958 research outputs found
Total scatter factors of small beams: a multidetector and Monte Carlo study.
No full textThe scope of this study was to estimate total scatter factors (S(c,p)) of the three smallest collimators of the Cyberknife radiosurgery system (5-10 mm in diameter), combining experimental measurements and Monte Carlo simulation. Two microchambers, a diode, and a diamond detector were used to collect experimental data. The treatment head and the detectors were simulated by means of a Monte Carlo code in order to calculate correction factors for the detectors and to estimate total scatter factors by means of a consistency check between measurement and simulation. Results for the three collimators were: S(c,p) (5 mm) = 0.677 +/- 0.004, S(c,p) (7.5 mm) = 0.820 +/- 0.008, S(c,p) (10 mm) = 0.871 +/- 0.008, all relative to the 60 mm collimator at 80 cm source-to-detector distance. The method also allows the full width at half maximum of the electron beam to be estimated; estimations made with different collimators and different detectors were in excellent agreement and gave a value of 2.1 mm. Correction factors to be applied to the detectors for the measurement of S(c,p) were consistent with a prevalence of volume effect for the microchambers and the diamond and a prevalence of scattering from high-Z material for the diode detector. The proposed method is more sensitive to small variations of the electron beam diameter with respect to the conventional method used to commission Monte Carlo codes, i.e., by comparison with measured percentage depth doses (PDD) and beam profiles. This is especially important for small fields (less than 10 mm diameter), for which measurements of PDD and profiles are strongly affected by the type of detector used. Moreover, this method should allow S(c,p) of Cyberknife systems different from the unit under investigation to be estimated without the need for further Monte Carlo calculation, provided that one of the microchambers or the diode detector of the type used in this study are employed. The results for the diamond are applicable only to the specific detector that was investigated due to excessive variability in manufacturing
Family caregivers of people with ALS: a qualitative study on two groups of mutual support.
No full textErratum: “Total scatter factors of small beams: A multidetector and Monte Carlo study”
No full textThis corrects the article "Total scatter factors of small beams: a multidetector and Monte Carlo study." in volume 35 on page 504
Biological aspects of Medorippe lanata (L., 1767) (Brachyura Dorippidae) from the eastern Ligurian Sea (western Mediterranean)
No full textThe aim of the present study is to investigate the demographic structure and to identify some aspects of the
biology of an exploited population of Medorippe lanata (Brachyura: Dorippidae) in the eastern Ligurian
Sea, western Mediterranean. 1364 specimens (639 males and 725 females) of M. lanata were collected on a
monthly basis from January to December 2001, in a wide area of the eastern Ligurian Sea usually exploited
by the Viareggio ‘rapido’ trawl fleet. M. lanata represented an important fraction of the discard, both in
weight and in number of individuals. Maximum abundance of this species occurred in late summer-early
autumn (up to 3369 ind. km)2 and 50.6 kg km)2 in August). The overall females:males sex-ratio was
1.13:1, while the monthly sex-ratio did not differ statistically from 1:1 in all months, except in September
and October, when females significantly outnumbered males. The sampled population was composed of
two cohorts from November to April. Sizes ranged from 10 to 29 mm carapace length (CL) for females and
from 9 to 29 mm CL for males. The von Bertalanffy growth curve, computed for both sexes, gave a higher
growth rate in males than in females. Recently moulted males and females were observed throughout the
year, except in summer, when the highest number of ovigerous females was present. Females with external
eggs were collected from March to November, with peaks in August and September. The monthly evolution
of the ovarian maturity stages showed no clear temporal trend. At 21 mm CL, 50% of females were
ovigerous or showed macroscopically mature ovaries. According to the dimorphism in chelae size, the
presence of adult males (post-puberty stage) was observed all year round, from 18 to 29 mm CL, without
evident temporal trends
Direct tumor in vivo dosimetry in highly-conformal radiotherapy: a feasibility study of implantable MOSFETs for hypofractionated extracranial treatments using the Cyberknife system.
No full textPURPOSE:
In highly-conformal radiotherapy, due to the complexity of both beam configurations and dose distributions, traditional in vivo dosimetry is unpractical or even impossible. The ideal dosimeter would be implanted inside the planning treatment volume so that it can directly measure the total delivered dose during each fraction with no additional uncertainty due to calculation models. The aim of this work is to verify if implantable metal oxide semiconductors field effect transistors (MOSFETs) can achieve a sufficient degree of dosimetric accuracy when used inside extracranial targets undergoing radiotherapy treatments using the Cyberknife system.
METHODS:
Based on the preliminary findings of this study, new prototypes for high dose fractionations were developed to reduce the time dependence for long treatment delivery times. These dosimeters were recently cleared and are marketed as DVS-HFT. Multiple measurements were performed using both Virtual Water and water phantoms to characterize implantable MOSFETs under the Cyberknife beams, and included the reference-dosimetry consistency, the dependence of the response on the collimator size, on the daily delivered dose, and the time irradiation modality. Finally a Cyberknife prostate treatment simulation using a body phantom was conducted, and both MOSFET and ionization readings were compared to Monte Carlo calculations. The feasibility analysis was conducted based on the ratios of the absorbed dose divided by the dose reading, named as "further calibration factor" (FCF).
RESULTS:
The average FCFs resulted to be 0.98 for the collimator dependence test, and about 1.00 for the reference-dosimetry test, the dose-dependence test, and the time-dependence test. The average FCF of the prostate treatment simulation test was 0.99.
CONCLUSIONS:
The obtained results are well within DVS specifications, that is, the factory calibration is still valid for such kind of treatments using the Cyberknife system, with no need of further calibration factors to be applied. The final accuracy of implantable MOSFETs when used for such kind of treatments was estimated to be within +/- 4%. Additional investigations using dose/fraction higher than 12 Gy, different beam configurations, and tracking systems could extend the present findings to other kind of treatments. MOSFET technology was proven to have high versatility in fast adaptation of existing detectors to new applications. It is plausible to expect a general feasibility of implantable MOSFET technology for in vivo dosimetry of the extracranial-targets treatments using the Cyberknife, provided each particular application will be validated by suitable both physical and clinical studies
Performance of a Motion Tracking System During Cyberknife Robotic Radiosurgery
No full textCyberknife (Accuracy Inc., Ca) is a robotic radio-surgery system that includes a compact 6 MV linac delivering up to 800 cGy per minute, and an automate arm to aim at any part of the body from any angle. An essential tool is the guidance system based on x-ray imaging cameras located on supports around the patient. A Cyberknife system has been operational at the Vicenza (Italy) Hospital for years and is mainly employed for treating benign and malignant tumors, and Arterior-Venous Malformations. In radiation therapy, delivery of high doses to targets that move with respiration is challenging because of possible spatial inaccuracies. The purpose of this work was to estimate the accuracy of the prediction algorithm used to compensate for system latency in a real-time respiratory tracking system. We have analyzed respiratory signals of 30 patients who had lung or liver Cyberknife treatments. The “Synchrony” (Accuracy Inc.) motion tracking system we use is based on the correlation between the position of LED markers, detected in real time, and the position of internal markers, sampled through x-ray imaging. The position of the external LED signals, though read in real time, must be predicted to compensate for a few hundred ms time lag in the feedback loop that redirects the beam to the current target position. The respiratory signals were described employing their frequency power spectrum, as recently proposed by other authors.
Prediction errors above 1.5 mm, lasting for periods longer than 5 seconds were observed for irregular breathers. These episodes correlate to the presence of a bimodal distribution in the power spectral density, and of very low frequencies contribution. A more refined approach would include a personalized choice of the prediction algorithm based on the very first minutes of treatment. Patient training aimed at reducing breathing irregularities might also result in improved spatial accuracy
Mutual support groups for family caregivers of people with amyotrophic lateral sclerosis: a pilot study
No full textFamily caregivers of people with amyotrophic lateral sclerosis (ALS) live stressful lives in which they spend most of their time caring for their loved ones and managing difficult situations, thereby reducing the time spent in taking care of themselves. This situation may last several years. Previous literature has widely highlighted that this situation reduces caregivers’ quality of life and increases their psychological distress and risk of health problems, but there is a lack of studies that focus on psychological interventions for these situations. This qualitative study examined a pilot experience of two mutual support groups for family caregivers of people with ALS. The aim was to identify caregivers’ needs, the prominent aspects of their experience, and to understand whether and how this intervention strategy might help them. Six partners (four men and two women) and six adult children (five women and one man) participated in the groups, which were conducted in northern Italy. After the support groups finished, participants underwent semi‐structured interviews. The authors conducted a content analysis of the transcripts of the interviews and the 20 group sessions. The thematic areas identified were “caregiving,” “being the son/daughter of a person with ALS,” “being the partner of a person with ALS,” “group experience” and “group evaluation.” The caregiving experience was profoundly different depending on whether the caregiver was a son/daughter or a partner of a patient with ALS. Moreover, comparison with peers and mutual support helped participants to better cope with ALS and its consequences, to improve their care for their relatives and to overcome typical caregiver isolation. These results suggest the usefulness of involving communities in caregiver support in order to create new networks and activate personal and social resources for well‐being
Morphometric aspects of Medorippe lanata (L., 1767) (Brachyura Dorippidae) in the Eastern Ligurian Sea
No full textNa-feldspar (F) and kaolinite (K) system at high temperature: Resulting phase composition, micro-structural features and mullite-glass Gibbs energy of formation, as a function of F/K ratio and kaolinite crystallinity
No full textThe system Na-feldspar (F) and kaolinite (K) was investigated at temperatures of interest in ceramic applications (1200-1280 degrees C) to study the effects of F/K ratios by weight and crystallinity degree of kaolinite on the final product, micro-structural features and mullite-glass Gibbs energy of formation (Delta G(eff)). Mullite and glass are the dominant phases; in general, the higher the temperature, the larger the former. An F/K increase promotes the formation of glass and secondary mullite, appearing along with the primary one. Delta G(eff) was modelled by alpha(T) x (F/K)(2) + beta(T) x F/K + gamma(T), alpha, beta and gamma being linear functions of temperature whose coefficients were determined by fitting the Delta G(eff)-theoretical to the Delta G(eff)-obtained from the measured phase compositions. Delta G(eff) is less affected by temperature than by F/K, whose increase shifts equilibrium towards glass phases. The Delta G(eff)-curves for ordered and disordered kaolinite intersect one another at F/K similar to 0.5, a ratio close to that used in industrial practice
Image-guided stereotactic radiosurgery for local control of unresectable liver metastases using the CyberKnife robotic system. Preliminary results
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