Evaluating very high energy electron RBE from nanodosimetric pBR322 plasmid DNA damage

This paper presents the first plasmid DNA irradiations carried out with Very High Energy Electrons (VHEE) over 100-200 MeV at the CLEAR user facility at CERN to determine the Relative Biological Effectiveness (RBE) of VHEE. DNA damage yields were measured in dry and aqueous environments to determine that ~ 99% of total DNA breaks were caused by indirect effects, consistent with other published measurements for protons and photons. Double-Strand Break (DSB) yield was used as the biological endpoint for RBE calculation, with values found to be consistent with established radiotherapy modalities. Similarities in physical damage between VHEE and conventional modalities gives confidence that biological effects of VHEE will also be similar-key for clinical implementation. Damage yields were used as a baseline for track structure simulations of VHEE plasmid irradiation using GEANT4-DNA. Current models for DSB yield have shown reasonable agreement with experimental values. The growing interest in FLASH radiotherapy motivated a study into DSB yield variation with dose rate following VHEE irradiation. No significant variations were observed between conventional and FLASH dose rate irradiations, indicating that no FLASH effect is seen under these conditions.

Experimental verification the electron return effect around spherical air cavities for the MR-Linac using Monte Carlo calculation

PURPOSE

Dose deposition around unplanned air cavities during magnetic resonance-guided radiotherapy (MRgRT) is influenced by the electron return effect (ERE). This is clinically relevant for gas forming close to or inside organs at risk (OARs) that lie in the path of a single beam, for example, intestinal track during pelvic treatment. This work aims to verify Monte Carlo calculations that predict the dosimetric effects of ERE around air cavities. For this, we use GafChromic EBT3 film inside poly-methyl methacrylate (PMMA) -air phantoms.

METHOD

Four PMMA phantoms were produced. Three of the phantoms contained centrally located spherical air cavities (0.5, 3.5, 7.5 cm diameter), and one phantom contained no air. The phantoms were split to sandwich GafChromic EBT3 film in the center. The phantoms were irradiated on an Elekta Unity system using a single 10 × 10 cm2 7-MV photon beam under the influence of a 1.5-T transverse magnetic field. The measurements were replicated using the Elekta Monaco treatment planning system (TPS). Gamma analysis with pass criteria 3%/3 mm was used to compare the measured and calculated dose distributions. We also consider 3%/2 mm, 2%/3 mm, and 2%/2 mm pass criteria for interest.

RESULTS

The gamma analysis showed that >95% of the points agreed between the TPS-calculated and measured dose distributions, using 3%/3 mm criteria. The phantom containing the largest air cavity had the lowest agreement, with most of the disagreeing points lying inside the air cavity (dose to air region).

CONCLUSIONS

The dose effects due to ERE around spherical air cavities are being calculated in the TPS with sufficient accuracy for clinical use.

Survey of intrathecal opioid usage in the UK

BACKGROUND AND OBJECTIVE

Intrathecal opioids are now used routinely in the UK for intra- and postoperative analgesia. The opioids of choice have altered over recent years and the dosage regimens used can vary between institutions. Concerns over safety have been reduced probably because much lower doses of opioids are now being used. This survey explored the practice of intrathecal opioid usage in the UK.

METHODS

We sent a questionnaire survey to 270 anaesthetic departments and received 199 replies, a response rate of 73.7%.

RESULTS

Intrathecal opioids were used in 175 (88.4%) departments. Of these departments, 107 (61.1%) had local guidelines or protocols in place. Opioids such as diamorphine (used in 136 (78.2%) of departments) and fentanyl (129 (74.1%)) with a shorter duration of action are now more commonly used than morphine (37 (21.3%)) for intrathecal analgesia. In 96 (54.5%) departments, patients were nursed on regular surgical wards following administration of spinal opioids.

CONCLUSIONS

The use of low-dose lipophilic intrathecal opioids for postoperative analgesia is widespread in the UK. Patients are commonly nursed in low-dependency post-anaesthetic care areas. The low incidence of adverse events reported by the respondents along with the popularity of the technique suggests that low-dose spinal opioid administration is safe.

Anaesthesiologists' views on the need for point-of-care information system in the operating room: a survey of the European Society of Anaesthesiologists

BACKGROUND AND OBJECTIVE

In this preliminary study we wanted to explore the attitudes of anaesthesiologists to a point-of-care information system in the operating room. The study was conducted as a preliminary step in the process of developing such a system by the European Society of Anaesthesiologists (ESA).

METHODS

A questionnaire was distributed to all 2240 attendees of the ESA's annual meeting in Gothenburg, Sweden, which took place in April 2001.

RESULTS

Of the 329 responders (response rate of 14.6%), 79% were qualified specialists with more than 10 yr of experience (68%), mostly from Western Europe. Most responders admitted to regularly experiencing lack of medical knowledge relating to real-time patient care at least once a month (74%) or at least once a week (46%), and 39% admitted to having made errors during anaesthesia due to lack of medical information that can be otherwise found in a handbook. The choice ofa less optimal but more familiar approach to patient management due to lack of knowledge was reported by 37%. Eighty-eight percent of responders believe that having a point-of-care information system for the anaesthesiologists in the operating room is either important or very important.

CONCLUSIONS

This preliminary survey demonstrates that lack of knowledge of anaesthesiologists may be a significant source of medical errors in the operating room, and suggests that a point-of-care information system for the anaesthesiologist may be of value.

Remifentanil sedation compared with propofol during regional anaesthesia

BACKGROUND

The short onset and offset of remifentanil may allow for accurate dosing of sedative effect with few side-effects and rapid recovery. In this study remifentanil is compared with propofol for sedation during successful regional anaesthetic blocks.

METHODS

After informed consent was given, 125 patients undergoing surgery under spinal or brachial plexus anaesthesia were randomized to receive, either propofol: bolus 500 microg/kg plus initial infusion 50 microgkg/min or remifentanil: bolus 0.5 microg/kg plus initial infusion 0.1 microgkg/min. Study drug infusion rate was titrated throughout the procedure according to level of sedation and side-effects. Pain, discomfort, sedation level and side-effects were recorded at regular intervals until discharge from the post operative care unit (PACU).

RESULTS

Two patients in the remifentanil group versus ten in the propofol group were treated for discomfort or pain during surgery (P<0.02). Due to a significantly higher rate of respiratory depression (46% vs. 19% with propofol, P<0.01) the mean remifentanil infusion rate was decreased to 0.078 +/- 0.028 microgkg/min, whereas it was kept stable with propofol. Propofol patients had significantly higher (P<0.05) sedation levels and experienced more frequent amnesia of the procedure. Eleven propofol patients experienced pain at injection site, versus two remifentanil patients (P<0.02). Nausea and vomiting were more frequent in the remifentanil patients during infusion (27% vs. 2% in the propofol group, P<0.001) but similar postoperatively. Time to discharge from PACU was similar in the two groups.

CONCLUSION

Propofol results in less respiratory depression and nausea when sedation is needed during a case with a successful regional block. Remifentanil may be considered as an alternative if pain during the procedure is a major concern or if amnesia is contraindicated.

Effects of the thalamus on the development of cerebral cortical efferents in vitro

The cerebral cortex is a multilayered tissue, with each layer differing in its cellular composition and connections. Axons from deep layer neurons project subcortically, many to the thalamus, whereas superficial layer neurons target other cortical areas. The mechanisms that regulate the development of this pattern of connections are not fully understood. Our experiments examined the potential of the thalamus to attract and/or select neurites from appropriate cortical layers. First, we cocultured murine cortical slices in close proximity to thalamic explants in collagen gels. The amount of neurite outgrowth from deep layer cells was enhanced by, but not attracted to, the thalamic explants. Second, we cocultured cortical slices in contact with thalamic or cortical explants to test for laminar specificity of connections. Specificity was apparent after culture for about a week, in that deep cortical layers contained the highest proportions of corticothalamic cells and superficial cortical layers contained the highest proportions of corticocortical cells. After shorter culture of only a few days, however, specificity was not apparent and there were larger numbers of corticothalamic projections from the superficial layers than after a week. To study how the early nonspecific pattern of corticothalamic connections was transformed into the more specific pattern, we labeled corticothalamic cells early, after 2 days, but let the cultures survive for 8 days. On day 8, the nonspecific pattern of early-labeled cells was still seen. We conclude that although the thalamus does not block the initial entry of inappropriate axons from the superficial layers, many of these axons are subsequently lost. This suggests that contact-mediated interactions between cortical axons and the thalamus allow cortical efferents from appropriate layers to be distinguished from those arising in inappropriate layers. This may contribute to the development of layer-specific cortical connections in vivo.

Cerebral protection

The term cerebral protection has been incorporated into medical terminology to imply amelioration of acute neurological damage caused by a relative lack of metabolic substrate for cells in the central nervous system. For example this may result from hypoxaemia, cardiac arrest, stroke, trauma, inflammation, or metabolic abnormalities.