bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐747: The Use of the EQD2 Formalism and Repair Estimates in the Re‐Irradiation Setting and Correlation with Patient Follow‐Up Data
Authors: Price R , Meyer J , Horwitz E , Ma C 
Published: June 2015

Purpose:Medical advances have resulted in cancer patients living longer as evidenced by the number of patients seen for possible re‐irradiation. Original normal tissue dose volume constraints remain in the re‐irradiation setting to minimize normal tissue toxicity. This work correlates estimates of equivalent dose and repair with sequelae.Methods:CNS and GI tract re‐irradiation patient follow‐up records (including imaging studies) were reviewed with side effects correlated with the calculated EQD2 and repair estimates.Results:Follow‐up records for 16 re‐irradiation patients with potential overlap to the spinal cord were analyzed. The mean time interval between 1st and last courses was 76.6 months. Three patients underwent a 3rd course of radiotherapy with a mean time interval between 2nd and final courses of 19.7 months. The mean values for assumed repair were 18.8% and 8.3%, respectively. The calculated total EQD2 doses were 48.09Gy and 50.98Gy with and without repair. At a mean follow‐up time of 5.0 months, 6 patients were deceased and no records indicate radiation related neurological deficits. The records for 11 patients with potential overlap to the bowel were also analyzed. The mean time interval between 1st and last courses was 105.9 months. The mean value for assumed repair was 15.9%. The calculated total EQD2 doses were 64.96Gy and 70.80Gy with and without repair. At a mean follow‐up time of 4.9 months, 6 patients were deceased, one having a potential enteric fistulization of the bladder. Clinical review of the case determined that the fistula was caused by tumor progression and not a side effect of radiotherapy treatments.Conclusion:Application of the EQD2 method in the re‐irradiation setting using conservative estimates of repair is presented. Adhering to accepted dose volume limits following this application is demonstrated to be safe through empirical records as limited by this small patient cohort and short follow‐up.
SU‐E‐T‐748: Theoretical Investigation On Using High Energy Proton Beam for Total‐Body‐Irradiation
Authors: Zhang M , Zou J , Chen T , Yue N 
Published: June 2015

Purpose:The broad‐slow‐rising entrance dose region proximal to the Bragg peak made by a mono‐energetic proton beam could potentially be used for total body irradiation (TBI). Due to the quasi‐uniform dose deposition, customized thickness compensation may not be required to deliver a uniform dose to patients with varied thickness. We investigated the possibility, efficacy, and hardware requirement to use such proton beam for TBI.Methods:A wedge shaped water phantom with thickness varying from 2 cm to 40 cm was designed to mimic a patient. Geant4 based Monte Carlo code was used to simulate broad mono‐energetic proton beams with energy ranging from 250 MeV to 300 MeV radiating the phantom. A 6 MV photon with 1 cm water equivalent build‐up used for conventional TBI was also calculated. A paired‐opposing beam arrangement with no thickness compensation was used to generate TBI plans for all beam energies. Dose from all particles were scored on a grid size of 2 mm3. Dose uniformity across the phantom was calculated to evaluate the plan. The field size limit and the dose uniformity of Mevion S250 proton system was examined by using radiochromic films placed at extended treatment distance with the open large applicator and 90° gantry angle.Results:To achieve a maximum ± 7.5% dose variation, the largest patient thickness variation allowed for 250 MeV, 275 MeV, and 300 MeV proton beams were 27.0 cm, 34.9 cm and 36.7 cm. The value for 6 MV photon beam was only 8.0 cm to achieve the same dose variation. With open gantry, Mevion S250 system allows 5 m source‐to‐surface distance producing an expected 70 cm2 field size.Conclusion:Energetic proton beam can potentially be used to deliver TBI. Treatment planning and delivery would be much simple since no thickness compensation is required to achieve a uniform dose distribution.
SU‐E‐T‐749: Thorough Calibration of MOSFET Dosimeters
Authors: Plenkovich D , Thomas J 
Published: June 2015

Purpose:To improve the accuracy of the MOSFET calibration procedure by performing the measurement several times and calculating the average value of the calibration factor for various photon and electron energies.Methods:The output of three photon and six electron beams of Varian Trilogy linear accelerator SN 5878 was calibrated. Five reinforced standard sensitivity MOSFET dosimeters were placed in the calibration jig and connected to the Reader Module. As the backscatter material was used 7 cm of Virtual Water. The MOSFET dosimeters were covered with 1.5 cm thick bolus for the regular and SRS 6 MV beams, 3 cm bolus for 15 MV beam, 1.5 cm bolus for 6 MeV electron beam, and 2 cm bolus for the electron energies of 9, 12, 15, 18, and 22 MeV. The dosimeters were exposed to 100 MU, and the calibration factor was determined using the mobileMOSFET software. To improve the accuracy of calibration, this procedure was repeated ten times and the calibration factors were averaged.Results:As the number of calibrations was increasing the variability of calibration factors of different dosimeters was decreasing. After ten calibrations, the calibration factors for all five dosimeters were within 1% of one another for all energies, except 6 MV SRS photons and 6 MeV electrons, for which the variability was 2%.Conclusions:The described process results in calibration factors which are almost independent of modality or energy. Once calibrated, the dosimeters may be used for in‐vivo dosimetry or for daily verification of the beam output. Measurement of the radiation dose under bolus and scatter to the eye are examples of frequent use of calibrated MOSFET dosimeters. The calibration factor determined for full build‐up is used under these circumstances. To the best of our knowledge, such thorough procedure for calibrating MOSFET dosimeters has not been reported previously.Best Medical Canada provided MOSFET dosimeters for this project.
SU‐E‐T‐750: Three Dimensional in Silico Study of Brachytherapy Application with In‐Situ Dose‐Painting Administered Via Gold‐Nanoparticle Eluters
Authors: Sinha N , Cifter G , Ngwa W 
Published: June 2015

Purpose:Brachytherapy Application with in‐situ Dose‐painting Administered via Gold‐Nanoparticle Eluters (BANDAGE) has been proposed as a new therapeutic strategy for radiation boosting of high‐risk prostate tumor subvolume while minimizing dose to neighboring organs‐at‐risk. In a previous study the one‐dimensional dose‐painting with gold nanoparticles (GNP) released from GNP‐loaded brachytherapy spacers was investigated. The current study investigates BANDAGE in three‐dimensions.Methods:To simulate GNPs transport in prostrate tumors, a three dimensional, cylindrically symmetric transport model was generated using a finite element method (FEM). A mathematical model of Gold nanoparticle (GNPs) transport provides a useful strategy to optimize potential treatment planning for BANDAGE. Here, treatment of tumors with a radius of 2.5 cm was simulated in 3‐D. This simulation phase considered one gold based cylindrical spacer (GBS of size 5mm × 0.8 mm) introduced at the center of the spherical tumor with initial concentration of 100 mg/g or 508 mol/m3 of GNP. Finite element mesh is used to stimulate the GNP transport. Gold concentrations within the tumor were obtained using a 3‐D FEM solution implemented by COMSOL.Results:The analysis shows the spread of the GNPs through‐out the tumor with the increase of concentration towards the periphery with time. The analysis also shows the concentration profiles and corresponding dose enhancement factors (dose boost factor) as a function of GNP size.Conclusion:This study demonstrates the use of computational modeling and optimal parameter estimation to predict local GNPs from central implant as a function of x, y and z axis . Such a study provides a useful reference for ongoing translational studies for the BANDAGE approach
SU‐E‐T‐751: Three‐Component Kinetic Model of Tumor Growth and Radiation Response for Stereotactic Radiosurgery
Authors: Watanabe Y , Dahlman E , Leder K , Hui S 
Published: June 2015

Purpose:To develop and study a kinetic model of tumor growth and its response to stereotactic radiosurgery (SRS) by assuming that the cells in irradiated tumor volume were made of three types.Methods:A set of ordinary differential equations (ODEs) were derived for three types of cells and a tumor growth rate. It is assumed that the cells were composed of actively proliferating cells, lethally damaged‐dividing cells, and non‐dividing cells. We modeled the tumor volume growth with a time‐dependent growth rate to simulate the saturation of growth. After SRS, the proliferating cells were permanently damaged and converted to the lethally damaged cells. The amount of damaged cells were estimated by the LQ‐model. The damaged cells gradually stopped dividing/proliferating and died with a constant rate. The dead cells were cleared from their original location with a constant rate. The total tumor volume was the sum of the three components. The ODEs were numerically solved with appropriate initial conditions for a given dosage. The proposed model was used to model an animal experiment, for which the temporal change of a rhabdomyosarcoma tumor volume grown in a rat was measured with time resolution sufficient to test the model.Results:To fit the model to the experimental data, the following characteristics were needed with the model parameters. The α‐value in the LQ‐model was smaller than the commonly used value; furthermore, it decreased with increasing dose. At the same time, the tumor growth rate after SRS had to increase.Conclusions:The new 3‐component model of tumor could simulate the experimental data very well. The current study suggested that the radiation sensitivity and the growth rate of the proliferating tumor cells may change after irradiation and it depended on the dosage used for SRS. These preliminary observations must be confirmed by future animal experiments.
SU‐E‐T‐754: Three‐Dimensional Patient Modeling Using Photogrammetry for Collision Avoidance
Authors: Popple R , Cardan R 
Published: June 2015

Purpose:To evaluate photogrammetry for creating a three‐dimensional patient model.Methods:A mannequin was configured on the couch of a CT scanner to simulate a patient setup using an indexed positioning device. A CT fiducial was placed on the indexed CT table‐overlay at the reference index position. Two dimensional photogrammetry targets were placed on the table in known positions. A digital SLR camera was used to obtain 27 images from different positions around the CT table. The images were imported into a commercial photogrammetry package and a 3D model constructed. Each photogrammetry target was identified on 2 to 5 images. The CT DICOM metadata and the position of the CT fiducial were used to calculate the coordinates of the photogrammetry targets in the CT image frame of reference. The coordinates were transferred to the photogrammetry software to orient the 3D model. The mannequin setup was transferred to the treatment couch of a linear accelerator and positioned at isocenter using in‐room lasers. The treatment couch coordinates were noted and compared with prediction. The collision free regions were measured over the full range of gantry and table motion and were compared with predictions obtained using a general purpose polygon interference algorithm.Results:The reconstructed 3D model consisted of 180000 triangles. The difference between the predicted and measured couch positions were 5 mm, 1 mm, and 1 mm for longitudinal, lateral, and vertical, respectively. The collision prediction tested 64620 gantry table combinations in 11.1 seconds. The accuracy was 96.5%, with false positive and negative results occurring at the boundaries of the collision space.Conclusion:Photogrammetry can be used as a tool for collision avoidance during treatment planning. The results indicate that a buffer zone is necessary to avoid false negatives at the boundary of the collision‐free zone. Testing with human patients is underway.Research partially supported by a grant from Varian Medical Systems
SU‐E‐T‐755: Timing Characteristics of Proton and Carbon Ion Treatments Using a Synchrotron and Modulated Scanning
Authors: Zhao J , Li Y , Sun L , Huang Z , Deng Y , Moyers M , Hsi W , Wu X 
Published: June 2015

Purpose:The time required to deliver a treatment impacts not only the number of patients that can be treated each day but also the accuracy of delivery due to potential movements of patient tissues. Both macroscopic and microscopic timing characteristics of a beam delivery system were studied to examine their impacts on patient treatments.Methods:35 patients were treated during a clinical trial to demonstrate safety and efficacy of a Siemens Iontris system prior to receiving approval from the Chinese Food and Drug Administration. The system has a variable cycle time and can provide proton beams from 48 to 221 MeV/n and carbon ions from 86 to 430 MeV/n. A modulated scanning beam delivery technique is used where the beam remains stationary at each spot aiming location and is not turned off while the spot quickly moves from one aiming location to the next. The treatment log files for 28 of the trial patients were analyzed to determine several timing characteristics.Results:The average portal time per target dose was 172.5 s/Gy for protons and 150.7 s/Gy for carbon ions. The maximum delivery time for any portal was less than 300 s. The average dwell time per spot was 12 ms for protons and 3.0 ms for carbon ions. The number of aiming positions per energy layer varied from 1 to 258 for protons and 1 to 621 for carbon ions. The average spill time and cycle time per energy layer were 1.20 and 2.68 s for protons and 0.95 and 4.73 s for carbon ions respectively. For 3 of the patients, the beam was gated on and off to reduce the effects of respiration.Conclusion:For a typical target volume of 153 cc as used in this clinical trial, the portal delivery times were acceptable.
SU‐E‐T‐764: Track Repeating Algorithm for Proton Therapy Applied to Intensity Modulated Proton Therapy for Head‐And‐Neck Patients
Authors: Yepes P , Mirkovic D , Mohan R 
Published: June 2015

Purpose:To determine the suitability of fast Monte Carlo techniques for dose calculation in particle therapy based on track‐repeating algorithm for Intensity Modulated Proton Therapy, IMPT. The application of this technique will make possible detailed retrospective studies of large cohort of patients, which may lead to a better determination of Relative Biological Effects from the analysis of patient data.Methods:A cohort of six head‐and‐neck patients treated at the University of Texas MD Anderson Cancer Center with IMPT were utilized. The dose distributions were calculated with the standard Treatment Plan System, TPS, MCNPX, GEANT4 and FDC, a fast track‐repeating algorithm for proton therapy for the verification and the patient plans. FDC is based on a GEANT4 database of trajectories of protons in a water. The obtained dose distributions were compared to each other utilizing the g‐index criteria for 3mm‐3% and 2mm‐2%, for the maximum spatial and dose differences. The γ‐index was calculated for voxels with a dose at least 10% of the maximum delivered dose. Dose Volume Histograms are also calculated for the various dose distributions.Results:Good agreement between GEANT4 and FDC is found with less than 1% of the voxels with a γ‐index larger than 1 for 2 mm‐2%. The agreement between MCNPX with FDC is within the requirements of clinical standards, even though it is slightly worse than the comparison with GEANT4.The comparison with TPS yielded larger differences, what is also to be expected because pencil beam algorithm do not always performed well in highly inhomogeneous areas like head‐and‐neck.Conclusion:The good agreement between a track‐repeating algorithm and a full Monte Carlo for a large cohort of patients and a challenging, site like head‐and‐neck, opens the path to systematic and detailed studies of large cohorts, which may yield better understanding of biological effects.
SU‐E‐T‐768: Treatment Time Nomogram for Strut‐Based Accelerated Partial Breast Applicators
Authors: Yock A , Reiff J , Morcovescu S , Scanderbeg D 
Published: June 2015

Purpose:The purpose of this work was to generate a tabular nomogram of treatment times for strut‐based APBI applicators. The nomogram is intended to provide guidance and a quality assurance check for clinics establishing new treatment techniques or transitioning from balloon‐based applicators.Methods:A retrospective analysis was conducted of 486 patients receiving APBI using strut‐based applicators at three separate institutions. Strut‐based applicators are composed of a central channel surrounded by 6 close‐range (“mini”), 6 mid‐range, 8, or 10 peripheral channels. Patient data was organized based on applicator size (a surrogate of treatment volume) and number of organs at risk. Three organs at risk categories were determined based on the proximity of the device to the patient's skin and/or chest wall (0, 1, or 2 OARs). The proximity criterion was defined as being < 5 mm from the cavity wall/peripheral struts. A tabular nomogram of treatment time (based on nominal 10 Ci source strength) was generated from descriptive statistics of each combination of applicator size and organs at risk category.Results:The average treatment time was observed to be directly related to applicator size and, to a lesser extent, inversely related to the number of nearby organs at risk. Distributions of treatment times observed for each combination of applicator size and organs at risk category are depicted in Figure 1. The tabular nomogram featuring average treatment times with standard deviations is presented in Table 1.Conclusion:Strutbased APBI treatment times were observed to depend in a consistent manner on applicator size and number of nearby organs at risk. Information provided in the nomogram presented here represents several hundred treatments performed at multiple institutions. This data can serve as guidance or quality assurance for institutions with limited experience using strut‐based APBI applicators.
SU‐E‐T‐773: Use of a Commercial TPS for Deriving Exit Dose Distribution for Patient Specific QA with An EPID
Authors: Haering P , Lang C , Splinter M 
Published: June 2015

Purpose:A method to derive exit dose distributions with a commercial treatment planning system for comparison to Epid measured doses.Methods:In contrast to published methods, we present an approach that uses a treatment planning system (Raystation, Raysearch) to calculate exit dose patterns based on a modified patient CT dataset. The EPID is assumed as water equivalent and therefore is represented as water filled ring in the images. This is done by: ‐Export a renamed copy of the patient CT and plan data set. —Manipulate the CT‐data to a field of view of 1000 mm. — Insert the water filled cylinder ring, centered to the target point. — Manipulate plan file with the new target and dose prescription point. — Import and recalculate dose on the manipulated data set. — Export and extract exit field dose matrix from the cylinder (optional entrance dose). — Calibrate matrix to size and rebin data from the cylinder to EPID equivalent data. — Correct Epid measurement for scatter, position and field size. ‐Evaluate and compare data in Verisoft (PTW). Data manipulation and extraction is done by a simple tool (IDL, Exelis).Results:This method was tested on a Siemens Artiste 6MV for field sizes up to 27×27cm2 limited by used geometry and EPID size. First phantom measurements show good results for fields up to 20×20cm (pass rate > 95% for 3%, 3mm Gamma index) while larger fields have higher discrepancies towards the field edges. This might Result from off axis softening of the beam and the higher sensitivity of the detector to beam scatter.Conclusion:This method might simplify the use of exit dosimetry with the EPID for patient specific QA as it uses the dose calculation of a commercial treatment planning system. The concept was proven by phantom data sets, giving acceptable results.
SU‐E‐T‐774: Use of a Scintillator‐Mirror‐Camera System for the Measurement of MLC Leakage Radiation with the CyberKnife M6 System
Authors: Goggin L , Kilby W , Noll M , Maurer C 
Published: June 2015

Purpose:A technique using a scintillator‐mirror‐camera system to measure MLC leakage was developed to provide an efficient alternative to film dosimetry while maintaining high spatial resolution. This work describes the technique together with measurement uncertainties.Methods:Leakage measurements were made for the InCise™ MLC using the Logos XRV‐2020A device. For each measurement approximately 170 leakage and background images were acquired using optimized camera settings. Average background was subtracted from each leakage frame before filtering the integrated leakage image to replace anomalous pixels. Pixel value to dose conversion was performed using a calibration image. Mean leakage was calculated within an ROI corresponding to the primary beam, and maximum leakage was determined by binning the image into overlapping 1mm × 1mm ROIs. 48 measurements were performed using 3 cameras and multiple MLC‐linac combinations in varying beam orientations, with each compared to film dosimetry. Optical and environmental influences were also investigated.Results:Measurement time with the XRV‐2020A was 8 minutes vs. 50 minutes using radiochromic film, and results were available immediately. Camera radiation exposure degraded measurement accuracy. With a relatively undamaged camera, mean leakage agreed with film measurement to ≤0.02% in 92% cases, ≤0.03% in 100% (for maximum leakage the values were 88% and 96%) relative to reference open field dose. The estimated camera lifetime over which this agreement is maintained is at least 150 measurements, and can be monitored using reference field exposures. A dependency on camera temperature was identified and a reduction in sensitivity with distance from image center due to optical distortion was characterized.Conclusion:With periodic monitoring of the degree of camera radiation damage, the XRV‐2020A system can be used to measure MLC leakage. This represents a significant time saving when compared to the traditional film‐based approach without any substantial reduction in accuracy.