bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐236: Deconvolution of the Total Nuclear Cross‐Sections of Therapeutic Protons and the Characterization of the Reaction Channels
Authors: Ulmer W. 
Published: June 2015

Purpose:The knowledge of the total nuclear cross‐section Qtot(E) of therapeutic protons Qtot(E) provides important information in advanced radiotherapy with protons, such as the decrease of fluence of primary protons, the release of secondary particles (neutrons, protons, deuterons, etc.), and the production of nuclear fragments (heavy recoils), which usually undergo β+/− decay by emission of γ‐quanta. Therefore determination of Qtot(E) is an important tool for sophisticated calculation algorithms of dose distributions. This cross‐section can be determined by a linear combination of shifted Gaussian kernels and an error‐function. The resonances resulting from deconvolutions in the energy space can be associated with typical nuclear reactions.Methods:The described method of the determination of Qtot(E) results from an extension of the Breit‐Wigner formula and a rather extended version of the nuclear shell theory to include nuclear correlation effects, clusters and highly excited/virtually excited nuclear states. The elastic energy transfer of protons to nucleons (the quantum numbers of the target nucleus remain constant) can be removed by the mentioned deconvolution.Results:The deconvolution of the term related to the error‐function of the type cerf*er((E‐ETh)/σerf] is the main contribution to obtain various nuclear reactions as resonances, since the elastic part of energy transfer is removed. The nuclear products of various elements of therapeutic interest like oxygen, calcium are classified and calculated.Conclusions:The release of neutrons is completely underrated, in particular, for low‐energy protons. The transport of seconary particles, e.g. cluster formation by deuterium, tritium and α‐particles, show an essential contribution to secondary particles, and the heavy recoils, which create γ‐quanta by decay reactions, lead to broadening of the scatter profiles. These contributions cannot be accounted for by one single Gaussian kernel for the description of lateral scatter.
SU‐E‐T‐244: Designing Low‐Z Targets To Enhance Surface Dose: A Monte Carlo Simulation
Authors: Kelly R , Robar J , Parsons D 
Published: June 2015

Purpose:Recent developments in The Varian Truebeam linac platform allows for the introduction of low‐Z targets into the beam line for the imaging purposes. We have proposed using a low‐Z target for radiation therapy purposes to enhance the surface dose during radiation treatment. The target arm of the Varian Truebeam accelerator consists of multiple targets with are linearly translated into the beam line. We have designed two Low‐Z targets made of carbon: 1) a step target consisting of three steps of 15%, 30% and 60% CSDA range for 2.5 MeV electrons Figure 1a; 2) and a ramp target, an incline plane 2cm long with thicknesses ranging from 0% to 60% CSDA range, Figure 1b. The purpose of this work will determine the spectral characteristics of these target designs and determine if they have practical clinical applications for enhancing surface dose.Methods:To calculate the spectral characteristics of these targets, a standard Monte Carlo model of a Varian Clinac accelerator was used. Simulations were performed with a carbon step target, and a carbon ramp target, located at the same position as the electron foil in the rotating carousel. Simulations were carried out using a 2.5 MeV electron beam.Results:The step target design produced spectral characteristics which were similar to spectral model using a single disk target of the same thickness. The ramp target provides a means to have positional variation of the spectral components of the beam, however, the electron component as 60% CSDA us much broader than the step target.Conclusion:The carbon step‐target provides a spectral distribution which is similar to a carbon disk of comparable thickness. The spectral distribution from the ramp‐target can be modified as a function of position to provide a wide range of low energy electrons for surface dose enhancement.
SU‐E‐T‐323: Dosimetric Evaluation of Small Fields for SBRT Treatment
Authors: Gupta R , Eldib A , Wang B , Ma C , Li J 
Published: June 2015

Purpose:Stereotactic body radiation therapy (SBRT) is commonly employed to treat small targets for effective tumor control with radiation beams of small field sizes. The goal of this work was to evaluate dosimetrically a treatment planning system (TPS) by comparing the calculated dose for SBRT treatment with ion‐chamber measurements.Methods:3D images of a solid‐water phantom with a pinpoint ion‐chamber (0.015cm3) inside were acquired with a CT scanner. Active volume of the ion‐chamber was delineated on CT images. Targets with a diameter of 1.5cm, 2cm, 3cm, 4cm and 5cm were drawn around the chamber. 3DCRT plans were generated for each target size with centrally opened 6MV beams and off‐axis beams by changing the isocenter location, respectively, using a TPS with the Analytical Anisotropic Algorithm. A 21iX linear accelerator was employed for plan delivery. The measured and calculated doses were compared. To evaluate the dose calculations in heterogeneity for small fields SBRT treatment, similar plans were also generated and delivered on a heterogeneous thoracic phantom for 5 different size targets in the lung.Results:Dose comparisons between measurements and calculations showed 5.2%, 1.88%, 1.34%, 1.01% and 0.85% difference for SBRT plans with small central axis beams and 0.96%, 0.15%, 0.58%, 0.22% and 0.77% difference for plans with off‐axis beams for five different size targets. For the thoracic phantom, the differences on dose between measurements and calculations are bigger, which are 8%, 5.9%, 4.5%, 3.9% and 4.5%, respectively.Conclusion:Dose verification for small fields used in the SBRT treatment has been performed based on ion‐chamber measurements in both homogenous and heterogeneous phantoms. More than a 5% difference has been observed in the heterogeneous phantom, especially for very small fields. To meet the ICRU recommendation on a dose difference of no more than 5%, some corrections on the commissioning parameters of the TPS are needed.
SU‐E‐T‐336: Dosimetric Properties of a New Solid Water High Equivalency Phantom for High‐Energy Photon Beams
Authors: Araki F , Ohno T , Onitsuka R , Shimohigashi Y 
Published: June 2015

Purpose:To investigate dosimetric properties in high‐energy photon beams for a Solid Water High Equivalency (SWHE, SW557) phantom (Gammex) which was newly developed as water mimicking material.Methods:The mass density of SWHE and SWHE/water electron density ratio are 1.032 g/cm3 and 1.005 according to the manufacturer information, respectively. SWHE is more water equivalent material in physical characteristics and uniformity than conventional SW457. This study calculated the relative ionization ratio of water and SWHE as a function of depth from the cavity dose in PTW30013 and Exradin A19 Farmer‐type ionization chambers using Monte Caro simulations. The simulation was performed with a 10 × 10 cm2 field at SAD of 100 cm for 4, 6, 10, 15, and 18 MV photons. The ionization ratio was also measured with the PTW30013 chamber for 6 and 15 MV photons. In addition, the overall perturbation factor of both chambers was calculated for both phantoms.Results:The relative ionization ratio curves for water and SWHE was in good agreement for all photon energies. The ionization ratio of water/SWHE for both chambers was 0.999–1.002, 0.999–1.002, 1.001–1.004, 1.004–1.007, and 1.006–1.010 at depths of over the buildup region for 4, 6, 10, 15, and 18 MV photons, respectively. The ionization ratio of water/SWHE increased up to 1% with increasing the photon energy. The measured ionization ratio of water/SWHE for 6 and 15 MV photons agreed well with calculated values. The overall perturbation factor for both chambers was 0.983–0.988 and 0.978–0.983 for water and SWHE, respectively, in a range from 4 MV to 18 MV.Conclusion:The depth scaling factor of water/SWHE was equal to unity for all photon energies. The ionization ratio of water/SWHE at a reference depth was equal to unity for 4 and 6 MV and larger up to 0.7% than unity for 18 MV.
SU‐E‐T‐337: Dosimetric Study of TMI Using Helical Tomotherapy
Authors: Phurailatpam R , Swamidas J , Sastri J , Josi K , Mathankar M , Paul S , Sawant M , Moundekar P 
Published: June 2015

Purpose:The purpose of this study is to evaluate the dosimtry of TMI using Helical Tomotherapy (HT).Methods:Whole body CT data sets of 4 patients (median age : range:12–37 years) with 5mm slice thickness were used for planning in HT (TPS version 4.2.3). The contouring of the target and organ at risks (OAR) were delineated ( Oncentra Master Plan v 4.1). Two plans were generated using 5cm and 2.5 cm field widths.The modulation factor and pitch was 3 and 0.3 respectively. Dose to PTV, OARs and the dose homogeneity were evaluated. The doses obtained were compared with the existimg literature. Dose delivery verification was carried out by point dose and 2D array measurements with ion chamber and Arc check dosimetry (Sun NuclearTM) system repectively. The prescribed dose was 14.4 Gy in 8 fractions.Results:The mean PTV volume was 7341.28cc (sd=2353) The dose homogeneity index of PTV was 12.03(sd=2.98) for 2.5cm_FW and 14.61 (sd=1.33) for 5cm_FW.The conformation number for 2.5 and 5 cm plans are 0.6328(sd=0.09) and 0.5915 (sd=0.0376) respectively. The mean dose(Gy) to the OARs were as follows for 2.5cm_FW : eyes, lens, lungs, kidneys, heart, liver,thyroid and testes for are 4.12,1.9,6.61,4.04,4.85,6.06,7.17 and 1.27. The mean dose(Gy) to the OARs were as follows for 5cm_FW :eyes, lens, lungs, kidneys, heart, liver,thyroid and testes for are 4.45,3.14,6.79,4.02,5.01,6.01,10.8 and 1.33. The mean variation of the point dose as compared to the expected dose was within 2% and the gamma analysis was at 91%.Conclusion:It was concluded that 5cm field width plans produces optimal dose volume parameters with deliverable treatment time. From this initial dissymmetric study, it was concluded that the treatment planning and the dose delivery verification was feasible considering the complexity of the TMI.
SU‐E‐T‐338: Dosimetric Study of Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiation Therapy (IMRT) for Stereotactic Body Radiation Therapy (SBRT) in Early Stage Lung Cancer
Authors: Ahmad I , Yah R , Quinn K , Seebach A , Wang H 
Published: June 2015

Purpose:This study evaluates the dosimetric differences using volumetric modulated arc therapy (VMAT) in patients previously treated with intensity modulated radiation therapy IMRT for stereotactic body radiotherapy (SBRT) in early stage lung cancer.Methods:We evaluated 9 consecutive medically inoperable lung cancer patients at the start of the SBRT program who were treated with IMRT from November 2010 to October 2011. These patients were treated using 6 MV energy. The 9 cases were then re‐planned with VMAT performed with arc therapy using 6 MV flattening filter free (FFF) energy with the same organs at risk (OARS) constraints. Data collected for the treatment plans included target coverage, beam on time, dose to OARS and gamma pass rate.Results:Five patients were T1N0 and four patients were T2N0 with all tumors less than 5 cm. The average GTV was 13.02 cm3 (0.83–40.87) and average PTV was 44.65 cm3 (14.06–118.08). The IMRT plans had a mean of 7.2 angles (6–9) and 5.4 minutes (3.6–11.1) per plan. The VMAT plans had a mean of 2.8 arcs (2–3) and 4.0 minutes (2.2–6.0) per plan. VMAT had slightly more target coverage than IMRT with average increase in D95 of 2.68% (1.24–5.73) and D99 of 3.65% (0.88–8.77). VMAT produced lower doses to all OARs. The largest reductions were in maximum doses to the spinal cord with an average reduction of 24.1%, esophagus with an average reduction of 22.1%, and lung with an average reduction in the V20 of 16.3% The mean gamma pass rate was 99.8% (99.2–100) at 3 mm and 3% for VMAT with comparable values for IMRT.Conclusion:These findings suggest that using VMAT for SBRT in early stage lung cancer is superior to IMRT in terms of dose coverage, OAR dose and a lower treatment delivery time with a similar gamma pass rate.
SU‐E‐T‐339: Dosimetric Verification of Acuros XB Dose Calculation Algorithm On An Air Cavity for 6‐MV Flattening Filter‐Free Beam
Authors: Kang S , Chung J , Suh T 
Published: June 2015

Purpose:This study was to verify the accuracy of Acuros XB (AXB) dose calculation algorithm on an air cavity for a single radiation field using 6‐MV flattening filter‐free (FFF) beam.Methods:A rectangular slab phantom containing an air cavity was made for this study. The CT images of the phantom for dose calculation were scanned with and without film at measurement depths (4.5, 5.5, 6.5 and 7.5 cm). The central axis doses (CADs) and the off‐axis doses (OADs) were measured by film and calculated with Analytical Anisotropic Algorithm (AAA) and AXB for field sizes ranging from 2 Χ 2 to 5 Χ 5 cm2 of 6‐MV FFF beams. Both algorithms were divided into AXB_w and AAA _w when included the film in phantom for dose calculation, and AXB_w/o and AAA_w/o in calculation without film. The calculated OADs for both algorithms were compared with the measured OADs and difference values were determined using root means squares error (RMSE) and gamma evaluation.Results:The percentage differences (%Diffs) between the measured and calculated CAD for AXB_w was most agreement than others. Compared to the %Diff with and without film, the %Diffs with film were decreased than without within both algorithms. The %Diffs for both algorithms were reduced with increasing field size and increased relative to the depth increment. RMSEs of CAD for AXB_w were within 10.32% for both inner‐profile and penumbra, while the corresponding values of AAA_w appeared to 96.50%.Conclusion:This study demonstrated that the dose calculation with AXB within air cavity shows more accurate than with AAA compared to the measured dose. Furthermore, we found that the AXB_w was superior to AXB_w/o in this region when compared against the measurements.
SU‐E‐T‐349: Effective Dose‐Volume‐Histogram Prediction Method Using Euclidean Distance Volume Histogram for Volumetric Modulated Arc Therapy to Treat Prostate Cancer
Authors: Shin J. , Liang J. , Schild S. , Wong W. , Liu W. 
Published: June 2015

Purpose:Manually checking the plan dose‐volume histograms (DVH) quality is time consuming, thereby limiting the patient throughput and leading to inconsistent plan quality across institutions. We propose to use Euclidean distance volume histogram (EDVH) to automate this process in volumetric‐modulated arch therapy (VMAT) to treat prostate cancer patients by predicting DVH of a new patient based on prior expert patients.Methods:52 prostate cancer patients treated by VMAT at our institution were randomly selected. 3D distance transformation was performed on the simulation CTs to get Euclidean distance for each voxel inside every organ‐at‐risk with respect to the tumor. EDVH was then constructed, analogous to computing a DVH. In order to evaluate our proposed method, we utilize the leave‐one‐patient‐out cross validation. For each test patient, we select 5 patients with the closest EDVHs from the remaining 51 patients and determine whether the DVH of this patient is within the band bounded by these 5 patients’ DVHs with a ratio defined as AREA5/AREA6, where AREA5 is the area‐between‐curves (ABC) bounded by the DVHs of the 5 selected patients and AREA6 is the ABC bounded by the DVHs of the 5 selected patients plus the test patient. The higher the ratio is, the better prediction performance is.Results:From the process of leave‐one‐patient‐out cross validation, we obtained a prediction ratio (0.94±0.11) for each patient. 48 out of 52 patients (92.3%) for bladder and 46 out of 52 patients (88.5%) for rectum had prediction ratios above 0.80. 41 out of 52 patients (78.9%) for bladder and 38 out of 52 patients (73.1%) for rectum had prediction ratios above 0.90.Conclusion:EDVH can effectively capture the overall geometric relationship between the tumor and organ‐at‐risks, which can be used to confidently predict the DVH based on prior expert patients for VMAT to treat prostate cancer.NIH/NCI K25CA168984, Eagles Cancer Research Career Development, The Lawrence W. and Marilyn W. Matteson Fund for Cancer Research, Mayo ASU Seed Grant, and The Kemper Marley Foundation.
SU‐E‐T‐354: Efficient and Enhanced QA Testing of Linear Accelerators Using a Real‐Time Beam Monitor
Authors: Jung J , Farrokhkish M , Norrlinger B , Wang Y , Heaton R , Jaffray D , Islam M 
Published: June 2015

Purpose:To investigate the feasibility of performing routine QA tests of linear accelerators (Linac) using the Integral Quality Monitoring (IQM) system. The system, consisting of a 1‐D sensitivity gradient large area ion‐chamber mounted at the collimator, allows automatic collection and analysis of beam data.Methods:The IQM was investigated to perform several QA constancy tests, similar to those recommended by AAPM TG142, of a Linac including: beam output, MLC calibration, beam symmetry, relative dose factor (RDF), dose linearity, output as a function of gantry angle and dose rate. All measurements by the IQM system accompanied a reference measurement using a conventional dosimetry system and were performed on an Elekta Infinity Linac with Agility MLC. The MLC calibration check is done using a Picket‐Fence type 2×10cm2 field positioned at different off‐axis locations along the chamber gradient. Beam symmetry constancy values are established by signals from an 4×4cm2 aperture located at various off‐axis positions; the sensitivity of the test was determined by the changes in the signals in response to a tilt in the beam. The data for various square field sizes were used to develop a functional relationship with RDF.Results:The IQM tracked the beam output well within 1% of the reference ion‐chamber readings. The Picket‐Fence type field test detected a 1mm shift error of one MLC bank. The system was able to detect 2.5% or greater beam asymmetry. The IQM results for all other QA tests were found to agree with the reference values to within 0.5%.Conclusion:It was demonstrated that the IQM system can effectively monitor the Linac performance parameters for the purpose of routine QA constancy tests. With minimum user interactions a comprehensive set of tests can be performed efficiently, allowing frequent monitoring of the Linac.The presenting author's salary is funded by the manufacturer of the QA device. All the other authors have financial interests with the commercialization of this QA device.
SU‐E‐T‐355: Efficient Scatter Correction for Direct Ray‐Tracing Based Dose Calculation
Authors: Chen M , Jiang S , Lu W 
Published: June 2015

Purpose:To propose a scatter correction method with linear computational complexity for direct‐ray‐tracing (DRT) based dose calculation. Due to its speed and simplicity, DRT is widely used as a dose engine in the treatment planning system (TPS) and monitor unit (MU) verification software, where heterogeneity correction is applied by radiological distance scaling. However, such correction only accounts for attenuation but not scatter difference, causing the DRT algorithm less accurate than the model‐based algorithms for small field size in heterogeneous media.Methods:Inspired by the convolution formula derived from an exponential kernel as is typically done in the collapsed‐cone‐convolution‐superposition (CCCS) method, we redesigned the ray tracing component as the sum of TERMA scaled by a local deposition factor, which is linear with respect to density, and dose of the previous voxel scaled by a remote deposition factor, D(i)=aρ(i)T(i)+(b+c(ρ(i)‐1))D(i‐1),where T(i)=e^(‐αr(i)+β(r(i))^2) and r(i)=Σ_(j=1,..,i)ρ(j).The two factors together with TERMA can be expressed in terms of 5 parameters, which are subsequently optimized by curve fitting using digital phantoms for each field size and each beam energy.Results:The proposed algorithm was implemented for the Fluence‐Convolution‐Broad‐Beam (FCBB) dose engine and evaluated using digital slab phantoms and clinical CT data. Compared with the gold standard calculation, dose deviations were improved from 20% to 2% in the low density regions of the slab phantoms for the 1‐cm field size, and within 2% for over 95% of the volume with the largest discrepancy at the interface for the clinical lung case.Conclusion:We developed a simple recursive formula for scatter correction for the DRT‐based dose calculation with much improved accuracy, especially for small field size, while still keeping calculation to linear complexity. The proposed calculator is fast, yet accurate, which is crucial for dose updating in IMRT optimization.
SU‐E‐T‐363: Error Detection Comparison of EPID and MLC Log File Based IMRT QA Systems
Authors: Defoor D , Obeidat M , Linden P , Kirby N , Mavroidis P , Papanikolaou N , Stathakis S 
Published: June 2015

Purpose:In this study we will compare the ability of three QA methods (Delta4, MU‐EPID, Dynalog QA) to detect specific errors.Methods:A Varian Novalis Tx with a HD120 MLC and aS1000 Electronic Portal Imaging Device (EPID) was used in our study. Multi‐leaf collimator (MLC) errors, gantry angle and dose errors were introduced into 5 volumetric arc therapy (VMAT) plans. 3D dose distributions calculated with data from the EPID and Dynalog QA methods were compared with the planned dose distribution. The gamma passing percentages as well as percentage error of planning target volume (PTV) dose were used for passing determination. Baselines for gamma passing percentages and PTV dose were established by measuring the original plan 5 times consecutively. Standard passing thresholds as well as thresholds derived from receiver operator characteristic (ROC) analysis and 2 standard deviation (SD) criteria were used.Results:When applying the standard 95% pass rate at 3%/3mm gamma analysis 14, 21 and 8 of 30 errors were detected by the Delta4, MU‐EPID and Dynalog QA methods respectively. Thresholds set at 2 SD from our base line measurements resulted in the detection of 18, 9 and 14 of 30 errors for the Delta4, MU‐EPID and Dynalog QA methods respectively. When using D2 of the PTV as a metric the Dynalog QA detected 20 of 30 errors while the EPID method detected 14 of 30 errors. Using D98 of the PTV, Dynalog QA detected 13 of 30 while the EPID detected 3 of 30 errors.Conclusion:Although MU‐EPID detected the most errors at the standard 95% cutoff it also produced the most false detections in the baseline data. The Dynalog QA was the most effective when the ROC adjusted passing threshold was used. D2 was more effective as a metric for detecting errors than D98.