Characterization of the public transit air microbiome and resistome reveals geographical specificity.

BACKGROUND: The public transit is a built environment with high occupant density across the globe, and identifying factors shaping public transit air microbiomes will help design strategies to minimize the transmission of pathogens. However, the majority of microbiome works dedicated to the public transit air are limited to amplicon sequencing, and our knowledge regarding the functional potentials and the repertoire of resistance genes (i.e. resistome) is limited. Furthermore, current air microbiome investigations on public transit systems are focused on single cities, and a multi-city assessment of the public transit air microbiome will allow a greater understanding of whether and how broad environmental, building, and anthropogenic factors shape the public transit air microbiome in an international scale. Therefore, in this study, the public transit air microbiomes and resistomes of six cities across three continents (Denver, Hong Kong, London, New York City, Oslo, Stockholm) were characterized. RESULTS: City was the sole factor associated with public transit air microbiome differences, with diverse taxa identified as drivers for geography-associated functional potentials, concomitant with geographical differences in species- and strain-level inferred growth profiles. Related bacterial strains differed among cities in genes encoding resistance, transposase, and other functions. Sourcetracking estimated that human skin, soil, and wastewater were major presumptive resistome sources of public transit air, and adjacent public transit surfaces may also be considered presumptive sources. Large proportions of detected resistance genes were co-located with mobile genetic elements including plasmids. Biosynthetic gene clusters and city-unique coding sequences were found in the metagenome-assembled genomes. CONCLUSIONS: Overall, geographical specificity transcends multiple aspects of the public transit air microbiome, and future efforts on a global scale are warranted to increase our understanding of factors shaping the microbiome of this unique built environment.

COMPARISON OF PERSONAL DOSE EQUIVALENT Hp(10) IN 137CS RADIATION BETWEEN THE PRIMARY STANDARDS LABORATORIES OF JAPAN AND AUSTRALIA USING BeO OSL PERSONAL DOSEMETERS.

A comparison of personal dose equivalent Hp(10) for 137Cs radiation was conducted between the primary standards laboratories of Japan and Australia. A set of 120 commercially available passive BeO OSL dosemeters were used (Dosimetrics GmbH, Munich). The aim was to investigate the precision which could be obtained with this technique, and to confirm the personal dose equivalent delivery methods in each standards laboratory. A dose of 5 mSv was delivered to 40 dosemeters in each country, and 40 dosemeters were used as controls. The result of the comparison was a ratio of Hp(10) in Japan to Australia of 1.006 with a combined standard uncertainty of 3.2%. The statistical uncertainty was 0.32% indicating that passive dosemeters can be used for comparisons of high precision.

Absorbed dose determination in kilovoltage X-ray synchrotron radiation using alanine dosimeters.

Alanine dosimeters from the National Physical Laboratory (NPL) in the UK were irradiated using kilovoltage synchrotron radiation at the imaging and medical beam line (IMBL) at the Australian Synchrotron. A 20 × 20 mm2 area was irradiated by scanning the phantom containing the alanine through the 1 mm × 20 mm beam at a constant velocity. The polychromatic beam had an average energy of 95 keV and nominal absorbed dose to water rate of 250 Gy/s. The absorbed dose to water in the solid water phantom was first determined using a PTW Model 31014 PinPoint ionization chamber traceable to a graphite calorimeter. The alanine was read out at NPL using correction factors determined for 60Co, traceable to NPL standards, and a published energy correction was applied to correct for the effect of the synchrotron beam quality. The ratio of the doses determined by alanine at NPL and those determined at the synchrotron was 0.975 (standard uncertainty 0.042) when alanine energy correction factors published by Waldeland et al. (Waldeland E, Hole E O, Sagstuen E and Malinen E, Med. Phys. 2010, 37, 3569) were used, and 0.996 (standard uncertainty 0.031) when factors by Anton et al. (Anton M, Büermann L., Phys Med Biol. 2015 60 6113-29) were used. The results provide additional verification of the IMBL dosimetry.

Comparison between the TRS-398 code of practice and the TG-51 dosimetry protocol for flattening filter free beams.

Dosimetry protocols for external beam radiotherapy currently in use, such as the IAEA TRS-398 and AAPM TG-51, were written for conventional linear accelerators. In these accelerators, a flattening filter is used to produce a beam which is uniform at water depths where the ionization chamber is used to measure the absorbed dose. Recently, clinical linacs have been implemented without the flattening filter, and published theoretical analysis suggested that with these beams a dosimetric error of order 0.6% could be expected for IAEA TRS-398, because the TPR20,10 beam quality index does not accurately predict the stopping power ratio (water to air) for the softer flattening-filter-free (FFF) beam spectra. We measured doses on eleven FFF linacs at 6 MV and 10 MV using both dosimetry protocols and found average differences of 0.2% or less. The expected shift due to stopping powers was not observed. We present Monte Carlo k Q calculations which show a much smaller difference between FFF and flattened beams than originally predicted. These results are explained by the inclusion of the added backscatter plates and build-up filters used in modern clinical FFF linacs, compared to a Monte Carlo model of an FFF linac in which the flattening filter is removed and no additional build-up or backscatter plate is added.

Absolute dosimetry on a dynamically scanned sample for synchrotron radiotherapy using graphite calorimetry and ionization chambers.

The absolute dose delivered to a dynamically scanned sample in the Imaging and Medical Beamline (IMBL) on the Australian Synchrotron was measured with a graphite calorimeter anticipated to be established as a primary standard for synchrotron dosimetry. The calorimetry was compared to measurements using a free-air chamber (FAC), a PTW 31 014 Pinpoint ionization chamber, and a PTW 34 001 Roos ionization chamber. The IMBL beam height is limited to approximately 2 mm. To produce clinically useful beams of a few centimetres the beam must be scanned in the vertical direction. In practice it is the patient/detector that is scanned and the scanning velocity defines the dose that is delivered. The calorimeter, FAC, and Roos chamber measure the dose area product which is then converted to central axis dose with the scanned beam area derived from Monte Carlo (MC) simulations and film measurements. The Pinpoint chamber measures the central axis dose directly and does not require beam area measurements. The calorimeter and FAC measure dose from first principles. The calorimetry requires conversion of the measured absorbed dose to graphite to absorbed dose to water using MC calculations with the EGSnrc code. Air kerma measurements from the free air chamber were converted to absorbed dose to water using the AAPM TG-61 protocol. The two ionization chambers are secondary standards requiring calibration with kilovoltage x-ray tubes. The Roos and Pinpoint chambers were calibrated against the Australian primary standard for air kerma at the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Agreement of order 2% or better was obtained between the calorimetry and ionization chambers. The FAC measured a dose 3-5% higher than the calorimetry, within the stated uncertainties.

High spatial resolution dosimetric response maps for radiotherapy ionization chambers measured using kilovoltage synchrotron radiation.

Small circular beams of synchrotron radiation (0.1 mm and 0.4 mm in diameter) were used to irradiate ionization chambers of the types commonly used in radiotherapy. By scanning the chamber through the beam and measuring the ionization current, a spatial map of the dosimetric response of the chamber was recorded. The technique is able to distinguish contributions to the large-field ionization current from the chamber walls, central electrode and chamber stem. Scans were recorded for the NE 2571 Farmer chamber, the PTW 30013, IBA FC65-G Farmer-type chambers, the NE 2611A and IBA CC13 thimble chambers, the PTW 31006 and 31014 pinpoint chambers, the PTW Roos and Advanced Markus plane-parallel chambers, and the PTW 23342 thin-window soft x-ray chamber. In all cases, large contributions to the response arise from areas where the incident beam grazes the cavity surfaces. Quantitative as well as qualitative information about the relative chamber response was extracted from the maps, including the relative contribution of the central electrode. Line scans using monochromatic beams show the effect of the photon energy on the chamber response. For Farmer-type chambers, a simple Monte Carlo model was in good agreement with the measured response.

Comparison of the NMIJ and the ARPANSA standards for absorbed dose to water in high-energy photon beams.

The authors report the results of an indirect comparison of the standards of absorbed dose to water in high-energy photon beams from a clinical linac and (60)Co radiation beam performed between the National Metrology Institute of Japan (NMIJ) and the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Three ionisation chambers were calibrated by the NMIJ in April and June 2013 and by the ARPANSA in May 2013. The average ratios of the calibration coefficients for the three ionisation chambers obtained by the NMIJ to those obtained by the ARPANSA were 0.9994, 1.0040 and 1.0045 for 6-, 10- and 15-MV (18 MV at the ARPANSA) high-energy photon beams, respectively. The relative standard uncertainty of the value was 7.2 × 10(-3). The ratio for (60)Co radiation was 0.9986(66), which is consistent with the results published in the key comparison of BIPM.RI(I)-K4.

Direct megavoltage photon calibration service in Australia.

The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) maintains the Australian primary standard of absorbed dose. Until recently, the standard was used to calibrate ionisation chambers only in (60)Co gamma rays. These chambers are then used by radiotherapy clinics to determine linac output, using a correction factor (k Q) to take into account the different spectra of (60)Co and the linac. Over the period 2010-2013, ARPANSA adapted the primary standard to work in megavoltage linac beams, and has developed a calibration service at three photon beams (6, 10 and 18 MV) from an Elekta Synergy linac. We describe the details of the new calibration service, the method validation and the use of the new calibration factors with the International Atomic Energy Agency's TRS-398 dosimetry Code of Practice. The expected changes in absorbed dose measurements in the clinic when shifting from (60)Co to the direct calibration are determined. For a Farmer chamber (model 2571), the measured chamber calibration coefficient is expected to be reduced by 0.4, 1.0 and 1.1 % respectively for these three beams when compared to the factor derived from (60)Co. These results are in overall agreement with international absorbed dose standards and calculations by Muir and Rogers in 2010 of k Q factors using Monte Carlo techniques. The reasons for and against moving to the new service are discussed in the light of the requirements of clinical dosimetry.

Absolute x-ray dosimetry on a synchrotron medical beam line with a graphite calorimeter.

PURPOSE: The absolute dose rate of the Imaging and Medical Beamline (IMBL) on the Australian Synchrotron was measured with a graphite calorimeter. The calorimetry results were compared to measurements from the existing free-air chamber, to provide a robust determination of the absolute dose in the synchrotron beam and provide confidence in the first implementation of a graphite calorimeter on a synchrotron medical beam line. METHODS: The graphite calorimeter has a core which rises in temperature when irradiated by the beam. A collimated x-ray beam from the synchrotron with well-defined edges was used to partially irradiate the core. Two filtration sets were used, one corresponding to an average beam energy of about 80 keV, with dose rate about 50 Gy/s, and the second filtration set corresponding to average beam energy of 90 keV, with dose rate about 20 Gy/s. The temperature rise from this beam was measured by a calibrated thermistor embedded in the core which was then converted to absorbed dose to graphite by multiplying the rise in temperature by the specific heat capacity for graphite and the ratio of cross-sectional areas of the core and beam. Conversion of the measured absorbed dose to graphite to absorbed dose to water was achieved using Monte Carlo calculations with the EGSnrc code. The air kerma measurements from the free-air chamber were converted to absorbed dose to water using the AAPM TG-61 protocol. RESULTS: Absolute measurements of the IMBL dose rate were made using the graphite calorimeter and compared to measurements with the free-air chamber. The measurements were at three different depths in graphite and two different filtrations. The calorimetry measurements at depths in graphite show agreement within 1% with free-air chamber measurements, when converted to absorbed dose to water. The calorimetry at the surface and free-air chamber results show agreement of order 3% when converted to absorbed dose to water. The combined standard uncertainty is 3.9%. CONCLUSIONS: The good agreement of the graphite calorimeter and free-air chamber results indicates that both devices are performing as expected. Further investigations at higher dose rates than 50 Gy/s are planned. At higher dose rates, recombination effects for the free-air chamber are much higher and expected to lead to much larger uncertainties. Since the graphite calorimeter does not have problems associated with dose rate, it is an appropriate primary standard detector for the synchrotron IMBL x rays and is the more accurate dosimeter for the higher dose rates expected in radiotherapy applications.

Direct MC conversion of absorbed dose to graphite to absorbed dose to water for 60Co radiation.

The ARPANSA calibration service for (60)Co gamma rays is based on a primary standard graphite calorimeter that measures absorbed dose to graphite. Measurements with the calorimeter are converted to the absorbed dose to water using the calculation of the ratio of the absorbed dose in the calorimeter to the absorbed dose in a water phantom. ARPANSA has recently changed the basis of this calculation from a photon fluence scaling method to a direct Monte Carlo (MC) calculation. The MC conversion uses an EGSnrc model of the cobalt source that has been validated against water tank and graphite phantom measurements, a step that is required to quantify uncertainties in the underlying interaction coefficients in the MC code. A comparison with the Bureau International des Poids et Mesures (BIPM) as part of the key comparison BIPM.RI(I)-K4 showed an agreement of 0.9973 (53).

Spectral differences in 6 MV beams with matched PDDs and the effect on chamber response.

The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) has installed an Elekta Synergy platform linac to establish a direct megavoltage primary standard calibration service, instead of relying on calibrations derived from (60)Co. One of the 6 MV beams of the ARPANSA linac has been approximately matched to the Varian high energy platform 6 MV photon beam. The electron beam energy was adjusted to match the percentage depth dose (PDD) curve and TPR(20,10). This work calculates the error introduced when using a calibration factor from this Elekta Synergy Platform linac on a Varian high-energy platform beam at 6 MV. Monte Carlo models of the Varian and matched Elekta accelerator accurately predict the measured PDDs and profiles, but show significantly different energy spectra, resulting mainly from differences in target thickness between the two accelerators. Monte Carlo modelling of the energy correction factor k(Q) of a secondary standard NE2561 chamber shows a difference of 0.4% between the Varian and the Varian-matched Elekta beams. Although small, this is a significant discrepancy for primary standard calibrations. Similar variations are expected for chambers of similar construction, and additional variations may occur with other linac manufacturers. The work has also investigated the design of a custom flattening filter to precisely match the energy spectrum of the Varian beam on the Elekta platform.

The Australian radiation protection and nuclear safety agency megavoltage photon thermoluminescence dosimetry postal audit service 2007-2010.

The Australian radiation protection and nuclear safety agency (ARPANSA) has continuously provided a level 1 mailed thermoluminescence dosimetry audit service for megavoltage photons since 2007. The purpose of the audit is to provide an independent verification of the reference dose output of a radiotherapy linear accelerator in a clinical environment. Photon beam quality measurements can also be made as part of the audit in addition to the output measurements. The results of all audits performed between 2007 and 2010 are presented. The average of all reference beam output measurements calculated as a clinically stated dose divided by an ARPANSA measured dose is 0.9993. The results of all beam quality measurements calculated as a clinically stated quality divided by an ARPANSA measured quality is 1.0087. Since 2011 the provision of all auditing services has been transferred from the Ionizing Radiation Standards section to the Australian Clinical Dosimetry Service (ACDS) which is currently housed within ARPANSA.

Enhanced epidermal dose caused by localized electron contamination from lead cutouts used in kilovoltage radiotherapy.

PURPOSE: To investigate and quantify electron contamination from the lead cutouts used in kilovoltage x-ray radiotherapy. METHODS: The lead cutouts were modeled with the Monte Carlo EGSnrc user codes DOSXYZnrc and DOSRZnrc for x-ray beams ranging from 50 to 300 kVp. The results from the model were confirmed with Gafchromic film measurements. The model and measurements investigated the dose distribution with and without gladwrap shielding under the lead, and dose distributions with round, square, and serrated edge cutouts. RESULTS: Large dose enhancement near the edges of the lead was observed due to electron contamination. At the epidermal/dermal border, there is double the dose at the edge of the lead compared to the central dose due to electron contamination for a 150 kVp beam and three times the dose for a 300 kVp beam. gladwrapTM shielding effectively removes the contaminant dose enhancement using ten and four layers for 300 and 150 kVp beams, respectively. CONCLUSIONS: The contaminant dose enhancement is undesirable as it could cause unnecessary erythema and hyperpigmentation at the border of the treated and untreated skin and lead to a poorer cosmetic outcome. The contamination is easily removed by gladwrap shielding placed under or around the lead cutout.

Shift in absorbed dose for megavoltage photons when changing to TRS-398 in Australia.

Australian primary standards of air kerma and absorbed dose are realized in 60Co gamma rays. To calibrate the megavoltage photon beams from linear accelerators, radiotherapy centres have their ionization chamber calibrated in a 60Co beam and then use a protocol to transfer this calibration to the higher energy. The radiotherapy community is in the process of changing from the ACPSEM Protocol (Second Edition 1998) based on an air kerma calibration to the IAEA's TRS-398 Code of Practice, based on an absorbed dose to water calibration. To evaluate the shift in absorbed dose resulting from the new protocol, the absorbed dose should be determined using both protocols and compared. We present a formula for this shift which can be used to check the result. To use this formula the centre needs to measure a displacement correction and know the ratio of the air kerma to absorbed dose to water calibration factors at 60Co. We calculate the change they should expect by using the average ratio of the air kerma and absorbed dose to water calibration factors for NE2571 and NE2561 chambers, based on Australian standards, and by estimating the displacement correction from published depth dose data. We find the absorbed dose in a megavoltage photon beam to increase by between 0.1 and 0.6% for NE2571 chambers and between 0.7 and 1.1% for NE2561 chambers, for beams up to 35 MV. The dose measured using TRS-398 is always higher.

Conference formats in family practice residencies.

BACKGROUND: This study was intended to establish national baseline data of the current structure of conferences at family practice residencies and to determine if there are differences in conference formats among types of residencies. METHODS: An author-developed survey was mailed to 331 programs stratified by type and randomly selected. Statistical analysis included chi-square tests and non-parametric tests. RESULTS: The response rate was 84%. The average time devoted to lectures was 4.5 hours a week, with the noon hour the most common time. Most speakers were from within the program, and community-based family physicians were rarely present. Structural changes were frequent. CONCLUSIONS: Results indicate that a variety of formats are implemented for meeting Residency Review Committee requirements in the structure of family practice residencies' conferences. Program settings do influence how conferences are structured. More research is needed on this neglected area of formal resident education.

Photometric observations of a polychromatic laser guide star.

We report the photometric observation of a polychromatic laser guide star (PLGS) using the AVLIS laser at the Lawrence Livermore National Laboratory (LLNL). The process aims at providing a measurement of the tilt of the incoming wave front at a telescope induced by atmospheric turbulence. It relies on the two-photon coherent excitation of the 4D5/2 energy level of sodium atoms in the mesosphere. We used two laser beams at 589 and 569 nm, with a maximum total average output power of approximately 350 W. For the purpose of photometric calibration, a natural star was observed simultaneously through the same instrument as the PLGS at the focus of the LLNL 50-cm telescope. Photometric measurements of the 330-nm return flux confirm our previous theoretical studies that the PLGS process should allow us at a later stage to correct for the tilt at wavelengths as short as approximately 1 microm at good astronomical sites. They show also that, at saturation of two-photon coherent absorption in the mesosphere, the backscattered flux increases by a factor of approximately 2 when the pulse repetition rate decreases by a factor of 3 at constant average power. This unexpected behavior is briefly discussed.

Post-traumatic stress reactions following motor vehicle accidents.

Despite improvements in road conditions, vehicle safety and driver education, over 3 million persons are injured in motor vehicle accidents each year. Many of these persons develop post-traumatic stress symptoms that can become chronic. Patients with post-traumatic stress disorder experience disabling memories and anxiety related to the traumatic event. Early identification of these patients is critical to allow for intervention and prevent greater impairment and restriction. The family physician is in an ideal position to identify, treat or refer patients with traumatic responses to traffic accidents. The physician's awareness of patient characteristics and pre-accident functioning allows him or her to critically evaluate symptoms that may begin to interfere with the resumption of daily activities.

Predicting resident confidence to lead family meetings.

BACKGROUND AND OBJECTIVES: Family physicians frequently encounter patients' family members in family meetings regarding health care. Although residents are expected to learn how to interview families, no quantitative studies have examined variables associated with building residents' confidence in their ability to lead family meetings. The current study sought to clarify the relationship between a number of training, participant, and situational components and resident confidence. METHODS: All family practice residents (n = 90) in a five-residency program system were sent a survey that examined their experience in and perceived competence to conduct family meetings. Responses were analyzed with a hierarchical regression analysis and an ex post facto univariate analysis. RESULTS: Residents with higher perceived confidence in their ability to run a family meeting were male, had specific training for leading family meetings, had participated in and initiated more family meetings, perceived stronger family physician faculty support, and had more family systems training than lower-confidence residents. CONCLUSIONS: The results highlight the experiential, curricular, and environmental variables that are associated with building resident confidence to lead family meetings. Residents may benefit from early exposure to the skills needed for family meetings and from reinforcement of these skills through observations of skilled practitioners, the expectation that they will initiate meetings, and the opportunity to debrief meetings with supportive faculty. Family meeting curricula should include conflict management skills and incorporate input from other specialists and hospital personnel who meet with families.

Fiber-diameter measurement by occlusion of a gaussian beam.

The amount of light occluded by a fiber as it passes through alaser beam can be used as the basis for fiber-diametermeasurement. This technique is analyzed with a two-dimensionalrigorous model. The occlusion seen for dielectric fibers as afunction of their diameter is highly oscillatory owing to interferencebetween the light transmitted by the fiber and the rest of thediffracted field. Scalar diffraction theory is shown to be adequatein modeling this effect. The oscillation sets a limit to theaccuracy of simple diameter measurement systems and is confirmedexperimentally for glass fibers. However, wool fibers are found tobe better treated as an absorbing material. The effect of beampolarization is investigated and found to be negligible for dielectricfibers but significant for metal fibers of small diameter.