bluuebunny/crossref_metadata_2025_split huggingface dataset:
TH‐CD‐207B‐06: Swank Factor of Segmented Scintillators in Multi‐Slice CT Detectors: Pulse Height Spectra and Light Escape
Authors: Howansky A , Peng B , Lubinsky A , Zhao W 
Published: July 2016

Purpose:Pulse height spectra (PHS) have been used to determine the Swank factor of a scintillator by measuring fluctuations in its light output per x‐ray interaction. The Swank factor and x‐ray quantum efficiency of a scintillator define the upper limit to its imaging performance, i.e. DQE(0). The Swank factor below the K‐edge is dominated by optical properties, i.e. variations in light escape efficiency from different depths of interaction, denoted e(z). These variations can be optimized to improve tradeoffs in x‐ray absorption, light yield, and spatial resolution. This work develops a quantitative model for interpreting measured PHS, and estimating e(z) on an absolute scale. The method is used to investigate segmented ceramic GOS scintillators used in multi‐slice CT detectors.Methods:PHS of a ceramic GOS plate (1 mm thickness) and segmented GOS array (1.4 mm thick) were measured at 46 keV. Signal and noise propagation through x‐ray conversion gain, light escape, detection by a photomultiplier tube and dynode amplification were modeled using a cascade of stochastic gain stages. PHS were calculated with these expressions and compared to measurements. Light escape parameters were varied until modeled PHS agreed with measurements. The resulting estimates of e(z) were used to calculate PHS without measurement noise to determine the inherent Swank factor.Results:The variation in e(z) was 67.2–89.7% in the plate and 40.2–70.8% in the segmented sample, corresponding to conversion gains of 28.6–38.1 keV−1 and 17.1–30.1 keV−1, respectively. The inherent Swank factors of the plate and segmented sample were 0.99 and 0.95, respectively.Conclusion:The high light escape efficiency in the ceramic GOS samples yields high Swank factors and DQE(0) in CT applications. The PHS model allows the intrinsic optical properties of scintillators to be deduced from PHS measurements, thus it provides new insights for evaluating the imaging performance of segmented ceramic GOS scintillators.
TH‐CD‐207B‐10: Effect of CT Reconstruction Filter On Measured Hounsfield Values in Lung Nodules
Authors: Little K , Reiser I , Sanchez A , Chung J , MacMahon H , Lu Z 
Published: July 2016

Purpose:Measured Hounsfield numbers in CT are used by radiologists to determine the presence of calcium or fat in lung nodules, either of which suggests a benign diagnosis. However, substantial variations in Hounsfield number may arise due to the use of different reconstruction parameters such as the filter/kernel, leading to measurement inaccuracies. This quality improvement project was developed to demonstrate measurement pitfalls and to identify acceptable conditions for incorporating Hounsfield values as a factor in lung nodule diagnosis.Methods:12 mm‐diameter spheres of polyurethane and urethane foam were placed into an anthropomorphic chest phantom, and 10 mm‐diameter tubes with varying iodine concentrations were placed into a 16 cm PMMA cylindrical phantom. Additionally, 11 mm‐diameter PMMA and HDPE spheres were placed in a 10 cm PMMA cylindrical phantom. Phantoms were scanned at 120 kVp using a Siemens Biograph mCT and on a Philips iCT and reconstructed using various reconstruction filters.Results:For the Siemens system, both sharp kernels and smooth kernels altered the Hounsfield numbers. Hounsfield numbers varied within a range of 8.9 HU for urethane foam and varied within 58.7 HU for polyurethane. The iodine measurements varied up to 37.9 HU for the lowest concentration. For the Philips system, Hounsfield numbers were relatively consistent but were higher for the “Detail” and “Lung Enhanced” filters, varying by 36.9 HU for PMMA and 15.9 HU for HDPE.Conclusion:Reconstruction filters can change the measured Hounsfield numbers of nodular objects, especially with detail‐enhancing (sharpening) filters commonly used in lung imaging. Measured values should only be used for diagnostic decision support with filters that have demonstrated accuracy and consistency. While filter accuracy statements are available from manufacturers, radiologists are likely not aware of the extent of potential variations that can occur in a clinical setting.
TH‐D‐BRC‐02: Panel Member
Authors: Hahn S. 
Published: July 2016

Interest in proton therapy has increased dramatically in the past couple of years, especially in the United States. There certainly is an important place for proton therapy in the arsenal of cancer treatments. Its dosimetric advantage and potential for low toxicity makes it the perfect partner for photons and other cancer treatment modalities.Often there is a belief that the new technology ought to be better but many believe that they should be widely adopted in the clinic only after evidence has shown that they are at least as safe and efficacious as existing technologies, which are often less expensive. This is the case for proton radiotherapy.This session being both educational and debate will provide a good review of basics and technological advancement as well as a comprehensive clinical update for both proton and photon therapy.Future technology developments and how they will impact the potential dosimetric advantage of proton therapy will be discussed. Particularly the debate will focus on whether these developments will close or widen the gap between photon and proton therapy.

Learning Objectives:
To review challenges, limitations, and recent and future developments in proton therapy.
To review challenges, limitations, recent and future developments in photon radiotherapy.
To review current clinical trials and challenging clinical cases.C. Yu, No company or organization that my presentation mentions provided me with financial support. I am the Founder and CEO of Xcision Medical Systems, LLC. However, my presentation will not mention any product or technology developed by Xcision.
TH‐EF‐204‐04: Experience of IMRT and Other Conformal Techniques in Russia
Authors: Krylova T. 
Published: July 2016

Joanna E. Cygler, Jan Seuntjens, J. Daniel Bourland, M. Saiful Huq, Josep Puxeu Vaque, Daniel Zucca Aparicio, Tatiana Krylova, Yuri Kirpichev, Eric Ford, Caridad BorrasStereotactic Radiation Therapy (SRT) utilizes small static and dynamic (IMRT) fields, to successfully treat malignant and benign diseases using techniques such as Stereotactic Radiosurgery (SRS) and Stereotactic Body Radiation Therapy (SBRT). SRT is characterized by sharp dose gradients for individual fields and their resultant dose distributions. For appropriate targets, small field radiotherapy offers improved treatment quality by allowing better sparing of organs at risk while delivering the prescribed target dose. Specialized small field treatment delivery systems, such as robotic‐controlled linear accelerators, gamma radiosurgery units, and dynamic arc linear accelerators may utilize rigid fixation, image guidance, and tumor tracking, to insure precise dose delivery to static or moving targets. However, in addition to great advantages, small field delivery techniques present special technical challenges for dose calibration due to unique geometries and small field sizes not covered by existing reference dosimetry protocols such as AAPM TG‐51 or IAEA TRS 398. In recent years extensive research has been performed to understand small field dosimetry and measurement instrumentation. AAPM, IAEA and ICRU task groups are expected to provide soon recommendations on the dosimetry of small radiation fields. In this symposium we will: 1] discuss the physics, instrumentation, methodologies and challenges for small field radiation dose measurements; 2] review IAEA and ICRU recommendations on prescribing, recording and reporting of small field radiation therapy; 3] discuss selected clinical applications and technical aspects for specialized image‐guided, small field, linear accelerator based treatment techniques such as IMRT and SBRT.

Learning Objectives:
To learn the physics of small fields in contrast to dosimetry of conventional fields
To learn about detectors suitable for small fields
To learn about the role of Monte Carlo simulations in determination of small field output factors
To provide an overview of the IAEA small field dosimetry recommendations
To provide an overview of the content of the ICRU report on Prescribing, Reporting and Recording of Small Field Radiation Therapy.
To learn about special technical considerations in delivering IMRT and SBRT treatments
To appreciate specific challenges of IMRT implementationJ. Seuntjens, Natural Sciences and Engineering Research Council; Canadian Institutes of Health Research
TH‐EF‐BRB‐01: BEST IN PHYSICS (THERAPY): Dosimetric Comparison of 4π and Clinical IMRT for Cortex‐Sparing High‐Grade Glioma Treatment
Authors: Woods K , Karunamuni R , Tran A , Yu V , Nguyen D , Hattangadi‐Gluth J , Sheng K 
Published: July 2016

Purpose:Thinning of the cerebral cortex has been observed in patients treated with fractionated partial brain radiation therapy and may contribute to cognitive decline following treatment. The extent of this thinning is dose‐dependent, and was shown comparable to that of neurodegenerative diseases such as Alzheimer's disease at one year post‐therapy. This study investigates whether 4π radiotherapy can enable better sparing of the cortex and other critical structures when compared to conventional clinical IMRT plans.Methods:Clinical cortex‐sparing IMRT plans for 15 high‐grade glioma patients were included in this study. 4π radiotherapy plans were created for each patient with 20 intensity‐modulated non‐coplanar fields selected with a greedy column‐generation optimization. All plans were normalized to deliver 100% of the prescribed dose to 95% of the planning target volume (PTV). The mean and maximum dose to the cerebral cortex and other organs at risk (OARs) were compared for the two plan types, as well as the conformity index (CI), homogeneity index (HI), and 50% dose spillage volume (R50).Results:The 4π plans significantly reduced the mean cortex dose by an average of 16% (range 6% to 27%) compared to the clinical plans. The mean dose to every other OAR compared was also reduced by 15% to 43%, with statistically significant reductions to the brainstem, chiasm, eyes, optic nerves, subcortical whit, and hippocampus. The average maximum doses were also reduced for 10/12 OARs. The R50 was significantly reduced with the 4π plans (>14%) and the homogeneity index was significantly improved.Conclusion:4π enables significant sparing of the cerebral cortex when treating high‐grade gliomas with fractionated partial brain radiation therapy, potentially reducing the risk of harmful dose‐dependent cortical thinning.NIH R43CA183390, NIH R01CA188300, Varian Medical Systems
TH‐EF‐BRB‐02: Feasibility of Optimization for Dynamic Trajectory Radiotherapy
Authors: Fix MK , Frei D , Volken W , Terribilini D , Aebersold DM , Manser P 
Published: July 2016

Purpose:Over the last years, volumetric modulated arc therapy (VMAT) has been widely introduced into clinical routine using a coplanar delivery technique. However, VMAT might be improved by including dynamic couch and collimator rotations, leading to dynamic trajectory radiotherapy (DTRT). In this work the feasibility and the potential benefit of DTRT was investigated.Methods:A general framework for the optimization was developed using the Eclipse Scripting Research Application Programming Interface (ESRAPI). Based on contoured target and organs at risk (OARs), the structures are extracted using the ESRAPI. Sampling potential beam directions, regularly distributed on a sphere using a Fibanocci‐lattice, the fractional volume‐overlap of each OAR and the target is determined and used to establish dynamic gantry‐couch movements. Then, for each gantry‐couch track the most suitable collimator angle is determined for each control point by optimizing the area between the MLC leaves and the target contour. The resulting dynamic trajectories are used as input to perform the optimization using a research version of the VMAT optimization algorithm and the ESRAPI. The feasibility of this procedure was tested for a clinically motivated head and neck case. Resulting dose distributions for the VMAT plan and for the dynamic trajectory treatment plan were compared based on DVH‐parameters.Results:While the DVH for the target is virtually preserved, improvements in maximum dose for the DTRT plan were achieved for all OARs except for the inner‐ear, where maximum dose remains the same. The major improvements in maximum dose were 6.5% of the prescribed dose (66 Gy) for the parotid and 5.5% for the myelon and the eye.Conclusion:The result of this work suggests that DTRT has a great potential to reduce dose to OARs with similar target coverage when compared to conventional VMAT treatment plans. This work was supported by Varian Medical Systems.This work was supported by Varian Medical Systems.
TH‐EF‐BRB‐03: Significant Cord and Esophagus Dose Reduction by 4π Non‐Coplanar Spine Stereotactic Body Radiation Therapy and Stereotactic Radiosurgery
Authors: Yu V , Tran A , Nguyen D , Woods K , Cao M , Kaprealian T , Chin R , Low D , Sheng K 
Published: July 2016

Purpose:To demonstrate significant organ‐at‐risk (OAR) sparing achievable with 4π non‐coplanar radiotherapy on spine SBRT and SRS patients.Methods:Twenty‐five stereotactic spine cases previously treated with VMAT (n = 23) or IMRT (n = 2) were included in this study. A computer‐aided‐design model of a Linac with a 3D‐scanned human surface was utilized to determine the feasible beam space throughout the 4π steradian and beam specific source‐to‐target‐distances (STD) required for collision avoidance. 4π radiotherapy plans integrating beam orientation and fluence map optimization were then created using a column‐generation algorithm. Twenty optimal beams were selected for each case. To evaluate the tradeoff between dosimetric benefit and treatment complexity, 4π plans including only isocentrically deliverable beams were also created. Beam angles of all standard and isocentric 4π plans were imported into Eclipse to recalculate the dose using the same calculation engine as the clinical plans for unbiased comparison. OAR and PTV dose statistics for the clinical, standard‐4π, and isocentric‐4π plans were compared.Results:Comparing standard‐4π to clinical plans, particularly significant average percent reduction in the [mean, maximum] dose of the cord and esophagus of [41%, 21.7%], and [38.7%, 36.4%] was observed, along with global decrease in all other OAR dose statistics. The average cord volume receiving more than 50% prescription dose was substantially decreased by 76%. In addition, improved PTV coverage was demonstrated with a maximum dose reduction of 0.93% and 1.66% increase in homogeneity index (D95/D5). All isocentric‐4π plans achieved dosimetric performance equivalent to that of the standard‐4π plans with higher delivery complexity.Conclusion:4π radiotherapy significantly improves stereotactic spine treatment dosimetry. With the substantial OAR dose sparing, PTV dose escalation is considerably safer. Isocentric‐4π is sufficient to achieve the dosimetric gain. The successful implementation of 4π using an FDA approved planning system paves the way for a prospective clinical trial.Varian Medical Systems, NIH R43CA183390 and R01CA188300, NSF graduate research fellowship DGE‐1144087
TH‐EF‐BRB‐04: 4π Dynamic Conformal Arc Therapy Dynamic Conformal Arc Therapy (DCAT) for SBRT
Authors: Chiu T , Long T , Modiri A , Tian Z. , Sawant A , Yan Y , Jiang S , Gu X 
Published: July 2016

Purpose:To develop an efficient and effective trajectory optimization methodology for 4π dynamic conformal arc treatment (4π DCAT) with synchronized gantry and couch motion; and to investigate potential clinical benefits for stereotactic body radiation therapy (SBRT) to breast, lung, liver and spine tumors.Methods:The entire optimization framework for 4π DCAT inverse planning consists of two parts: 1) integer programming algorithm and 2) particle swarm optimization (PSO) algorithm. The integer programming is designed to find an optimal solution for arc delivery trajectory with both couch and gantry rotation, while PSO minimize a non‐convex objective function based on the selected trajectory and dose‐volume constraints. In this study, control point interaction is explicitly taken into account. Beam trajectory was modeled as a series of control points connected together to form a deliverable path. With linear treatment planning objectives, a mixed‐integer program (MIP) was formulated. Under mild assumptions, the MIP is tractable. Assigning monitor units to control points along the path can be integrated into the model and done by PSO. The developed 4π DCAT inverse planning strategy is evaluated on SBRT cases and compared to clinically treated plans.Results:The resultant dose distribution of this technique was evaluated between 3D conformal treatment plan generated by Pinnacle treatment planning system and 4π DCAT on a lung SBRT patient case. Both plans share the same scale of MU, 3038 and 2822 correspondingly to 3D conformal plan and 4π DCAT. The mean doses for most of OARs were greatly reduced at 32% (cord), 70% (esophagus), 2.8% (lung) and 42.4% (stomach).Conclusion:Initial results in this study show the proposed 4π DCAT treatment technique can achieve better OAR sparing and lower MUs, which indicates that the developed technique is promising for high dose SBRT to reduce the risk of secondary cancer.
TH‐EF‐BRB‐09: Total Body Irradiation with Uniform MU and Modulated Arc Segments, UMMS‐TBI
Authors: Yi B , Chung H , Mutaf Y , Prado K 
Published: July 2016

Purpose:To test a novel total body irradiation (TBI) system using conformal partial arc with patient lying on the stationary couch which is biologically equivalent to a moving couch TBI. This improves the scanning field TBI, which is previously presented.Methods:The Uniform MU Modulated arc Segments TBI or UMMS‐TBI scans the treatment plane with a constant machine dose rate and a constant gantry rotation speed. A dynamic MLC pattern which moves while gantry rotates has been designed so that the treatment field moves same distance at the treatment plane per each gantry angle, while maintaining same treatment field size (34cm) at the plane. Dose across the plane varies due to the geometric differences including the distance from the source to a point of interest and the different attenuation from the slanted depth which changes the effective depth. Beam intensity is modulated to correct the dose variation across the plane by assigning the number of gantry angles inversely proportional to the uncorrected dose.Results:Measured dose and calculated dose matched within 1 % for central axis and 3% for off axis for various patient scenarios. Dose from different distance does not follow the inverse square relation as it is predicted from calculation. Dose uniformity better than 5% across 180 cm at 10cm depth is achieved by moving the gantry from −55 to +55 deg. Total treatment time for 2 Gy AP/PA fields is 40–50 minutes excluding patient set up time, at the machine dose rate of 200 MU/min.Conclusion:This novel technique, yet accurate but easy to implement enables TBI treatment in a small treatment room with less program development preparation than other techniques. The VMAT function of treatment delivery is not required to modulate beams. One delivery pattern can be used for different patients by changing the monitor units.
TH‐EF‐BRA‐05: A MethodÂ of Near Real‐Time 4D MRI Using Volumetric Dynamic Keyhole (VDK) in the Presence of Respiratory Motion for MR‐Guided Radiotherapy
Authors: Lewis B , Kim S , Kim T 
Published: July 2016

Purpose:To develop a novel method that enables 4D MR imaging in near real‐time for continuous monitoring of tumor motion in MR‐guided radiotherapy.Methods:This method is mainly based on an idea of expanding dynamic keyhole to full volumetric imaging acquisition. In the VDK approach introduced in this study, a library of peripheral volumetric k‐space data is generated in given number of phases (5 and 10 in this study) in advance. For 4D MRI at any given time, only volumetric central k‐space data are acquired in real‐time and combined with pre‐acquired peripheral volumetric k‐space data in the library corresponding to the respiratory phase (or amplitude). The combined k‐space data are Fourier‐transformed to MR images. For simulation study, an MRXCAT program was used to generate synthetic MR images of the thorax with desired respiratory motion, contrast levels, and spatial and temporal resolution. 20 phases of volumetric MR images, with 200 ms temporal resolution in 4 s respiratory period, were generated using balanced steady‐state free precession MR pulse sequence. The total acquisition time was 21.5s/phase with a voxel size of 3×3×5 mm3 and an image matrix of 128×128×56. Image similarity was evaluated with difference maps between the reference and reconstructed images. The VDK, conventional keyhole, and zero filling methods were compared for this simulation study.Results:Using 80% of the ky data and 70% of the kz data from the library resulted in 12.20% average intensity difference from the reference, and 21.60% and 28.45% difference in threshold pixel difference for conventional keyhole and zero filling, respectively. The imaging time will be reduced from 21.5s to 1.3s per volume using the VDK method.Conclusion:Near real‐time 4D MR imaging can be achieved using the volumetric dynamic keyhole method. That makes the possibility of utilizing 4D MRI during MR‐guided radiotherapy.
TH‐EF‐BRA‐06: A Novel Retrospective 3D K‐Space Sorting 4D‐MRI Technique Using a Radial K‐Space Acquisition MRI Sequence
Authors: Liu Y , Subashi E , Yin F , Cai J 
Published: July 2016

Purpose:Current retrospective 4D‐MRI provides superior tumor‐to‐tissue contrast and accurate respiratory motion information for radiotherapy motion management. The developed 4D‐MRI techniques based on 2D‐MRI image sorting require a high frame‐rate of the MR sequences. However, several MRI sequences provide excellent image quality but have low frame‐rate. This study aims at developing a novel retrospective 3D k‐space sorting 4D‐MRI technique using radial k‐space acquisition MRI sequences to improve 4D‐MRI image quality and temporal‐resolution for imaging irregular organ/tumor respiratory motion.Methods:The method is based on a RF‐spoiled, steady‐state, gradient‐recalled sequence with minimal echo time. A 3D radial k‐space data acquisition trajectory was used for sampling the datasets. Each radial spoke readout data line starts from the 3D center of Field‐of‐View. Respiratory signal can be extracted from the k‐space center data point of each spoke. The spoke data was sorted based on its self‐synchronized respiratory signal using phase sorting. Subsequently, 3D reconstruction was conducted to generate the time‐resolved 4D‐MRI images. As a feasibility study, this technique was implemented on a digital human phantom XCAT. The respiratory motion was controlled by an irregular motion profile. To validate using k‐space center data as a respiratory surrogate, we compared it with the XCAT input controlling breathing profile. Tumor motion trajectories measured on reconstructed 4D‐MRI were compared to the average input trajectory. The mean absolute amplitude difference (D) was calculated.Results:The signal extracted from k‐space center data matches well with the input controlling respiratory profile of XCAT. The relative amplitude error was 8.6% and the relative phase error was 3.5%. XCAT 4D‐MRI demonstrated a clear motion pattern with little serrated artifacts. D of tumor trajectories was 0.21mm, 0.23mm and 0.23mm in SI, AP and ML directions, respectively.Conclusion:A novel retrospective 3D k‐space sorting 4D‐MRI technique has been developed and evaluated on human digital phantom.NIH (1R21CA165384‐01A1)