共查询到20条相似文献,搜索用时 15 毫秒
1.
Hatice Bilge Aydın Cakir Murat Okutan Hilal Acar 《Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)》2009,25(2):101-104
The aim of this study was to determine the surface doses using GafChromic EBT films and compare them with plane-parallel ionization chamber measurements for 6 and 18 MV high energy photon beams. The measurements were made in a water equivalent solid phantom in the build-up region of the 6 and 18 MV photon beams at 100 cm SSD for various field sizes. Markus type plane-parallel ion chamber with fixed-separation between collecting electrodes was used to measure the percent depth doses. GafChromic EBT film measurements were performed both on the phantom surface and maximum dose depth at the same geometry with ion chamber measurements. The surface doses found using GafChromic EBT film were 15%, 20%, 29%and 39% ± 2% (1SD) for 6 MV photons, 6%, 11%, 23% and 32% ± 2% (1SD) for 18 MV photons at 5, 10, 20 and 30 cm2 field sizes, respectively. GafChromic EBT film provides precise measurements for surface dose in the high energy photons. Agreement between film and plane-parallel chamber measurements was found to be within ±3% for 18 MV photon beams. There was 5% overestimate on the surface doses when compared with the plane-parallel chamber measurements for all field sizes in the 6 MV photon beams. 相似文献
2.
PurposeTo investigate and improve the domestic standard of radiation therapy in the Republic of Korea.MethodsOn-site audits were performed for 13 institutions in the Republic of Korea. Six items were investigated by on-site visits of each radiation therapy institution, including collimator, gantry, and couch rotation isocenter check; coincidence between light and radiation fields; photon beam flatness and symmetry; electron beam flatness and symmetry; physical wedge transmission factors; and photon beam and electron beam outputs.ResultsThe average deviations of mechanical collimator, gantry, and couch rotation isocenter were less than 1 mm. Those of radiation isocenter were also less than 1 mm. The average difference between light and radiation fields was 0.9 ± 0.6 mm for the field size of 20 cm × 20 cm. The average values of flatness and symmetry of the photon beams were 2.9% ± 0.6% and 1.1% ± 0.7%, respectively. Those of electron beams were 2.5% ± 0.7% and 0.6% ± 1.0%, respectively. Every institutions showed wedge transmission factor deviations less than 2% except one institution. The output deviations of both photon and electron beams were less than ±3% for every institution.ConclusionsThrough the on-site audit program, we could effectively detect an inappropriately operating linacs and provide some recommendations. The standard of radiation therapy in Korea is expected to improve through such on-site audits. 相似文献
3.
PurposeTo assess the dosimetric impact of a patient positioning device for prone breast radiotherapy and assess the accuracy of a treatment planning system (TPS) in predicting this impact.MethodsBeam attenuation and build-up dose perturbations, quantified by ionization chamber and radiochromic film dosimetry, were evaluated for 3 components of the patient positioning device: the carbon fiber baseplate, the support cushions and the support wedge for the contralateral breast. Dose calculations were performed using the XVMC dose engine implemented in the Monaco TPS. All components were included during planning CT acquisition.ResultsBeam attenuation amounted to 7.57% (6 MV) and 5.33% (15 MV) for beams obliquely intersecting the couchtop–baseplate combination. Beams traversing large sections of the support wedge were attenuated by 12.28% (6 MV) and 9.37% (15 MV). For the support cushion foam, beam attenuation remained limited to 0.11% (6 MV) and 0.08% (15 MV) per centimeter thickness. A substantial loss of dose build-up was detected when irradiating through any of the investigated components. TPS dose calculations accurately predicted beam attenuation by the baseplate and support wedge. A manual density overwrite was needed to model attenuation by the support cushion foam. TPS dose calculations in build-up regions differed considerably from measurements for both open beams and beams traversing the device components.ConclusionsIrradiating through the components of the positioning device resulted in a considerable degradation of skin sparing. Inclusion of the device components in the treatment planning CT allowed to accurately model the most important attenuation effect, but failed to accurately predict build-up doses. 相似文献
4.
《Reports of Practical Oncology and Radiotherapy》2020,25(1):91-99
AimTo examine the application of Statistical Process Control (SPC) and Ishikawa diagrams for retrospective evaluation of machine Quality Assurance (QA) performance in radiotherapyBackgroundSPC is a popular method for supplementing the performance of QA techniques in healthcare. This work investigates the applicability of SPC techniques and Ishikawa charts in machine QA.Materials and MethodsSPC has been applied to recommend QA limits on the particular beam parameters using the QUICKCHECKwebline QA portable constancy check device for 6 MV and 10 MV flattened photon beams from the Elekta Versa HD linear accelerator (Linac). Four machine QA parameters – beam flatness, beam symmetry along gun target direction and left-right direction, and beam quality factor (BQF) – were selected for retrospective analysis. Shewhart charts, Exponentially Weighted Moving Average (EWMA) charts and Cumulative Sum (CUSUM) charts were obtained for each parameter. The root causes for a failure in machine QA were broken down into an Ishikawa diagram enabling the user to identify the root cause of error and rectify the problem subsequently.ResultsShewhart charts and EWMA charts applied could detect loss in control in one variable in the 6 MV beams and in all four variables in 10 MV beams. CUSUM charts detected offsets in the readings. The Ishikawa chart exhaustively included the possible errors that lead to loss of control.ConclusionSPC is proven to be effective for detection of loss in control in machine QA. The Ishikawa chart provides the set of probable root causes of machine error useful while troubleshooting. 相似文献
5.
PurposeTo measure the environmental doses from stray neutrons in the vicinity of a solid slab phantom as a function of beam energy, field size and modulation width, using the proton pencil beam scanning (PBS) technique.MethodMeasurements were carried out using two extended range WENDI-II rem-counters and three tissue equivalent proportional counters. Detectors were suitably placed at different distances around the RW3 slab phantom. Beam irradiation parameters were varied to cover the clinical ranges of proton beam energies (100–220 MeV), field sizes ((2 × 2)–(20 × 20) cm2) and modulation widths (0–15 cm).ResultsFor pristine proton peak irradiations, large variations of neutron H1(10)/D were observed with changes in beam energy and field size, while these were less dependent on modulation widths. H1(10)/D for pristine proton pencil beams varied between 0.04 μSv Gy−1 at beam energy 100 MeV and a (2 × 2) cm2 field at 2.25 m distance and 90° angle with respect to the beam axis, and 72.3 μSv Gy−1 at beam energy 200 MeV and a (20 × 20) cm2 field at 1 m distance along the beam axis.ConclusionsThe obtained results will be useful in benchmarking Monte Carlo calculations of proton radiotherapy in PBS mode and in estimating the exposure to stray radiation of the patient. Such estimates may be facilitated by the obtained best-fitted simple analytical formulae relating the stray neutron doses at points of interest with beam irradiation parameters. 相似文献
6.
《Reports of Practical Oncology and Radiotherapy》2020,25(2):168-173
Irradiating a tumor bed with boost dose after whole breast irradiation helps reducing the probability of local recurrence. However, the success of electron beam treatment with a small area aiming to cover a superficial lesion is a dual challenge as it requires an adequate dosimetry beside a double check for dose coverage with an estimation of various combined uncertainty of tumor location and losing lateral electron equilibrium within small field dimensions.Aim of workthis work aims to measure the electron beam fluence within different field dimensions and the deviation from measurement performed in standard square electron applicator beam flatness and symmetry, then to calculate the average range of the correction factor required to overcome the loss of lateral electron equilibrium.Material and methodthe electron beam used in this work generated from the linear accelerator model ELEKTA Precise and dosimetry system used were a pair of PTW Pin Point ion chambers for electron beam dosimetry at standard conditions and assessment of beam quality at a reference depth of measurement, with an automatic water phantom, then a Roos ion chamber was used for absolute dose measurement, and PTW 2Darray to investigate the beam fluence of four applicators 6, 10, 14 and 20 cm2 and 4 rectangular cutouts 6 × 14, 8 × 14, 6 × 17 and 8 × 17 cm2, the second part was clinical application which was performed in a precise treatment planning system and examined boost dose after whole breast irradiation.Resultsrevealed that lower energy (6MeV and 8MeV) showed the loss of lateral electron equilibrium and deviation from measurements of a standard applicator more than the high energy (15 MeV) which indicated that the treatment of superficial dose with 6MeV required higher monitor unit to allow for the loss of lateral electron equilibrium and higher margin as well. 相似文献
7.
K. Asnaashari James C.L. Chow Mostafa Heydarian 《Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)》2013,29(4):350-356
In this work dosimetric parameters of two multi-leaf collimator (MLC) systems, namely the beam modulator (BM), which is the MLC commercial name for Elekta “Synergy S” linear accelerator and Radionics micro-MLC (MMLC), are compared using measurements and Monte Carlo simulations. Dosimetric parameters, such as percentage depth doses (PDDs), in-plane and cross-plane dose profiles, and penumbras for different depths and field sizes of the 6 MV photon beams were measured using ionization chamber and a water tank. The collimator leakages were measured using radiographic films. MMLC and BM were modeled using the EGSnrc-based BEAMnrc Monte Carlo code and above dosimetric parameters were calculated. The energy fluence spectra for the two MLCs were also determined using the BEAMnrc and BEAMDP. Dosimetric parameters of the two MLCs were similar, except for penumbras. Leaf-side and leaf-end 80–20% dose penumbras at 10 cm depth for a 10 × 10 cm2 field size were 4.8 and 5.1 mm for MMLC and 5.3 mm and 6.3 mm for BM, respectively. Both Radionics MMLC and Elekta BM can be used effectively based on their dosimetric characteristics for stereotactic radiosurgery and radiotherapy, although the former showed slightly sharper dose penumbra especially in the leaf-end direction. 相似文献
8.
PurposeTo investigate the degree of 18 and 22 MeV electron beam dose perturbations caused by unilateral hip titanium (Ti) prosthesis.MethodsMeasurements were acquired using Gafchromic EBT2 film in a novel pelvic phantom made out of Nylon-12 slices in which a Ti-prosthesis is embedded. Dose perturbations were measured and compared using depth doses for 8 × 8, 10 × 10 and 11 × 11 cm2 applicator-defined field sizes at 95 cm source-surface-distance (SSD). Comparisons were also made between film data at 100 cm SSD for a 10 × 10 cm2 field and dose calculations made on CMS XiO treatment planning system utilizing the pencil beam algorithm. The extent of dose deviations caused by the Ti prosthesis based on film data was quantified through the dose enhancement factor (DEF), defined as the ratio of the dose influenced by the prosthesis and the unchanged beam.ResultsAt the interface between Nylon-12 and the Ti implant on the prosthesis entrance side, the dose increased to values of 21 ± 1% and 23 ± 1% for 18 and 22 MeV electron beams, respectively. DEFs increased with increasing electron energy and field size, and were found to fall off quickly with distance from the nylon-prosthesis interface. A comparison of film and XiO depth dose data for 18 and 22 MeV gave relative errors of 20% and 25%, respectively.ConclusionThis study outlines the lack of accuracy of the XiO TPS for electron planning in highly heterogeneous media. So a dosimetric error of 20–25% could influence clinical outcome. 相似文献
9.
PurposeThis study evaluates the radiological properties of different 3D printing materials for a range of photon energies, including kV and MV CT imaging and MV radiotherapy beams.MethodsThe CT values of a number of materials were measured on an Aquilion One CT scanner at 80 kVp, 120 kVp and a Tomotherapy Hi Art MVCT imaging beam. Attenuation of the materials in a 6 MV radiotherapy beam was investigated.ResultsPlastic filaments printed with various infill densities have CT values of −743 ± 4, −580 ± 1 and −113 ± 3 in 120 kVp CT images which approximate the CT values of low-density lung, high-density lung and soft tissue respectively. Metal-infused plastic filaments printed with a 90% infill density have CT values of 658 ± 1 and 739 ± 6 in MVCT images which approximate the attenuation of cortical bone. The effective relative electron density REDeff is used to describe the attenuation of a megavoltage treatment beam, taking into account effects relating to the atomic number and mass density of the material. Plastic filaments printed with a 90% infill density have REDeff values of 1.02 ± 0.03 and 0.94 ± 0.02 which approximate the relative electron density RED of soft tissue. Printed resins have REDeff values of 1.11 ± 0.03 and 1.09 ± 0.03 which approximate the RED of bone mineral.Conclusions3D printers can model a variety of body tissues which can be used to create phantoms useful for both imaging and dosimetric studies. 相似文献
10.
Mohammad Reza Ay Abolfazl Mehranian Asghar Maleki Hossien Ghadiri Pardis Ghafarian Habib Zaidi 《Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)》2013,29(3):249-260
Beam hardening filters have long been employed in X-ray Computed Tomography (CT) to preferentially absorb soft and low-energy X-rays having no or little contribution to image formation, thus allowing the reduction of patient dose and beam hardening artefacts. In this work, we studied the influence of additional copper (Cu) and aluminium (Al) flat filters on patient dose and image quality and seek an optimum filter thickness for the GE LightSpeed VCT 64-slice CT scanner using experimental phantom measurements. Different thicknesses of Cu and Al filters (0.5–1.6 mm Cu, 0.5–4 mm Al) were installed on the scanner’s collimator. A planar phantom consisting of 13 slabs of Cu having different thicknesses was designed and scanned to assess the impact of beam filtration on contrast in the intensity domain (CT detector’s output). To assess image contrast and image noise, a cylindrical phantom consisting of a polyethylene cylinder having 16 holes filled with different concentrations of K2HPO4 solution mimicking different tissue types was used. The GE performance and the standard head CT dose index (CTDI) phantoms were also used to assess image resolution characterized by the modulation transfer function (MTF) and patient dose defined by the weighted CTDI. A 100 mm pencil ionization chamber was used for CTDI measurement. Finally, an optimum filter thickness was determined from an objective figure of merit (FOM) metric. The results show that the contrast is somewhat compromised with filter thickness in both the planar and cylindrical phantoms. The contrast of the K2HPO4 solutions in the cylindrical phantom was degraded by up to 10% for a 0.68 mm Cu filter and 6% for a 4.14 mm Al filter. It was shown that additional filters increase image noise which impaired the detectability of low density K2HPO4 solutions. It was found that with a 0.48 mm Cu filter the 50% MTF value is shifted by about 0.77 lp/cm compared to the case where the filter is not used. An added Cu filter with approximately 0.5 mm thickness accounts for 50% reduction in radiation-absorbed dose as measured by the weighted CTDI. The FOM results indicate that with an additional filter of 0.5 mm Cu or minimum 4 mm Al, a good compromise between image quality and patient dose is achieved for CT images acquired at tube voltages of 120 and 140 kVp. The results seem to indicate that an optimum filter for high kVp acquisitions, routinely used in cardiovascular imaging, should be 0.5 mm copper or 4 mm aluminium minimum. 相似文献
11.
《Reports of Practical Oncology and Radiotherapy》2019,24(4):331-337
AimIn this study, we investigated initial electron parameters of Siemens Artiste Linac with 6 MV photon beam using the Monte Carlo method.BackgroundIt is essential to define all the characteristics of initial electrons hitting the target, i.e. mean energy and full width of half maximum (FWHM) of the spatial distribution intensity, which is needed to run Monte Carlo simulations. The Monte Carlo is the most accurate method for simulation of radiotherapy treatments.Materials and methodsLinac head geometry was modeled using the BEAMnrc code. The phase space files were used as input file to DOSXYZnrc simulation to determine the dose distribution in a water phantom. We obtained percent depth dose curves and the lateral dose profile. All the results were obtained at 100 cm of SSD and for a 10 × 10 cm2 field.ResultsWe concluded that there existed a good conformity between Monte Carlo simulation and measurement data when we used electron mean energy of 6.3 MeV and 0.30 cm FWHM value as initial parameters. We observed that FWHM values had very little effect on PDD and we found that the electron mean energy and FWHM values affected the lateral dose profile. However, these effects are between tolerance values.ConclusionsThe initial parameters especially depend on components of a linac head. The phase space file which was obtained from Monte Carlo Simulation for a linac can be used as calculation of scattering, MLC leakage, to compare dose distribution on patients and in various studies. 相似文献
12.
《Reports of Practical Oncology and Radiotherapy》2020,25(2):233-240
AimThe aim of this study was to characterize the radiation contamination inside and outside the megavoltage radiotherapy room.BackgroundRadiation contamination components in the 18 MV linac room are the secondary neutron, prompt gamma ray, electron and linac leakage radiation.Materials and MethodsAn 18 MV linac modeled in a typical bunker employing the MCNPX code of Monte Carlo. For fast calculation, phase-space distribution (PSD) file modeling was applied and the calculations were conducted for the radiation contamination components dose and spectra at 6 locations inside and outside the bunker.ResultsThe results showed that the difference of measured and calculated percent depth-dose (PDD) and photo beam-profile (PBP) datasets were lower than acceptable values. At isocenter, the obtained photon dose and neutron fluence were 2.4 × 10−14 Gy/initial e° and 2.22 × 10-8 n°/cm2, respectively. Then, neutron apparent source strength (QN) value was found as 1.34 × 1012 n°/Gy X at isocenter and the model verified to photon and neutron calculations. A surface at 2 cm below the flattening filter was modeled as phase-space (PS) file for PDD and PBP calculations. Then by use of a spherical cell in the center of the linac target as a PS surface, contaminant radiations dose, fluence and spectra were estimated at 6 locations in a considerably short time, using the registered history of all particles and photons in the 13GB PSD file as primary source in the second step.ConclusionDesigning the PSD file in MC modeling helps user to solve the problems with complex geometry and physics precisely in a shorter run-time. 相似文献
13.
The temperature-size rule (TSR) is a well-established phenomenon to describe the growth response of ectotherms to temperature by which individuals maintained at low temperatures grow more slowly, but attain a larger size upon maturity. Although there are adaptive and non-adaptive theories about the plasticity of body size in response to temperature, these cannot be applied to all ectotherms, and little is known about the changes in growth and development rates through ontogeny. The ostracod species Heterocypris bosniaca, an inhabitant of freshwater temporary ponds, was used to examine the growth and development rates of its nine growth stages and female fecundity at four different temperatures (15 °C, 20 °C, 25 °C and 30 °C). The development rate of this species accelerates with increasing temperature, reaching a maximum value at 25 °C. The growth factor has a reverse-TSR in younger instars, and the typical TSR is followed only in the last two moults, resulting in non-monotonic response of adult size to temperature. Fecundity (total offspring per female) was not directly related to adult size and was generally higher at lower temperatures. Our results agree with recent research showing that the TSR may vary during ontogeny, and may not be a general trend in ostracod species from temporary waters. Indeed, adult carapace size seems to follow the pattern of a thermal reaction norm, probably influenced by the reduction of oxygen bioavailability at low temperature and the drastic increase in metabolic demand at the upper extreme of the thermal gradient. 相似文献
14.
《Journal of electromyography and kinesiology》2014,24(3):387-393
Forces at different heights and orientations are often carried by hands while performing occupational tasks. Trunk muscle activity and spinal loads are likely dependent on not only moments but also the orientation and height of these forces. Here, we measured trunk kinematics and select superficial muscle activity of 12 asymptomatic subjects while supporting forces in hands in upright standing. Magnitude of forces in 5 orientations (−25°, 0°, 25°, 50° and 90°) and 2 heights (20 cm and 40 cm) were adjusted to generate flexion moments of 15, 30 and 45 N m at the L5-S1 disc centre. External forces were of much greater magnitude when applied at lower elevation or oriented upward at 25°. Spinal kinematics remained nearly unchanged in various tasks.Changes in orientation and elevation of external forces substantially influenced the recorded EMG, despite similar trunk posture and identical moments at the L5-S1. Greater EMG activity was overall recorded under larger forces albeit constant moment. Increases in the external moment at the L5-S1 substantially increased EMG in extensor muscles (p < 0.001) but had little effect on abdominals; e.g., mean longissimus EMG for all orientations increased by 38% and 75% as the moment level altered from 15 N m to 30 N m and to 45 N m while that in the rectus abdominus increased only by 2% and 4%, respectively. Under 45 N m moment and as the load orientation altered from 90° to 50°, 25°, 0° and −25°, mean EMG dropped by 3%, 12%, 12% and 1% in back muscles and by 17%, 17%, 19% and 13% in abdominals, respectively. As the load elevation increased from 20 cm to 40 cm, mean EMG under maximum moment decreased by 21% in back muscles and by 17% in abdominals.Due to the lack of EMG recording of deep lumbar muscles, changes in relative shear/compression components and different net moments at cranial discs despite identical moments at the caudal L5-S1 disc, complementary model studies are essential for a better comprehension of neuromuscular strategies in response to alterations in load height and orientation. 相似文献
15.
Sally J. Derbyshire Andrew M. Morgan Rosemary C.A. Thompson Ann M. Henry David I. Thwaites 《Reports of Practical Oncology and Radiotherapy》2009,14(6):205-213
ObjectiveTo determine the optimum energy and beam arrangement for prostate intensity-modulated radiation therapy (IMRT) delivery using an Elekta Beam Modulator? linear accelerator, in order to inform decisions when commissioning IMRT for prostate cancer.MethodsCMS XiO was used to create IMRT plans for a prostate patient. Arrangements with 3, 5, 7, 9 and 11 equally spaced fields, containing both a direct anterior and a direct posterior beam were used, with both 6 MV and 10 MV photons. The effects of varying the maximum number of iterations, leaf increment, number of intensity levels and minimum segment size were investigated. Treatment plans were compared using isodose distributions, conformity indices for targets and critical structures, target dose homogeneity, body dose and plan complexity.ResultsTarget dose conformity and homogeneity and sparing of critical structures improved with an increasing number of beams, although any improvements were small for plans containing more than five fields. Set-ups containing a direct posterior field provided superior conformality around the rectum to anterior beam arrangements. Mean non-target dose and total number of monitor units were higher with 6 MV for all beam arrangements. The dose distribution resulting from seven 6 MV beams was considered clinically equivalent to that with five 10 MV beams.ConclusionMethods have been developed to plan IMRT treatments using XiO for delivery with a Beam Modulator? that fulfil demanding dose criteria, using many different set-ups. This study suggests that 6 MV photons can produce prostate IMRT plans that are comparable to those using 10 MV. Work is ongoing to develop a complete class solution. 相似文献
16.
Adam Konefał Andrzej Orlef Marcin Łaciak Aleksander Ciba Marek Szewczuk 《Reports of Practical Oncology and Radiotherapy》2012,17(6):339-346
BackgroundHigh-energy photon and electron therapeutic beams generated in medical linear accelerators can cause the electronuclear and photonuclear reactions in which neutrons with a broad energy spectrum are produced. A low-energy component of this neutron radiation induces simple capture reactions from which various radioisotopes originate and in which the radioactivity of a linac head and various objects in the treatment room appear.AimThe aim of this paper is to present the results of the thermal/resonance neutron fluence measurements during therapeutic beam emission and exemplary spectra of gamma radiation emitted by medical linac components activated in neutron reactions for four X-ray beams and for four electron beams generated by various manufacturers’ accelerators installed in typical concrete bunkers in Polish oncological centers.Materials and methodsThe measurements of neutron fluence were performed with the use of the induced activity method, whereas the spectra of gamma radiation from decays of the resulting radioisotopes were measured by means of a portable high-purity germanium detector set for field spectroscopy.ResultsThe fluence of thermal neutrons as well as resonance neutrons connected with the emission of a 20 MV X-ray beam is ~106 neutrons/cm2 per 1 Gy of a dose in water at a reference depth. It is about one order of magnitude greater than that for the 15 MV X-ray beams and about two orders of magnitude greater than for the 18–22 MeV electron beams regardless of the type of an accelerator.ConclusionThe thermal as well as resonance neutron fluence depends strongly on the type and the nominal potential of a therapeutic beam. It is greater for X-ray beams than for electrons. The accelerator accessories and other large objects should not be stored in a treatment room during high-energy therapeutic beam emission to avoid their activation caused by thermal and resonance neutrons. Half-lives of the radioisotopes originating from the simple capture reaction (n,γ) (from minutes to hours) are long enough to accumulate radioactivity of components of the accelerator head. The radiation emitted by induced radioisotopes causes the additional doses to staff operating the accelerators. 相似文献
17.
Many frogs from temperate climates can tolerate low temperatures and increase their thermal tolerance through hardening and acclimation. Most tropical frogs, on the other hand, fail to acclimate to low temperatures. This lack of acclimation ability is potentially due to lack of selection pressure for acclimation because cold weather is less common in the tropics. We tested the generality of this pattern by characterizing the critical temperature minimum (CTMin), hardening, and acclimation responses of túngara frogs (Engystomops pustulosus). These frogs belong to a family with unknown thermal ecology. They are found in a tropical habitat with a highly constant temperature regime. The CTMin of the tadpoles was on average 12.5 °C. Pre-metamorphic tadpoles hardened by 1.18 °C, while metamorphic tadpoles hardened by 0.36 °C. When raised at 21 °C, tadpoles acclimated expanding their cold tolerance by 1.3 °C in relation to larvae raised at 28 °C. These results indicate that the túngara frog has a greatly reduced cold tolerance when compared to species from temperate climates, but it responds to cold temperatures with hardening and acclimation comparable to those of temperate-zone species. Cold tolerance increased with body length but cold hardening was more extensive in pre-metamorphic tadpoles than in metamorphic ones. This study shows that lack of acclimation ability is not general to the physiology of tropical anurans. 相似文献
18.
PurposePancreatic tumor treatment dose distribution variations associated with supine and prone patient positioning were evaluated.MethodsA total of 33 patients with pancreatic tumors who underwent CT in the supine and prone positions were analyzed retrospectively. Gross tumor volume (GTV), planning target volume (PTV), and organs at risk (OARs) (duodenum and stomach) were contoured. The prescribed dose of 55.2 Gy (RBE) was planned from four beam angles (0°, 90°, 180°, and 270°). Patient collimator and compensating boli were designed for each field. Dose distributions were calculated for each field in the supine and prone positions. To improve dose distribution, patient positioning was selected from supine or prone for each beam field.ResultsCompared with conventional beam angle and patient positioning, D2cc of 1st-2nd portion of duodenum (D1-D2), 3rd-4th portion of duodenum (D3-D4), and stomach could be reduced to a maximum of 6.4 Gy (RBE), 3.5 Gy (RBE), and 4.5 Gy (RBE) by selection of patient positioning. V10 of D1-D2, D3-D4, and stomach could be reduced to a maximum of 7.2 cc, 11.3 cc, and 11.5 cc, respectively. D95 of GTV and PTV were improved to a maximum of 6.9% and 3.7% of the prescribed dose, respectively.ConclusionsOptimization of patient positioning for each beam angle in treatment planning has the potential to reduce OARs dose maintaining tumor dose in pancreatic treatment. 相似文献
19.
It is not understood how the knee joint angle affects the relationship between electromyography (EMG) and force of four individual quadriceps femoris (QF) muscles. The purpose of this study was to examine the effect of the knee joint angle on the EMG–force relationship of the four individual QF muscles, particularly the vastus intermedius (VI), during isometric knee extensions. Eleven healthy men performed 20–100% of maximal voluntary contraction (MVC) at knee joint angles of 90°, 120° and 150°. Surface EMG of the four QF synergists was recorded and normalized by the root mean square during MVC. The normalized EMG of the four QF synergists at a knee joint angle of 150° was significantly lower than that at 90° and 120° (P < 0.05). Comparing the normalized EMG among the four QF synergists, a significantly lower normalized EMG was observed in the VI at 150° as compared with the other three QF muscles (P < 0.05). These results suggest that the EMG–force relationship of the four QF synergists shifted downward at an extended knee joint angle of 150°. Furthermore, the neuromuscular activation of the VI was the most sensitive to change in muscle length among the four QF synergistic muscles. 相似文献
20.
The influence of temperatures on the life parameters of the solitary oothecal parasitoid Evania appendigaster, was investigated in the laboratory. Parasitized oothecae of Periplaneta americana were left to develop under seven constant temperatures: 15, 17, 20, 25, 30, 35, and 40 °C. At the end, we found that: (i) E. appendigaster was able to complete development within the temperature range of 17–34 °C; (ii) mean adult longevity decreased as temperature increased, with the temperature of 40 °C being fatal in a matter of hours; (iii) males lived longer than females between 15 and 30 °C; (iv) adult emergence rate was the highest at 25 °C, and (v) no wasps emerged at 15 or 40 °C. Non-emerged oothecae contained either unhatched eggs or dead larvae. We determined the theoretical lower developmental threshold and thermal constant for the complete development as 12.9 °C and 584.8 day-degrees for males, and 13.1 °C and 588.2 day-degrees for females, respectively. A good balance between faster development, maximum adult longevity and good egg viability was obtained between 25–30 °C, and that would be the best temperature range for rearing E. appendigaster. 相似文献