bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐165: Characterization of Dose Distributions in High‐Dose‐Rate Surface Brachytherapy
Authors: Buzurovic I , Hansen J , Bhagwat M , O'Farrell D , Damato A , Friesen S , Devlin P , Cormack R 
Published: June 2015

Purpose:To characterize dose distributions in high‐dose‐rate(HDR) surface brachytherapy using an Ir‐125 source for different geometries, field sizes and topology of the clinical targets(CT). To investigate the depth doses at the central axis(CAX), edges of the treatment fields(E), and lateral dose distributions(L) present when using flap applicators in skin cancer treatments.Methods:When malignancies diagnosed on the skin are treated, various geometries of the CT require proper adaptation of the flap or custom‐made applicators to the treatment site. Consequently, the dose at the depth on CAX and field edges changes with variation of the curvatures and size of the applicators. To assess the dose distributions, we created a total of 10 treatment plans(TP) for 10×10 and 20×20 field sizes(FS) with a step size of 1cm. The geometry of the applicators was: planar(PA), curved to 30(CA30) and 60(CA60) degrees with respect to the CAX, half‐cylinder(HC), and cylindrical shape(CS). One additional TP was created in which the applicators were positioned to form a dome shape(DS) with a diameter of 16cm. This TP was used to emulate treatment of the average sized scalp. All TPs were optimized to deliver a prescription dose at 8mm equidistantly from the planes containing the dwell positions. This optimization is equivalent to the clinical arrangement since the SSD for the flap applicators is 5mm and the prescription depth is 3mm in the majority of clinical cases.Results:The depths (in mm) of the isodose lines were: FS(10×10):PA[90%(9.1CAX,8.0E,7.6L),50%(28.3CAX,20E,17.3L), 25%(51.1CAX,40E,27L)],CA30[90%(10.3CAX,8.2E,7.9L),50%(32.1CAX, 16.2E,15.8L),25%(61.3CAX,36.7E,31.8L)],CA60[90%(12.2CAX,6.1E,6.3L ),50%(47CAX,14E,16.6L),25%(70.8CAX,31.9E,35.4L)],HC[90%(11.1CA X,6.3E,7.3L),50%(38.3CAX,14.6E,16.1L),25%(66.2CAX,33.8E,34.2L)];FS (20×20):PA[90%(11.1CAX,9.0E,7.0L),50%(34.4CAX,21.9E,15.3L),25%(7 0.4CAX,50.9E,34.8L)],CA30[90%(10.9CAX,7.5E,7.1L),50%(38.8CAX,16. 7E,15.4L),25%(80.7CAX,39.9E,35.7L)],HC[90%(11.1CAX,10.9E,10.6L),5 0%(34.4CAX,38.8E,47.2L),25%(70.4CAX,80.7E,96.6L);DS[90%(12.1CA X,8.5E,6.8L),50%(60.6CAX,17.7E,15.8L),25%(109.6CAX,40.3E,34.3L)].Conclusion:These results can be used for the approximate calculation and quick assessment of the radiation dose to the organs‐at‐risk at depth (heart,brain,thyroid, optical nerve) or at the surface distance from the CT (breast,eyes, gonads), and only the geometry of the CT needs to be measured. Understanding of the dose distributions in HDR surface brachytherapy may improve clinical decision making process.
SU‐E‐T‐172: Characterization of TLD‐100 (LiF:Mg,Ti) Microcube Energy Response in a Cylindrical Chamber Phantom
Authors: Desai V , Hammer C , Kunugi K , Culberson W , DeWerd L 
Published: June 2015

Purpose:To characterize the energy response of TLD‐100 microcubes inside a Virtual Water chamber phantom.Methods:Four TLD microcubes were placed inside a water‐proof Virtual Water (VW) chamber phantom and irradiated to a known dose on a Varian linac in a 1D water tank. These chamber phantoms were then replaced by TLD‐100 chips inside a separate VW paddle and irradiated to the same dose. Each energy response reading was calculated as light output per unit dose in nC/cGy and normalized to a calibration set irradiated to the same dose in 60Co. The differences in response between the TLD chips and microcubes were then analyzed.Results:Across all energies, the average microcube response was less sensitive to energy than the average chip response with both falling consistently within 2.8% of previously established values in the literatureConclusion:TLD microcubes showed a lower average sensitivity to energy than their TLD chip counterparts. The use of TLD‐100 microcubes inside the chamber phantom was validated against TLD‐100 chips inside of VW paddles.
SU‐E‐T‐177: Clinical Experience with Spirometer Guided Breath Hold Lung SBRT
Authors: Liu H , Manning M , Sintay B , Maurer J , Hayes L , Wiant D 
Published: June 2015

Purpose:Tumor motion in lung SBRT is typically managed by creating an internal target volume (ITV) based on 4D‐CT information. Another option, which may reduce lung dose and imaging artifact, is to use a breath hold (BH) during simulation and delivery. Here we evaluate the reproducibility of tumor position at repeated BH using a newly released spirometry system.Methods:Three patients underwent multiple BH CT's at simulation. All patients underwent a BH cone beam CT (CBCT) prior to each treatment. All image sets were registered to a patient's first simulation CT based on local bony anatomy. The gross tumor volume (GTV), and the diaphragm or the apex of the lung were contoured on the first image set and expanded in 1 mm increments until the GTVs and diaphragms on all image sets were included inside an expanded structure. The GTV and diaphragm margins necessary to encompass the structures were recorded.Results:The first patient underwent 2 BH CT's and fluoroscopy at simulation, the remaining patients underwent 3 BH CT's at simulation. In all cases the GTV's remained within 1 mm expansions and the diaphragms remained within 2 mm expansions on repeat scans. Each patient underwent 3 daily BH CBCT's. In all cases the GTV's remained within a 2 mm expansions, and the diaphragms (or lung apex in one case) remained within 2 mm expansions at daily BH imaging.Conclusions:These case studies demonstrate spirometry as an effective tool for limiting tumor motion (and imaging artifact) and facilitating reproducible tumor positioning over multiple set‐ups and BH's.This work was partially supported by Qfix.
SU‐E‐T‐182: Clinical Implementation of TG71‐Based Electron MU Calculation and Comparison with a Commercial Secondary Calculation
Authors: Xu H , Guerrero M , Yang X , Chen S , Langen K , Prado K , Schinkel C 
Published: June 2015

Purpose:The TG‐71 report was published in 2014 to present standardized methodologies for MU calculations and determination of dosimetric quantities. This work explores the clinical implementation of a TG71‐based electron MU calculation algorithm and compares it with a recently released commercial secondary calculation program–Mobius3D (Mobius Medical System, LP).Methods:TG‐71 electron dosimetry data were acquired, and MU calculations were performed based on the recently published TG‐71 report. The formalism in the report for extended SSD using air‐gap corrections was used. The dosimetric quantities, such PDD, output factor, and f‐air factors were incorporated into an organized databook that facilitates data access and subsequent computation. The Mobius3D program utilizes a pencil beam redefinition algorithm. To verify the accuracy of calculations, five customized rectangular cutouts of different sizes–6×12, 4×12, 6×8, 4×8, 3×6 cm2–were made. Calculations were compared to each other and to point dose measurements for electron beams of energy 6, 9, 12, 16, 20 MeV. Each calculation / measurement point was at the depth of maximum dose for each cutout in a 10×10 cm2 or 15×15cm2 applicator with SSDs 100cm and 110cm. Validation measurements were made with a CC04 ion chamber in a solid water phantom for electron beams of energy 9 and 16 MeV.Results:Differences between the TG‐71 and the commercial system relative to measurements were within 3% for most combinations of electron energy, cutout size, and SSD. A 5.6% difference between the two calculation methods was found only for the 6MeV electron beam with 3×6 cm2cutout in the 10×102cm applicator at 110cm SSD. Both the TG‐71 and the commercial calculations show good consistency with chamber measurements: for 5 cutouts, <1% difference for 100cm SSD, and 0.5–2.7% for 110cm SSD.Conclusions:Based on comparisons with measurements, a TG71‐based computation method and a Mobius3D program produce reasonably accurate MU calculations for electron‐beam therapy.
SU‐E‐T‐185: Clinically‐Relevant Investigation of Flattening Filter Free Skin Dose
Authors: Guy C , Karki K , Sharma M , Kim S 
Published: June 2015

Purpose:Flattening‐filter‐free (FFF) beams are increasingly used for small‐field treatments due to inherent advantages like higher MU efficiency and reduced treatment time and scatter dose. Removal of the flattening‐filter increases the electron contamination and low‐energy x‐rays. As such, surface‐dose characteristics are different from traditional flattened (FF) beams. The goal of this work is to investigate surface dose of 6/10 MV FFF and FF beams under conditions representative of emerging complex techniques like small‐field stereotactic treatments which use small fields formed with multi‐leaf‐collimators (MLCs) at closer SSDs.Methods:A parallel‐plate PTW Markus‐chamber (N23343) placed in custom air‐ and water‐equivalent phantoms was used to measure surface‐dose at 2/3/4/6/8/10/20/30 cm2 field sizes, at 80/90/100 cm source‐to‐surface distances, and at fields defined by jaws and MLCs. The effect of dose rate (600 and 1400/2400 MU/min) was also investigated at 100 cm SSD. Measurements were performed on TrueBeam linac (Varian Medical Systems, Palo Alto, CA) for 6X/6XFFF/10X/10XFFF beam energies.Results:No dose‐rate dependence was seen for FFF skin‐dose. Air‐phantom measurements were, on average, 5±3% larger than for water‐phantom measurements. With SSD increase from 80 to 100 cm, skin‐dose decreased by an average of 3.9±2.5%. FFF beams were found to be more sensitive to SSD changes in comparison to FF beams. The difference in skin dose between MLC‐ and jaw‐fields was less variable with field size for FFF compared to FF beams. 10 MV beams showed greater difference in FFF‐to‐FF ratio, 50% (jaws) and 22% (MLC), between the largest and smallest field sizes compared to 6 MV beams, 30% (jaws) and 9% (MLC).Conclusion:Under clinically‐relevant conditions, surface dose for FFF beams was higher at small field size (<10 cm), lower at largest field size (30 cm), more sensitive to SSD changes, and had less variation with field size compared to dose for FF beams.
SU‐E‐T‐186: Cloud‐Based Quality Assurance Application for Linear Accelerator Commissioning
Authors: Rogers J 
Published: June 2015

Purpose:To identify anomalies and safety issues during data collection and modeling for treatment planning systemsMethods:A cloud‐based quality assurance system (AQUIRE ‐ Automated QUalIty REassurance) has been developed to allow the uploading and analysis of beam data aquired during the treatment planning system commissioning process. In addition to comparing and aggregating measured data, tools have also been developed to extract dose from the treatment planning system for end‐to‐end testing. A gamma index is perfomed on the data to give a dose difference and distance‐to‐agreement for validation that a beam model is generating plans consistent with the beam data collection.Results:Over 20 linear accelerators have been commissioning using this platform, and a variety of errors and potential saftey issues have been caught through the validation process. For example, the gamma index of 2% dose, 2mm DTA is quite sufficient to see curves not corrected for effective point of measurement. Also, data imported into the database is analyzed against an aggregate of similar linear accelerators to show data points that are outliers. The resulting curves in the database exhibit a very small standard deviation and imply that a preconfigured beam model based on aggregated linear accelerators will be sufficient in most cases.Conclusion:With the use of this new platform for beam data commissioning, errors in beam data collection and treatment planning system modeling are greatly reduced. With the reduction in errors during acquisition, the resulting beam models are quite similar, suggesting that a common beam model may be possible in the future. Development is ongoing to create routine quality assurance tools to compare back to the beam data acquired during commissioning.I am a medical physicist for Alzyen Medical Physics, and perform commissioning services
SU‐E‐T‐193: Commissioning of An IntraOp Mobetron
Authors: Grzetic S , Hessler J , Carlson M , James Arthur G. 
Published: June 2015

Purpose:This study will describe the commissioning process of an Intra‐Op Mobetron following the guidance of TG72 and includes a detailed method for measuring gap factors.Methods:Beam data was collected for 6, 9, and 12MeV electrons on the Mobetron using a PTW water tank and a Markus chamber. Commissioning data was collected for 3 sets of cones (0°, 15°, and 30° with respect to the water surface) that ranged in size from 3cm to 10cm diameter in half centimeter increments. Profiles were collected at six depths for all integer cones. PDI's were taken for all cones in a path perpendicular to the water surface and then converted to dose using MEPHYSTO's internal algorithm. The depth of maximum dose was determined from the PDD's and used for measurement of output factors. Output factors were normalized to the 10cm flat cone. Gap factors were measured for all flat cones by raising the cone away from the water surface in defined gaps. These gap factors were measured at dmax for gaps of 1cm to 5cm in 1cm increments Gap factors and effective SSD values were calculated.Results:Output factors measured for all cones were within 3% of the representative beam data for flat cones. There is no published data on beveled cones, but the angled cone output factors agreed with the flat cones within 5%. Gap factors follow a linear pattern with the output decreasing 3–7% per centimeter gap depending on the size of the cone and energy. Effective SSD values calculated and fit a 3rd order polynomial curve with R2>0.98 for all energies.Conclusion:Commissioning of an Intra‐Op Mobetron was completed with general agreement to published data. New data was published for beveled cones and a method for determining gap factors was established.
SU‐E‐T‐201: Comparison Between Two Immobilization Systems for Cranial Stereotactic Radiosurgery Using The ExacTrac Image‐Guidance System
Authors: Nedialkova L , Ostenson J , Sabbas A , Kulidzhanov F , Wernicke G , Trichter S 
Published: June 2015

Purpose:The ExacTrac Image‐Guidance system enables frameless stereotactic radiosurgeries with real‐time image guidance that allows repositioning on a sub‐millimetric scale. In order for such treatments to be effective, the patient's head has to be immobilized using a custom mask created to conform to the patient's anatomy. There are two cranial immobilization systems used in our institution: masks manufactured by Brainlab and Civco. For both systems, it is not evident what the achievable level of intrafraction immobilization is for each system in our patient population. The ExacTrac system makes it possible to quantitatively assess the immobilization the two mask systems offer.Methods:The ExacTrac imaging system was used to assess intrafraction geometric displacement in the three Cartesian directions for each of these masks multiple times during Stereotactic Radiosurgery, SRS or hypofractionated treatment. Intrafraction motions were considered uncorrelated random movements away from isocenter. The displacement from isocenter, excluding initial correction, was calculated in over 100 instances for each mask system. The distances from isocenter were compared with histograms, average, median, and by percentile.Results:It was found that the Brainlab mask had mean distance from isocenter of 0.5 mm (SD 0.45 mm, median 0.37 mm) compared to 1.0 mm (SD 1.25, median 0.61 mm) for Civco. The distributions were compared with a Mann‐Whitney U test and were found to be significantly different (P < 0.001). The 75th and 95th percentile of displacements were 1.2 and >3 mm and 0.6 mm and <1.5 mm, for the Civco and Brainlab systems respectively. As a rule of thumb, the averages, medians, and percentiles for the Civco system were approximately twice that of the Brainlab system.Conclusion:Given the results, the Brainlab mask system should be used to minimize risk of geometric error in delivery of SRS or high dose gradient techniques.
SU‐E‐T‐207: Comparison of Integrated Tissue Air Ratio (ITAR) to Traditional TAR for Kilovoltage Pencil‐Beams
Authors: Hanlon J , Koruga I , Chell E , Pintaske R 
Published: June 2015

Purpose:Clinically viable depth dose determination in kilovoltage pencil‐beams is a great challenge that resulted in a published dosimetry method called ITAR, which involves measurement of air kerma and attenuation with a detector in a low scatter environment coupled with MCNP scatter calculations. The objective of this work is to compare ITAR to traditional TAR using inherently water‐proof microchambers that have only recently become commercially available.Methods:An Exradin A26 microchamber was centered 150 mm from a 100 kVp x‐ray source with 2 mm aluminum HVL. Depth dose in water from 16 to 24 mm in 2 mm increments was determined by: (1) placing blocks of Plastic Water LR near the source to minimize scatter and using previously published conversion coefficients [ITAR method] and (2) submerging the detector in a water tank with 2 mm thick Plastic Water LR walls and jogging the tank with motor controllers while keeping the detector position fixed [traditional TAR method]. Each method was repeated four to five times. For each repetition, dose was measured free in‐air to normalize the data for exponential regression.Results:Traditional TAR indicated higher depth dose than ITAR; differences ranged from 2.1% at 24 mm depth to 2.5% at 16 mm depth. However, the results of traditional TAR did not include a correction for Pq,cham because it is unknown for this detector type in these conditions. It is estimated that the component of Pq,cham due to the effect of water displacement alone is ∼0.94, but Pq,cham is likely several percent larger than 0.94 due to the energy dependency of the microchamber in the presence of low energy scatter that is not present during in‐air calibration.Conclusion:The ITAR method remains preferable for clinical depth dose determination in kilovoltage pencil‐beams due to Pq,cham being unknown for suitable detectors in relevant conditions.All four of the authors are either current full time employees, which include stock option grants, or consultants of Oraya Therapeutics Inc.
SU‐E‐T‐208: Comparison of MR Image Quality of Various Brachytherapy Applicators for Cervical Cancer
Authors: Soliman A , Elzibak A , Fatemi A , Safigholi H , Han D , Leung E , Ravi A , Song W 
Published: June 2015

Purpose:To compare the quality of Magnetic Resonance (MR) images of a recently‐proposed novel direction‐modulated brachytherapy (DMBT) tandem applicator against two conventional clinical applicators, using the current MRI clinical protocol.Methods:Three tandem applicators were compared: (1) tungsten‐based DMBT applicator, (2) conventional plastic applicator and (3) conventional stainless steel applicator. Physical dimensions were 5.4, 3.8 and 3.2 for tandems (1), (2) and (3), respectively. Each applicator was placed in the same water‐phantom and independently scanned using the same parameters and coil settings on a 1.5 T 450w GE scanner. Images were acquired using T2‐weighted turbo‐spin‐echo (TSE) with 8‐channel body coil. Acquisition parameters were TR/TE =7000/108 ms; acquisition matrix = 320 × 256; 30 slices with 4 mm thickness and 0.5 gap; pixel bandwidth = 122 Hz and voxel size = 0.5 × 0.625 mm2 and number of excitations (NEX) = 4. Multiple acquisitions were obtained in para‐sagittal and para‐axial views (with respect to the tandem axis) for each applicator. Diameters of the tandem were measured at multiple angles and multiple locations and compared to the physical dimensions of the corresponding tandems.Results:Minimal susceptibility artifact was observed with the DMBT and the plastic tandems. The stainless steel tandem produced significantly larger artifact than the first two tandems. The average diameter of the DMBT applicator measured 5.94 ± 0.3 mm. The average diameter of the plastic tandem measured 3.9 ± 0.1 mm. The maximum extent of artifact was 1.5 mm and 0.7 mm for DMBT and plastic tandems, respectively. The susceptibility artifact induced by the stainless steel tandem prevented the measurement of its diameter, and the edges of the tandem could not be identified in any acquisition.Conclusion:This work demonstrated that the plastic and the tungsten‐based DMBT tandem applicators are both suitable for MRI‐guided brachytherapy of cervical cancer.
SU‐E‐T‐210: Comparison of Proton with Electron Boost in Breast Cancer Treatment
Authors: Zheng Y , Liu Y , Chang A 
Published: June 2015

Purpose:Electron beams are commonly used for boost radiation following whole breast irradiation (WBI) to improve the in‐breast local control. Proton beams have a finite range and a sharper distal dose falloff compared to electron beams, thus potentially sparing more heart and lung in breast treatment. The purpose of the study is to compare protons with electrons for boost breast treatment in terms of target coverage and normal tissue sparing.Methods:Six breast cancer patients were included in this study. All women received WBI to 45–50 Gy, followed by a 10–16.2 Gy boost with standard fractionation. If proton beams were used for the boost treatment, an electron plan was retrospectively generated for comparison using the same CT set and structures, and vice versa if electron beams were used for treatment. Proton plans were generated using the treatment planning system (TPS) with two to three uniform scanning proton beams. Electron plans were generated using the Pinnacle TPS with one single en face beam. Dose‐volume histograms (DVH) were calculated and compared between proton and electron boost plans.Results:Proton plans show a similar boost target coverage, similar skin dose, and much better heart and lung sparing. For an example patient, V95% for PTV was 99.98% and skin (5 mm shell) received a max dose close to the prescription dose for both protons and electrons; however, V2 and V5 for the ipsilateral lung and heart were 37.5%, 17.9% and 19.9%, 4.9% respectively for electrons, but were essentially 0 for protons.Conclusions:This dosimetric comparison demonstrates that while both proton therapy and electron therapy provided similar coverage and skin dose, proton therapy could largely reduce the dose to lung and heart, thus leading to potential less side effects.