A Monte Carlo study of organ and effective doses of cone beam computed tomography (CBCT) scans in radiotherapy

Cone-beam CT (CBCT) scans utilized for image guided radiation therapy (IGRT) procedures have become an essential part of radiotherapy. The aim of this study was to assess organ and effective doses resulting from new CBCT scan protocols (head, thorax, and pelvis) released with a software upgrade of the kV on-board-imager (OBI) system. Influence of the scan parameters that were changed in the new protocols on the patient dose was also investigated. Organ and effective doses for protocols of the new software (V2.5) and a previous version (V1.6) were assessed using Monte Carlo (MC) simulations for the International Commission on Radiological Protection (ICRP) adult male and female reference computational phantoms. The number of projections and the mAs values were increased and the size of the scan field was extended in the new protocols. Influence of these changes on organ and effective doses of the scans was investigated. The OBI system was modelled in EGSnrc/BEAMnrc, and organ doses were estimated using EGSnrc/DOSXYZnrc. The MC model was benchmarked against experimental measurements. Organ doses resulting from the V2.5 protocols were higher than those of V1.6 for organs that were partially or fully inside the scans fields, and increased by (3 to 13)%, (10 to 77)%, and (13 to 21)% for the head, thorax, and pelvis protocols for both phantoms, respectively. As a result, effective doses rose by 14%, 17%, and 16% for the male phantom, and 13%, 18%, and 17% for the female phantom for the three scan protocols, respectively. The scan field extension for the V2.5 protocols contributed significantly in the dose increases, especially for organs that were partially irradiated such as the thyroid in head and thorax scans and colon in the pelvic scan. The contribution of the mAs values and projection numbers was minimal in the dose increases, up to 2.5%. The field size extension plays a major role in improving the treatment output by including more markers in the field of view to match between CBCT and CT images and hence setting up the patient precisely. Therefore, a trade-off between the risk and benefits of CBCT scans should be considered, and the dose increases should be monitored. Several recommendations have been made for optimization of the patient dose involved for IGRT procedures

Protecting interventional radiology and cardiology staff: Are current designs of lead glasses and eye dosemeters fit for purpose?

No abstract available

Diagnostic reference levels and optimization in radiology: where do we go from here?

No abstract available

Evaluation of coefficients to derive organ and effective doses from cone-beam CT (CBCT) scans: a Monte Carlo study

Regular imaging is used throughout image guided radiation therapy (IGRT) to improve treatment delivery. In order for treatment procedures to be optimized, the doses delivered by imaging exposures should be taken into account. CT dosimetry methods based on the CT dose index (CTDI), measured with a 100 mm long pencil ionization chamber (CTDI<sub>100</sub>) in standard phantoms, are not designed for the cone beam CT (CBCT) imaging systems used in radiotherapy, therefore a modified version has been proposed for CBCT by the International Electrotechnical Commission (CTDI<sub>IEC</sub>). Monte Carlo simulations based on a Varian On Board Imaging (OBI) system have been used to derive conversion coefficients that enable organ doses for ICRP reference phantoms to be determined from the CTDI<sub>IEC</sub> for different scan protocols and different beam widths (80 - 320) mm. A dose-width product calculated by multiplying the CTDI<sub>IEC</sub> by the width of the CBCT beam is proposed as a quantity that can be used for estimating effective dose. The variation in coefficients with CBCT beam width has been studied. Coefficients to allow estimation of effective doses have been derived, namely 0.0034 mSv(mGy cm)<sup>-1</sup> for the head, 0.0252 mSv(mGy cm)<sup>-1</sup> for the thorax, 0.0216 mSv(mGy cm)<sup>-1</sup> for the abdomen and 0.0150 mSv(mGy cm)<sup>-1</sup> for the pelvis, and these may be applicable more generally to other CBCT systems in radiotherapy. If data on effective doses are available, these can be used in making judgements on the contributions to patient dose from imaging, and thereby assist in optimization of the treatment regimes. The coefficients can also be employed in converting dosimetry data recorded in patient records into quantities relating directly to patient doses

University Student-Athletes’ Experiences of Facilitators and Barriers to Contribution: A Narrative Account

University student-athletes’ contributions in the form of volunteering, community engagement, and civic engagement have been the subject of recent research; however, no studies have specifically examined the factors that facilitate or serve as barriers to contribution in this population. As such, the purpose of this study is to explore the facilitators and barriers relating to university student-athletes’ contributions. Individual semi-structured interviews were conducted with eight university student-athletes (two males, six females) between 18 and 21 years of age (M = 19.25) from two Canadian universities. The analysis led to the identification of two qualitatively distinct profiles regarding how facilitators and barriers to contributions were experienced: (a) the first-year student-athletes and (b) the sustained contributors. Although the participants in each profile identified teammates, coaches, and athletics department staff as facilitators to contribution, they differed in their interpretation of how these individuals facilitated contributions. First-year student-athletes were more reliant than sustained contributors on having facilitators create contribution opportunities. The profiles also differed in regards to how time constraints were overcome. First-year student-athletes utilized less complex, individual time-management strategies, while sustained contributors collaboratively made use of more advanced time-management strategies to optimize their time

Effects of stage of lactation and time of year on plasmin-derived proteolytic activity in bovine milk in New Zealand

The objective of this study was to determine the effects of stage of lactation (SOL) and time of year on plasmin-derived proteolytic activity in the milk of pasture-fed dairy cows in New Zealand. Four herds of 20 Friesian cows were used, one herd calving in each of January, April, July and October. Cows grazed ryegrass/white clover pasture only, except during June (winter) when all cows received supplementary pasture silage. Milk samples were collected on four occasions during the year (spring, summer, autumn and winter) from each cow in milk, to give a total of three samples per cow (early, mid and late lactation; c. 30, 120 and 220 days after calving, respectively). Milk samples were analysed for plasmin-derived proteolytic activity. There was no effect of either SOL or time of year on plasmin activity and therefore yields of plasmin followed patterns in milk yield (highest in early lactation and in summer). There were effects of both SOL and time of year on plasminogen-derived and total plasmin plus plasminogen-derived activity, both of which were highest in late lactation and in spring. Changes in plasminogen-derived activity and total plasmin plus plasminogen-derived activity due to SOL were not only due to the decrease in milk yield associated with advancing lactation, because enzyme yields were also increased with advancing lactation. Similarly, effects of time of year on plasminogen-derived activity and total plasmin plus plasminogen-derived activity could not be attributed solely to concomitant changes in milk yield, and may be influenced by the variation in the quality and quantity of feed during the year inherent in a pasture-based dairy system. Effects of SOL on proteolytic activity were greater than, and independent of, effects of time of year

Anthropocene: its stratigraphic basis

As officers of the Anthropocene Working Group (AWG; J.Z. and C.W.) and chair of the Subcommission on Quaternary Stratigraphy (SQS; M.J.H.) of the International Commission on Stratigraphy (ICS), we note that the AWG has less power than Erle Ellis and colleagues imply (Nature 540, 192–193; 2016). Its role is merely advisory — to evaluate the Anthropocene as a formal unit in the geological timescale. Proposals must pass scrutiny by the AWG, the SQS and the ICS before being ratified by the Executive Committee of the International Union of Geological Sciences