Biomedical subjects
Lesley Hughes
Publications and source records attributed to Lesley Hughes.
Salvage of suboptimal prostate seed implantation: Reimplantation of underdosed region of prostate base.
PURPOSE: To demonstrate how a suboptimal (125)I prostate implant can be salvaged by reimplantation. METHODS AND MATERIALS: A (125)I implant was preplanned to deliver 150 Gy to the prostate of a patient with early stage prostate cancer. A CT scan at 35 days postimplant indicated that V(100) and D(90) were 46% and 49 Gy, respectively. The cause was a systematic source placement error that left the base significantly underdosed. A reimplantation of the underdosed region was planned by superimposing a template grid onto the 35-day postimplant CT scan images and digitizing them into the treatment planning computer as if they were TRUS images. The reimplantation was carried out under fluoroscopy guidance so that the initial implant was visible. RESULTS: The reimplantation increased V(100) and D(90) to 98% and 201 Gy, respectively. The misplaced seeds resulted in a high dose to the apical region and urethra, which was further increased by the reimplantation. The patient experienced increased urinary morbidity, which was relieved by medication. CONCLUSION: It is feasible to salvage a suboptimal prostate seed implant by reimplanting the underdosed regions under fluoroscopy guidance based on a plan generated from the postimplant CT scan.
ASTRO's core physics curriculum for radiation oncology residents.
In 2002, the Radiation Physics Committee of the American Society of Therapeutic Radiology and Oncology (ASTRO) appointed an Ad-hoc Committee on Physics Teaching to Medical Residents. The main initiative of the committee was to develop a core curriculum for physics education. Prior publications that have analyzed physics teaching have pointed to wide discrepancies among teaching programs. The committee was composed of physicists or physicians from various residency program based institutions. Simultaneously, members had associations with the American Association of Physicists in Medicine (AAPM), ASTRO, Association of Residents in Radiation Oncology (ARRO), American Board of Radiology (ABR), and the American College of Radiology (ACR). The latter two organizations' representatives were on the physics examination committees, as one of the main agendas was to provide a feedback loop between the examining organizations and ASTRO. The document resulted in a recommended 54-h course. Some of the subjects were based on American College of Graduate Medical Education (ACGME) requirements (particles, hyperthermia), whereas the majority of the subjects along with the appropriated hours per subject were devised and agreed upon by the committee. For each subject there are learning objectives and for each hour there is a detailed outline of material to be covered. Some of the required subjects/h are being taught in most institutions (i.e., Radiation Measurement and Calibration for 4 h), whereas some may be new subjects (4 h of Imaging for Radiation Oncology). The curriculum was completed and approved by the ASTRO Board in late 2003 and is slated for dissemination to the community in 2004. It is our hope that teaching physicists will adopt the recommended curriculum for their classes, and simultaneously that the ABR for its written physics examination and the ACR for its training examination will use the recommended curriculum as the basis for subject matter and depth of understanding. To ensure that the subject matter and emphasis remain current and relevant, the curriculum will be updated every 2 years.
Mobile gene cassettes: a fundamental resource for bacterial evolution.
Horizontal gene transfer increases genetic diversity in prokaryotes to a degree not allowed by the limitations of reproduction by binary fission. The integron/gene cassette system is one of the most recently characterized examples of a system that facilitates horizontal gene transfer. This system, discovered in the context of multidrug resistance, is recognized in a clinical context for its role in allowing pathogens to adapt to the widespread use of antibiotics. Recent studies suggest that gene cassettes are common and encode functions relevant to many adaptive traits. To estimate the diversity of mobile cassettes in a natural environment, a molecular technique was developed to provide representative distributions of cassette populations at points within a sampling area. Subsequently, statistical methods analogous to those used for calculating species diversity were employed to assess the diversity of gene cassettes within the sample area in addition to gaining an estimate of cassette pool size. Results indicated that the number of cassettes within a 5x10-m sample area was large and that the overall mobile cassette metagenome was likely to be orders of magnitude larger again. Accordingly, gene cassettes appear to be capable of mobilizing a significant genetic resource and consequently have a substantial impact on bacterial adaptability.
Extinction risk from climate change.
Climate change over the past approximately 30 years has produced numerous shifts in the distributions and abundances of species and has been implicated in one species-level extinction. Using projections of species' distributions for future climate scenarios, we assess extinction risks for sample regions that cover some 20% of the Earth's terrestrial surface. Exploring three approaches in which the estimated probability of extinction shows a power-law relationship with geographical range size, we predict, on the basis of mid-range climate-warming scenarios for 2050, that 15-37% of species in our sample of regions and taxa will be 'committed to extinction'. When the average of the three methods and two dispersal scenarios is taken, minimal climate-warming scenarios produce lower projections of species committed to extinction ( approximately 18%) than mid-range ( approximately 24%) and maximum-change ( approximately 35%) scenarios. These estimates show the importance of rapid implementation of technologies to decrease greenhouse gas emissions and strategies for carbon sequestration.