bluuebunny/crossref_metadata_2025_split huggingface dataset:
TH‐A‐BRF‐07: Retrospective Reconstruction of 3D Radial MRI Data to Evaluate the Effect of Abdominal Compression On 4D Abdominal Organ Motion
Authors: Stemkens B , Tijssen R , Denis de Senneville B , Lagendijk J , van den Berg C 
Published: July 2014

Purpose:To assess the immobilization effect of an abdominal corset on the spatial and temporal motion characteristics of the pancreas and kidneys using a novel 4D‐MRI method.Methods:Four healthy subjects were scanned with and without a fiberglass corset on a 1.5T clinical MRI. For each subject the best fitting corset was chosen from a range of available corsets. For one subject a custom‐fit corset was used. The free‐breathing 4D‐MRI scan consisted of a balanced‐TFE sequence with radial in‐plane sampling (TE/TR=1.45ms/3.0ms, FA=30°, FOV=350×350×96mm3, voxelsize=2.0×2.0×4.0mm3, 30 dynamics, Tacq=10m17s). Turbo direction was along kz acquiring all kz lines within a single TFE shot (shot duration 93ms). A respiratory diaphragm navigator was interleaved with the TFE shots to acquire the breathing signal, which was used to retrospectively assign each k‐space segment to one of the ten respiratory phases. A 3D optical flow algorithm was used to estimate the non‐rigid displacement between the respiratory phases. The respiration frequency changes were assessed by means of power spectrum analysis (PSA) of the navigator signal.Results:Image quality was adequate for delineation and registration. Cranio‐caudal motion calculated by the 3D optical flow algorithm correlated with the navigator signal, but inter‐organ motion amplitude variation was observed between all organs. Motion reduction induced by the corset was primarily observed in the CC‐direction, but varied substantially across the subjects. Our method additionally showed that the antero‐posterior motion was slightly increased for both kidneys in all subjects (left: 1.2mm, right: 0.8mm). Visual inspection of PSA showed no trend in breathing frequency changes.Conclusion:We have demonstrated a novel, navigator based, freebreathing 4D‐MRI technique to assess the immobilization effect of abdominal compression in four healthy subjects. This technique can be clinically used to assess the effect of a custom‐fit corset on the motion of both tumor motion and surrounding organs at risk.
TH‐A‐BRF‐09: Integration of High‐Resolution MRSI Into Glioblastoma Treatment Planning
Authors: Schreibmann E , Cordova J , Shu H , Crocker I , Curran W , Holder C , Shim H 
Published: July 2014

Purpose:Identification of a metabolite signature that shows significant tumor cell infiltration into normal brain in regions that do not appear abnormal on standard MRI scans would be extremely useful for radiation oncologists to choose optimal regions of brain to treat, and to quantify response beyond the MacDonald criteria. We report on integration of high‐resolution magnetic resonance spectroscopic imaging (HR‐MRSI) with radiation dose escalation treatment planning to define and target regions at high risk for recurrence.Methods:We propose to supplement standard MRI with a special technique performed on an MRI scanner to measure the metabolite levels within defined volumes. Metabolite imaging was acquired using an advanced MRSI technique combining 3D echo‐planar spectroscopic imaging (EPSI) with parallel acquisition (GRAPPA) using a multichannel head coil that allows acquisition of whole brain metabolite maps with 108 μl resolution in 12 minutes implemented on a 3T MR scanner. Elevation in the ratio of two metabolites, choline (Cho, elevated in proliferating high‐grade gliomas) and N‐acetyl aspartate (NAA, a normal neuronal metabolite), was used to image infiltrating high‐grade glioma cells in vivo.Results:The metabolite images were co‐registered with standard contrast‐enhanced T1‐weighted MR images using in‐house registration software and imported into the treatment‐planning system. Regions with tumor infiltration are identified on the metabolic images and used to create adaptive IMRT plans that deliver a standard dose of 60 Gy to the standard target volume and an escalated dose of 75 Gy (or higher) to the most suspicious regions, identified as areas with elevated Cho/NAA ratio.Conclusion:We have implemented a state‐of‐the‐art HR‐MRSI technology that can generate metabolite maps of the entire brain in a clinically acceptable scan time, coupled with introduction of an imaging co‐registration/ analysis program that combines MRSI data with standard imaging studies in a clinically useful fashion.
TH‐A‐18C‐05: Scatter Reduction and Correction for Dual‐Source CBCT Using the Synchronized Moving Grid (SMOG) System
Authors: Chen Y , Zhang Y , Giles W , Jin J , Yin F , Ren L 
Published: July 2014

Purpose:to implement the newly developed synchronized moving grid (SMOG) system on a prototype dual‐source CBCT system to evaluate its efficacy for scatter reduction and correction under various settings, including different phantom size, grid ratio and image acquisition modes.Methods:A 1D grid was designed for each tube in our dual‐source CBCT system. Projections were acquired with the grid at different complementary positions from each scan angle and merged for reconstruction. The scatter signal was measured from the grid blocked area and the scatter distribution was estimated by using a cubic spline interpolated/extrapolated in each projection for scatter correction. The projections without grid were also acquired as the comparing group. Three sets of images were reconstructed from projections: a) without grid, b) with grid but without scatter correction and c) with grid and with scatter correction to evaluate CNR (contrast‐to‐noise ratio) and CT number linearity enhancement. The efficacy of the SMOG system was evaluated using CAT phantoms with different diameters (15cm, 20cm and 30cm), grids (grid ratios of 1:1 and 2:1) and acquisition modes (simultaneous: two tubes firing at the same time and sequential: only one tube firing in one rotation).Results:That scatter artifacts were substantially reduced with our scatter correction algorithm. CNR, degraded by the cross scatter in dual‐source system, were increased by 74%, 32% and 28% for phantom size of 15cm, 20cm and 30cm respectively after using scatter correction with 1:1 grid. And in 20 cm phantom case with simultaneous acquisition, the CT number linearity improved from 0.9969 to 0.9997. Higher grid ratio (more blocked area) resulted in better scatter artifact removal and CNR improvement at the cost of complexity and increased exposure.Conclusion:The SMOG system can effectively reduce the scatter artifacts and enhance CNR and CT number linearity for the dual‐source CBCT system.This work was supported by NIH grant R01CA166948.
TH‐A‐18C‐06: A Scatter Elimination Scheme for Cone Beam CT Using An Oscillating Narrow Beam
Authors: Yan H , Xu Y , Folkerts M , Jia X , Jiang S 
Published: July 2014

Purpose:While cone beam CT (CBCT) has been widely used in image guided radiation therapy, its low image quality, primarily caused by scattered x‐rays, hinders advanced clinical applications, e.g., CBCT based on‐line adaptive re‐planning. We propose in this abstract a new scheme called oscillating narrow beam CBCT (ONB‐CBCT) to eliminate scatter signals.Methods:ONB‐CBCT consists of two major components. 1) Oscillating narrow beam (ONB) scan and 2) partitioned flat panel containing multiple individual detector strips and their own readouts. Both the beam oscillation and detector partition are along the superior‐inferior (SI) direction. During data acquisition, at a given projection, the narrow beam sweep through the detector region, and different portions of the detector acquires projection data in synchrony with the narrow beam. ONB can be generated by a rotating slit collimator design with conventional tube with single focal spot, or by directly using a new source with multiple focal spots. A proof‐of‐principle study via Monte Carlo simulation is conducted to demonstrate the feasibility of ONB‐CBCT.Results:As the beam becomes narrower, more and more scatter signals are eliminated. For the case with a bowtie filter and using 15 ONBs, the maximum and the average intensity error due to scatter are below 20 and 10 HU, respectively.Conclusion:ONB yields a narrowed exposure field at each snapshot and hence an inherently negligible scatter effect. Meanwhile, the individualized detector units guarantee high frame rate detection and hence a same large volume coverage as that in conventional CBCT. In summary, ONB‐CBCT is a promising design to achieve high‐quality CBCT imaging.This study is supported in part by NIH (1R01CA154747‐01).
TH‐C‐18A‐11: Investigating the Minimum Scan Parameters Required to Generate Free‐Breathing Fast‐Helical CT Scans Without Motion‐Artifacts
Authors: Thomas D , Tan J , Neylon J , Dou T , Jani S , Lamb J , Low D 
Published: July 2014

Purpose:A recently proposed 4D‐CT protocol uses deformable registration of free‐breathing fast‐helical CT scans to generate a breathing motion model. In order to allow accurate registration, free‐breathing images are required to be free of doubling‐artifacts, which arise when tissue motion is greater than scan speed. This work identifies the minimum scanner parameters required to successfully generate free‐breathing fast‐helical scans without doubling‐artifacts.Methods:10 patients were imaged under free breathing conditions 25 times in alternating directions with a 64‐slice CT scanner using a low dose fast helical protocol. A high temporal resolution (0.1s) 4D‐CT was generated using a patient specific motion model and patient breathing waveforms, and used as the input for a scanner simulation. Forward projections were calculated using helical cone‐beam geometry (800 projections per rotation) and a GPU accelerated reconstruction algorithm was implemented. Various CT scanner detector widths and rotation times were simulated, and verified using a motion phantom. Doubling‐artifacts were quantified in patient images using structural similarity maps to determine the similarity between axial slices.Results:Increasing amounts of doubling‐artifacts were observed with increasing rotation times > 0.2s for 16×1mm slice scan geometry. No significant increase in doubling artifacts was observed for 64×1mm slice scan geometry up to 1.0s rotation time although blurring artifacts were observed >0.6s. Using a 16×1mm slice scan geometry, a rotation time of less than 0.3s (53mm/s scan speed) would be required to produce images of similar quality to a 64×1mm slice scan geometry.Conclusion:The current generation of 16 slice CT scanners, which are present in most Radiation Oncology departments, are not capable of generating free‐breathing sorting‐artifact‐free images in the majority of patients. The next generation of CT scanners should be capable of at least 53mm/s scan speed in order to use a fast‐helical 4D‐CT protocol to generate a motion‐artifact free 4D‐CT.NIH R01CA096679
TH‐C‐12A‐01: Develop a Patient‐Specific QA Program for Radiation Therapy with On‐Board MRI
Authors: Li H , Rodriguez V , Green O , Hu Y , Kashani R , Wooten H , Yang D , Mutic S 
Published: July 2014

Purpose:This work describes development of the first patient‐specific quality assurance (QA) program for magnetic resonance imaging guided radiation therapy (MR‐IGRT).Methods:The program consisted of following components: 1) multipoint ionization chamber (IC) measurement using a 15 cm3 cubic phantom, 2) 2D stacked radiographic film dosimetry using a 30×30×20 cm3 phantom with multiple inserted ICs, 3) 3D ArcCHECK measurement with a centrally inserted IC, 4) machine delivery file verification, 5) 3D Monte‐Carlo dose re‐calculation with machine delivery file and phantom CT, 6) 2‐head mode delivery validation in case of a malfunctioning head, and 7) independent beam‐on time calculation for non‐IMRT fields. Both ADCL calibrated ICs and ArcCHECK were MRI compatible. Experimental data were analyzed for the first 10 patients treated at our institution.Results:The customized phantoms allowed measuring multiple points with ICs in one delivery. Absolute IC measurements were all within 3% in all phantom geometry/shape/material combinations. Despite known uncertainty associated with film dosimetry, passing rates greater than 90% were achieved in both absolute and composite modes using TG‐129 criteria. Due to the simultaneous irradiation by three radiation sources, ArcCHECK was used as a 3D relative dosimeter with angular and energy dependences uncorrected. 95–100% passing rates were obtained and the centrally inserted IC measurement assured that the overall dose normalization was within 3%. Machine delivery file verification and MC recalculated dose to the phantom results showed 98–100% passing rates, providing opportunity of moving from gamma passing rates to patient DVHbased QA metrics. Same results were obtained for the 2‐head delivery mode. Manual beam‐on time calculation for non‐IMRT fields showed better than 5% agreement.Conclusion:We have successfully developed the first MRIGRT patient specific QA program by adopting experimental and computational dosimetry methods that were developed in the past decade for other radiation therapy modalities.
TH‐C‐12A‐02: Comparison of Two RapidArc Delivery Strategies in Stereotactic Body Radiotherapy of Stage I and II Peripheral Lung Tumors with Unflattened Beams
Authors: Huang B , Lu J , Lin P , Chen J , Kuang Y , Chen C 
Published: July 2014

Purpose:The full arcs strategy used in SBRT with RapidArc and unflattened (FFF) beams in large and heterogeneous peripheral non‐smallcell lung cancer (NSCLC) appears to be suboptimal as it increases the disadvantageous dose to the contralateral lung, which potentially increases the toxicity to surrounding tissues. In this study, we investigated, for the first time, the dose delivery strategies using partial arcs (PA) and the fully rotational arcs with avoidance sectors (FAAS) for SBRT with FFF beams in peripheral NSCLC patients.Methods:Eighteen patients with NSCLC (stage I and II) were selected for this study. Nine patients with a GTV <= 10cc were designated as the small tumor group. The remaining nine patients with a GTV between 10 cc and 44 cc were assigned to the large tumor group. The treatment plans were generated in eighteen patients using PA and FAAS, respectively, and delivered with a Varian TrueBeam Linac. Dosimetry of the target and organs at risk (OAR), total MU, out‐of‐field dose, and delivery time were analyzed. Delta4 and Portal dosimetry were employed to evaluate the delivery accuracy.Results:or the small tumor group, the FAAS plans significantly achieved a better conformity index, the lower total MU and out‐of‐field dose, a shorter treatment time, and the reduced doses to cord, heart, and lung (p < 0.05). But the target doses were slightly higher than that delivered by PA plans. For the large tumor group, the PA plans significantly attained a better conformity index and a shorter treatment time (p < 0.05). Furthermore, all plans achieved a high pass rate, with all the gamma indices greater than 97% at the Г3mm, 3% threshold.Conclusion:This study suggests that FAAS strategy is more beneficial for small tumor patients undergoing lung SBRT with FFF beams. However, for large tumor patients, PA strategy is recommended.NIH/NIGMS grant U54 GM104944, Lincy Endowed Assistant Professorship
TH‐C‐12A‐04: Dosimetric Evaluation of a Modulated Arc Technique for Total Body Irradiation
Authors: Tsiamas P , Czerminska M , Makrigiorgos G , Karen M , Zygmanski P 
Published: July 2014

Purpose:A simplified Total Body Irradiation (TBI) was developed to work with minimal requirements in a compact linac room without custom motorized TBI couch. Results were compared to our existing fixed‐gantry double 4 MV linac TBI system with prone patient and simultaneous AP/PA irradiation.Methods:Modulated arc irradiates patient positioned in prone/supine positions along the craniocaudal axis. A simplified inverse planning method developed to optimize dose rate as a function of gantry angle for various patient sizes without the need of graphical 3D treatment planning system. This method can be easily adapted and used with minimal resources. Fixed maximum field size (40×40 cm2) is used to decrease radiation delivery time. Dose rate as a function of gantry angle is optimized to result in uniform dose inside rectangular phantoms of various sizes and a custom VMAT DICOM plans were generated using a DICOM editor tool. Monte Carlo simulations, film and ionization chamber dosimetry for various setups were used to derive and test an extended SSD beam model based on PDD/OAR profiles for Varian 6EX/ TX. Measurements were obtained using solid water phantoms. Dose rate modulation function was determined for various size patients (100cm − 200cm). Depending on the size of the patient arc range varied from 100° to 120°.Results:A PDD/OAR based beam model for modulated arc TBI therapy was developed. Lateral dose profiles produced were similar to profiles of our existing TBI facility. Calculated delivery time and full arc depended on the size of the patient (∼8min/ 100° − 10min/ 120°, 100 cGy). Dose heterogeneity varied by about ±5% − ±10% depending on the patient size and distance to the surface (buildup region).Conclusion:TBI using simplified modulated arc along craniocaudal axis of different size patients positioned on the floor can be achieved without graphical / inverse 3D planning.
TH‐C‐12A‐05: Dynamic Couch Motion for Improvement of Radiation Therapy Trajectories in DCA and VMAT
Authors: MacDonald L , Thomas Christopher 
Published: July 2014

Purpose:To investigate the potential improvement in dosimetric external beam radiation therapy plan quality using an optimized dynamic gantry and couch motion trajectory which minimizes exposure to the organs at risk.Methods:Patient‐specific anatomical information of head‐and‐neck and cranial cancer patients was used to quantify the geometric overlap between target volumes and organs‐at‐risk (OARs) based on their two‐dimensional projection from source to a plane at isocentre as a function of gantry and couch angle. QUANTEC dose constraints were then used as weighting factors for the OARs to generate a map of couch‐gantry coordinate space indicating degree of overlap at each point in space. A couch‐gantry collision space was generated by direct measurement on a Varian Truebeam linac using an anthropomorphic solid‐water phantom. A dynamic, fully customizable algorithm was written to generate a navigable ideal trajectory for the patient specific couch‐gantry space. The advanced algorithm includes weighting factors which can be used to balance the implementation of absolute minimum values of overlap, with the clinical practicality of largescale couch motion and delivery time. Optimized trajectories were calculated for cranial DCA treatments and for head‐and‐neck VMAT treatments and compared to conventional DCA and VMAT treatment trajectories.Results:Comparison of optimized treatment trajectories with conventional treatment trajectories indicates a decrease in dose to the organs‐at‐risk between 4.64% and 6.82% (2.39 and 3.52 Gy) of the prescription dose per patient per organ at risk.Conclusion:Using simultaneous couch and gantry motion during radiation therapy to minimize the geometrical overlap in the beams‐eye‐view target volumes and the organs‐at‐risk can have an appreciable dose reduction to organs‐at‐risk.
TH‐C‐12A‐07: Implementation of a Pulsed Low Dose Date Radiotherapy (PLRT) Protocol for Recurrent Cancers Using Advanced Beam Delivery
Authors: Ma C , Lin M , Chen L , Price R , Li J , Kang S , Wang P , Lang J 
Published: July 2014

Purpose:Recent in vitro and in vivo experimental findings provided strong evidence that pulsed low‐dose‐rate radiotherapy (PLDR) produced equivalent tumor control as conventional radiotherapy with significantly reduced normal tissue toxicities. This work aimed to implement a PLDR clinical protocol for the management of recurrent cancers utilizing IMRT and VMAT.Methods:Our PLDR protocol requires that the daily 2Gy dose be delivered in 0.2Gy×10 pulses with a 3min interval between the pulses. To take advantage of low‐dose hyper‐radiosensitivity the mean dose to the target is set at 0.2Gy and the maximum dose is limited to 0.4Gy per pulse. Practical planning strategies were developed for IMRT and VMAT: (1) set 10 ports for IMRT and 10 arcs for VMAT with each angle/arc as a pulse; (2) set the mean dose (0.2Gy) and maximum dose (0.4Gy) to the target per pulse as hard constraints (no constraints to OARs); (3) select optimal port/arc angles to avoid OARs; and (4) use reference structures in or around target/OARs to reduce maximum dose to the target/OARs. IMRT, VMAT and 3DCRT plans were generated for 60 H&N, breast, lung, pancreas and prostate patients and compared.Results:All PLDR treatment plans using IMRT and VMAT met the dosimetry requirements of the PLDR protocol (mean target dose: 0.20Gy±0.01Gy; maximum target dose < 0.4Gy). In comparison with 3DCRT, IMRT and VMAT exhibited improved target dose conformity and OAR dose sparing. A single arc can minimize the difference in the target dose due to multi‐angle incidence although the delivery time is longer than 3DCRT and IMRT.Conclusion:IMRT and VMAT are better modalities for PLDR treatment of recurrent cancers with superior target dose conformity and critical structure sparing. The planning strategies/guidelines developed in this work are practical for IMRT/VMAT treatment planning to meet the dosimetry requirements of the PLDR protocol.
TH‐C‐12A‐09: Planning and Delivery of the Fully Dynamic Trajectory Modulated Arc Therapy: Application to Accelerated Partial Breast Irradiation
Authors: Liang J , Atwood T , Fahimian B , Chin E , Otto K , Hristov D 
Published: July 2014

Purpose:A novel trajectory modulated arc therapy (TMAT) system was developed that uses source motion trajectory involving synchronized gantry rotation with translational and rotational couch movement. MLC motion and dose rate were fully optimized for dynamic beam delivery. This work presents a platform for planning deliverable TMAT on a collision free coronal trajectory and evaluates its benefit for accelerated partial breast irradiation (APBI) in a prone position.Methods:The TMAT algorithm was built on VMAT with modifications (physical properties on couch movement were defined) and enhancements (pencil beam dose calculation engine to support extended SSDs) to make it feasible for TMAT delivery. A Matlab software environment for TMAT optimization and dose calculation was created to allow any user specified motion axis. TMAT delivery was implemented on Varian TrueBeamTM STx via XML scripts. 10 prone breast irradiation cases were evaluated in VMAT and compared with a 6‐ field non‐coplanar IMRT plan. Patient selection/exclusion criteria and structure contouring followed the guidelines of NSABP B‐39/RTOG 0413 protocol.Results:TMAT delivery time was ∼4.5 minutes. 251.5°±7.88° of non‐isocentric couch arc was achieved by the optimized trajectory with 180– 210 control points at 1°–2° couch increments. The improved dose distribution by TMAT was most clearly observed by the marked reduction in the volume of irradiated normal breast tissue in the high dose region. The ratios of the normal breast tissue volume receiving more than 50%, 80% and 100% of the prescription dose for TMAT versus IMRT were: V50%(TMAT/IMRT) = 78.38%±13.03%, V80%(TMAT/IMRT) = 44.19%±9.04% and V100% (TMAT/IMRT) = 9.96%±7.55%, all p≤0.01.Conclusion:The study is the first demonstration of planning and delivery implementation of a fully dynamic APBI TMAT system with continuous couch motion. TMAT achieved significantly improved dosimetry over noncoplanar IMRT on dose volume parameters correlated with toxicity and cosmetic outcome of APBI.This project was supported by Varian Research Grant.