bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐23: TomoTherapy Patient QA Using Exit Detector Measurement of Pre‐Treatment In‐Air Delivery
Authors: Chen Q , Levinson L , Ding K , Read P , Benedict S
Published: June 2012

Purpose: Currently, the recommended TomoTherapy patient specific QA involves setting up a DQA procedure and delivering it to a phantom with an ion chamber and film measurement. The process is time‐consuming and the DQA result is susceptible to errors in phantom setup. Our study explores the feasibility of using TomoTherapy's intrinsic exit detectors to perform patient specific QA by measuring the fluence received by the detectors during pre‐treatment in‐air delivery for our STAT‐RAD workflow. Methods: A TomoTherapy patient plan is converted into a calibration procedure in which the couch remains out of the gantry. The signal measured by the exit detector is exported through manufactory provided software. In‐house developed software is used to reconstruct exit detector signal from the dicom‐exported delivery plan. The software relies on individual leaf profiles as well as tongue‐and‐groove profiles of each adjacent leaf‐pair extracted from an in‐house developed calibration procedure. The difference between the reconstructed and measured detector signal can be analyzed by a simple algorithm which has been developed to estimate the dose difference of any given point inside a patient or phantom. Several patient plans have been tested with this in‐air delivery QA method. In some of the tested plans, errors have been introduced to assure the estimated point dose error agrees with the ion chamber measurement in a phantom. Results: The in‐house exit detector reconstruction software has been validated to be able to reconstruct the exit detector signal with errors <1%. The software estimated point dose agrees within 3% to the ion chamber measurement. Conclusions: Our study shows that it is feasible and efficient to perform patient specific QA using the exit detector signal recorded during the in‐air pretreatment delivery. This approach is easy to perform and it is faster than conventional QA approach.
SU‐E‐T‐104: Commissioning and Dosimetric Characteristics of TrueBeam System: Composite Data of Three TrueBeam Machines
Authors: Chang Z , Wu Q , Adamson J , Ren L , Bowsher J , Yan H , Thomas A , Yin F
Published: June 2012

Introduction: A TrueBeam linear accelerator (TB‐LINAC) is designed to deliver standard flattened and flattening‐filter‐free (FFF) beams. In our institute, three TB‐LINAC units are installed. In this work, composite data of the three units and multi‐unit comparison are presented. Methods: Each TB‐LINAC can deliver photon beams from 4MV to 15MV, electron beams from 6MeV to 22MeV, and 6MV‐FFF and 10MV‐FFF. Dosimetric characteristics are systematically measured for commissioning including percent depth dose (PDD), beam profile, relative scatter factor, dynamic leaf shift, output factor and MLC leakage. Critic considerations of Pion of FFF photon beams and dosimetric penumbra are investigated. Results: All measured PDDs and profiles of photon and electron matched well across the three machines. Beam data were quantitatively compared and combined through average to yield composite beam data. The discrepancies among the machines were quantified using standard deviation (SD). For example, the mean SD of the PDDs among the three units is 0.12%, and the mean SD of the profiles is 0.40% for 10MV‐FFF open fields. The variations of Pion of the chamber CC13 is 1.2±0.1% under 6MV‐FFF and 2.0±0.5% from dmax to the 18cm‐off‐axis point at 35cm depth under 40×40cm2. The measured relative output factors range from 0.866 to 1.141 with the mean discrepancy of 0.06±0.04% among the three units. The measured wedge factors range from 0.863 to 1.254 with the mean overall discrepancy of 0.04±0.04%. The mean MLC transmission and dynamic leaf shift were measured from 1.0% to 1.5% and from 0.77mm to 0.96 mm from 4MV to 15MV. The mean penumbra of various photon beams are measured from 5.88±0.09mm to 5.99±0.13mm from 4MV to 15MV at 10cm depth of 10×10 cm2. Conclusions: Dosimetric data demonstrated that the three units could and had been matched well. The systematically measured data might be useful for future reference.
SU‐E‐T‐112: Experimental Characterization of a Novel Thermal Reservoir for Consistent and Accurate Annealing of High‐Sensitivity TLDs
Authors: Donahue W , Bongiorni P , Hearn R , Rodgers J , Nath R , Chen Z
Published: June 2012

Purpose: To develop and characterize a novel thermal reservoir for consistent and accurate annealing of high‐sensitivity thermoluminescence dosimeters (TLD‐100H) for dosimetry of brachytherapy sources. Methods: The sensitivity of TLD‐100H is about 18 times that of TLD‐100 which has clear advantages in for interstitial brachytherapy sources. However, the TLD‐100H requires a short high temperature annealing cycle (15 min.) and opening and closing the oven door causes significant temperature fluctuations leading to unreliable measurements. A new thermal reservoir made of aluminum alloy was developed to provide stable temperature environment in a standard hot air oven. The thermal reservoir consisted of a 20 cm × 20 cm × 8 cm Al block with a machine‐milled chamber in the middle to house the aluminum TLD holding tray. The thermal reservoir was placed inside the oven until it reaches thermal equilibrium with oven chamber. The temperatures of the oven chamber, heat reservoir, and TLD holding tray were monitored by two independent thermo‐couples which interfaced digitally to a control computer. A LabView interface was written for monitoring and recording the temperatures in TLD holding tray, the thermal reservoir, and oven chamber. The temperature profiles were measured as a function of oven‐door open duration. The settings for oven chamber temperature and oven door open‐close duration were optimized to achieve a stable temperature of 240 0C in the TLD holding tray. Complete temperature profiles of the TLD annealing tray over the entire annealing process were obtained. Results: A LabView interface was written for monitoring and recording the temperatures in TLD holding The use of the thermal reservoir has significantly reduced the temperature fluctuations caused by the opening of oven door when inserting the TLD holding tray into the oven chamber. It has enabled consistent annealing of high‐sensitivity TLDs. Conclusions: A comprehensive characterization of a custom‐built novel thermal reservoir for annealing high‐sensitivity TLD has been carried out. It enabled consistent and accurate annealing of high‐ sensitivity TLDs which could significantly improve the efficiency of brachytherapy source characterizations. Supported in part by NIH grant R01‐CA134627
SU‐E‐T‐120: Minimum Absorbed Dose Limit for Gafchromic EBT2 Film Response after Exposure to Low‐Energy Photons
Authors: Massillon‐JL G , Domingo‐Muñoz I , Díaz‐Aguirre P
Published: June 2012

Purpose: To investigate the accuracy of the absorbed dose measured with Gafchromic EBT2 film in low‐energy photon radiation fieldsMethods: Six EBT2 film (lot # F06110901) pieces (1cm2) per dose were exposed to x‐rays of 50 kV, 80 kV, 120 kV and 60Co gamma rays from a Leksell Gamma Knife at dose values from 50 mGy to 100 Gy. The x‐ray beams were calibrated following the AAPMTG‐61 protocol using ionization chambers calibrated at NIST or Wisconsin University depending on the beam quality, while the 60Co gamma was calibrated in water using MD‐V2‐55 film. Each film piece was scanned once using a HP Scanjet 7650 document flatbed scanner in transmission mode, 48‐bit color at 300 dpi spatial‐resolution. The data analysis was made through the ImageJ. The measured light intensity for the red channel with its associate standard deviation was used to evaluate the netOD and its standard combined uncertainty. The absorbed dose as a function of the netOD was fitted using the logistic model and the relative combined uncertainties were evaluated for each energy photon beam. Results: EBT2 film response curve depends on the low‐energy photons and the degree of energy‐dependence is a function of absorbed dose. The absorbed dose relative combined uncertainty as a function of the absorbed dose indicates that the minimum absorbed dose limit is also energy dependent. Lower is the energy photon; more accurate is the measurement at low dose value. This can be explain by the fact that comparing to high energy photons, low energy photons can produce locally enough ionization density to create more color centre in the same film area. Conclusions: Minimum absorbed dose limit of Gafchromic EBT2 films were found to be energy dependent. The response curve depends on the low‐energy photons and the degree of energy‐dependence is a function of absorbed dose This work is partially supported by DGAPA‐UNAM grant IN102610 and Conacyt Mexico grant 127409
SU‐E‐T‐130: IMAT Patient Specific Quality Assurance Using ArcCHECK Diode Array Detector
Authors: Thiyagarajan Rajesh , Sinha S , Yadav G , Ashokkumar S , Raman Kothanda , Mishra M , Nambiraj N Arunai
Published: June 2012

Purpose: To evaluate the IMAT patient specific quality assurance (QA) performed using ArcCHECK detector array in reference with standard ion chamber for routine clinical use. Methods: Twelve patient plans having different tumor sites chosen for this study. On Eclipse planning system,IMAT patient plans were calculated on ArcCHECK phantom inserted with Ion chamber using superposition algorithm. ArcCHECK is a cylindrical phantom with a three‐dimensional array of 1386 diode detectors, arranged in a spiral pattern, with 10 mm diode spacing. These plans delivered from Clinac‐iX linac equipped with 120 MLC. Point dose and Dose/fluence map were measured simultaneously with ion chamber (IC‐15) and ArcCHECK diode array detector respectively. Point doses, dose/fluences map and dose at central axis (CAX) on ArcCHECK phantom were compared with their respective TPS calculated values. Results: The ion chamber measurements are in good agreement with TPS calculated doses. Mean difference between them is 0.50% with standard deviation is 0.51%. Concordance correlation coefficient (CCC) obtained for ion chamber base absolute dose measurements is 0.9996. These results demonstrate a strong correlation between the absolute dose predicted by our TPS and the measured dose. The precision of the TPS software was 0.9999, and its accuracy was 0.9997.The agreement between ArcCHECK doses and TPS predictions on the CAX, shown CCC of 0.9978 (the mean difference in the central axis dose is 2.11%). The 95% Confidence Interval is from 0.9932 to 0.9995. In gamma analysis of dose/fluence map the mean passing rate was 98.53% for 3% dose difference and 3mm distance to agreement. Conclusions: The IMAT patient specific QA with Ion chamber and ArcCHECK phantom are consistent with the TPS calculated dose. Statistically good agreement observed between ArcCHECK measured and TPS calculated. Hence it can be used for routine IMAT QA.
SU‐E‐T‐138: Quantification of Dwell Position Inaccuracy in Varian GammaMed HDR Titanium Ring Applicators
Authors: Iftimia I , Cirino E , Mower H , McKee A
Published: June 2012

Purpose: To quantify the dwell position inaccuracy in Titanium ring applicators and develop a test to be performed quarterly, after source exchange. Methods: All three rings from our Titanium kit (30, 45, 60 deg.) were used for this study. EDR2 film was placed on the Simulator table and a ring was taped to the film, with a solid water slab as buildup. A 1‐cm spacing dummy wire was inserted into the ring. The film was exposed using 135 kV, 80 mA, 400 mAs. An HDR treatment was then delivered using the even source dwell positions from 2 to 16, with a 5 mm step size, nominal dwell time 0.4 sec/position. The procedure was repeated three times for each ring. The films were scanned and analyzed with the RIT software. The distance between the center of each source position to the adjacent dummy dots was measured for each ring on all three films. An average shift (AS) was obtained for each ring.New films were exposed with a treatment offset equal and in the opposite direction relative to the AS for the ring used. The films were visually inspected to assess if the source positions are centered in between two adjacent dummy dots, and also scanned and analyzed with the RIT software. This test will be performed quarterly to verify if the shifts remain stable. Results: The average shift was 2.5, 2.4, and 2.4 mm distally for the 30, 45, and 60 deg. rings, respectively. The offset for the quarterly test was set to 2 mm proximally, to take into account the 1 mm tolerance for the source position. Conclusions: The dwell position inaccuracy in Titanium ring applicators was quantified and the quarterly test was successfully performed for two quarters. Work is started to assess the dosimetric implications of this shift.
SU‐E‐T‐149: Scatter Factors Comparison of 6MV Flattened and 7MV Unflattened Beams
Authors: Ashokkumar S , Sinha SN , Yadav Girigesh , Raman Kothanda , Thiyagarajan Rajesh , Nambiraj N Arunai
Published: June 2012

Purpose: To compare the Collimator scatter factor (Sc), Phantom scatter factor (Sp) and Total scatter factors (Sc,p) of 6MV flattened Beam (6MV FB) and 7MV Unflattened beams (7MV UFB). Methods: The flattening filter and primary collimator are the major sources of producing the scattered radiation. In this study, the field sizes from 5×5 cm2 to 40 × 40 cm2 compared for 6MV FB and 7MV UFB. We measured Sc,p with CC 13 chamber at the depth of 10 g/cm2 using IBA blue phantom and Sc measured with CC 13 chamber at the depth of 10 g /cm2 using columnar phantom (TG 74) for 6MV FB and 7MV UFB x‐ray beams from a Siemens ‐ ARTISTE linear accelerator. The Sp values derived from the Sc,p and Sc Values. Results: All the values of Sc,p, Sc and Sp are normalized to 10 × 10 cm2 field size the measured values of Sc,p for 6MV FB and 7MV UFB varies from 0.9437 to 1.0651 and 0.9690 to 1.0283 respectively. The Sc values for 6MV FB and 7MV UFB varies from 0.9676 to 1.0212 and 0.9882 to 1.0075 respectively. The Sp values for 6MV FB and 7MV UFB varies from 0.9752 to 1.0429 and 0.9806 to 1.0206 respectively. Our study results shows that Sc, Sp & Sc,p for 7MV UFB for smaller fields up to 10 × 10 cm2 were higher than 6MV FB and for larger fields greater than 10 ×10 cm2it is vice versa. Conclusions: A scatter factors are measured and compared for 6MV FB and 7MV UFB. A significant variation observed for Sc, Sp and Sc,p values of 6MV FB and 7MV UFB .This is may be due to flattening filter and beam quality.
SU‐E‐T‐153: Detector‐Grade CVD Diamond for Radiotherapy Dosimetry
Authors: Lansley S , Betzel G , McKay D , Meyer J
Published: June 2012

Purpose: To evaluate the use of commercially available detector‐grade synthetic diamond films made via chemical vapor deposition (CVD) as x‐ ray detectors for radiotherapy dosimetry. Methods: A detector was fabricated using high‐quality single crystal CVD diamond films (0.5 × 3 × 3 mm̂3) with 0.4 mm̂3 sensitive volumes, which were encapsulated with PMMA. The detector was placed in a (30 × 30 × 30 cm̂3) PTW water phantom. Six‐ and ten‐MV photons from an Elekta Synergy linac were measured using an SSD of 90 cm and typically a 10‐cm phantom depth with a 10 × 10 cm̂2 field size in the central axis of the beam. Data acquisition was performed using a PTW UNIDOS E electrometer with a 100‐V bias. The detector was evaluated by measuring leakage current, priming dose, response dynamics, dose linearity, dependence on dose rate, percent depth dose (6 and 10 MV photons) and output factors. Some measurements were compared with a Si diode detector, 0.04 and/or 0.13‐cc ion chamber(s). Results: Leakage currents were negligible (∼1 pA) given the overall average sensitivity of the material (680 nC/Gy at 100 V). Detector current rise and fall times were < 2 s. Dose measurements up to 5 Gy were linear. A slight dependence on nominal dose rates up to 500 MU/min was seen with Fowler fitting parameter delta = 0.981. Percent depth dose profiles compared well to a 0.13‐cc ion chamber up to 25 cm depths for 10‐MV photons. Output factors measured well for field widths 5‐15 cm; below 5 cm, differences are seen between all four different detectors as expected. Conclusions: The type of diamond tested has potential to be used for small field dosimetry due to its small sensitive volume and high sensitivity. Further experiments are ongoing and detector packaging is yet to be optimized.
SU‐E‐T‐155: Dose Response Curve of EBT2 and EBT3 Radiochromic Films to a Synchrotron‐Produced Monochromatic X‐Ray Beam
Authors: Brown TAD , Hogstrom KR , Alvarez D , Ham K , Dugas JP , Matthews KL
Published: June 2012

Purpose: This work investigates the dose‐response curves of Gafchromic EBT2 and EBT3 radiochromic films using synchrotron‐produced monochromatic x‐ray beams. These dosimeters are being utilized for dose verification in photoactivated Auger electron therapy at the LSU Center for Advanced Microstructures and Devices (CAMD) synchrotron facility. Methods: Monochromatic beams of 25, 30 and 35 keV were generated on the tomography beamline at CAMD. Ion chamber depth‐dose measurements were used to calculate the dose delivered to films irradiated simultaneously at depths from 0.7 ‐ 8.5 cm in a 10×10×10‐cms polymethylmethacrylate phantom. AAPM TG‐61 protocol was applied to convert measured ionization into dose. Calibrations of films at 4 MV were obtained for comparison using a Clinac 21 EX radiotherapy accelerator at Mary Bird Perkins Cancer Center. Films were digitized using an Epson 1680 Professional flatbed scanner and analyzed using the optical density (OD) derived from the red channel. Results: For EBT2 film the average sensitivity (OD/dose) at 50, 100, and 200 cGy relative to that for 4‐MV x‐ rays was 1.07, 1.20, and 1.23 for 25, 30, and 35 keV, respectively. For EBT3 film the average sensitivity was within 3 % of unity for all three monochromatic beams. Conclusions: EBT2 film sensitivity shows strong energy dependence over an energy range of 25 keV ‐ 4 MV. EBT3 film shows weak energy dependence, indicating that it would be the better dosimeter for Auger electron therapy. This research was supported by contract W81XWH‐10‐1‐0005 awarded by The U.S. Army Research Acquisition Activity, 820 Chandler Street, Fort Detrick, MD 21702‐5014. This report does not necessarily reflect the position or policy of the Government, and no official endorsement should be inferred.
SU‐E‐T‐182: Delivery Verification of Tomotherapy Treatments Using Exit Detector Sinograms: A Phantom Study
Authors: Rodriguez V , Richardson S , Ghosh T , Kashani R , Goddu S
Published: June 2012

Purpose: The objective of this study was to use a liquid water female body phantom to investigate the feasibility of using helical Tomotherapy's exit detector data sinograms (EDDS) for quality assurance of Tomotherapy treatments. Methods: Delivery Verification software (DV‐Tool), described by Kapatoes et al., uses EDDS and daily mega‐voltage‐CT images for delivery sinogram reconstruction and subsequent dose computations. These dose distributions should reflect variations in patient's anatomy and machine delivery. Phantom was used to verify the robustness of the DV‐Tool for machine consistency over 2months, and sensitivity to weight loss and setup errors. Weight loss simulations were done by removing layers of bolus from the phantom's pelvis. Setup errors were simulated by performing known table shifts before the treatment. Two treatment plans simulating a breast and gynecological treatment plans were used for these evaluations. Reconstructed doses and dose volume histograms (DVHs) were analyzed in comparison to the plan DVHs by scaling the reconstructed PTV mean dose (PTV‐MD) to match the plan. PTV‐MD differences before and after machine output adjustments were evaluated. Results: Machine consistency check of gynecological plan revealed that the deviations were greater (±5%) during the week prior to target replacement. After output adjustments, the deviations for breast and gynecological plans agreed within ±1.0% and ±2.5%, respectively. Weight loss on the gynecological plan showed a correlation (R2=0.998) between lost thickness and increasing PTV‐MD by approximately 5%/cm. Setup errors on the breast plan showed broadening shoulder of the PTV DVH for shifts greater than 5mm. Volume at 20Gy for the right lung increased by 6% for 10mm shifts in both x and z directions. Conclusions: The DV‐Tool is sensitive to simulated weight loss, setup errors, and machine output. Exit detector data and the DV‐Tool have great potential for monitoring patient's delivered treatments. However, clinical workflow needs to be established.
SU‐E‐T‐207: Flatness and Symmetry Threshold Detection Using Statistical Process Control
Authors: Able C , Hampton C , Baydush A
Published: June 2012

Purpose: AAPM TG‐142 guidelines state that beam uniformity (flatness and symmetry) should maintain a constancy of 1 % relative to baseline. The focus of this study is to determine if statistical process control (SPC) methodology using process control charts (PCC) of steering coil currents (SCC) can detect changes in beam uniformity prior to exceeding the 1% constancy criteria. Methods: SCCs for the transverse and radial planes are adjusted such that a reproducibly useful photon or electron beam is available. Transverse and radial ‐ positioning and angle SCC are routinely documented in the Morning Check file during daily warm‐up. The 6 MV beam values for our linac were analyzed using average and range (Xbar/R) PCC. Using this data as a baseline, an experiment was performed in which each SCC was changed from its mean value (steps of 0.01 or 0.02 Ampere) while holding the other SCC constant. The effect on beam uniformity was measured using a beam scanning system. These experimental SCC values were plotted in the PCC to determine if they would exceed the predetermined limits. Results: The change in SCC required to exceed the 1% constancy criteria was detected by the PCC for 3 out of the 4 steering coils. The reliability of the result in the one coil not detected (transverse position coil) is questionable because the SCC slowly drifted during the experiment (0.05 A) regardless of the servo control setting. Conclusions: X‐bar/R charts of SCC can detect exceptional variation prior to exceeding the beam uniformity criteria set forth in AAPM TG‐142. The high level of PCC sensitivity to change may result in an alarm when in fact minimal change in beam uniformity has occurred. Further study is needed to determine if a combination of individual SCC alarms would reduce the false positive rate for beam uniformity intervention. This project was supoorted by a grant from Varian Medical Systems, Inc.
SU‐E‐T‐214: Predicting Plan Quality from Patient Geometry: Feature Selection and Inference Modeling
Authors: Ruan D , Shao W , DeMarco J , Kupelian P , Low D
Published: June 2012

Purpose: To investigate and develop methods to infer treatment plan quality from the geometric features of PTV/OAR structures; to discover and identify features of high prognostic values. Methods: This study explores the prognostic utility of geometric features of two categories: (1) absolute geometry, characterizing the volumes of single structures (PTV, OARs); and (2) relative geometry, based on the minimal 3D distance and/or overlapping volume between pairs of structures. Using prostate as a pilot site, we developed inference models to ‘predict’ SBRT plan quality of DVH end points. We developed and assessed (1) a full linear regression model based on both absolute and relative geometric features, (2) a sparsity‐penalized linear regression model, (3) a linear regression model based on absolute geometry features only; (4) a learning‐based nonparametric model. Cross‐validation was used for both selecting the parameter values as well as quantifying the inference performance. The best inference method for each of the DVH end points was identified to reveal the structural and prognostic differences among them. Results: For linear regression, using sparsity‐regularization discovered geometric features that were mostly absolute, demonstrating their dominant linear prognostic utility. However, introducing relative geometric features improved the plan quality prediction by 15% for all DVH end points. In contrast, nonparametric models had a heavier dependence on relative geometry features. While linear regression based on both features sets predicted OAR DVH points slightly better, the nonparametric method excelled in predicting PTV coverage and conformality. Conclusions: The inference result from this study provides an ‘expectation’ for the plan quality before the planning is to be performed, providing reference goals for the planner and a baseline for detecting abnormality. The use of relative geometry complements the absolute geometry with information on spatial configuration of the PTV/OAR structures of individual patients, and the variation in achievable conformality as a consequence.
SU‐E‐T‐221: Evaluation of Technology Using Probabilistic Decision Models
Authors: Phillips M
Published: June 2012

Purpose: Medical physicists are often asked to evaluate or choose appropriatetechnology for clinical applications. These are multidimensionalproblems that also suffer from different degrees of uncertainty in thevariables. Probabilistic decision models are a robust andmathematically correct means of handling these issues. The principlesof constructing such models are presented along with practicalexamples in the areas of IGRT, IMRT and proton therapy. Methods: Influence diagrams are used to model the variables and theiruncertainties and include action and reward variables. Influencediagrams are directed acyclic graphs that use Bayesian probabilitycalculus to propagate probabilities and to update prior probabilitiesin the presence of evidence. An influence diagram was used to modelthe question of whether brain tumors are better treated with x‐rayIMRT or proton therapy, with or without CT‐guided localization. Datafor the conditional probabilities of the model were obtained from theliterature and included models of TCP, NTCP and induction of secondmalignancies, as well as data on the probability density functions forinterfraction patient motion. Dosimetric data were obtained using theCMS treatment planning system. Results: Several different tumor types and sites were studied. The critical variables in the model were identified andstudied using analyses of evidence, parameters and value ofinformation. The impact of imaging was significant, regardless of theradiation type. The models used in determining some of theconditional probabilities parameters also played an important role inranking alternatives. Conclusions: Although such choices are difficult, physicists mustproceed with the best data at hand. Without a rigorous framework onwhich to build a model of the process, decisions are likely to be based onunstated assumptions and incorrect inference. The example ofcomparing irradiation modalities for brain tumors shows the power ofinfluence diagrams in this critical context.
SU‐E‐T‐222: How to Define and Manage Quality Metrics in Radiation Oncology
Authors: Harrison A , Cooper K , DeGregorio N , Doyle L , Yu Y
Published: June 2012

Purpose: Since the 2001 IOM Report Crossing the Quality Chasm: A New Health System for the 21st Century, the need to provide quality metrics in health care has increased. Quality metrics have yet to be defined for the field of radiation oncology. This study represents one institutes initial efforts defining and measuring quality metrics using our electronic medical record and verify system(EMR) as a primary data collection tool. This effort began by selecting meaningful quality metrics rooted in the IOM definition of quality (safe, timely, efficient, effective, equitable and patient‐centered care) that were also measurable targets based on current data input and workflow. Methods: Elekta MOSAIQ 2.30.04D1 was used to generate reports on the number of Special Physics Consults(SPC) charged as a surrogate for treatment complexity, daily patient time in department(DTP) as a measure of efficiency and timeliness, and time from CT‐simulation to first LINAC appointment(STL). The number of IMRT QAs delivered in the department was also analyzed to assess complexity. Results: Although initial MOSAIQ reports were easily generated, the data needed to be assessed and adjusted for outliers. Patients with delays outside of radiation oncology such as chemotherapy or surgery were excluded from STL data. We found an average STL of six days for all CT‐simulated patients and an average DTP of 52 minutes total time, with 23 minutes in the LINAC vault. Annually, 7.3% of all patient require additional physics support indicated by SPC. Conclusions: Utilizing our EMR, an entire year's worth of useful data characterizing our clinical experience was analyzed in less than one day. Having baseline quality metrics is necessary to improve patient care. Future plans include dissecting this data into more specific categories such as IMRT DTP, workflow timing following CT‐simulation, beam‐on hours, chart review outcomes, and dosimetric quality indicators.
SU‐E‐T‐238: Annual QA of Proton Gantry with Robotic Table
Authors: Wang N , Ghebremedhin A , Simpson R , Patyal B
Published: June 2012

Purpose: To perform the annual QA of proton gantry with a robotic table. Methods: A new proton gantry with robotic table has been commissioned and is being used in clinic for patient treatment. The gantry is equipped with a robotic table with 6‐degrees of freedom and dual cardinal angle KV imagers for patient registration. The system allows direct movement from one beam location to another without additional image registration, which effectively reduces portal setup time and increases treatment efficiency. The annual QA has four main components: Beam parameter checks included proton depth dose, output, linearity, modulation factor, field size factor, effective source distance, compensator gap factor, and monitor unit comparison between model calibration and physical measurements for every energy. Mechanical checks included gantry and robotic table isocenter, gantry and robotic couch isocentricity, and mechanical movement of fully loaded couch and corresponding digital readout. Imaging system checks included proton, X‐ray beam, laser and image receptor alignment, image quality of KV imagers, and image registration accuracy. The last were the system safety checks. Methods used to perform these checks, especially those pertaining to robotic positioner will be discussed. Results: The new proton gantry and robotic table had the isocentric accuracy of about 1 mm. The accuracy of mechanical movements of the robotic table was within 1mm/0.5 degree in the clinical motion range. The accuracy of proton outputs determined by IAEA TRS 398 protocol was within +/−2% and the consistency of beam range for all clinical energies at cardinal gantry angles was within 1mm. Conclusions: The results of the gantry annual QA demonstrate that the machine satisfies the highest standards of quality assurance for proton radiation treatment. The annual QA verifies the proton output, robotic table movement accuracy, image registration and safety of the machine and thus increases our confidence level in the uncertainties of daily proton treatments.
SU‐E‐T‐242: Effect of Skull Surgical Clips and Bone Artifacts on Treatment Planning for Brain Tumors with Proton Beam
Authors: Dimofte A
Published: June 2012

Purpose: To study the effect of skull surgical clips and bone artifacts on dose distribution using proton beams for treatment planning. Methods: Proton treatment plans with double scattering technique for ten patients were generated on patients with brain tumors having had prior surgery with skull bone surgical clips. Appropriate clinical, dosimetric and geometric margins were added for each tumor volume and dose was prescribed to clinical target volume (CTV). The CT images used for treatment planning show streaking artifacts due to the clips and there are also soft artifacts on tissue adjacent to skull bone due to high density of bone. We performed two plans for each patient; a plan without correcting for artifacts and a second plan replacing the artifacts with normal tissue. For the second plan, the artifacts were contoured and a CT numbers obtained by sampling pixels in adjacent areas without artifacts was assigned to the contours. We compared the two plans by evaluating the dose volume histogram (DVH) for tumor coverage and the mean, median, and maximum dose for normal tissue structures. Results: Volume of CTV receiving 99% of the prescribed dose (PD) show a mean difference of 3% higher dose for artifact corrected plans. The normal tissue structures comparison shows and average dose difference of 5%, 8%, 11%, and 30% lower doses for optical chiasm, temporal lobes, brain and optic nerves for artifact corrected plans respectively. Conclusions: In general when using artifact correction for surgical skull clips and skull bone, the tumor coverage tends to be slightly higher. Overall, the normal tissue structures tend to have lower doses depending on the volume, position and the geometry for artifact corrected plans. We recommend the correction of artifacts due to surgical clips and skull bone for brain region proton planning.
SU‐E‐T‐263: Luminescent Dosimetry to Measure the Out‐Of‐Field Low and High LET Dose Components in High Energy Photon and Proton Therapy Beams
Authors: Reft C
Published: June 2012

Purpose: Luminescent dosimetry using thermoluminescent detectors (TLDs) and optically stimulated luminescent detectors (OSLDs) were used in mixed radiation fields containing both low LET (photons and protons) and high LET (neutrons)components to obtain their out‐of‐field absorbed dose, dose equivalent and quality factor. Method and Materials: LiF Thermoluminescent Detectors (TLDs) 600 and 700 chips with dimensions 0.31×0.31×0.038 cm3 were used in a 25.4 cm diameter Bonner sphere centered 42 cm from the isocenter of a 15×x15 cm2 field to measure the secondary doses for 10, 15 and 18 MV photons and a 200 MeV proton therapy beam. From the sensitivity difference to LET radiation between the210 and 280 C peaks in the glow curve, the areas under the peaks were used to obtain the absorbed dose, dose equivalent and QF of the secondary radiation. The OSLD detector measured the low LET dose component to compare with the TLD dose measurement. The neutron calibration of the TLDs was obtained from an Am‐Be source at the Argonne National Laboratory. The photon and proton TLD and OSLD calibrations were obtained in 6 MV and 200 MeV beams, respectively. Results: From the two‐peak analysis of the TLDs in the Bonner sphere the ratios of the neutron dose to photon dose were 0.001, 0.014 and 0.17 for 10, 15 and 18 MV, respectively. The low LET OSLD measurements agreed within 10% of the TLD results. From the dose equivalent measurements the QFs (+/−14%) obtained were 4.5, 3.9 and 4.0 for these beam energies. For the 200 MeV proton beam the ratio of neutron to proton dose was 0.28 with a measured QF of 13. Conclusion: Luminescent detectors in a Bonner Sphere provide measurements of the secondary photon, proton and neutron doses and provide an estimate of the neutron QF.
SU‐E‐T‐264: New Concrete Designed and Evaluation for Megavoltage X Radiotherapy Facilities (CONTEK—RFH2)
Authors: Mera M , Pereira L , Mera M , Pereira L , Meilán E , Moral F Del , Teijeiro A , Salgado M , Andrade B , Gomez F , Fuentes‐Vázquez V , Caruncho J , Medina A
Published: June 2012

Purpose: The most common material for shielding is concrete, which can be made using various materials of different densities as aggregates. New techniques in radiotherapy, as IMRT and VMAT, require more monitor units and it is important to develop specifically designed shielding materials. Methods: Arraela S.L. has developed new concrete (CONTEK®‐RFH2), which is made from an arid with a high percentage in iron (> 60%), and using the suitable sieve size, enables optimum compaction of the material and a high mass density, about 4.1–4.2 g/cm3. Moreover, aluminate cement, used as base, gives high resistance to high temperatures what makes this product be structurally resistant to temperatures up to 1200 ° C. The measurements were made in a LINAC Elekta SL18 to energies 6MV and 15 MV with a field size of 10×10 cm2 for concrete samples in the form of tile 25cm×25cm with variable thickness. Results: The linear attenuation coefficient, μm, was determined for each energy by fitting the data to Eq. 1, where Xxm is the exposure in air behind a thickness xm of the material, and X0 is the exposure in the absence of shielding. These results are compared with the ordinary concrete (2.35 g cm−3) for 6MV and 15MV energies (Ref. NCRP Report No.151). Results are tabulated in Table1. Results of attenuation are compared with ordinary concrete in Fig. 1. Conclusions: The new concrete CONTEK®‐RFH2 increases photon attenuation and reduces the size of a shielded wall. A very high percentage in iron and a suitablesieve size approximately double the density of ordinary concrete. High mass attenuation coefficient makes this concrete an extremely desirable material for use in radiation facilities as shielding material for photon beam, and for upgrading facilities designed for less energy or less workload.
SU‐E‐T‐273: Commissioning Motorized Jaws for a Micro‐CT/RT
Authors: Jensen M , Hrinivich T , Drangova M , Holdsworth D , Chen J , Wong E
Published: June 2012

Purpose: To design, construct and commission a set of computer‐controlled motorized jaws for a micro‐CT to perform conformal image‐guided small animal radiotherapy. Methods: We report on the design and evaluation of our custom‐built motorized orthogonal jaws, which allows the delivery of off‐axis rectangular fields, installed on a GE eXplore CT 120 preclinical imaging system. The jaws in the x direction are independently driven, while the y direction jaws are symmetric. All motors have backup encoders, verifying their positions. Measurements were performed using the large focal spot (1.0 mm) at 140 kVp, 50 mA, 25 ms pulse duration, with 220 ms between pulses. Additionally, a Monte Carlo beam model of the micro‐CT and jaws has been created in BEAMnrc. Square beam profiles (2 × 2, 5 × 5, 10 × 10, 20 × 20 and 30 × 30 mm) were measured using EBT2 film in the center of a 40 × 40 × 40 mm solid water block. A calibrated Farmer ion chamber in a 50 × 20 × 70 mm solid water block was used to measure the output of three field sizes: 50 × 50, 40 × 40 and 30 × 30 mm. Both setups were simulated in DOSXYZnrc. Films were scanned on a flatbed scanner (Epson 1000XL) and converted to dose using a fitted calibration curve. Results:Relative output factors measured with the ion chamber agree with Monte Carlo simulations within 2%. Penumbra widths from film agree well with simulations. The averaged random error of positioning both jaws is estimated at less than 0.1 mm. Finer calibration points will improve the absolute jaw positioning errors. Conclusion: The computer‐controlled motorized jaws can be positioned reliably down to sub‐millimeter resolutions. Upon completion of small field dosimetry (< 1 cm), this will be ready for conformal radiotherapy for small animals.
SU‐E‐T‐275: Dose Verification in a Small Animal Image‐Guided Radiation Therapy X‐Ray Machine: A Dose Comparison between TG‐61 Based Look‐Up Table and MOSFET Method for Various Collimator Sizes
Authors: Rodrigues A , Nguyen G , Li Y , Roy Choudhury K , Kirsch D , Das S , Yoshizumi T
Published: June 2012

Purpose: To verify the accuracy of TG‐61 based dosimetry with MOSFET technology using a tissue‐equivalent mouse phantom. Methods: Accuracy of mouse dose between a TG‐61 based look‐up table was verified with MOSFET technology. The look‐up table followed a TG‐61 based commissioning and used a solid water block and radiochromic film. A tissue‐equivalent mouse phantom (2 cm diameter, 8 cm length) was used for the MOSFET method. Detectors were placed in the phantom at the head and center of the body. MOSFETs were calibrated in air with an ion chamber and f‐factor was applied to derive the dose to tissue. In CBCT mode, the phantom was positioned such that the system isocenter coincided with the center of the MOSFET with the active volume perpendicular to the beam. The absorbed dose was measured three times for seven different collimators, respectively. The exposure parameters were 225 kVp, 13 mA, and an exposure time of 20 s. Results:For a 10 mm, 15 mm, and 20 mm circular collimator, the dose measured by the phantom was 4.3%, 2.7%, and 6% lower than TG‐61 based measurements, respectively. For a 10 × 10 mm, 20 × 20 mm, and 40 × 40 mm collimator, the dose difference was 4.7%, 7.7%, and 2.9%, respectively. Conclusions: The MOSFET data was systematically lower than the commissioning data. The dose difference is due to the increased scatter radiation in the solid water block versus the dimension of the mouse phantom leading to an overestimation of the actual dose in the solid water block. The MOSFET method with the use of a tissue‐ equivalent mouse phantom provides less labor intensive geometry‐specific dosimetry and accuracy with better dose tolerances of up to ± 2.7%.
SU‐E‐T‐276: Treatment Planning Strategies for Lung Injury Studies in Rat Models in 6 MV Delivery
Authors: Serban M , Ybarra N , Lee S , Jeyaseelan K , Seuntjens J
Published: June 2012

Purpose: To study planning strategies that can be used in small animal radiation‐induced lung toxicity experiments using 6 MV accelerator with high density MLC. Methods: Three different types of plans were designed on CT images of a Sprague Dawley rat model to irradiate 50% of the total lung volume (lung divided into apex and base) with a prescription dose of 24 Gy to the partial lung. Two VMAT arc therapy plans were optimized to cover to the prescription dose, either the apex or base of the lung. Two AP‐ PA plans were designed to completely block either lung apex or base while irradiating the remaining 50% of the lung. Finally, two AP‐PA plans were designed to cover, to the prescription dose, the apex or base of the lung. The plans were designed and optimized using the Eclipse AAA algorithm and recalculated using the MMCTP/EGS/Beam Monte Carlo system. Results: When completely blocking the lung base, the apex will be underdosed by up to 30%; when completely covering the apex by the prescribed dose, the base will receive overdosing (V50%=73%). The VMAT plan leads to a more conformal dose distribution and spares unnecessary skin exposure when compared to AP‐PA MV or kV delivery. Despite the small size of rat model, the 6 MV VMAT delivery is superior in terms of dose conformality and sparing of the heart and the non‐irradiated 50% of the lung compared to the standard, simpler, AP‐PA delivery. MC dosimetry in lung shows that the delivered dose is 10% higher than predicted by AAA because of the predominance of small fields in the delivery. Conclusions: Clinical state‐of‐ the‐art planning and delivery techniques can be scaled down accurately to rats. The use of these techniques is essential in small animal studies to render conclusions of radiation response investigations translatable to human studies.
SU‐E‐T‐277: Hypothesis and Design of an Integrated X‐Ray/Bioluminescent Imaging (BLI) and Tomography (BLT) System for the Study of Radiation and Treatment in Small Animals
Authors: Eslami S , Patterson M , Wong J , Iordachita I
Published: June 2012

Purpose: Design and construct an integrated x‐ray/bioluminescent tomography (BLT) system (with BLT being our initial focus) that can function as a standalone research apparatus and also on‐board the SARRP to guide focal irradiation. In addition, it is aimed to enhance the BLT of the system to improve target localization by incorporating multi‐projection, multi‐spectral BL images, as well as CT ‘priors'. Methods: The SARRP system integrates a portable robotic translational/rotational stages system and an x‐ray source which in the new system development the x‐ray source is replaced with the PXS10‐65 W model rated at maximum 130 kV having a variable small focal. A high performance, low noise, CCD camera mounted on a light‐tight housing along is used for the aim of the BL imaging and tomography. In the new setup of the BLI system, the camera‐filter‐mirror assembly is attached to a motorized gantry to acquire images in angles between to while the position of the camera does not block the path of the x‐ ray beam. Innovatively, a 3‐mirror arrangement is implemented to eliminate the need to rotate the CCD camera for capturing images. Furthermore, the robotic stage can be vertically adjusted to allow BLI imaging of multiple animals. Results:To validate the accuracy with the on‐board x‐ray and BL tomography can be used to localize a BL tumor target and the minimum beam expansion to ensure radiation coverage of the target. The validation will employ phantoms and immunohistochemistry analysis of radiation damage in irradiated BL tumor models in vivo. The proposed system is currently under development and envisioned to be calibrated and evaluated along with the stand‐alone radiation system. Conclusions: The novelty of embedded BLI guidance system is to enable the unprecedented focal irradiation of the small volumes of tumors which are more realistic in human disease.
SU‐E‐T‐280: Optimal Angle for a Dual‐Field Stanford Technique for TSET
Authors: Timmerman J , Wang K , Tang S , Zhu T
Published: June 2012

Purpose: This study examines the optimal angle for a dual‐field Stanford technique for TSET at extended SSD (SSD= 1, 2, 3, 4, 5 m) to predict a readily available optimal angle for any SSD. Methods: The optimal angle at various SSDs is found using detector array. The diode array consists of 9 diodes placed on a vertical board with a measured vertical scale with the origin placed at isocenter. The lateral distance ranges from −100 to +75 cm. A square 36×36 cm2 field is used to deliver dose in HDTSe‐ delivery mode with a dose rate 2500 MU/min from a Varian Clinic 2300IX linac. Several pairs of gantry angles for the dual field are used, with the first gantry being 70°–78° and the second being 110° –102°. These Result in a dual field of 90° ± θ (θ = 10° − 20°) to build a suitable flatness profile on the vertical axis for treatment. The best group is chosen to determine the optimal angle for each SSD considered. From these optimal angles, an algorithm is determined for any extended SSD treatment. Results:It is found that the optimal angle for TSET does change as one varies the SSD. These angle groups are specific for each SSD giving definite markers for the algorithm. At an SSD of 5 m it has been shown that an optimal angle of θ = 106° produces the best flatness on the vertical axis. While at SSD of 4 m, 9 = 18° Conclusions: An algorithm can now be applied for any treatment center considering a dual‐ field Stanford technique for TSET simplifying the physics commissioning process for the center in consideration.