bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐C‐BRD‐01: Multi‐Centre Collaborative Quality Assurance Program for IMRT Planning and Delivery: Year 3 Results
Authors: McNiven A , Jaffray D , Letourneau D 
Published: June 2015

Purpose:A multi‐centre quality assurance program was developed to enable quality improvement by coupling measurement of intensity modulated radiotherapy (IMRT) planning and delivery performance for site‐specific planning exercises with diagnostic testing. The third year of the program specifically assessed the quality of spine stereotactic body radiotherapy (SBRT) planning and delivery amongst the participating centres.Methods:A spine SBRT planning exercise (24 Gy in 2 fractions) was created and completed by participants prior to an on‐site visit. The delivery portion of the on‐site visit included spine SBRT plan delivery and diagnostic testing, which included portal image acquisition for quantification of phantom positioning error and multi‐leaf collimator (MLC) calibration accuracy. The measured dose was compared to that calculated in the treatment planning system (TPS) using 3%/2mm composite analysis and 3%/3mm gamma analysis.Results:Fourteen institutions participated, creating 17 spine SBRT plans (15 VMAT and 2 IMRT). Three different TPS, two beam energies (6 MV and 6 MV FFF), and four MLC designs from two linac vendors were tested. Large variation in total monitor units (MU) per plan (2494–6462 MU) and dose‐volume parameters was observed. The maximum point dose in the plans ranged from 116–149% and was dependent upon the TPS used. Pass rates for measured to planned dose comparison ranged from 89.4–100% and 97.3–100% for 3%/2mm and 3%/3mm criteria respectively. The largest measured MLC error did Result in one of the poorer pass rates. No direct correlation between phantom positioning error and pass rates overall.Conclusion:Significant differences were observed in the planning exercise for some plan and dose‐volume parameters based on the TPS used. Standard evaluation criteria showed good agreement between planned and measured dose for all participants, however on an individual plan basis, diagnostic tests were able to identify contributing factors for poorer results, when using more stringent evaluation criteria.Funding from Cancer Care Ontario is acknowledged.
SU‐C‐BRD‐02: Monte Carlo Based VMAT Dose Re‐Optimization for Patient Specific Quality Assurance and Failed Plan Recovery Using Re‐Weighted Aperture MUs
Authors: Folkerts M , Modiri A , Ungun B , Jia X , Jiang S , Sawant A 
Published: June 2015

Purpose:To offer an answer to the question: “What do we do if a treatment plan is shown to be sub‐optimal or unsafe after patient specific VMAT QA based on Monte Carlo (MC) dose calculations?” We attempt to disprove the null hypothesis that re‐weighting the MUs delivered through each aperture of a VMAT plan will not improve the MC delivered dose distribution.Methods:We interface with a GPU‐based patient specific MC quality assurance (QA) system to generate dose distributions for apertures of a multiple arc VMAT head‐and‐neck treatment plan. The distributions were combined into a dose‐per‐aperture matrix. We tested and compared the results of two optimization schemes. To solve the convex problem of re‐weighting the MC dose matrix to match the dose provided by the treatment planning system (TPS), the least‐squares (LSQ) algorithm was used. To meet or improve our DVH goals, a particle swarm optimization (PSO) algorithm was implemented. After normalizing each Result to match the 66.0Gy D95 prescription requirement, we used QUANTEC guidelines to evaluate the clinical impact of each approach.Results:Our non‐convex PSO scheme to re‐weight MUs was able to produce matching if not better OAR DVH results for the one plan we tested when compared to the original plan. For example, the spinal cord was prescribed a Dmax of 42.8Gy, however, the MC QA results reported 44.7Gy; the PSO was able to reduce that Result to 42.0Gy, a 6% improvement; the LSQ optimization produced 45.2Gy. Also, the PSO reduced the max dose of the PTV from 81.7Gy (MC QA) to 75.1Gy, while the LSQ algorithm produced 77.4Gy.Conclusion:We successfully disproved our null hypothesis and showed that it is indeed possible to improve the MC dose distribution of a VMAT plan by re‐weighting MUs delivered through each aperture.This project was partially funded by NIH grant #R01CA169102
SU‐C‐BRD‐05: Non‐Invasive in Vivo Biodosimetry in Radiotherapy Patients Using Electron Paramagnetic Resonance (EPR) Spectroscopy
Authors: Bahar N , Roberts K , Stabile F , Mongillo N , Decker RD , Wilson LD , Husain Z , Contessa J , Williams BB , Flood AB , Swartz HM , Carlson DJ 
Published: June 2015

Purpose:Medical intervention following a major, unplanned radiation event can elevate the human whole body exposure LD50 from 3 to 7 Gy. On a large scale, intervention cannot be achieved effectively without accurate and efficient triage. Current methods of retrospective biodosimetry are restricted in capability and applicability; published human data is limited. We aim to further develop, validate, and optimize an automated field‐deployable in vivo electron paramagnetic resonance (EPR) instrument that can fill this need.Methods:Ionizing radiation creates highly‐stable, carbonate‐based free radicals within tooth enamel. Using a process similar to nuclear magnetic resonance, EPR directly measures the presence of radiation‐induced free radicals. We performed baseline EPR measurements on one of the upper central incisors of total body irradiation (TBI) and head and neck (H&N) radiotherapy patients before their first treatment. Additional measurements were performed between subsequent fractions to examine the EPR response with increasing radiation dose. Independent dosimetry measurements were performed with optically‐stimulated luminescent dosimeters (OSLDs) and diodes to more accurately establish the relationship between EPR signal and delivered radiation dose.Results:36 EPR measurements were performed over the course of four months on two TBI and four H & N radiotherapy patients. We observe a linear increase in EPR signal with increasing dose across the entirety of the tested range. A linear least squares‐weighted fit of delivered dose versus measured signal amplitude yields an adjusted R‐square of 0.966. The standard error of inverse prediction (SEIP) is 1.77 Gy. For doses up to 7 Gy, the range most relevant to triage, we calculate an SEIP of 1.29 Gy.Conclusion:EPR spectroscopy provides a promising method of retrospective, non‐invasive, in vivo biodosimetry. Our preliminary data show an excellent correlation between predicted signal amplitude and delivered dose. With further development, a robust means of predicting delivered radiation dose from EPR measurements is expected.This project was funded by the Biomedical Advanced Research and Development Authority (BARDA) within the U.S. Department of Health and Human Services subcontracted through the Geisel School of Medicine at Dartmouth and by the Dartmouth Physically‐Based Biodosimetry Center for Medical Countermeasures Against Radiation (Dart‐Dose CMCR) Pilot Program.
SU‐C‐BRD‐07: Three‐Dimensional Dose Reconstruction in the Presence of Inhomogeneities Using Fast EPID‐Based Back‐Projection Method
Authors: Ren Q , Cao R , Pei X , Wang H , Hu L 
Published: June 2015

Purpose:Three‐dimensional dose verification can detect errors introduced by the treatment planning system (TPS) or differences between planned and delivered dose distribution during the treatment. The aim of the study is to extend a previous in‐house developed three‐dimensional dose reconstructed model in homogeneous phantom to situtions in which tissue inhomogeneities are present.Methods:The method was based on the portal grey images from an electronic portal imaging device (EPID) and the relationship between beamlets and grey‐scoring voxels at the position of the EPID. The relationship was expressed in the form of grey response matrix that was quantified using thickness‐dependence scatter kernels determined by series of experiments. From the portal grey‐value distribution information measured by the EPID the two‐dimensional incident fluence distribution was reconstructed based on the grey response matrix using a fast iterative algorithm. The accuracy of this approach was verified using a four‐field intensity‐modulated radiotherapy (IMRT) plan for the treatment of lung cancer in anthopomorphic phantom. Each field had between twenty and twenty‐eight segments and was evaluated by comparing the reconstructed dose distribution with the measured dose.Results:The gamma‐evaluation method was used with various evaluation criteria of dose difference and distance‐to‐agreement: 3%/3mm and 2%/2 mm. The dose comparison for all irradiated fields showed a pass rate of 100% with the criterion of 3%/3mm, and a pass rate of higher than 92% with the criterion of 2%/2mm.Conclusion:Our experimental results demonstrate that our method is capable of accurately reconstructing three‐dimensional dose distribution in the presence of inhomogeneities. Using the method, the combined planning and treatment delivery process is verified, offing an easy‐to‐use tool for the verification of complex treatments.
SU‐C‐BRB‐01: Development of Dynamic Gimbaled X‐Ray Head Swing Irradiation Technique
Authors: Ono T , Miyabe Y , Yokota K , Takahashi K , Akimoto M , Mukumoto N , Ishihara Y , Nakamura M , Mizowaki T , Hiraoka M 
Published: June 2015

Purpose:The Vero4DRT has a unique gimbaled x‐ray head with rotating around orthogonal two axes. The purpose of this study was to develop a new irradiation technique using the dynamic gimbaled x‐ray head swing function.Methods:The Vero4DRT has maximum field size of 150Χ150 mm2. The expanded irradiation field (expanded‐field) for the longitudinal direction which is vertical to the MLC sliding direction, was created by the MLC motion and the gimbaled x‐ray head rotation. The gimbaled x‐ray head was rotated ± 35 mm, and the expanded‐field size was set as 150Χ220 mm2. To irradiate uniform dose distribution, the diamond‐shaped radiation field was created and continuously moved for the longitudinal direction. It was achieved by combination of opening and closing of the MLC and gimbal swing rotation. To evaluate dosimetric characteristic of the expanded‐field, films inserted in water‐equivalent phantoms at 100 mm depth were irradiated and the field size, penumbra, flatness and symmetry were analyzed.In addition, the expanded‐field irradiation technique was applied to virtual wedge irradiation. Wedged beam was acquired with the delta–shaped radiation field. 150Χ 220 mm2 fields with 15, 30, 45, and 60 degree wedge were examined. The wedge angles were measured with irradiated film and compared with assumed wedge angles.Results:The field size, penumbra, flatness and symmetry of the expanded‐field were 150.0 mm, 8.1–8.4 mm, 2.8% and −0.8% for the lateral direction and 220.1 mm, 6.3–6.4 mm, 3.2% and −0.4% for the longitudinal direction at 100 mm depth. The measured wedge angles were 15.1, 30.2, 45.2 and 60.2 degrees. The differences between assumed and measured angles were within 0.2 degrees.Conclusion:A new technique of the gimbal swing irradiation was developed. To extend applied targets, especially for whole breast irradiation, the expanded‐field and virtual wedge irradiations would be effective.
SU‐C‐BRB‐02: Symmetric and Asymmetric MLC Based Lung Shielding and Dose Optimization During Translating Bed TBI
Authors: Ahmed S , Kakakhel MB , Ahmed SBS , Hussain A 
Published: June 2015

Purpose:The primary aim was to introduce a dose optimization method for translating bed total body irradiation technique that ensures lung shielding dynamically. Symmetric and asymmetric dynamic MLC apertures were employed for this purpose.Methods:The MLC aperture sizes were defined based on the radiological depth values along the divergent ray lines passing through the individual CT slices. Based on these RD values, asymmetrically shaped MLC apertures were defined every 9 mm of the phantom in superior‐inferior direction. Individual MLC files were created with MATLAB™ and were imported into Eclipse™ treatment planning system for dose calculations. Lungs can be shielded to an optimum level by reducing the MLC aperture width over the lungs. The process was repeated with symmetrically shaped apertures.Results:Dose‐volume histogram (DVH) analysis shows that the asymmetric MLC based technique provides better dose coverage to the body and optimum shielding of the lungs compared to symmetrically shaped beam apertures. Midline dose homogeneity is within ±3% with asymmetric MLC apertures whereas it remains within ±4.5% with symmetric ones (except head region where it drops down to −7%). The substantial over and under dosage of ±5% at tissue interfaces has been reduced to ±2% with asymmetric MLC technique. Lungs dose can be reduced to any desired limit. In this experiment lungs dose was reduced to 80% of the prescribed dose, as was desired.Conclusion:The novel asymmetric MLC based technique assures optimum shielding of OARs (e.g. lungs) and better 3‐D dose homogeneity and body‐dose coverage in comparison with the symmetric MLC aperture optimization.The authors acknowledge the financial and infrastructural support provided by Pakistan Institute of Engineering & Applied Sciences (PIEAS), Islamabad and Aga Khan University Hospital (AKUH), Karachi during the course of this research project. Authors have no conflict of interest with any national / international body for the presented work.
SU‐C‐BRB‐06: Utilizing 3D Scanner and Printer for Dummy Eye‐Shield: Artifact‐Free CT Images of Tungsten Eye‐Shield for Accurate Dose Calculation
Authors: Park J , Lee J , Kim H , Kim I , Ye S 
Published: June 2015

Purpose:To evaluate the effect of a tungsten eye‐shield on the dose distribution of a patient.Methods:A 3D scanner was used to extract the dimension and shape of a tungsten eye‐shield in the STL format. Scanned data was transferred into a 3D printer. A dummy eye shield was then produced using bio‐resin (3D systems, VisiJet M3 Proplast). For a patient with mucinous carcinoma, the planning CT was obtained with the dummy eye‐shield placed on the patient's right eye. Field shaping of 6 MeV was performed using a patient‐specific cerrobend block on the 15 × 15 cm2 applicator. The gantry angle was 330° to cover the planning target volume near by the lens. EGS4/BEAMnrc was commissioned from our measurement data from a Varian 21EX. For the CT‐based dose calculation using EGS4/DOSXYZnrc, the CT images were converted to a phantom file through the ctcreate program. The phantom file had the same resolution as the planning CT images. By assigning the CT numbers of the dummy eye‐shield region to 17000, the real dose distributions below the tungsten eye‐shield were calculated in EGS4/DOSXYZnrc. In the TPS, the CT number of the dummy eye‐shield region was assigned to the maximum allowable CT number (3000).Results:As compared to the maximum dose, the MC dose on the right lens or below the eye shield area was less than 2%, while the corresponding RTP calculated dose was an unrealistic value of approximately 50%.Conclusion:Utilizing a 3D scanner and a 3D printer, a dummy eye‐shield for electron treatment can be easily produced. The artifact‐free CT images were successfully incorporated into the CT‐based Monte Carlo simulations. The developed method was useful in predicting the realistic dose distributions around the lens blocked with the tungsten shield.
SU‐C‐BRB‐07: Optimizing Fiducial Visibility On Periodically Acquired Megavoltage and Kilovoltage Image Pairs During Volumetric Modulated Arc Therapy
Authors: Zhang P , Wang P , Laura H , Ravindranath B , Mageras G , Hunt M 
Published: June 2015

Purpose:Robust detection of implanted fiducials is essential for monitoring intra‐fractional motion during hypo‐fractionated treatment. We developed a plan optimization strategy to ensure clear visibility of implanted fiducials, and facilitate 3D localization during volumetric modulated arc therapy (VMAT).Method:Periodic kilovoltage (kV) images were acquired at 20° gantry intervals, and paired with simultaneously acquired 4.4° short arc megavoltage digital tomosynthesis (MV‐DTS) to localize three fiducials during VMAT delivery for prostate cancer. Beginning with the original optimized plan, control point segments where fiducials (with 1cm margin to account for potential motion) were consistently blocked by MLC within each 4.4° MV‐DTS interval were first identified. For each segment, MLC apertures were edited to expose the fiducial that led to the least increase in a dosimetric cost function. Subsequently, MLC apertures of all control points not involved with fiducial visualization were re‐optimized to compensate for plan quality losses and match the original DVH. MV dose for each MV‐DTS was also kept above 0.4 MU to ensure acceptable image quality. Different imaging (gantry) intervals and visibility margins around fiducials were also evaluated.Result:Fiducials were consistently blocked by the MLC for, on average, 38% of the imaging control points for five hypofractionated prostate VMAT plans but properly exposed after re‐optimization. Optimization resulted in negligible dosimetric differences compared with original plans, and outperformed simple aperture editing: on average, PTV D98 recovered from 87% to 94% of prescription, and PTV dose homogeneity improved from 9% to 7%. Without violating plan objectives and compromising delivery efficiency, the highest imaging frequency and largest margin that can be achieved are a 10° gantry interval, and 15mm, respectively.Conclusion:VMAT plans can be made to accommodate MV‐kV imaging of fiducials. Fiducial visualization rate and workflow efficiency are significantly improved with an automatic modification and re‐optimization approach.Research supported by Varian Medical System
SU‐C‐BRA‐03: Prediction of Laser Induced Thermal Therapy: Results of Model Training and Cross Validation
Authors: Fahrenholtz SJ , Madankan R , Hazle JD , Stafford RJ , Fuentes D 
Published: June 2015

Purpose:MR‐guided laser induced thermal therapy (MRgLITT) is a minimally invasive surgery with applications in the brain, among other sites. In especially precise interventions, like neurosurgery, accurate planning may behoove surgical planning by aiding in the decision of where and how many laser ablations are required. Previous models of tissue heating have relied on literature values extrapolated primarily from normal brain animal research and ex vivo data. In this abstract, an inverse problem provides model parameter data from retrospective analysis of MR temperature imaging data in patient tumor tissue, which represent a training cohort. Within the same cohort, leave‐one‐out cross validation (LOOCV) estimates the predictive accuracy of the trained model.Methods:The training has three parts: MR temperature datasets (n=20), a relatively simple steady state bioheat model, and a global optimization algorithm maximizing the Dice similarity coefficient (DSC). DSC ranges from 0 to one; >0.7 is considered a ‘successful’ prediction. DSC compares the regions exceeding 57 °C—i.e. ablated tissue regions—and measures accuracy. Blood perfusion and optical parameters are optimized according to DSC, creating a library of 20 pairs of parameters that are used in prediction. The predictive accuracy is estimated by using LOOCV. LOOCV begins by dropping an optimal parameter pair from the library and makes a model prediction, given the average from the remaining 19 pairs. This procedure is permuted so that every dataset is predicted using the other parameter pairs.Results:The distribution of DSC during predictive LOOCV is described by: mean=0.822; median=0.849; standard deviation=0.0872; minimum=0.583; maximum=0.930; 19/20 datasets pass (i.e. DSC>0.7). Best available literature values perform comparably worse: mean=0.668; median=0.656; standard deviation=0.115; minimum=0.455; maximum=0.857; 8/20 pass.Conclusion:Data strongly indicate population‐based parameter optimization is potentially useful in treatment planning, as the model far outperforms available literature values in this preliminary study.Research reported in this publication was supported by the National Center for Advancing Translational Sciences of the National Institutes of Health under Award Number TL1TR000369. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
SU‐C‐BRA‐05: Fast Generation of Respiratory Gated CT Images at User Selected Breathing Phases On a Graphics Processing Unit
Authors: O'Connell D. P. , Thomas D. H. , Dou T. H. , Lamb J. M. , Yang L. , Low D. A. 
Published: June 2015

Purpose:The previously published 5DCT respiratory gated image acquisition and analysis technique enables generation of images at any user selected breathing phase. This work describes acceleration of the image generation process using a graphics processing unit (GPU) and its application to internal target volume (ITV) definition and the creation of simulated cine scans.Methods:25 fast helical, free breathing CT scans of 7 lung cancer patients were acquired using a low dose protocol with simultaneous breathing surrogate monitoring. For each patient, the first scan was deformably registered to the following 24. Deformation vectors were used to determine voxel‐specific parameters of a motion model. A single, low noise reference image in the geometry of the first scan was created using image averaging. The motion model was used to predict the deformation from the reference image to selected breathing phases. Internal target volumes were generated by deforming a single contour of the gross tumor volume (GTV) to the most common breathing phases accounting for 90% of observed respiration. Simulated cines were created by generating volumetric images at 0.25 second intervals along the measured breathing trace and taking slices at desired positions. Computations were performed on an NVIDIA Tesla K40.Results:Calculation of motion model parameters took approximately 3 seconds per dataset. Image generation took approximately 0.25 seconds total for a 450 × 450 × 300 image with isotropic 1 mm3 resolution.Conclusion:GPU acceleration enabled rapid generation of breathing gated CT images using the 5DCT technique and facilitated use of a novel method for defining customized lung tumor ITVs that account for a specified percentage of observed respiration, and the creation of simulated cine images in a clinically acceptable time frame. Investigation of the differences between ITVs generated using the technique described here and ITVs defined on conventional 4DCT datasets is ongoing.