Biomedical subjects

J Denham

Publications and source records attributed to J Denham.

31 records · Page 2Linked to original sources

PubMed1997

Normal variation in cutaneous blood content and red blood cell velocity in humans.

This study was designed to determine normal variations in cutaneous blood content, red blood cell content and skin thickness in healthy human volunteers. The blood content (BC) of human skin and the velocity of red blood cells (RBV) has been comprehensively mapped over 30 anatomical sites in 28 volunteers between the age of 7 and 77 years using reflectance spectrophotometry (RFS) and laser Doppler (LD) techniques respectively. Total skin thickness, which may have a relationship with blood content, has been mapped at the same anatomical sites in six of the volunteers using two-dimensional array, 12 MHz ultrasound equipment. The major determinant of BC and RBV was found to be anatomical site. Regardless of age, gender or prior sun exposure, anatomical sites above the waist produced higher readings than below. BC and RBV were found to be dependent on age and gender at most sites with higher readings being observed in males and younger volunteers. The largest difference was seen in males under 55 years whose RFS readings above the waist were significantly higher than in older males or females of any age. Heavy prior sun exposure and skin thickness could not be demonstrated to impact on either RFS or LD readings independently of the effects of anatomical site, gender or age. In general, RFS and LD readings paralleled one another and correlated linearly at most anatomical sites. While RFS readings tended to decrease in the cranio-caudal direction, LD readings were relatively uniform across the body except for the head and groin where they were higher, and the abdomen where they were lower. The site-to-site variations in RFS readings observed in this study correspond well to capillary density variations noted in previous studies.

Adolescent↗

PubMed1996

TLD extrapolation for skin dose determination in vivo.

Prediction of skin reactions requires knowledge of the dose at various depths in the human skin. Using thermoluminescence dosimeters of three different thicknesses, the dose can be extrapolated to the surface and interpolated between the different depths. A TLD holder was designed for these TLD extrapolation measurements on patients during treatment which allowed measurements of entrance and exit skin dose with a day to day variability of +/-7% (S.D. of mean reading). In a pilot study on 18 patients undergoing breast irradiation, it was found that the angle of incidence of the radiation beam is the most significant factor influencing skin entrance dose. In most of these measurements the beam exit dose contributed 50% more to the surface dose than the entrance dose.

Breast Neoplasms↗

PubMed1995

Verification of surface dose on patients undergoing low to medium energy X-ray therapy.

About 5% of patients still undergo cancer treatment with superficial (peak energy < or = 120 kVp) X-ray radiation. Dosimetry of these beams is difficult since the maximum dose is delivered at the surface and backscatter contributes significantly to the dose. This is particularly a problem in the difficult geometries encountered in superficial treatments in the head and neck area. It has recently been shown that surface dose measurements in mega-voltage X-ray beams can be performed using TLD (Thermoluminescence Dosimetry) extrapolation. In this technique, LiF TLD chips with a surface area of 3.15 x 3.15 cm2 and three different thicknesses (0.230, 0.099, and 0.038 g/cm2) are used together in the same radiation beam which allows the extrapolation of the measured dose back to the true surface. The energy response curve of the three thicknesses of LiF chips was measured for the energy range of 60kVp, HVL 1.6 mm Al to 300kVp, 4 mm Cu. LiF was found to over respond by a factor of 1.7 at 60kVp HVL 1.6 mm Al with respect to a 6MV photon beam. A feasibility study was carried out on three patients undergoing treatment at 120kVp. Because of the small field sizes involved it was necessary to limit irradiation to one or two chips at a time. The dose fall off in the first millimetre of tissue could be clearly detected. TLD extrapolation, in low to medium energy beams, was found to be useful to assess the dose of patients undergoing treatment for superficial lesions.

Feasibility Studies↗

PubMed1995

A perspex flattening filter for a 300k Vp orthovoltage X-ray beam.

For economic reasons modern equipment which produces low to medium energy X-rays covers the whole range of beam qualities from traditional superficial to orthovoltage radiation qualities. A recent trend shows an increasing number of installations of orthovoltage units in the cancer therapy community in the last five years. The use of a single anode for accelerating voltages between 60 and 300 kVp leads to compromises with regards to beam flatness and symmetry in the anode/cathode direction of the Siemens Stabilipan II radiation beam. A perspex flattening filter was designed to improve these beam parameters of the 300 kVp radiation beam (HVT 4mm Cu) at 50 cm and 60 cm FSD using a diaphragm-mounted field defining device. The filter design correlates with focal spot characteristics of the beam. The use of the filter improves flatness and symmetry for all measured field sizes from 6 x 6 cm2 to 18 x 18 cm2 by up to 8% (flatness) and 7% (symmetry) respectively. No significant difference in the depth dose characteristic of the 300 kVp beam was found with and without the filter. The only modification in the planning procedures required is the use of an attenuation factor of 0.89 for the filter. The use of the filter improves the dose distribution in treatment of patients undergoing orthovoltage radiotherapy--in particular treatments with large field sizes such as for metastases in the spinal column.

Radiographic Image Enhancement↗

PubMed1990

Treatment of adenocarcinoma of the cardia with synchronous chemotherapy and radiotherapy.

Twenty-nine evaluable patients with adenocarcinoma of the cardia were treated with synchronously administered chemotherapy (two cycles of 5-fluouracil and cisplatin and 30-36 Gy of radiation to determine whether these tumours are responsive to such treatment. Complete regression of tumour was observed endoscopically in 19 patients, and partial regression in four. Fourteen patients had their tumours resected and in six no microscopic tumour was found in the specimen. Nine patients received additional radiotherapy to a total dose of 54-60 Gy instead of surgery. Tumour response was associated with rapid reversal of dysphagia. Only one patient required subsequent intervention for relief of dysphagia due to fibrous stricture. Enhanced survival was associated with a complete endoscopic response to initial chemotherapy and radiotherapy, and a tumour of less than 5 cm in length. The median survival of responding patients was 15 months. Synchronous chemotherapy and radiotherapy was of major palliative benefit in this series and merits further evaluation.

Adenocarcinoma↗

PubMed1990

Micronuclei in cytokinesis-blocked lymphocytes of cancer patients following fractionated partial-body radiotherapy.

We applied the cytokinesis-block micronucleus assay to measure chromosome damage in lymphocytes of 11 cancer patients undergoing fractionated partial-body irradiation. Measurements performed before, during and after cessation of radiotherapy showed a dose-related increase in micronucleus frequency in each of the patients studied. When the results for micronucleus frequency (Y) were plotted against the estimated equivalent whole-body dose (X) the dose-response relationship obtained was Y = 75.8X + 49.5 (r = 0.783, P less than 0.0001). A general decline in MN frequency was observed during the post-treatment period down to 57 per cent (+/- 10) after 12 months but there was considerable variation between individuals. The advantages and disadvantages of the application of the cytokinesis-block micronucleus assay as a biological dosimeter for lymphocytes irradiated in vivo are discussed.

Adult↗

PubMed1989

Two- versus 24-hour infusion of cisplatin: pharmacokinetic considerations.

The disposition of unchanged cisplatin was compared after two- and 24-hour intravenous (IV) infusion to eight patients with germ cell cancer (dose, 100 mg/m2), 14 patients with head and neck cancer (dose, seven patients 50 mg/m2; seven patients, 100 mg/m2). Patients were randomized to receive either a two- or 24-hour infusion in the first course of treatment and the reverse in the second course. Cisplatin renal clearance, total clearance, and the percentage of the dose excreted unchanged in urine were significantly lower with the longer infusion. Total clearance was 345 +/- 97.0 mL/min/m2 after the two-hour infusion and 268 +/- 70.7 mL/min/m2 after the 24-hour infusion (P less than .0001). Renal clearance was 79.1 +/- 35.3 mL/min/m2 and 34.1 +/- 14.9 mL/min/m2 (P less than .0001). The percentage of the dose excreted unchanged in urine was 22.9 +/- 6.5% and 12.8 +/- 4.0%, respectively (P less than .0001). The ratio of cisplatin renal clearance to creatinine clearance was 1.95 +/- .96 after the two-hour infusion and .90 +/- .40 after the 24-hour infusion (P less than .001). There was only a poor relationship between cisplatin renal clearance and creatinine clearance after a two-hour infusion (r2 = .05, P greater than .1) or 24-hour infusion (r2 = .18, P greater than .05). The severity of emesis was graded on a four-point scale and was significantly less with the 24-hour infusion than with the two-hour infusion (P less than .05). Twenty-four-hour infusion of cisplatin resulted in greater drug retention in patients due to reduced renal clearance, but was also associated with reduced emetic toxicity, probably as a result of lower peak plasma levels.

Adolescent↗

PubMed1986