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PubMed1998

Rolf Wideröe and the development of particle accelerators.

The development of particle accelerators is traced from the simple but ingenious table-top devices conceived during the late 1920s to the present day's large, complex machines which extend over tens of kilometers. The emphasis is on Rolf Wideröe and his seminal contributions to the field. Not only did Wideröe construct the first accelerator which accelerated charged particles to an energy higher than the maximum voltage difference is the accelerator proper, he also invented particle colliders, today's work horse in experimental particle physics.

History, 20th Century↗

PubMed1999

Monte Carlo modelling of electron beams from medical accelerators.

Monte Carlo simulation of radiation transport is considered to be one of the most accurate methods of radiation therapy dose calculation. With the rapid development of computer technology, Monte Carlo based treatment planning for radiation therapy is becoming practical. A basic requirement for Monte Carlo treatment planning is a detailed knowledge of the radiation beams from medical accelerators. A practical approach to obtain the above is to perform Monte Carlo simulation of radiation transport in the medical accelerator. Additionally, Monte Carlo modelling of the treatment machine head can also improve our understanding of clinical beam characteristics, help accelerator design and improve the accuracy of clinical dosimetry by providing more realistic beam data. This paper summarizes work over the past two decades on Monte Carlo simulation of clinical electron beams from medical accelerators.

Electrons↗

PubMed2006

A virtual-accelerator-based verification of a Monte Carlo dose calculation algorithm for electron beam treatment planning in homogeneous phantoms.

By introducing Monte Carlo (MC) techniques to the verification procedure of dose calculation algorithms in treatment planning systems (TPSs), problems associated with conventional measurements can be avoided and properties that are considered unmeasurable can be studied. The aim of the study is to implement a virtual accelerator, based on MC simulations, to evaluate the performance of a dose calculation algorithm for electron beams in a commercial TPS. The TPS algorithm is MC based and the virtual accelerator is used to study the accuracy of the algorithm in water phantoms. The basic test of the implementation of the virtual accelerator is successful for 6 and 12 MeV (gamma < 1.0, 0.02 Gy/2 mm). For 18 MeV, there are problems in the profile data for some of the applicators, where the TPS underestimates the dose. For fields equipped with patient-specific inserts, the agreement is generally good. The exception is 6 MeV where there are slightly larger deviations. The concept of the virtual accelerator is shown to be feasible and has the potential to be a powerful tool for vendors and users.

Algorithms↗

PubMed1994

Phantoms for studying the acceleration and turbulence of liquids using magnetic resonance imaging.

Magnetic resonance angiography is a relatively new method used to image vascular structure. However, a limitation manifested through signal loss due to non-stable flow makes this technique unreliable for directly visualizing occlusions and estimating the degree of stenosis. In this study, a quantitative approach is developed to understand further the situations where signal loss occurs and a phase mapping technique is used quantitatively to study acceleration in test objects designed to generate flow disturbance. In regions of acceleration the correlation coefficient between magnetic resonance imaging velocity and the inverse of area was r > 0.999 (p < 0.001). The range of acceleration calculated was 6514-63,053 mm s-2 and at maximum acceleration the measured velocity had a systematic error of 4.0(+/- 2.0)% and coefficient of variation of 3.1%. Test objects were devised and utilized for demonstrating non-stable flow and jet formation with comparison being made to predictions from fluid dynamics theory.

Acceleration↗

PubMed2001

Special radiation protection aspects of medical accelerators.

Radiation protection aspects relevant to medical accelerators are discussed. An overview is first given of general safety requirements. Next, shielding and labyrinth design are discussed in some detail for the various types of accelerators, devoting more attention to hadron machines as they are far less conventional than electron linear accelerators. Some specific aspects related to patient protection are also addressed. Finally, induced radioactivity in accelerator components and shielding walls is briefly discussed. Three classes of machines are considered: (1) medical electron linacs for 'conventional' radiation therapy, (2) low energy cyclotrons for production of radionuclides mainly for medical diagnostics and (3) medium energy cyclotrons and synchrotrons for advanced radiation therapy with protons or light ion beams (hadron therapy).

Electrons↗

PubMed2001

Radiation safety systems for accelerator facilities.

The radiation safety system RSS) of an accelerator facility is used to protect people from prompt radiation hazards associated with accelerator operation. The RSS is a fully interlocked, engineered system with a combination of passive and active elements that are reliable, redundant and fail-safe. The RSS consists of the access control system (ACS) and the radiation containment system (RCS). The ACS is to keep people away from the dangerous radiation inside the shielding enclosure. The RCS limits and contains the beam/radiation conditions to protect people from the prompt radiation hazards outside the shielding enclosure in both normal and abnormal operations. The complexity of an RSS depends on the accelerator and its operation. as well as associated hazard conditions. The approaches of RSS among different facilities can be different. This report gives a review of the RSS for accelerator facilities.

Humans↗

PubMed2005

The PDS-XADS reference accelerator and its radioprotection issues.

At the start-up of the FP5 project PDS-XADS, the main initial specifications for the accelerator system (e.g. beam energy, beam intensity, beam profile, their stability and the accelerator availability and reliability) have been defined by Working Package 1 (WP1), 'Global Coherence', in connection with the other WPs of the project. From this, WP3 ('The Accelerator') has assessed the main requirements and the corresponding technical answers. A reference solution, based on a linear superconducting accelerator with its associated doubly achromatic beam line has been worked out to some detail. For high reliability, the proposed design is intrinsically fault tolerant, relying on highly modular 'de-rated' components associated with a fast digital feedback system. The proposed solution also appears to be robust in terms of operational aspects like maintenance and radioprotection. A programme for the remaining R&D required has been elaborated and is proposed within the FP6 project EUROTRANS.

Equipment Design↗

PubMedDate not supplied

Forces, moments, and accelerations acting on an unrestrained dummy during simulations of three wheelchair accidents.

To determine the magnitude and distribution of the forces, moments, and accelerations acting on an individual sitting in a wheelchair during three possible accidents occurring while negotiating a sidewalk curb, experimental trials were performed in a bioengineering laboratory using a 50th percentile Hybrid III dummy seated in a standard wheelchair. A ramp was designed with an adjustable incline to allow the wheelchair to reach the edge of a sidewalk height platform at the desired forward speed of 2.5 miles per hour (comfortable walking speed). The wheelchair velocity was monitored via an optical pickup. Three types of accidents were simulated: (1) a wheelchair hitting straight into a curb; (2) a wheelchair falling forward straight off a curb; (3) a wheelchair falling diagonally off a curb. Each experiment was repeated three times. Each run was photographed using high-speed cameras and videotaped from three perspectives: frontal, lateral, and overhead. The results were averaged and compared with published injury Assessment Values (IAV) and Head Injury Criteria (HIC). Of significance were the following results. In the straight into a curb experiments, the wheelchair remained upright and the dummy seated. Low magnitude forces (23-73 N), moments (1-12 Nm), and accelerations (0.2-1 G) were recorded at the neck and head. The HIC was low at 0.3. These results were of no clinical significance. In the straight off a curb experiments, properly attached footrests prevented the wheelchair from toppling over but did not prevent the dummy from falling off the wheelchair. Forces (187-4,176 N), moments (3-178 Nm), and accelerations (131-206 G) of great magnitude were recorded at the head and neck when the dummy fell off the wheelchair. These values were above IAV. The HIC was 960. In the diagonally off a curb experiments, both the wheelchair and the dummy fell sideways. High-magnitude forces (274-2,313 N), moments (4-110 Nm), and acceleration (140-236 G) were recorded in the head and neck regions. The HIC was 975. These values were close to IAV and may signify potential serious injuries.

Acceleration↗

PubMed2003

Contribution of accelerated body masses to able-bodied gait.

OBJECTIVE: The objectives of this study were to demonstrate that data from a video-based system could be used to estimate the net effect of the external forces during gait, to determine the contribution of the trunk and upper and lower limbs using their accelerated body masses, and to test the hypothesis that the thigh mainly assumed lower limb propulsion during able-bodied locomotion. METHODS: The gait of 16 able-bodied subjects was assessed using an eight-camera video-based system and two force plates. The right limb was the leading limb, and there were two trials per subject. Although data from all the body segments were used to answer the first two objectives, only right limb information was used to address the third objective. RESULTS: Pearson's coefficients of correlation and root mean square errors were calculated to determine the difference between the curves obtained from the sum of the external forces and that of the accelerated masses. These were >0.85, and the mean root mean square error was <4 N. Analyses of variance were performed on the peak forces developed by the trunk and the upper and lower limbs along each axis. Tukey's posthoc tests (P < 0.05) revealed that the trunk was the principal contributor of external forces in the frontal and transverse planes, whereas the lower limbs were found to be more important in the plane of progression. Analyses of variance and Tukey's posthoc tests (P < 0.05) were performed on the peak forces developed by each segment of the right limb. In decreasing order, the thigh, shank, and foot displayed the highest mass-acceleration products in the right limb during gait. CONCLUSIONS: A video-based system was able to determine the net effect of the external forces with the summation of the mass-acceleration products during able-bodied gait. The trunk and lower limbs were the dominant body segments responsible for the production of external forces during able-bodied gait, whereas the thighs contributed more to the ground reaction force than the foot and shank for forward progression in able-bodied gait.

Acceleration↗

PubMed1995

Shielding design and dose assessment for accelerator based neutron capture therapy.

Preparations are ongoing to test the viability and usefulness of an accelerator source of epithermal neutrons for ultimate use in a clinical environment. This feasibility study is to be conducted in a shielded room located on the Massachusetts Institute of Technology campus and will not involve patient irradiations. The accelerator production of neutrons is based on the 7Li(p, n)7Be reaction, and a maximum proton beam current of 4 mA at an energy of 2.5 MeV is anticipated. The resultant 3.58 x 10(12) neutrons s-1 have a maximum energy of 800 keV and will be substantially moderated. This paper describes the Monte Carlo methods used to estimate the neutron and photon dose rates in a variety of locations in the vicinity of the accelerator, as well as the shielding configuration required when the device is run at maximum current. Results indicate that the highest absorbed dose rate to which any individual will be exposed is 3 microSv h-1 (0.3 mrem h-1). The highest possible yearly dose is 0.2 microSv (2 x 10(-2) mrem) to the general public or 0.9 mSv (90 mrem) to a radiation worker in close proximity to the accelerator facility. The shielding necessary to achieve these dose levels is also discussed.

Biophysical Phenomena↗

PubMed2002

Induced radioactive potential for a medical accelerator.

Medical accelerators operating over 10 MV can induce short-lived radionuclides in components near the beam and in the air (McGinley 1992). We evaluated a Clinac 2100 C/D at 18 MV photon mode for radionuclidic exposure, contamination, and airborne potential to the accelerator staff entering the room after patient radiation treatment. The gantry, patient couch, wedges, floor, and air were activated. Most activated components appear to decay with a half-life of 2.5 min, except the gantry and port with half-lives approaching 10 min. The highest exposure was from the port at <2 mR h(-1). No removable contamination on any activated component was detected including coolant water in the machine. Airborne radionuclides were measured in the room and at the roof exhaust. The airborne potential is short lived because of ventilation and decay with the highest exposure of 0.3 mR h(-1) lasting for 1 s. Our measurements support the insignificant exposures received by accelerator staff wearing whole body personnel monitors. Accelerator roof effluents to unrestricted areas during patient treatments indicate that regulatory limits are not exceeded.

Environmental Exposure↗

PubMed2002

Internal loads in the cervical spine during motor vehicle rear-end impacts: the effect of acceleration and head-to-head restraint proximity.

STUDY DESIGN: This study used rigid-body and finite-element models of forces in the cervical spine resulting from a rear-end motor vehicle impact based on data from 26 volunteer experiments. OBJECTIVES: To define the magnitudes and directions of internal forces acting on the cervical spine during rear-end impact, and to determine the effects of increasing the impact acceleration and the initial position of the occupant's head with respect to the head restraint. SUMMARY OF BACKGROUND DATA: In a number of studies using volunteers or cadavers, the kinematics of the occupant during a rear-end impact related to "whiplash" of the cervical spine have been reported. Few studies have described the mechanism by which internal spine forces are produced and how they may be affected by interaction of the occupant with the seat and head restraint during impact. METHODS: From a companion study on the response of 26 volunteers to rear-end impact, experimental data on head and torso accelerations were developed. Rigid-body mathematical dynamic modeling of a 50th-percentile male was implemented, along with a finite-element seat model, lap belt, and shoulder belt. The model was first subjected to a rear-impact pulse similar to that used in the volunteer study, first with a peak of 3.5 G, then with a peak up to 12 G. Initial head-to-head restraint distance in the model was varied from 1 to 12.5 cm. RESULTS: The major cervical spine forces were upper and lower neck shear causing intervertebral relative anterior displacements. Increasing the peak acceleration magnitude caused increased neck shear force magnitudes. With the head initially positioned closer to the head restraint, the time difference between the occurrences of the peak upper and lower neck shear forces was smaller; the C7-T1 intervertebral shear displacements were reduced; the head moved more in phase with the torso; extension of the head and neck was reduced; and late head flexion was increased. CONCLUSIONS: In this simulation, anterior shear was the major internal force acting in the cervical spine during rear-end impact. Increasing impact acceleration magnitude directly increased shear force. When the head was initially closer to the head restraint, the magnitude of the shear force was unaffected, but the time difference between its occurrences in the upper and lower neck was decreased and intervertebral translations were reduced. These results suggest how the seat could be improved to reduce peals forces and the time differences between them.

Acceleration↗

PubMed1999

Kinetics of stiff-legged gait: induced acceleration analysis.

Treating spastic paretic stiff-legged gait, defined as reduced knee flexion in swing, holds a high priority in the rehabilitation of patients with upper motor neuron lesions. We propose a method to determine the relative contributions of hip, knee, and ankle impairments to this disability. We analyzed the gait of ten patients with stiff-legged gait (SLG) due to a single stroke and ten healthy, able-bodied controls. Using subject specific models, we analyzed the induced accelerations (IA's) at the knee. Knee IA's throughout the gait cycle were calculated and the sum of the IA's was compared to the knee joint angular acceleration estimated from kinematic data. The preswing and early swing IA's were the focus of our examination as these largely determine knee kinematics in swing. Knee angular accelerations estimated from IA's and kinematic data agreed for both controls and patients. Gait cycle IA analysis of individual patients identified highly variable causes of SLG including ankle and hip joint impairments. Induced acceleration analysis (IAA) suggested that multiple impairments, not just about the knee, but also about the hip and ankle, lead to this disability. Individual subjects are likely to have individual reasons for their stiff-legged gait. Defining the link between the patients specific impairments and their gait disability should be a goal of clinical gait analysis. IAA is a useful tool for this purpose with a strong potential for clinical application.

Acceleration↗

PubMed1988

Measurement of acceleration: a new method of monitoring neuromuscular function.

A new method for monitoring neuromuscular function based on measurement of acceleration is presented. The rationale behind the method is Newton's second law, stating that the acceleration is directly proportional to the force. For measurement of acceleration, a piezo-electric ceramic wafer was used. When this piezo electrode was fixed to the thumb, an electrical signal proportional to the acceleration was produced whenever the thumb moved in response to nerve stimulation. The electrical signal was registered and analysed in a Myograph 2000 neuromuscular transmission monitor. In 35 patients anaesthetized with halothane, train-of-four ratios measured with the accelerometer (ACT-TOF) were compared with simultaneous mechanical train-of-four ratios (FDT-TOF). Control ACT-TOF ratios were significantly higher than control FDT-TOF ratios: 116 +/- 12 and 98 +/- 4 (mean +/- s.d.), respectively. In five patients not given any relaxant during the anaesthetic procedure (20-60 min), both responses were remarkably constant. In 30 patients given vecuronium, a close linear relationship was found during recovery between ACT-TOF and FDT-TOF ratios. It is concluded that the method fulfils the basic requirements for a simple and reliable clinical monitoring tool.

Acceleration↗

PubMed2004

An algorithm for estimating acceleration magnitude and impact location using multiple nonorthogonal single-axis accelerometers.

Accelerations of the head are the likely cause of concussion injury, but identifying the specific etiology of concussion has been difficult due to the lack of a valid animal or computer model. Contact sports, in which concussions are a rising health care concern, offer a unique research laboratory environment. However, measuring head acceleration in the field has many challenges including the need for large population sampling because of the relatively low incidence of concussions. We report a novel approach for calculating linear acceleration that can be incorporated into a head-mounted system for on-field use during contact sports. The advantages of this approach include the use of single-axis linear accelerometers, which reduce costs, and a nonorthogonal arrangement of the accelerometers, which simplifies the design criteria for a head-mounted and helmet compatible system. The purpose of this study was to describe the algorithm and evaluate its accuracy for measuring linear acceleration magnitude and impact location using computer simulation and experimental tests with various accelerometer configurations. A 10% error in magnitude and a 10 deg error in impact location were achieved using as few as six single-axis accelerometers mounted on a hemispherical headform.

Acceleration↗

PubMed2002

Accelerator-based neutron brachytherapy.

The development and evaluation of a new approach to neutron brachytherapy is described. This approach, accelerator-based fast neutron brachytherapy, involves the interstitial or intracavity insertion of a narrow, evacuated accelerator beam tube such that its tip, containing the neutron-producing target, is placed in or near the tumor. Tumor irradiation via brachytherapy should result in a reduction in the healthy tissue complication rate observed when poorly collimated and/or low energy external neutron beam are used for treatment. Use of a variable energy accelerator provides an advantage over isotope sources for neutron brachytherapy in that the neutron beam can be turned on and off and the neutron energy spectrum varied for different treatment applications. A prototype accelerator-based fast neutron brachytherapy device, 10 cm long and 6 mm outer diameter, has been constructed and evaluated in terms of its dosimetric output, treatment time, and practical feasibility. The prototype device is a tube-in-tube design with cooling water running between the inner and outer tubes to cool a beryllium target located at the tip of the inner tube. Cooling experiments were performed and coupled with Monte Carlo simulations to determine treatment times as a function of heat load for various neutron-producing reactions. Using the 9Be(d,n) 10B reaction at Ed= 1.5 MeV, 66 RBE-Gy (12 Gy physical dose) can be delivered to the boundary of a 4.5-cm-diam treatment volume in 8 min at a heat load of 130 W. Other reactions offer similar treatment times at somewhat higher bombarding energies and also show higher potential for dose enhancement with the boron-10 neutron capture reaction due to their softer neutron spectra. Dose distributions in a water phantom were measured with the prototype brachytherapy tube using the dual-ion chamber technique for the 9Be(d,n) 10B reaction at Ed = 1.5 MeV. The measurements and simulations agree within uncertainties and demonstrate that fast neutrons contribute more than 90% of the dose to the target volume.

Brachytherapy↗

PubMed2003

Which accelerator photon beams are "clinic-like" for reference dosimetry purposes?

Previous work has demonstrated that, for photon beam dosimetry, TPR10(20) is not an ideal beam quality specifier for all bremsstrahlung beams, especially for lightly filtered beams in some standards laboratories. This paper addresses the following questions: Is TPR10(20) an adequate beam quality specifier for all modern clinical therapy accelerators? When can nonclinical beams in standards laboratories be used to calibrate ion chambers or measure kQ factors as a function of TPR10(20)? Based on detailed Monte Carlo simulations of Varian, Siemens, Elekta, and GE (Saturn) accelerators one can conclude that TPR10(20) is an adequate beam quality specifier for all these machines in the sense that for a given value of TPR10(20), the value of stopping-power ratios is the same. It is shown that, for the heavily filtered beams used in standards laboratories, TPR10(20) is an adequate beam quality specifier. It is also demonstrated that, for a larger range of bremsstrahlung beams than previously, %dd(10)x is a good beam quality specifier for all clinical beams as well as the lightly and heavily filtered beams in some standards laboratories. A criterion, based on the measured values of TPR10(20) and %dd(10)x for the beam, is proposed for determining whether a nonclinical beam is well specified by TPR10(20). Agreement between calculations for specific accelerators and measured beam quality specifiers is shown to be good, but agreement with published data for a variety of clinical accelerators is not as good. Possible reasons for the discrepancy are discussed.

Energy Transfer↗

PubMed2003

Focal spot motion of linear accelerators and its effect on portal image analysis.

The focal spot of a linear accelerator is often considered to have a fully stable position. In practice, however, the beam control loop of a linear accelerator needs to stabilize after the beam is turned on. As a result, some motion of the focal spot might occur during the start-up phase of irradiation. When acquiring portal images, this motion will affect the projected position of anatomy and field edges, especially when low exposures are used. In this paper, the motion of the focal spot and the effect of this motion on portal image analysis are quantified. A slightly tilted narrow slit phantom was placed at the isocenter of several linear accelerators and images were acquired (3.5 frames per second) by means of an amorphous silicon flat panel imager positioned approximately 0.7 m below the isocenter. The motion of the focal spot was determined by converting the tilted slit images to subpixel accurate line spread functions. The error in portal image analysis due to focal spot motionwas estimated by a subtraction of the relative displacement of the projected slit from the relative displacement of the field edges. It was found that the motion of the focal spot depends on the control system and design of the accelerator. The shift of the focal spot at the start of irradiation ranges between 0.05-0.7 mm in the gun-target (GT) direction. In the left-right (AB) direction the shift is generally smaller. The resulting error in portal image analysis due to focal spotmotion ranges between 0.05-1.1 mm for a dose corresponding to two monitor units (MUs). For 20 MUs, the effect of the focal spot motion reduces to 0.01-0.3 mm. The error in portal image analysis due to focal spot motion can be reduced by reducing the applied dose rate.

Artifacts↗