bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐52: A New Device for Quality Assurance of a Single Isocenter Technique for the Simultaneous Treatment of Multiple Brain Metastases
Authors: Maurer J , Sintay B , Varchena V 
Published: June 2015

Purpose:Comprehensive quality assurance (QA) of a single isocenter technique for the simultaneous treatment of multiple brain metastases is presently impractical due to the time consuming nature of measuring each lesion's dose on film or with a micro‐chamber. Three dimensional diode array and full field film measurements are sometimes used to evaluate these plans, but gamma analysis may not reveal local errors that have significant effects on one or a few of several targets. This work aimed to design, build and test a phantom to simplify comprehensive measurement and evaluation.Methods:A phantom was designed with 28 stackable slabs. The top and bottom slabs are 1.5 centimeters (cm) in thickness, and central 26 slabs are 0.5 cm thick. When assembled with radiochromic film in all 27 gaps, the phantom measures 16.5 × 15 × 19 cm. Etchings were designed to aide in identification of specific film planes on computed tomography (CT) images and correlation of individual PTVs with closest bisecting planes. Patient verification plans with a total of 16 PTVs were calculated on the phantom CT, and test deliveries both with and without couch kicks were performed to test the ability to identify correct film placements and subsequent PTV specific dose distributions on the films.Results:Bisecting planes corresponding to PTV locations were easily identified, and PTV specific dose distributions were clear for all 16 targets. For deliveries with couch kicks, the phantom PTV dose distributions closely approximated those calculated on the patient's CT. For deliveries without couch kicks, PTV specific dosimetry was also possible, although the distributions had ‘ghosts’ equaling the number of couch kicks, with distance between ghosts increasing with distance from the isocenter.Conclusion:A new phantom facilitates fast comprehensive commissioning validation and PTV specific dosimetry for a single isocenter technique for treating multiple brain metastases.This work was partially funded by CIRS, Inc.
SU‐E‐T‐70: A Radiobiological Model of Reoxygenation and Fractionation Effects
Authors: Guerrero M , Carlson DJ 
Published: June 2015

Purpose:To develop a simple reoxygenation model that fulfills the following goals:1‐Quantify the reoxygenation effect in biologically effective dose (BED) and compare it to the repopulation effect.2‐Model the hypoxic fraction in tumors as a function of the number of fractions.3‐Develop a simple analytical expression for a reoxygenation term in BED calculations.Methods:The model considers tumor cells in two compartments: one normoxic population of cells and one hypoxic compartment including cells under a range of reduced oxygen concentrations. The surviving fraction is predicted using the linear‐quadratic (LQ) model. A hypoxia reduction factor (HRF) is used to quantify reductions in radiosensitivity parameters α_A and β_A as cellular oxygen concentration decreases. The HRF is defined as the ratio of the dose at a specific level of hypoxia to the dose under fully aerobic conditions to achieve equal cell killing. The model assumes that a fraction of the hypoxic cells ( ) moves from the hypoxic to the aerobic compartment after each daily fraction. As an example, we consider standard fractionation for NSCLC (d=2Gy,n=33) versus a SBRT (n=5, d=10Gy) fractionation and compare the loss in reoxygenation biological effect with the gain in repopulation biological effect.Results:An analytic expression for the surviving fraction after n daily treatments is derived and the reoxygenation term in the biological effect is calculated. Reoxygenation and repopulation effects are the same order of magnitude for potential doubling time Td values of 2 to 5 days. The hypoxic fraction increases or decreases with n depending on the reoxygenation rate Δ. For certain combinations of parameters, the biological effect of reoxygenation goes as ‐(n‐1)*ln(1‐Δ) providing a simple expression that can be introduced in BED calculations.Conclusion:A novel radiobiological model was developed that can be used to evaluate the effect of reoxygenation in fractionated radiotherapy.
SU‐E‐T‐74: A Simple Model of Dose Falloff for Highly Convergent SBRT Beams
Authors: Hoban P , Niu Y , Yu C 
Published: June 2015

Purpose:The purpose of this study was to create a simple model of dose falloff outside the target for a SBRT system employing a highly convergent beam geometry. With an estimate of the rate of reduction in dose away from a target of a given size, dose to tissues at a given distance from the target can be estimated. Our hypothesis is that dose at a given distance away from the edge of a target can be approximated using an inverse square model.Methods:With the GammaPod™ system used for this study, thirty‐six rotating Co‐60 beams with circular cross section converge at an isocenter and then diverge distal to the isocenter. Dose falloff beyond the target is mainly due to reduction in beam overlap, which in turn depends on projected area of all beams and projected beam area swept out during rotation. Beams also decrease in intensity beyond the isocenter. The GammaPod™ TPS calculates dose via superposition of Monte Carlo‐generated kernels, each corresponding to the convergence of beams at an isocenter within a stereotactic breast cup.Results:The factors above yield a simple inverse square‐based model that has been compared with TPS predictions and measurements for a variety of targets. Good agreement is seen considering the simple nature of the model. Fitting of the treatment planning and measured dose falloff data with a power law expression yields a negative exponent close to 2, confirming the inverse square nature of dose falloff.Conclusion:It is possible to apply a simple inverse square dose falloff model for SBRT or SRS systems such as the GammaPod which employ a highly‐convergent beam geometry. This can be useful in estimating the “worst case scenario” for dose to critical organs at a known distance from the edge of the target volume.Authors are employees of Xcision Medical Systems
SU‐E‐T‐77: A Statistical Approach to Manage Quality for Pre‐Treatment Verification in IMRT/VMAT
Authors: Jassal K , Sarkar B , Mohanti B , Roy S , Ganesh T , Munshi A , Chougule A , Sachdev K 
Published: June 2015

Objective:The study presents the application of a simple concept of statistical process control (SPC) for pre‐treatment quality assurance procedure analysis for planar dose measurements performed using 2D‐array and a‐Si electronic portal imaging device (a‐Si EPID).Method:A total of 195 patients of four different anatomical sites: brain (n1=45), head & neck (n2=45), thorax (n3=50) and pelvis (n4=55) were selected for the study. Pre‐treatment quality assurance for the clinically acceptable IMRT/VMAT plans was measured with 2D array and a‐Si EPID of the accelerator. After the γ‐analysis, control charts and the quality index Cpm was evaluated for each cohort.Results:Mean and σ of γ ( 3%/3 mm) were EPID γ %≤1= 99.9% ± 1.15% and array γ %<1 = 99.6% ± 1.06%. Among all plans γ max was consistently lower than for 2D array as compared to a‐Si EPID. Fig.1 presents the X‐bar control charts for every cohort. Cpm values for a‐Si EPID were found to be higher than array, detailed results are presented in table 1.Conclusion:Present study demonstrates the significance of control charts used for quality management purposes in newer radiotherapy clinics. Also, provides a pictorial overview of the clinic performance for the advanced radiotherapy techniques.Higher Cpm values for EPID indicate its higher efficiency than array based measurements.
SU‐E‐T‐80: A Study of the Effect of Dose Grid Resolution On Stereotactic Plan Evaluation as a Function of Target Size
Authors: Pappas E , Papanikolaou N , Gutierrez A , Kirby N , Mavroidis P , Efstathopoulos E , Makris D , Crownover R , Stathakis S 
Published: June 2015

Purpose:To investigate and quantify the impact of dose‐calculation grid‐size on dose volume histogram (DVH) for small targets, such as those in stereotactic radiosurgery (SRS).Methods:A cohort of ten patients with multiple metastasis was used in this planning study. All patients were treated with SRS and had target volumes ranging from 0.1 to 4.3cc. The Varian eclipse planning system was used for planning using a mono‐isocentric VMAT technique with four arcs. Each plan was calculated twice using a 1×1×1 mm3 and 3×3×3 mm3 dose grid respectively. Moreover, we used an open source DICOM‐RT viewer to read the raw‐RDose data (1×1×1 mm3 resolution) and were subsequently rescaled by linear interpolation to dose grids of 1.5×1.5×1.5, 2×2×2, 2.5×2.5×2.5 and 3×3×3 mm3. DVHs for all targets were recalculated and inter‐compared for the native and post‐processed resolutions to quantify the effect on DVH of dose grid resolution and correlate that with the PTV volume size.Results:DVHs shape and numerical values have a significant dependence on dose grid size resulting to a reduced Dmean, Dmax and Dmin with volume averaging effect being the main reason for these changes. Moreover, the magnitude of the DVH alteration is inversely proportional to tumor volume size. As the dose grid increases from 1×1×1 to 3×3×3 mm3, the DVH‐derived Dmean value is underestimated by ∼4, ∼7 and ∼10 % for tumors with volume sizes of 1.3, 0.5 and 0.1 cc respectively.Conclusion:The dose grid size that is used for the final dose calculation is affecting significantly the DVHs of small PTVs. The higher the dose grid size, the more noticeable is the DVH alteration, especially for tumors with a volume less than 1cc. For SRS planning, a dose grid of 1×1×1 mm3 should be used, especially for tumors with a volume < 1cc, to avoid erroneous DVHs.UTHSCSA, division of medical physics, has a research grant with Brainlab
SU‐E‐T‐81: A Study On Correlation Between Gamma Analysis for Midline and Lateralized Tumors Using VMAT
Authors: Kumar Syam , Anjana  
Published: June 2015

Purpose:To evaluate the fluence for the midline and lateralized tumors for VMAT technique using 2D seven29 detector array combined with the Octavius phantom.Methods:60 cases that are already being treated with volumetric modulated arc therapy (VMAT) have selected for this study. This includes tumors situated at the medial and lateral. Medial refers to the tumor situated at the midline of the body and lateral means toward the side or away from the midline of the body. Verification plans were created for each treatment plan in Varian Eclipse treatment planning system (version10, Varian medical systems, Palo Alto,CA) with the 2D Seven29 detector array and the Octavius phantom(PTW, Freiburg, Germany). Measurements were performed on a Varian Clinac 2100 iX, linear accelerator equipped with a millennium 120 leaf collimator. Analysis was done by comparing the fluence measured for the tumors situated on the midline and tumors situated laterally.Results:Fluence measured for all the delivered plans were analyzed using Verisoft software (PTW, Freiburg, Germany). The gamma pass percentage for midline tumors were found to be higher compared with the lateralized ones. The standard deviation between gamma values for midline and lateralized tumors is 2.18 and 3.5 respectively. Also the standard deviation between the point doses for midline and lateralized tumors is 0.38 and 0.29 respectively. The average gamma passing rate for midline tumors is 96.55% and for lateralized tumors are 94.94% for 3%DD and 3mm DTA criteria. From the T test, it was found that there is no significant difference between the gamma pass percentage between midline and lateralized tumors with p value of 0.28.Conclusion:There is no particular correlation found in the gamma pass criteria for midline and lateralized tumors.
SU‐E‐T‐87: A TG‐100 Approach for Quality Improvement of Associated Dosimetry Equipment
Authors: Manger R , Pawlicki T , Kim G 
Published: June 2015

Purpose:Dosimetry protocols devote so much time to the discussion of ionization chamber choice, use and performance that is easy to forget about the importance of the associated dosimetry equipment (ADE) in radiation dosimetry ‐ barometer, thermometer, electrometer, phantoms, triaxial cables, etc. Improper use and inaccuracy of these devices may significantly affect the accuracy of radiation dosimetry. The purpose of this study is to evaluate the risk factors in the monthly output dosimetry procedure and recommend corrective actions using a TG‐100 approach.Methods:A failure mode and effects analysis (FMEA) of the monthly linac output check procedure was performed to determine which steps and failure modes carried the greatest risk. In addition, a fault tree analysis (FTA) was performed to expand the initial list of failure modes making sure that none were overlooked. After determining the failure modes with the highest risk priority numbers (RPNs), 11 physicists were asked to score corrective actions based on their ease of implementation and potential impact. The results were aggregated into an impact map to determine the implementable corrective actions.Results:Three of the top five failure modes were related to the thermometer and barometer. The two highest RPN‐ranked failure modes were related to barometric pressure inaccuracy due to their high lack‐of‐detectability scores. Six corrective actions were proposed to address barometric pressure inaccuracy, and the survey results found the following two corrective actions to be implementable: 1) send the barometer for recalibration at a calibration laboratory and 2) check the barometer accuracy against the local airport and correct for elevation.Conclusion:An FMEA on monthly output measurements displayed the importance of ADE for accurate radiation dosimetry. When brainstorming for corrective actions, an impact map is helpful for visualizing the overall impact versus the ease of implementation.
SU‐E‐T‐91: Accuracy of Dose Calculation Algorithms for Patients Undergoing Stereotactic Ablative Radiotherapy
Authors: Tajaldeen A , Ramachandran P , Geso M 
Published: June 2015

Purpose:The purpose of this study was to investigate and quantify the variation in dose distributions in small field lung cancer radiotherapy using seven different dose calculation algorithms.Methods:The study was performed in 21 lung cancer patients who underwent Stereotactic Ablative Body Radiotherapy (SABR). Two different methods (i) Same dose coverage to the target volume (named as same dose method) (ii) Same monitor units in all algorithms (named as same monitor units) were used for studying the performance of seven different dose calculation algorithms in XiO and Eclipse treatment planning systems. The seven dose calculation algorithms include Superposition, Fast superposition, Fast Fourier Transform ( FFT) Convolution, Clarkson, Anisotropic Analytic Algorithm (AAA), Acurous XB and pencil beam (PB) algorithms. Prior to this, a phantom study was performed to assess the accuracy of these algorithms. Superposition algorithm was used as a reference algorithm in this study. The treatment plans were compared using different dosimetric parameters including conformity, heterogeneity and dose fall off index. In addition to this, the dose to critical structures like lungs, heart, oesophagus and spinal cord were also studied. Statistical analysis was performed using Prism software.Results:The mean±stdev with conformity index for Superposition, Fast superposition, Clarkson and FFT convolution algorithms were 1.29±0.13, 1.31±0.16, 2.2±0.7 and 2.17±0.59 respectively whereas for AAA, pencil beam and Acurous XB were 1.4±0.27, 1.66±0.27 and 1.35±0.24 respectively.Conclusion:Our study showed significant variations among the seven different algorithms. Superposition and AcurosXB algorithms showed similar values for most of the dosimetric parameters. Clarkson, FFT convolution and pencil beam algorithms showed large differences as compared to superposition algorithms. Based on our study, we recommend Superposition and AcurosXB algorithms as the first choice of algorithms in lung cancer radiotherapy involving small fields. However, further investigation by Monte Carlo simulation is required to confirm our results.
SU‐E‐T‐94: An Advanced Rotating Gamma Ray System for Stereotactic Radiosurgery
Authors: Ma C , Chibani O , Mora G , Li J , Chen L 
Published: June 2015

Purpose:Co‐60 beams have unique dosimetric properties that are ideally suited for cranial treatments. Co‐60 sources with cone‐shaped collimators provide conformal dose distributions allowing for ablative treatments with rapid dose falloff to spare nearby critical structures. This work investigates a novel, image‐guided, rotational Gamma ray system that provides both superior dose conformity/gradient and accurate stereotaxy for stereotactic radiosurgery (SRS).Methods:The SupeRay system (Cyber Medical Corp., China) consists of a rotating source chamber containing 30 gamma sources focusing at the isocenter with 4 collimators measuring 3, 4, 8 and 16mm in diameter. A novel switch design enables the 30 Gamma sources to be turned off at any arbitrarily selected 60° interval in order to avoid critical structures. The 3D treatment couch provides automatic treatment positioning between individual shots and the kV imaging system provides orthogonal images with a spatial resolution of 0.24mm to facilitate target localization. Monte Carlo simulations were used to compute dose distributions and compare with measurements and other Gamma ray SRS systems.Results:Monte Carlo results confirmed the SupeRay design parameters including output factors and 3D dose distributions. Its beam penumbra/dose gradient is similar to or slightly better than that of the Elekta Gamma Knife. The penumbra in the (x,y,z) direction was (7.38mm,7.38mm,3.86mm) for the 16mm collimator, (4.83mm,4.83mm,3.12mm) for the 8mm collimator, and (3.03mm,3.03mm,2.38mm) for the 4mm collimator, respectively, on the SupeRay system while it was (9.5mm,10.0mm,2.9mm), (4.3mm,4.3mm,2.9mm) and (3.2mm,3.2mm,1.9mm) for the same collimator sizes, respectively, on the Perfexion system. The kV imaging system together with a non‐invasive relocatable frame provides accurate target localization (<0.5mm) for cases requiring multiple treatment fractions.Conclusion:Because of the unique dosimetric properties of Co‐60 sources and its accurate stereotaxy/dose delivery, SupeRay is ideally suited for single and multiple‐session ablative treatments of cranial lesions.This work was partially supported by Cyber Medical Corp.
SU‐E‐T‐96: An Analysis of VMAT SBRT Lung Treatment Plans
Authors: Wilson D , James J , Wang B , Dunlap N , Woo S , Silverman C , Dragun A , El‐Ghamry M 
Published: June 2015

Purpose:To present an analysis of 218 lung sbrt treatment plans delivered using Varian Eclipse RapidArc software and delivered with Varian linear accelerators.Methods:A retrospective analysis of treatment plans generated using the Varian Eclipse PRO RapidArc VMAT optimization and AAA photon beam calculation algorithms was done for 218 plans delivered using Varian Trilogy and TrueBeam linear accelerators. Some of the patients were enrolled in the RTOG 0813 and RTOG 0915 lung protocols. All of the patients’ plans were optimized using the guidelines outlined by these protocols. The plans presented were normalized so that 95% of the PTV volume received 100% of the prescribed dose.Results:The dose co formality constraints from the RTOG protocols and the number of plans within those constraints were:Tumor dose between 60% of maximum dose and 90% of maximum: 218/218 = 100%.Volume of 105% tumor dose outside put less than 15% of the PTV volume: 218/218 = 100%.Maximum dose 2 cm away from PTV within protocol table guidelines: No minor deviation: 188/218 = 86.2%. No major deviation: 216/218 = 99.1%.Ratio of 50% dose volume to PTV volume less than R50 in protocol table: No minor deviation 148/218 = 67.9%. No major deviation: 213/218 = 97.7%.Percent of lung receiving 20 Gy less than 10% (no minor violation): 218/218 = 100%.99% of PTV receiving at least 90% of the tumor dose: 214/218 = 98.2%.Conclusion:Varian RapidArc VMAT can successfully deliver lung SBRT treatments as outlined in the RTOG 0813 and 0915 protocols. The largest deviations were seen in the R50 constraints for the larger PTV volumes.
SU‐E‐T‐97: An Analysis of Knowledge Based Planning for Stereotactic Body Radiation Therapy of the Spine
Authors: Foy J , Marsh R , Owen D , Matuszak M 
Published: June 2015

Purpose:Creating high quality SBRT treatment plans for the spine is often tedious and time consuming. In addition, the quality of treatment plans can vary greatly between treatment facilities due to inconsistencies in planning methods. This study investigates the performance of knowledge‐based planning (KBP) for spine SBRT.Methods:Treatment plans were created for 28 spine SBRT patients. Each case was planned to meet strict dose objectives and guidelines. After physician and physicist approval, the plans were added to a custom model in a KBP system (RapidPlan, Varian Eclipse v13.5). The model was then trained to be able to predict estimated DVHs and provide starting objective functions for future patients based on both generated and manual objectives. To validate the model, ten additional spine SBRT cases were planned manually as well as using the model objectives. Plans were compared based on planning time and quality (ability to meet the plan objectives, including dose metrics and conformity).Results:The average dose to the spinal cord and the cord PRV differed between the validation and control plans by <0.25% demonstrating iso‐toxicity. Six out of 10 validation plans met all dose objectives without the need for modifications, and overall, target dose coverage was increased by about 4.8%. If the validation plans did not meet the dose requirements initially, only 1–2 iterations of modifying the planning parameters were required before an acceptable plan was achieved. While manually created plans usually required 30 minutes to 3 hours to create, KBP can be used to create similar quality plans in 15–20 minutes.Conclusion:KBP for spinal tumors has shown to greatly decrease the amount of time required to achieve high quality treatment plans with minimal human intervention and could feasibly be used to standardize plan quality between institutions.Supported by Varian Medical Systems