bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐199: A Software Tool for the Efficient Correction and Analysis of IMRT QA Experimental Data Using MatriXX
Authors: Wagar M , Zygmanski P , Cormack R
Published: July 2013

Purpose: The rationale for developing this software was to address shortcomings found while using OmniPro‐I' mRT software to evaluated patient specific IMRT QA measurements taken with MatriXXEvolution 2D ion chamber array. Our software addresses three major issues. It calculates average doses within each ion chamber of the array using 3D TPS DICOM field‐by‐field doses exported as input, corrects the resulting doses to account for gantry angle dependence of Matrixx, and automates the analysis of the measured data resulting in a concise report document ideal for patient electronic medical records (EMR).Materials/Methods: The software was developed in MATLAB to improve and streamline analysis of patient‐specific IMRT QA. It compares measured Matrixx doses to average doses within each ion chamber of the array, which are computed from 3D DICOM doses exported from TPS for each field. A correction factor is applied to the TPS doses to account for angular dependence. The Data is automatically evaluated using the 2D gamma analysis, evaluating a range of passing criteria (3%,4%,5%). This software allows for user‐defined passing criteria and automated reporting of quantitative results, eliminating potential user errors. A single‐sheet report is generated displaying patient information, planar dose distributions, x‐y‐profiles, and gamma plot noting the pixel based passing criteria. The effect of misalignment in direction perpendicular to detector plane is simulated by allowing a non‐zero shift along that direction. Results: This home‐built IMRT QA analysis tool gives a clear quantitative answer based on the user defined criteria. The implementation of an angular dependence correction and the averaging over the volume of the ion chambers improves the accuracy of the analysis accounting for ion chamber size (∼5mm x 5mm x5mm) and spacing (∼7mm × 7mm) Conclusion: Though this tool does not replace the commercial software completely, it improves the accuracy of the analysis and streamlines the process.
SU‐E‐T‐201: Dosimetric Comparison of Patient Specific IMRT QA Using Varian DynaLog Files and TPS Calculations in a Phantom Geometry
Authors: Qiu Y , Kim S , Mavroidis P , Papanikolaou N , Stathakis S
Published: July 2013

Purpose: To evaluate significance of gamma index between the planned 2D doses by Eclipse treatment planning system and the calculated 2D doses based on DMLC Dynalog information for patient specific IMRT QA. Methods: DMLC (Dynamic Multi‐Leaf Collimator) of IMRT (Intensity Modulated Radio Therapy) delivery information recorded in log files during delivery. The Dynalog file includes amongst other, the beam on and off status, segment dose index, and individual leaf positions. In this study, previous treated IMRT patient plans are selected and delivered using a Varian CLINAC 600 C/D linear accelerator equipped with Millennium 120 MLC. IMRT verification plans were generated on PTW OCTAVIUS phantom using Eclipse TPS. Dynalog file data were recorded during delivery and were converted to fluence maps using an in‐house Matlab code. The fluence maps were imported to Elipse TPS and dose distributions on the OCTAVIUS phantom. PTW VeriSoft was used to compare the planned and recalculated IMRT plans. Gamma index, profiles and isodose distributions were used to evaluate the dosimetric difference. Results: The comparison of the planned and the recalculated dose distribution showed that the gamma index passing rate was 90% or greater for all plans using a 3%/3mm criteria. The analysis of the results based on the complete 3D dose distributions is under investigation. Conclusion: Our preliminary results show that the dynalog files can be an alternative method for patient specific IMRT QA. Good agreement between measurements and calculations was achieved in all cases tested and further investigation for calculations using patient geometry and for VMAT is in progress.
SU‐E‐T‐202: Statistical Analysis of Patient's Treatment Site Specific QA Using MapCHECK2 for Local Delivery Guideline
Authors: Ding X , Olszanski A
Published: July 2013

Purpose: We statistically evaluated the results of dosimetry quality assurance (DQA) measurements and derived local confidence limits for different treatment site to establish our institutional guideline for patient's treatment site specific QA procedure. Methods: 104 patients were treated using IMRT and VMAT with head and neck (H&N) cancer (16 cases,15.4%), prostate or pelvis cancer (28 cases 26.9%), breast cancer (21 cases 20.2%), lung cancer (12 cases 11.5%) and brain tumor (27 cases, 26.0%) in which all H&N patients were treated using VMAT while others were treated with IMRT. All IMRT's composite‐fields were measured with MapCHECK2 while 16 H&N VMAT plans were undertaken using MapCHECK2 with an isocentric setup holder. The Distance‐to‐Agreement (DTA) 3%3mm criteria were used to evaluate the QA plans. The mean DTA values and standard deviations were used to develop the local confidence for each treatment site. Local confidence limits (CL) were derived using concept confident limit of (100‐mean)+1.96σ. T‐test was used to compare DTA 3%/3mm between different treatment site. Results: The percentage of points passing the DTA 3%/3mm for different treatment site as follow: H&N cancer was 96.8±2.2%, Prostate or pelvis cancer was 98.0±2.6%, Lung cancer was 97.5±3.1%, Brain tumor was 98.4±2.4%, Breast cancer was 99.4±1.1%. The Results shows breast IMRT DTA passing rate is significantly higher than lung IMRT(p=0.020), prostate or pelvis IMRT(p=0.028) and H&N VMAT (p=0.00005). Brain IMRT DTA passing rate is significantly higher than H&N VMRT(p= 0.045). Confident limit for H&N site is 7.6% (92.4% passing), prostate or pelvis cancer is 7.1% (92.9% passing), Breast site is 2.8%(97.1% passing), lung cancer is 8.6% (91.4% passing)and brain tumor is 6.2% (93.8% passing). Conclusion: This study indicates that different treatment site may have different degree of intensity modulation resulting different DTA passing rate. Different local confident limit may be needed for different treatment sites or techniques.
SU‐E‐T‐207: Establishing Institution‐Specific Action Levels for EPID‐Based QA for IMRT
Authors: Gray A , Saldan A , Rosenzweig D , Meiler R , Clark D , Abu‐Aita R , Schell M , Cavanaugh D
Published: July 2013

Purpose: To establish institutionally specific action levels for quality assurance (QA) ofintensity‐modulated radiation therapy (IMRT) treatment plans based on the guidelines andstatistical principles presented by Howell et al. in 2008 for the University of Texas MD Anderson. Methods: A review of 3937 fields of 364 patients treatment plans was undertaken to findinstitutional action level values unique to this clinic. Data analysis focused on the commonlyused gamma parameter. Institutional averages and standard deviations were found formaximum gamma, average gamma, and percentage of a field's fluence area exhibiting a gammavalue greater than 1.0. Additional analysis reviewed action level dependence on disease site and EPID acquisition software version. Results: These observations were used to create action levels specific to this clinic and which were found to be substantially stricter than those recorded by Howell et al; this difference perhaps reflects institution‐specific aspects such as updated acquisition software and individual treatment planning styles. Conclusion: Results suggest that action levels for Portal Dosimetry‐based IMRT QA should beadjusted based on individual institutional experience.
SU‐E‐T‐209: Deconvolution of An Integral Film Exposure in a Cylindrical Phantom for VMAT QA
Authors: Barbiere J , Ndlovu A
Published: July 2013

Purpose: Present an algorithm that is capable of deconvoluting a single radiochromic film exposed in a cylindrical phantom into the basic control point components. Changes noted in the measured control points can be incorporated into a delivered treatment plan using a commercial treatment planning system to compare the delivered dose with the planned dose using DVH tools. Methods: A 180 degree VMAT verification plan was subdivided into control points every 5 degrees. Dose matrices for the individual control points were exported for analysis to a PC with MATLAB software. The dose in the center ring of the cylindrical phantom represents the simulated film measurement. The plan dose is equal to the sum of the control points. Mathematically, the control points are the basis vectors of thedelivered plan. The deconvolution algorithm utilizes linear optimization to first determine the coefficients of the vectors and then to check for changes in the individual control points. Changes in the control points were introduced to test the deconvolution algorithm. For development purposes only a single plane was investigated. Measurement of both the entrance and exit doses improves the accuracy and is also used to compute the control point angle. Results: (1) Measured film has superior resolution compared to electronic detectors, (2) the deconvolution algorithm can determine the individual delivered control point parameters, (3) the measured control points can be used to calculate the delivered dose distribution, and (4) the treatment planning system can be used to compare the plan and delivered dose distribution within the patient using its DVH tools. Conclusion: Deconvolution of an integral film in a cylindrical phantom for a VMAT plan represents the delivered control points that can be entered into the treatment planning system for patient specific VMAT QA utilizing DVH tools.
SU‐E‐T‐210: An Investigation for the Use of OSLDs for in Vivo Patient‐Specific Quality Assurance for Patients Requiring Bolus
Authors: Savacool M , Yaparpalvi R , Mynampati D , Chen Y , Tome W
Published: July 2013

Purpose: For treatments that require addition of bolus, dose to the skin and superficial regions must be known for adequate plan evaluation. Dose calculation inaccuracies in these regions may occur because they are in the build‐up region, as well as a Results of the IMRT/VMAT optimization algorithm ignoring the bolus during optimization. In this study, we evaluated the routine use of optically‐stimulated luminescent dosimeters (OSLDs) as a means of in vivo quality assurance for superficial dosimetry in patients requiring bolus during treatment. Methods: Landauer nanoDot OSLDs were used to perform measurements on 11 patients (total 13 sites) including head and neck, anal, groin, and breast. Treatment techniques included RapidArc, IMRT, and 3D‐CRT. All patients were treated with nominal energy 6MV. One OSLD was placed on the patient's skin, under the prescribed bolus, for one fraction. Bolus thickness was 0.5 cm. Each OSLD was read using the Landauer MicroStar reader, which operates in cw mode with a 1‐s read period, and corrected for sensitivity. Three readings were taken and the average calculated. Readings that were out of tolerance (15 percent) were repeated. OSLD readings were compared with TPS(Eclipse) calculations at a depth of 4mm (corresponding to the inherent OSLD build‐up). Results: 10 sites passed with less than 10 percent deviation (measurement accuracy of standard nanoDot). 6 Sites showed less than 3 percent deviation, 8 sites showed less than 5 percent deviation. 1 Site showed greater than 13 percent deviation. 2 sites showed greater than 25 percent deviation, and upon repetition, yielded similar results. Large deviations correlated to treatment sites with irregular surfaces (tracheotomy, skin creases). Conclusion: OSLDs are a quick and efficient way to perform in vivo quality assurance of doses in the superficial regions in patients requiring bolus for treatments. For simple geometries studied, TPS calculations show sufficient accuracy.
SU‐E‐T‐211: Development of Correction Factors for a 2D Ion Chamber Array Inserted in a Cubic and Homogeneous Phantom for VMAT Patient‐Specific QA
Authors: Clemente F , Perez‐Vara C
Published: July 2013

Purpose: Volumetric modulated arc therapy (VMAT) requires, as another kind of intensity‐modulated radiation therapy (IMRT), patient‐specific QA procedures. 2D ion chamber arrays are used to analyze and compare dose distributions. When these detectors are used in a stationary phantom, the measured dose is dependent on the angle of the beam. This work shows the development of correction factors (CFs) needed to obtain good agreement between calculated and measured dose distribution. Methods: VMAT treatments are delivered in our institution with an Elekta Synergy linac. 2D ion chamber array (MatriXX, IBA Dosimetry) is used to perform dose distribution comparisons for patient‐specific QA, inserted in a cubic and homogeneous special phantom (MultiCube, IBA Dosimetry). CFs are determined for each individual chamber in MatriXX detector by comparing measurements taken with MatriXX/MultiCube set to dose reference values calculated by our TPS (Monaco 3.1, Elekta) with the same setup. The detector has been set up to avoid irradiation through the treatment couch. Measurements consist on a set of open fields of 27×27 cm2 with gantry angles covering the range from 0° to 180° (interval of 1° between 85° y 95° and 5° for any other angle). Assuming a symmetric response, values from 180° to 360° are the same. An external gantry angle sensor has been used to match the measurements with their gantry angle. Results: CFs have been evaluated for each chamber in all gantry positions. Deviations of up to 18% and 7% are observed for gantry angles at 90° and 180°. These values must be used to correct dose measurements performed with MatriXX/MultiCube set. Conclusion: Angular dose dependency of MatriXX detector inserted on MultiCube phantom has been studied and calibrated. This calibration should be used to evaluate actual treatments as a part of patient‐specific QA procedures.
SU‐E‐T‐214: Patient‐Specific QA for HDR Brachytherapy Skin Treatments
Authors: Palaniswaamy G , Massingill B , Deb N , Mutyala S , Rangaraj D
Published: July 2013

Purpose: HDR treatments require high precision and accuracy but with current techniques and processes, there is higher probability for error. So we propose performing patient‐specific QA for HDR skin treatment plans before the first treatment to eliminate the possibility of errors on first fraction that might lead to partial treatments or treatment delays. Methods: A CT simulation is performed for skin patients before a week of their first fraction. The applicator is built at the time of simulation using HAM surface applicator. The applicator is then retained at the clinic to check the catheter orientation during treatment plan. There are several processes that are indirectly connected which increase the chance for errors that might propagate from the treatment plan to the patient's treatment. In the worst‐case scenario, it might lead to partial treatment being delivered to the patient. These errors can be avoided by performing patient‐specific QA before the first treatment which involves the following steps. 1. Catheter length measurements made independently by two personnel and verification at the treatment console.2. Performing an autoradiograph with a film affixed at the outside edge of the applicator's target area. Results: During 5 month period of treating 36 skin patients without patient‐specific QA, we had 4/36 (>10%) instances of partial treatments and delays due to incorrect catheter lengths. After implementing QA, there were 0/12 partial treatments and we also detected two instances of dwell positions activated outside target. Conclusion: By establishing the proposed QA technique, we were able to verify and eliminate the following errors: 1. Incorrect catheter lengths specified in the treatment planning system.2. Active dwell positions in an optimized treatment plan that are outside the target area.3. Unintended source obstruction errors during the first fraction.4. Possibility of delivering partial fraction due to the above specified errors.
SU‐E‐T‐220: Comparison of Two Different Setups for VMAT Patient‐Specific QA
Authors: Clemente F , Perez‐Vara C
Published: July 2013

Purpose: Patient‐specific QA methods are needed for verification of intensisty‐modulated radiation therapy (IMRT). VMAT treatment is delivered through dynamic arcs with a continuous variation of gantry speed, dose rate and MLC position. 2D ion chamber arrays can be used to compare dose distributions as a part of patient‐specific QA procedure in VMAT technique. This work shows the gamma tests results for two different setups using a 2D array in the verification of VMAT plans. Methods: VMAT treatments are delivered with an Elekta Synergy linac. A 2D ion chamber array (MatriXX Evolution, IBA Dosimetry) is used to measure and evaluate dose distributions calculated by the TPS (Monaco 3.1, Elekta). Detector is calibrated to perform absolute dose measurements. Two different setups are presented as a part of QA verification procedure. First setup mounts the MatriXX detector inserted in a dedicated gantry holder with SSD of 100 cm. Dose measurements are compared with calculations collapsed to 0° because the detector is attached to the gantry during the gantry arcing. Second setup consists on MatriXX inserted in a cubic and homogeneous phantom (MultiCube, IBA Dosimetry). Coronal and sagital dose planes are measured. A set of correction factors are needed in order to correct dose in this arrangement. The sampling time is 150 ms. 111 patients have been verified with previous setups with a gamma index criteria of 3%/3mm. Results: Mean value for % points meeting gamma test criteria is (99.02±1.14)% in the first setup. The worst value is 92.9%. Results for second setup are (99.05±0.67)% for the coronal planes and (98.19±1.10)% for the sagital planes. The worst value is 95.22% for a sagital plane. Conclusion: The suitability of MatriXX detector for patient‐specific QA in VMAT techniques has been tested for two different setups with excellent agreement between calculation and measurement.
SU‐E‐T‐221: Evaluation of Quality Assurance for Rapid Arc Treatments Using EPIQA Software
Authors: Karunakaran Kaviarasu , Raj Arunai Nambi , Murthy K Krishna , Babu Ananda Giri , Prasad B Durga
Published: July 2013

Purpose: To evaluate the patient specific quality assurance of Rapid Arc treatments using EPID and EpiQA software. Methods: Eclipse TPS is used for the creation and calculation of patient and verification plans. The treatments were delivered on aS1000 EPID attached to the Varian Clinac iX Linear Accelerator. EpiQA software supplied by the EPIdos is used for the analysis of calculated and measured dose maps. In this retrospective study 75 Rapidarc treatment plans consisting of 150 arc fields were considered from three different sites of 25 plans each namely head & neck, pelvis and brain. All plans were treated with 6 MV photons with two arcs and QA measurements acquired with Portal Vision aS1000 and analyzed by EpiQA software. To evaluate the QA results, we used Gamma agreement Index (GAI). GAI represents the percentage of the field area with gamma value greater than 1.0 to the gamma criteria of 3mm DTA and 3% Dose Difference. Results: Calculated mean values and standard deviations are 1.95 ± 1.25, 2.44 ± 1.35 and 2.69 ± 1.13 for Brain, Pelvis and Head & Neck respectively. It is noted that all the results were well within 95% of pass criteria of gamma agreement index. We found that the mean GAI values for head & neck and pelvis plans are greater than that of brain plans. This deviation may be attributed due to the variations in the geometry of the field, volume of irradiation, depth of penetration and complexity of planning objectives (more critical organs) etc. However further data of measurements is needed for further evaluation. Conclusion: Since all the plans were passed the GAI and the results are comparable with phantom studies, we conclude that the portal dosimetry can be used conveniently to carryout patient specific QA measurements of Rapidarc plans.
SU‐E‐T‐223: Dose Distribution Verification in a Moving Target Using Moving Platform and 2D Diode Array
Authors: Adamczyk S , Adamczyk M , Piotrowski T
Published: July 2013

Purpose: The aim of this study was to carry out a dosimetric verification of statically planned sliding window IMRT for respiratory‐like moving targets using 2D diode array. Methods: Ten 5‐field IMRT plans for mobile lung tumors were created. The target volumes were delineated on the free breathing CT scans. Three tumor motion trajectories have been simulated, with the largest movement amplitude in cranio‐caudal direction of 4 mm, 6 mm and 8 mm, and breathing periods of 4 s. The breathing motion was simulated using the motion kernels derived from the literature data. The moving platform (MotionSim XY/4D‐Sun Nuclear) with the diode array MapCHECK 2 (Sun Nuclear) was used.The evaluation was based on the Gamma analysis (3mm, 3%). The scoring parameter was the percentage of the field area (defined by the jaws plus 1 cm margin) resulting with γ < 1 (%score). Results: The average score for static target equals 99.43% (γ=0.330). When the breathing trajectory with maximum amplitude of 4 mm was applied we have found an average score of 97.81% (γ=0.386), which fitted well to the plan acceptance criteria (%score > 95% and average gamma < 0.6). For 6 mm amplitude average score was 94.18% (γ=0.468). However when 8 mm movement of target was applied we have observed significant change in analysed parameters: average score and γ of 83.68% and 0.572, respectively. Conclusion: This study showed that statically planned nonuniform dose distribution could cause the tumor under‐dosage due to interplay effect. It is therefore crucial to verify amplitude of individual patient breathing motion trajectory and take it into account by increased margins.For maximal amplitudes of breathing trajectory below 4 mm the disagreement between planned and delivered dose distribution can be neglected. Whereas respiratory motion with amplitude above 6 mm leads to significant changes in delivered dose distribution.
SU‐E‐T‐241: Achieving Optimal Treatment Workflow Configurations in Multi‐Room Proton Centers Via Monte Carlo Simulation
Authors: Zhang H , Prado K , Mehta M , Regine W , D' Souza W
Published: July 2013

Purpose: To determine the optimal workflow configuration in a multi‐room proton center using Monte Carlo simulation. Methods: The patient's likely path through a four‐room proton center was identified. A simulation describing the sequence of events that each patient would go through within the center was then constructed. The proton center layout was modeled with two “loading rooms” that would service each treatment room. The “loading rooms” were equipped with either setup lasers alone or lasers and CT simulators. It provided either gross patient alignment or fine patient alignment. The duration of each step (input to the Monte Carlo simulation) was randomly drawn from analytical distributions based on clinical estimates of means and variances. Patient flow within the facility included checking in, immobilization and positioning, transit to gantry room, treatment delivery, and discharge. Patient positioning time consisted of laser time and different imaging time. Other parameters modeled stochastically included cancer case mix, cyclotron switching time between gantry rooms, gantry rotation time and treatment fields. We simulated 100 working days and each day consisted of 14 hours (two shifts). Decision variables were patient arrival rate, in‐room imaging or out‐of‐room imaging. We examined our results by evaluating patient throughput, patient wait times and cyclotron and treatment room utilization. Results: Both out‐of‐room setups (gross patient alignment or fine patient alignment) resulted in high utilization of cyclotron (93% and 98%) when comparing to in‐room setup (83%). For the two out‐of‐room setups, there was a trade‐off between cyclotron utilization and treatment room utilization. Although fine patient alignment increased the patient throughput by 14% comparing to gross patient alignment, it was not cost effective to equip all eight loading rooms with CT simulators. Conclusion: The impact of out‐of‐room imaging was significant in increasing patient throughput and cyclotron utilization with either gross or fine patient alignment.
SU‐E‐T‐258: Commissioning of a Commercial Treatment Planning System Verification Software Package
Authors: Nelson C , Davidson S , Mason B , Kirsner S
Published: July 2013

Purpose: A commercial software package (Mobius3d, Mobius Medical Systems) was acquired for use as an additional QA tool of our current treatment planning system (TPS). The system reads DICOM RT files generated from the TPS and performs an independent dose calculation for comparison to the TPS. This work summarizes our methods for commissioning a system such as this. Methods: Preliminary comparisons of our TPS and measured data to the QA softwares beam model were done by comparing PDDs and profiles with field sizes ranging from 4&×;4 to 40×40. Static fields and step and shoot IMRT plans were generated on a homogeneous medium for comparisons of 6x photons. For the homogeneous IMRT cases, ion chamber measurements were compared to the dose calculated in the TPS and in the verification system. Results: Analysis of PDD data showed that the average PDD error of the verification model (relative to the TPS) was 0.5% compared to our measured data which was 0.1%. The average infield profile error over all field sizes and depths of the TPS to our reference measured data set was 0.3% whereas the verification system relative to the TPS was 1.7%. Simple beam geometries between the TPS and the verification system were 0.8% difference on average. Ion chamber measurements on a homogeneous phantom differed from the TPS on average by 0.5% whereas the verification system was 2%. The results indicate an adjustment in the beam model of the verification system is needed to better match our current beam model/measured data. Conclusion: Preliminary commissioning results of a commercial QA dose algorithm were completed. Adjustment of the verification softwares beam model is necessary before further testing is done. Further analysis is needed to fully investigate this system to be used clinically as a QA tool of our current TPS. “Evaluation equipment provided by Mobius Medical Systems, LP”
SU‐E‐T‐338: Calculation of Dose Distributions From 106 Ruthenium COC‐Type Eye Applicator
Authors: Futaguchi M , Haga A , Sakumi A , Okamoto H , Hamada M , Fuse M , Abe Y , Murakami N , Itami J , Nakagawa K
Published: July 2013

Purpose: In the treatment of retinoblastoma, 106Ru brachytherapy is one of the important methods to control the tumor with preserving eye function. So far, we had some clinical experiences that the tumor on optic disc was effectively shrunk by using the COC‐type applicator (BEBIG), which has a notch. In this study, the dose distribution was evaluated by Monte Carlo simulation to investigate a dose to the notched area of COC applicator. Methods: The model of the COC‐type applicator was created and registered in EGS5 Monte Carlo simulation code. Here, the applicator thickness was 1mm including 0.1mm of the silver radiation window and 0.2 mm of radioactive layer. The notched area was also reproduced from the measurement of actual geometry. The dose to the notched area was represented with the polar coordinate, in which the two‐dimensional relative dose distributions of the spherical shells with 0.2 mm thickness at distances of 0.1, 1.3, and 2.5 mm from the surface were calculated. For comparison, the dose profile was also calculated by the Plaque simulator (BEBIG). Results: The Monte Carlo Result showed that the scattered electron largely contributed to the dose to the notched area. This contribution became dominant as the distance from the surface was larger. The calculation Result of the Plaque simulator was significantly different from that of the Monte Carlo simulation around the notched area of the applicator. Conclusion: The dose distribution with the COC‐type applicator could be quantified by the Monte Carlo Conclusion: The dose distribution with the COC‐type applicator could be quantified by the Monte Carlo calculation. It was found that the notched area of COC‐type applicator was irradiated sufficiently by the scattered electron. The Plaque simulator could not reproduce the dose distribution around the notched area.
SU‐E‐T‐355: A Novel Ophthalmic Applicator Design for Brachytherapy for Conjunctival Melanoma
Authors: Lee C , Demirci H , Hayman J
Published: July 2013

Purpose: To design and construct a novel ophthalmic brachytherapy applicator for the treatment of conjunctival melanoma using I‐125 radioactive seed sources to overcome the dosimetric limitations of the commonly used standard Collaborative Ocular Melanoma Study (COMS) plaques. Methods: A commercially available polymethylmethacrylate conformer (Gulden Ophtalmics, Elkins Park, PA) was employed to hold a total of 12 low dose I‐125 seeds (model IAI‐125A, IsoAid, LLC, Port Richey, FL) distributed along the periphery of the conformer. Three dimensional dose distribution was calculated using the Plaque Simulator software (EyePhysics, LLC, Los Alamitos, CA) to optimize seed distribution pattern. The AAPM TG‐43 dose calculation formulism was utilized within the software. Results: The seed distribution pattern was designed in a way that dose would be delivered to the conjunctival tissue,while limiting the dose to the cornea and lens. Once the design was finalized, each slot for the seed was fabricated using a 6‐axis computer numerical control (CNC) machine available at our institution. The slots were milled into the convex side of the conformer to minimize any patient discomfort and to protect the cornea from direct contact with the seeds. Conclusion: The difficulty of treating conjunctival melanomas with COMS eyeplaques due to its unique anatomical distribution called for a custom design brachytherapy applicator. The applicator designed in the current study can effectively deliver radiation dose to affected area while minimizing the dose to the centrally located unaffected tissues.
SU‐E‐T‐359: Patients Could (and Should) Be Treated in An Upright Position
Authors: Court L , Yang J , Fullen D , Han N , Ko J , Mason S , Nguyen K , Stein S , Fave X , Hsieh M , Kuruvila S , Hillebrandt E , Palmer J , Beadle B , Dabaja B , Skinner H , Ibbott G , Balter P
Published: July 2013

Purpose: Treating patients in an upright (seated) position has several potential advantages including increased lung volume/reduced respiratory motion (lung patients) giving an improved lung DVH, moving other healthy tissue away from the treatment beams (e.g. breast for Hodgkins lymphoma patients), and improved comfort (H&N patients with excess mucus secretion, patients with compromised lung function, etc.). We report on efforts to develop the tools/techniques to add upright treatments to the modern radiotherapy armory. Methods: The following steps have been taken towards treating patients in an upright position: (1) A novel MRI scanner that allows scans to be taken at any angle between vertical and horizontal positions was used to take volume scans and sagittal movies of 5 volunteers in vertical and supine positions. Lung volumes and motion were compared. (2) An innovative treatment chair and immobilization approach has been prototyped. The chair attaches to the treatment couch, allowing full use of the LINACs on‐board imaging and remote motion functions. (3) kV cone‐beam CT images have been acquired of upright phantoms using the Truebeam with the gantry at 0degrees and rotating the couch instead of the gantry. (4) Treatment planning studies have been completed for H&N and thoracic treatments. Results: (1) Lung volume is increased by 6–53% and motion reduced by 1‐4mm, when patients are positioned in an upright position. (2) The chair has good comfort and immobilization. End‐of‐couch weight‐constraint is sufficient with the TrueBeam couch, but limits use for older couches. (3) Upright CBCTs are possible, although work is needed to improve the image quality. (4) We have quantified gantry/patient collision risks, and understand the gantry/couch angle combinations that will be used for treatment. Conclusion: Good progress has been made in developing the techniques/tools to treat patients in an upright position. Partially funded by Varian Medical Systems
SU‐E‐T‐377: Evaluation and Implementation of An IMRT Quality Assurance Procedure to Include Patient‐Specific Volumetric Dose Analysis
Authors: Mathews B , Grant E , Maricle S
Published: July 2013

Purpose: he purpose of this study is to evaluate and implement a digital IMRT quality assurance (QA) procedure for patient‐specific volumetric dose using commercially available products. Dose distributions generated from a treatment planning system (TPS) were delivered and analyzed with dose‐volume‐histogram (DVH) analysis software. Methods: The MapCheck2 device along with 3DVH (Sun Nuclear, Melbourne, FL) software was studied for IMRT QA capabilities. All manufacturer specifications were followed in order to properly set up the diode array device for accurate absolute dose measurements. Planar dose maps were generated by the Pinnacle3 TPS (Philips Medical Systems, Andover, MA) for field‐by‐field IMRT QA analysis. Also exported from patient plans were RT dose, RT plan, RT structure, and CT data DICOM files. Dose delivery was done using a step‐and‐shoot, en‐face technique onto the MapCheck2 device. After measured‐vs‐calculated planar dose analysis for each beam, a planned‐dose‐perturbation (PDP™) file was generated. This PDP file allows the software to manipulate the TPS‐calculated dose distributions to include actual measured dose differences from a phantom onto a patient CT‐dataset. These dose perturbations are then able to be observed through differences of a TPS‐calculated DVH and a measured‐DVH within the 3DVH software. Simple tests were performed to assess MapCheck2 performance and 3DVH sensitivity to errors. Results: All planar dose measurements in this study have met the clinical tolerance of 3% absolute dose/3mm gamma analysis. For volumetric analysis, the 3D results comparing planned‐vs‐delivered matching doses (gamma criterion of 3%/3mm) were 99.3% and 98.2% for a rectum and prostate plan, respectively. Measurements with introduction of intentional errors produced reasonable results when analyzing dose to critical structures with DVHs. Conclusion: The implementation of a digital QA procedure will facilitate a more efficient workflow for physicists with the added benefit of a patient‐specific volumetric dose analysis for physicians.
SU‐E‐T‐402: Comparison of Two Methods for Minimizing the Effect of Delayed Charge On the Dose Delivered with a Synchrotron Based Discrete Spot Scanning Proton Beam
Authors: Whitaker T , Beltran C , Remmes N , Kruse J , Bues M , Tryggestad E , Tasson A , Herman M
Published: July 2013

Purpose: This study compares two methods for minimizing the effect of delayed charge on the dose delivered with a discrete‐spot‐scanning‐proton beam. Delayed charge (DC) is the charge received after the planned MU are delivered. Methods: The delivery of phantom and patient were simulated by applying normally distributed values for DC, with a mean of 0.001(SD 0.00025) MU, to each spot. Two correction methods (CM1, CM2) were used account for the DC. CM1 accounts for the DC by setting the beam monitor based on the cumulative received MU. CM2 reduces the beam monitor setting by a predicted value for the DC in addition to CM1. Each fraction was simulated and then recomputed in the treatment planning system. The dose difference between the original plan and the simulated treatment was evaluated. Both methods were tested while varying the dose per fraction from 0.5 to 2 Gy and the fractions per plan from 1 to 25. Results: While varying the dose per fraction, the maximum dose difference was 0.37–0.39 Gy and 0.03–0.05 Gy for CM1 and CM2 respectively. While changing the total number of fractions, the maximum dose difference grew at a rate of 0.015 and 0.0018 Gy per fraction for CM1 and CM2 respectively. For CM1, the maximum dose difference corresponded to the first spot in each layer. For CM2, dose variations were only related to the variation in DC. CM1 and CM2 showed the same characteristics for each beam in the patient plans. The area of excess dose for each beam overlapped in the patients. Conclusion: CM1 did not minimize DC effects for the first spot delivered in a layer. CM2 minimized the effect of the DC for all spots. DC effects and dose per fraction are not correlated. DC effects are proportional to the number of fractions and beams.
SU‐E‐T‐413: Dosimetric Evaluation and Clinical Implementation of IPlan Monte Carlo Algorithm For Lung Stereotactic Ablative Radiotherapy (SABR)
Authors: Badkul R , Pokhrel D , Jiang H , Wang F , Kumar P
Published: July 2013

Purpose: To evaluate, validate and compare dosimetric accuracy of commercially available iPlan Monte‐Carlo(MC) dose algorithm for lung‐SABR. Due to short comings of Pencil‐Beam(PB) algorithm in regions of tissue inhomogeneity and advent of faster computing environment, ability to use more accurate MC based dose calculation algorithms is becoming more of a reality. This study presents a comparative analysis of dose calculations with 6MV using iPlan PB and MC algorithms with measured data utilizing lung anthropomorphic phantom.Materials & Methods: For treatment planning and dose measurement purposes a QUASAR™ phantom with lung inserts and Ion‐Chamber drills was utilized. Three different PTVs were drawn in phantom; two were in lungs and one in homogeneous region in midline of phantom. SABR planning were performed using three different techniques: DynamicArc, ConformalBeams and IMRT for each PTV. For planning purposes NovalisTx with HDMLC, 6MVSRS were used. Three different Ion‐Chambers; 0.6cc, CC01 and CC13 were utilized to measure doses. PTV‐maximum, PTV‐minimum, PTV‐mean doses and Ion‐Chamber mean doses were collected from plans which were calculated using PB‐corrected, PB‐uncorrected and MC. Results: Agreement between MC and Ion‐Chamber measurement were −1.1–1.64% (mean0.6%), 0.5–1.55% (mean1.17%) and −2.7−0.4% (mean‐0.55%) for DynamicArc, ConformalBeams and IMRT respectively. Deviations between PB‐corrected and measured values were 1.81–6.83% (mean4.4%), 2.73–8.63% (mean5.13%) and −1.28−1.24% (mean0.13%) for DynamicArc, ConformalBeams and IMRT respectively. Deviations between PB‐uncorrected and measured values were −2.36– −3.8% (mean‐2.96%), −1.88–− 3.04% (mean‐2.46%) and −3.88–−7.1% (mean‐5.29%) for DynamicArc, ConformalBeams and IMRT respectively. The mean deviations for all techniques were 0.4%,3.22%,−1.93% for MC, PB‐corrected and PB‐uncorrected respectively. PTV dose comparison between different algorithms has also been analyzed. Conclusions: This phantom study shows excellent agreement between doses calculated using iPlan Monte‐Carlo versus measurements for 6MV beam in lung equivalent material. MC algorithm not only predicts accurate dose at isocenter but also at borders of tumors where Pencil‐Beam overestimates the doses.
SU‐E‐T‐419: To Validate Dose Delivery in Static Field Stereotactic Body Radiation Therapy (SBRT) of Lung Cancer
Authors: Joshi CP , Garcia L , Olding T , Alexander K , Owen T , Kerr A
Published: July 2013

Purpose: To validate dose delivery in static field stereotactic body radiation therapy (SBRT) of lung cancerMethods: An Exradin A16 0.007cc ion chamber, EBT3 Gafchromic film and Fricke‐Xylenol‐Orange‐Gelatin (FXG) gel dose measurements were performed providing measurements for point, planar and volumetric dose comparisons. CT images (GE Lightspeed RT16 CTSIM) of a Quasar respiratory motion phantom (Modus Medical) with stationary and moving inserts were acquired. Respiratory motion was recorded using a Varian RPM system. Standard cedar inserts with 3cm diameter solid tumors for the ion chamber and film, and an in‐house fabricated custom insert for FXG gel were used. Internal target volumes (ITV) were obtained from 4DCT scans. A typical 15BPM, 20mm amplitude peak‐to‐peak breathing pattern for ion chamber; and sinusoidal 15BPM/10mm respiratory cycles for film and gel dosimetry were used. Nine‐field SBRT plans using 6MV beams were calculated on Eclipse treatment planning system (v10.0; Varian). CBCT scans were used to reproduce the treatment setup; and irradiations were performed on a Trilogy (Varian) linear accelerator. Percentage dose difference and gamma analysis for 3% dose difference and 3mm distance‐to‐agreement were used to compare measured and calculated dose distributions. Results: Measured vs. calculated point dose differences (at a point inside the ITV) for the moving insert geometry were −2.1%, −1.5% and −0.5% for the ion chamber, film and gel measurements, respectively. The planar and volumetric gamma analysis of measured and calculated dose distributions for moving insert geometry showed 99.9% agreements for both EBT3 film and FXG gel dosimetry. Similar comparisons for a stationary insert geometry showed 100% and 98.5% agreements for film and gel measurements, respectively. Conclusion: A consistent level of agreement observed between measured and calculated doses for the point, planar and volumetric dose measurements validates the lung SBRT dose delivery. Research funding support provided by the Canadian Institutes of Health Research (CIHR)
SU‐E‐T‐434: A Comparison Between Cyberknife‐Based and LINAC‐Based Fiducial‐Less Stereotactic Body Radiotherapy of Lung Lesions Without Respiratory Gating Or Tracking
Authors: Monterroso M , Wang Z , Arsenault D , Amestoy W
Published: July 2013

Purpose: To benchmark the tracking accuracy of Accuray Cyberknife (CK) newly released Lung Optimized Treatment (LOT) tracking algorithm in 0‐View mode and investigate the dosimetric differences of lung Stereotactic Body Radiotherapy (SBRT) based on internal target volume (ITV) using Cyberknife and LINAC. Methods: CT scans at normal inspiration and normal expiration of CIRIS thorax motion phantom were fused and an ITV was created. A 5mm expansion around the ITV resulted in the planning target volume (PTV). Two individual plans were generated in Accuray MultiPlan using LOT 0‐View technique, with two tracking distances (3.9cm and 7.1cm) from the target. Kodak EBT Gafchromic film, carefully marked to identify the target volume, was inserted in the moving target of the phantom during delivery. H‐D calibration of the film was performed for absolute dosimetry purposes. An in‐house program processed the scanned films after delivery to perform a dosimetric comparison between plan and treatment and verify tracking accuracy. Also, a LINAC‐based plan (Eclipse) and CK‐based plan (Multiplan) for the same PTV were generated to compare the two systems in the planning stage. Results: The film dosimetric results indicate that LOT algorithm in 0‐View mode is accurate. Good target coverage was achieved in both CK‐based and LINAC‐based plans: 96% and 98%, respectively. Critical structure doses for CK‐based and LINAC‐based plans, respectively, were: total lung V20/V5 9.2%/37.3% and 7.5%/21.1%, and maximum cord dose 9.8Gy and 11.14Gy. Conclusion: Current results show LINAC‐based plans are superior to CK‐based plans, achieving lower lung integral dose with minor differences in cord dose and target coverage, and having added advantages of faster delivery and confidence during setup with lesion visualization using cone beam CT (CBCT). More work will be done to examine if CK‐based plans are advantageous when treating more complex cases, when no fiducial placement and no respiratory tracking is desired.
SU‐E‐T‐437: Dosimetric Effect of Uncorrected Rotations in Lung SBRT with Stereotactic Imaging Guidance
Authors: Zhuang T , Markovich A , Xia P
Published: July 2013

Purpose: The stereoscopic imaging guidance can detect three translational and three rotational corrections for the treatment setup in lung SBRT. The rotational corrections may not be performed if a 6‐degree treatment table is not available. We aim to investigate the dosimetric effect of uncorrected rotations for Lung SBRT. Methods: Twelve patients with NSCLC who received SBRT were selected for this study. To simulate uncorrected rotations, the planning CT and contours were rotated around the iso‐center by 1°, 2°, 3°, 4°, 5° in all three axes. For each patient, the initial plan was then applied to the rtated CT and contours, and the dose to the rotated CT was recalculated using a Monde Carlo dose calculation method. The ratio of D1, D95 and D99 of the PTV between plans on the original and rotated CT were computed. Results: The ratios of D95 for different rotations were: 100.0±0.6% (1°), 99.6±0.7% (2°), 99.4±1.0% (3°), 98.7±2.4% (4°), 98.6±1.0% (5°). The ratios of D1 were: 99.8±0.7% (1°), 99.6±0.8% (2°), 99.6±0.7% (3°), 99.5±1.0% (4°), 99.4±1.0% (5°). The ratios of D99 were: 99.0±1.1% (1°), 98.7±1.5% (2°), 98.1±2.2% (3°), 96.2±4.8% (4°), 96.0±4.4% (5°). Compared to the dose distribution in the original plans, less than 1% reduction in D95 of the PTV was observed if the uncorrected rotations were less than 3°. D1 of the PTV was less than 1% for uncorrected rotations up to 5°. D99 of the PTV exceeded 4% for uncorrected rotation greater than 4°. Conclusion: The rotation of less than 3° in all directions has negligible dose effects in Lung SBRT under stereoscopic image guidance.
SU‐E‐T‐450: Dose Perturbation of Spinal Metal Implants in Proton Beam Therapy
Authors: Jia Y , Zhao L , Cheng C , McDonald M , Das I
Published: July 2013

Purpose: To investigate the effect of dose perturbations for different spinal metallic screws in proton beam therapy. Methods: A 5.5mm (diameter) × 45mm (length) stainless steel (SS) screw and a 5.5mm × 35mm titanium (Ti) screw used for spinal fixation were CT‐scanned in a small water phantom. The CT data was processed with a metal artifact reduction (MAR) software. Two treatment plans were generated using Eclipse treatment planning system (TPS) for each metal screw with a proton beam parallel and perpendicular to the longitudinal axis of the metal, respectively. The calculated dose profiles were compared with measured ion chamber and EBT2 films results. Results: With the perpendicular setup, the measured dose immediately downstream from the screw exhibited dose enhancement up to 12% and 8% for SS and Ti respectively, but such dose perturbation was not observed outside the lateral shadow of the screws. The TPS showed 5% and 2% dose reductions immediately at the interface for the SS and Ti screws respectively and up to 9% dose enhancements within 1cm outside of the lateral shadow of the screws. The measured dose enhancement was only observed within 5mm from the interface along the beam path. At deeper depths, the lateral dose profiles appeared to be similar between the measurement and TPS, with dose reduction in the screw shadow region and dose enhancement within 1–2cm outside of the lateral edge of the metals. For the parallel setup, no significant dose perturbation was detected at lateral distance beyond 3 mm away from both screws. Conclusion: Streaking artifacts in CT images are significantly reduced with MAR but significant dose discrepancies between measurements and TPS in close proximity of the high‐Z inhomogeneities are clearly visible. Dose enhancement effect is not correctly modeled by TPS, thus extra caution should be given for dosimetry with metallic implants.