bluuebunny/crossref_metadata_2025_split huggingface dataset:
TU‐F‐BRE‐05: Experimental Determination of K Factor in Small Field Dosimetry
Authors: Das I , Akino Y , Francescon P 
Published: July 2014

Purpose:Small‐field dosimetry is challenging due to charged‐particle disequilibrium, source occlusion and more importantly finite size of detectors. IAEA/AAPM has published approach to convert detector readings to dose by k factor. Manufacturers have been trying to provide various types of micro‐detectors that could be used in small fields. However k factors depends on detector perturbations and are derived using Monte Carlo simulation. PTW has introduced a microDiamond for small‐field dosimetry. An experimental approach is presented to derive the k factor for this detector.Methods:PTW microDiamond is a small volume detector with 1.1 mm radius and 1.0 micron thick synthetic diamond. Output factors were measured from 1×1cm2 to 12×12 cm2 on a Varian machine at various depths using various micro‐detectors with published k factors. Dose is calculated as reading * K. Assuming k factor is accurate, output factor should be identical with every micro‐detectors. Hence published k values (Francescon et al Med Phys 35, 504‐513,2008) were used to covert readings and then output factors were computed. Based on the converged curve from other detectors, k factor for microDiamond was computed versus field size.Results:Traditional output factors as ratio of readings normalized to 10×10 cm2 differ significantly for micro‐detectors for fields smaller than 3×3 cm2 which are now being used extensively. When readings are converted to dose, the output factor is independent of detector. Based on this method, k factor for microDiamond was estimated to be nearly constant 0.993±0.007 over varied field sizes.Conclusion:Our method provides a unique opportunity to determine the k factor for any unknown detector. It is shown that even though k factor depends on machine type due to focal spot, however for fields ≥1×1 cm2 this method provides accurate evaluation of k factor. Additionally microDiamond could be used with assumption that k factor is nearly unity.
TU‐F‐BRD‐01: Biomedical Informatics for Medical Physicists
Authors: Phillips M , Kalet I , McNutt T , Smith W 
Published: July 2014

Biomedical informatics encompasses a very large domain of knowledge and applications. This broad and loosely defined field can make it difficult to navigate. Physicists often are called upon to provide informatics services and/or to take part in projects involving principles of the field. The purpose of the presentations in this symposium is to help medical physicists gain some knowledge about the breadth of the field and how, in the current clinical and research environment, they can participate and contribute.Three talks have been designed to give an overview from the perspective of physicists and to provide a more in‐depth discussion in two areas. One of the primary purposes, and the main subject of the first talk, is to help physicists achieve a perspective about the range of the topics and concepts that fall under the heading of “informatics”. The approach is to de‐mystify topics and jargon and to help physicists find resources in the field should they need them.The other talks explore two areas of biomedical informatics in more depth. The goal is to highlight two domains of intense current interest‐‐databases and models‐‐in enough depth into current approaches so that an adequate background for independent inquiry is achieved. These two areas will serve as good examples of how physicists, using informatics principles, can contribute to oncology practice and research.Learning Objectives:

To understand how the principles of biomedical informatics are used by medical physicists.
To put the relevant informatics concepts in perspective with regard to biomedicine in general.
To use clinical database design as an example of biomedical informatics.
To provide a solid background into the problems and issues of the design and use of data and databases in radiation oncology.
To use modeling in the service of decision support systems as an example of modeling methods and data use.
To provide a background into how uncertainty in our data and knowledge can be incorporated into modeling methods.
TU‐F‐BRF‐02: MR‐US Prostate Registration Using Patient‐Specific Tissue Elasticity Property Prior for MR‐Targeted, TRUS‐Guided HDR Brachytherapy
Authors: Yang X , Rossi P , Ogunleye T , Jani A , Curran W , Liu T 
Published: July 2014

Purpose:High‐dose‐rate (HDR) brachytherapy has become a popular treatment modality for prostate cancer. Conventional transrectal ultrasound (TRUS)‐guided prostate HDR brachytherapy could benefit significantly from MR‐targeted, TRUS‐guided procedure where the tumor locations, acquired from the multiparametric MRI, are incorporated into the treatment planning. In order to enable this integration, we have developed a MR‐TRUS registration with a patient‐specific biomechanical elasticity prior.Methods:The proposed method used a biomechanical elasticity prior to guide the prostate volumetric B‐spline deformation in the MRI and TRUS registration. The patient‐specific biomechanical elasticity prior was generated using ultrasound elastography, where two 3D TRUS prostate images were acquired under different probe‐induced pressures during the HDR procedure, which takes 2‐4 minutes. These two 3D TRUS images were used to calculate the local displacement (elasticity map) of two prostate volumes. The B‐spline transformation was calculated by minimizing the Euclidean distance between the normalized attribute vectors of the prostate surface landmarks on the MR and TRUS. This technique was evaluated through two studies: a prostate‐phantom study and a pilot study with 5 patients undergoing prostate HDR treatment. The accuracy of our approach was assessed through the locations of several landmarks in the post‐registration and TRUS images; our registration results were compared with the surface‐based method.Results:For the phantom study, the mean landmark displacement of the proposed method was 1.29±0.11 mm. For the 5 patients, the mean landmark displacement of the surface‐based method was 3.25±0.51 mm; our method, 1.71±0.25 mm. Therefore, our proposed method of prostate registration outperformed the surfaced‐based registration significantly.Conclusion:We have developed a novel MR‐TRUS prostate registration approach based on patient‐specific biomechanical elasticity prior. Successful integration of multi‐parametric MR and TRUS prostate images provides a prostate‐cancer map for treatment planning, enables accurate dose planning and delivery, and potentially enhances prostate HDR treatment outcome.
TU‐F‐17A‐03: An Analytical Respiratory Perturbation Model for Lung Motion Prediction
Authors: Li G , Yuan A , Wei J 
Published: July 2014

Purpose:Breathing irregularity is common, causing unreliable prediction in tumor motion for correlation‐based surrogates. Both tidal volume (TV) and breathing pattern (BP=ΔVthorax/TV, where TV=ΔVthorax+ΔVabdomen) affect lung motion in anterior‐posterior and superior‐inferior directions. We developed a novel respiratory motion perturbation (RMP) model in analytical form to account for changes in TV and BP in motion prediction from simulation to treatment.Methods:The RMP model is an analytical function of patient‐specific anatomic and physiologic parameters. It contains a base‐motion trajectory d(x,y,z) derived from a 4‐dimensional computed tomography (4DCT) at simulation and a perturbation term Δd(ΔTV,ΔBP) accounting for deviation at treatment from simulation. The perturbation is dependent on tumor‐specific location and patient‐specific anatomy. Eleven patients with simulation and treatment 4DCT images were used to assess the RMP method in motion prediction from 4DCT1 to 4DCT2, and vice versa. For each patient, ten motion trajectories of corresponding points in the lower lobes were measured in both 4DCTs: one served as the base‐motion trajectory and the other as the ground truth for comparison. In total, 220 motion trajectory predictions were assessed. The motion discrepancy between two 4DCTs for each patient served as a control. An established 5D motion model was used for comparison.Results:The average absolute error of RMP model prediction in superior‐inferior direction is 1.6±1.8 mm, similar to 1.7±1.6 mm from the 5D model (p=0.98). Some uncertainty is associated with limited spatial resolution (2.5mm slice thickness) and temporal resolution (10‐phases). Non‐corrected motion discrepancy between two 4DCTs is 2.6±2.7mm, with the maximum of ±20mm, and correction is necessary (p=0.01).Conclusion:The analytical motion model predicts lung motion with accuracy similar to the 5D model. The analytical model is based on physical relationships, requires no training, and therefore is potentially more resilient to breathing irregularities. On‐going investigation introduces airflow into the RMP model for improvement.This research is in part supported by NIH (U54CA137788/132378). AY would like to thank MSKCC summer medical student research program supported by National Cancer Institute and hosted by Department of Medical Physics at MSKCC.
WE‐D‐BRD‐01: Innovation in Radiation Therapy Delivery: Advanced Digital Linac Features
Authors: Xing L , Wong J , Li R 
Published: July 2014

Last few years has witnessed significant advances in linac technology and therapeutic dose delivery method. Digital linacs equipped with high dose rate FFF beams have been clinically implemented in a number of hospitals. Gated VMAT is becoming increasingly popular in treating tumors affected by respiratory motion. This session is devoted to update the audience with these technical advances and to present our experience in clinically implementing the new linacs and dose delivery methods. Topics to be covered include, technical features of new generation of linacs from different vendors, dosimetric characteristics and clinical need for FFF‐beam based IMRT and VMAT, respiration‐gated VMAT, the concept and implementation of station parameter optimized radiation therapy (SPORT), beam level imaging and onboard image guidance tools. Emphasis will be on providing fundamental understanding of the new treatment delivery and image guidance strategies, control systems, and the associated dosimetric characteristics. Commissioning and acceptance experience on these new treatment delivery technologies will be reported. Clinical experience and challenges encountered during the process of implementation of the new treatment techniques and future applications of the systems will also be highlighted.Learning Objectives:

Present background knowledge of emerging digital linacs and summarize their key geometric and dosimetric features.
SPORT as an emerging radiation therapy modality specifically designed to take advantage of digital linacs.
Discuss issues related to the acceptance and commissioning of the digital linacs and FFF beams.
Describe clinical utility of the new generation of digital linacs and their future applications.
WE‐D‐BRF‐02: Acoustic Signal From the Bragg Peak for Range Verification in Proton Therapy
Authors: Reinhardt S , Assmann W , Kellnberger S , Omar M , Fink A , Gaebisch C , Thirolf P , Moser M , Dollinger G , Sergiadis G , Ntziachristos V , Parodi K 
Published: July 2014

Purpose:Range verification in ion beam therapy relies to date on nuclear imaging techniques which require complex and costly detector systems. A different approach is the detection of thermoacoustic signals that are generated due to localized energy loss of ion beams. Aim of this work is to study the feasibility of determining the ion range with sub‐mm accuracy by use of high frequency ultrasonic (US) transducers and to image the Bragg peak by tomography.Methods:A water phantom was irradiated by a pulsed 20 MeV proton beam with varying pulse intensity, length and repetition rate. The acoustic signal of single proton pulses was measured by different PZT‐based US detectors (3.5 MHz and 10 MHz central frequencies). For tomography a 64 channel US detector array was used and moved along the ion track by a remotely controlled motor stage.Results:A clear signal of the Bragg peak was visible for an energy deposition as low as 1012 eV. The signal amplitude showed a linear increase with particle number per pulse and thus, dose. Range measurements were reproducible within +/− 20 micrometer and agreed well with Geant4 simulations. The tomographic reconstruction does not only allow to measure the ion range but also the beam spot size at the Bragg peak position.Conclusion:Range verification by acoustic means is a promising new technique for treatment modalities where the tumor can be localized by US imaging. Further improvement of sensitivity is required to account for higher attenuation of the US signal in tissue, as well as lower energy density in the Bragg peak in realistic treatment cases due to higher particle energy and larger spot sizes. Nevertheless, the acoustic range verification approach could offer the possibility of combining anatomical US imaging with Bragg Peak imaging in the near future.The work was funded by the DFG cluster of excellence Munich Centre for Advanced Photonics (MAP).
WE‐D‐BRF‐03: Proton Beam Range Verification with a Single Prompt Gamma‐Ray Detector
Authors: Verburg J , Testa M , Cascio E , Bortfeld T , Lu H , Seco J 
Published: July 2014

Purpose:To present an experimental study of a novel range verification method for scanned and scattered proton beams.Methods:A detection system consisting of an actively shielded lanthanum(III)bromide scintillator and a one‐sided lead collimator was used to measure prompt gamma‐rays emitted during the delivery of proton beams to a water phantom and an anthropomorphic head phantom. The residual proton range at the collimator position was determined by comparing gamma‐ray intensities while the proton energy was modulated to the distal end of the target. We used a clinical field to deliver a 50 cGy dose to a 12 cm diameter target in the water phantom and to a 175 cc tumor‐shaped target in the head phantom. The detector signals were acquired with a custom data acquisition system enabling energy and time‐of‐flight discrimination of prompt gamma‐rays.Results:Range deviations were detected with a statistical accuracy of ± 0.2 mm and ± 1.4 mm at 90% confidence level, respectively for the water and head phantom. We obtained a time resolution of 1 ns FWHM and an energy resolution < 2% FWHM for the main gamma lines from proton‐induced nuclear reactions with carbon and oxygen. This allowed for an accurate separation of the prompt gamma‐rays from neutron‐induced background.Conclusion:Proton range deviations can be detected with millimeter accuracy using a single prompt gamma‐ray measurement point acquired during the delivery of a few proton energy layers to the distal part of the target. The method is also feasible in the presence of background radiation from passively scattered proton beam delivery.
WE‐D‐BRF‐04: Experimental Investigations On Ion Radiography with Beam Scanning Using a Range Telescope
Authors: Rinaldi I , Marcelos T , Magallanes L , Takechi M , Brons S , Jaekel O , Voss B , Parodi K 
Published: July 2014

Purpose:Ion beams exhibit a finite range and an inverted depth‐dose profile, the Bragg peak. These favorable properties allow superior tumordose conformality, but introduce sensitivity to range uncertainties. Hence, imaging techniques play an increasingly important role to support the treatment planning and the in‐vivo monitoring of the actual ion beam treatment.Methods:This work presents the experimental investigations carried out to address the feasibility of ion transmission imaging at the Heidelberg Ion Therapy center using an active raster scanning beam delivery system and a prototype range telescope set‐up based on a stack of 61 parallel‐plate ionization chambers (PPIC) interleaved with 3 mm absorber plates of PMMA.Results:An extensive characterization of the set‐up in terms of beam parameters and settings of the read‐out electronics was performed and results will be presented. A data processing method to increase the range resolution (MIRR) of the PPIC stack was developed. In this approach, the position of the maximum of the Bragg curve is deduced from the ratio of measured signals in adjacent PPIC channels. MIRR evaluation is based on Bragg curves obtained from Monte Carlo simulations and validated with experimental data acquired with the PPIC stack using ion beams. MIRR was applied to the carbon ion radiography of an anthropomorphic Alderson head phantom yielding a resolution of 0.8 mm water equivalent thickness (WET) compared to the nominal value of 3.495 mm WET given by the thickness of the absorber slabs in the PPIC stack. An absolute comparison of the Alderson phantom carbon ion transmitted image with an X‐ray digitally reconstructed radiography, both converted into WET, will also be shown.Conclusion:The obtained results are very promising and motivate further developments of the system towards an eventual clinical use. This work is supported by the German Research Foundation and the German Academic Exchange Service.This work is supported by the German Research Foundation (DFG) and the German Academic Exchange Service (DAAD).
WE‐D‐17A‐01: A Dynamic Collimation System for Spot Scanned Proton Therapy: Conceptual Overview
Authors: Hyer D , Hill P , Wang D , Smith B , Flynn R 
Published: July 2014

Purpose:In the absence of a collimation system, the lateral penumbra in pencil beam scanning (PBS) proton therapy delivered at low energies is highly dependent on the spot size. This dependence, coupled with the fact that spot sizes increase with decreasing energy, reduces the benefit of the PBS technique for treating shallow tumors such as those found in the head and neck region. In order to overcome this limitation, a dynamic collimation system (DCS) was developed for sharpening the lateral penumbra of low energy proton therapy dose distributions delivered by PBS.Methods:The proposed DCS consists of two pairs of orthogonal trimmer blades which intercept the edges of the proton beam near the target edge in the beam's eye view. Each trimmer blade is capable of rapid motion in the direction perpendicular to the central beam axis by means of a linear motor, with maximum velocity and acceleration of 2.5 m/s and 19.6 m/s2, respectively. Two‐dimensional treatment plans were created both with and without the DCS for in‐air spot sizes (σ_air) of 3, 5, 7, and 9 mm, representing a wide array of clinically available equipment.Results:In its current configuration, the snout of the DCS has outer dimensions of 22.6 × 22.6 cm2 and is capable of delivering a minimum treatment field size of 15 × 15 cm2. Using off the shelf components, the constructed system would weigh less than 20 kg. The treatment plans created with the DCS yielded a reduction in the mean dose to normal tissue surrounding the target of 26.2–40.6% for spot sizes of 3–9 mm, respectively.Conclusion:The DCS can be integrated with current or future proton therapy equipment and we believe it will serve as a useful tool to further improve the next generation of proton therapy delivery.
WE‐D‐17A‐03: Improvement of Accuracy of Spot‐Scanning Proton Beam Delivery for Liver Tumor by Real‐Time Tumor‐Monitoring and Gating System: A Simulation Study
Authors: Matsuura T , Shimizu S , Miyamoto N , Takao S , Toramatsu C , Nihongi H , Yamada T , Fujii Y , Umezawa M , Umegaki K , Shirato H 
Published: July 2014

Purpose:To improve the accuracy of spot‐scanning proton beam delivery for target in motion, a real‐time tumor‐monitoring and gating system using fluoroscopy images was developed. This study investigates the efficacy of this method for treatment of liver tumors using simulation.Methods:Three‐dimensional position of a fiducial marker inserted close to the tumor is calculated in real time and proton beam is gated according to the marker's distance from the planned position (Shirato, 2012). The efficient beam delivery is realized even for the irregular and sporadic motion signals, by employing the multiple‐gated irradiations per operation cycle (Umezawa, 2012). For each of two breath‐hold CTs (CTV=14.6cc, 63.1cc), dose distributions were calculated with internal margins corresponding to freebreathing (FB) and real‐time gating (RG) with a 2‐mm gating window. We applied 8 trajectories of liver tumor recorded during the treatment of RTRT in X‐ray therapy and 6 initial timings. Dmax/Dmin in CTV, mean liver dose (MLD), and irradiation time to administer 3 Gy (RBE) dose were estimated assuming rigid motion of targets by using in‐house simulation tools and VQA treatment planning system (Hitachi, Ltd., Tokyo).Results:Dmax/Dmin was degraded by less than 5% compared to the prescribed dose with all motion parameters for smaller CTV and less than 7% for larger CTV with one exception. Irradiation time showed only a modest increase if RG was used instead of FB; the average value over motion parameters was 113 (FB) and 138 s (RG) for smaller CTV and 120 (FB) and 207 s (RG) for larger CTV. In RG, it was within 5 min for all but one trajectory. MLD was markedly decreased by 14% and 5–6% for smaller and larger CTVs respectively, if RG was applied.Conclusions:Spot‐scanning proton beam was shown to be delivered successfully to liver tumor without much lengthening of treatment time.This research was supported by the Cabinet Office, Government of Japan and the Japan Society for the Promotion of Science (JSPS) through the Funding Program for World‐Leading Innovative R&D on Science and Technology (FIRST Program), initiated by the Council for Science and Technology Policy (CSTP).
WE‐D‐17A‐05: Measurement of Stray Radiation Within An Active Scanning Proton Therapy Facility: EURADOS WG9 Intercomparison Exercise of Active Dosimetry Systems
Authors: Farah J , Stolarczyk L , Algranati C , Domingo C , Dufek V , Fellin F , Frojdh E , George S , Harrison R , Klodowska M , Kubancak J , Knezevic Z , Liszka M , Majer M , Mares V , Miljanic S , Ploc O , Romero‐Exposito M , Ruhm W , Schinner K , Schwarz M , Trinkl S , Trompier F , Wielunski M , Olko P 
Published: July 2014

Purpose:Intercomparison of active dosemeters in the measurement of stray radiation at the Trento active‐scanning proton therapy facility.Methods:EURADOS WG9 carried out a large intercomparison exercise to test different dosemeters while measuring secondary neutrons within a 230 MeV scanned proton therapy facility. Detectors included two Bonner Sphere Spectrometers (BSS), three tissue equivalent proportional counters (TEPCHawk) and six rem‐counters (Wendi II, Berthold, RadEye, a regular and an extended‐range Anderson & Braun NM2B counters). Measurements of neutron ambient dose equivalents, H*(10), were done at several positions inside (8 positions) and outside (3 positions) the treatment room while irradiating a water tank phantom with a 10 × 10 × 10 cc field.Results:A generally good agreement on H*(10) values was observed for the tested detectors. At distance of 2.25 m and angles 45°, 90° and 180° with respect to the beam axis, BSS and proportional counters agreed within 30%. Higher differences (up to 60%) were observed at the closest and farthest distances, i.e. at positions where detectors sensitivity, energy, fluence and angular response are highly dependent on neutron spectra (flux and energy). The highest neutron H*(10) value, ∼60 microSv/Gy, was measured at 1.15 m along the beam axis. H*(10) decreased significantly with the distance from the isocenter dropping to 1.1 microSv/Gy at 4.25 m and 90° from beam axis, ∼2 nanoSv/Gy at the entrance of the maze, 0.2 nanoSv/Gy at the door outside the room and below detection limit in the gantry control room and at an adjacent room. These values remain considerately lower than those of passively scattered proton beams. BSS and Hawk unfolded spectra provide valuable inputs when studying the response of each detector.Conclusion:TEPCs and BSS enable accurate measurements of stray neutrons while other rem‐meters also give satisfactory results but require further improvements to reduce uncertainties.