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Biomedical subjects

P Bloch

Publications and source records attributed to P Bloch.

At least 37 records · Page 2Linked to original sources
PubMed1995

Calculation of the dose in the build-up region for high energy photon beam. Treatment planning when beam spoilers are employed.

Recoil electrons from a polystyrene sheet (beam spoiler) placed in a photon beam were used to modulate the dose in the build-up region. The effects of the beam spoiler on the dosimetry in simple phantoms were studied for both 6 MV and 15 MV photon beams at 100 cm source-to-surface distance (SSD) as a function of (1) the thickness of the spoiler, (2) the spoiler-to-surface distance (SD) and (3) the field size. A radiotherapy treatment planning (RTP) algorithm was used that employs pencil beam dose deposition kernels to evaluate the three-dimensional (3D) dose distribution due to photons and electrons in the build-up region. To determine the energy deposition kernels for the recoil electrons emanating from the spoiler, their energy spectrum needs to be known. Monte Carlo simulations were performed to derive the spectrum of electrons from the beam spoiler. The recoil electron spectrum was found to be nearly independent of field size, SD, and spoiler thickness. The pencil beam energy deposition kernel was calculated for the recoil electrons from the spoiler and inserted in the treatment planning algorithm. The dose calculation algorithm permits merging the photon and recoil electron dose components. In all cases the calculation agrees to within 3% of the measured results.

Algorithms↗
PubMed1994

Influence of cone design on the electron beam characteristics on clinical accelerators.

Electron beam characteristics were investigated for different applicator cone designs. Low-energy scattered electrons from the cone housing can contribute to the skin dose. The depth dose was measured as a function of electron energies and field size for different cones. The measurements were compared with calculated 3-D dose distributions obtained from Monte-Carlo-derived energy deposition kernels [Phys. Med. Biol. 37, 391 (1992)]. This comparison shows that beam-defining cones can be fabricated to eliminate low-energy scattered electrons from the cone housing. Eliminating low-energy electrons from the cones provides depth dose (DD) characteristics for clinical electron beams that are comparable to those (1) from nearly monoenergetic electrons (as determined from the practical range of the electrons), and (2) for which the DD is nearly independent of source-to-skin distance. Measurements of DD for small circular fields were also performed. For very small field sizes, corresponding to the width of the lateral spread of a pencil beam, the theoretical and measured DD were found to depend on field size. Three-dimensional dose calculations of small and irregularly shaped electron fields are necessary to appreciate these effects.

Biophysical Phenomena↗
PubMed1994

The effect of antibiotic- and hydrocortisone-containing ointments in preventing secondary infections in guinea worm disease.

A randomized, single-blind, controlled study comparing the efficacy of an ointment containing two antibiotics, one containing one antibiotic plus hydrocortisone, and no treatment in reducing secondary infections in patients with patent Guinea worm was undertaken in the northern region of Ghana. Seventy-seven patients were included. Time to complete healing was significantly shorter in the treatment groups compared with the controls (P = 0.044 and P = 0.003, respectively). Secondary infections occurred more often in the controls (P = 0.00014). Ointments containing antibiotics are recommended for application at the early stage of patent Guinea worm infection.

Administration, Topical↗
PubMed1994

Urinary and intestinal schistosomiasis in the Tono Irrigation Scheme, Kassena/Nankana District, upper east region, Ghana.

Human- and snail-related aspects of transmission of urinary and intestinal schistosomiasis were studied in the Tono Irrigation Scheme in northern Ghana. The scheme became operational in 1977. In some schools, prevalences and intensities of both Schistosoma mansoni and S. haematobium infection were alarmingly high, pointing to human schistosomiasis being at least focally a health problem of major public health concern. Positive correlations between intensity of schistosome infection, as measured by egg output, with frequency of visible haematuria and history of haematuria point to opportunities for community-based assessment of morbidity and identification of high risk population subgroups. Bulinus globosus is the most important snail host for S. haematobium while Biomphalaria pfeifferi serves as host for S. mansoni. While transmission of S. mansoni is taking place only in the main canal, transmission of S. haematobium takes place in all parts of the irrigation system (lateral canal, night storage dam, main reservoir). Transmission of both S. mansoni and S. haematobium is rather focal and a seasonal pattern of transmission is indicated with peak transmission taking place during the beginning of the dry season. The high endemicity and the transmission patterns described in this study call for an integrated approach to schistosomiasis morbidity control in the area.

Adolescent↗
PubMed1994

Recurrent hemobilia after laparoscopic cholecystectomy.

Hemobilia occurred 1 month after a laparoscopic cholecystectomy, the result of an aneurysm of the right branch of the hepatic artery. The aneurysm was treated by selective arterial embolization. Recurrent bleeding 28 days later was treated by embolization with platinum coils. The mechanism of occurrence of the aneurysm and its treatment are discussed.

Adult↗
PubMed1993

[Ogilvie's syndrome and non-mechanical obstructions].

Ogilvie's syndrome and chronic intestinal pseudo-obstructions are two aspects of non-mechanical obstruction. The syndrome consists of acute colonic obstruction due to multiple causes and is characterized by passive dilatation of the colon without downstream obstacle. Treatment is primarily medical, except in cases with complications such as perforation by symptomatic treatment and, sometimes, by decompression colonoscopy. The most severe complication is perforation of the colon which may require colonic excision. Chronic intestinal pseudo-obstruction is characterized by chronic disorders mostly due to abnormalities of nervous plexuses and smooth muscle of the small and large bowels. It occurs in children and surgical abstention may lead to repeated but unfortunately ineffective operations. The only treatment recognized is digestive tract bypass combined with total parenteral feeding.

Acute Disease↗
PubMed1993

Initiation of multi-leaf collimator conformal radiation therapy.

Clinical studies have been initiated in conformal radiotherapy using a computer controlled multi-leaf collimator. Quantitative dosimetry and treatment planning studies comparing field shaping by lead alloy blocks and the multi-leaf collimator demonstrate the clinical acceptability of the multi-leaf collimator. Sixteen patients with tumors in multiple sites have received some part of their treatments with both blocking systems. Studies of dosimetry and field shaping show that the multi-leaf collimator produces clinically acceptable blocking for most field shapes and disease sites. The 80-20% penumbra was characterized for a wide range of shaped beams. For straight edges perpendicular to the leaf travel, the penumbra of measured dose distributions from the multi-leaf collimator is equal to conventional divergent blocking. When the multi-leaf collimator leaves approach a contour at an angle, the penumbra increases. At forty-five degrees, the maximum angle of approach, the penumbra is approximately 4 mm wider than that for divergent blocks. Three-dimensional treatment planning demonstrates that equivalent dose distributions can be obtained from the two field shaping systems. The multi-leaf collimator can be used effectively and efficiently to treat a variety of disease sites. Its optimal utility may be in treating complex fields--five or more shaped coplanar or non-coplanar beams. It is well suited for conformal therapy applications.

Humans↗
PubMed1993

The antibody response to Dracunculus medinensis in an endemic human population of northern Ghana.

The serum antibody response (total, and isotypes IgG1, IgG4, IgM, IgA and IgE) to Guinea worm infection was examined in humans from a highly endemic area of northern Ghana by ELISA and SDS-PAGE/Western blot techniques using an adult D. medinensis antigen. Sera were obtained early and late in the peak transmission period, from persons with patent and postpatent infections, as well as from persons from the same endemic area who claimed never to have had Guinea worm infection. To observe for potential cross-reactions in the tests, sera were also obtained from areas with no transmission of Guinea worm from patients with hookworm, O. volvulus and W. bancrofti infections, and from non-infected controls. Sera from persons living in the Guinea worm endemic area reacted extensively with Guinea worm antigen in both tests, and large numbers of bands were produced in the Western blots (up to 35 identified for some sera). For most antibody isotypes, the ELISA absorbance values obtained with sera from the same individuals varied between the two transmission seasons, with the highest titres present towards the end of the peak transmission period. The mean antibody titres for persons in the patent and postpatent infection categories were not significantly different when sera were obtained at the same season of the year. Persons from the endemic area, who claimed never to experience patent infections, also had antibodies to Guinea worm, although at significantly lower mean levels than for the patent and postpatent categories. The highest specificity in the ELISA and the most homogenous Western blots were obtained when detecting for antibodies of the IgG4 isotype.

Adolescent↗
PubMed1993

Workshop on the X-ray fluorescence of lead in bone: conclusions, recommendations and summary.

A workshop on the use of X-ray fluorescence (XRF) to noninvasively measure lead in bone was convened by the National Institutes of Environmental Health Sciences (NIEHS) and the Environmental Health Sciences Center of the Mount Sinai School of Medicine. The impetus for the workshop stemmed partly from NIEHS' concern that XRF machines produced for this purpose are licensed by the Food and Drug Administration as research devices, a designation that indicates they are safe to use on people but says nothing about the precision and accuracy of the data they generate. Therefore, a major purpose of the workshop was to scientifically examine these issues in a multi-disciplinary setting, to explore the current status of XRF research employing two different XRF techniques for lead-bone measurements: K-shell and L-shell XRF spectroscopy (K-XRF, L-XRF) and to make recommendations for future research in these techniques.

Bone and Bones↗
PubMed1992

[Diffuse leiomyomatosis of the esophagus. Analysis of a case and review of the literature].

Diffuse leiomyomatosis of the esophagus is a rare affection which is characterized by a diffuse hypertrophy of esophageal muscles, without involvement of the muscularis mucosae. This disease involves children and young adults, occasionally associated with other localisations of leiomyomatosis. The case of a 21 year old female, successfully treated by total esophagectomy, is reported herein. In this patient, proteinuria and hematuria led to the discussion of an aspect of Alport's syndrome which is characterized by association of leiomyomatosis, deafness, cataract, and hematuria.

Adult↗
PubMed1992

[The value of computer reconstruction of the frontal and sagittal planes of the facial structures].

The authors evaluate the merits of computer reconstructions in the coronal and sagittal planes to assess the anatomy of the facial structures. If the patient can be kept motionless, the coronal plane provides information similar to those obtained by a study with direct sections. The ethmoidofrontal recesses, the lamina cribrosa, the thin relief of the middle meatus, the floor of the orbit are perfectly examined. The sagittal plane provides a new approach of the anterior and posterior cortical bone, of the frontal sinus, of the nasofrontal canal, of the ethmoidal cells, of the sphenoid sinus and of the vault of the palate.

Ethmoid Sinus↗
PubMed1991

The use of T2 distribution to study tumor extent and heterogeneity in head and neck cancer.

Demarcation of the extent of malignant tissue is essential for planning a course of radiotherapy. MR images may provide additional information for delineating the target volume because of the large difference in the proton magnetic resonance relaxation times between normal and malignant tissues. In 13 patients with head and neck tumors the distribution of the proton spin-spin relaxation times, T2, at 1.5 Tesla were evaluated throughout the physician designated target volume and normal surrounding tissue. The T2 values within the tumor were always elevated compared with normal tissue, the highest values being in the nominal center of the tumor and decreasing toward the periphery. The regional distribution of T2 values within the tumor is a measure of the tissue heterogeneity within the tumor volume. In addition, the large differences in T2 relaxation times between normal and disease tissues were used in a computer algorithm to automatically demarcate the boundary of abnormal tissue in each axial MRI section. This potentially could significantly expedite the time required to identify the target volume on multiple sections and thus remove one of the major time constraints for 3D treatment planning.

Head and Neck Neoplasms↗
PubMed1990

31P localized magnetic resonance spectroscopy of head and neck tumors--preliminary findings.

Magnetic resonance imaging (MRI) is a powerful tool for accurate assessment of the anatomic extent of head and neck neoplasms. The development of methods for spatial localization by use of multiply tuned radio frequency coils that permit the measurement of multiple nuclear MR spectra (1H and 31P) from precisely defined volumes of interest has provided a basis for integrating spectroscopy into the clinical MRI examination. This offers a means for noninvasive monitoring of relative concentrations of mobile metabolites within a tumor. With the use of imaging to determine proper coil placement, a test-retest variance of about 17% is seen on MR spectroscopy. Data are presented from MRI/MRS studies for four head and neck lesions: (1) a squamous cell carcinoma of the lip; (2) a juvenile angiofibroma extending into the nasal cavity; (3) a massive chondrosarcoma of the nasal septum; and (4) a cervical nodal metastasis of a squamous cell carcinoma of the pharynx. Spectra are evaluated by comparison of relative concentrations of phosphorus compounds. The concentrations of phosphomonoesters and phosphodiesters are significantly higher in the neoplasms studied than in normal skeletal muscle. The developing role of integrated MRI/MRS to monitor the response of malignant neoplasm to radiation therapy is discussed.

Adult↗
PubMed1990

[Post-surgical inflammatory rectal stenosis].

A case of mid rectum stenosis after pelvic surgery is reported. The conservative treatment used here seems to be the more effective compared to the cases reported in the literature.

Adult↗
PubMed1989

[Diffuse retroperitoneal lymphangioleiomatosis].

A case of diffuse retroperitoneal lymphangiomatosis manifested by oedema of the left lower limb is reported. Non-invasive exploratory methods revealed a retroperitoneal pseudo-tumoral image. At laparotomy, a retro- and subperitoneal infiltration was discovered, and histology showed benign smooth muscle proliferation developed from the muscular layer of lymph vessels. There is no known successful surgical procedure for this type of lesion, and none of the treatments tested (oophorectomy or hormonal therapy) has proved to be effective.

Adult↗
PubMed1989

The use of magnetic resonance imaging and spectroscopy in the assessment of patients with head and neck and other superficial human malignancies.

The proper demarcation of diseased tissue is important for radiation therapy planning and treatment. The volume to be irradiated is usually identified on radiographs or on x-ray computed tomography (CT) sections. Magnetic resonance (MR)-derived images of the proton T2 relaxation times in small pixel elements, typically 0.5 mm2 or less, provide significantly sharper differentiation between normal and diseased tissue. The T2 values in tissue depend on the tissue composition, histologic condition, and physiologic environment within the tumor. Furthermore, for many tumors the histogram of T2 values has a clear biphasic distribution suggesting that T2 maps may be useful for the identification of necrotic or hypoxic regions within tumors. The distribution of T2 values within the tumor bed shows the general pattern that the T2 values are elevated with a range greater than that seen in normal muscle. Elevated T2 values are not by themselves diagnostic of malignancy; however, they demonstrate the heterogeneity of the microenvironment present within a tumor. The spatial distribution of T2 values is being explored as a method for computer assistance in the delineation of the target volume for treatment planning. In addition, MR P-31 spectroscopic examinations were performed on 30 patients with squamous cell carcinomas of the head and neck. Although hampered by muscle contamination in some P-31 spectra obtained with surface coil profile localization techniques, significant trends can still be appreciated in our data. These trends include the following: (1) the P-31 spectra from malignant tissue have well-resolved spectral lines in the upfield region that correspond to Pi, phosphomonoester (PME), and phosphodiester (PDE) not usually seen in normal muscle; (2) the PDE/B-ATP and PME/B-ATP ratios are greater than unity in all cases; and (3) most of the tumors have higher PME peaks than PDE peaks. The P-31 spectra from patients treated with ionizing radiation changed during and after therapy. Some of the changes could be associated with alteration of the tumor metabolic activity or synthesis and breakdown of lipoproteins. These studies suggest that magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) studies may be useful for both radiotherapy treatment planning and the noninvasive monitoring of patients both before and during treatment.

Carcinoma, Squamous Cell↗