Paleo-biodegradation and hydrocarbon mixing in a major hybrid petroleum reservoir.

Some of the parental material for hydrocarbons produced from low-permeability reservoirs in Western Canada corresponds to thermal products from biodegraded oil. This has been proved by the occurrence of framboidal pyrite, which is often formed during microbial sulfate reduction (MSR). In addition, the identified pyrite framboids are associated with the presence of phosphorus (P). Phosphorus (as phosphate) is a key nutrient and energy carrier for sulfate-reducing bacteria. The pyrite-P assemblage occurs embedded in solid bitumen (thermal residue), which confirms that migrated hydrocarbons provided the environment for microbial growth. Molecular products of severe biodegradation such as 17-nortricyclic terpanes were also detected. Biodegradation effects have been masked not only by thermal degradation of biodegraded oil during maximum burial, but also due to hydrocarbon mixing with late gas-condensate charges. Suitable conditions for biodegradation (< 80 °C, basin uplift) occurred during the Early Cretaceous. The confirmation of paleo-biodegradation means that there was a significant hydrocarbon loss that we have not accounted for. Likewise, MSR and Early Cretaceous seawater sulfate might have played an important role in the generation of the hydrogen sulfide (H2S) detected today.

MRI-TRUS registration methodology for TRUS-guided HDR prostate brachytherapy.

PURPOSE: High-dose-rate (HDR) prostate brachytherapy is an established technique for whole-gland treatment. For transrectal ultrasound (TRUS)-guided HDR prostate brachytherapy, image fusion with a magnetic resonance image (MRI) can be performed to make use of its soft-tissue contrast. The MIM treatment planning system has recently introduced image registration specifically for HDR prostate brachytherapy and has incorporated a Predictive Fusion workflow, which allows clinicians to attempt to compensate for differences in patient positioning between imaging modalities. In this study, we investigate the accuracy of the MIM algorithms for MRI-TRUS fusion, including the Predictive Fusion workflow. MATERIALS AND METHODS: A radiation oncologist contoured the prostate gland on both TRUS and MRI. Four registration methodologies to fuse the MRI and the TRUS images were considered: rigid registration (RR), contour-based (CB) deformable registration, Predictive Fusion followed by RR (pfRR), and Predictive Fusion followed by CB deformable registration (pfCB). Registrations were compared using the mean distance to agreement and the Dice similarity coefficient for the prostate as contoured on TRUS and the registered MRI prostate contour. RESULTS: Twenty patients treated with HDR prostate brachytherapy at our center were included in this retrospective evaluation. For the cohort, mean distance to agreement was 2.1 ± 0.8 mm, 0.60 ± 0.08 mm, 2.0 ± 0.5 mm, and 0.59 ± 0.06 mm for RR, CB, pfRR, and pfCB, respectively. Dice similarity coefficients were 0.80 ± 0.05, 0.93 ± 0.02, 0.81 ± 0.03, and 0.93 ± 0.01 for RR, CB, pfRR, and pfCB, respectively. The inclusion of the Predictive Fusion workflow did not significantly improve the quality of the registration. CONCLUSIONS: The CB deformable registration algorithm in the MIM treatment planning system yielded the best geometric registration indices. MIM offers a commercial platform allowing for easier access and integration into clinical departments with the potential to play an integral role in future focal therapy applications for prostate cancer.

Dosimetric consequences of seed placement accuracy in permanent breast seed implant brachytherapy.

PURPOSE: This study quantifies the dosimetric impact of implant accuracy and derives a quantitative relationship relating implant accuracy to target dosimetry. METHODS AND MATERIALS: A framework was developed to simulate multiple implants for error combinations. Spherical clinical target volumes (CTVs) were modeled with volumes 1.4 cm3, 9.2 cm3, and 20.6 cm3, representing the range seen clinically. Each CTV was expanded 10 mm isotropically to create a planning target volume (PTV).. Random and systematic seed placement errors were simulated by shifting needles from their planned positions. Implant errors were simulated over the range of clinically practical errors in permanent breast seed implant. The relative effect on target coverage was evaluated. Regression analysis was performed to derive relationships between CTV dosimetry and the magnitude of implant accuracy. The validity of the clinically used 10 mm PTV margin for each of the CTVs was assessed. RESULTS: Introducing practical implant errors resulted in CTV V90% median (10th and 90th percentile) of 97.7% (85.9% and 100%), 96.2% (86.8% and 99.7%), and 100% (77.8% and 100%) for the typical, large, and small CTV, respectively. All CTVs show similar trends in target coverage. Polynomials were derived relating seed placement accuracy to median (R2 = 0.82) and 10th percentile (R2 = 0.78) CTV V90%.. CONCLUSIONS: This work quantitatively describes the relationship between implant accuracy and CTV coverage. Based on simulations, the 10 mm PTV margin is adequate to maintain target coverage. These equations can be used with institutional seed placement accuracy to estimate coverage.

Implementation of high-dose-rate brachytherapy for prostatic carcinoma in an unshielded operating room facility.

PURPOSE: The purpose of the study was to describe our approach towards safe delivery of single-fraction high-dose-rate (HDR) brachytherapy (BT) boost in patients with prostate cancer in the setting of an unshielded operating room (OR). METHODS AND MATERIALS: A total of 95 patients received 15 Gy HDR BT boost. The procedure involved transrectal ultrasound-based catheter insertion and planning in the OR, after which the patient was moved to a shielded treatment room for radiation. This required three vital components: (1) an OR table capable of transporting the patient in lithotomy position, (2) robust motion management checks to ensure reproducibility of prostate and catheter positions in the treatment room before radiation delivery, (3) remote monitoring of patient vitals while under anesthesia, during the radiation. Initial viability of this approach was confirmed by assessing acute toxicities using the Common Terminology Criteria for Adverse Events v4.0 and American Urologic Association symptom scores. RESULTS: We found good stability in prostate and catheter position, with less than 1 mm shifts in each direction due to patient transfer. The median baseline American Urologic Association score was 7 (3-11), which increased to 12 (7-17) at 4 weeks and 9 (5-14) at 3 months (p = 0.003). Common Terminology Criteria for Adverse Events ≥ grade 2 genitourinary and gastrointestinal toxicities were experienced by 7% and 0% patients, respectively, at 3 months posttreatment completion. CONCLUSIONS: Single-fraction HDR prostate BT can be delivered safely in an unshielded OR facility with a distant shielded treatment room using rigorous motion management checks and supplementary procedural equipment.

Peer-based credentialing for brachytherapy: Application in permanent seed implant.

PURPOSE: The purpose of the study was to establish a quantitative method for implant quality evaluation in permanent seed implant brachytherapy for credentialing. Delivery-based credentialing will promote consistency in brachytherapy seed delivery and improve patient outcomes. METHODS: A workflow for delivery-based credentialing was outlined and applied to permanent breast seed implant brachytherapy. Delivery simulations were performed on implantable anthropomorphic breast phantoms. Two institutions experienced in permanent seed implant brachytherapy demonstrated the peer credentialing process. Each delivery was evaluated for seed placement accuracy as the measure of implant quality, both for implant accuracy and across five simulations to assess implant variation. Initial credentialing criteria are set based on two factors; the mean seed placement accuracy (implant accuracy) and the mean standard deviation (seed variation) with the threshold for each set with the addition of two standard deviations. RESULTS: Across two institutions, seed placement accuracy (±standard deviation) was calculated for all five delivery simulations to yield 6.1 (±2.6) mm. To set credentialing criteria, the implant accuracy (6.1 mm) plus two standard deviations (2.0 mm) and the seed variation (2.6 mm) plus two standard deviations (0.8) mm yield a threshold of 8.1 ± 3.4 mm. It is expected that 95% of experienced institutions would perform the phantom simulation within this threshold. CONCLUSION: Brachytherapy programs should validate delivery accuracy by formal credentialing, which is standard in external beam programs. This quantitative implant evaluation should be combined with current credentialing standards for permanent seed brachytherapy to form a comprehensive validation of institutional brachytherapy program quality.

Establishing a simulation-based education program for radiation oncology learners in permanent seed implant brachytherapy: Building validation evidence.

PURPOSE: The purpose of this study was to establish a simulation-based education program for radiation oncology learners in permanent seed implant brachytherapy. The first step in formalizing any education program is a validation process that builds evidence-based verification that the learning environment is appropriate. METHODS AND MATERIALS: The primary education task allowed practitioners to use an anthropomorphic breast phantom to simulate a permanent seed implant brachytherapy delivery. Validation evidence is built by generating data to assess learner and expert cohorts according to their proficiency. Each practitioner's performance during the simulation was evaluated by seed placement accuracy, procedural time-to-complete, and two qualitative evaluation tools-a global rating scale and procedural checklist. RESULTS: The average seed placement accuracy (±SD) was 8.1 ± 3.5 mm compared to 6.1 ± 2.6 mm for the learner and expert cohort, respectively. The median (range) procedural time-to-complete was 64 (60-77) minutes and 43 (41-50) minutes for the learner and expert cohort, respectively. Seed placement accuracy (student t-test, p < 0.05) and procedural time-to-complete (Mann-Whitney U-test, p < 0.05) were statistically different between the cohorts. In both the global rating scale and procedural checklist, the expert cohort demonstrated improved proficiency compared to the learner cohort. CONCLUSIONS: This validation evidence supports the utilization of this simulation environment toward appropriately capturing the delivery experience of practitioners. The results demonstrate that, in all areas of evaluation, expert cohort proficiency was superior to learner cohort proficiency. This methodology will be used to establish a simulation-based education program for radiation oncology learners in permanent seed implant brachytherapy.

A Framework for Clinical Validation of Automatic Contour Propagation: Standardizing Geometric and Dosimetric Evaluation.

PURPOSE: The objective of this work was to outline and demonstrate a standardized framework for evaluating automatically propagated contour quality against expert contours. A 2-pronged approach is used to evaluate contour quality: a geometric evaluation to identify geometric and spatial discrepancies between propagated and expert contours, and a comprehensive dosimetric comparison to provide clinical context for the results. METHODS AND MATERIALS: The standardized framework requires a primary image, with reference contours and a radiation therapy treatment plan, and a secondary image. Reference contours are automatically propagated onto the secondary image anatomy and compared with expert contours obtained in an interobserver study. The standardized framework outlines geometric and dosimetric evaluation methodologies for determining indistinguishability between propagated and expert contours in a cohort analysis. Propagated contours are geometrically compared with expert contours in terms of the Dice similarity coefficient and the mean distance to agreement. Statistical analysis is performed on the central tendency and variability of Dice similarity coefficient and mean distance to agreement values over the patient cohort. Dosimetric evaluation involves computing the mean and 95% confidence intervals for the differences in cumulative dose-volume histograms for propagated and expert contours. A case study in accelerated partial breast irradiation was shown to demonstrate the framework. RESULTS: The standardized framework was applied to a case study of 24 patient data sets with 3 radiation oncologists providing the expert contours. Cohort analysis indicated that propagated contours were geometrically indistinguishable and dosimetrically distinguishable from expert contours. CONCLUSIONS: The recommended framework standardizes the comparison of geometric and dosimetric parameters to demonstrate indistinguishability of propagated contours from expert contours. Adoption of this framework is vital for consistent and comprehensive validation of automatic contour propagation for use in large-scale cohort analyses.

Post-implant analysis in permanent breast seed implant: automated plan reconstruction using simulated annealing.

PURPOSE: Post-implant analysis in permanent breast seed implant (PBSI) brachytherapy is an important component of the quality assurance process that indicates dosimetric quality relevant to patient outcome, indicating salvage therapy if inadequate, as well as providing feedback to the brachytherapy team to improve future treatments. To measure geometric indices on implant quality, plan reconstruction must be performed to correlate each planned and post-implant seed location. In this work, a simulated-annealing-based algorithm is developed to perform this plan reconstruction automatically. MATERIAL AND METHODS: The plan reconstruction algorithm was developed in MATLAB, taking the patient pre-treatment and post-implant (Day 0) plan and associated contours as inputs. For 19 treated patients, a reconstruction was obtained that defined the correspondence between each planned and post-implant seed. The simulated-annealing algorithm was used to reconstruct each patient 10 times to assess the variability in convergence. Manual reconstructions performed by at least two independent observers to obtain consensus were defined as the ground truth; these were compared to the automatic reconstructions obtained by the algorithm. Metrics on seed placement accuracy and needle strand angulation were calculated for the patients. RESULTS: The algorithm performed reconstructions on 19 patients (1235 seeds) with ground-truth reconstructions, obtaining 97 ± 8% correct matches. This strong performance indicates the ability to incorporate this algorithm into the clinical quality assurance workflow. CONCLUSIONS: The plan reconstruction algorithm developed herein performed very well in a 19-patient cohort. This algorithm can be incorporated into the clinical process to assist in the assessment of center-specific seed placement accuracy and can be used to gather implant metrics in an automated, standardized fashion for future PBSI trials.

Appropriate timing for postimplant imaging in permanent breast seed implant: Results from a serial CT study.

PURPOSE: Postimplant analysis in permanent breast seed implant (PBSI) is performed at inconsistent times subsequent to seed implantation across cancer centers, creating challenges in the interpretation of dosimetric data and ultimately the correlation with clinical outcomes. The purpose of this study is to determine the most appropriate time postimplant to perform this analysis. METHODS AND MATERIALS: Nine patients treated at our institution with PBSI were included in this analysis. Each underwent 4 postimplant CT scans: 0, 15, 30, and 60 days postimplant. A model of the accumulated dose was created by deformably registering the Day 15, 30, and 60 postimplant CT scans and dose matrices to the Day 0 scan, scaling for seed decay. The results from this model were compared to each individual postplan by integral comparison of dose-volume histogram curves for a dose evaluation volume. RESULTS: The Day 30 postplan showed the best agreement with the accumulated dose model and the smallest interpatient variability across the patient cohort. The mean (±SD) for the dose evaluation volume V90, V100, V150, and V200 for the accumulated dose model was 90 ± 7%, 86 ± 8%, 66 ± 14%, and 41 ± 16%, respectively. CONCLUSIONS: Based on the results of this patient cohort, we recommend that postimplant dosimetric analysis for PBSI be performed approximately 30 days following the implant.

Deep inspiration breath hold level variability and deformation in locoregional breast irradiation.

PURPOSE: The purpose of this study was to evaluate the dosimetric effect of breath hold level variability and deformation on breast, chest wall, internal mammary chain (IMC) nodes, and heart. METHODS AND MATERIALS: Left-sided post-lumpectomy (n = 12) and postmastectomy (n = 3) patients underwent deep inspiration breath hold (DIBH) and exhale breath hold (EBH) computed tomography (CT) scans. Forward-planned locoregional breast plans were created on the DIBH scan. Two effects were modeled assuming no setup uncertainties: residual motion within the gating window and systematically shallow breath hold levels (BHLs). Real-time position management (RPM) was used to monitor BHL at simulation and during treatment. The RPM data were scaled to simulate BHL variation within symmetric gating window widths of ±1, 3, 5, and 7 mm; the dosimetric impact of this motion was simulated in the treatment planning system. Systematically "shallow" BHL errors were modeled using deformable image registration to map the patient trajectory from DIBH to EBH (n = 12). The deformable vector fields were scaled to produce synthetic CT scans modeling patient position during breath holds 1, 3, 5, and 7 mm shallower than simulator BHL. The original treatment plans were applied to the synthetic CTs and dose was recalculated. RESULTS: Acceptable plan quality was maintained for most patients with motion within gating windows up to ±7 mm. Patients with shallow median BHLs experienced loss of coverage at simulated gating windows ±5 mm or larger. At systematic 3 mm shallow BHL error, 4/12 patients had clinical target volume IMC V80% < 99%; this increased to 11/12 patients at 5 mm. Change in heart dose from systematic BHL errors was negligible. CONCLUSIONS: Motion within gating windows has minimal dosimetric impact for most BHL variability; however, loss of IMC coverage can occur even for small gating windows when BHLs are systematically shallow. This can be mitigated by restricting lower BHL tolerances or accounting for known uncertainties in planning.

Demonstration of simulated annealing optimization for permanent breast seed implant treatment planning.

PURPOSE: Permanent breast seed implant (PBSI) is a developing brachytherapy technique for the treatment of early-stage breast cancer. In current practice, PBSI uses manual planning strategies to generate clinical treatment plans. In this work, a simulated annealing-based algorithm is developed to demonstrate the first application of inverse optimization for PBSI. METHODS AND MATERIALS: Target, skin, and chest wall muscle contours, exported from a treatment planning system in digital imaging and communications in medicine format, are used as inputs. To optimize, the user defines the dose-volume histogram objectives for the target and specifies a relative weighting for target and skin constraints. A 10-patient cohort of previously treated patients was planned by using the inverse optimization algorithm. Plan quality was compared to the clinically treated manually generated plans using the V90%, V100%, V150%, and V200% for the planning target volume (PTV), V90% and D0.2 cc for skin dose, and PTV conformity indices. RESULTS: For each of the 10 patients, patient-wise paired differences between inverse and manual plans were analyzed and presented in box plots. Comparing inverse and manual planning techniques, a statistical difference was not observed (p > 0.05) in PTV coverage criteria (V90%, V100%) and dose to skin2mm. A statistical difference was observed in the inverse plans as a reduction of the V150% (mean of 6.2%) and increase in conformity index of the 20%, 50%, 90%, and 100% isodose lines. CONCLUSIONS: This work presents the first application of inverse optimization used to generate PBSI treatment plans. A 10-patient cohort previously treated with PBSI was retrospectively planned for comparison with the clinically treated manually generated plans.

Development and characterization of an anthropomorphic breast phantom for permanent breast seed implant brachytherapy credentialing.

PURPOSE: To develop an anthropomorphic breast phantom for use in credentialing of permanent breast seed implant brachytherapy. METHODS AND MATERIALS: A representative external contour and target volume was used as the basis of mold manufacturing for anthropomorphic breast phantom development. Both target and normal tissue were composed of gel-like materials that provide suitable computed tomography and ultrasound contrast for brachytherapy delivery. The phantoms were evaluated for consistency in construction (target location) and Hounsfield unit (computed tomography contrast). For both target and normal tissue, the speed of sound was measured and compared to the image reconstruction algorithm's expectation value. Five phantoms were imaged preimplant and postimplant to assess interphantom similarity as well as to evaluate the uncertainty in quantifying seed position. RESULTS: The average Hounsfield units of the target and normal tissue gels is -146 ± 5 and 23 ± 1, respectively. The average speed of sound of the target and normal tissue gels is 1485 ± 7 m/s and 1558 ± 9 m/s, respectively, resulting in an estimated 0.4 mm uncertainty in image guidance. The registration/deformation uncertainty was determined to be 0.8 mm. The standard combined uncertainty in assessing seed position spatial accuracy, also including a 0.9 mm estimate based on literature for seed localization, is estimated to be 1.3 mm. CONCLUSIONS: The development of the anthropomorphic breast phantom and evaluation of both the consistency as well as overall seed position uncertainty illustrates the suitability of this phantom for use in brachytherapy end-to-end delivery and implant accuracy evaluation. When evaluating a user's implant accuracy, we estimate a standard combined uncertainty of 1.3 mm.

Technical Note: Empirical altitude correction factors for well chamber measurements of permanent prostate and breast seed implant sources.

PURPOSE: Previous studies in the literature have measured an altitude effect for low-energy brachytherapy seeds; a correction factor applied in addition to PTP to account for the breakdown of Bragg-Gray cavity theory at low energies in well-type ionization chambers. In clinical practice, many centers use altitude correction factors that are not seed-model-specific. The purpose of this work is to present altitude correction factors for several seed models without documented factors in the literature. METHODS: An in-house constructed pressure vessel was used with a well-type ionization chamber to measure the air-kerma strength of the IsoAid Advantage (Pd-103), Theragenics AgX100 (I-125), and Nucletron selectSeed (I-125) at a pressure range representative of those encountered worldwide. The TheraSeed 200 (Pd-103) was also measured for comparison to the originally published correction factor for validation of the experimental process. When correction factors derived in this work were within experimental uncertainties of those published, no new correction factors were proposed. RESULTS: The three seed models measured herein all demonstrated a similar response to change in pressure as previously documented in the literature with the HDR 1000 Plus well-type ionization chamber. Correction factors of the functional form PA=k1(P[torr])k2, consistent with those previously published, were found to be appropriate for these seed models. A new correction factor is proposed for the Theragenics AgX100 and Nucletron selectSeed (k1  = 0.0417, k2  = 0.479). The IsoAid Advantage, however, agreed to within uncertainty with the published altitude correction factor for the TheraSeed 200; thus the application of the same correction factor is appropriate (k1  = 0.0241, k2  = 0.562). CONCLUSIONS: This work presents altitude correction factors for three permanent implant brachytherapy seed models in clinical use. This will allow clinics to utilize model-specific factors, reducing systematic errors in their air-kerma strength verifications.

Patient experiences of caring and person-centredness are associated with perceived nursing care quality.

AIMS: To explore the extent to which patient ratings of perceived caring and person-centredness are associated with perceived nursing care quality in an acute hospital sample of inpatients. BACKGROUND: Self-reported patient experiences have had limited attention in conceptualizations of healthcare quality as described in policy and national standards, as well as in health and nursing care practice. The impact of central nursing concepts such as caring and person-centredness on patient ratings of nursing care quality is largely unknown. DESIGN: A descriptive non-experimental correlational design was used to collect and analyse data from a sample of Australian acute hospital inpatients (n = 210) in December 2012. METHODS: The study collected self-report patient data through a study survey including demographic data and the Caring Behaviours Inventory, the Person-centred Climate Questionnaire, the SF-36 and the Distress thermometer. Descriptive statistics together with Pearson correlation and hierarchical linear regression were used. FINDINGS: Perceived caring behaviours of staff and the person-centredness of wards were significantly associated with nursing care quality as evidenced by Pearson correlations being significant and exceeding the pre-set cut-off of r > 0·5. Staff caring behaviours and ward person-centredness also accounted for more than half of the total variance in perceived nursing care quality as evidenced by the final regression model. Knowledgeable and communicable staff, timeliness of assistance and environmental support stood out as most significantly related to patient perceived nursing care quality. CONCLUSIONS: Patient experiences of caring and person-centredness seem to have an influential role in the extent to which patients experience the quality of nursing care. Knowledgeable and communicable staff, timeliness of assistance and environmental support stand out as most significantly related to patient-perceived nursing care quality.

'Care in a chair' - The impact of an overcrowded Emergency Department on the time to treatment and length of stay of self-presenting patients with abdominal pain.

OBJECTIVES: The aim in this study was to investigate the impact of overcrowding on the Australasian Triage Score's (ATS) time to treatment target and the National Emergency Access Target (NEAT) for patients who self-present to the Emergency Department (ED) with abdominal pain. BACKGROUND: The causes and effects of ED overcrowding have been well described in the literature. It is a widespread phenomenon throughout the world and it can cause serious harm to patients and have a negative impact on access to emergency care. There is however, little research investigating the effect of overcrowding when patients self-present to the ED and experience a delay in being allocated a cubicle. METHODS: A retrospective analysis of 12-months of computerised records was carried out in order to determine if self-presenting patients with abdominal pain allocated a category 3 triage score who were required to 'queue' for a cubicle would meet ATS target and NEAT requirements. A multiple regression analysis was used to determine whether or not queuing for an ED cubicle, age and gender were predictors of meeting the ATS guidelines and NEAT requirements. RESULTS: Three hundred and five patients met the inclusion criteria and were included in the study. Of these 149 patients waited more than 15min to be allocated a cubicle while 156 did not experience any delay. A multiple regression analysis revealed that gender and age were not predictive of meeting the ATS target and NEAT requirements, while delay in allocation to a cubicle was a significant predictor of not being assessed within 30min and discharged within 4h. Furthermore, 61.2% of patients allocated to the waiting room queue for any amount of time were admitted to the ward. CONCLUSION: Queuing in the waiting room for an ED bed was a significant predictor of whether or not category three patients with abdominal pain had treatment commenced within 30min of presentation and was associated with a longer total ED length of stay.

Evaluation of target and cardiac position during visually monitored deep inspiration breath-hold for breast radiotherapy.

A low-resource visually monitored deep inspiration breath-hold (VM-DIBH) technique was successfully implemented in our clinic to reduce cardiac dose in left-sided breast radiotherapy. In this study, we retrospectively characterized the chest wall and heart positioning accuracy of VM-DIBH using cine portal images from 42 patients. Central chest wall position from field edge and in-field maximum heart distance (MHD) were manually measured on cine images and compared to the planned positions based on the digitally reconstructed radiographs (DRRs). An in-house program was designed to measure left anterior descending artery (LAD) and chest wall separation on the planning DIBH CT scan with respect to breath-hold level (BHL) during simulation to determine a minimum BHL for VM-DIBH eligibility. Systematic and random setup uncertainties of 3.0 mm and 2.6 mm, respectively, were found for VM-DIBH treatment from the chest wall measurements. Intrabeam breath-hold stability was found to be good, with over 96% of delivered fields within 3 mm. Average treatment MHD was significantly larger for those patients where some of the heart was planned in the field compared to patients whose heart was completely shielded in the plan (p < 0.001). No evidence for a minimum BHL was found, suggesting that all patients who can tolerate DIBH may yield a benefit from it.

An evaluation of a structured learning program as a component of the clinical practicum in undergraduate nurse education: A repeated measures analysis.

BACKGROUND: There is evidence that nursing students experience stress and anxiety and a reduction in self-efficacy when undertaking clinical placements. Previous reports have identified that a structured three-day program within the Bachelor of Nursing (BN) clinical practicum reduces the students self-report of anxiety and increases self-efficacy. However, it is unreported whether these improved outcomes are sustained for the duration of the clinical placement. OBJECTIVE: The aim of this study was to evaluate the duration of the effect of a three-day structured learning program within the clinical placement on final year Bachelor of Nursing student's report of anxiety and self-efficacy pre- and post-program participation in this intervention and following completion of the clinical practicum. DESIGN: A repeated measures design. SETTING: University-based Clinical School of Nursing, acute care clinical practicum. PARTICIPANTS: Final year Bachelor of Nursing students. METHODS: The intervention comprised the three-day program on starting the clinical practicum. A questionnaire included the anxiety subscale of The Hospital Anxiety & Depression Scale (The HAD) and the General Self-Efficacy Scale (GSES-12). The questionnaire was completed on day one (time one), upon completion of the three-day program (time two) and upon completion of placement on day 18 (time three). RESULTS: The questionnaire response rate varied over time. There was a statistically significant effect in reducing anxiety over time: F(1.73,74.46)=25.20, p<0.001 and increasing self-efficacy over time F(1.32,41.04)=7.72, p<0.004. CONCLUSIONS: This is the first report that we are aware of that has measured final year Bachelor of Nursing student's report of both anxiety and self-efficacy over repeated measures of time. Students continue to benefit from a structured learning program and the benefit of the intervention is sustained for the clinical placement duration.

Dosimetric variations in permanent breast seed implant due to patient arm position.

PURPOSE: Planning and delivery for permanent breast seed implant (PBSI) are performed with the ipsilateral arm raised; however, changes in implant geometry can be expected because of healing and anatomical motion as the patient resumes her daily activities. The purpose of this study is to quantify the effect of ipsilateral arm position on postplan dosimetry. METHODS AND MATERIALS: Twelve patients treated at the Tom Baker Cancer Centre were included in this study. Patients underwent two postimplant CT scans on the day of implant (Day 0) and two scans approximately 8 weeks later (Day 60). One scan at each time was taken with the ipsilateral arm raised, recreating the planning scan position, and the other with both arms down in a relaxed position beside the body, recreating a more realistic postimplant arm position. Postplans were completed on all four scans using deformable image registration (MIM Maestro). RESULTS: On the Day 0 scan, the V200 for the evaluation planning target volume was significantly increased in the arm-down position compared with the arm-up position. Lung, rib, and chest wall dose were significantly reduced at both time points. Left anterior descending coronary artery, heart, and skin dose showed no significant differences at either time point. CONCLUSIONS: Although some dosimetric indices show significant differences between the arm-up and arm-down positions, the magnitude of these differences is small and the values remain indicative of implant quality. Despite the delivery of the majority of dose with the arm down, it is reasonable to use CT scans taken in the arm-up position for postplanning.