bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐537: Local Multi‐Criteria Optimization for Clinical Tradeoff Decision Guidance in RT Planning
Authors: Yuan L , Wu Q J , Sheng Y , Liu J , Benitez A , Yin F , Ge Y 
Published: June 2015

Purpose:We present a novel method for generating a local segment of Pareto surface around the best achievable plan predicted by a knowledge model. This local‐MCO will provide an efficient method to enable clinically viable tradeoff decisions in IMRT planning tailored to the patient's specific needs.Methods:Multi‐criteria optimization (MCO) methods provide physicians and planners the ability to explore tradeoff options in RT planning. However, generic MCO methods are often time consuming because a global Pareto surface (PS) need to be explored if patient‐specific clinical conditions and planners’ planning experiences are not taken into consideration. We have developed a local‐MCO approach, which incorporates the knowledge model prediction based on the individual patient's features and planning experience into the generation of a local PS around a predicted plan. In the proposed method, the starting points of clinical relevant organ sparing objectives are predicted by the knowledge models, and then a local PS is searched near the model predictions. As an initial assessment, the local PS is compared with the global PS generated for two prostate cancer cases. The mean minimum distance from each plan on the local PS to the global PS and the range of clinical acceptable dosimetric parameters covered by the local and global PS are calculated.Results:The local PS agrees well with the global PS. The mean minimum distance between the local and global PS in the PTV‐bladder‐rectum dose objective space are about 3% and 1% of prescription dose for the two plans, respectively. Although the local PS is only a small portion of the global PS, they cover most of the clinically relevant dose range.Conclusion:The local MCO results in a smaller but clinically more relevant PS. It is an efficient method to provide physicians with guidance of patient‐specific trade‐off options based on practice experience.Partially supported by NIH/NCI under grant #R21CA161389 and a master research grant by Varian Medical Systems.
SU‐E‐T‐538: Lung SBRT Dosimetric Comparison of 3D Conformal and RapidArc Planning
Authors: Jiang R , Zhan L , Osei E 
Published: June 2015

Purpose:Dose distributions of RapidArc Plan can be quite different from standard 3D conformal radiation therapy. SBRT plans can be optimized with high conformity or mimic the 3D conformal treatment planning with very high dose in the center of the tumor. This study quantifies the dosimetric differences among 3D conformal plan; flattened beam and FFF beam RapidArc Plans for lung SBRT.Methods:Five lung cancer patients treated with 3D non‐coplanar SBRT were randomly selected. All the patients were CT scanned with 4DCT to determine the internal target volume. Abdominal compression was applied to minimize respiratory motion for SBRT patients. The prescription dose was 48 Gy in 4 fractions. The PTV coverage was optimized by two groups of objective function: one with high conformity, another mimicking 3D conformal dose distribution with high dose in the center of PTV. Optimization constraints were set to meet the criteria of the RTOG‐0915 protocol. All VMAT plans were optimized with the RapidArc technique using four full arcs in Eclipse treatment planning system. The RapidArc SBRT plans with flattened 6MV beam and 6MV FFF beam were generated and dosimetric results were compared with the previous treated 3D non‐coplanar plans.Results:All the RapidArc plans with flattened beam and FFF beam had similar results for the PTV and OARs. For the high conformity optimization group, The DVH of PTV exhibited a steep dose fall‐off outside the PTV compared to the 3D non‐coplanar plan. However, for the group mimicking the 3D conformal target dose distribution, although the PTV is very similar to the 3D conformal plan, the ITV coverage is better than 3D conformal plan.Conclusion:Due to excellent clinical experiences of 3D conformal SBRT treatment, the Rapid Arc optimization mimicking 3D conformal planning may be suggested for clinical use.
SU‐E‐T‐549: Modeling Relative Biological Effectiveness of Protons for Radiation Induced Brain Necrosis
Authors: Mirkovic D , Peeler C , Grosshans D , Titt U , Taleei R , Mohan R 
Published: June 2015

Purpose:To develop a model of the relative biological effectiveness (RBE) of protons as a function of dose and linear energy transfer (LET) for induction of brain necrosis using clinical data.Methods:In this study, treatment planning information was exported from a clinical treatment planning system (TPS) and used to construct a detailed Monte Carlo model of the patient and the beam delivery system. The physical proton dose and LET were computed in each voxel of the patient volume using Monte Carlo particle transport. A follow‐up magnetic resonance imaging (MRI) study registered to the treatment planning CT was used to determine the region of the necrosis in the brain volume. Both, the whole brain and the necrosis volumes were segmented from the computed tomography (CT) dataset using the contours drawn by a physician and the corresponding voxels were binned with respect to dose and LET. The brain necrosis probability was computed as a function of dose and LET by dividing the total volume of all necrosis voxels with a given dose and LET with the corresponding total brain volume resulting in a set of NTCP‐like curves (probability as a function of dose parameterized by LET).Results:The resulting model shows dependence on both dose and LET indicating the weakness of the constant RBE model for describing the brain toxicity. To the best of our knowledge the constant RBE model is currently used in all clinical applications which may Result in increased rate of brain toxicities in patients treated with protons.Conclusion:Further studies are needed to develop more accurate brain toxicity models for patients treated with protons and other heavy ions.
SU‐E‐T‐551: Monitor Unit Optimization in Stereotactic Body Radiation Therapy for Stage I Lung Cancer
Authors: Huang B‐T , Lu J‐Y 
Published: June 2015

Purpose:The study aims to reduce the monitor units (MUs) in the stereotactic body radiation therapy (SBRT) treatment for lung cancer by adjusting the optimizing parameters.Methods:Fourteen patients suffered from stage I Non‐Small Cell Lung Cancer (NSCLC) were enrolled. Three groups of parameters were adjusted to investigate their effects on MU numbers and organs at risk (OARs) sparing: (1) the upper objective of planning target volume (UOPTV); (2) strength setting in the MU constraining objective; (3) max MU setting in the MU constraining objective.Results:We found that the parameters in the optimizer influenced the MU numbers in a priority, strength and max MU dependent manner. MU numbers showed a decreasing trend with the UOPTV increasing. MU numbers with low, medium and high priority for the UOPTV were 428±54, 312±48 and 258±31 MU/Gy, respectively. High priority for UOPTV also spared the heart, cord and lung while maintaining comparable PTV coverage than the low and medium priority group. It was observed that MU numbers tended to decrease with the strength increasing and max MU setting decreasing. With maximum strength, the MU numbers reached its minimum while maintaining comparable or improved dose to the normal tissues. It was also found that the MU numbers continued to decline at 85% and 75% max MU setting but no longer to decrease at 50% and 25%. Combined with high priority for UOPTV and MU constraining objectives, the MU numbers can be decreased as low as 223±26 MU/Gy.Conclusion::The priority of UOPTV, MU constraining objective in the optimizer impact on the MU numbers in SBRT treatment for lung cancer. Giving high priority to the UOPTV, setting the strength to maximum value and the max MU to 50% in the MU objective achieves the lowest MU numbers while maintaining comparable or improved OAR sparing.
SU‐E‐T‐553: Monte Carlo Calculation of Proton Bragg Peak Displacements in the Presence of Al2O3:C Dosimeters
Authors: Young L , Yang F 
Published: June 2015

Purpose:The application of optically stimulated luminescence dosimeters (OSLDs) may be extended to clinical investigations verifying irradiated doses in small animal models. In proton beams, the accurate positioning of the Bragg peak is essential for tumor targeting. The purpose of this study was to estimate the displacement of a pristine Bragg peak when an Al2O3:C nanodot (Landauer, Inc.) is placed on the surface of a water phantom and to evaluate corresponding changes in dose.Methods:Clinical proton pencil beam simulations were carried out with using TOPAS, a Monte Carlo platform layered on top of GEANT4. Point‐shaped beams with no energy spread were modeled for energies 100MV, 150MV, 200MV, and 250MV. Dose scoring for 100,000 particle histories was conducted within a water phantom (20cm × 20cm irradiated area, 40cm depth) with its surface placed 214.5cm away from the source. The modeled nanodot had a 4mm radius and 0.2mm thickness.Results:A comparative analysis of Monte Carlo depth dose profiles modeled for these proton pencil beams did not demonstrate an energy dependent in the Bragg peak shift. The shifts in Bragg Peak depth for water phantoms modeled with a nanodot on the phantom surface ranged between 2.7 to 3.2 mm. In all cases, the Bragg Peaks were shifted closer to the irradiation source. The peak dose in phantoms with an OSLD remained unchanged with percent dose differences less than 0.55% when compared to phantom doses without the nanodot.Conclusion:Monte Carlo calculations show that the presence of OSLD nanodots in proton beam therapy will not change the position of a pristine Bragg Peak by more than 3 mm. Although the 3.0 mm shift will not have a detrimental effect in patients receiving proton therapy, this effect may not be negligible in dose verification measurements for mouse models at lower proton beam energies.
SU‐E‐T‐555: Monte Carlo Evaluation of the Dose Calculation Algorithm of TomoTherapy for Clinical Cases in Dynamic Jaws Mode
Authors: Sterpin E 
Published: June 2015

Purpose:for the TomoTherapy™ system, longitudinal conformation can be improved by selecting a smaller field width but at the expense of longer treatment time. Recently, the TomoEdge™ feature has been released with the possibility to move dynamically the jaws at the edges of the target volume, improving longitudinal penumbra and enabling faster treatments. Such delivery scheme requires additional modeling of treatment delivery. Using a previously validated Monte Carlo model (TomoPen), we evaluated the accuracy of the implementation of TomoEdge in the new dose engine of TomoTherapy for 15 clinical cases.Methods:TomoPen is based on PENELOPE. Particle tracking in the treatment head is performed almost instantaneously by 1) reading a particle from a phase‐space file corresponding to the largest field and 2) correcting the weight of the particle depending on the actual jaw and MLC configurations using Monte Carlo pre‐generated data. 15 clinical plans (5 head‐and‐neck, 5 lung and 5 prostate tumors) planned with TomoEdge and with the last release of the treatment planning system (VoLO™) were re‐computed with TomoPen. The resulting dose‐volume histograms were compared.Results:Good agreement was achieved overall, with deviations for the target volumes typically within 2% (D95), excepted for small lung tumors (17 cm3), where a maximum deviation of 4.4% was observed for D95. However, such deviations were not observed for quality assurance measurements in homogeneous phantoms and were therefore attributed to dose calculation in patient geometry, not the modeling of TomoEdge. Such deviations for small lung tumors are also consistent with previously reported values for static field widths.Conclusion:For the clinical cases considered in the present study, the introduction of TomoEdge did not impact significantly the accuracy of the computed dose distributions.The author is partially supported by Accuray
SU‐E‐T‐558: Monte Carlo Photon Transport Simulations On GPU with Quadric Geometry
Authors: Chi Y , Tian Z , Jiang S , Jia X 
Published: June 2015

Purpose:Monte Carlo simulation on GPU has experienced rapid advancements over the past a few years and tremendous accelerations have been achieved. Yet existing packages were developed only in voxelized geometry. In some applications, e.g. radioactive seed modeling, simulations in more complicated geometry are needed. This abstract reports our initial efforts towards developing a quadric geometry module aiming at expanding the application scope of GPU‐based MC simulations.Methods:We defined the simulation geometry consisting of a number of homogeneous bodies, each specified by its material composition and limiting surfaces characterized by quadric functions. A tree data structure was utilized to define geometric relationship between different bodies. We modified our GPU‐based photon MC transport package to incorporate this geometry. Specifically, geometry parameters were loaded into GPU's shared memory for fast access. Geometry functions were rewritten to enable the identification of the body that contains the current particle location via a fast searching algorithm based on the tree data structure.Results:We tested our package in an example problem of HDR‐brachytherapy dose calculation for shielded cylinder. The dose under the quadric geometry and that under the voxelized geometry agreed in 94.2% of total voxels within 20% isodose line based on a statistical t‐test (95% confidence level), where the reference dose was defined to be the one at 0.5cm away from the cylinder surface. It took 243sec to transport 100million source photons under this quadric geometry on an NVidia Titan GPU card. Compared with simulation time of 99.6sec in the voxelized geometry, including quadric geometry reduced efficiency due to the complicated geometry‐related computations.Conclusion:Our GPU‐based MC package has been extended to support photon transport simulation in quadric geometry. Satisfactory accuracy was observed with a reduced efficiency. Developments for charged particle transport in this geometry are currently in progress.
SU‐E‐T‐561: Monte Carlo‐Based Organ Dose Reconstruction Using Pre‐Contoured Human Model for Hodgkins Lymphoma Patients Treated by Cobalt‐60 External Beam Therapy
Authors: Jung J , Lee C , Kim J , Pelletier C , Pyakuryal A , Lee C 
Published: June 2015

Purpose:Organ doses for the Hodgkin's lymphoma patients treated with cobalt‐60 radiation were estimated using an anthropomorphic model and Monte Carlo modeling.Methods:A cobalt‐60 treatment unit modeled in the BEAMnrc Monte Carlo code was used to produce phase space data. The Monte Carlo simulation was verified with percent depth dose measurement in water at various field sizes. Radiation transport through the lung blocks were modeled by adjusting the weights of phase space data. We imported a precontoured adult female hybrid model and generated a treatment plan. The adjusted phase space data and the human model were imported to the XVMC Monte Carlo code for dose calculation. The organ mean doses were estimated and dose volume histograms were plotted.Results:The percent depth dose agreement between measurement and calculation in water phantom was within 2% for all field sizes. The mean organ doses of heart, left breast, right breast, and spleen for the selected case were 44.3, 24.1, 14.6 and 3.4 Gy, respectively with the midline prescription dose of 40.0 Gy.Conclusion:Organ doses were estimated for the patient group whose threedimensional images are not available. This development may open the door to more accurate dose reconstruction and estimates of uncertainties in secondary cancer risk for Hodgkin's lymphoma patients.This work was partially supported by the intramural research program of the National Institutes of Health, National Cancer Institute, Division of Cancer Epidemiology and Genetics.
SU‐E‐T‐562: Motion Tracking Optimization for Conformal Arc Radiotherapy Plans: A QUASAR Phantom Based Study
Authors: Xu Z , Wang I , Yao R , Podgorsak M 
Published: June 2015

Purpose:This study is to use plan parameters optimization (Dose rate, collimator angle, couch angle, initial starting phase) to improve the performance of conformal arc radiotherapy plans with motion tracking by increasing the plan performance score (PPS).Methods:Two types of 3D conformal arc plans were created based on QUASAR respiratory motion phantom with spherical and cylindrical targets. Sinusoidal model was applied to the MLC leaves to generate motion tracking plans. A MATLAB program was developed to calculate PPS of each plan (ranges from 0–1) and optimize plan parameters. We first selected the dose rate for motion tracking plans and then used simulated annealing algorithm to search for the combination of the other parameters that resulted in the plan of the maximal PPS. The optimized motion tracking plan was delivered by Varian Truebeam Linac. In‐room cameras and stopwatch were used for starting phase selection and synchronization between phantom motion and plan delivery. Gaf‐EBT2 dosimetry films were used to measure the dose delivered to the target in QUASAR phantom. Dose profiles and Truebeam trajectory log files were used for plan delivery performance evaluation.Results:For spherical target, the maximal PPS (PPSsph) of the optimized plan was 0.79: (Dose rate: 500MU/min, Collimator: 90°, Couch: +10°, starting phase: 0.83π). For cylindrical target, the maximal PPScyl was 0.75 (Dose rate: 300MU/min, Collimator: 87°, starting phase: 0.97π) with couch at 0°. Differences of dose profiles between motion tracking plans (with the maximal and the minimal PPS) and 3D conformal plans were as follows: PPSsph=0.79: %ΔFWHM: 8.9%, %Dmax: 3.1%; PPSsph=0.52: %ΔFWHM: 10.4%, %Dmax: 6.1%. PPScyl=0.75: %ΔFWHM: 4.7%, %Dmax: 3.6%; PPScyl=0.42: %ΔFWHM: 12.5%, %Dmax: 9.6%.Conclusion:By achieving high plan performance score through parameters optimization, we can improve target dose conformity of motion tracking plan by decreasing total MLC leaf travel distance and leaf speed.
SU‐E‐T‐564: Multi‐Helix Rotating Shield Brachytherapy for Cervical Cancer
Authors: Dadkhah H , Flynn R , Wu X , Kim Y 
Published: June 2015

Purpose:To present a novel and practical brachytherapy technique, called multi‐helix rotating shield brachytherapy (H‐RSBT), for the precise positioning of a partial shield in a curved applicator. H‐RSBT enables RSBT delivery using only translational motion of the radiation source/shield combination. H‐RSBT overcomes the challenges associated with previously proposed RSBT approaches based on a serial (S‐RSBT) step‐and‐shoot delivery technique, which required independent translational and rotational motion.Methods:A Fletcher‐type applicator, compatible with the combination of a Xoft Axxent™ electronic brachytherapy source and a 0.5 mm thick tungsten shield, is proposed. The wall of the applicator contains six evenly‐spaced helical keyways that rigidly define the emission direction of the shield as a function of depth. The shield contains three protruding keys and is attached to the source such that it rotates freely. S‐RSBT and H‐RSBT treatment plans with 180° and 45° azimuthal emission angles were generated for five cervical cancer patients representative of a wide range of high‐risk clinical target volume (HR‐CTV) shapes and applicator positions. The number of beamlets used in the treatment planning process was nearly constant for S‐RSBT and H‐RSBT by using dwell positions separated by 5 and 1.7 mm, respectively, and emission directions separated by 22.5° and 60°, respectively. For all the treatment plans the EQD2 of the HR‐CTV was escalated until the EQD2cc tolerance of either the bladder, rectum, or sigmoid colon was reached.Results:Treatment times for H‐RSBT tended to be shorter than for S‐RSBT, with changes of −38.47% to 1.12% with an average of −8.34%. The HR‐CTV D90 changed by −8.81% to 2.08% with an average of −2.46%.Conclusion:H‐RSBT is a mechanically feasible technique in the curved applicators needed for cervical cancer brachytherapy. S‐RSBT and H‐RSBT dose distributions were clinically equivalent for all patients considered, with the H‐RSBT deliveries tending to be faster.Ryan Flynn has ownership interest in pxAlpha, LLC, which is a startup company developing a rotating shield brachytherapy system.
SU‐E‐T‐569: Neutron Shielding Calculation Using Analytical and Multi‐Monte Carlo Method for Proton Therapy Facility
Authors: Cho S , Shin E H , Kim J , Ahn S H , Chung K , Kim D‐H , Han Y , Choi D H 
Published: June 2015

Purpose:To evaluate the shielding wall design to protect patients, staff and member of the general public for secondary neutron using a simply analytic solution, multi‐Monte Carlo code MCNPX, ANISN and FLUKA.Methods:An analytical and multi‐Monte Carlo method were calculated for proton facility (Sumitomo Heavy Industry Ltd.) at Samsung Medical Center in Korea. The NCRP‐144 analytical evaluation methods, which produced conservative estimates on the dose equivalent values for the shielding, were used for analytical evaluations. Then, the radiation transport was simulated with the multi‐Monte Carlo code. The neutron dose at evaluation point is got by the value using the production of the simulation value and the neutron dose coefficient introduced in ICRP‐74.Results:The evaluation points of accelerator control room and control room entrance are mainly influenced by the point of the proton beam loss. So the neutron dose equivalent of accelerator control room for evaluation point is 0.651, 1.530, 0.912, 0.943 mSv/yr and the entrance of cyclotron room is 0.465, 0.790, 0.522, 0.453 mSv/yr with calculation by the method of NCRP‐144 formalism, ANISN, FLUKA and MCNP, respectively. The most of Result of MCNPX and FLUKA using the complicated geometry showed smaller values than Result of ANISN.Conclusion:The neutron shielding for a proton therapy facility has been evaluated by the analytic model and multi‐Monte Carlo methods. We confirmed that the setting of shielding was located in well accessible area to people when the proton facility is operated.
SU‐E‐T‐575: Novel Quality Assurance Procedure for the Small Animal Radiation Research Platform Using Commercial OSLDs
Authors: Keller J , Lockamy V , Glenn S , Harrison A 
Published: June 2015

Purpose:To support radiobiological research with the Xstrahl small animal radiation research platform (SARRP) by developing a simple and effective method using commercially available optically stimulated luminescent dosimeters (OSLDs) that ensures dose output consistency.Methods:The SARRP output is calibrated according to the vendor standards and TG‐61 protocol utilizing an ADCL calibrated ion chamber and electrometer at 2 cm depth of solid water. A cross calibration is performed by replacing the ion chamber with five OSLDs at the 2 cm depth. The OSLDs are irradiated to 500 cGy with 220 keV at 13 mA (78s delivery time) with a copper filter for an uncollimated 17×17 cm2 aperture. Instead of the absolute dose, the total amount of raw counts are collected from the OSLD reader and used for analysis. This constancy procedure was performed two more times over the course of three weeks with two OLSDs for validity.Results:The average reading for all OSLDs is 494939 with a 1‐sigma standard deviation of the 5.8%. With an acceptable dose output range of ±10%, the OSLD readings have a counts range of [445445, 544433].Conclusion:This method of using nanoDot™ OSLDs to perform output constancy checks for the SARRP ensures the output of the device is within 10% from the time of calibration and is convenient as well as time efficient. Because this, the frequency of output checks can be increased, which can improve the output stability for research with this device. The output trend of the SARRP will continue to be monitored in the future to establish a timeline for constancy checks and recalibration.