The development of iron-free partially stabilized cement for use as dental root-end filling material.

AIM: To determine the effect of increasing the proportion of zinc on partially stabilized cement (PSC) produced using a one-step sol gel process. METHODOLOGY: A one-step sol-gel process of Portland cement-based PSC with Zn was synthesized by replacing iron nitrate. The crystalline phases of the PSC-Zn powder were analysed by using X-ray diffraction (XRD). The experimental groups [i.e., MTA, PSC-Fe (control), PSC with 1% Zn, PSC with 3% Zn, and PSC with 5% Zn] were immersed in simulated body fluid for 3 h, 1 and 3 days to evaluate the hydration product formation. The microstructure and surface morphology were analysed using scanning electron microscopy (SEM). Initial and final setting times of the materials were determined using an ASTM Vicat needle testing machine. To evaluate the cytotoxicity of PSC-Zn system, primary osteoblasts cell lines were used. RESULTS: The addition of increased weight percentages of Zn, resulted in a more unstable phase which favoured the formation of a monoclinic structure of C3 S with an increased hydration reaction of PSC and reduced setting time. The cytotoxicity testing of PSC with Zn revealed that the material was not toxic. CONCLUSIONS: The newly synthesized PSC-Zn material had short setting time and was biocompatible.

SU-E-T-14: Modeling of 3D Positron Emission Activity Distributions Induced by Proton Irradiation: A Semi-Empirical Method.

PURPOSE: to present and validate a method for modeling three-dimensional positron emission (PE) activity distributions induced by proton beam irradiation for PET/CT delivery verification studies in homogeneous media. METHODS: the method relies on modeling the 3D proton flux distribution by combining the analytical expression for the depth reduction of proton flux with the empirically obtained lateral distribution. The latter is extracted from the corresponding dose distribution under the assumption that the projectile energy is nearly constant in the lateral plane. The same assumption allows calculating the 3D induced activity distributions from proton flux distributions by parameterizing the energy-dependent activation cross-sections in terms of depth via the energy-range relation. Results of this modeling approach were validated against experimental PET/CT data from three phantom deliveries: unmodulated (pristine) beam, spread-out Bragg peak (SOBP) delivery without a range compensator, and SOBP with a range compensator. BANG3-Pro2 polymer gel was used as a phantom material because of its elemental soft-tissue equivalence. RESULTS: the agreement between modeled and measured activity distributions was evaluated using 3D gamma index analysis method, which, despite being traditionally reserved for dose distribution comparisons, is sufficiently general to be applied to other quantities. The evaluation criteria were dictated by limitations of PET imaging and were chosen to correspond to count rate uncertainty (6% value difference) and spatial resolution (4 mm distance to agreement). With these criteria and the threshold of 6%, the fraction of evaluated voxels passing the gamma evaluation was 97.9% for the pristine beam, 98.9% for the SOBP without compensator, and 98.5% for SOBP with compensator. CONCLUSIONS: results of gamma evaluation indicate that the activity distributions produced by the model are consistent with experimental data within the uncertainties of PET imaging for clinical proton beams deliveries. This work was supported by the Bankhead-Coley Florida Biomedical Research Program under Grant No. 1BD10-34212.

SU-E-J-76: Clinical Use of a Real-Time Surface Image-Guided Positioning and Tracking System in Proton Therapy.

Topic of interest: Clinical applications of AlignRT 3-cameras real-time surface image-guided positioning system (IGPS) for positioning patients to reduce the number of X-ray images and tracking intra-fractional movements in proton therapy. PURPOSES: To position patients and track the intra-fractional movements, the AlignRT system was implemented in proton incline-beam-line (IBL) at Procure Oklahoma-City center. METHODS: The AlignRT3c system was configured near perpendicular to the gantry rotation for accommodating the X-ray IGPS. To evaluate positioning accuracy, more than 10 surfaces of each patient for ten patients with intracranial tumors were acquired after patients positioned by X-ray IGPS. Displacements between acquired surfaces and the reference surface taken at 1st day of treatment were examined. Intra-fractional movements with respiratory was studied with gated surface that allows setting the reference surface for patient at exhale during breathing. Intra-fractional movements due to respiratory were monitored on 10 sections of each patient for three patients with thoracic tumors. RESULTS: Accuracy of positioning patient is 2.0 mm at both anterior-posterior and lateral directions, and is 3.5 mm in superior-inferior (SI) direction by aligning the surfaces of masks. Observed larger displacements along SI direction can be due to patient's movements within the mask. Periodical displacements within 5 mm compared to its reference were seen for the three patients with thorax tumors. However, 10 mm sharp displacements with a few seconds were observed when patient moved the body. CONCLUSIONS: We have implemented the first AlignRT3c IGPS for proton therapy for positioning patients within 2.0 mm, and successfully tracked intra-fractional respiratory motion during treatment after positioning patient.

SU-E-T-301: A Novel Daily QA Device for Proton Therapy.

PURPOSE: We describe the design and use of a daily QA device for proton therapy. The device is designed for therapists to check the readiness of the IBA Proton Therapy System (IBA, Louvain-la-Neuve, Belgium) during morning QA. The checks include connectivity, positioning, mechanical, imaging and dosimetric parameters of the proton therapy system. METHODS: The device consists of a commercial QA device, (rf-DailyQA3 -Sun Nuclear Corporation, Melbourne, FL), in conjunction with a home-made acrylic phantom and mechanical indexing jig. The indexing jig indexes the rf-DailyQA3 to treatment couch. Fiducial markers embedded in the phantom are used for checking the x-ray image and alignment accuracy of the imaging system (VeriSuite, MedCom, Darmstadt- Germany). The rf- DailyQA3 is used to check the proton beam output, range and symmetry, which are acquired during one single beam delivery of 100 monitor units. We developed in-house software to calculate the variation of beam range and symmetry, based on readings from the various ion chambers inside the rf-DailyQA3. RESULTS: The device has been employed to perform daily QA since June 2010 at two operational proton treatment centers and will soon be implemented at ProCure's New Jersey center. All QA tests are performed by radiation therapists and reviewed by the medical physicist on duty. Due to the simplicity of the device and the associated processing software, the QA time is less than 20 minutes per room. The measurement data collected by the device during daily QA are recorded in the OIS. The integrity of the data is validated by comparing against other independent measurements. CONCLUSIONS: The daily QA device has been proven to be robust, reliable and user-friendly. The performance of this system has been proven to be stable and accurate using trend analyses. Key words:proton therapy, daily QA, output, range, symmetry.

MO-A-213AB-03: Commissioning of a Clinical Chair for Patients Treated in the Seated Position Using an Inclined Beam Line Treatment Room.

PURPOSES: A chair, coupled to a robotic patient positioning system (PPS) was manufactured to treat an intracranial tumor in a proton incline beam-line system. Treating patients in the seated position as accurately and efficiently as a treatment table requires the essential functions of isocentric rotation and a weight-sagging-correction algorithm for positioning patients in the seated position. METHODS AND MATERIALS: The chair design incorporated a down-slope arm to achieve the desired beam-line height. To overcome this limitation of only 125 degree rotation on PPS, five indexed positions of the seat-base-plate (SBP) were implemented. An in-house developed optical tracking system using a six degree-of-freedom optical camera system was used to align the treatment room coordinate system with the chair coordinate system at all SBP positions. Furthermore, this optical tracking system quantified the sagging effect due to both the height and weight of a variety of patients. RESULTS: The optical tracking system can measure accuracy of 0.1 degree and 0.1 mm. The SBP rotating axis was aligned within 0.1 degree to PPS rotating axis. A residual precession of chair rotation was found to be an ellipse with long axis of 2.0 mm and short axis of 1.0 mm. An additional 0.75 mm deviation occurred between rotating of SBP and PPS axes. Sagging tilt of 0.6 degree was found on the SBP for the home position for every additional 162 lbs load. This resulted in a 1.1cm shift (0.65 cm forward and 0.87 cm) for an isocenter 90 cm away from the SBP plate. CONCLUSIONS: Using in-house developed optical tracking system, the overall maximum displacement of treatment chair system from isocenter is within 3.0 mm with known sagging characteristics. This characterization is essential to reduce the total treatment time and limited the number of X-rays required for accurate patient alignment in the seated position.

SU-E-T-202: Comprehensive Quality Assurance Procedures for Uniform Scanning Proton Therapy Machines.

PURPOSE: Quality assurance (QA) is essential in safe and accurate delivery of radiation therapy. However, QA in proton therapy is challenging due to complicated and often facility-specific beam delivery systems and limited beam time for QA. The purpose of this study is to develop an efficient and comprehensive QA procedure for a multi-room proton therapy center using uniform scanning beams. METHODS: Our proton therapy center is comprised of a 230 MeV cyclotron, one fixed beam room, two inclined beam rooms, and one gantry room. Uniform scanning is employed exclusively in all treatment rooms. A rfDaily QA3 (Sun Nuclear Inc., Melbourne, Florida) together with home-made devices is used for daily QA. Parallel plane chambers, a multi-layer ionization chamber array (Zebra, IBA dosimetry, Schwarzenbruck, German), and an IC profiler (Sun Nuclear Inc., Melbourne, Florida) are used to QA the characteristics of the uniform scanning beams, including output, range, modulation width, flatness, symmetry, and penumbra, for both monthly and annual QA. QA procedures and acceptance criteria were developed, taking into account the likelihood and potential risk of failure, as well as the available equipment, personnel and other resources. RESULTS: QA procedures and tolerances were developed for daily, monthly and annual QA at our proton therapy center. Daily QA is performed by radiation therapists, and can be completed within 30 minutes for all rooms. Monthly QA and annual QA are performed by physicists, taking about 4 hours and a weekend respectively. Trend analysis was performed for various machine characteristics, such as machine output, range, flatness, and symmetry. CONCLUSION: QA standards are desired in Radiation Oncology, but not many standards are developed and available for proton therapy. In the mean time, facility-specific QA procedures should be developed based on the equipment failure modes and available resources.

Dosimetric evaluation of a novel polymer gel dosimeter for proton therapy.

PURPOSE: The aim of this study is to evaluate the dosimetric performance of a newly developed proton-sensitive polymer gel formulation for proton therapy dosimetry. METHODS: Using passive scattered modulated and nonmodulated proton beams, the dose response of the gel was assessed. A next-generation optical CT scanner is used as the readout mechanism of the radiation-induced absorbance in the gel medium. Comparison of relative dose profiles in the gel to ion chamber profiles in water is performed. A simple and easily reproducible calibration protocol is established for routine gel batch calibrations. Relative stopping power ratio measurement of the gel medium was performed to ensure accurate water-equivalent depth dose scaling. Measured dose distributions in the gel were compared to treatment planning system for benchmark irradiations and quality of agreement is assessed using clinically relevant gamma index criteria. RESULTS: The dosimetric response of the gel was mapped up to 600 cGy using an electron-based calibration technique. Excellent dosimetric agreement is observed between ion chamber data and gel. The most notable result of this work is the fact that this gel has no observed dose quenching in the Bragg peak region. Quantitative dose distribution comparisons to treatment planning system calculations show that most (> 97%) of the gel dose maps pass the 3%/3 mm gamma criterion. CONCLUSIONS: This study shows that the new proton-sensitive gel dosimeter is capable of reproducing ion chamber dose data for modulated and nonmodulated Bragg peak beams with different clinical beam energies. The findings suggest that the gel dosimeter can be used as QA tool for millimeter range verification of proton beam deliveries in the dosimeter medium.

Clinical characterization of a proton beam continuous uniform scanning system with dose layer stacking.

A proton beam delivery system on a gantry with continuous uniform scanning and dose layer stacking at the Midwest Proton Radiotherapy Institute has been commissioned and accepted for clinical use. This paper was motivated by a lack of guidance on the testing and characterization for clinical uniform scanning systems. As such, it describes how these tasks were performed with a uniform scanning beam delivery system. This paper reports the methods used and important dosimetric characteristics of radiation fields produced by the system. The commissioning data include the transverse and longitudinal dose distributions, penumbra, and absolute dose values. Using a 208 MeV cyclotron's proton beam, the system provides field sizes up to 20 and 30 cm in diameter for proton ranges in water up to 27 and 20 cm, respectively. The dose layer stacking method allows for the flexible construction of spread-out Bragg peaks with uniform modulation of up to 15 cm in water, at typical dose rates of 1-3 Gy/min. For measuring relative dose distributions, multielement ion chamber arrays, small-volume ion chambers, and radiographic films were employed. Measurements during the clinical commissioning of the system have shown that the lateral and longitudinal dose uniformity of 2.5% or better can be achieved for all clinically important field sizes and ranges. The measured transverse penumbra widths offer a slight improvement in comparison to those achieved with a double scattering beam spreading technique at the facility. Absolute dose measurements were done using calibrated ion chambers, thermoluminescent and alanine detectors. Dose intercomparisons conducted using various types of detectors traceable to a national standards laboratory indicate that the measured dosimetry data agree with each other within 5%.

Event-by-event analysis of proton-induced nuclear multifragmentation: determination of the phase transition universality class in a system with extreme finite-size constraints.

A percolation model of nuclear fragmentation is used to interpret 10.2 GeV/c p+197Au multifragmentation data. Emphasis is put on finding signatures of a continuous nuclear matter phase transition in finite nuclear systems. Based on model calculations, corrections accounting for physical constraints of the fragment detection and sequential decay processes are derived. Strong circumstantial evidence for a continuous phase transition is found, and the values of two critical exponents, sigma = 0.5+/-0.1 and tau = 2.35+/-0.05, are extracted from the data. A critical temperature of T(c) = 8.3+/-0.2 MeV is found.

Modulation of radiotherapy photon beam intensity using magnetic field.

The purpose of this study was to explore the potential advantages of using strong magnetic fields to increase tumor dose and to decrease normal tissue dose in radiation therapy. Strong magnetic fields are capable of altering the trajectories of charged particles. A magnetic field applied perpendicularly to the X-ray beam forces the secondary electrons and positrons to spiral and produces a dose peak. The same magnetic field also prevents the electrons and positrons from traveling downstream and produces a lower dose region distal to the dose peak. The locations of these high- and low-dose regions are potentially adjustable to enhance the dose to the target volume and decrease the dose to normal tissues. We studied this effect using the Monte Carlo simulation technique. The EGS4 code was used to simulate the effect produced by a coil magnet currently under construction. The coil magnet is designed to support up to 350 A operating current and 15 T peak field on windings. Dose calculations in a water phantom show that the transverse magnetic field produces significant dose effects along the beam direction of radiation therapy X-rays. Depending on the beam orientation, the radiation dose at different depths along the beam can be increased or reduced. This dose effect varies with photon energy, field size, magnetic field strength, and relative magnet/beam geometry. The off-axis beam profiles also show considerable skewness under the influence of the magnetic field. The magnetic field-induced dose shift may result in high dose regions outside the geometrical boundary of the initial radiation beam. We have demonstrated that current or near-term magnet technology is capable of producing significant dose enhancement and reduction in radiation therapy photon beams. This technology should be further developed to improve our ability to deliver higher doses to the tumor and lower doses to normal tissues in radiation therapy.

Signals for a transition from surface to bulk emission in thermal multifragmentation.

Excitation-energy-gated two-fragment correlation functions have been studied between E(*)/A = (2-9)A MeV for equilibriumlike sources formed in 8-10 GeV/c pi(-) and p+197Au reactions. Comparison with an N-body Coulomb-trajectory code shows an order of magnitude decrease in the fragment emission time in the interval E(*)/A = (2-5)A MeV, followed by a nearly constant breakup time at higher excitation energy. The decrease in emission time is strongly correlated with the onset of multifragmentation and thermally induced radial expansion, consistent with a transition from surface-dominated to bulk emission expected for spinodal decomposition.

In-shoe pressure measurements with a viscoelastic heel orthosis.

OBJECTIVE: To detect the mechanical effect of a viscoelastic heel orthosis. DESIGN: Two-factor analysis of variance with interactions between the orthosis and the subjects. The number of subjects was determined by presuming the effect of the orthosis to be twice as large as the error-free standard deviation (SD) of the interactions, the step-to-step SD four times as large as the error-free SD of the interactions, type 1 error probability equal to .05, and type 2 error probability equal to .20. SETTING: A gait laboratory in a university hospital. SUBJECTS: Twenty-two consecutive patients with treated heel pain. MAIN OUTCOME MEASURES: Peak pressure (PP), pressure-time integral (PTI), and foot-to-sensor contact time (CoT) measured for five steps at 24 discrete sensors of predetermined positions in the foot with treated heel pain. RESULTS: The orthosis reduced PPs, PTIs, and CoT (p < .05) in the median midfoot and lateral midfoot; reduced PPs and PTIs (p < .05) in the posterior heel and medial midfoot; increased PP and PTI (p < .05) in the anterior part of the first metatarsal head; and increased PTI (p < .05) in the lateral part of the hallux. The ratios of the estimated step-to-step SDs to the estimated error-free SDs of the interactions of PPs, PTIs, and CoT were less than four at all the sensors. CONCLUSION: Proper design and estimation of the variations ensured that there was sufficient power to detect the effect of an a priori specified size as statistically significant: the orthosis reduced the mechanical loads in the posterior heel and the midfoot and increased the mechanical loads in the anterior part of the first metatarsal head and the lateral part of the hallux during walking.

Effects of overlapping parametric resonances on the particle diffusion process.

The evolution of the beam distribution in a double-rf system with a phase modulation on either the primary or secondary rf cavity was measured. We find that the particle diffusion process obeys the Einstein relation if the phase space becomes globally chaotic. When dominant parametric resonances still exist in the phase space, particles stream along the separatrices of the dominant resonance, and the beam width exhibits characteristic oscillatory structure. The particle-tracking simulations for the double-rf system are employed to reveal the essential diffusion mechanism. Coherent octupolar motion has been observed in the bunch beam excitation. The evolution of the longitudinal phase space in the octupole mode is displayed.

Normal standards for cardiopulmonary responses to exercise using a cycle ergometer test.

The purpose of the study was to establish standards for cardiopulmonary responses to exercise in healthy Chinese subjects in Taiwan. One hundred and five sedentary healthy subjects, 55 men and 50 women aged between 20 and 75 years, were tested. They pedalled a cycle ergometer with the work rate increased by 10 W every minute until they were exhausted. Expiratory gas volume, oxygen concentration, carbon dioxide concentration, and heart rate were measured during the exercise test. Work rate (WRmax), oxygen consumption (VO2max), oxygen consumption divided by body weight (VO2max/BW), heart rate (HRmax), and ventilation (VEmax) at maximal exercise, and oxygen consumption at anaerobic threshold (VO2AT) were determined. These parameters were regressed by age (A, in year), height (H, in cm), body weight (G, in kg), and gender (S, 0 = women, and 1 = men), and the following predictive equations were obtained: 1) WRmax (W) = -1.2 A + 1.1 H + 0.7 G + 28 S - 56, R = 0.90; 2) VO2max (ml/min) = -20 A + 9.5 H + 16 G + 461 S - 237, R = 0.90; (3) VO2max/BW (ml/kg/min) = -0.31 A + 0.14 H - 0.14 G - 7.2 S + 22, R = 0.87; 4) HRmax (beat/min) = -0.81 A + 209, R = 0.61; 5) VEmax (L/min) = -0.74 A - 0.04 H + 0.93 G + 22.2 S + 42, R = 0.83; 6) VO2AT (ml/min) = -9.5 A + 3.5 H + 9.4 G + 140 S - 122, R = 0.79. Our results provide normal standards for cardiopulmonary responses to exercise during cycle ergometer testing in Taiwan.

Submaximal oxygen pulse divided by body weight during incremental exercise test.

The purpose of this study was to examine whether submaximal oxygen pulse divided by body weight (O2 pulse/BW) during an incremental exercise test discriminated between trained and untrained men, correlated to left ventricular ejection fraction (LVEF) at rest in post-myocardial infarction patients, and was sensitive and specific in detecting ventricular dysfunction and mild ventricular dysfunction with myocardial ischemia during exercise. Forty-three trained men, 44 untrained men, and 21 post-myocardial infarction patients pedaled a cycle ergometer, with O2 consumption, heart rate, and myocardial ischemia monitored during the exercise test. Work rate started at 10 W and increased 10 W/min stepwise; the O2 pulse and O2 pulse/BW at 10 through 120 W were calculated. The LVEF of the patients was measured at rest using radionuclide ventriculography three weeks after myocardial infarction. The results revealed that O2 pulse/BW was significantly different between trained and untrained men at 80, 90, 100, 110, and 120 W, whereas O2 pulse was significantly different only at 110 and 120 W. Oxygen pulse/BW at 10 W, as well as 30 through 120 W, significantly correlated to LVEF in the patients. The three patients with ventricular dysfunction (LVEF, < 40%) plus the two patients with mild ventricular dysfunction (LVEF between 40 and 50%) and ST segment depression during exercise all had submaximal O2 pulse/BW significantly lower than untrained men (sensitivity, 100%). Among the 11 patients with normal ventricular function (LVEF, > 50%) plus the 5 patients with mild ventricular dysfunction but no ST segment depression, 13 patients did not have submaximal O2 pulse/BW significantly lower than untrained men (specificity, 81%).

The mechanism of plantar unloading in total contact casts: implications for design and clinical use.

Although the total contact cast (TCC) has been shown to be an extremely effective treatment for the healing of plantar ulcers in diabetic patients, little is known about the biomechanics of its action. In this study, plantar pressure and ground reaction force measurements were obtained from over 750 foot contacts as five subjects with known elevated plantar forefoot pressures walked barefoot, in a padded cast shoe, and a TCC. Peak plantar pressures in the forefoot were markedly reduced in the cast compared with both barefoot and shoe walking (reductions of 75% and 86% respectively, P < 0.05). Peak plantar pressures in the heel were not, however, significantly different between the shoe and the TCC, and the longer duration of heel loading resulted in an impulse that was more than twice as great in the cast compared with the shoe (P < 0.05). An analysis of load distribution indicated that the mechanisms by which the TCC achieves forefoot unloading are (1) transfer of approximately 30% of the load from the leg directly to the cast wall, (2) greater proportionate load sharing by the heel, and (3) removal of a load-bearing surface from the metatarsal heads because of the "cavity" created by the soft foam covering the forefoot. These results point out some of the "essential design features" of the TCC (which are different from what had been previously supposed), support the use of the TCC for healing plantar ulcers in the forefoot, but raise questions about its utility in the healing of plantar ulcers on the heel.

Exercise test in acute myocardial infarction.

Although maximal oxygen consumption (VO2max) and oxygen consumption at anaerobic threshold (VO2AT) were used to measure cardiac function, the clinical significance in acute myocardial infarction (MI) has not been reported. The purpose of this study was to compare VO2max and VO2AT between post-MI patients and healthy men and to correlate the parameters to other clinical measures. Forty-three active healthy men, 44 sedentary healthy men, and 43 post-MI patients were studied using incremental cycle exercise test. Their work rates, oxygen consumption, heart rates, oxygen pulses, ventilation, and other parameters at VO2max and VO2AT were determined with spirometer, gas concentration analyzer, and electrocardiograph. Anaerobic threshold was determined by analyzing the ventilatory parameters. Most of the exercise test parameters at VO2max were greatest in the active men, intermediate in the sedentary men, and least in the post-MI patients (P < 0.01) whereas the rate-pressure products of the active men and sedentary men were not significantly different from each other and were greater than those of the post-MI patients (P < 0.01). In the post-MI patients, VO2max was inversely correlated to the peak serum level of creatine phosphokinase MB isoenzyme (P < 0.01) and associated with extensive infarction (P < 0.05). Most of the parameters at VO2AT were greater in the active men than in the sedentary men (P < 0.01) but not significantly different between the sedentary men and post-MI patients. In the post-MI patients, VO2AT was significantly correlated to left ventricular ejection fraction (P < 0.01) and associated with heart failure (P < 0.05). The results revealed that VO2max and VO2AT had different clinical significance in post-MI patients; VO2max was related to the infarct size, and VO2AT was related to the pumping function of heart.