bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐460: Image Based Treatment Planning for Intraluminal Brachytherapy in Bile Duct Carcinoma
Authors: Chaudhari S , Engineer R , Deshpande D , Shrivastava S
Published: July 2013

Purpose: 3D Image based treatment planning for intraluminal brachytherapy in bile duct carcinoma. Methods: Five patients with bile duct carcinoma were treated with definitive radiation therapy. Radiation therapy was delivered by means of external beam radiation therapy (EBRT) combined with HDR brachytherapy.Eclipse v8.6 TPS (Varian Medical Systems, USA) was used for treatment planning.In the diagnostic radiology suite, a flexible guide wire was passed through the biliary stent to a point past the stenosis. Subsequently catheter localisation, dummy wire was inserted and orthogonal films were used to confirm the position. All the patients were scanned on CT scanner (Siemens, Germany) with a slice thickness of 3 mm without any radio opaque dummy. The GTV, CTV OAR were contoured according to ICRU 62.Since the catheter is inserted in biliary stent, the applicator reconstruction is not possible. The first source point was reconstructed from the tip of the stent. From the orthogonal topograph the offset was calculated by measuring the tip of the stent to first dummy source distance. This offset was set in the planning. With the optimum source length the dose was calculated and CTV, OAR doses were quantified. The External and brachytherapy plans were summed to produce resultant DVH. Results: The applicator reconstruction accuracy was found to be within ±2mm. The mean, median dose of GTV, CTV was 32Gy, 23Gy and 18Gy, 13Gy respectively. The mean, median dose for duodenum was 7.6Gy and 2.8Gy. Conclusion: In radiography assisted planning, dose distribution is usually calculated according to the applicator geometry and in addition to fixed reference points. But with 3D brachytherapy planning the doses can be optimised to GTV and can be summed with external plan for clinical evaluation.
SU‐E‐T‐463: A Dosimetric Evaluation of CBCT Guided Intra‐Fractional Adaptive Radiotherapy for VMAT
Authors: Kearney V , Jiang L , Gu X , Solberg T , Mao W
Published: July 2013

Purpose: To investigate the dosimetric advantages of an image guided replanning strategy utilizing on‐board CBCTs for VMAT plans. An intensity corrected grey‐scale based CBCT to planning CT deformable image registration algorithm, combined with an intra‐fractional morphing aperture optimization algorithm (ICDIR‐MAO), is dosimtrically evaluated for head and neck cancer patients. Methods: : Head and neck VMAT plans were retrospectively adapted using the ICDIR‐MAO algorithm. Patient CBCT and CT images are deformably registered with an intensity corrected demons based deformable image registration algorithm. The deformation vector field is applied to the PTV on the structure set to obtain a deformed PTV. Digitally reconstructed radiographs of the original PTV and deformed PTV are created for each treatment angle. MLC positions are generated to contour both PTVs and a ratio of original vs. deformed MLC positions that outline the PTV beam's eye view contour is applied to each angle of the planned MLC sequence. The deformed image is then sliced up and reformatted back into dicom files, with the associated metadata. The deformation vector field is added to the structure set at every point and a new dicom structure set is created. The new mlc sequences are reformatted back into dicom plans. All three dicom files are imported back into eclipse, and dose is re‐calculated on the deformed plan, deformed image set, and associated deformed structures. Results: The mean and maximum dose ratios for the OARS were lowered for all cases. The mean dose for the PTV70Gy, PTV60Gy, and PTV54Gy was the same or better for the deformed plans. The dosimetric improvement was proportional to the contour volume overlap between the deformed CT and the original CT. Conclusion: : ICDIR‐MAO for adaptive VMAT replanning improves the dosimetric quality for head and neck patients. This research is supported by CPRIT Individual Investigator Award RP110329
SU‐E‐T‐466: A New Evaluation Method of Deformable Image Registration Algorithms for Image‐Guided Radiation Therapy
Authors: Saito Y , Tateoka K , Nakata A , Nakazawa T , Abe T , Yano M , Sakata K
Published: July 2013

Purpose: Non‐rigid image registration (NIR) is an essential image processing tool for image‐guided adapted radiation therapy. The current radiotherapy process requires three‐dimensional (3D) quantification of the registration error, which is not accurately achieved by existing evaluation methods. The objective of this study is to develop a method for 3D evaluation of NIR algorithms. Methods: Cone‐beam (reference) and planning (moving) CT scan images of five prostate cancer patients were scanned using the VelocityAI (Velocity Medical Solutions) platform, which employs B‐spline‐based NIR algorithms. The NIR algorithms were evaluated by measuring the distance between two factors: (1) the outlines (reference contours) of the bladder, the dorsal right and left seminal vesicles (SV), the proximal SV, the prostate, and the rectum in the reference images; and (2) other outlines (deformed contours) in the deformed images of the same CT slice. This distance is the difference between two points that indicate the point of intersection of the reference and the deformed contours that cross a straight line every 10° from the center of gravity of the reference contour. However, the difference in direction was determined as being negative if it was inside the reference contours for the deformed contours, and positive if it was outside the reference contours for the deformed contours. The measurement values were displayed on a two‐dimension (2D) difference map. Results: The 2D map showing differences in the prostate indicated an error of −3 to +3 mm on the bladder side, −3 to +3 mm on the proximal SV side, −2 to +8 mm on the rectum side, and −5 to +1 mm on the apex side. Conclusion: This method measures the distance and the difference in direction between the contours in the reference and those in deformable images, and it can be used to accurately evaluate the non‐rigid image registration.
SU‐E‐T‐471: Potential of Using Simultaneous Integrated Boost (SIB) to Significantly Improve the Normal Tissue Sparing For Advanced Staged Non‐Small Cell Lung Cancer(NSCLC)
Authors: Wang X , Liao L , Wang H , Li H , Li Y , Li X , Quan M , Liao Z , Zhang X
Published: July 2013

Purpose: To investigate advantages of SIB technique using IMPT for advanced stage NSCLCMethod: The 4DCT data sets were randomly selected from 9 patients with stage III NSCLC. The SIB volume (SIBV) was defined as GTV with 3mm expansion to account for uncertainties. PTV was defined as CTV with 5mm expansion. Conventional IMPT plan delivering 74Gy/37Fractions to at least 95% of PTV and IMPT SIB plans delivering 72Gy (BED:89.3Gy), 78Gy (BED:98.3Gy) and 84Gy (BED:107.5Gy) in 30 fractions to at least 95% of SIBV as well as 60 Gy to at least 95% of PTV were designed for each patient using robust optimization. TCP and NTCP were calculated and worst case robustness was analyzed for one patient. Results: The NTCP for lung and esophagus were 0.02 and 0.38 respectively for IMPT SIB 72Gy, 0.1 and 0.32 lower than those for IMPT 74Gy respectively, while TCP of PTV and SIBV are 0.87 and 0.9 for IMPT 74Gy, and 0.89 and 0.9 for IMPT SIB 72Gy respectively. The dose coverage of CTV and GTV in worst scenario was at least 95% of prescribed dose for both IMPT SIB 72Gy and IMPT 74Gy plans. The comparison of IMPT SIB plans showed no significant differences of normal structures sparing at different escalation dose level, such as percentage lung volume received 20Gy (V20, 29%) and mean dose (20Gy), esophagus V60 (16%), and maximum cord dose (36Gy). Our results suggest that dose escalation to SIBV only (TCP of SIBV are 0.9, 0.93 and 0.95 for SIB dose level 72Gy, 78Gy and 84Gy) in IMPT SIB technique will have minimal impact for normal structures sparing. Conclusion: IMPT SIB showed significantly advantages in target dose escalation with minimal impact on normal structures sparing. We are currently testing the impact of IMPT SIB on patient outcome in a prospective trial.
SU‐E‐T‐472: Personalized 3D Dose Prediction for Intrabeam Treatments Based On Patient CT Imaging with Monte Carlo GATE Simulations
Authors: Bouzid D , Nicolas B , Dupre P , Bert J , Pradier O , Visvikis D
Published: July 2013

Purpose: The aim of partial breast irradiation is to reduce the risk of local recurrence into the tumor bed. After surgical resection of the tumor, the Intrabeam™ system delivers a single dose fraction of 20 Gy at the surface of the applicator, irradiating the tumor bed through a 50keV X‐ray beam. However, there is currently no latitude for personalized dose prescription which is in contrast to official recommendations for individual dose optimization in radiotherapy. In this context, the study aim was to perform personalized 3D dose prediction for Intrabeam™ treatments based on patient CT imaging using Monte Carlo (MC) simulations. Methods: A model of the Intrabeam™ system was developed with GATE taking into account the different parts of the device. A preoperative CT acquisition of the patient breast is performed and included in the simulation allowing accurate dose calculation. During intra‐operative radiotherapy, thermo‐luminescent dosimeters are placed on the skin at 1 and 3 cm around the spherical applicator. Comparison between simulation results and TLD measurements are performed to confirm the dose prediction at the TLD locations. This study was performed on 10 patients, including 3 who had an intra‐operative CT acquisition in order to validate the overall dosimetry evaluation protocol. Results: Patient results show good agreement between clinical experiments and simulations. Indeed the relative mean deviation between TLD dose measurements and GATE dose scoring is 0.09% ± 0.11% with a maximum of 0.334% and less than 1% of dose estimation uncertainty (min 0.41% max 0.95%). Conclusion: We propose the use of an accurate model of the Intrabeam system on the GATE platform based on Geant4 MC toolkit. The dosimetric evaluation of the proposed platform with patient datasets supports its use for patient specific dosimetry planning.
SU‐E‐T‐481: Treatment Plans of Brain Metastasis with Cutting Edge Radiation Therapy Techniques: A Dosimetric Comparison Study of 3D Conformational Radiotherapy, Intensity Modulation Radiation Therapy, Dynamic Stereotactic Radiation Therapy and Contrast‐Enhanced Synchrotron Radiation Therapy
Authors: Tessier A , Vautrin M , Benkebil M , Adam J
Published: July 2013

Purpose: Contrast‐enhanced stereotactic synchrotron radiation therapy (SSRT) is an innovative technique based on localized dose‐enhancement effects obtained by reinforced photoelectric absorption in the target using medium energy monochromatic x‐rays (50–100 keV). The purpose of this study is to compare three cutting edge radiation therapy techniques with conventional 3D conformational radiotherapy: intensity modulated radiation therapy (IMRT), dynamic stereotactic arctherapy and contrast enhanced SSRT. Methods: A patient bearing a single parenchymal brain metastasis has received two helical 3D CT scans, the head being immobilized by a stereotactic frame. The fisrt scan is performed without contrast injection for high energy radiotherapy dosimetry. The second scan is performed 15 min after the injection of 200 mL of iodinated contrast agent contrast‐enhanced SSRT dosimetry. 3D conformational radiotherapy, IMRT, dynamic arctherapy contrast enhanced dosimetry plans have been performed on dedicated treatment planing softwares (Eclipse, IPlan and Isogray, respectively). The objective of each plans is such as the 100% of the prescribed dose is delivered at the beams isocentre and that the 70% isodose should contain all the target volume. The volume of the 70% isodose and the average and maximal dosed delivered to the organs at risk (brainstem, optical nerves, chiasma, eyes, skull bone and healthy brain parenchyma) are compared for each technique. Results: Among all high energy techniques, the stereotactic dynamic arctherapy gave the best results in terms of dose conformation and organs at risk sparing effect. However contrast enhanced SSRT provide a serious added value in terms of dosimetry by significantly reducing the dose delivered to the brainstem and the brain parenchyma. Conclusion: This study validates the dosimetric advantages of contrast enhanced SSRT for treating brain metastasis. This is another crucial step toward SSRT clinical trials.
SU‐E‐T‐497: A Method for Automatic Commissioning of a GPU‐Based Monte Carlo Code for Clinical Photon Beam Dose Calculation
Authors: Tian Z , Townson R , Graves Y , Jia X , Jiang S
Published: July 2013

Purpose: Monte Carlo (MC) method is recognized as the most accurate method for dose calculation. The commissioning of beam models is crucial for the clinical implementation of a MC code. We propose an automatic commissioning method for our GPU‐based MC dose engine (gDPM) using a source model based on the concept of phase‐space‐let (PSL). Methods: A PSL contains a group of particles that are of the same type and close in space and energy. PSLs for a reference phase‐space file are first generated, and dose for each PSL is pre‐calculated in water. Weighting factor of each PSL is adjusted to fine tune the fluence distribution and energy spectrum, so that the corresponding calculated dose matches the standard measured dose in water such as PDD and dose profiles. This is essentially an underdetermined least‐square minimization problem. Therefore, we add symmetric and smooth regularizations to the optimization problem, assuming that the dose profiles are symmetric and smooth. A split Bregman method is adopted to solve this optimization problem. Results: The phase‐space file of a Varian TrueBeam 6MV beam was used to generate PSLs for all 6MV beams. First, for a simulation study, the ‘measurement’ data was obtained from MC dose calculation using a set of field‐size‐dependent phase‐space files of a Siemens 6MV beam. The PDD and dose profiles calculated from the commissioned beam model agree well (within 1%) with the ‘measurement’ data. Second, realistic clinical data of Varian, Siemens, and Elekta machines were also used to test our method and achieved similar commissioning accuracy of less than 1% dose difference. Conclusion: Using the PSL source model, the proposed commissioning method can automatically fine tune the fluence distribution and energy spectrum of the reference phase‐space file to match measured data for clinical beam to be commissioned, relieving clinical MC users from conventional cumbersome commissioning process.
SU‐E‐T‐499: A Geant4/TOPAS Monte Carlo System for Validating Proton Therapy Treatment Plan Calculations at Mayo Clinic
Authors: Tseung H Wan Chan , Beltran C
Published: July 2013

Purpose: To build a Geant4‐based Monte Carlo (MC) dose verification system for proton therapy with a scanning nozzle. This system will be used routinely at the upcoming Mayo Clinic proton center for both research and verification of pencil beam dose calculations. Methods: Geant4 is a well‐verified MC toolkit that is applied extensively in many branches of physics, including medical physics. We implemented our dose verification system using TOPAS, a proton MC package that facilitates the use of Geant4. The system consists of: scripts that read in data from DICOM files and create TOPAS input parameter files; TOPAS geometry extensions to accommodate our scanning nozzle, and TOPAS code additions to input ‘parameterized’ phase space data for beam spots at the nozzle exit. Typically, a phase space file containing source events for a grid of beam spots covering the scanning area at the nozzle exit is about 500 Gb. To reduce the size of this file down to ∼30 Mb, we fit MC‐generated beam spot position and direction distributions to extract Twiss parameters. The beam energy distributions are fitted with skewed Gaussians. The phase space is then represented by a set of skewed Gaussian and Twiss parameters for each beam spot in the grid. Results: Using our MC dose calculation system, we show MC and pencil beam comparisons for: (1) water phantom, (2) prostate and (3) head and neck cases. Good agreement is obtained. To reach 2% statistical error on the MC dose calculations, a tumor 200 cm3 in volume would require around 1×107 protons. On a 100‐node cluster, such a calculation takes ∼1 hour to complete. Conclusion: A TOPAS‐based dose verification system for proton treatment plans has been built at Mayo Clinic. The typical computation time per plan is expected to be a few hours on a dedicated cluster. This work is supported by a grant from Varian Medical Systems.
SU‐E‐T‐500: 3D‐Personalized Monte Carlo Dosimetry in 90Y‐Microspheres Therapies of Primary and Secondary Hepatic Cancers: Absorbed Dose and Biological Effective Dose Considerations
Authors: Petitguillaume A , Bernardini M , Michel C , de Labriolle‐Vaylet C , Franck D , Desbree A
Published: July 2013

Purpose: To develop and evaluate a 3D‐Personalized Monte Carlo Dosimetry (PMCD) for treatment planning in 90Y‐microspheres therapies of unresectable hepatic cancers. Methods: The PMCD method was evaluated from the 99mTc‐MAA distribution of 20 patients treated for hepatic metastases or hepatocellular carcinoma. Using the OEDIPE software, regions of interest outlines, drawn on CT images, were used to create patient‐specific voxel phantoms and 99mTc‐MAA SPECT data were used to generate 3D‐matrices of cumulated activity. Absorbed doses and BED at the voxel scale were calculated using the MCNPX Monte Carlo transport code. OEDIPE was used to determine the maximum injectable activity (MIA) for tolerance criteria on organs at risk (OARs), i.e. the lungs and non tumoral liver (NTL). Tolerance criteria based on mean absorbed doses, mean BED (Biological Effective Dose), Dose‐Volume Histograms (DVHs) or BED‐Volume Histograms (BVHs) were considered. Those MIAs were compared to the ones recommended by conventional Methods: the Body Surface Area (BSA) method and the Partition Model with tolerance criteria on mean absorbed doses. Results: Compared to Partition Model recommendations, performing dosimetry using the PMCD method enables to increase the activity prescription while ensuring OARs radiation protection. Moreover, considering tolerance criteria based on DVHs further enhances treatment planning efficiency by taking advantage of the parallel characteristic of the liver and the lungs whose functions are not impaired if the level of irradiation to a fraction of the organ is kept sufficiently low. Finally, tolerance criteria on mean BED and BVHs further improve treatment planning by taking into account biological considerations such as cell repair, radiosensibility or dose‐rate distribution. Conclusion: Besides its feasibility and applicability in clinical routine, the interest of a personalized Monte Carlo dosimetry for treatment planning in 90Y‐microspheres therapies was confirmed from those patient studies.
SU‐E‐T‐505: Monte Carlo Simulations for TrueBeam Using 4D IAEA Phase Spaces
Authors: Lobo J , Popescu IA
Published: July 2013

Purpose: To provide a tool for Monte Carlo simulations of dynamic beam delivery in the highly relevant situations where the full linac model is unavailable (such as is currently the case of the TrueBeam linac), which also includes the capability of reading and scoring 4D phase spaces. Methods: We have redesigned DOSXYZnrc source 20 to enable it to dynamically load a BEAMnrc shared library at run time and preserve synchronization between dynamic linac components and the beam motion in the patient geometry, even when starting from a phase space. We have enabled BEAMnrc and DOSXYZnrc to use the actual z coordinate of each particle, when reading a 3D IAEA phase space. Moreover, these codes can now read and output 4D phase spaces by reading/scoring the MU index of each particle. These 4D phase spaces can be used for further synchronization. Results: The updated source 20 has been validated, using film and ion chamber measurements (typically, differences around 1%), and comparisons with a commercial treatment planning system (3D gamma pass rates over 97% for a 3%‐3 mm criterion), for a variety of interesting clinical applications, including jaw‐tracking, non‐coplanar, and multiple‐arc VMAT, for both standard and flattening filter free (FFF) photon beams, starting from curved or general 4D IAEA phase space files. Conclusion: It is now possible to use source 20 for Monte Carlo simulations of TrueBeam and other modern radiotherapy technologies, starting from phase spaces (including curved or, more generally, 4D IAEA phase spaces). The simulations are performed in a single run, continuously, regardless of the complexity of the beam delivery. The new features have been extensively tested in clinical applications, with excellent results. The new 4D phase space capability could prove invaluable in other applications, such as in vivo portal dosimetry or adaptive planning. This work was supported, in part, by research grants provided by British Columbia Cancer Agency and Varian Medical Systems.
SU‐E‐T‐506: Modification of the Low‐Energy Electron Energy Spectrum in the Presence of Gold Nanoparticle
Authors: Jia J , Chow J , Leung M , Jaffray D
Published: July 2013

Purpose: This study investigated how the low‐energy electron energy spectrum is modified when a water nanoparticle is substituted by a gold nanoparticle irradiated by photon and electron beams. The distribution of low‐energy electrons was recently found playing an important role in the damage to DNA. Methods: Spherical gold nanoparticle with diameter of 100 nm was irradiated by electron (50 keV ∼ 4 MeV) and photon (50 kV ∼ 6 MV) beams in water. The cross‐sectional diameter of the beam was equal to the nanoparticle diameter with the beam central axis positioned at the center of the nanoparticle. Monte Carlo simulations were carried out using the Geant4 code to track all the secondary electrons from the gold nanoparticle in low‐energy range (< 100 eV). For comparison, Monte Carlo simulations were repeated with the gold nanoparticle replaced by water. Results: It is found that the yield of the low‐energy electron increases when gold nanoparticle is added to water. For 4 MeV electron beams, the number of low‐energy electron increases about 234% in the energy range < 100 eV, when the water nanoparticle is replaced by gold. In the energy range < 20 eV, the mean energy of the low‐energy electron is 12.8 eV in the presence of the gold nanoparticle. This is higher than that of the water nanoparticle (4.5 eV). With a larger number of low‐energy electron produced, the distribution of electron is more even when gold nanoparticle is present in water. Conclusion: From the results of increased yield of low‐energy electrons distributed more evenly in the low‐energy range in the presence of gold nanoparticle, it is concluded that gold nanoparticle can modify the low‐energy electron spectrum and production. This low‐energy electron spectral modification can enhance the DNA damage of cancer cell in radiotherapy. Natural Science Foundation of Anhui Province (11040606M132), Fundamental Research Funds for the Central Universities (Nos. 2012HGXJ0057, 2012HGXJ0062, 2012HGXJ0071, 2012HGBZ0190) and Seed Foundation of Hefei University of Technology (2012HGZY0007), P.R.China
SU‐E‐T‐509: DICOM Test Case Plans for Model‐Based Dose Calculations Methods in Brachytherapy
Authors: Papagiannis P , Ballester F , Tedgren A Carlsson , Haworth A , Ibbott G , Mourtada F , Rivard M , Siebert F , Sloboda R , Thomson R , Verhaegen F , Wareing T , Beaulieu L
Published: July 2013

Purpose: The TG‐186 report provides guidance to early adopters of model‐based dose calculation algorithms (MBDCAs) for brachytherapy. A charge of the AAPM‐ESTRO Working Group on MBDCA is to develop well‐defined test case plans, available as references for the software commissioning process to be performed by end‐users. The aim of this work is to develop test case plans for a generic HDR 192Ir source alone and in combination with a vaginal cylinder applicator with 180° tungsten‐alloy shielding in a DICOM‐based water phantom. Methods: A DICOM CT dataset was created with a 30 cm diameter water sphere surrounded by air. The voxel size was 1.33×1.33×1.33 mm3 for evaluating absorbed dose rate (cGy.h−1.U−1). Dose distributions were obtained in the planes x=0, y=0 and z=0. Three geometries were considered with the HDR source (a) at the center of sphere, (b) displaced 12.75 cm laterally, and (c) at the center of the applicator. Monte Carlo (MC) codes (Geant4, Penelope2009, MCNP5, and EGSnrc‐based BrachyDose) and Acuros were used. MC simulations were performed by multiple users to validate consistency of the DICOM reading, calculation set‐up, and dose reporting. Results: For all three geometries, MC results were generally within 2% agreement for r < 14 cm except at the sphere boundary where volume averaging occurred in voxels comprising two materials. There were no trends for r > 14 cm except that dosimetric agreement amongst the codes was limited by computational statistics. Results from Acuros and Penelope2009 were compared using a 2%/1.33 mm λ‐index criteria for r < 7 cm. Voxel pass rates were 100%, 100%, and 94% for geometries (a), (b), and (c), respectively. Conclusions: Dose rate distributions were consistent within statistical uncertainties among MC codes and for different users. Acuros reproduces MC data for the three geometries. These geometries may serve as test case plans for MBDCAs. T. Wareing is employee of Transpire Inc. that developed Acuros.
SU‐E‐T‐514: Building a Brachytherapy Parallel Monte Carlo Simulation Framework Through Source Parameterization
Authors: Zhang M , Zou W , Chen T , Kim L , Yue N
Published: July 2013

Purpose: This work aimed to parameterize a brachytherapy source phase space file by using multiple probability density functions. Based on this, we built a brachytherapy parallel Monte Carlo (MC) simulation framework with simple geometry input, light memory consumption, accurate dose calculation, and fast speed. Methods: A Varian VariSource HDR brachytherapy source (Ir‐192) was generated in Geant4. A phase space file with 7 indexes for each particle (3 positions, 3 directions, 1 energy) was scored at the source surface. A parameterization was performed on the phase space file with the following assumptions: (1) A particle's energy is independent of its position and direction; (2) Particle locations in the transverse plane (x‐y) are uniform; (3) A particle's direction depends on its position along the source axis (z). Parameterization accuracy was evaluated by comparing radial dose function and anisotropic function as defined in TG‐43 between the phase space file‐represented source (S_phase) and the parameterized source (S_para). A brachytherapy MC framework was designed by parallel computing the dose contributions from individual dwell positions using the parameterized source. Results: The phase space file was successfully parameterized. Compared to the 2 GB phase space file, the parameterized source input was 300 kB without sacrificing computation speed. The radial dose function difference between S_phase and S_para was at most 2%. The anisotropic function agreed well between the two sources. The largest difference of about 5% was only observed within 10 degrees of the source axis. This difference has no significant impact on clinical applications. Conclusion: A method is developed to parameterize the source phase space file for MC brachytherapy dose calculation at almost no expense of accuracy. With much less memory consumption, using a parameterized source allows parallel computing for clinical implementation of brachytherapy MC dose calculation.
SU‐E‐T‐515: Clinical Evaluation of Dose Calculation Algorithms in Stereotactic Radiation Therapy for Lung Cancer
Authors: Tomiyama Y , Araki F , Ono T , Hioki K
Published: July 2013

Purpose: To evaluate the dose calculation accuracy of the model‐based algorithms and a new grid‐based Boltzmann equation solver by comparing with Monte Carlo‐based algorithm in stereotactic lung irradiation with photon beams. Methods: The stereotactic body radiation therapy (SBRT) for 20 clinical lung cancer cases was planned using Eclipse (Varian Medical Systems) treatment planning system (TPS). The prescribed dose at isocenter was 48 Gy with 4 fractions and six non‐coplanar fields. First, the dose distributions were calculated with analytical anisotropic algorithm (AAA). Next, pencil beam convolution (PBC) and Acuros XB (AXB) based on a new grid‐based Boltzmann equation in Eclipse, and Voxel Monte Carlo algorithm (VMC) in iPlan (BrainLAB) were implemented under identical planning conditions as AAA. The dose distributions and dose volume histograms (DVHs) for SBRT were compared among algorithms. Similarly, the dose indices and monitor unit (MU) for the planning target volume (PTV) were also compared. The grid size for all dose calculations was 2.5×2.5×2.5 mm3. Results: AAA tended to underestimate the PTV dose compared to VMC. In contrast, PBC overestimated the PTV dose in almost all plans. The discrepancies in the D95 evaluation of AAA and PBC for VMC were up to 4.4% and 16.1%, respectively. AXB tended to slightly overestimate the PTV dose compared to VMC but the discrepancy was within 3% in D95. This discrepancy was attributed to differences in material assignments, material voxelization methods, and an energy cut‐off for electron interactions. The differences in MU of AXB, AAA and PBC for VMC were up to 1.7%, 3.5%, and 7.8%, respectively. Conclusion: The dose distributions in lung regions significantly differ based on the principle of the calculation algorithms. The dose calculation accuracy of AXB is comparable to VMC and is more suitable than AAA.
SU‐E‐T‐517: Ray Tracing and Mote Carlo Based Dose Computation for Chest Wall and Ribs for Lung Cancer Patients Treated with Cyberknife
Authors: Podder T , Biswas T , Yao M , Lo S , Machtay M
Published: July 2013

Purpose: Chest wall and ribs are considered organs at risk while treating lung tumors adjacent to chest wall. This study was to evaluate the dosimetric differences in chest wall and ribs irradiation for Cyberknife stereotactic body radiation therapy (SBRT) when treatment plans were computed using Ray Tracking Algorithm (RTA) and Monte Carlo Algorithm (MCA). Methods: Twenty eight lung cancer patients who had tumors abutting the chest wall were selected for this study. A uniform 2cm thickness of chest wall and appropriate portions of rib were contoured for evaluating dose distribution using RTA and MCA of Cyberknife MultiPlan software (version‐3.5.2). Treatment plans were first computed using RTA and then were recomputed using MCA without changing the total monitor unit (MU). Range of prescription dose was 50Gy‐60Gy (mean=54.6Gy). Studied dosimetric parameters were maximum point dose and doses to 1cc, 5cc, 10cc, 30cc, 50cc, 70cc, and 100cc of chest wall. Maximum point dose and doses to 1cc, 2cc, 5cc, and 10cc of ribs were also studied. These parameters were considered as clinically more relevant. Results: Dosimetric computation results revealed that RTA overestimated dose to both the chest wall and the ribs for all the studied parameters. Increase of average dose was in the range of 7.5–12.1% (p‐value<0.05, except 50–100cc p‐value>0.05), and 10.3–13.4% (p‐value <0.05) for chest wall and ribs, respectively. The lower the volume of interest, the larger was the difference in dose for the two algorithms. Average difference in maximum point dose for chest wall was 11.2% (p‐value <0.001) and that was 13.4% for ribs (p‐value <0.002). Conclusion: As compared to Monte Carlo algorithm, Ray Tracing algorithm significantly overestimates dose to chest wall and ribs. Although treatment planning with Monte Carlo is more involved, it should be used because of accuracy and significant difference in dose distribution in chest wall and ribs.
SU‐E‐T‐579: Effect of Dose Calculation Grid Size On Proton Dose Calculation
Authors: Zhao L
Published: July 2013

Purpose: The effect of dose calculation grid size for highly conformal proton planning is evaluated for the first time. Our goal is to find the optimal dose calculation grid size for different cases to increase the treatment planning efficiency while maintaining the dose calculation accuracy within clinical tolerance. Methods: Four clinical head& neck, prostate, lung and CSI cases are studied and calculated at three different calculation grid sizes (1 mm, 3 mm, 5 mm). To further understand the dose accuracy, a phantom simulating lung treatment with small fields and large fields is measured with EBT films. The measured results are compared with the calculated results in the form of point dose and dose profiles in regions of low and high dose gradients, dosimetric parameters, DVHs, and gamma analysis. The calculation time difference is investigated against the grid resolution as well. Results: There is no significant difference in pass rate of gamma analysis with 3 mm/3% acceptance criteria. The grid size effect is observed more clearly for small field size in inhomogeneous media. When comparing varying calculation grid sizes and measurements, the variation of the dose difference histogram is insignificant, but a local effect is observed in the dose difference map and point dose comparisons. Conclusion: The effect of calculation grid size on proton dose calculation can be clinically significant, depending on the disease sites, patient anatomy and treatment target volume and organ at risk. Small grid sizes (1 or 2mm) are necessary for small structures in and near inhomogeneous geometries such as in the head and neck regions.
SU‐E‐T‐587: Evaluation of Dosimetric Effect in Vaginal Cylindrical Application Using HDR Brachy Therapy
Authors: Palani D , Arun B , Prasath S , Selvan T , Gowardan D , Achari R
Published: July 2013

Purpose: This study is to quantify the amount of dose reduction on the tip of the dome in vaginal application due to the source self attenuation and inverse square law(ISL)along the longitudinal axis of the source during the Iridium‐192 high dose rate brachytherapy using different source dwell step size. Methods: This brachytherapy dosimetric study was carried out in Varian HDR brachytherapy unit having single (Ir‐192)source. The appropriate vaginal cylinder with applicator was chosen for the patients. 1.5 mm CT slice thickness of CT scan was taken, then exported to Eclipse and reconstructed the applicator. Two normalization lines were created one on the surface and other on 5mm distance from the surface of cylindrical dome. Four plans were made with the combination of 2.5 mm and 5mm of source step size with normalization on the surface and 5mm from surface of cylindrical dome for each case for 10 patients. Thus the doses were compared to study the influence due to source self attenuation and ISL. Results: In the case of surface normalisation, the Percentage of dose reduction using 2.5 mm and 5mm step size are −13.22% and −7.6% respectively. Similarly for the case of normalization at 0.5 cm distance from surface, the Percentage of dose reduction using 2.5 mm and 5mm step size are −33.02% and −28.15% respectively. Conclusion: The deviation of dose delivered at reference points with respect to the prescription is more with the 2.5 mm step size when compared to that of the 5 mm step size in both the cases namely prescription at the surface of the dome as well as the prescription at the 0.5 cm away from the surface of the dome. It is concluded that by using 5mm step size, the dose reduction due to above mentioned effects can be minimized by 5 %.
SU‐E‐T‐592: Investigation of Volumetric Modulated Arc Therapy for Total Body Irradiation with Lung Blocks
Authors: Wang H , Tung S , Wang C , Mahajan A , Dabaja B , Martel M
Published: July 2013

Purpose: Uncertainties from the use of lung blocks during total body irradiation (TBI) are present due to the process of block cutting and block mounting required for treatment. We investigated the use of volumetric modulated arc therapy (VMAT) to improve clinical TBI practice. Methods: Two pediatric patients (Pat‐1, Pat‐2) and one adult patient (Pat‐3) had CT scans from head to upper thigh. The treatment targets (12Gy) included bony structures (all patients) and lymph nodes+spleen (LNS) (Pat‐1, Pat‐3). Three plans were generated in Pinnacle for each patient: TBI plans with AP/PA fields at 380cm SAD with and without lung blocks and a VMAT plan at 100 SAD with 3–4 couch positions. Target coverage V12Gy and dose to lung V6Gy were compared among three plans for each patient. Treatment times as well as doses to other critical structures were also compared for different techniques. Results: for AP/PA plans, lung blocks reduced lung V6Gy to 28.7%, 6.3% and 24.9% for these three patients from 100% (without block), however, target V12Gy decreased to 72.5%, 68.6%, and 88.7% from 84.9%, 86.3%, 95.5% (without block), respectively. VMAT plan achieved 44.3%, 53.7% and 71.5% for lung V6Gy with excellent target coverage of 91.7%, 96.2% and 95.3%. While lung blocks only be used 3/8 treatments for AP/PA TBI, VMAT plan lung mean doses were 21–35% lower than AP/PA+block technique. Meanwhile, average mean dose to the brain, heart, kidneys and liver was also reduced 40%, 43.7%, 41.1% and 40.6% using VMAT plans. VMAT planning was more challenging when targets include LNS and/or for large patients (shoulder>40cm, Pat‐3). Setup and beam‐on time for VMAT were comparable to or less than AP/PA technique for Pat‐1, Pat‐2, but were much longer for Pat‐3. Conclusion: VMAT plans have potential to reduce uncertainties for treating small‐medium sized patients who need lung blocks in TBI treatments.
SU‐E‐T‐594: Software Application for Comparison and Verification of Radiotherapy Treatment Plans
Authors: Bacchus I , Gopalakrishnan M , Kang Z
Published: July 2013

Purpose: The physics check of a patient treatment plan is one of many that guard against treatment errors in radiation oncology departments. The process would be improved by adding a comparison of treatment plan and prescription parameters, but this would be inordinately time consuming, if not impossible, to do by eye, and would raise the potential for human error. The goal of this project was to develop a software application that would automatically compare treatment parameters from the treatment planning system (Pinnacle3) and the electronic record and verifying system (Mosaiq), supplementing the physics check without sacrificing speed or accuracy. Methods: Both Mosaiq and Pinnacle3 can generate .RTP files. These files contain relevant plan information, are delimited, and have comparable structures. MATLAB code was used to create a GUI‐based application that can run outside of the MATLAB environment. Using .RTP files as inputs, the application compares linac name, beam energy and modality, patient position, DICOM position, field names, gantry angles (checking that the field names contain the gantry angles), MU/fraction, SSD to reference point, beam weights, collimator angles, field sizes, and leaf positions. Program alerts user to any discrepancies and results are written to .txt files and an Excel spreadsheet (for leaf positions) that highlight any discrepancies. Results: The application is currently being rolled out in the Oncology Department for beta testing. During preliminary testing, the application flagged errors in cases with known discrepancies between treatment plan and prescription, indicating the applications effectiveness. Conclusion: The application adds another layer of safety for patients by providing a check for human error immediately before treatment. It focuses the user on patient care by ensuring he or she is cognizant of the current treatment plan. Finally, it produces digitally compact, easy‐to‐read records of the parameters of a given patients treatment.
SU‐E‐T‐599: A Dosimetric Comparison Between Multiple Junction Shifts and Single Gradient Dose Junction for Craniospinal Irradiation (CSI)
Authors: Hadley A , Ding G
Published: July 2013

Purpose: To evaluate the impact of patient treatment setup errors on the dose distributions between multiple junction shifts and a single gradient dose junction for craniospinal irradiation (CSI). Methods: Conventionally, two lateral brain fields and a posterior spine field are used for CSI. A weekly 1cm shift of the field junction is used to reduce the hot/cold spots due to patient positioning errors. This study retrospectively investigates the use of a single gradient dose falloff junction between two lateral brain fields and a posterior spine field. These fields were extended to allow for minimum 3cm overlap at the brain and spine junction. The dose gradient at the junction is achieved using IMRT and planned using Eclipse System (v10) . Optimization was set to create a gradient dose falloff from each contributing field throughout the overlapped area. The impact of patient positioning setup errors on the dose distributions for both techniques were simulated by applying shifts of +/− 3 and 5mm. The resulting dose profiles across the field junction for both techniques were calculated and compared. For the conventional plan, the dose profiles were calculated over the sum of the fractionation to include the effects from the weekly 1cm shift. Results: Systematic positioning errors throughout the course of treatment resulted in comparable hot/cold spots for both the gradient (112.7%/85.7% 3mm; 116.2%/80.2% 5mm) and conventional (115.2%/84.1% 3mm; 119.2%/81.9% 5mm) techniques. In most cases, the gradient technique provided slightly better uniformity in dosimetry. A single fraction positioning error provided significantly larger hot/cold spots in the conventional technique compared to the gradient technique. Conclusion: The advantages of the single gradient dose junction technique include improved single fraction dose uniformity and one plan for the entire treatment course, which reduces the possibility of human error compared to delivering the conventional four shifted plans.
SU‐E‐T‐600: Exploration of Reduced Order Prioritized Optimization for IMRT Treatment Planning
Authors: Kalantzis G , Rivera L , Apte A , Radke R , Jackson A
Published: July 2013

Purpose: Investigate the feasibility of reduced order prioritized optimization for IMRT treatments. Methods: The proposed method consists of three stages. Firstly, we sample the intensities space by solving a series of unconstrained optimizations of a scalar weighted sum of partial objectives for the target and the organs at risk (OARs). Secondly, the dimensionality of the search space is reduced using principal component analysis on the solution samples. Finally, treatment planning goals/objectives are prioritized and the problem is solved sequentially in the reduced order space: low priority objectives are optimized provided they do not interfere with the higher priority objectives. In the current study a quadratic deviation of the prescribed dose and the mean dose was used for the objectives of the PTV and the OARs respectively. Finally, a slip factor s, a dimensionless parameter, was used in order to relax the hard constraints regarding the PTV coverage within the established max and min dose limits and offer more flexibility to the algorithm for the lower order priorities. Results: The method was applied to a prostate IMRT plan with five coplanar beams. Two OARs were considered: rectum and bladder. On completion of the sequential prioritized optimization the mean dose at the rectum and the bladder was reduced by 20.5% and 21.5% respectively compared to the mean dose at the first step of the optimization for a slip factor s = 3. Finally, a max speedup of ∼22 was achieved for the prioritized optimization steps. Conclusion: A proof of concept was demonstrated for reduced order prioritized optimization for IMRT planning. Dimensionality reduction techniques may be applied to reduce the complexity time of the constraint prioritization optimization steps for IMRT planning.
SU‐E‐T‐604: 16‐MV Photon Beams Do Not Improve Plan Quality Compared to 6‐MV Photon Beams in Prostate Cancer IMRT
Authors: Yaparpalvi R , Mynampati D , Tome W , Shen J , Hong L , Kuo H , Garg M , Bodner W , Kalnicki S
Published: July 2013

Purpose: Photon energies 10 MV or higher are generally considered optimal for treatment of deep‐seated pelvic targets. We performed dosimetric quality assessment of Prostate IMRT plans in patients treated with 6‐MV and 16‐MV Photons, to discern if 16‐MV plan quality was superior to 6‐MV treatment plans. Methods: From our institutional database, treatment plans of 84 patients previously treated for early stage prostate cancers were included in this retrospective study. Forty‐two patients were treated with 6‐MV and forty‐two with 16‐MV. Beam energy choice was based on linac capability, physician preference and not on patient separation. All patients were planned with a coplanar 7‐F IMRT technique. The prescription dose (75.6‐Gy), optimization technique and planning objectives were similar in all patients. Dose distributions were evaluated using various indices‐Conformity‐Index (CI), Healthy‐Tissue Conformity Index (HTCI), Homogeneity‐Index (HI), Gradient‐Index (GI), Conformity‐Number (CN), Normal‐Tissue Integral Dose (NTID), Body‐mass‐index (BMI) and quality of coverage (QC). Rectal and Bladder dose‐volume indices were evaluated per RTOG guidelines. Non‐parametric Mann‐Whitney test was applied in the statistical analysis and for a p‐value <0.05, the null hypothesis is rejected. Results: Mean PTV was 197.9cc (±13.1) for the 6‐MV group and 191.8cc (±10.3) for the 16‐MV group. MUs per fraction were 905 (±32) for 6‐MV and 862 (±41) for 16‐MV plans. The CI, HTCI and GI were statistically similar between 6‐MV and 16‐MV plans (p=0.22). Indices HI, QC and CN all showed statistically significant improvement for 6‐MV plans compared to 16‐MV plans (p<0.03). NTID was slightly lower for 16‐MV plans, but not statistically significant, compared to 6‐MV plans. NTID correlated with BMI for 16‐MV group (r=0.70) and weakly for 6‐MV group (r=0.28). Rectal V65, V40 and Bladder V65 were similar between 6‐MV and 16‐MV plans. Conclusion: We conclude that 16‐MV photon beams do not provide additional dosimetric advantage compared to 6‐MV photon beams in Prostate IMRT.
SU‐E‐T‐605: A Modified Adaptive Radiotherapy Based On CT‐CT Image Fusion with a Repeat CT in the VMAT Treatment of Nasopharyngeal Cancer Patients
Authors: Jin X , Xie C , Han C
Published: July 2013

Purpose: To investigate the volumetric and dosimetric changes of a CT‐CT image fusion based adaptive radiotherapy by using a repeat CT as contour references. Methods: Nine nasopharyngeal cancer (NPC) patients underwent a modified adaptive volumetric modulated arc radiotherapy (VMAT) based on CT‐CT image fusion were enrolled in this study. The volumetric and dosimetric changes of gross tumor volume (GTV) and organs at risk (OARs) were investigated with a repeat CT at 23rd fraction. A commercially deformable registration software package, MIMVista, was applied to verify the contour and dosimetric changes accuracy of the CT‐CT image fusion based modified adaptive radiotherapy. Results: The average volume of GTV decreased from78.83±38.42 cm3 in the initial planning CT to 71.44±37.46 cm3 in the repeat CT, but with no significant difference (p=0.66). The average volume of the left parotid and right parotid decreased from 19.91±4.89 cm3 and 21.58±6.16 cm3 in initial planning CT to 11.80±2.79 cm3 and 13.29±4.17 cm3 in the repeat CT (both p<0.01), respectively. The volume of other OARs did not shrink very much. Dice similarity coefficient (DSC) and mass center distance (MCD) verified the accuracy of CT‐CT image fusion. No significant difference on GTV and CTV coverage was observed. Significant differences in volume of left parotid (p=0.03) and right parotid (p<0.01) receiving 5 Gy were observed between the initial plan and the re‐optimized plan. The mean dose of left parotid (p=0.08) and right parotid (p<0.01) were also significantly different. There was no significant difference on the dose delivered to other OARs. Conclusion: Patients with NPC undergoing VMAT have significant anatomic and dosimetric changes to parotids. Repeat CT as an anatomic changes reference and re‐optimization with initial CT based on CT‐CT image fusion was accurate enough to identify the volume changes and to ensure safe dose to parotids.