Measurement of multiple scattering of 13 and 20 MeV electrons by thin foils.

To model the transport of electrons through material requires knowledge of how the electrons lose energy and scatter. Theoretical models are used to describe electron energy loss and scatter and these models are supported by a limited amount of measured data. The purpose of this work was to obtain additional data that can be used to test models of electron scattering. Measurements were carried out using 13 and 20 MeV pencil beams of electrons produced by the National Research Council of Canada research accelerator. The electron fluence was measured at several angular positions from 0 degree to 90 degrees for scattering foils of different thicknesses and with atomic numbers ranging from 4 to 79. The angle, theta 1/e at which the fluence has decreased to 1/e of its value on the central axis was used to characterize the distributions. Measured values of theta 1/e ranged from 1.5 degrees to 8 degrees with a typical uncertainty of about 1%. Distributions calculated using the EGSnrc Monte Carlo code were compared to the measured distributions. In general, the calculated distributions are narrower than the measured ones. Typically, the difference between the measured and calculated values of theta 1/e is about 1.5%, with the maximum difference being 4%. The measured and calculated distributions are related through a simple scaling of the angle, indicating that they have the same shape. No significant trends with atomic number were observed.

Sci-Fri PM: Planning-01: Measured electron and x-ray angular distribution data for benchmarking Monte Carlo codes.

Monte Carlo (MC) studies of the output of medical linear accelerators have demonstrated that in-air profiles are useful in the beam commissioning process. A recent investigation of x-ray profiles (Tonkopi et al, Med. Phys 32 (9), 2005) showed very good agreement between measurement and EGSnrc calculations but to achieve this level of agreement the beam linac spot size, energy and angular divergence had to be treated as variables. In this project we carried out measurements and MC calculations for an electron accelerator for which the initial beam parameters are well known. Two sets of investigations were carried out. In the first we measured electron scatter distributions for a range of scattering foils and electron energies of 13 and 20 MeV. The profiles were parameterised and compared to EGSnrc Monte Carlo calculations. It was found that generally the EGSnrc calculations gave agreement with the measurements within 1.5 %. In the second investigation, which is on-going, in-air profiles were obtained for photon beams produced using different targets (from beryllium to lead). Measured angular distributions were obtained using ion chambers with different build-up caps (low and high-Z) and the sensitivity of the data to small changes in geometry (e.g., moving the x-ray target) was investigated. The photon energy fluence was calculated using EGSnrc and preliminary indications are that the measured and calculated distributions agree to better than 5 %. Work supported in part by NIH grant R01 CA104777-01A2.

Bone density in asthmatic patients taking high dose inhaled beclomethasone dipropionate and intermittent systemic corticosteroids.

BACKGROUND: Asthmatic patients taking low to moderate doses of inhaled topical corticosteroids have been shown to have lower bone density than those taking bronchodilators only. There is little information on bone density in asthmatic patients taking high dose inhaled corticosteroids. METHODS: Bone mass was studied in three age matched groups of asthmatic patients. These comprised: 17 asthmatic patients who had never taken inhaled or systemic corticosteroids (group 1); 20 patients who had taken beclomethasone diproprionate in a dosage of 1000-2000 micrograms daily for at least a year, who had also received courses of systemic corticosteroids in the past (group 2); and 20 patients who were taking both high dose inhaled corticosteroids and regular low dose prednisolone, at a median dose of 7 mg daily (group 3). Vertebral bone density was measured by quantitative computed tomography. Biochemical indices of bone formation and resorption were also measured. RESULTS: Mean bone density in group 2 (127.5(22.6) mg/ml) was similar to that in group 3 (114.5 (36.0) mg/ml). Bone density was significantly lower in both of these groups than in group 1 (160.4 (27.4) mg/ml). There were no significant differences between groups for any of the markers of bone formation and resorption. CONCLUSIONS: Asthmatic patients receiving high dose inhaled beclomethasone and intermittent courses of systemic corticosteroids have reduced vertebral bone density. The bone loss is similar in degree to that seen in patients taking high dose inhaled topical corticosteroids and continuous low dose systemic corticosteroids.

Gallium scanning in lymphoma.

The findings on gallium-67 scans were compared with the findings of standard techniques (X-ray chest, lymphangiography, clinical examination, and laparotomy findings) in patients with lymphoma, mainly at presentation, but sometimes on follow-up. The objective was to ascertain the reliability of this non-invasive technique in detecting lymphomatous deposits, and to assess its place in the battery of investigations which may be used in clinical staging of lymphomas. One hundred and sixty-six patients were studied, in whom 198 gallium-67 scans were performed. The results indicated that detection of mediastinal and upper para-aortic node involvement was the most significant function, and such detection might alter clinical staging, and, therefore, therapy. Gallium-67 was unhelpful in splenic scanning, being positive usually only in cases which had clinically detectable involvement. Unsuspected lung and bone lesions were found occasionally, and this was of considerable importance. Gallium-67 scanning is regarded as an important, non-traumatic additional investigation, clinically useful in staging lymphomas.