PubMed Health⌕ Search

Biomedical subjects

M D Evans

Publications and source records attributed to M D Evans.

At least 55 records · Page 3Linked to original sources
PubMed1996

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

PURPOSE: This study reports the clinical outcome of fifteen patients with low rectal adenocarcinoma treated with the long source-skin distance (SSD) of endorectal irradiation technique. This method was designed at McGill University in 1986 as an alternative to the standard short SSD rectal irradiation that was developed by Papillon (Proc. R. Soc. Med. 66: 1179-1181, 1973). METHODS AND MATERIALS: Between April 1986 and May 1993, six females and nine males were treated with this technique. Fourteen patients were treated with curative intent and one woman for palliation. The median total dose was 85 Gy (range 60-135 Gy) in a median of 3 fractions (range 3-5) over a median treatment time of 5 weeks (range 2-9.5 weeks). RESULTS: With a mean follow-up of 39 months and a median of 24 months (range 3 months-8.7 years), actuarial overall survival and disease-free survival rates are 50.8% and 71.4%, respectively, at 8.7 years. No patients have died of recurrent disease, but one patient has distant metastatic disease. One patient treated with curative intent required an abdominoperineal resection for progressive disease. Treatments were tolerated well by all patients. Four patients required steroid enemas for localized proctitis for a short period of time. They all responded well and had complete resolution of symptoms. CONCLUSIONS: Our results are comparable with those in other reports in the literature. The complications are similar in type and frequency to other published series. The long SSD technique may be an acceptable alternative to the standard short SSD technique.

Adenocarcinoma↗
PubMed1996

Evidence for sensitisation of DNA to oxidative damage during isolation.

The oxidative base lesion 8-oxo-deoxyguanosine (8-oxo-dG) has been identified in DNA isolated from normal tissue and may occur at elevated levels during disease. However, the use of phenol during DNA extraction may artificially elevate the detected levels of this lesion. Herein, we have performed a comparative methodological study using both pronase E and phenol extraction techniques; native or oxidatively stressed DNA was isolated to determine the validity of each extraction technique for the subsequent determination of 8-oxo-dG. Whilst the yields of DNA were comparable, after pronase E extraction there was no detectable induction of 8-oxo-dG in reextracted naked DNA or peripheral blood mononuclear cell DNA that had been oxidatively stressed. However, phenol extraction enhanced the basal levels of 8-oxo-dG detected, and also induced a significant increase in levels of the modified base after exposure to oxidative stress. The latter was dependent on the presence of foetal calf serum in the extracellular medium. We have confirmed that phenol extraction sensitises native DNA to subsequent oxidative damage. In addition, this work shows that the extent of sensitisation occurring during phenol extraction varies with the degree of oxidative damage already incurred and infers that labile guanine sites generated during oxidative stress may be detected as 8-oxo-dG residues after phenol extraction.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1996

A novel HPLC procedure for the analysis of 8-oxoguanine in DNA.

The chromatographic quantitation of 8-oxoguanine adducts in DNA is widespread in the literature, although results obtained by HPLC of 8-oxodeoxyguanosine do not always agree with levels determined by GC-MS. To help explain this discrepancy, here we describe a novel procedure for the analysis of 8-oxoguanine adducts in DNA. Although it proved difficult to directly quantitate 8-oxoguanine in the presence of high levels of endogenous guanine using conventional reversed-phase HPLC, a simple preincubation of DNA acid hydrolysates with guanase allowed such analyses. The assay relied on our observation that 8-oxoguanine was not a substrate for guanase, and on sensitive electrochemical detection. The limit of detection for 8-oxoguanine was 5 nM or 250 fmol on column. Using this procedure, the background level of 8-oxoguanine in commercially available calf thymus DNA was 0.4 nmol/mg DNA or 3.2 mol/10(5) mol guanine.

Animals↗
PubMed1996

Equivalent square as a predictor of depth of dose maximum for megavoltage therapy beams.

The depths of dose maxima, dmax, and surface doses of 6 MV, 10 MV, and 18 MV photon beams were measured for various square fields and rectangular fields with elongation ratios from 1 to 27. Rectangular fields with elongation ratios below 2 have essentially the same depths of dose maxima and surface doses as their corresponding equivalent square fields. For rectangular fields with elongation ratios above 2, the surface doses increase, and depths of dose maxima decrease with increasing elongation ratio in comparison to their respective values for their corresponding equivalent square fields. The shift of dmax toward the surface is more pronounced when the upper jaws rather than the lower jaws define the long axis of the field. This collimator exchange effect does not influence the surface dose. Even for the largest elongation ratios, the changes in dmax and surface dose from their equivalent square field values were minor and clinically insignificant, suggesting that the equivalent square approach provides a reliable method for predicting the values of dmax and surface dose for rectangular fields from square fields data.

Forecasting↗
PubMed1995

Analysis of internucleosomal DNA fragmentation in apoptotic thymocytes by dynamic sieving capillary electrophoresis.

The analysis, by slab gel electrophoresis, of internucleosomal DNA cleavage or laddering, characteristic of apoptosis in many cell systems, is labour intensive, difficult to automate and at best only semi-quantitative. In this report we show that CE, using dilute solutions of hydroxyethylcellulose as a replaceable sieving matrix, can be applied to the relatively rapid analysis of DNA laddering in whole digests of apoptotic rat thymocytes. Also, using the sensitivity of laser-induced fluorescence detection and the highly sensitive nuclei acid stain YO-PRO-1, the CE method reported here can use 1000-2000 fold fewer cells than needed for traditional slab gel methods.

Animals↗
PubMed1994

Rectal complications in patients with carcinoma of the cervix treated with concomitant cisplatin and external beam irradiation with high dose rate brachytherapy: a dosimetric analysis.

PURPOSE: This paper reports a dosimetric study of 43 patients treated with a combination of concomitant radiotherapy and chemotherapy (cisplatin) for locally advanced carcinoma of the cervix with the aim of investigating the correlation between the radiation dose to the rectum and the incidence of late rectal complications. METHODS AND MATERIALS: Radiotherapy consisted of 46 Gy external beam irradiation plus three high dose rate intracavitary treatments given weekly, concurrent with the last 3 weeks of external beam therapy, to a total dose of 30 Gy to point A. Cisplatin 30 mg/m2 was given weekly throughout the duration of the external beam irradiation. The brachytherapy irradiated volume was reconstructed from the orthogonal treatment radiographs to accurately locate the reference points defined by the International Commission of Radiation Units and Measurements (ICRU), report 38. The doses calculated at these points were compared to in vivo dose measurements performed immediately prior to treatment. RESULTS: The group of patients who were calculated to have received a dose to the rectal reference point greater than the prescribed point A dose (9/13) had a significantly greater probability of development of late rectal complications compared to the group of patients who were calculated to have received less than the prescribed point A dose at this rectal point (7/30), p = 0.003. There was no correlation of rate of complication with the in vivo measured dose in the rectum, stage of disease, or age. At 40 months post treatment, the group of patients receiving the higher dose to the rectal reference point had an actuarial rate of serious (Grade 3 and 4) rectal complications of 46% compared to a rate of 14% in the remainder. In terms of survival, the group of patients receiving the higher dose to the rectal reference point have all survived, whereas the group of patients receiving the lower dose to the rectal reference point have a significantly different rate of survival of 72%, p = 0.046. CONCLUSION: This investigation has revealed a significant correlation between the dose calculated at the rectal point defined by the ICRU and the incidence of late rectal complications in patients with carcinoma of the cervix undergoing concomitant radiotherapy and chemotherapy. Thus, this rectal reference point appears to be a useful prognostic indicator of late rectal complications in these patients and we recommend that the brachytherapy dose delivered to this rectal point be limited to the dose prescribed to point A for treatment regimens using three fractions of 8-10 Gy each, limiting the total dose to this point, including the external beam component, to 76 Gy. Further study will be required to determine whether this rule should be applied to patients receiving irradiation alone.

Brachytherapy↗
PubMed1994

Mechanism of initial attachment of cells derived from human bone to commonly used prosthetic materials during cell culture.

The suitability of polymeric biomaterials as surfaces for the attachment and growth of cells has often been investigated in cell culture. In this study 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 of culture was determined for metallic and ceramic surfaces. The requirement for Fn or Vn for attachment and spreading of bone-derived cells onto stainless steel 316 (SS), titanium (Ti) and alumina (Al2O3) and to polyethyleneterephthalate (PET) was directly tested by selective removal of Fn or Vn from the serum prior to addition to the culture medium. Attachment and spreading of bone-derived cells onto SS, Ti and Al2O3 surfaces were reduced by 73-83% when the cells were seeded in medium containing serum from which the Vn had been removed. Cell attachment and spreading on these surfaces when seeded in medium containing Fn-depleted serum (which contained Vn) were not reduced to the same extent as in the medium containing Vn-depleted serum. The bone-derived cells failed to attach to the surfaces to the same extent when seeded in medium containing serum depleted of both Vn and Fn. Our results show that for human bone-derived cells, the attachment and spreading of cells onto SS, Ti and Al2O3 as well as PET during the first 90 min of a cell culture attachment assay are a function of adsorption of serum Vn onto the surface.

Aluminum Oxide↗
PubMed1994

Imaging of HDR brachytherapy dose distributions using NMR Fricke-gelatin dosimetry.

The application of NMR Fricke-gelatin dosimetry to the imaging of dose distributions around high dose rate (HDR) radioactive Ir-192 seeds in brachytherapy is presented. The duration of the irradiations required to give changes of the Fricke-gelatin NMR characteristics, which were readily detected by the magnetic resonance imager, typically ranged from 4 to 25 min for single source and multiple source (33 source positions distributed among three catheters) geometries, respectively. A fast approach for determining radiation dose from MR image intensity using a calibration curve is described. NMR Fricke-gel dosimetry is shown to be a viable means of verifying the dose distributions from brachytherapy sources.

Brachytherapy↗
PubMed1994

Postoperative radiotherapy for chondrosarcoma of the L1 vertebral body: a case report.

A 51-year-old man presented with a low-grade chondrosarcoma of the L1 vertebral body, which had been completely resected. Radiotherapy was indicated; however, the close proximity of critical structures such as the spinal cord and the kidneys complicated the delivery of the high radiation dose required. In this paper we present the clinical and technical aspects of the radiotherapy technique used to treat this patient; we also describe the patient immobilization and radiation dose verification techniques used. The patient was treated with 18 MV photons using multiple field arc rotations with fields asymmetric with respect to the rotational axis of the collimator head. The spinal cord was aligned along the horizontal axis of the linear accelerator isocenter, and the patient was immobilized using a 10 degrees styrofoam wedge combined with an Alpha Cradle mold. In this manner, the patient was stabilized in a comfortable position, which facilitated the daily check of the isocenter position within the patient. Radiation dose verification was carried out with films in an anthropomorphic phantom and with an ionization chamber in a water phantom. These measurements confirmed the accuracy of the isodose distributions calculated for the treatment with asymmetric fields in the arc therapy mode. The use of this technique in conjunction with the positioning device permitted the delivery of 64 Gy to the L1 vertebral body with relatively low doses to the critical structures, amounting to 32 Gy at the surface of the spinal cord and less than 16 Gy to half of both kidneys.

Chondrosarcoma↗
PubMed1994

Dosimetry of centrally shielded electron beams.

In electron beams, the dose in phantom under the central shielding depends on electron-beam energy, depth in phantom, and shield area and thickness. In our experiments, all shield thicknesses were larger than the range of electrons in the shield material. At a given depth, the dose under the shield never exceeds the open field value; however, it can attain quite a large proportion of the open field value despite a shield thickness which exceeds the range of electrons in the shield material. The effects of shield area on the dose under the central shields were studied in detail and dose distributions are given as a function of shield lateral dimensions and electron-beam energy. It is shown that in clinical use of central shielding, the best approach to dose estimation under the shield is direct measurement in phantom under conditions of the actual clinical setup.

Humans↗
PubMed1994

Cigarette smoking, emphysema, and damage to alpha 1-proteinase inhibitor.

The proteinase-antiproteinase theory for the pathogenesis of emphysema proposes that the connective tissue destruction associated with emphysema arises from excessive proteinase activity in the lower respiratory tract. For this reason, the relative activities of neutrophil elastase and alpha 1-proteinase inhibitor (alpha 1-PI) are considered important. Most emphysema is observed in smokers; therefore, alpha 1-PI has been studied as a target for smoke-induced damage. Damage to alpha 1-PI in lung fluid could occur by several mechanisms involving species delivered to the lung by cigarette smoke and/or stimulated inflammatory cells. Oxidative damage to alpha 1-PI has received particular attention, since both cigarette smoke and inflammatory cells are rich sources of oxidants. In this article we review almost two decades of research on mechanistic studies of damage to alpha 1-PI by cigarette smoke and phagocytic cells in vitro, studies emphasizing the importance of elastinolytic activity in the pathogenesis of emphysema in vivo and studies of human lung lavage fluid to detect defects in alpha 1-PI at the molecular and functional levels.

Animals↗