FWHM Measurements Research Articles

On the field size definition and field output factors in small field dosimetry.

There is a major conceptual difference between small-field and large field dosimetry that is, different definition of the field size. The dosimetry protocol IAEA TRS-483 recommends the use of the field size defined by measured dose profiles (full-width half maximum, FWHM) that is significantly different from conventional field size definition by the geometric field opening of MLC/Jaw at the isocenter. The application of the effective field size concept, Sclin , was introduced by Cranmer-Sargison etal. (DOI:10.1016/j.radonc.2013.10.002) as a reporting mechanism for field output factors of rectangular fields. The study by Das etal. (DOI:10.1002/mp.15624) indicated the limitations of obtaining the field size by experimentally measuring FWHM, for example, the measured FWHM is smaller than beam geometric size, which is contradictory to what is expected as a result of partial occlusion of the primary photon source by the collimating devices. Cranmer-Sargison etal. and Das et al suggested that additional investigations are needed to evaluate its limitations. This study investigates the validity of the field size definition by FWHM and by MLC/Jaw opening and finds the pros and cons between these two methods to resolve the controversial issue. The FWHM can be obtained by measuring or calculating dose profiles. Using Monte Carlo simulations this study compares the field size obtained by FWHM and by field geometric field opening. The EGSnrc system is used to simulate 6 MV beam to generate square and rectangular fields from 5-30mm with every possible permutation (keeping one jaw fixed and varying other jaw from 5 to 30mm). The calculated FWHM and output factors are compared with measurements obtained by a microSilicon detector. The results show that field width (FWHM) derived from MC calculations generally agrees with machine geometric field width within 0.5mm for square or rectangular fields with a minimum field width of ≥8mm. For the extremely small fields with a minimum field width of 5mm the discrepancies are up to 1.6mm. The field width (FWHM) obtained by measuring dose profiles are unreliable for small fields due to the measurement uncertainties for an extremely small field. The effect of partial occlusion of the primary photon source by the jaws on the beam axis is clearly observed in the calculated dose profiles. For the extremely small field width of 5mm, Monte Carlo predicted up to 10% exchange factor differences which are confirmed by the measurements. The field size defined by the geometric opening of the beam-defining system, is still valid for small fields. The field size defined by geometric opening is independent of measurement uncertainties, independent of machine design, and highly reproducible. It is feasible to accurately tabulate the output factors as a function of geometric field opening thus eliminating user and detector choice for FWHM measurements. The field output factor of a small rectangular field cannot be related to an equivalent field size without considering the exchange factor due to partial occlusion of the photon source.

Validity of equivalent square field concept in small field dosimetry.

The equivalent square (ES) concept has been used for traditional radiation fields defined by the machine collimating system. For small fields, the concept Sclin was introduced based on measuring dosimetric field width (full-width half maximum, FWHM) of the cardinal axis of the beam profiles. The pros and cons of this concept are evaluated in small fields and compared with the traditional ES using area and perimeter (4A/P) method based on geometric field size settings, for example, light field settings. One hundred thirty-seven square and rectangular fields from 5-50mm with every possible permutation (keeping one jaw fixed and varying other jaw from 5 to 50 mm) were utilized to measure FWHM for the validation of Sclin . Using a microSilicon detector and a scanning water tank, measurements were performed on an Elekta (Versa) machine with Agility head and a Varian TrueBeam with different MLC/Jaw design to evaluate the Sclin concept and to understand the effect of exchange factor in small fields. Field output factors were also measured for all 137 fields. The data fitting for fields ranging from 5-50mm between the traditional 4A/P method and Sclin shows differences and indicates a linear relationship with distinct separation of slope for Elekta and Varian machines. ForElekta Agility machine ES based on 4A/P<Sclin and for the VarianTrueBeam 4A/P>Sclin for square fields. Our measured data show that both methods are equally valid but does vary by the machine design. The field output factor is dependent on the elongation factor as well as machine design. For fields with sides ≥10mm, the exchange factor is nearly identical in both machines with magnitude up to 4%, which is close to measurement uncertainty (±3%), but for small fields (<10mm), the Elekta machine has higher exchange factors compared to the Varian machine. The results demonstrate that the two concepts for defining equivalent field (Sclin and 4A/P) are equivalent and can be directly related through an empirical equation. This study confirms that 4A/P is still valid for small fields except for very small fields (≤10mm) where source occlusion is a dominating factor. The Sclin method is potentially sensitive to measurement uncertainty due to measurement of FWHM which is machine-, detector- and user-dependent, while the 4A/P method relies mainly on geometry of the machine and has less dependency on type of machine, detector, and user. The exchange factors are comparable for both types of machines. The conclusion is based on data from an Elekta with Agility head and a Varian TrueBeam machine that may have potential for bias due to light field/collimator set up and alignment. Care should be taken in extrapolating these data to any other machine.

Surface Severe Plastically Deformed Nanostructured AA7075 Alloy: Assessment on Tribological and Axial Fatigue Behaviors

AA7075 alloy is exposed to severe shot peening (SSP) with an Almen intensity of 20A. The microstructure is analyzed via FEGSEM and EBSD microscopy. X-ray diffraction (XRD) analysis is used to evaluate the crystallite size in terms of FWHM measurements. The residual stress measurements show a thicker compressed layer (600 µm) formed by SSP. Microhardness improvements are observed as 30% on topmost surface and releases substantially after 600 µm. Coefficient of friction (COF) of treated material remains higher throughout the sliding distance, however, is reduced particularly in the early stage of sliding distance for the wear load of 20 N. The effect of SSP is vanished particularly at lower loads with longer sliding distances. Besides, improvement on fatigue behavior is observed after SSP despite the increase of roughness remarkably.

Data-driven optimal binning for respiratory motion management in PET.

Respiratory gating has been used in PET imaging to reduce the amount of image blurring caused by patient motion. Optimal binning is an approach for using the motion-characterized data by binning it into a single, easy to understand/use, optimal bin. To date, optimal binning protocols have utilized externally driven motion characterization strategies that have been tuned with population-derived assumptions and parameters. In this work, we are proposing a new strategy with which to characterize motion directly from a patient's gated scan, and use that signal to create a patient/instance-specific optimal bin image. Two hundred and nineteen phase-gated FDG PET scans, acquired using data-driven gating as described previously, were used as the input for this study. For each scan, a phase-amplitude motion characterization was generated and normalized using principle component analysis. A patient-specific "optimal bin" window was derived using this characterization, via methods that mirror traditional optimal window binning strategies. The resulting optimal bin images were validated by correlating quantitative and qualitative measurements in the population of PET scans. In 53% (n=115) of the image population, the optimal bin was determined to include 100% of the image statistics. In the remaining images, the optimal binning windows averaged 60% of the statistics and ranged between 20% and 90%. Tuning the algorithm, through a single acceptance window parameter, allowed for adjustments of the algorithm's performance in the population toward conservation of motion or reduced noise-enabling users to incorporate their definition of optimal. In the population of images that were deemed appropriate for segregation, average lesion SUV max were 7.9, 8.5, and 9.0 for nongated images, optimal bin, and gated images, respectively. The Pearson correlation of FWHM measurements between optimal bin images and gated images were better than with nongated images, 0.89 and 0.85, respectively. Generally, optimal bin images had better resolution than the nongated images and better noise characteristics than the gated images. We extended the concept of optimal binning to a data-driven form, updating a traditionally one-size-fits-all approach to a conformal one that supports adaptive imaging. This automated strategy was implemented easily within a large population and encapsulated motion information in an easy to use 3D image. Its simplicity and practicality may make this, or similar approaches ideal for use in clinical settings.

Dosimetric characterization of small fields using a plastic scintillator detector: A large multicenter study

PurposeIn modern radiation therapy accurate small fields dosimetry is a challenge and its standardization is fundamental to harmonize delivered dose in different institutions. This study presents a multicenter characterization of MLC-defined small field for Elekta and Varian linear accelerators. Measurements were performed using the Exradin W1 plastic scintillator detector. Materials and methodsThe project enrolled 24 Italian centers. Each center performed Tissue Phantom Ratio (TPR), in-plane and cross-plane dose profiles of 0.8×0.8cm2 field, and Output Factor (OF) measurements for square field sizes ranging from 0.8 to 10cm. Set-up conditions were 10cm depth in water phantom at SSD 90cm. Measurements were performed using two twin Exradin W1 plastic scintillator detectors (PSD) correcting for the Cerenkov effect as proposed by the manufacturer. ResultsData analysis from 12 Varian and 12 Elekta centers was performed. Measurements of 7 centers were not included due to cable problems. TPR measurements showed standard deviations (SD)<1%; SD<0.4mm for the profile penumbra was obtained, while FWHM measurements showed SD<0.5mm. OF measurements showed SD<1.5% for field size greater than 2×2cm2. Median OFs values were in agreement with the recent bibliography. ConclusionsHigh degree of consistency was registered for all the considered parameters. This work confirmed the importance of multicenter dosimetric intercomparison. W1 PSD could be considered as a good candidate for small field measurements.

Novel calibrations of virial black hole mass estimators in active galaxies based on X-ray luminosity and optical/near-infrared emission lines

Accurately weigh the masses of SMBH in AGN is currently possible for only a small group of local and bright broad-line AGN through reverberation mapping (RM). Statistical demographic studies can be carried out considering the empirical scaling relation between the size of the BLR and the AGN optical continuum luminosity. However, there are still biases against low-luminosity or reddened AGN, in which the rest-frame optical radiation can be severely absorbed/diluted by the host and the BLR emission lines could be hard to detect. Our purpose is to widen the applicability of virial-based SE relations to reliably measure the BH masses also for low-luminosity or intermediate/type 2 AGN that are missed by current methodology. We achieve this goal by calibrating virial relations based on unbiased quantities: the hard X-ray luminosities, in the 2-10 keV and 14-195 keV bands, that are less sensitive to galaxy contamination, and the FWHM of the most important rest-frame NIR and optical BLR emission lines. We built a sample of RM AGN having both X-ray luminosity and broad optical/NIR FWHM measurements available in order to calibrate new virial BH mass estimators. We found that the FWHM of the H$\alpha$, H$\beta$ and NIR lines (i.e. Pa$\alpha$, Pa$\beta$ and HeI$\lambda$10830) all correlate each other having negligible or small offsets. This result allowed us to derive virial BH mass estimators based on either the 2-10 keV or 14-195 keV luminosity. We took also into account the recent determination of the different virial coefficients $f$ for pseudo and classical bulges. By splitting the sample according to the bulge type and adopting separate $f$ factors we found that our virial relations predict BH masses of AGN hosted in pseudobulges $\sim$0.5 dex smaller than in classical bulges. Assuming the same average $f$ factor for both populations, a difference of $\sim$0.2 dex is still found.

Dosimetric characterization of linac small beams using a plastic scintillator detector: A multicenter study

Purpose In modern radiation therapy accurate dosimetry within small photon fields is a challenge. This study presents a multicenter characterization of MLC-defined small field for the two major linear accelerator manufacturers. Materials and methods The project enrolled 31 Italian centers, 15 equipped with Elekta Linacs and 16 equipped with Varian Linacs. Each center performed TPR, in-plane and cross-plane dose profile of 0.8 × 0.8 cm2 field and OFs measurements for field sizes ranging from 0.6 × 0.6 to 10 × 10 cm2. Set-up conditions were 10 cm depth in water phantom at SSD 90 cm. Measurements were performed using two Exradin W1 plastic scintillator detectors correcting for the Cerenkov effect as proposed by the manufacturer. Results Analysis of the measurements performed by 12 Varian and 13 Elekta centers was performed. TPR measurements showed standard deviations within 0.6%; penumbra values of dose profiles showed standard deviations within 0.5 mm. FWHM measurements showed a greater variability. OF measurements showed standard deviations within 1.5% for field size greater than 2 × 2 cm2; for field size less than 2 × 2 cm2 measurements’ variability increases with decreasing field size. OF values show no dependence from the effective field size. Conclusions Relatively high degree of consistency regarding TPR and penumbra values was registered. FWHM and OF instead show greater variability. Our work confirmed the importance of multicenter dosimetric studies and W1 PSD as a candidate for small field clinical radiation dosimetry in advanced radiation therapy techniques.

Origins of hillock defects on GaN templates grown on Si(111)

The origin of surface hillocks (also known as pancake defects) on GaN-on-Si wafers grown by MOVPE has been investigated. FIB/TEM observations confirmed that the appearance of the hillocks is due to the formation of Ga-rich precipitates within the AlGaN buffer layer. XRD (002) FWHM measurements also show that the surface hillocks are associated with a high degree of crystal tilt in the AlN nucleation layer. Two factors are considered to be the cause of such a phase separation: (1) a high density of surface steps associated with the regions of large crystal tilt which act as nucleation centers and (2) a lower mobility of Al adatoms at the growth surface compared with Ga, leading to a preferential incorporation of Ga in the precipitates. The impact of these precipitates on the wafer bow of the structures is considered.

SU-E-T-296: Dosimetric Analysis of Small Animal Image-Guided Irradiator Using High Resolution Optical CT Imaging of 3D Dosimeters

Purpose: To verify the dosimetric characteristics of a small animal image-guided irradiator using a high-resolution of optical CT imaging of 3D dosimeters. Methods: PRESAEGE 3D dosimeters were used to determine dosimetric characteristics of a small animal image-guided irradiator and compared with EBT2 films. Cylindrical PRESAGE dosimeters with 7cm height and 6cm diameter were placed along the central axis of the beam. The films were positioned between 6×6cm2 cubed plastic water phantoms perpendicular to the beam direction with multiple depths. PRESAGE dosimeters and EBT2 films were then irradiated with the irradiator beams at 220kVp and 13mA. Each of irradiated PRESAGE dosimeters named PA1, PA2, PB1, and PB2, was independently scanned using a high-resolution single laser beam optical CT scanner. The transverse images were reconstructed with a 0.1mm high-resolution pixel. A commercial Epson Expression 10000XL flatbed scanner was used for readout of irradiated EBT2 films at a 0.4mm pixel resolution. PDD curves and beam profiles were measured for the irradiated PRESAGE dosimeters and EBT2 films. Results: The PDD agreements between the irradiated PRESAGE dosimeter PA1, PA2, PB1, PB2 and the EB2 films were 1.7, 2.3, 1.9, and 1.9% for the multiple depths at 1, 5, 10, 15, 20, 30, 40 and 50mm, respectively. The FWHM measurements for each PRESAEGE dosimeter and film agreed with 0.5, 1.1, 0.4, and 1.7%, respectively, at 30mm depth. Both PDD and FWHM measurements for the PRESAGE dosimeters and the films agreed overall within 2%. The 20%–80% penumbral widths of each PRESAGE dosimeter and the film at a given depth were respectively found to be 0.97, 0.91, 0.79, 0.88, and 0.37mm. Conclusion: Dosimetric characteristics of a small animal image-guided irradiator have been demonstrated with the measurements of PRESAGE dosimeter and EB2 film. With the high resolution and accuracy obtained from this 3D dosimetry system, precise targeting small animal irradiation can be achieved.

TU-F-CAMPUS-T-03: A Novel Iris Quality Assurance Phantom for the CyberKnife Radiosurgery System

Purpose: A novel CCD camera and conical scintillator based phantom that is capable of measuring the targeting and field size accuracy of a robotic radiosurgery system has been developed. This work investigates its application in measuring the field sizes and beam divergence of the CyberKnife variable aperture collimator (Iris). Methods: The phantom was placed on the treatment couch and the robot position was adjusted to obtain an anterior -posterior beam perpendicular to the cone’s central axis. The FWHM of the 12 Iris apertures (5, 7.5, 10, 12.5, 15, 20, 25, 30, 35, 40, 50, and 60 mm) were measured from the beam flux map on the conical scintillator surface as seen by the CCD camera. For each measurement 30 MU were delivered to the phantom at a dose rate of 1000 MU/min. The measurements were repeated at 4 SAD distances between 75 and 85 cm. These readings were used to project the aperture size as if the flux map on the scintillator were located 80 cm from the source (SSD). These projected FWHM beam diameters were then compared to the commissioning data. Results: A series of 12 beam divergence equations were obtained from the 4 sets of data using linear trend lines on Excel scatter plots. These equations were then used to project the FWHM measurements at 80 cm SSD. The average aperture accuracy for beams from 5 through 40 mm was 0.08 mm. The accuracy for the 50 and 60 mm beams were 0.33 and 0.58 mm when compared to film commissioning data. Conclusion: The experimental results for 10 apertures agree with the stated Iris accuracy of ±0.2 mm at 80 cm SAD. The results for the 50 and 60 mm aperture were repeatable and can serve as a reliable trend indicator of any deviations away from the commissioning values. Brett Nelson is President/CTO of Logos Systems

Investigating the accuracy of microstereotactic-body-radiotherapy utilizing anatomically accurate 3D printed rodent-morphic dosimeters.

Sophisticated small animal irradiators, incorporating cone-beam-CT image-guidance, have recently been developed which enable exploration of the efficacy of advanced radiation treatments in the preclinical setting. Microstereotactic-body-radiation-therapy (microSBRT) is one technique of interest, utilizing field sizes in the range of 1-15 mm. Verification of the accuracy of microSBRT treatment delivery is challenging due to the lack of available methods to comprehensively measure dose distributions in representative phantoms with sufficiently high spatial resolution and in 3 dimensions (3D). This work introduces a potential solution in the form of anatomically accurate rodent-morphic 3D dosimeters compatible with ultrahigh resolution (0.3 mm(3)) optical computed tomography (optical-CT) dose read-out. Rodent-morphic dosimeters were produced by 3D-printing molds of rodent anatomy directly from contours defined on x-ray CT data sets of rats and mice, and using these molds to create tissue-equivalent radiochromic 3D dosimeters from Presage. Anatomically accurate spines were incorporated into some dosimeters, by first 3D printing the spine mold, then forming a high-Z bone equivalent spine insert. This spine insert was then set inside the tissue equivalent body mold. The high-Z spinal insert enabled representative cone-beam CT IGRT targeting. On irradiation, a linear radiochromic change in optical-density occurs in the dosimeter, which is proportional to absorbed dose, and was read out using optical-CT in high-resolution (0.5 mm isotropic voxels). Optical-CT data were converted to absolute dose in two ways: (i) using a calibration curve derived from other Presage dosimeters from the same batch, and (ii) by independent measurement of calibrated dose at a point using a novel detector comprised of a yttrium oxide based nanocrystalline scintillator, with a submillimeter active length. A microSBRT spinal treatment was delivered consisting of a 180° continuous arc at 225 kVp with a 20 × 10 mm field size. Dose response was evaluated using both the Presage/optical-CT 3D dosimetry system described above, and independent verification in select planes using EBT2 radiochromic film placed inside rodent-morphic dosimeters that had been sectioned in half. Rodent-morphic 3D dosimeters were successfully produced from Presage radiochromic material by utilizing 3D printed molds of rat CT contours. The dosimeters were found to be compatible with optical-CT dose readout in high-resolution 3D (0.5 mm isotropic voxels) with minimal artifacts or noise. Cone-beam CT image guidance was possible with these dosimeters due to sufficient contrast between high-Z spinal inserts and tissue equivalent Presage material (CNR ∼10 on CBCT images). Dose at isocenter measured with optical-CT was found to agree with nanoscintillator measurement to within 2.8%. Maximum dose in line profiles taken through Presage and film dose slices agreed within 3%, with FWHM measurements through each profile found to agree within 2%. This work demonstrates the feasibility of using 3D printing technology to make anatomically accurate Presage rodent-morphic dosimeters incorporating spinal-mimicking inserts. High quality optical-CT 3D dosimetry is feasible on these dosimeters, despite the irregular surfaces and implanted inserts. The ability to measure dose distributions in anatomically accurate phantoms represents a powerful useful additional verification tool for preclinical microSBRT.

Preliminary investigations of two types of silica-based dosimeter for small-field radiotherapy

Two thermoluminescent dosimeters (SiO 2 –GeO 2 doped fibres and glass beads (GB)) were used to measure small photon field doses and compared against GAFCHROMIC film, a small ionisation chamber (RK-018) and a p-type silicon diode (SCANDITRONIX, F1356), as well as Monte Carlo simulations with FLUKA and BEAMnrc/DOSXYZnrc. Ge-doped SiO 2 fibres have been shown by this group to offer a viable system for use as dosimeters. The fibres and GB offer good spatial resolution (~120 μm and 2 mm respectively), large dynamic dose range (with linearity from tens of mGy up to well in excess of many tens of Gy), are non-hygroscopic and are of low cost. Measurements of beam profiles for field sizes of 10 mm×10 mm, 20 mm×20 mm, 30 mm×30 mm, 40 mm×40 mm, and 100 mm×100 mm were carried out. Through the use of a customised solid water phantom, doped optical fibres and GBs were placed at defined positions along the x -and y -axes to allow accurate beam profile measurement. The maximum difference between FWHM measurements was 1.8 mm. For penumbra measurements (measured between 80% and 20% isodoses), the maximum difference was<1 mm. These measurements indicate good agreement, within measurement uncertainty, with Gafchromic film, data obtained from the use of two commonly used detectors and FLUKA and BEAMnrc/ DOSXYZnrc simulations. • SiO 2 –GeO 2 doped fibres and glass beads (GB) investigated as TLDs for their small field dosimetry. • The maximum inter-difference between FWHM measurements was 1.8 mm. • The maximum difference for penumbra measurements (80% to 20% beam fall off points) was<1 mm.

Influence of sputtering power on crystal quality and electrical properties of Sc-doped AlN film prepared by DC magnetron sputtering

Scandium-doped aluminum nitride alloy (ScAlN) thin films were deposited on (100) silicon substrates by DC reactive magnetron sputtering method using a scandium aluminum alloy (Sc0.06Al0.94) target. The influence of sputtering power on the crystalline structure, surface morphology and electrical properties of ScAlN thin films were investigated. The XRD patterns indicated all the films showed a single pronounced hexagonal (002) peak. According to the peak intensities in θ/2θ scans and rocking curve FWHM measurements of the (002) peaks, the crystalline quality of ScAlN thin film first increased and then decreased, reaching the best crystalline state at a sputtering power of 130W. The best surface morphology of ScAlN thin film was obtained at 130W and the surface roughness reached a minimum of 2.612nm. Then the piezoelectric response of ScAlN thin films was measured and the highest value, 8.9pC/N, was achieved at the sample with the best crystal quality. The resistivity and dielectric constant change in the same rule as the crystal quality, first increasing to a maximum value of 3.35×1012Ωcm and 13.6, and then decreasing with the sputtering power increasing. In addition, when the sputtering power was 130W, the highest breakdown field strength and lowest leakage current were obtained, with values 1.12MV/cm and 3×10−8A, respectively.

Two strategies of lowering surface deformations of internally cooled X-ray optics

Internally cooled X-ray optics, like X-ray monochromators and reflecting X-ray mirrors, play a crucial role in defining a beamlines resolution, degree of coherence and flux. A great effort is invested in the development of these optical components. An important aspect of the functionality of high heat load optics is its cooling and its influence on surface deformation. The authors present a study of two different geometrical cooling approaches. Its influence on beam inhomogeneity due to the strain from the manufacturing process is presented. X-ray topographic images and FWHM measurements are presented. FEA simulations of cooling efficiency and surface deformations were performed. The best achieved results are under an enlargement of 0.4μrad of the measured rocking curve.

Influence of N2/Ar-flow ratio on crystal quality and electrical properties of ScAlN thin film prepared by DC reactive magnetron sputtering

Scandium aluminum nitride alloy (ScAlN) thin films were prepared using DC reactive magnetron sputtering with a scandium aluminum alloy (Sc0.06Al0.94) target on n-type silicon substrates. We have investigated the influence of N2/Ar-flow ratio on the crystalline structure, the surface morphology and the electrical properties of ScAlN thin films. Consequently, it was statistically proved that the N2/Ar-flow ratio was an important control factor in the process of sputtering. According to the peak intensities in θ/2θ scans and rocking curve FWHM measurements of the (002) peaks, the crystalline quality of ScAlN thin film first increased and then decreased, reaching the best crystalline state at a N2/Ar-flow ratio of 3.3:7. The best surface morphology of ScAlN thin film was obtained at N2/Ar-flow ratios of 3.2:7, 3.3:7 and 3.4:7 and the surface roughness reached a minimum of 2.612nm at 3.3:7. The resistivity and dielectric constant first increased to maximum values of 3.35×1012Ωcm and 13.6, and then decreased with the ratio increasing. Moreover, ScAlN thin film exhibited a higher value of resistivity and dielectric constant when compared with un-doped AlN thin film. In addition, when the N2/Ar-flow ratio was 3.3:7, the highest breakdown field strength and lowest leakage current were obtained, with values 1.12MV/cm and 3×10−8A, respectively.

SU-E-E-04: Automated Analysis of Quality Assurance Phantom Scan Image in Functional Lung CT Study by Using Simulated CT Imaging Technique

Purpose: Quality assurance is of crucial importance in functional lung studies and yet requires time consuming manual measurements on phantom scan images. We present an automated method for analyzing CT scan images of quality assurance phantom. Methods: COPDgene™ quality assurance phantom was scanned in 4 commercial scanners (Discovery750, GE, Sensation16, Siemens, Ingenuity, Philips, Aquillion One, Toshiba) with 45 different combinations of mAs, reconstruction kernels and display FOV. In addition, simulated CT images were generated by using geometric and attenuation properties of design sheet of phantom and applying projection and filtered backprojection algorithms. In order to mimic real CT images, filter kernels were derived from measured MTFs of the CT scanners. Rigid image registration technique was used to find best matching translation and rotation parameters between simulated and real CT scan images, followed by measurements of FWHM and ROI statistic for the known positions and sizes of artificial airways and simulated lung foam materials. Results: Image registration was performed successfully in all CT scan images, yielding rotation and translation parameters within accuracy range less than 0.8 mm. FWHM measurements were extracted for 14 holes and 6 tubes ranging 2mm ∼ 10mm in diameter. Discrepancies between measured FWHM and ground truth value ranged from 0.02 ∼ 1.5mm. Conclusion: Proposed method could successfully recognize locations and types of objects in the quality assurance phantom, and thereby carrying out measurements required for the quality assurance procedure. This technique has the potential to improve quality of functional lung CT studies.

SU-E-T-148: Fluence/Dose Comparison

Purpose: To determine if X‐ray beam fluence measured at the CyberKnife is collimator can be used to reliably predict dose FWHM at 800 mm SAD. Method: A camera‐scintillator system (Iris Beam Aperture Caliper‐Logos Systems) was connected to the CyberKnife such that the scintillator surface was within a millimeter of the collimator. X‐ray fluence images were captured for the 12 Ms apertures. The IBAC software measured 72 FWHM diameters at 5 degree intervals on each beam spot in order to develop the average. EDR2 film was used to capture beam images of the 12 aperture sizes at 800 mm SAD. This film was scanned with a Vidar scanner and the images brought into RIT software to measure FWHM dose diameters for each beam. In addition, these film images were input into the IBAC software to measure the agreement between the IBAC and RIT image processing algorithms. Results: The IBAC fluence diameters when projected from 400 to 800 mm SAD were equivalent to the film dose measurements with an average delta of 0.30 mm (standard deviation 0.06 mm). The IBAC measurements of the film diameters matched the RIT measurements with an average delta of 0.032 mm (standard deviation 0.015 mm). The time required to perform the IBAC measurements was 20 minutes while the time needed to expose, scan, and measure the film was 2 hours. Conclusion: This work indicates that the IBAC system can be used to produce fluence FWHM measurements that closely correlate with the Results of conventional film based systems. Since no film is used and the total amount of time saved is more than 1.5 hours, measuring the fluence at the collimator source with the IBAC can be seen as an effective Ms QA alternative, having a lower incremental cost per measurement.

Performance of the linear ion trap Orbitrap mass analyzer for qualitative and quantitative analysis of drugs of abuse and relevant metabolites in sewage water

This work illustrates the potential of liquid chromatography coupled to a hybrid linear ion trap Fourier Transform Orbitrap mass spectrometer for the simultaneous identification and quantification of 24 drugs of abuse and relevant metabolites in sewage water. The developed methodology consisted of automatic solid-phase extraction using Oasis HLB cartridges, chromatographic separation of the targeted drugs, full-scan accurate mass data acquisition under positive electrospray ionization mode over an m/z range of 50–600Da at a resolution of 30,000 FWHM and simultaneous MSn measurements to obtain information of fragment ions generated in the linear ion trap. Accurate mass of the protonated molecule, together with at least one nominal mass product ion and retention time allowed the confident identification of the compounds detected in these complex matrices. In addition to the highly reliable qualitative analysis, Orbitrap analyzer also proved to have satisfactory potential for quantification at sub-ppb analyte levels, a possibility that has been very little explored in the literature until now. The limits of quantification ranged from 4 to 68ngL−1 in influent sewage water, and from 2 to 35ngL−1 in effluent, with the exception of MDA, morphine and THC that presented higher values as a consequence of the high ionization suppression in this type of samples. Satisfactory recoveries (70–120%) and precision (<30%) for the overall procedure were obtained for all compounds with the exception of meta-chlorophenylpiperazine, methylphenidate and ketamine. Isotope-labelled internal standards were added to sewage samples as surrogates in order to correct for matrix effects and also for possible losses during sample treatment. The methodology developed was applied to sewage water samples from the Netherlands (influent and effluent), and the results were compared with those obtained by LC–MS/MS with triple quadrupole. Several drugs of abuse could be identified and quantified, mainly MDMA, benzoylecgonine, codeine, oxazepam and temazepam. Orbitrap also showed potential for retrospective investigation of ketamine metabolites in the samples without the need of additional analysis.

Ultrafast Decay of Trp in Biological Macromolecules

Femtosecond (<300fs fwhm) measurements of fluorescence decay and quenching of Tryptophan (Trp) were performed in a variety of proteins, including GB1, Thioredoxin (both wild type from two species and a human Trx mutant with a single Trp), Cyanovirin and Interleukin-1beta using an upconversion spectrophotofluorometer combined with a time correlated single photon counting apparatus to span the ∼200fs to 20ns time scale. Trp is subject both to ultrafast quenching in proteins and spectral energy loss coupled to nearby water dynamics. All fluorescence transients of tryptophan in proteins reveal complex, i.e. multiexponential behavior. In addition to a “bulk water” relaxation (∼2 ps), a 50 ps fluorescence decay was found in single-Trp thioredoxin which matched the component we had found previously in two-Trp Anabaena and E. coli thioredoxins . In fact, a sub-100ps component is consistently found in all but one of these proteins with positive amplitudes even at longer wavelengths (e.g., 390nm). The exception is GB1, a protein which Toptygin and Brand previously found carried a negative preexponential term near 390nm. Since the lifetime associated with that negative was 65ps, it was just within the edge of TCSPC detection. The more prevalent positive amplitude DAS (decay-associated spectra) we see in the other proteins on these timescales are indicative of ultrafast quenching processes depleting the partly relaxed singlet state. Candidate mechanisms include ET to nearby acceptors and/or collisional quenching. This is similar to our prior observation (J. Am. Chem. Soc., 2006, 128, 1214) that ultrafast quenching, not desorbing water, dominates the time-resolved emission spectra (TRES) of monellin. We will discuss the −/+ data signatures for both water relaxation and fast quenching, including simulations to lay out the circumstances where a fast relaxation accompanied by a direct radiative rate reduction might mask the negative term.

ROTATIONAL VELOCITY DETERMINATIONS FOR 118 δ SCUTI VARIABLES

A calibration method is presented for the determination of projected rotational velocities of 118 δ Scuti variables from FWHM measurements of metal lines near 4500 Å. The calibration relation used was derived from measurements of 29 stars. Of the 44 stars brighter than 8th magnitude and north of −1° declination which did not have values in the Rodríguez catalog (Rodríguez, E., López González, M. J., & López de Coca, P. 2000, A&AS, 144, 469) we present values for 38. In addition, we present new projected rotational velocity, vsin i, values for 10 stars south of −1° or fainter than 8th magnitude for a total of 48 vsin i values for stars with no previously published values.