Plasminogen binding and degradation by Treponema denticola: Identification of the plasminogen binding interface on the FhbB protein.

Treponema denticola is a proteolytic-anaerobic spirochete whose abundance in the subgingival crevice correlates with periodontal disease severity. Treponema denticola evades serum-mediated killing through the binding of factor H (FH), a negative regulator of the complement system. The T. denticolaFH receptor has been identified as FhbB, an 11.4kDa immunodominant lipoprotein. Three distinct subfamilies of FhbB proteins have been delineated and designated as FhbB1, FhbB2 and FhbB3. In this study we demonstrate that all FhbB variants bind human plasminogen (Plg). Competitive binding analyses revealed that FH and Plg do not compete for binding. Binding studies with FhbB135405 site-directed amino acid substitution mutants demonstrated that the interaction domains for FH and Plg on FhbB are separable. Inhibition of Plg-FhbB binding by ε-aminocaproic acid (a lysine analog) indicates that binding is mediated by electrostatic interactions that presumably occur with Lys binding sites contained within Plg "Kringle" domains 1, 2, 4 or 5. Similar to that demonstrated for FH, Plg can also serve as a substrate for the T. denticola protease, dentilisin. The in vivo consequences of dentilisin-mediated cleavage of Plg remained to be determined. The data presented demonstrate that FhbB is a multi-functional protein that may contribute to virulence through several mechanisms including immune evasion, manipulation of the host immune response, adherence or tissue invasion.

The accuracy of the pencil beam convolution and anisotropic analytical algorithms in predicting the dose effects due to attenuation from immobilization devices and large air gaps.

When a photon beam passes through the treatment couch or an immobilization device, it may traverse a large air gap (up to 15 cm or more) prior to entering the patient. Previous studies have investigated the ability of various treatment planning systems to calculate the dose immediately beyond small air gaps, typically less than 5 cm thick, such as those within the body. The aim of this study is to investigate the ability of the Eclipse anisotropic analytical algorithm (AAA) and pencil beam convolution (PBC) algorithm to calculate the dose beyond large air gaps. Depth dose data in water for a 6 MV photon beam, 10 x 10 cm2 field size, and 100 cm SSD were measured beyond a range of air gaps (1-15 cm). The thickness of the water equivalent material positioned before the air gap ranged from 0.2 to 4 cm. Dose was calculated with the Eclipse PBC algorithm and AAA. The scattered and primary dose components were calculated from the measurements. The measured results indicate that as the air gap increases (from 1 to 15 cm) the dose reduces at the water surface and that beyond an air gap a secondary buildup region is required to re-establish electronic equilibrium. The dose beyond the air gap is also reduced at depths beyond the secondary buildup region. The PBC algorithm did not predict any reduction in dose beyond the air gap. AAA predicted the secondary buildup region but did not predict the reduction in dose at depths beyond it. The reduction in dose beyond the secondary buildup region was shown to be particularly relevant for air gaps of 5 cm or more when there was a 2 cm of water equivalent material positioned before the air gap. For these cases, where electronic equilibrium is established in the material positioned before the air gap, both algorithms were found to overestimate the dose by 2.0%-5.5%. It was concluded that the dose to depths of up to 15 cm beyond a large air gap is reduced due to a decrease in scattered radiation, produced in the material positioned before the air gap, reaching the point of interest. This effect is not well modeled by the Eclipse AAA and PBC algorithm and may result in dose calculation errors greater than 2.5%. Due to the contribution of other uncertainties in the radiation therapy treatment planning and delivery process, dose calculation errors of this magnitude are not consistent with the recommendation of the International Commission on Radiation Units and Measurements that the absorbed dose to the target volume be delivered with an uncertainty of less than +/- 5%.

Thirty year celebration of journal publications on radiation oncology medical physics.

The Australasian Physical & Engineering Sciences in Medicine Journal (APESM) is an avenue for the profession to report scientific work in medicine; provide a facility for the publication of current work, new research and new techniques developed or reviewed; report on professional news from elsewhere and; publish the Australasian College of Physical Scientists and Engineers in Medicine (ACPSEM) policies and protocols. The journal is a vital instrument within the ACPSEM organisation with a worldwide circulation. This review of APESM on medical physics in radiation oncology is meant to be a progress summary of work in that specialty. Even so, it has become a lengthy appraisal due to the many years involved. In considering publications related to medical physics in radiation oncology, this review has shown the progression of the College journal to an international journal. There is an increase in the number of papers contributed from Asia and other countries world wide for this discipline. Growth in the number of contributions should continue to rise. In order to provide some appreciation of where the present medical physics activity arose from, this article commences its discussion in 1959 and progresses towards the present, describing along the way, from radiation oncology papers published in APESM, the use of linear accelerators, brachytherapy, the medical physics workforce, the formation of the ACPSEM, and the more modern developments in radiotherapy such as 3-D treatment planning and IMRT.

A comparative study of the work involved in measuring profiles using an ion chamber, a linear diode array and film.

In this work a method of using Kodak X-Omat V film to measure beam profiles for dynamically wedged fields is presented. Also, the profiles determined by film measurement are compared with those measured with an ion chamber (0.12 cm3 Scanditronix RFA 300 RK) and an array of silicon diodes (11 channel Scanditronix linear diode array). The beam investigated is a 6 MV photon beam from a Varian 2100 C linear accelerator. The geometric method of positioning film and determining the central axis (CAX) position of the beam yielded results which agreed to within 1 mm with the software determined position of the CAX. The profiles measured by film agreed well with the ion chamber measured profiles in terms of overall field size, position, penumbral width, height and position of maximum and profile shape between the 20% dose levels. Film profiles deviated most from ion chamber profiles in the post-penumbra regions. Linear diode array (LDA) measured profiles matched ion chamber profiles in the post-penumbra regions, field size and general profile shape. In the region of maximum dose differences in dose of up to 4% were seen along with horizontal shifts of around 2 mm between LDA and ion chamber profiles.

Disseminated Mycobacterium chelonei infection following cadaveric renal transplantation: favorable response to cefoxitin.

This article describes a case of disseminated Mycobacterium chelonei infection in a renal transplant recipient. This patient, who underwent thoracic duct drainage prior to cadaveric renal transplantation, developed M chelonei bacteremia and numerous subcutaneous nodules a few weeks after transplantation. The M chelonei initially responded to amikacin and tetracycline. Because of side effects and bacterial resistance, however, these drugs had to be discontinued. Subsequent treatment with cefoxitin led to reduction in size of subcutaneous nodules, but control of the infection was not achieved until an intravascular nidus of infection at the anastomotic site of an arteriovenous fistula was removed.