bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐J‐174: Volume Based Analysis of Several Doses Point and Their Relation to Changing Volume in a 4DCT
Authors: Nawaz AO , Schanne R , Ochsner G , Chang W 
Published: June 2015

Purpose:To evaluate several dose points in the low dose region of healthy lungs during XRT and their relationship to lung volume.Methods:10 lung cancer patients that had 4DCT simulations were selected for this study retrospectively. The lungs were countered in each of the 10 respiratory cycles. The clinical treatment plan was copied to each phase and the dose was recomputed. DVHs were tabulated for each phase and the V5, V20 and V30 dose points of the total lung, along with the volume of the lung for each phase was recorded. All these dose points and volumes were normalized to the free breathing scan and plan so as to establish if there was a trend, and what the nature of this trend was as a function of lung volume.Results:Of the first 4 patient analyzed, there was an established and reoccurring trend of the V5, V20, V30 dose normalized to the free breathing scan and plan. In the example of the two patients’ data(attached figure), normalized dose point and volumes are graphed as a function of the breathing phases. The precise variation of each point is not the same across each patient; however the trend of each variation seems predictive in nature. The next steps would be to run a statistical T‐test with all the patient data and see if there is a statistical significance and then try to establish a predictive model.Conclusion:Dose points for the lung such as V5, V20 and V30 are now better understood as toxicity end points for lung XRT. Although attention is paid to the low dose region of healthy lung tissue, this study shows that the volumetric affect on dose during breathing phases is measurable and could be statically significant. It therefore warrants further study to better understand this relationship.
SU‐E‐J‐179: Assessment of Tumor Volume Change and Movement During Stereotactic Body Radiotherapy (SBRT) for Lung Cancer: Is Adaptive Radiation Therapy (ART) Necessary?
Authors: Lee C , Lee C 
Published: June 2015

Purpose:Delineation of gross tumor volumes (GTVs) is important for stereotactic body radiotherapy (SBRT). However, tumor volume changes during treatment response. Here, we have investigated tumor volume changes and movement during SBRT for lung cancer, as a means of examining the need for adaptive radiation therapy (ART).Methods:Fifteen tumors in 15 patients with lung cancer were treated with SBRT (total dose: 60 Gy in 4 fractions). GTVs were obtained from cone‐beam computed tomography scans (CBCT1–4) taken before each of the 4 fractions was administered. GTVs were delineated and measured by radiation oncologists using a treatment planning system. Variance in the tumor position was assessed between the planning CT and the CBCT images. To investigate the dosimetric effects of tumor volume changes, planning CT and CBCT4 treatment plans were compared using the conformity index (CI), homogeneity index (HI), and Paddick's index (PCI).Results:The GTV on CBCT1 was employed as a baseline for comparisons. GTV had decreased by a mean of 20.4% (range: 0.7% to 47.2%) on CBCT4. Most patients had smaller GTVs on CBCT4 than on CBCT1. The interfractional shifts of the tumor position between the planning CT and CBCT1–4 were as follows: right‐left, −0.4 to 1.3 mm; anterior‐posterior, −0.8 to 0.5 mm; and superiorinferior, −0.9 to 1.1 mm. Indices for plans from the planning CT and CBCT4 were as follows: CI = 0.94±0.02 and 1.11±0.03; HI= 1.1±0.02 and 1.10±0.03; and PCI = 1.35±0.16 and 1.11±0.02, respectively.Conclusion:CI, HI, and PCI did not differ between the planning CT and CBCTs. However, daily CBCT revealed a significant decrease in the GTV during lung SBRT. Furthermore, there was an obvious interfractional shift in tumor position. Using ART could potentially lead to a reduced GTV margin and improved regional tumor control for lung cancer patients with significantly decreased GTV.
SU‐E‐J‐180: Imaging‐Based ITV May Provide Insufficient Internal Margin for Lung SBRT Patients with Tumor Misalignments Between 3D and 4D Planning CTs
Authors: Zheng D , Zhen W , Lei Y , Denniston K , Driewer J , Zhang Q , Zhu X , Wang S , Zhou S 
Published: June 2015

Purpose:To evaluate the target positional differences between 3D/4D planning CTs (pCTs) and daily CBCTs, and assess ITV coverage of daily GTVs, for lung SBRT patients with misaligned tumor positions between the 3D and 4D pCTs.Methods:Simulation 3D and 4D pCTs, both under free breathing, were acquired on a Sensation Open (Siemens) with RPM (Varian). ITV_All is the union of the GTVs delineated on the 3D pCT (GTV_3D) and on all phases of the 4D pCT (ITV_4D). While for most patients GTV_3D is included in ITV_4D, for some patients GTV_3D shows a substantial misalignment in the axial plane from ITV_4D with spine‐based rigid registration. Under IRB approval, pCTs of 51 patients were retrospectively reviewed to assess the frequency of such misalignments. For one patient with daily kV CBCTs available, all planning and treatment CTs were rigidly registered. GTV_3D, ITV_4D, GTV_F1 through GTV_F5 (on daily CBCTs of Fractions 1–5) were delineated. ITV_All and ITV_5mm (5mm uniform expansion of GTV_3D) were generated. Volumes and centers‐of‐mass (COMs) of all structures were analyzed. The inclusion relations (percentage of Structure‐A included in Structure‐B) were studied between GTV_F1 to GTV_F5 (Structure‐As) and GTV_3D, ITV_4D, ITV_All, ITV_5mm (Structure‐Bs).Results:Three patients showed substantial target misalignments between the 3D and 4D pCTs. For the analyzed patient, daily GTV positions agreed better with GTV_3D than with ITV_4D, with a median (range) COM vector difference of 2.45mm (1.00–4.58) and 16.06mm (15.39–17.44), respectively. The average inclusion of daily GTVs was 99.47% and 69.53% in ITV_5mm and ITV_All, respectively; although ITV_5mm was ∼35% larger than ITV_All for the ∼2cc tumor (GTV_3D).Conclusion:Substantial lung tumor misalignments were observed between 3D and 4D pCTs for some patients. For one such patient, daily tumor positions agreed better with the 3D pCT. Using spinebased localization for SBRT, ITV_All may provide insufficient internal margin.
SU‐E‐J‐181: Effect of Prostate Motion On Combined Brachytherapy and External Beam Dose Based On Daily Motion of the Prostate
Authors: Narayana V , Ealbaj J , McLaughlin P 
Published: June 2015

Purpose:In this study, the adequacy of target expansions on the combined external beam and implant dose was examined based on the measured daily motion of the prostate.Methods:Thirty patients received an I–125 prostate implant prescribed to dose of 90Gy. This was followed by external beam to deliver a dose of 90Gyeq (external beam equivalent) to the prostate over 25 to 30 fractions. An ideal IMRT plan was developed by optimizing the external beam dose based on the delivered implant dose. The implant dose was converted to an equivalent external beam dose using the linear quadratic model. Patients were set up on the treatment table by daily orthogonal imaging and aligning the marker seeds in the prostate. Orthogonal images were obtained at the end of treatment to assess prostate intrafraction motion. Based on the observed motion of the markers between the initial and final images, 5 individual plans showing the actual dose delivered to the patient were calculated. A final true dose distribution was established based on summing the implant dose and the 5 external beam plans. Dose to the prostate, seminal vesicles, lymphnodes and normal tissues, rectal wall, urethra and lower sphincter were calculated and compared to ideal. On 18 patients who were sexually active, dose to the corpus cavernosum and internal pudendal artery was also calculated.Results:The average prostate motion in 3 orthogonal directions was less than 1 mm with a standard deviation of less than +2 mm. Dose and volume parameters showed that there was no decrease in dose to the targets and a marginal decrease in dose to in normal tissues.Conclusion:Dose delivered by seed implant moves with the prostate, decreasing the impact of intrafractions dose movement on actual dose delivered. Combined brachytherapy and external beam dose delivered to the prostate was not sensitive to prostate motion.
SU‐E‐J‐187: Management of Optic Organ Motion in Fractionated Stereotactic Radiotherapy
Authors: Manning M , Maurer J 
Published: June 2015

Purpose:Fractionated stereotactic radiotherapy (FSRT) for optic nerve tumors can potentially use planning target volume (PTV) expansions as small as 1–5 mm. However, the motion of the intraorbital segment of the optic nerve has not been studied.Methods:A subject with a right optic nerve sheath meningioma underwent CT simulation in three fixed gaze positions: right, left, and fixed forward at a marker. The gross tumor volume (GTV) and the organs‐at‐risk (OAR) were contoured on all three scans. An IMRT plan using 10 static non‐coplanar fields to 50.4 Gy in 28 fractions was designed to treat the fixed‐forward gazing GTV with a 1 mm PTV, then resulting coverage was evaluated for the GTV in the three positions. As an alternative, the composite structures were computed to generate the internal target volume (ITV), 1 mm expansion free‐gazing PTV, and planning organat‐risk volumes (PRVs) for free‐gazing treatment. A comparable IMRT plan was created for the free‐gazing PTV.Results:If the patient were treated using the fixed forward gaze plan looking straight, right, and left, the V100% for the GTV was 100.0%, 33.1%, and 0.1%, respectively. The volumes of the PTVs for fixed gaze and free‐gazing plans were 0.79 and 2.21 cc, respectively, increasing the PTV by a factor of 2.6. The V100% for the fixed gaze and free‐gazing plans were 0.85 cc and 2.8 cc, respectively increasing the treated volume by a factor of 3.3.Conclusion:Fixed gaze treatment appears to provide greater organ sparing than free‐gazing. However unanticipated intrafraction right or left gaze can produce a geometric miss. Further study of optic nerve motion appears to be warranted in areas such as intrafraction optical confirmation of fixed gaze and optimized gaze directions to minimize lens and other normal organ dose in cranial radiotherapy.
SU‐E‐J‐190: Development of Abdominal Compression & Respiratory Guiding System Using Gas Pressure Sensor
Authors: Kim T , Kim S , Kim D , Kang S , Cho M , Kim K , Shin D , Suh T 
Published: June 2015

Purpose:Abdominal compression is known to be effective but, often makes external‐marker‐based monitoring of breathing motion not feasible. In this study, we developed and evaluated a system that enables both abdominal compression and monitoring of residual abdominal motion simultaneously. The system can also provide visual‐biofeedback capability.Methods:The system developed consists of a compression belt, an abdominal motion monitoring sensor (gas pressure sensor) and a visual biofeedback device. The compression belt was designed to be able to compress the frontal side of the abdomen. The pressure level of the belt is controlled by air volume and monitored in real time using the gas pressure sensor. The system displays not only the real‐time monitoring curve but also a guiding respiration model (e.g., a breath hold or shallow breathing curve) simultaneously on the head mounted display to help patients keep their breathing pattern as consistent as possible. Three healthy volunteers were enrolled in this pilot study and respiratory signals (pressure variations) were obtained both with and without effective abdominal compression to investigate the feasibility of the developed system. Two guidance patterns, breath hold and shallow breathing, were tested.Results:All volunteers showed smaller abdominal motion with compression (about 40% amplitude reduction compared to without compression). However, the system was able to monitor residual abdominal motion for all volunteers. Even under abdominal compression, in addition, it was possible to make the subjects successfully follow the guide patterns using the visual biofeedback system.Conclusion:The developed abdominal compression & respiratory guiding system was feasible for residual abdominal motion management. It is considered that the system can be used for a respiratory motion involved radiation therapy while maintaining the merit of abdominal compression.This work was supported by the Radiation Technology R&D program (No. 2013M2A2A7043498) and the Mid‐career Researcher Program (2014R1A2A1A10050270) through the National Research Foundation of Korea funded by the Ministry of Science, ICT&Future Planning.
SU‐E‐J‐200: Operation of An Electron Accelerator On An Integrated MR‐Linac System
Authors: Harasimowicz J , Kok J , Overweg J , Roberts D , Shinton I , Sund S , Wang H , Zhong M 
Published: June 2015

Purpose:An integrated MRI guided radiotherapy system poses a challenge of operating a linear accelerator in the presence of a magnetic field as the magnetic force acting on the electrons could Result in radiation source displacement and subsequent reduction of dose output. It was the purpose of this work to test the performance of a linac in the presence of a 1.5T MRI system.Methods:The first experimental MRI guided radiotherapy system at UMC‐Utrecht consisting of an Elekta linac rotating around a 1.5T Magnex magnet was examined. A passive magnetic shield was simulated, designed and installed to reduce the influence of the MRI magnet stray field on the electron beamline. The B field inside the shield was measured as a function of gantry angle and measurements of dose rate constancy upon gantry rotation were performed.Results:The magnitude of the magnetic field on the electron beam path without the shield was as high as 70G. It varied by up to 15G with gantry rotation due to the presence of metal beams in the bunker floor which resulted in dose output drop of up to 70% at certain gantry angles. With the prototype shield, field magnitude was reduced to well below 0.5G everywhere along the electron beam path. Field variation with gantry rotation was decreased to below 0.2G and enabled dose output of the linac to be recovered at all gantry angles. The homogeneity of the field inside the MRI magnet has not been compromised.Conclusion:It was demonstrated that the influence of the 1.5T magnet and the bunker design on the linac operation has been minimised. The performance will be further improved on the Elekta Atlantic system which incorporates a newly developed and optimised Philips magnet design and bunker construction.J Harasimowicz, D Roberts, I Shinton and S Sund are employed by Elekta Limited Crawley, H Wang and M Zhong are employed by Elekta Beijing Medical Systems Co. Ltd., J Overweg is employed by Philips Technologie GmbH Forschungslaboratorien.
SU‐E‐J‐201: Investigation of MRI Guided Proton Therapy
Authors: Li JS 
Published: June 2015

Purpose:Image‐guided radiation therapy has been employed for cancer treatment to improve the tumor localization accuracy. Radiation therapy with proton beams requires more on this accuracy because the proton beam has larger uncertainty and dramatic dose variation along the beam direction. Among all the image modalities, magnetic‐resonance image (MRI) is the best for soft tissue delineation and real time motion monitoring. In this work, we investigated the behavior of the proton beam in magnetic field with Monte Carlo simulations.Methods:A proton Monte Carlo platform, TOPAS, was used for this investigation. Dose calculations were performed with this platform in a 30cmx30cmx30cm water phantom for both pencil and broad proton beams with different energies (120, 150 and 180MeV) in different magnetic fields (0.5T, 1T and 3T). The isodose distributions, dose profiles in lateral and beam direction were evaluated. The shifts of the Bragg peak in different magnetic fields for different proton energies were compared and the magnetic field effects on the characters of the dose distribution were analyzed.Results:Significant effects of magnetic field have been observed on the proton beam dose distributions, especially for magnetic field of 1T and up. The effects are more significant for higher energy proton beam because higher energy protons travel longer distance in the magnetic field. The Bragg peak shift in the lateral direction is about 38mm for 180MeV and 11mm for 120MeV proton beams in 3T magnetic field. The peak positions are retracted back for 6mm and 2mm, respectively. The effect on the beam penumbra and dose falloff at the distal edge of the Bragg peak is negligible.Conclusion:Though significant magnetic effects on dose distribution have been observed for proton beams, MRI guided proton therapy is feasible because the magnetic effects on dose is predictable and can be considered in patient dose calculation.
SU‐E‐J‐210: Characterizing Tissue Equivalent Materials for the Development of a Dual MRI‐CT Heterogeneous Anthropomorphic Phantom Designed Specifically for MRI Guided Radiotherapy Systems
Authors: Steinmann A , Stafford R , Yung J , Followill D 
Published: June 2015

Purpose:MRI guided radiotherapy (MRIgRT) is an emerging technology which will eventually require a proficient quality auditing system. Due to different principles in which MR and CT acquire images, there is a need for a multi‐imaging‐modality, end‐to‐end QA phantom for MRIgRT. The purpose of this study is to identify lung, soft tissue, and tumor equivalent substitutes that share similar human‐like CT and MR properties (i.e. Hounsfield units and relaxation times).Methods:Materials of interested such as common CT QA phantom materials, and other proprietary gels/silicones from Polytek, SmoothOn, and CompositeOne were first scanned on a GE 1.5T Signa HDxT MR. Materials that could be seen on both T1‐weighted and T2‐weighted images were then scanned on a GE Lightspeed RT16 CT simulator and a GE Discovery 750HD CT scanner and their HU values were then measured. The materials with matching HU values of lung (−500 to −700HU), muscle (+40HU) and soft tissue (+100 to +300HU) were further scanned on GE 1.5T Signa HDx to measure their T1 and T2 relaxation times from varying parameters of TI and TE.Results:Materials that could be visualized on T1‐weighted and T2‐weighted images from a 1.5T MR unit and had an appropriate average CT number, −650, −685, 46,169, and 168 HUs were: compressed cork saturated with water, Polytek Platsil™ Gel‐00 combined with mini styrofoam balls, radiotherapy bolus material, SmoothOn Dragon‐Skin™ and SmoothOn Ecoflex™, respectively.Conclusion:Post processing analysis is currently being performed to accurately map T1 and T2 values for each material tested. From previous MR visualization and CT examinations it is expected that Dragon‐Skin™, Ecoflex™ and bolus will have values consistent with tissue and tumor substitutes. We also expect compressed cork statured with water, and Polytek™‐styrofoam combination to have approximate T1 and T2 values suitable for lung‐equivalent materials.
SU‐E‐J‐216: A Sequence Independent Approach for Quantification of MR Image Deformations From Brachytherapy Applicators
Authors: van Wieringen N , van Heerden L , Gurney‐Champion O , van Kesteren Z , Houweling A , Pieters B , Bel A 
Published: June 2015

Purpose:MRI is increasingly used as a single imaging modality for brachytherapy treatment planning. The presence of a brachytherapy applicator may cause distortions in the images, especially at higher field strengths. Our aim is to develop a procedure to quantify these distortions theoretically for any MR‐sequence and to verify the estimated deformations for clinical sequences.Methods:Image distortions due to perturbation of the B0‐field are proportional to the ratio of the induced frequency shift and the read‐out bandwidth of the applied sequence. By reconstructing a frequency‐shift map from the phase data from a multi‐echo sequence, distortions can be calculated for any MR‐sequence. Verification of this method for estimating distortions was performed by acquiring images with opposing read‐out directions and consequently opposing distortions. The applicator shift can be determined by rigidly matching these images. Clinically, T2W‐TSE‐images are used for this purpose. For pre‐clinical tests, EPI‐sequences with narrow read‐out bandwidth (19.5–47.5Hz), consequently large distortions, were added to the set of clinical MRsequences. To quantify deformations of the Utrecht Interstitial CT/MR applicator (Elekta Brachytherapy) on a Philips Ingenia 3T MRI, pre‐clinical tests were performed in a phantom with the applicator in water, followed by clinical validation.Results:Deformations observed in the narrow bandwidth EPI‐images were well predicted using the frequency‐shift, the latter giving an overestimation up to 30%/up to 1 voxel. For clinically applied MR‐sequences distortions were well below the voxel size. In patient setup distortions determined from the frequency‐shift map were at sub‐voxel level (<0.7mm). Using T2W‐images larger distortions were found (1–2mm). This discrepancy was caused by patient movement between/during acquisition of the T2W‐images with opposing read‐out directions.Conclusion:Phantom experiments demonstrated the feasibility of a clinical procedure for quantification of MR‐image distortions for any MR‐sequence. In a clinical set‐up the distortions from a Utrecht interstitial CT/MR applicator are sub‐voxel level.This work was partially funded by Elekta Brachytherpy
SU‐E‐J‐220: Assessment of MRI Geometric Distortion in Head and Neck Cancer Patients Scanned in Immobilized Radiation Treatment Position
Authors: Hansen C , Mohamed A , Weygand J , Ding Y , Fuller C , Frank S , Wang J 
Published: June 2015

Purpose:Uncertainties about geometric distortion have somewhat hindered MRI simulation in radiation therapy. Most of the geometric distortion studies were performed with phantom measurements but another major aspect of MR distortion is patient related. We studied the geometric distortion in patient images by comparing their MRI scans with the corresponding CT, using CT as the non‐distorted gold standard.Methods:Ten H&N cancer patients were imaged with MRI as part of a prospective IRB approved study. All patients had their treatment planning CT done on the same day or within one week of the MRI. MR Images were acquired with a T2 SE sequence (1×1×2.5mm voxel size) in the same immobilization position as in the CT scans. MRI to CT rigid registration was then done and geometric distortion comparison was done by measuring the corresponding anatomical landmarks on both the MRI and the CT images by two observers. Several skin to skin (9 landmarks), bone to bone (8 landmarks), and soft tissue (3 landmarks) were measured at specific levels in horizontal and vertical planes of both scans.Results:The mean distortion for all landmark measurements in all scans was 1.8±1.9mm. For each patient 11 measurements were done in the horizontal plane while 9 were done in the vertical plane. The measured geometric distortion were significantly lower in the horizontal axis compared to the vertical axis (1.3±0.16 mm vs 2.2±0.19 mm, respectively, P=0.003*). The magnitude of distortion was lower in the bone to bone landmarks compared to the combined soft tissue and skin to skin landmarks (1.2±0.19 mm vs 2.3±0.17 mm, P=0.0006*). The mean distortion measured by observer one was not significantly different compared toobserver 2 (2.3 vs 2.4 mm, P=0.4).Conclusion:MRI geometric distortions were quantified in H&N patients with mean error of less than 2 mm.JW received a corporate sponsored research grant from Elekta