was at least equal to that of VN.

Bone and Bones↗
PubMed1993

Long source-skin distance rectal irradiation technique: a review of results.

Endocavitary rectal irradiation is a well established curative treatment for patients with selected early cases of adenocarcinoma of the rectum. At McGill we use a long source-skin distance (SSD) rectal irradiation technique as an alternative to the standard short SSD rectal irradiation technique originally described by Papillon. Eight patients, seven women and one man, were treated between April 1986 and November 1988. Median age was 72.5 years (range 46-86 years). Seven patients were treated with curative intent, and one for palliation. The mean follow-up period for all patients was 43 months, with a median of 54 months (range 3-65 months). Actuarial survival and disease-free survival were 86% and 72% at 65 months for the seven patients treated with curative intent. Treatments were well tolerated by all patients and only one patient developed localized proctitis that required steroid enemas, which resulted in complete resolution of symptoms. Our results are comparable with those in other reports in the literature. The complications were similar in type and frequency to other published series.

Adenocarcinoma↗
PubMed1993

Moral reasoning and political conflict: the abortion controversy.

We argue that the abortion controversy has one major source--religion--and two less important ones--attitudes towards sexual permissiveness and women's employment. Traditional Christianity promotes opposition to abortion using three distinct modes of moral reasoning: through deductive moral reasoning, by the Christian world view's implication that abortion violates the sanctity of life and is a rebellion against God's design; through authoritative moral reasoning by appeal to Catholic dogma; and through consequentialist moral reasoning, as a means of control over sexuality and as a means of confining women's activities to the home. Even aside from Christian belief, adherence to traditional morality promotes opposition to abortion on these consequentialist grounds. We posit a model in which religious belief, anti-feminism, sexual permissiveness, and attitudes towards abortion are distinct concepts (a four-factor model) rather than all simply aspects of a single conservatism factor. We develop reliable, multiple item attitude scales; show that our four-factor model fits the data much better than the one-factor alternative; and test our hypotheses on new data from a large, representative national sample of Australia (N = 4540). Using maximum likelihood structural equation methods, we find that deductive reasoning from Christian belief is the most important source of opposition to abortion, with strong effects both direct and indirect. Exposure to the authority of the Catholic hierarchy is a real but weaker source of opposition. Consequentialist reasoning from traditional moral views on sex--partly buttressed by religion, partly independent of it--is also influential. But views on women's employment matter only a little, contrary to received wisdom.

Abortion, Legal↗
PubMed1993

Women's labour force participation and socioeconomic development: influences of local context and individual characteristics in Brazil.

We address several key hypotheses about the effects of socioeconomic development on women's labour force participation during the transition from agriculture to industrialism. To this end, we explore differences in women's labour force participation in Brazil by education, marital status, age, and urban or rural residence. We also show how socioeconomic development affects the overall level of women's participation and the differentials by education, etc. Our data are drawn from a large 1973 PNAD (Pequisa Nacional por Amostra de Domicilos) survey conducted by the Brazilian census bureau. Socioeconomic development in different parts of Brazil ranges from pre-industrial agriculture to heavy industry. Using logistic regression, we show that the general level of women's labour force participation does not change with the level of development. Highly educated women are much more likely than the less educated to be in the labour force (net of other influences); this difference is substantially greater than in post-industrial societies. Somewhat surprisingly, the influence of education is the same across the range of development levels in Brazil. Single women are more likely to be in the labour force than married women, and the difference grows during development. Age has a curvilinear relationship to labour force participation, and the old are much less likely to participate in more developed places. Rural women are slightly more likely to be in the labour force at all levels of development.

Adolescent↗
PubMed1992

Cognitive therapy and pharmacotherapy for depression. Singly and in combination.

Cognitive therapy and imipramine hydrochloride tricyclic pharmacotherapy, each singly and in combination, were compared in the treatment of nonpsychotic, nonbipolar depressed outpatients. One hundred seven patients were randomly assigned to 12 weeks of active treatment; 64 patients completed the full course of treatment. Rates of attrition were high but not differential. Cognitive therapy and pharmacotherapy did not differ in terms of symptomatic response, either in the primary analyses or in secondary analyses restricted to more severely depressed outpatients. Initial severity did predict response within pharmacotherapy alone, but not within cognitive therapy. Combining cognitive therapy with pharmacotherapy did not markedly improve response over that observed for either modality alone, although such nonsignificant differences as were evident did favor the combined treatment. Two patients died as a consequence of suicide attempts, both of which involved study medication.

Adolescent↗
PubMed1992

Differential relapse following cognitive therapy and pharmacotherapy for depression.

Patients successfully treated during a 3-month period with either imipramine hydrochloride pharmacotherapy, cognitive therapy, or combined cognitive-pharmacotherapy were monitored during a 2-year posttreatment follow-up period. Half of the patients treated with pharmacotherapy alone continued to receive study medications for the first year of the follow-up. All other patients discontinued treatment at the end of the acute treatment phase. Patients treated with cognitive therapy (either alone or in combination with medication) evidenced less than half the rate of relapse shown by patients in the medication--no continuation condition, and their rate did not differ from that of patients provided with continuation medication. It appears that providing cognitive therapy during acute treatment prevents relapse. Whether this preventive effect extends to recurrence remains to be determined.

Adolescent↗
PubMed1992

A simple technique for film dosimetry.

Dose distributions showing the effect of custom made compensators may be produced using measured data unique to the compensator. A fast method of obtaining this data with film is described. The problem of dose versus density response is avoided by an appropriate choice of the given dose to the film.

Body Constitution↗
PubMed1992

Examination of pre- and posttreatment MHPG during cognitive therapy.

Sixteen unipolar depressed patients were treated with cognitive therapy for 12 weeks. Pretreatment 24-hour urinary MHPG levels were unable to predict treatment response. There was a nonsignificant trend for cognitive therapy responders to show a decrease in MHPG during treatment when compared to nonresponders.

Adult↗
PubMed1991

Response of depression to very high plasma levels of imipramine plus desipramine.

Forty-five depressed patients were treated with imipramine for 6 weeks. Seven of 7 patients (100%) who had plasma levels of imipramine plus desipramine greater than 500 ng/ml showed a 50% or greater improvement in Hamilton depression scores compared with 23 of 38 patients (60%) with plasma levels less than 500 ng/ml (p less than 0.057).

Adult↗
PubMed1991

Aqueous cigarette tar extracts damage human alpha-1-proteinase inhibitor.

The elastase inhibitory capacity (EIC) of human alpha-1-proteinase inhibitor (alpha 1PI) is severely compromised by aqueous cigarette tar extract (ACTE). An aqueous extract of the tar from two cigarettes causes a loss of EIC of at least 60% in 24 h at 37 degrees C (pH 7.4) and the damaging capability of the ACTE is retained for many hours. Hydrogen peroxide appears to be an essential component of the mechanism by which ACTE damages alpha 1 PI, since catalase substantially protects alpha 1PI from ACTE-mediated damage. Only mild protection is offered by 10 mM diethylenetriamine pentaacetic acid, indicating only a minor role for transition metal ions in the alpha 1PI-damaging process. Hydroxyl radicals are unlikely agents of alpha 1PI damage in the ACTE system, as judged from hydroxyl radical scavenger studies. Ascorbate and various thiols offer protection to different degrees, dependent on the incubation conditions. Of several amino acids tested, cysteine and methionine (but not methionine sulfoxide) are the only two that protect alpha 1PI. We suggest that components of cigarette smoke particulate matter extracted into the aqueous lung fluid environment may cause local deficiencies in alpha 1PI in smokers' lungs.

Amino Acids↗
PubMed1991

High dose rate afterloading intracavitary therapy in carcinoma of the cervix.

From January 1984 through December 1986, 87 patients with previously untreated carcinoma of the cervix received external beam pelvic irradiation and high dose rate intracavitary therapy (HDRT). There were 18 Stage IIA patients, 39 Stage IIB, and 30 Stage IIIB. The median age was 60 years and the median follow-up time was 42 months for patients at risk. Radiotherapy consisted of external megavoltage irradiation to the whole pelvis (median dose 4600 cGy) combined with one (6 patients), two (51 patients), or three (30 patients) HDRT insertions. A high dose rate remote afterloading unit with 60Co sources was used to deliver the HDRT. The prescribed dose to point A was between 800 and 1000 cGy per treatment. The dose rate at point A initially was approximately 150 cGy/min and dropped to approximately 100 cGy/min during the duration of the study. Treatments with multiple fractions were given at weekly intervals. The overall actuarial survival at 5 years was 88% for Stage IIA, 64% for Stage IIB and 32% for Stage IIIB patients. Pelvic recurrence remained the major cause of failure. Grade III and IV late complications included proctitis and bowel obstruction in six patients each. We conclude that HDRT results are similar to those obtained with conventional low dose rate intracavitary systems. HDRT is cost effective and minimizes exposure to personnel. Several questions, such as the total number of insertions required, dose per HDRT insertion, and optimal HDRT insertion schedule remain unanswered and further experience is needed to better clarify these issues.

Adult↗