bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐563: Multi‐Fraction Stereotactic Radiosurgery with Extend System of Gamma Knife: Treatment Verification Using Indigenously Designed Patient Simulating Multipurpose Phantom
Authors: Bisht R , Kale S , Gopishankar N , Rath G , Julka P , Agarwal D , Singh M , Garg A , Kumar P , Thulkar S , Sharma B 
Published: June 2015

Purpose:Aim of the study is to evaluate mechanical and radiological accuracy of multi‐fraction regimen and validate Gamma knife based fractionation using newly developed patient simulating multipurpose phantom.Methods:A patient simulating phantom was designed to verify fractionated treatments with extend system (ES) of Gamma Knife however it could be used to validate other radiotherapy procedures as well. The phantom has options to insert various density material plugs and mini CT/MR distortion phantoms to analyze the quality of stereotactic imaging. An additional thorax part designed to predict surface doses at various organ sites. The phantom was positioned using vacuum head cushion and patient control unit for imaging and treatment. The repositioning check tool (RCT) was used to predict phantom positioning under ES assembly. The phantom with special inserts for film in axial, coronal and sagittal plane were scanned with X‐Ray CT and the acquired images were transferred to treatment planning system (LGP 10.1). The focal precession test was performed with 4mm collimator and an experimental plan of four 16mm collimator shots was prepared for treatment verification of multi‐fraction regimen. The prescription dose of 5Gy per fraction was delivered in four fractions. Each fraction was analyzed using EBT3 films scanned with EPSON 10000XL Scanner.Results:The measurement of 38 RCT points showed an overall positional accuracy of 0.28mm. The mean deviation of 0.28% and 0.31 % were calculated as CT and MR image distortion respectively. The radiological focus accuracy test showed its deviation from mechanical center point of 0.22mm. The profile measurement showed close agreement between TPS planned and film measured dose. At tolerance criteria of 1%/1mm gamma index analysis showed a pass rate of > 95%.Conclusion:Our results show that the newly developed multipurpose patient simulating phantom is highly suitable for the verification of fractionated stereotactic radiosurgery using ES of Gamma knife.The study is a part of intramural research project of Research Section, All India Institute of Medical Sciences New Delhi India (A 247).
SU‐E‐T‐565: Multiple Channel Radiochromic Film Calibration with Spatial Dose Gradient Regularization
Authors: Li Darrell T H , Lee Louis K Y , Chan Anthony T C 
Published: June 2015

Purpose:To develop a new algorithm for multiple channel radiochromic film calibration and to evaluate the accuracy of the algorithm with virtual simulated film images.Methods:The proposed calibration method was based on least‐square optimization of discrepancies between measured and estimated optical density of the three colour channels, with the inclusion of the weighted dose gradient as penalty to this minimization problem. The regularization parameter λ was selected using the L‐curve method to reduce the L2‐norm of the dose gradient while preserving the data consistency. The situation of λ = 0 represented no regularization and the least‐square solution would be obtained. The algorithm was tested with 4 virtual film images which were produced from dose planes exported from the planning system. Zero‐mean Gaussian noise were added to simulate the real situation. The resultant dose maps calculated by both least‐square method and regularization method were then compared with the original dose planes.Results:Comprehensive study of the 4 simulated cases with the L‐curve method yielded an optimal regularization parameters of 2×10−8. The dose planes generated by least‐square method showed significant noise retained when compared with that from the regularization method. In performing Gamma Index analysis with tolerance of 1% and 1 mm, it was observed that in the least‐square solution, failed points exist everywhere on the dose plane, while only a small amount in the sharp dose gradient region of the regularized solution. It was also noted that the number of failed point in the least‐square solution can be 20 to 150 times more than that in the regularized solution.Conclusion:The calibration algorithm proposed in this study successfully recovered the original dose plane from the noise contaminated film image with the regularization method. Regularization should be a better option to the least‐square one in solving the radiochromic film calibration problem.
SU‐E‐T‐568: Neutron Dose Survey of a Compact Single Room Proton Machine
Authors: Chen Y , Prusator M , Islam M , Johnson D , Ahmad S 
Published: June 2015

Purpose:To ensure acceptable radiation limits are maintained for those working at and near the machine during its operation, a comprehensive radiation survey was performed prior to the clinical release of Mevion S250 compact proton machine at Stephenson Oklahoma Cancer Center.Methods:The Mevion S250 proton therapy system consists of the following: a superconducting cyclotron to accelerate the proton particles, a passive double scattering system for beam shaping, and paired orthogonal x‐ray imaging systems for patient setup and verification via a 6D robotic couch. All equipment is housed within a single vault of compact design. Two beam delivery applicators are available for patient treatment, offering field sizes of as great as 14 cm and 25 cm in diameter, respectively. Typical clinical dose rates are between 1 and 2 Gy/min with a fixed beam energy of 250 MeV. The large applicator (25 cm in diameter) was used in conjunction with a custom cut brass aperture to create a 20 cm × 20 cm field size at beam isocenter. A 30 cm − 30 cm − 35 cm high density plastic phantom was placed in the beam path to mimic the conditions creating patient scatter. Measurements integrated‐ambient‐neutron‐dose‐equivalence were made with a SWENDII detector. Gantry angles of 0, 90 and 180 degrees, with a maximum dose rate of 150 MU/min (for large applicator) and beam configuration of option 1 (range 25 cm and 20 cm modulation), were selected as testing conditions. At each point of interest, the highest reading was recorded at 30 cm from the barrier surface.Results:The highest neutron dose was estimated to be 0.085 mSv/year at the console area.Conclusion:All controlled areas are under 5 mSv/year and the uncontrolled areas are under 1 mSv/year. The radiation protection provided by the proton vault is of sufficient quality.
SU‐E‐T‐570: New Quality Assurance Method Using Motion Tracking for 6D Robotic Couches
Authors: Cheon W , Cho J , Ahn S , Han Y , Choi D 
Published: June 2015

Purpose:To accommodate geometrically accurate patient positioning, a robotic couch that is capable of 6‐degrees of freedom has been introduced. However, conventional couch QA methods are not sufficient to enable the necessary accuracy of tests. Therefore, we have developed a camera based motion detection and geometry calibration system for couch QA.Methods:Employing a Visual‐Tracking System (VTS, BonitaB10, Vicon, UK) which tracks infrared reflective(IR) markers, camera calibration was conducted using a 5.7 × 5.7 × 5.7 cm3 cube attached with IR markers at each corner. After positioning a robotic‐couch at the origin with the cube on the table top, 3D coordinates of the cube's eight corners were acquired by VTS in the VTS coordinate system. Next, positions in reference coordinates (roomcoordinates) were assigned using the known relation between each point. Finally, camera calibration was completed by finding a transformation matrix between VTS and reference coordinate systems and by applying a pseudo inverse matrix method. After the calibration, the accuracy of linear and rotational motions as well as couch sagging could be measured by analyzing the continuously acquired data of the cube while the couch moves to a designated position. Accuracy of the developed software was verified through comparison with measurement data when using a Laser tracker (FARO, Lake Mary, USA) for a robotic‐couch installed for proton therapy.Results:VTS system could track couch motion accurately and measured position in room‐coordinates. The VTS measurements and Laser tracker data agreed within 1% of difference for linear and rotational motions. Also because the program analyzes motion in 3‐Dimension, it can compute couch sagging.Conclusion:Developed QA system provides submillimeter/ degree accuracy which fulfills the high‐end couch QA.This work was supported by the National Research Foundation of Korea funded by Ministry of Science, ICT & Future Planning. (2013M2A2A7043507 and 2012M3A9B6055201)
SU‐E‐T‐571: Newly Emerging Integrated Transmission Detector Systems Provide Online Quality Assurance of External Beam Radiation Therapy
Authors: Hoffman D , Chung E , Hess C , Stern R , Benedict S 
Published: June 2015

Purpose:Two newly emerging transmission detectors positioned upstream from the patient have been evaluated for online quality assurance of external beam radiotherapy. The prototype for the Integral Quality Monitor (IQM), developed by iRT Systems GmbH (Koblenz, Germany) is a large‐area ion chamber mounted on the linac accessory tray to monitor photon fluence, energy, beam shape, and gantry position during treatment. The ion chamber utilizes a thickness gradient which records variable response dependent on beam position. The prototype of Delta4 Discover™, developed by ScandiDos (Uppsala, Sweden) is a linac accessory tray mounted 4040 diode array that measures photon fluence during patient treatment. Both systems are employable for patient specific QA prior to treatment delivery.Methods:Our institution evaluated the reproducibility of measurements using various beam types, including VMAT treatment plans with both the IQM ion chamber and the Delta4 Discover diode array. Additionally, the IQM's effect on photon fluence, dose response, simulated beam error detection, and the accuracy of the integrated barometer, thermometer, and inclinometer were characterized. The evaluated photon beam errors are based on the annual tolerances specified in AAPM TG‐142.Results:Repeated VMAT treatments were measured with 0.16% reproducibility by the IQM and 0.55% reproducibility by the Delta4 Discover. The IQM attenuated 6, 10, and 15 MV photon beams by 5.43±0.02%, 4.60±0.02%, and 4.21±0.03% respectively. Photon beam profiles were affected <1.5% in the non‐penumbra regions. The IQM's ion chamber's dose response was linear and the thermometer, barometer, and inclinometer agreed with other calibrated devices. The device detected variations in monitor units delivered (1%), field position (3mm), single MLC leaf positions (13mm), and photon energy.Conclusion:We have characterized two new transmissions detector systems designed to provide in‐vivo like measurements upstream from the patient. Both systems demonstrate substantial utility for online treatment verification and QA of photon external beam radiotherapy.
SU‐E‐T‐573: Normal Tissue Dose Effect of Prescription Isodose Level Selection in Lung Stereotactic Body Radiation Therapy
Authors: Zhang Q , Lei Y , Zheng D , Zhu X , Wahl A , Lin C , Zhou S , Zhen W 
Published: June 2015

Purpose:To evaluate dose fall‐off in normal tissue for lung stereotactic body radiation therapy (SBRT) cases planned with different prescription isodose levels (IDLs), by calculating the dose dropping speed (DDS) in normal tissue on plans computed with both Pencil Beam (PB) and Monte‐Carlo (MC) algorithms.Methods:The DDS was calculated on 32 plans for 8 lung SBRT patients. For each patient, 4 dynamic conformal arc plans were individually optimized for prescription isodose levels (IDL) ranging from 60% to 90% of the maximum dose with 10% increments to conformally cover the PTV. Eighty non‐overlapping rind structures each of 1mm thickness were created layer by layer from each PTV surface. The average dose in each rind was calculated and fitted with a double exponential function (DEF) of the distance from the PTV surface, which models the steep‐ and moderate‐slope portions of the average dose curve in normal tissue. The parameter characterizing the steep portion of the average dose curve in the DEF quantifies the DDS in the immediate normal tissue receiving high dose. Provided that the prescription dose covers the whole PTV, a greater DDS indicates better normal tissue sparing. The DDS were compared among plans with different prescription IDLs, for plans computed with both PB and MC algorithms.Results:For all patients, the DDS was found to be the lowest for 90% prescription IDL and reached a highest plateau region for 60% or 70% prescription. The trend was the same for both PB and MC plans.Conclusion:Among the range of prescription IDLs accepted by lung SBRT RTOG protocols, prescriptions to 60% and 70% IDLs were found to provide best normal tissue sparing.
SU‐E‐T‐578: On Definition of Minimum and Maximum Dose for Target Volume
Authors: Gong Y , Yu J , Xiao Y 
Published: June 2015

Purpose:This study aims to investigate the impact of different minimum and maximum dose definitions in radiotherapy treatment plan quality evaluation criteria by using tumor control probability (TCP) models.Methods:Dosimetric criteria used in RTOG 1308 protocol are used in the investigation. RTOG 1308 is a phase III randomized trial comparing overall survival after photon versus proton chemoradiotherapy for inoperable stage II‐IIIB NSCLC. The prescription dose for planning target volume (PTV) is 70Gy. Maximum dose (Dmax) should not exceed 84Gy and minimum dose (Dmin) should not go below 59.5Gy in order for the plan to be “per protocol” (satisfactory).A mathematical model that simulates the characteristics of PTV dose volume histogram (DVH) curve with normalized volume is built. The Dmax and Dmin are noted as percentage volumes Dη% and D(100‐δ)%, with η and d ranging from 0 to 3.5. The model includes three straight line sections and goes through four points: D95%= 70Gy, Dη%= 84Gy, D(100‐δ)%= 59.5 Gy, and D100%= 0Gy. For each set of η and δ, the TCP value is calculated using the inhomogeneously irradiated tumor logistic model with D50= 74.5Gy and γ50=3.52.Results:TCP varies within 0.9% with η; and δ values between 0 and 1. With η and η varies between 0 and 2, TCP change was up to 2.4%. With η and δ variations from 0 to 3.5, maximum of 8.3% TCP difference is seen.Conclusion:When defined maximum and minimum volume varied more than 2%, significant TCP variations were seen. It is recommended less than 2% volume used in definition of Dmax or Dmin for target dosimetric evaluation criteria.This project was supported by NIH grants U10CA180868, U10CA180822, U24CA180803, U24CA12014 and PA CURE Grant.
SU‐E‐T‐579: On the Relative Sensitivity of Monte Carlo and Pencil Beam Dose Calculation Algorithms to CT Metal Artifacts in Volumetric‐Modulated Arc Spine Radiosurgery (RS)
Authors: Wong M , Lee V , Blanck O , Leung R , Lee K , Law G , Tung S , Chan M 
Published: June 2015

Purpose:Investigating the relative sensitivity of Monte Carlo (MC) and Pencil Beam (PB) dose calculation algorithms to low‐Z (titanium) metallic artifacts is important for accurate and consistent dose reporting in post¬operative spinal RS.Methods:Sensitivity analysis of MC and PB dose calculation algorithms on the Monaco v.3.3 treatment planning system (Elekta CMS, Maryland Heights, MO, USA) was performed using CT images reconstructed without (plain) and with Orthopedic Metal Artifact Reduction (OMAR; Philips Healthcare system, Cleveland, OH, USA). 6MV and 10MV volumetric‐modulated arc (VMAT) RS plans were obtained for MC and PB on the plain and OMAR images (MC‐plain/OMAR and PB‐plain/OMAR).Results:Maximum differences in dose to 0.2cc (D0.2cc) of spinal cord and cord +2mm for 6MV and 10MV VMAT plans were 0.1Gy between MC‐OMAR and MC‐plain, and between PB‐OMAR and PB‐plain. Planning target volume (PTV) dose coverage changed by 0.1±0.7% and 0.2±0.3% for 6MV and 10MV from MC‐OMAR to MC‐plain, and by 0.1±0.1% for both 6MV and 10 MV from PB‐OMAR to PB‐plain, respectively. In no case for both MC and PB the D0.2cc to spinal cord was found to exceed the planned tolerance changing from OMAR to plain CT in dose calculations.Conclusion:Dosimetric impacts of metallic artifacts caused by low‐Z metallic spinal hardware (mainly titanium alloy) are not clinically important in VMAT‐based spine RS, without significant dependence on dose calculation methods (MC and PB) and photon energy ≥ 6MV. There is no need to use one algorithm instead of the other to reduce uncertainty for dose reporting. The dose calculation method that should be used in spine RS shall be consistent with the usual clinical practice.
SU‐E‐T‐581: On the Value of LET as a Radiation Quality Descriptor for RBE
Authors: Pater P , Backstrom G , Enger S , Villegas F , Ahnesjo A , Seuntjens J , Naqa I El 
Published: June 2015

Purpose:To investigate the relationship between linear energy transfer (LET) and relative biological effectiveness (RBE) for protons and light ions, and the corresponding role of LET as a descriptor of radiation quality of hadron therapy.Methods:Monte Carlo (MC) proton and light ion (He, Li, C) tracks with LET < 30 eV nm‐1 were generated in an event‐by‐event mode. They were overlaid on a cell nucleus model containing 6×109 nucleotide base pairs using an isotropic irradiation procedure that provides electronic equilibrium. Strand breaks (sbs) were scored in the DNA sugar‐phosphate groups and further sub‐classified into single or double sbs (ssbs or dsbs). Distributions of ssbs and dsbs for 2 Gy fractions were calculated to estimate RBE for the induction of initial dsbs with reference to 60Co. Additionally, sbs were classified based on their complexity (i.e. the number of sbs in each cluster).Results:An increase in LET for light ions of the same atomic number or a decrease in atomic number for ions of the same LET resulted in a lower kinetic energy of emitted secondary electrons. The clustering of DNA damage was more pronounced as reflected by the increase in proton RBE from ∼ 1.75 to 4 for LET values of 7 to 28 eV nm‐1. A significant RBE decrease between protons, He, Li and C ions of the same LET was also noticed as function of the atomic number. Significant differences in ssbs and dsbs complexities were also seen for particles with the same LET, potentially supporting a clustering‐based radiation quality descriptor.Conclusion:The LET‐RBE relationships were simulated for proton and light ions and exhibited expected trends, including different RBEs for particles with the same LET but different atomic numbers. A complexity based radiation quality descriptor may allow better differentiation of RBE between radiation fields of similar LET.We would like to acknowledge support from the Fonds de recherche du Quebec Sante (FRQS), from the CREATE Medical Physics Research Training Network grant (number 432290) of NSERC, support from NSERC under grants RGPIN 397711‐11 and RGPIN‐2014‐06475 and support from CIHR under grants MOP‐114910, MOP‐136774 and MOP‐102550.
SU‐E‐T‐584: Optical Tracking Guided Patient‐Specific VMAT QA with ArcCHECK
Authors: Fan Q , Park C , Lu B , Barraclough B , Lebron S , Li J , Liu C , Yan G 
Published: June 2015

Purpose:To investigate the novel use of an in‐house optical tracking system (OTS) to improve the efficacy of VMAT QA with a cylindrical dosimeter (ArcCHECK™).Methods:The translational and rotational setup errors of ArcCHECK are convoluted which makes it challenging to position the device efficiently and accurately. We first aligned the ArcCHECK to the machine cross‐hair at three cardinal angles (0°, 90°, and 270°) to establish a reference position. Four infrared reflective markers were attached to the back of the device. An OTS with 0.2mm/0.2° accuracy was used to control its setup uncertainty. Translational uncertainties of 1 mm and 2 mm in three directions (in, right, and up) were applied on the device. Four open beams of various field sizes and six clinical VMAT arcs were delivered and measured for all simulated setup errors. The measurements were compared with Pinnacle™ calculations using Gamma analysis to evaluate the impact of setup uncertainty. This study also evaluated the improvement in setup reproducibility and efficiency with the aid of the OTS.Results:For open beams, with 3%/3mm, the mean passing rates dropped by less than 5% for all shifts; with 2%/2mm, two significant drops(>5%) were observed: 15.38±6.75% for 2 mm lateral shift and 9.35±4.88% for 2 mm longitudinal shift. For VMAT arcs, the mean passing rates using 2%/2mm dropped by 10.47±7.46% and 22.02±11.39% for 1 and 2 mm shift, respectively. With 3%/3mm, significant drop only occurred with 2 mm longitudinal shift (13.73±8.30%). Setup time could be reduced by >15 min with the aid of the OTS.Conclusion:OTS is an effective tool for separating translational and rotational uncertainties. The current VMAT QA solution was not strongly sensitive to translation errors of 2mm with widely accepted criterion (3%/3mm). This finding raises concerns regarding the efficacy of such QA system in detecting errors in the dynamic VMAT delivery.
SU‐E‐T‐591: Optimizing the Flattening Filter Free Beam Selection in RapidArc‐Based Stereotactic Body Radiotherapy for Stage I Lung Cancer
Authors: Huang B‐T , Lu J‐Y 
Published: June 2015

Purpose:To optimize the flattening filter free (FFF) beam energy selection in stereotactic body radiotherapy (SBRT) treatment for stage I lung cancer with different fraction schemes.Methods:Twelve patients suffering from stage I lung cancer were enrolled in this study. Plans were designed using 6XFFF and 10XFFF beams with the most widely used fraction schemes of 4*12 Gy, 3*18 Gy and 1*34 Gy, respectively. The plan quality was appraised in terms of planning target volume (PTV) coverage, conformity of the prescribed dose (CI100%), intermediate dose spillage (R50% and D2cm), organs at risk (OARs) sparing and beam‐on time.Results:The 10XFFF beam predicted 1% higher maximum, mean dose to the PTV and 4–5% higher R50% compared with the 6XFFF beam in the three fraction schemes, whereas the CI100% and D2cm was similar. Most importantly, the 6XFFF beam exhibited 3–10% lower dose to all the OARs. However, the 10XFFF beam reduced the beam‐on time by 31.9±7.2%, 38.7±2.8% and 43.6±4.0% compared with the 6XFFF beam in the 4*12 Gy, 3*18 Gy and 1*34 Gy schemes, respectively. Beam‐on time was 2.2±0.2 vs 1.5±0.1, 3.3±0.9 vs 2.0±0.5 and 6.3±0.9 vs 3.5±0.4 minutes for the 6XFFF and 10XFFF one in the three fraction schemes.Conclusion:The 6XFFF beam obtains better OARs sparing in SBRT treatment for stage I lung cancer, but the 10XFFF one provides improved treatment efficiency. To balance the OARs sparing and intrafractional variation as a function of prolonged treatment time, the authors recommend to use the 6XFFF beam in the 4*12 Gy and 3*18 Gy schemes for better OARs sparing. However, for the 1*34 Gy scheme, the 10XFFF beam is recommended to achieve improved treatment efficiency.