Monte Carlo simulations of patient dose perturbations in rotational-type radiotherapy due to a transverse magnetic field: a tomotherapy investigation.

PURPOSE: Several groups are exploring the integration of magnetic resonance (MR) image guidance with radiotherapy to reduce tumor position uncertainty during photon radiotherapy. The therapeutic gain from reducing tumor position uncertainty using intrafraction MR imaging during radiotherapy could be partially offset if the negative effects of magnetic field-induced dose perturbations are not appreciated or accounted for. The authors hypothesize that a more rotationally symmetric modality such as helical tomotherapy will permit a systematic mediation of these dose perturbations. This investigation offers a unique look at the dose perturbations due to homogeneous transverse magnetic field during the delivery of Tomotherapy(®) Treatment System plans under varying degrees of rotational beamlet symmetry. METHODS: The authors accurately reproduced treatment plan beamlet and patient configurations using the Monte Carlo code geant4. This code has a thoroughly benchmarked electromagnetic particle transport physics package well-suited for the radiotherapy energy regime. The three approved clinical treatment plans for this study were for a prostate, head and neck, and lung treatment. The dose heterogeneity index metric was used to quantify the effect of the dose perturbations to the target volumes. RESULTS: The authors demonstrate the ability to reproduce the clinical dose-volume histograms (DVH) to within 4% dose agreement at each DVH point for the target volumes and most planning structures, and therefore, are able to confidently examine the effects of transverse magnetic fields on the plans. The authors investigated field strengths of 0.35, 0.7, 1, 1.5, and 3 T. Changes to the dose heterogeneity index of 0.1% were seen in the prostate and head and neck case, reflecting negligible dose perturbations to the target volumes, a change from 5.5% to 20.1% was observed with the lung case. CONCLUSIONS: This study demonstrated that the effect of external magnetic fields can be mitigated by exploiting a more rotationally symmetric treatment modality.

The value of clinical examination in diagnosing pelvic fractures in blunt trauma patients: a brief review.

PURPOSE OF THE STUDY: To evaluate the value of a pelvic X-ray compared to clinical examination in diagnosing pelvic ring fractures, using computed tomography (CT) as the gold standard, in alert [Glasgow Coma Scale (GCS) ≥ 13] adult blunt trauma patients in the emergency room. METHODS: A systematic literature search was performed in PubMed and Embase. The results were screened on their titles and abstracts using in- and exclusion criteria. Subsequently, the selected articles were critically appraised for their relevance and validity. RESULTS: Two studies investigating the diagnostic value of clinical examination and pelvic X-ray compared to CT were identified. Both studies demonstrate higher negative predictive values for clinical examination [0.99 (95% confidence interval [CI] 0.98-1.0) and 1.0 (95% CI 0.99-1.0)] compared to the negative predictive values of pelvic X-ray [0.98 (95% CI 0.93-0.99) and 0.99 (95% CI 0.99-1.0)]. The positive predictive values for clinical examination were low [0.18 (95% CI 0.16-0.23) and 0.35 (95% CI 0.30-0.42)] compared to pelvic X-ray [0.97 (95% CI 0.96-0.98) and 0.97 (95% CI 0.90-0.99)]. CONCLUSIONS: In alert blunt trauma patients, pelvic X-ray only has additional diagnostic value for the detection of pelvic ring fractures if the clinical examination is positive. Pelvic X-ray should not be performed if the clinical examination is negative. In this manner, the expenditure of time, costs, and radiation are optimized.

Brain-behavior relationships in young traumatic brain injury patients: fractional anisotropy measures are highly correlated with dynamic visuomotor tracking performance.

Traumatic brain injury (TBI) patients have a high incidence of eye-hand coordination deficits. Diffuse axonal injury is common in TBI and is presumed to contribute to persistent motor problems. Using Diffusion Tensor Imaging (DTI), this study sought to identify changes in (sensori)motor white matter (WM) pathways/regions in a TBI group during the chronic recovery stage. A secondary objective was to examine the relationship between WM integrity and upper-limb visuomotor tracking performance. A young TBI (n=17) and control (n=14) group performed a dynamic tracking task, characterized by increasing information processing speed and predictive movement control. DTI scans were administered along with standard anatomical scans. The TBI group was found to perform inferior to the control group on the tracking task. Decreased fractional anisotropy was found in the TBI group in dedicated pathways involved in transmission of afferent and efferent information, i.e., corticospinal tract, posterior thalamic radiation, and optic radiation, due to increased diffusivity parallel and perpendicular to axonal fibre direction. This decrease in WM integrity was associated with inferior visuomotor tracking performance. Moreover, discriminant function analysis demonstrated that the model, based on the combined application of DTI and behavioral measures, was the most effective in distinguishing between TBI patients and controls. This study shows that specific eye-hand coordination deficits in a young TBI group are related to microstructural abnormalities in task-specific cerebral WM structures. Measures of white matter integrity are potentially important biomarkers for TBI that may support prognosis of motor deficits.

Longitudinal study using a diode phantom for helical tomotherapy IMRT QA.

PURPOSE: The Caribbean Radiation Oncology Center acquired a DELTA4 diode phantom for helical tomotherapy IMRT QA and presents the results of their first 264 clinical cases. METHODS: The validation consisted of several case studies comparing existing ionization chamber and Gafchromic film IMRT QA results to diode phantom results, along with a longitudinal study analyzing the IMRT QA results against other machine QA procedures for a complete sample of IMRT patients. RESULTS: The case studies resulted in a maximum observed difference of 0.7% between the diode phantom and the ionization chamber measurements in low dose-gradient regions. Over the longitudinal study, every IMRT QA plan passed a gamma specification of a 3%/3 mm and 98% of the diodes yielded a value of less than 1. In addition, the mean 90% isodose absolute difference for all plans was 0.05% with a (lsigma) standard deviation of 1.19%. CONCLUSIONS: The phantom measurements closely match the planned dose distributions in high and low dose-gradient regions. In addition, a significant positive statistical correlation was determined between the IMRT QA, daily QA, and rotational variation output measurements. Together, these results signify high degree of accuracy of both the DELTA4 phantom as well as the TomoTherapy Hi-Art system.

Environmental exposure assessment of ethinyl estradiol (EE) from a combined hormonal vaginal contraceptive ring after disposal; leaching from landfills.

In this study an environmental exposure assessment and experiments were carried out to identify the leaching potential of ethinyl estradiol (EE) present in a vaginal contraceptive (NuvaRing) when disposed of in landfills. Landfill material and a sandy soil were used to investigate the mobility of EE. Log K(oc) values determined in the range of 3 to 4 indicate that EE does not have a high mobility in landfills and soils. Column experiments were used to estimate that it takes approximately 40 years before EE leaches from a column of 1 m of landfill material or sandy soil. This column experiment, which was performed with an EE concentration based on worst-case assumptions, demonstrates that the emission of EE from landfills is negligible. Sandy soils below landfills also act as a strong sorbent of EE, thereby further reducing the potential for groundwater contamination.

Chronic treatment with certain antipsychotic drugs preserves upregulation of regulator of G-protein signalling 2 mRNA in rat striatum as opposed to c-fos mRNA.

Quantitative in situ hybridization on rat coronal brain sections with radiolabelled oligonucleotide probes was performed to investigate the effects of antipsychotic drugs on mRNA levels of regulator of G-protein signalling (RGS) 2 and c-fos. This study demonstrated a similar increase of RGS2 mRNA level in the striatum upon both a single and a 21-day treatment with either haloperidol (2 mg/kg) or risperidone (7.5 mg/kg) in contrast to clozapine (20 mg/kg). Otherwise, the acute c-fos mRNA induction in the striatum was abolished by 74 to 89% upon chronic treatment with either haloperidol or risperidone. In conclusion, the induction of RGS2 mRNA in the striatum, in contrast to the immediate early gene c-fos mRNA, is preserved upon chronic treatment with haloperidol and risperidone.

Selective destruction of nigrostriatal dopaminergic neurons does not alter [3H]-ryanodine binding in rat striatum.

Dopamine nigrostriatal neurons are important for motor control and may contain a particularly dense population of ryanodine receptors involved in the control of dopamine release. To test this hypothesis, we used a classical model of unilateral selective lesion of these neurons in rats based on 6-hydroxydopamine (6-OHDA) injection into the substantia nigra. Binding of [3H]-GBR 12935, used as a presynaptic marker since it labels specifically the dopamine uptake complex, was dramatically decreased by 83-100% in striatum homogenates after 6-OHDA lesion. On the contrary, no reduction of [3H]-ryanodine binding was observed. The present data indicate that [3H]-ryanodine binding sites present in rat striatum are not preferentially localized in dopaminergic terminals.

Selective destruction of nigrostriatal dopaminergic neurons does not alter [3H]-ryanodine binding in rat striatum

Dopamine nigrostriatal neurons are important for motor control and may contain a particularly dense population of ryanodine receptors involved in the control of dopamine release. To test this hypothesis, we used a classical model of unilateral selective lesion of these neurons in rats based on 6-hydroxydopamine (6-OHDA) injection into the substantia nigra. Binding of [3H]-GBR 12935, used as a presynaptic marker since it labels specifically the dopamine uptake complex, was dramatically decreased by 83-100 percent in striatum homogenates after 6-OHDA lesion. On the contrary, no reduction of [3H]-ryanodine binding was observed. The present data indicate that [3H]-ryanodine binding sites present in rat striatum are not preferentially localized in dopaminergic terminals