bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐456: Tomotherapy MLC Synchronization and Leaf Open Time Measurements Using ArcCheck
Authors: Yang B , Wong R , Lam W , Geng H , Cheung K , Yu S 
Published: July 2016

Purpose:To develop a practical method for routine QA of the MLC of a Tomotherapy unit using ArcCheck.Methods:Two standard test plans were used in this study. One was a helical test, in which the central leaves No. 32 and 33 opened simultaneously for 277.8ms at projections centered at 0°, 120° and 240° gantry angles. The other test plan was a static test with the gantry angle set at 0°, 45°, 90° and 135° respectively and leaves No. 32 and 33 opened sequentially for total 20s which was further divided into eleven or ten segments at each beam angle. The ArcCheck was isocentrically set up and adjusted for couch sag. Movie files which took a snapshot exposure every 50ms were recorded. The start/stop time of leaf open was decided by the ramp‐up/ramp‐down of the detectors.Results:The percentage differences between measured and planned leaf open time were calculated to be within 0.5% in all the tests. In static test, if leaves are synchronized perfectly, the sum of the two detectors’ signals after normalization should equal one when the leaves are in transition. Our results showed mean values of 0.982, 0.983, 0.978 and 0.995 at static gantry angle 0°, 45°, 90° and 135° respectively.Conclusion:A method for estimating the Tomotherapy binary MLC leaf open time using ArcCheck is proposed and proved to be precise enough to verify the planned leaf open time as small as 277.8ms. This method also makes the observation and quantification of the synchronization of leaves possible.
SU‐F‐T‐458: Tracking Trends of TG‐142 Parameters Via Analysis of Data Recorded by 2D Chamber Array
Authors: Alexandrian A , Kabat C , Defoor D , Saenz D , Rasmussen K , Kirby N , Gutierrez A , Papanikolaou N , Stathakis S 
Published: July 2016

Purpose:With increasing QA demands of medical physicists in clinical radiation oncology, the need for an effective method of tracking clinical data has become paramount. A tool was produced which scans through data automatically recorded by a 2D chamber array and extracts relevant information recommended by TG‐142. Using this extracted information a timely and comprehensive analysis of QA parameters can be easily performed enabling efficient monthly checks on multiple linear accelerators simultaneously.Methods:A PTW STARCHECK chamber array was used to record several months of beam outputs from two Varian 2100 series linear accelerators and a Varian NovalisTx−. In conjunction with the chamber array, a beam quality phantom was used to simultaneously to determine beam quality. A minimalist GUI was created in MatLab that allows a user to set the file path of the data for each modality to be analyzed. These file paths are recorded to a MatLab structure and then subsequently accessed by a script written in Python (version 3.5.1) which then extracts values required to perform monthly checks as outlined by recommendations from TG‐142. The script incorporates calculations to determine if the values recorded by the chamber array fall within an acceptable threshold.Results:Values obtained by the script are written to a spreadsheet where results can be easily viewed and annotated with a “pass” or “fail” and saved for further analysis. In addition to creating a new scheme for reviewing monthly checks, this application allows for able to succinctly store data for follow up analysis.Conclusion:By utilizing this tool, parameters recommended by TG‐142 for multiple linear accelerators can be rapidly obtained and analyzed which can be used for evaluation of monthly checks.
SU‐F‐T‐459: ArcCHECK Machine QA : Highly Efficient Quality Assurance Tool for VMAT, SRS & SBRT Linear Accelerator Delivery
Authors: Mhatre V , Patwe P , Dandekar P 
Published: July 2016

Purpose:Quality assurance (QA) of complex linear accelerators is critical and highly time consuming. ArcCHECK Machine QA tool is used to test geometric and delivery aspects of linear accelerator. In this study we evaluated the performance of this tool.Methods:Machine QA feature allows user to perform quality assurance tests using ArcCHECK phantom. Following tests were performed 1) Gantry Speed 2) Gantry Rotation 3) Gantry Angle 4)MLC/Collimator QA 5)Beam Profile Flatness & Symmetry. Data was collected on trueBEAM stX machine for 6 MV for a period of one year. The Gantry QA test allows to view errors in gantry angle, rotation & assess how accurately the gantry moves around the isocentre. The MLC/Collimator QA tool is used to analyze & locate the differences between leaf bank & jaw position of linac. The flatness & Symmetry test quantifies beam flatness & symmetry in IEC‐y & x direction. The Gantry & Flatness/Symmetry test can be performed for static & dynamic delivery.Results:The Gantry speed was 3.9 deg/sec with speed maximum deviation around 0.3 deg/sec. The Gantry Isocentre for arc delivery was 0.9mm & static delivery was 0.4mm. The maximum percent positive & negative difference was found to be 1.9 % & – 0.25 % & maximum distance positive & negative diff was 0.4mm & – 0.3 mm for MLC/Collimator QA. The Flatness for Arc delivery was 1.8 % & Symmetry for Y was 0.8 % & X was 1.8 %. The Flatness for gantry 0°,270°,90° & 180° was 1.75,1.9,1.8 & 1.6% respectively & Symmetry for X & Y was 0.8,0.6% for 0°, 0.6,0.7% for 270°, 0.6,1% for 90° & 0.6,0.7% for 180°.Conclusion:ArcCHECK Machine QA is an useful tool for QA of Modern linear accelerators as it tests both geometric & delivery aspects. This is very important for VMAT, SRS & SBRT treatments.
SU‐F‐T‐460: Dosimetric Matching Between Trilogy Tx and TrueBeam STx
Authors: Choi Y , Kwak J , Jeong C , Ahn S , Lee S , Cho B 
Published: July 2016

Purpose:To compare the commissioned beam data for one flattening filter photon mode (6 MV) and two flattening filter‐free (FFF) photon modes (6 and 10 MV‐FFF) between Trilogy Tx and TrueBeam STx and evaluate the possibility of dosimetric matchingMethods:Dosimetric characteristics of the new Trilogy Tx including percent depth doses (PDDs), profiles, and output factors were measured for commissioning. Linear diode array detector and ion chambers were used to measure dosimetric data. The depth of dose maximum (dmax) and PDD at 10 cm (PDD10) were evaluated: 3×3 cm2, 10×10 cm2, and 40×40 cm2. The beam profiles were compared and then penumbras were evaluated. As a further test of the dosimetric matching, the same VMAT plans were delivered, measured with film, and compared with TPS calculation.Results:All the measured PDDs matched well across the two units. PDD10 showed less than 0.5% variation and dmax were within 1.5 mm at the field sizes evaluated. Within the central 80% of transverse axis, profile data were almost identical. TrueBeam data resulted in a slightly greater penumbra width (up to 1.9 mm). The greatest differences of output factors were found at 40 × 40 cm2: 2.40%, 2.03%, and 2.22% for 6 MV, 6 MV‐FFF, and 10 MV‐FFF, respectively. For smaller field sizes, less than 1% differences were observed. The film measurements demonstrated over 97.3% pixels passing‐gamma analysis (2%/2mm). The results showed excellent agreement between measurements of two machines.Conclusion:The differences between Trilogy Tx and TrueBeam STx found could possibly affect small field and also very large field sizes in dosimetric matching considerations. These differences encountered are mostly related with the changes in the head design of the TrueBeam. Although it cannot guarantee full interchangeability of two machines, dosimetric matching by field size of 25 × 25 cm2 might be clinically acceptable.
SU‐F‐T‐462: Lessons Learned From a Machine Incident Reporting System
Authors: Sutlief S , Hoisak J 
Published: July 2016

Purpose:Linear accelerators must operate with minimal downtime. Machine incident logs are a crucial tool to meet this requirement. They providing a history of service and demonstrate whether a fix is working. This study investigates the information content of a large department linear accelerator incident log.Methods:Our department uses an electronic reporting system to provide immediate information to both key department staff and the field service department. This study examines reports for five linac logs during 2015. The report attributes for analysis include frequency, level of documentation, who solved the problem, and type of fix used.Results:Of the reports, 36% were documented as resolved. In another 25% the resolution allowed treatment to proceed although the reported problem recurred within days. In 5% only intermediate troubleshooting was documented. The remainder lacked documentation. In 60% of the reports, radiation therapists resolved the problem, often by clearing the appropriate faults or reinitializing a software or hardware service. 22% were resolved by physics and 10% by field service engineers. The remaining 8% were resolved by IT, Facilities, or resolved spontaneously. Typical fixes, in order of scope, included clearing the fault and moving on, closing and re‐opening the patient session or software, cycling power to a sub‐unit, recalibrating a device (e.g., optical surface imaging), and calling in Field Service (usually resolving the problem through maintenance or component replacement).Conclusion:The reports with undocumented resolution represent a missed opportunity for learning. Frequency of who resolves a problem scales with the proximity of the person's role (therapist, physicist, or service engineer), which is inversely related to the permanence of the resolution. Review of lessons learned from machine incident logs can form the basis for guidance to radiation therapists and medical physicists to minimize equipment downtime and ensure safe operation.
SU‐F‐T‐463: Light‐Field Based Dynalog Verification
Authors: Atwal P , Ramaseshan R 
Published: July 2016

Purpose:To independently verify leaf positions in so‐called dynalog files for a Varian iX linac with a Millennium 120 MLC. This verification provides a measure of confidence that the files can be used directly as part of a more extensive intensity modulated radiation therapy / volumetric modulated arc therapy QA program.Methods:Initial testing used white paper placed at the collimator plane and a standard hand‐held digital camera to image the light and shadow of a static MLC field through the paper. Known markings on the paper allow for image calibration. Noise reduction was attempted with removal of ‘inherent noise’ from an open‐field light image through the paper, but the method was found to be inconsequential. This is likely because the environment could not be controlled to the precision required for the sort of reproducible characterization of the quantum noise needed in order to meaningfully characterize and account for it. A multi‐scale iterative edge detection algorithm was used for localizing the leaf ends. These were compared with the planned locations from the treatment console.Results:With a very basic setup, the image of the central bank A leaves 15–45, which are arguably the most important for beam modulation, differed from the planned location by [0.38±0.28] mm. Similarly, for bank B leaves 15–45 had a difference of [0.42±0.28] mmConclusion:It should be possible to determine leaf position accurately with not much more than a modern hand‐held camera and some software. This means we can have a periodic and independent verification of the dynalog file information. This is indicated by the precision already achieved using a basic setup and analysis methodology. Currently, work is being done to reduce imaging and setup errors, which will bring the leaf position error down further, and allow meaningful analysis over the full range of leaves.
SU‐F‐T‐464: Development of a Secondary Check Procedure to Evaluated Flatness and Symmetry Discrepancies Detected During Daily Morning QA
Authors: Wagar M , Friesen S , Lyatskaya Y , O'Farrell D , Bhagwat M 
Published: July 2016

Purpose:A daily QA device is used to monitor output, flatness and symmetry constancy for all linac photon and electron energies. If large deviations from baseline in flatness or symmetry are reported it becomes necessary to crosscheck the measurements with a second device. Setting up another device such as Matrixx (IBA Dosimetry) can be time consuming, due to its warm‐up time, and trained personnel may not be readily available to analyze the results. Furthermore, this discrepancy is frequently isolated to a single energy. Unaffected energies could still be used, avoiding further patient delays, if a method to gather data for offline analysis could be developed. We find that optically stimulated luminescent dosimeters (OSLDs) provide a quick, simple, and inexpensive solution to this important clinical problem.Methods:The exact geometry of the detectors on the daily tracker (Keithley Therapy Beam Evaluator) was reproduced by placing nanoDot OSLDs (Landauer) on a solid water phantom. A combination of bolus and solid water was placed on top to provide buildup and prevent air gaps. Standard daily measurements of output, flatness and symmetry were taken for 2 photon energies (6x,10x) and 5 electron energies (6e,9e,12e,15e,18e) using the tracker. These measurements were then repeated with the OSLD phantom.Results:The time it took to set up the OSLD phantom was comparable to that of the tracker. The inline and crossline OSLD phantom measurements of flatness and symmetry agreed with the tracker results to within 2%.Conclusion:OSLDs provide a good solution for a quick second check when questionable flatness and symmetry results are detected with the tracker during daily QA.
SU‐F‐T‐472: Validation of Absolute Dose Measurements for MR‐IGRT With and Without Magnetic Field
Authors: Green O , Li H , Goddu S , Mutic S , Kawrakow I 
Published: July 2016

Purpose:To validate absolute dose measurements for a MR‐IGRT system without presence of the magnetic field.Methods:The standard method (AAPM's TG‐51) of absolute dose measurement with ionization chambers was tested with and without the presence of the magnetic field for a clinical 0.32‐T Co‐60 MR‐IGRT system. Two ionization chambers were used ‐ the Standard Imaging (Madison, WI) A18 (0.123 cc) and the PTW (Freiburg, Germany). A previously reported Monte Carlo simulation suggested a difference on the order of 0.5% for dose measured with and without the presence of the magnetic field, but testing this was not possible until an engineering solution to allow the radiation system to be used without the nominal magnetic field was found. A previously identified effect of orientation in the magnetic field was also tested by placing the chamber either parallel or perpendicular to the field and irradiating from two opposing angles (90 and 270). Finally, the Imaging and Radiation Oncology Core provided OSLD detectors for five irradiations each with and without the field ‐ with two heads at both 0 and 90 degrees, and one head at 90 degrees only as it doesn't reach 0 (IEC convention).Results:For the TG‐51 comparison, expected dose was obtained by decaying values measured at the time of source installation. The average measured difference was 0.4%±0.12% for A18 and 0.06%±0.15% for Farmer chamber. There was minimal (0.3%) orientation dependence without the magnetic field for the A18 chamber, while previous measurements with the magnetic field had a deviation of 3.2% with chamber perpendicular to magnetic field. Results reported by IROC for the OSLDs with and without the field had a maximum difference of 2%.Conclusion:Accurate absolute dosimetry was verified by measurement under the same conditions with and without the magnetic field for both ionization chambers and independently‐verifiable OSLDs.
SU‐F‐T‐475: An Evaluation of the Overlap Between the Acceptance Testing and Commissioning Processes for Conventional Medical Linear Accelerators
Authors: Morrow A , Rangaraj D , Perez‐Andujar A , Krishnamurthy N 
Published: July 2016

Purpose:This work's objective is to determine the overlap of processes, in terms of sub‐processes and time, between acceptance testing and commissioning of a conventional medical linear accelerator and to evaluate the time saved by consolidating the two processes.Method:A process map for acceptance testing for medical linear accelerators was created from vendor documentation (Varian and Elekta). Using AAPM TG‐106 and inhouse commissioning procedures, a process map was created for commissioning of said accelerators. The time to complete each sub‐process in each process map was evaluated. Redundancies in the processes were found and the time spent on each were calculated.Results:Mechanical testing significantly overlaps between the two processes ‐ redundant work here amounts to 9.5 hours. Many beam non‐scanning dosimetry tests overlap resulting in another 6 hours of overlap. Beam scanning overlaps somewhat ‐ acceptance tests include evaluating PDDs and multiple profiles but for only one field size while commissioning beam scanning includes multiple field sizes and depths of profiles. This overlap results in another 6 hours of rework. Absolute dosimetry, field outputs, and end to end tests are not done at all in acceptance testing. Finally, all imaging tests done in acceptance are repeated in commissioning, resulting in about 8 hours of rework. The total time overlap between the two processes is about 30 hours.Conclusion:The process mapping done in this study shows that there are no tests done in acceptance testing that are not also recommended to do for commissioning. This results in about 30 hours of redundant work when preparing a conventional linear accelerator for clinical use. Considering these findings in the context of the 5000 linacs in the United states, consolidating acceptance testing and commissioning would have allowed for the treatment of an additional 25000 patients using no additional resources.
SU‐F‐T‐476: Performance of the AS1200 EPID for Periodic Photon Quality Assurance
Authors: DeMarco J , Moran J , Barnes M , Greer P , Kim G , Fraass B , Yang W , McKenzie Boehnke E 
Published: July 2016

Purpose:To assess the dosimetric performance of a new amorphous silicon flat‐panel electronic portal imaging device (EPID) suitable for high‐intensity, flattening‐filter‐free delivery mode.Methods:An EPID‐based QA suite was created with automation to periodically monitor photon central‐axis output and two‐dimensional beam profile constancy as a function of gantry angle and dose‐rate. A Varian TrueBeamTM linear accelerator installed with Developer Mode was used to customize and deliver XML script routines for the QA suite using the dosimetry mode image acquisition for an aS1200 EPID. Automatic post‐processing software was developed to analyze the resulting DICOM images.Results:The EPID was used to monitor photon beam output constancy (central‐axis), flatness, and symmetry over a period of 10 months for four photon beam energies (6x, 15x, 6xFFF, and 10xFFF). EPID results were consistent to those measured with a standard daily QA check device. At the four cardinal gantry angles, the standard deviation of the EPID central‐axis output was <0.5%. Likewise, EPID measurements were independent for the wide range of dose rates (including up to 2400 mu/min for 10xFFF) studied with a standard deviation of <0.8% relative to the nominal dose rate for each energy. Also, profile constancy and field size measurements showed good agreement with the reference acquisition of 0° gantry angle and nominal dose rate. XML script files were also tested for MU linearity and picket‐fence delivery. Using Developer Mode, the test suite was delivered in <60 minutes for all 4 photon energies with 4 dose rates per energy and 5 picket‐fence acquisitions.Conclusion:Dosimetry image acquisition using a new EPID was found to be accurate for standard and high‐intensity photon beams over a broad range of dose rates over 10 months. Developer Mode provided an efficient platform to customize the EPID acquisitions by using custom script files which significantly reduced the time.This work was funded in part by Varian Medical Systems.
SU‐F‐T‐479: Estimation of the Accuracy in Respiratory‐Gated Radiotherapy
Authors: Kurosawa T , Tachibana H , Moriya S , Miyakawa S , Sato M 
Published: July 2016

Purpose:Irregular respiratory patterns affects dose outputs in respiratorygated radiotherapy and there is no commercially available quality assurance (QA) system for it. We designed and developed a patient specific QA system for respiratory‐gated radiotherapy to estimate irradiated output.Methods:Our in‐house QA system for gating was composed of a personal computer with the USB‐FSIO electronic circuit connecting to the linear accelerator (ONCOR‐K, Toshiba Medical Systems). The linac implements a respiratory gating system (AZ‐733V, Anzai Medical). During the beam was on, 4.2 V square‐wave pulses were continually sent to the system. Our system can receive and count the pulses. At first, our system and an oscilloscope were compared to check the performance of our system. Next, basic estimation models were generated when ionization‐chamber measurements were performed in gating using regular sinusoidal wave patterns (2.0, 2.5, 4.0, 8.0, 15 sec/cycle). During gated irradiation with the regular patterns, the number of the pulses per one gating window was measured using our system. Correlation between the number of the pulses per one gating and dose per the gating window were assessed to generate the estimation model. Finally, two irregular respiratory patterns were created and the accuracy of the estimation was evaluated.Results:Compared to the oscilloscope, our system worked similarly. The basic models were generated with the accuracy within 0.1%. The results of the gated irradiations with two irregular respiratory patterns show good agreement within 0.4% estimation accuracy.Conclusion:Our developed system shows good estimation for even irregular respiration patterns. The system would be a useful tool to verify the output for respiratory‐gated radiotherapy.
SU‐F‐T‐482: Using Cerenkov Light Emission for the Measurement of Output Factors at Clinical Linear Accelerators
Authors: Zink K , Burg J 
Published: July 2016

Purpose:A potential method of quality assurance for clinical accelerators is using the signal from Cerenkov light generated during irradiation. The example of measuring output factors (OF) of a clinical accelerator was used to investigate the potential of Cerenkov light as a dosimetry tool.Methods:OF as a function of field size were measured under reference conditions using ionization chambers at 18 MV‐X. Furthermore, for selected field sizes, the produced Cerenkov light within the water Phantom was imaged by a CCD‐Camera. In order to improve the optical signal, any light source in the treatment room was blocked. The measurement was repeated three times for better statistics. Images were median filtered to reduced errors due to direct ionization of the CCD‐chip. Afterwards, raw images were averaged and evaluated at ROI in 10 cm depth. Considering cone shaped geometrical corrections, the measured Cerenkov signal in relation to the signal from 10×10 cm field was compared with OF measured under reference conditions.Results:Comparing the OF as a function of field size with the measured signal change in Cerenkov images, a comparable trend is observable. A limiting factor was the small signal to noise ratio caused by the insufficient sensitivity of the CCD‐Camera which results in large error bars.Conclusion:The correlation between Cerenkov light production and dose deposition has already been published. The geometrical correction of the optical system for the non‐isotropic Cerenkov signal represents a big challenge of defining correction factors for the system. A highly developed image system is required to image and use Cerenkov signals as a dosimetry tool with an acceptable signal to noise ratio. Moreover, correction factors for the measurement system have to be established. In further work, Monte Carlo simulation should be used in order to define correction factors for the given measuring setup.