Trends in repeat general anaesthesia for treatment of dental caries at a children's hospital in Toronto, Canada: a 10-year retrospective investigation.

BACKGROUND: Treatment of early childhood caries (ECC) under general anaesthesia (GA) was the most common day surgical procedure performed for preschool children in Canada. Evidence with regard to the rate of repeat GA for dental care for Canadian Children is limited. AIM: To determine the rate of repeat dental caries treatment performed under GA over a 10-year period and to assess the relationship between the frequency of repeat dental treatment under GA and medical comorbidities. DESIGN: This was a retrospective assessment of the dental records of 973 children who required repeat dental treatment under GA over a 10-year period. The rate of repeat dental treatment under GA was calculated. A Chi-square analysis was performed to determine associations between medical comorbidities and the frequency of repeat dental treatment under GA. RESULTS: The rate of repeat dental treatment under GA over a 10-year period was 10.8%. The yearly repeat rate and simple moving 5-year rate of repeat dental treatment under GA increased. Having a medical comorbidity was not associated with repeat dental treatment under GA. CONCLUSIONS: The rate of repeat dental treatment under GA was consistent with the rates reported in the dental literature and increased over the 10-year period.

The association between labour epidural case volume and the rate of accidental dural puncture.

Accidental dural puncture is a recognised complication of labour epidural placement and can cause a debilitating headache. We examined the association between labour epidural case volume and accidental dural puncture rate in specialist anaesthetists and anaesthesia trainees. We performed a retrospective cohort study of labour epidural and combined spinal-epidural nerve blocks performed between 1 July 2013 and 31 December 2017 at Waitemata District Health Board, Auckland, New Zealand. The mean (SD) annual number of obstetric epidural and combined spinal-epidural procedures for high-case volume specialists was 44.2 (15.0), and for low-case volume specialists was 10.0 (6.8), after accounting for caesarean section combined spinal-epidural procedures. Analysis of 7976 labour epidural and combined spinal-epidural procedure records revealed a total of 92 accidental dural punctures (1.2%). The accidental dural puncture rate (95%CI) in high-case volume specialists was 0.6% (0.4-0.9%) and in low-case volume specialists 2.4% (1.4-3.9%), indicating probable skill decay. The odds of accidental dural puncture were 3.77 times higher for low- compared with high-case volume specialists (95%CI 1.72-8.28, p = 0.001). Amongst trainees, novices had a significantly higher accidental dural puncture complication rate (3.1%) compared with registrars (1.2%), OR (95%CI) 0.39 (0.18-0.84), p = 0.016, or fellows (1.1%), 0.35 (0.16-0.76), p = 0.008. Accidental dural puncture complication rates decreased once trainees progressed past the 'novice' training stage.

Prevalence and presentation patterns of enamel hypomineralisation (MIH and HSPM) among paediatric hospital dental patients in Toronto, Canada: a cross-sectional study.

PURPOSE: The purpose of the study was to determine the prevalence and presentation patterns of molar incisor hypomineralisation (MIH) and hypomineralised second primary molars (HSPM) in the Division of Paediatric Dentistry at The Hospital for Sick Children (SickKids) in Toronto, Canada. METHODS: A cross-sectional study of 429 eligible participants was carried out by nine trained and calibrated examiners. The European Academy of Paediatric Dentists (EAPD) criteria for diagnosis and documentation of MIH and HSPM defects were used. RESULTS: Molar incisor hypomineralisation and HSPM prevalence was 12.4% and 5.2%, respectively. Regarding MIH, the affected molars and incisors attributed to 5.6% of the total prevalence, the remaining having only molars affected. Demarcated white opacities were most common in MIH (60%) and HSPM (67%), followed by yellow/brown opacities (MIH 22%, HSPM 9%), post-eruptive breakdown (MIH 8%, HSPM 24%), atypical caries (MIH 6%, HSPM 0%), and atypical restorations (MIH 4%, HSPM 0%). In both MIH and HSPM, single surface hypomineralised lesions were significantly more common than multi-surface lesions (p < 0.0001). Most lesions affected buccal enamel (MIH 55%, HSPM 47%). Lesion extension was most frequently less than 1/3 of a tooth surface (MIH 58%, HSPM 67%) and this was significantly more common in teeth affected by HSPM than MIH (p = 0.03). Individuals with HSPM were more likely to present with two affected molars than individuals with MIH (p = 0.03). Hypomineralised second primary molars were not predictive for MIH. CONCLUSIONS: The prevalence of MIH and HSPM was within the range of published studies. The most common MIH and HSPM lesions affected single surface of a tooth, mostly on the buccal surface and were less than 1/3 of the surface area size.

Teaching and learning in undergraduate anaesthesia: a quantitative and qualitative analysis of practice at the University of Auckland.

Anaesthesia encompasses a broad range of knowledge and skills of relevance to graduating doctors. For the majority of new doctors, an undergraduate clinical rotation is their only exposure to anaesthesia practice. However, the content and approach to undergraduate anaesthesia education varies between institutions. We explored our students' views and experiences, and teaching approaches and expectations of consultant anaesthetists during a clinical attachment in anaesthesia. Our mixed-method design included student and staff surveys, logbook analysis and student focus groups. Logbook analysis of all 202 students showed mean numbers of attempts for bag-mask ventilation, laryngeal mask insertion, tracheal intubation and IV cannulation were 6.8, 3.9, 3.3 and 4.5, respectively. Focus group responses (11 students, three groups) suggested a mismatch between students' expectations of performing clinical skills and the available opportunities, particularly for IV cannulation. Students often felt reluctant to ask anaesthetists to teach them, and appreciated clinician-led engagement in all aspects of learning patient management. Among the 78 anaesthetists (29.3%) responding to the survey, the five tasks most frequently identified as suitable for teaching to students all related to airway management. Our study found much unanticipated variability in student exposure, teaching practice and attitudes to teaching various skills or procedures between anaesthetists, and student opinion of their clinical attachment. The findings resulted in a review of many aspects of the attachment. It is likely that other institutions will have similar variability and we recommend they undertake similar exercises to optimise teaching and learning opportunities for undergraduate anaesthesia.

Medical linear accelerator mounted mini-beam collimator: design, fabrication and dosimetric characterization.

The goal of this work was to design, build and experimentally characterize a linear accelerator mounted mini-beam collimator for use at a nominal 6 MV beam energy. Monte Carlo simulation was used in the design and dosimetric characterization of a compact mini-beam collimator assembly mounted to a medical linear accelerator. After fabrication, experimental mini-beam dose profiles and central axis relative output were measured and the results used to validate the simulation data. The simulation data was then used to establish traceability back to an established dosimetric code of practice. The Monte Carlo simulation work revealed that changes in collimator blade width have a greater influence on the valley-to-peak dose ratio than do changes in blade height. There was good agreement between the modeled and measured profile data, with the exception of small differences on either side of the central peak dose. These differences were found to be systematic across all depths and result from limitations associated with the collimator fabrication. Experimental mini-beam relative output and simulation data agreed to better than ± 2.0%, which is well within the level of uncertainty required for dosimetric traceability of non-standard field geometries. A mini-beam collimator has now been designed, built and experimentally characterized for use with a commercial linear accelerator operated at a nominal 6 MV beam energy.

The teaching portfolio as a professional development tool for anaesthetists.

A teaching portfolio (TP) is a document containing a factual description of a teacher's teaching strengths and accomplishments, allowing clinicians to display them for examination by others. The primary aim of a TP is to improve quality of teaching by providing a structure for self-reflection, which in turn aids professional development in medical education. Contents typically include a personal statement on teaching, an overview of teaching accomplishments and activities, feedback from colleagues and learners, a reflective component and some examples of teaching material. Electronic portfolios are more portable and flexible compared to paper portfolios. Clinicians gain the most benefit from a TP when it is used as a tool for self-reflection of their teaching practice and not merely as a list of activities and achievements. This article explains why and how anaesthetists might use a TP as a tool for professional development in medical education.

Oral choline supplementation for postoperative pain.

BACKGROUND: Activation of nicotinic receptors with nicotine has been shown to reduce post-surgical pain in clinical and preclinical studies. Choline is a selective agonist at α7-type nicotinic receptors that does not have addictive or sympathetic activating properties. It is anti-nociceptive in animal studies. We conducted a double-blind randomized trial of oral choline supplementation with lecithin to aid in the treatment of pain after gynaecological surgery. METHODS: Sixty women having open gynaecological surgery were randomly assigned to receive 20 g of lecithin before surgery or placebo. Plasma choline concentration and tumour necrosis factor (TNF) were measured. Pain report was the primary outcome measure. RESULTS: We achieved a small but statistically significant increase in choline after surgery with oral supplementation. Plasma TNF was not decreased and pain report was not different between groups at rest or with movement. There were no adverse effects of treatment. CONCLUSIONS: Oral supplementation with lecithin during the perioperative period resulted in very slow absorption and thus only a small increase in plasma choline was achieved. This concentration was inadequate to reduce TNF as has been shown in other studies. The absence of an anti-inflammatory effect was likely related to our failure to demonstrate efficacy in pain reduction.

Monte Carlo modelling of diode detectors for small field MV photon dosimetry: detector model simplification and the sensitivity of correction factors to source parameterization.

The goal of this work was to examine the use of simplified diode detector models within a recently proposed Monte Carlo (MC) based small field dosimetry formalism and to investigate the influence of electron source parameterization has on MC calculated correction factors. BEAMnrc was used to model Varian 6 MV jaw-collimated square field sizes down to 0.5 cm. The IBA stereotactic field diode (SFD), PTW T60016 (shielded) and PTW T60017 (un-shielded) diodes were modelled in DOSRZnrc and isocentric output ratios (OR(fclin)(detMC)) calculated at depths of d = 1.5, 5.0 and 10.0 cm. Simplified detector models were then tested by evaluating the percent difference in (OR(fclin)(detMC)) between the simplified and complete detector models. The influence of active volume dimension on simulated output ratio and response factor was also investigated. The sensitivity of each MC calculated replacement correction factor (k(fclin,fmsr)(Qclin,Qmsr)), as a function of electron FWHM between 0.100 and 0.150 cm and energy between 5.5 and 6.5 MeV, was investigated for the same set of small field sizes using the simplified detector models. The SFD diode can be approximated simply as a silicon chip in water, the T60016 shielded diode can be modelled as a chip in water plus the entire shielding geometry and the T60017 unshielded diode as a chip in water plus the filter plate located upstream. The detector-specific (k(fclin,fmsr)(Qclin,Qmsr)), required to correct measured output ratios using the SFD, T60016 and T60017 diode detectors are insensitive to incident electron energy between 5.5 and 6.5 MeV and spot size variation between FWHM = 0.100 and 0.150 cm. Three general conclusions come out of this work: (1) detector models can be simplified to produce OR(fclin)(detMC) to within 1.0% of those calculated using the complete geometry, where typically not only the silicon chip, but also any high density components close to the chip, such as scattering plates or shielding material is necessary to be included in the model, (2) diode detectors of smaller active radius require less of a correction and (3) (k(fclin,fmsr)(Qclin,Qmsr)) is insensitive to the incident the electron energy and spot size variations investigated. Therefore, simplified detector models can be used with acceptable accuracy within the recently proposed small field dosimetry formalism.

Poster - Thur Eve - 56: Verification of buildup region dose calculation of a treatment planning system.

Buildup region dose calculation of Pinnacle3 (version 9.0), a treatment planning system (TPS) commissioned using cylindrical ionization chamber measurements, have been verified experimentally. Dose values measured using Attix parallel plate ionization chamber were compared with those calculated by Pinnacle3 for a variety of clinical setups involving: 6 MV and 15 MV photon beams, open fields, enhanced dynamic wedges, physical wedges, block tray, 85, 100 and 120 cm source-to-surface distances, and square field sizes ranging from 3 × 3 to 30 × 30 cm2 . The dose difference (DD) and distance-to-agreement (DTA) techniques were used to evaluate the discrepancy between measured and calculated dose values. Based on the criteria of DD less than 2% or DTA less than 2mm, 93.7% of 1,710 dose points for the 6 MV and 96.1% of 2,244 dose points for 15 MV passed. Dose points that failed were mostly for open fields, block tray fields, and physical wedges (15 and 30 degrees) fields; this is attributed to high electron contamination (EC) associated with these fields. The levels of discrepancies between measured and calculated dose values were greatly reduced after remodeling the EC in Pinnacle3 using Attix chamber measurements, an indication that the EC equation in Pinnacle3 may be adequate for modeling EC in the dose buildup region, and the commissioning of a TPS using cylindrical ionization chamber measurements may not provide accurate buildup region dose calculation. Attix chamber measurements were validated using GafChromic EBT2 film; the disagreement was less than 3% for 89.9% of dose values compared.

Implementing a newly proposed Monte Carlo based small field dosimetry formalism for a comprehensive set of diode detectors.

PURPOSE: The goal of this work was to implement a recently proposed small field dosimetry formalism [Alfonso et al., Med. Phys. 35(12), 5179-5186 (2008)] for a comprehensive set of diode detectors and provide the required Monte Carlo generated factors to correct measurement. METHODS: Jaw collimated square small field sizes of side 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, and 3.0 cm normalized to a reference field of 5.0 cm × 5.0 cm were used throughout this study. Initial linac modeling was performed with electron source parameters at 6.0, 6.1, and 6.2 MeV with the Gaussian FWHM decreased in steps of 0.010 cm from 0.150 to 0.100 cm. DOSRZnrc was used to develop models of the IBA stereotactic field diode (SFD) as well as the PTW T60008, T60012, T60016, and T60017 field diodes. Simulations were run and isocentric, detector specific, output ratios (OR(det)) calculated at depths of 1.5, 5.0, and 10.0 cm. This was performed using the following source parameter subset: 6.1 and 6.2 MeV with a FWHM = 0.100, 0.110, and 0.120 cm. The source parameters were finalized by comparing experimental detector specific output ratios with simulation. Simulations were then run with the active volume and surrounding materials set to water and the replacement correction factors calculated according to the newly proposed formalism. RESULTS: In all cases, the experimental field size widths (at the 50% level) were found to be smaller than the nominal, and therefore, the simulated field sizes were adjusted accordingly. At a FWHM = 0.150 cm simulation produced penumbral widths that were too broad. The fit improved as the FWHM was decreased, yet for all but the smallest field size worsened again at a FWHM = 0.100 cm. The simulated OR(det) were found to be greater than, equivalent to and less than experiment for spot size FWHM = 0.100, 0.110, and 0.120 cm, respectively. This is due to the change in source occlusion as a function of FWHM and field size. The corrections required for the 0.5 cm field size were 0.95 (± 1.0%) for the SFD, T60012 and T60017 diodes and 0.90 (± 1.0%) for the T60008 and T60016 diodes-indicating measured output ratios to be 5% and 10% high, respectively. Our results also revealed the correction factors to be the same within statistical variation at all depths considered. CONCLUSIONS: A number of general conclusions are evident: (1) small field OR(det) are very sensitive to the simulated source parameters, and therefore, rigorous Monte Carlo linac model commissioning, with respect to measurement, must be pursued prior to use, (2) backscattered dose to the monitor chamber should be included in simulated OR(det) calculations, (3) the corrections required for diode detectors are design dependent and therefore detailed detector modeling is required, and (4) the reported detector specific correction factors may be applied to experimental small field OR(det) consistent with those presented here.

Relative biological effectiveness (RBE) of 210Po alpha-particles versus X-rays on lethality in bovine endothelial cells.

PURPOSE: Alpha-radiation from polonium-210 ((210)Po) can elevate background radiation dose by an order of magnitude in people consuming large quantities of meat and seafood, particularly caribou and reindeer. Because up to 50% of the ingested (210)Po body burden is initially found in the blood, a primary target for the short range alpha-particles is the endothelial cells lining the blood vessels. This study examined the relative biological effectiveness (RBE) of (210)Po alpha-particles versus 250 kVp X-rays in producing injury to cultured bovine aortic endothelial cells. MATERIALS AND METHODS: Radiation effects on cells were measured in four different ways: the percentage viable cells by trypan blue dye exclusion, the number of live cells, the lactate dehydrogenase (LDH) release to medium and the ability to form colonies (clonogenic survival). RESULTS: Comparison of dose-response curves yielded RBE values of 13.1+/-2.5 (SEM) for cell viability, 10.3+/-1.0 for live cell number and 11.1+/-3.0 for LDH activity. The RBE values for clonogenic survival were 14.0+/-1.0 based on the ratio of the initial slopes of the dose-response curves and 13.1, 9.9 and 7.7 for 50, 10 and 1% survival rate, respectively. At X-ray doses <0.25 Gy, a pronounced stimulatory effect on proliferation was noted. CONCLUSIONS: Exposure to (210)Po alpha-particles was seven to 14 times more effective than X-ray exposure in causing endothelial cell damage.

Dosimetric considerations for validation of a sequential IMRT process with a commercial treatment planning system.

Commercial multileaf collimator (MLC) systems can employ leaves with rounded ends. Treatment planning beam modelling should consider the effects of transmission through rounded leaf ends to provide accurate dosimetry for IMRT treatments delivered with segmented MLC. We determined that an MLC leaf gap reduction of 1.4 mm is required to obtain an agreement between calculated and measured profile 50% dose points. A head and neck dosimetry phantom, supplied by the Radiological Physics Center (RPC), was planned and irradiated as a necessary credentialing requirement for the RTOG H-0022 protocol. The agreement between the RPC TLD measurements and treatment planning calculations was within experimental error for the primary and secondary planning target volumes (PTVs); however, the calculated mean dose for the critical structure was approximately 9% lower than the RPC TLD measurements. RPC radiochromic film profile measurements also indicated significant discrepancies (>5%) with calculated values especially in the high dose gradient region in the vicinity of the critical structure. These results substantiate our own in-house phantom measurements, performed with the same IMRT fields as for the RPC phantom experiment, using Kodak EDR2 film to measure absolute dose. Our results indicate a maximum underestimate of calculated dose of 12% with no leaf gap reduction. The discrepancy between measured and calculated phantom values is reduced to +/- 5% when a leaf gap reduction of 1.4 mm is used. A further improvement in the accuracy of dose calculation is not possible without a more accurate modelling of the leaf end transmission by the planning system. In the absence of published dosimetric criteria for IMRT our results stress the need for stringent in-house dosimetric QA and validation for IMRT treatments. We found the dosimetric validation service provided by the RPC to be a valuable component of our IMRT validation efforts.

Feasibility of penumbra compensating filters for conformal prostate radiotherapy.

Radiation therapy beams demonstrate a gradual dose fall off at the field edges, due to factors affecting the physical penumbra and transport of radiation. Adequate target coverage requires an increase in field size larger than the target volume itself for a uniform dose to be delivered to that target volume. A method is presented for the design and fabrication of penumbra compensating filters (PCFs) which essentially sharpen the penumbra on a field-by-field basis and are used in conjunction with custom shielding blocks. We have explored the feasibility of using PCFs to reduce the field margins required for our four-field conformal prostate treatments. The penumbra compensation is designed based on a profile measured along the direction perpendicular to the blocked field edge that shows the greatest 50% to 95% isodose distance for a typical conformal prostate patient. Rigid foam material is milled and filled with a low melting point alloy material to create a filter which provides dose compensation in the field periphery of the custom shielding block. The accuracy of our methodology has been established using film dosimetry. By employing PCFs, the reduction in the rectal margin ranges from approximately 4 mm in the posterior region to 13 mm in the superior-posterior region, as compared with the shielding blocks alone. The reduction in bladder margin ranges from approximately 4 mm in the superior-anterior region to 10 mm in the superior region. Dose-volume histograms for an idealized cylindrical rectum indicate a substantial reduction in the volume treated to high doses. The calculated normal tissue complication probability values were 8.7% and 10.5% with and without PCFs included in the blocked fields respectively. The advantages of using PCFs, compared with multileaf collimator based techniques, are discussed.

Use of a radioactive check device for redundancy check of ionization chambers.

The use of a radioactive check device containing Strontium 90 was investigated to carry out the redundancy checks of Farmer-type ionization chambers. It was not possible to meet the recommended tolerance limits of the redundancy checks without taking into account the angular response of the ionization chambers. The ionization chambers exhibited a maximum variation of 1% in the angular response in this check device. After accounting for the angular response the maximum variation of the short-term repeatability was 0.14% with a standard deviation of +/-0.05%. The long-term constancy checked over a period of nine months was less than +/-0.6% for measurements, taking into account the angular response of the ionization chambers. No significant effect of the background radiation levels was observed on the measurements.

Comparison of superheated drop detector with phosphorous pentoxide powder for the detection of neutrons in 18 MV x rays.

Neutron dose equivalent measurements were performed in and around an 18 MV x-ray beam using superheated drop detectors (SDD) and phosphorous pentoxide (P2O5) powder. The neutron dose equivalent profiles for various field sizes of 10 X 10 cm2, 20 X 20 cm2, and 30 X 30 cm2 were measured. The results measured with the P2O5 were checked for any gross systematic errors by comparing with the published results computed by using Monte Carlo calculations. A comparison was then made between the neutron dose equivalent profiles measured with the P2O5 and the SDD. The results of this comparison show that the neutron dose equivalents measured with the two types of detectors agree with each other for measurements about 20 cm away from the beam edges. However, in and near the beam edges the SDD measurements are upto 50% less than the neutron dose equivalents measured using P2O5 for the 18 MV x-ray beam.

Interfacing a linear diode array to a conventional water scanner for the measurement of dynamic dose distributions and comparison with a linear ion chamber array.

A linear diode array was interfaced to a conventional water scanner for the measurement of dose distribution of dynamically wedged treatment fields. The system was validated by comparing the dose distribution of an open field measured with the system and with a scanning ionization chamber. The system was also compared with a commercial ion chamber array scanner for the measurement of dose distributions of dynamic wedges. The dose distributions of enhanced dynamic wedge fields measured with the two dosimetry systems agree well beyond the depth of maximum dose. However, in the buildup region, the measurements made with the linear diode array system differ by more than 10% from that of the ion chamber array scanner.