Correcting organ motion artifacts in x-ray CT systems based on tracking of motion phase by the spatial overlap correlator. II. Experimental study

This paper presents the experimental part of an investigation on tracking and eliminating organ motion artifacts in x-ray CT cardiac applications with emphasis on imaging coronary calcification. The system methodology consists of a software implementation of the spatial overlap correlator (SSOC) concept in x-ray CT scanners to track the net amplitude and phase of organ motion during the CT data acquisition process. A coherent sinogram synthesis (CSS) method is then used to identify the repeated phases of a periodic organ motion from the information provided by the SSOC process and hence synthesize a new sinogram with no motion effects. Since the SSOC scheme is capable of tracking cardiac motion, it identifies also the projection points associated with minimum amplitude cardiac motion effects. These points are used to identify a 180 degrees plus the fan angle sinogram for image reconstruction. This leads to a retrospective gating (RG) scheme that is based on the output of the SSOC process. Performance comparison of the proposed methodology with the retrospective ECG gating using real data sets with phantoms and human patients provides a performance assessment of the merits of the proposed methods. Real results demonstrate that the new methodology eliminates the requirement for ECG gating. Moreover, the CSS and the new RG methods do not require breath holding and they can be implemented in x-ray CT scanners to image coronary calcification and the heart's ventricles.     

Dosimetry comparison of 192Ir sources

192Ir sources besides being widely utilized in the field of conventional brachytherapy also find use in contemporary peripheral and coronal intravascular applications. In this study, the same Monte Carlo simulation code and input data were used to investigate differences between the dose rate distributions of the most commonly used 192Ir sources in the cm and mm distance range. Findings are discussed in view of differences in source and encapsulation dimensions as well as structural details. Results are presented in the AAPM TG-43 formalism, as generalized by AAPM TG-60, for five 192Ir HDR source designs as well as an LDR seed and an LDR wire source. Dose rate constants of the sources at r0 = 1 cm and r0 = 2 mm were found proportional to the corresponding geometry factors along the transverse source bisectors and an equation of the form lambda r0(cGyh(-1) U(-1)) = 1.12 x G(r0,90 degrees) provides results within clinical accuracy (less than 2%) for any 192Ir source. Radial dose functions do not depend significantly on source and encapsulation geometry and agree within 2% with that of a point 192Ir source. Anisotropy is of importance for accurate dosimetry at the cm distance range but it does not affect dose rate in the mm distance range significantly. At such short radial distances the source geometry factor defines the shape of isodose lines. Dose uniformity at given distances from the sources is strongly dependent on source dimensions as indicated by dose rate profiles in polar and Cartesian coordinates.     

Dosimetry close to an 192Ir HDR source using N-vinylpyrrolidone based polymer gels and magnetic resonance imaging

In this work, the utilization of polymer gel-MRI dosimetry for measurements at distances relevant to clinical brachytherapy and intravascular applications [i.e., in the mm range, where steep three-dimensional (3-D) dose gradients exist] is investigated using N-vinylpyrrolidone-based gels. Transverse axis radial dose distributions, dose distributions parallel to the source axis, and 2-D dose distributions around the commonly used microSelectron 192Ir HDR source are measured for single source dwell position irradiations. Experimental results are found in good agreement with verified Monte Carlo calculations, even for distances less than 3 mm from the source. The effect of various MRI parameters, such as slice thickness, slice mispositioning, and in-plane resolution, on the accuracy of the method is also investigated. Possible limitations of the method are discussed, and its' overall potential in brachytherapy dosimetry is evaluated. Experimental 2-D dose distributions for an intravascular application following the Paris irradiation protocol are compared to corresponding commercial treatment planning system calculations. Results suggest that polymer gel-MRI dosimetry is capable of experimentally verifying dose distributions in relevant clinical intravascular applications.     

Thermoluminescent dosimetry of the selectseed 125I interstitial brachytherapy seed

This work presents experimental dosimetry results for the new selectSeed 125I prostate seed design for use with the seedSelectron afterloading device, in accordance with the AAPM advisory that all new low energy interstitial brachytherapy seeds should undergo one Monte Carlo (MC) and at least one experimental dosimetry characterization. TLD dosimetry was performed using 120 cylindrical LiF TLD type-100 rods calibrated using a 6 MV photon beam. They were irradiated in solid water phantoms for the experimental determination of the seed dose rate constant, radial dose functions and anisotropy functions. MC simulations were performed for the determination of the TLDs relative energy response that was found position independent and equal to 1.40+/-0.03, and for the calculation of the ratio of dose in liquid water to dose in solid water that was found to be well described by Dliquidwater/Dsolidwater= 1.013*r+0.030 presenting only a minor dependence on polar angle. The selectSeed dose rate constant in liquid water was found equal to 0.938+/-0.065 cGy h(-1) U(-1), which agrees within experimental uncertainties with corresponding MC results of lambdaselect Seed=0.954+/-0.005 cGy h(-1) U(-1). The experimental radial dose and anisotropy function results were also found in good agreement with corresponding MC calculations.     

Monte Carlo dosimetry of the selectSeed 125I interstitial brachytherapy seed

This work provides full dosimetric data for the new selectSeed 125I prostate seed source to be distributed by Nucletron B.V. The AAPM TG-43 dosimetric formalism and the new 1999 NIST air kerma strength calibration standard have been followed. Air kerma strength, dose rate constant, radial dose functions, anisotropy functions, and anisotropy factors were calculated using Monte Carlo simulation. Corresponding calculations were also performed for the commercially available 6711 seed source, which is of similar design, for reasons of comparison. The calculated dose rate constant of the selectSeed was 0.954+/-0.005 cGy h(-1) U(-1) compared to 0.953+/-0.005 cGy h(-1) U(-1) for the 6711 source design. The latter value for the 6711 source suggests that the correction factor proposed by NIST for conversion of dose rate constants to the new 1999 NIST calibration standard may be overestimated by 2-3%. Radial dose functions of the two sources were found in good agreement for radial distances up to 4 cm, the selectSeed being less penetrating at greater radial distances (approximately 4% at 10 cm). The selectSeed source presents similar anisotropy characteristics with the 6711 source design. For both source designs, a distance and polar angle dependent discontinuity of anisotropy function values was observed owing to the dose contribution of radioactivity distributed on the ends of the cylindrical source cores. Variation of dosimetric parameters with possible variation in radioactive silver halide coating thickness of the silver source core of the new source was also investigated.     

3D conformal HDR brachytherapy and external beam irradiation combined with temporary androgen deprivation in the treatment of localized prostate cancer.

PURPOSE: To evaluate treatment outcome of 3D conformal high dose rate (HDR) brachytherapy and external beam irradiation (EBRT) combined with temporary androgen deprivation for patients with localized prostate cancer. PATIENTS AND METHODS: Between January 1997 and September 1999 we treated 102 patients with stage T1-3 N0 M0 prostate cancer. Stage T1-2 was found in 71, T3 in 31 patients. Median pretreatment PSA level was 15.3 ng/ml. After ultrasound-guided transrectal implantation of four afterloading needles, CT based 3D brachytherapy planning was performed. All patients received four HDR implants using a reference dose per implant of 5 or 7Gy. Time between each implant was 14 days. After brachytherapy EBRT followed up to 39.6 or 45.0 Gy. All patients received temporary androgen deprivation, starting 2-19 months before brachytherapy, ending 3 months after EBRT. RESULTS: Median follow-up was 2.6 years (range 2.0-4.1 years). Actuarial biochemical control rate was 87% at 2 years and 82% at 3 years. In 14 patients we noted biochemical failure, in five patients clinical failure. Overall survival was 90%, disease specific survival 98.0% at 3 years. Acute grade 3 toxicity occurred in 4%, late grade 3 toxicity in 5%. One patient developed a prostatourethral-rectal fistula as late grade 4 toxicity. The conformal quality of 300 HDR implants was analyzed using dose volume histograms. CONCLUSIONS: 3D conformal HDR brachytherapy and EBRT combined with temporary androgen deprivation is an effective treatment modality for prostate cancer with minimal associated toxicity and encouraging biochemical control rates after a median follow-up of 2.6 years.     

Guideline on the use of onabotulinumtoxinA in chronic migraine: a consensus statement from the European Headache Federation

OnabotulinumtoxinA is being increasingly used in the management of chronic migraine (CM). Treatment with onabotulinumtoxinA poses challenges compared with traditional therapy with orally administered preventatives. The European Headache Federation identified an expert group that was asked to develop the present guideline to provide recommendations for the use of onabotulinumtoxinA in CM. The expert group recommend onabotulinumtoxinA as an effective and well-tolerated treatment of CM. Patients should preferably have tried two to three other migraine prophylactics before start of onabotulinumtoxinA. Patients with medication overuse should be withdrawn from the overused medication before initiation of onabotulinumtoxinA if feasible, if not onabotulinumtoxinA can be initiated from the start or before withdrawal. OnabotulinumtoxinA should be administered according to the PREEMPT injection protocol, i.e. injecting 155 U–195 U to 31–39 sites every 12-weeks. We recommend that patients are defined as non-responders, if they have less than 30% reduction in headache days per month during treatment with onabotulinumtoxinA. However other factors such as headache intensity, disability and patient preferences should also be considered when evaluating response. Treatment should be stopped, if the patient does not respond to the first two to three treatment cycles. Response to continued treatment with onabotulinumtoxinA should be evaluated by comparing the 4 weeks before with the 4 weeks after each treatment cycle. It is recommended that treatment is stopped in patients with a reduction to less than 10 headache days per month for 3 months and that patients are re-evaluated 4–5 months after stopping onabotulinumtoxinA to make sure that the patient has not returned to CM. Questions regarding efficacy and tolerability of onabotulinumtoxinA could be answered on the basis of scientific evidence. The other recommendations were mainly based on expert opinion. Future research on the treatment of CM with onabotulinumtoxinA may further improve the management of this highly disabling disorder.     

Isolated pituitary granuloma by atypical Mycobacterium in a nonimmunosuppressed woman

A 32-year-old woman presented with a 10-day history of fever (38.0 degrees C), headaches, nausea, vomiting and a 6-month history of diabetes insipidus and amenorrhoea. Two months previously she had undergone a surgical drilling of the right mastoid area because of mastoiditis. Endocrine investigation showed elevated serum prolactin levels, secondary adrenal and gonadal failure and a normal thyroid function. Cranial MRI scan revealed a contrast enhancing intrasellar mass (approximately 2 cm) of heterogeneous appearance with suprasellar extension and thickening of the pituitary stalk. Lumbar puncture was suggestive of aseptic meningitis. The Ziehl-Neelsen stain of cerebrospinal fluid (CSF) and the tuberculin skin test were both negative. The pituitary mass was removed with a transsphenoidal approach. Histological examination demonstrated destruction of the adenohypophysis by epithelioid granulomas with partial caseous necrosis and microabscess formation, suggestive of a mycobacterial infection. A polymerase chain reaction analysis performed on paraffin-embedded tissue was positive for mycobacterial DNA. According to the individual 16S sequence, it was identified as Mycobacterium malmoense, an atypical nontuberculous mycobacterium (NTM). In conclusion, this is the first case of an isolated pituitary granuloma caused by an NTM infection in a nonimmunosuppressed patient.     

‘They said it was bronchiolitis; is it going to turn into asthma doctor?’

Acute bronchiolitis is a common paediatric disease of infancy. Its association with subsequent asthma development has puzzled clinicians and epidemiologists for decades. This article reviews the current state of knowledge regarding the role of acute bronchiolitis in the inception of asthma. There is little doubt that acute bronchiolitis is associated with an increased risk of recurrent wheezing throughout the primary school years although the direction of causality—i.e. whether bronchiolitis in infancy leads to asthma or it merely represents the first clinical presentation of predisposition to asthma—is uncertain. Existing evidence suggests that both host factors (e.g. prematurity, atopic predisposition) and acute viral infection characteristics (e.g. type of virus, severity) are operating in this relationship, perhaps with variable involvement in different individuals. Further clarification of these issues will help paediatricians provide evidence‐based information regarding the long‐term prognosis of this common disease to the families, and at the same time, it will facilitate prophylactic approaches and therapeutic strategies.