In Response: "Oral versus IV treatment for catheter-related bloodstream infections - by Burke A. Cunha"

In his letter Cunha suggests that oral antibiotic therapy is safer and less expensive than intravenous therapy via central venous catheters (CVCs) (1). The implication is that costs will fall and increased health benefits will be enjoyed resulting in a gain in efficiency within the healthcare system. CVCs are often used in critically ill patients to deliver antimicrobial therapy, but expose patients to a risk of catheter-related bloodstream infection (CRBSI). Our current knowledge about the efficiency (i.e. costeffectiveness) of allocating resources toward interventions that prevent CRBSI in patients requiring a CVC has already been reviewed (2). If for some patient groups antimicrobial therapy can be delivered orally, instead of through a CVC, then the costs and benefits of this alternate strategy should be evaluated...

Sensitivity of an Elekta iView GT a-Si EPID model to delivery errors for pre-treatment verification of IMRT fields

A Monte Carlo model of an Elekta iViewGT amorphous silicon electronic portal imaging device (a-Si EPID) has been validated for pre-treatment verification of clinical IMRT treatment plans. The simulations involved the use of the BEAMnrc and DOSXYZnrc Monte Carlo codes to predict the response of the iViewGT a-Si EPID model. The predicted EPID images were compared to the measured images obtained from the experiment. The measured EPID images were obtained by delivering a photon beam from an Elekta Synergy linac to the Elekta iViewGT a-Si EPID. The a-Si EPID was used with no additional build-up material. Frame averaged EPID images were acquired and processed using in-house software. The agreement between the predicted and measured images was analyzed using the gamma analysis technique with acceptance criteria of 3% / 3 mm. The results show that the predicted EPID images for four clinical IMRT treatment plans have a good agreement with the measured EPID signal. Three prostate IMRT plans were found to have an average gamma pass rate of more than 95.0 % and a spinal IMRT plan has the average gamma pass rate of 94.3 %. During the period of performing this work a routine MLC calibration was performed and one of the IMRT treatments re-measured with the EPID. A change in the gamma pass rate for one field was observed. This was the motivation for a series of experiments to investigate the sensitivity of the method by introducing delivery errors, MLC position and dosimetric overshoot, into the simulated EPID images. The method was found to be sensitive to 1 mm leaf position errors and 10% overshoot errors.

Fracture load for short versus standard cemented hip stems : an experimental in vitro study

Introduction: In an attempt to reduce stress shielding in the proximal femur multiple new shorter stem design have become available. We investigated the load to fracture of a new polished tapered cemented short stem in comparison to the conventional polished tapered Exeter stem. Method: A total of forty-two stems, twenty-one short stems and twenty-one conventional stems both with three different offsets were cemented in a composite sawbone model and loaded to fracture. Results: study showed that femurs will break at a significantly lower load to failure with a shorter compared to conventional length Exeter stem. Conclusion: This Both standard and short stem design are safe to use as the torque to failure is 7–10 times as much as the torques seen in activities of daily living.

Doctors' knowledge of the law on withholding and withdrawing life-sustaining medical treatment

Objectives To examine the level of knowledge of doctors about the law on withholding and withdrawing life-sustaining treatment from adults who lack decision-making capacity, and factors associated with a higher level of knowledge. Design, setting and participants Postal survey of all specialists in emergency medicine, geriatric medicine, intensive care, medical oncology, palliative medicine, renal medicine and respiratory medicine on the AMPCo Direct database in New South Wales, Victoria and Queensland. Survey initially posted to participants on 18 July 2012 and closed on 31 January 2013. Main outcome measures Medical specialists’ levels of knowledge about the law, based on their responses to two survey questions. Results Overall response rate was 32%. For the seven statements contained in the two questions about the law, the mean knowledge score was 3.26 out of 7. State and specialty were the strongest predictors of legal knowledge. Conclusions Among doctors who practise in the end-of-life field, there are some significant knowledge gaps about the law on withholding and withdrawing life-sustaining treatment from adults who lack decision-making capacity. Significant consequences for both patients and doctors can flow from a failure to comply with the law. Steps should be taken to improve doctors’ legal knowledge in this area and to harmonise the law across Australia.

The use of penumbrae to define and analyse non-standard fields

Aim A new method of penumbral analysis is implemented which allows an unambiguous determination of field size and penumbra size and quality for small fields and other non-standard fields. Both source occlusion and lateral electronic disequilibrium will affect the size and shape of cross-axis profile penumbrae; each is examined in detail. Method A new method of penumbral analysis is implemented where the square of the derivative of the cross-axis profile is plotted. The resultant graph displays two peaks in the place of the two penumbrae. This allows a strong visualisation of the quality of a field penumbra, as well as a mathematically consistent method of determining field size (distance between the two peak’s maxima), and penumbra (full-widthtenth-maximum of peak). Cross-axis profiles were simulated in a water phantom at a depth of 5 cm using Monte Carlo modelling, for field sizes between 5 and 30 mm. The field size and penumbra size of each field was calculated using the method above, as well as traditional definitions set out in IEC976. The effect of source occlusion and lateral electronic disequilibrium on the penumbrae was isolated by repeating the simulations removing electron transport and using an electron spot size of 0 mm, respectively. Results All field sizes calculated using the traditional and proposed methods agreed within 0.2 mm. The penumbra size measured using the proposed method was systematically 1.8 mm larger than the traditional method at all field sizes. The size of the source had a larger effect on the size of the penumbra than did lateral electronic disequilibrium, particularly at very small field sizes. Conclusion Traditional methods of calculating field size and penumbra are proved to be mathematically adequate for small fields. However, the field size definition proposed in this study would be more robust amongst other nonstandard fields, such as flattening filter free. Source occlusion plays a bigger role than lateral electronic disequilibrium in small field penumbra size.

The automation of radiotherapy treatment planning assessment

Aim The assessment of treatment plans is an important component in the education of radiation therapists. The establishment of a grade for a plan is currently based on subjective assessment of a range of criteria. The automation of assessment could provide a number of advantages including faster feedback, reduced chance of human error, and simpler aggregation of past results. Method A collection of treatments planned by a cohort of 27 second year radiation therapy students were selected for quantitative evaluation. Treatment sites included the bladder, cervix, larynx, parotid and prostate, although only the larynx plans had been assessed in detail. The plans were designed with the Pinnacle system and exported using the DICOM framework. Assessment criteria included beam arrangement optimisation, volume contouring, target dose coverage and homogeneity, and organ-at-risk sparing. The in-house Treatment and Dose Assessor (TADA) software1 was evaluated for suitability in assisting with the quantitative assessment of these plans. Dose volume data were exported in per-student and per-structure data tables, along with beam complexity metrics, dose volume histograms, and reports on naming conventions. Results The treatment plans were exported and processed using TADA, with the processing of all 27 plans for each treatment site taking less than two minutes. Naming conventions were successfully checked against a reference protocol. Significant variations between student plans were found. Correlation with assessment feedback was established for the larynx plans. Conclusion The data generated could be used to inform the selection of future assessment criteria, monitor student development, and provide useful feedback to the students. The provision of objective, quantitative evaluations of plan quality would be a valuable addition to not only radiotherapy education programmes but also for staff development and potentially credentialing methods. New functionality within TADA developed for this work could be applied clinically to, for example, evaluate protocol compliance.