A scalable and deformable stylized model of the adult human eye for radiation dose assessment.
In this study, we present a geometric eye model that is both scalable (allowing for changes in eye size) and deformable (allowing for changes in eye shape), and that is suitable for use in radiation transport studies of ocular exposures and radiation treatments of eye disease. The model allows continuous and variable changes in eye size (axial lengths from 20 to 26 mm) and eye shape (diopters from -12 to +6). As an explanatory example of its use, five models (emmetropic eyes of small, average, and large size, as well as average size eyes of -12D and +6D) were constructed and subjected to normally incident beams of monoener...
Source: Physics in Medicine and Biology - March 23, 2018 Category: Physics Authors: El Basha D, Furuta T, Iyer SSR, Bolch WE Tags: Phys Med Biol Source Type: research

High resolution propagation-based imaging system for < i > in vivo < /i > dynamic computed tomography of lungs in small animals.
High resolution propagation-based imaging system for in vivo dynamic computed tomography of lungs in small animals. Phys Med Biol. 2018 Mar 22;: Authors: Preissner M, Murrie RP, Pinar I, Werdiger F, Carnibella RP, Zosky GR, Fouras A, Dubsky S Abstract We have developed an X-ray imaging system for &lt;i&gt;in vivo&lt;/i&gt; four-dimensional computed tomography (4DCT) of small animals for pre-clinical lung investigations. Our customized laboratory facility is capable of high resolution &lt;i&gt;in vivo&lt;/i&gt; imaging at high frame rates. Characterization using phantoms...
Source: Physics in Medicine and Biology - March 22, 2018 Category: Physics Authors: Preissner M, Murrie RP, Pinar I, Werdiger F, Carnibella RP, Zosky GR, Fouras A, Dubsky S Tags: Phys Med Biol Source Type: research

Signal intensity analysis and optimization for < i > in vivo < /i > imaging of Cherenkov and excited luminescence.
Signal intensity analysis and optimization for in vivo imaging of Cherenkov and excited luminescence. Phys Med Biol. 2018 Mar 20;: Authors: LaRochelle EPM, Shell JR, Gunn JR, Davis SC, Pogue BW Abstract During external beam radiotherapy (EBRT), in vivo Cherenkov optical emissions can be used as a dosimetry tool or to excite luminescence, termed Cherenkov-excited luminescence (CEL) with microsecond-level time-gated cameras. The goal of this work was to develop a complete theoretical foundation for the detectable signal strength, in order to provide guidance on optimization of the limits of detection an...
Source: Physics in Medicine and Biology - March 20, 2018 Category: Physics Authors: LaRochelle EPM, Shell JR, Gunn JR, Davis SC, Pogue BW Tags: Phys Med Biol Source Type: research

Collimated proton pencil-beam scanning for superficial targets: impact of the order of range shifter and aperture.
CONCLUSIONS: Although experiments and calculations indicate a ranking of the three delivery options regarding lateral dose fall-off, there seems to be a limited impact on a multi-field treatment plan. . PMID: 29553047 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - March 19, 2018 Category: Physics Authors: Baeumer C, Janson M, Timmermann B, Wulff J Tags: Phys Med Biol Source Type: research

Optimization of the reconstruction parameters in [ < sup > 123 < /sup > I]FP-CIT SPECT.
Optimization of the reconstruction parameters in [123I]FP-CIT SPECT. Phys Med Biol. 2018 Mar 19;: Authors: Niñerola-Baizán A, Gallego J, Cot A, Aguiar P, Lomeña F, Pavía J, Ros D Abstract The aim of this work was to obtain a set of parameters to be applied in [123I]FP-CIT SPECT reconstruction in order to minimize the error between standardized and true values of the Specific Uptake Ratio (SUR) in dopaminergic neurotransmission SPECT studies. To this end, Monte Carlo simulation was used to generate a database of 1,380 projection data-sets from 23 subjects, including normal c...
Source: Physics in Medicine and Biology - March 19, 2018 Category: Physics Authors: Niñerola-Baizán A, Gallego J, Cot A, Aguiar P, Lomeña F, Pavía J, Ros D Tags: Phys Med Biol Source Type: research

The influence of medium elasticity on the prediction of histotripsy-induced bubble expansion and erythrocyte viability.
In this study, an analytic model to predict histotripsy-induced bubble expansion in a fluid was extended to include the effects of medium elasticity. Good agreement was observed between the predictions of the analytic model and numerical computations utilizing highly nonlinear excitations (shock-scattering histotripsy) and purely tensile pulses (microtripsy). No bubble expansion was computed for either form of histotripsy when the elastic modulus was greater than 20 MPa and the peak negative pressure was less than 50 MPa. Strain in the medium due to the expansion of a single bubble was also tabulated. The viability of red ...
Source: Physics in Medicine and Biology - March 19, 2018 Category: Physics Authors: Bader KB Tags: Phys Med Biol Source Type: research

Validation of a virtual source model of medical linac for Monte Carlo dose calculation using multi-threaded Geant4.
Abstract The use of phase space in medical linear accelerator Monte Carlo (MC) simulations significantly improves the execution time and leads to results comparable to those obtained from full calculations. The classical representation of phase space stores directly the information of millions of particles, producing bulky files. This paper presents a virtual source model (VSM) based on a reconstruction algorithm, taking as input a compressed file of roughly 800 kb derived from phase space data freely available in the International Atomic Energy Agency (IAEA) database. This VSM includes two main components; primar...
Source: Physics in Medicine and Biology - March 19, 2018 Category: Physics Authors: Aboulbanine Z, El Khayati N Tags: Phys Med Biol Source Type: research

Individualized adjustments to reference phantom internal organ dosimetry - scaling factors given knowledge of patient internal anatomy.
Abstract Various computational tools are currently available that facilitate patient organ dosimetry in diagnostic nuclear medicine, yet they are typically restricted to reporting organ doses to ICRP-defined reference phantoms. The present study, while remaining computational phantom based, provides straightforward tools to adjust reference phantom organ dose for both internal photon and electron sources. A wide variety of monoenergetic specific absorbed fractions (SAFs) were computed using radiation transport simulations for tissue spheres of varying size and separation distance. Scaling methods were then constru...
Source: Physics in Medicine and Biology - March 16, 2018 Category: Physics Authors: Wayson MB, Bolch WE Tags: Phys Med Biol Source Type: research

Motion compensation for MRI-compatible patient-mounted needle guide device: estimation of targeting accuracy in MRI-guided kidney cryoablations.
Conclusion. Our simulation study demonstrated that the software system could significantly improve the targeting accuracy both in patients treated under MAC and GA. Intra-procedural image-based device-to-image registration was feasible. PMID: 29546845 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - March 16, 2018 Category: Physics Authors: Tokuda J, Chauvin L, Ninni B, Kato T, King F, Tuncali K, Hata N Tags: Phys Med Biol Source Type: research

Individualized adjustments to reference phantom internal organ dosimetry - scaling factors given knowledge of patient external anatomy.
This study aims to better personalize internal radiation dose estimates for individual patients by modifying the dose estimates calculated for reference individuals based on easily obtainable morphometric characteristics of the patient. Phantoms of different sitting heights and waist circumferences were constructed based on computational reference phantoms for the newborn, 10-year-old, and adult. Monoenergetic photons and electrons were then simulated separately at 15 energies. Photon and electron specific absorbed fractions (SAFs) were computed for the newly constructed non-reference phantoms and compared to SAFs previous...
Source: Physics in Medicine and Biology - March 16, 2018 Category: Physics Authors: Wayson MB, Bolch WE Tags: Phys Med Biol Source Type: research

A low-count reconstruction algorithm for Compton-based prompt gamma imaging.
In this study, we proposed a low-count reconstruction algorithm to improve the image quality of a characteristic PG emission by pooling information from other characteristic PG emissions. PGs were simulated from a proton beam irradiated on a water phantom, and a two-stage Compton camera was used for PG detection. The results show that the image quality of the reconstructed characteristic PG emission is improved with our proposed method in contrast to the standard reconstruction method using events from only one characteristic PG emission. For the 4.44 MeV PG rays, both methods can be used to predict the positions of the pe...
Source: Physics in Medicine and Biology - March 16, 2018 Category: Physics Authors: Huang HM, Liu CC, Jan ML, Lee MW Tags: Phys Med Biol Source Type: research

Fixed, object-specific intensity compensation for cone beam optical CT radiation dosimetry.
We present transmission images and solution phantom reconstructions to demonstrate that (1) placing compensators beyond the focal zone of the imaging lens prevents high spatial frequency features of the printed films from generating reconstruction artifacts, and (2) object-specific compensation considerably reduces the range of intensities measured in projection images. This will improve the measurable dose range in optical CT dosimetry, and will enable imaging of larger gel volumes (∼15 cm diameter). Additionally, it should enable re-use of dosimeters by printing a new compensator for a second experiment. ...
Source: Physics in Medicine and Biology - March 16, 2018 Category: Physics Authors: Dekker KH, Hazarika R, Silveira MA, Jordan KJ Tags: Phys Med Biol Source Type: research

American Association of Physicists in Medicine Task Group 263: Standardizing Nomenclatures in Radiation Oncology.
ller RC, Hurkmans C, Adams J, Jackie Wu QR, Fox CJ, Siochi RA, Brown NL, Verbakel W, Archambault Y, Chmura SJ, Dekker AL, Eagle DG, Fitzgerald TJ, Hong T, Kapoor R, Lansing B, Jolly S, Napolitano ME, Percy J, Rose MS, Siddiqui S, Schadt C, Simon WE, Straube WL, St James ST, Ulin K, Yom SS, Yock TI Abstract A substantial barrier to the single- and multi-institutional aggregation of data to supporting clinical trials, practice quality improvement efforts, and development of big data analytics resource systems is the lack of standardized nomenclatures for expressing dosimetric data. To address this issue, the America...
Source: Physics in Medicine and Biology - February 28, 2018 Category: Physics Authors: Mayo CS, Moran JM, Bosch W, Xiao Y, McNutt T, Popple R, Michalski J, Feng M, Marks LB, Fuller CD, Yorke E, Palta J, Gabriel PE, Molineu A, Matuszak MM, Covington E, Masi K, Richardson SL, Ritter T, Morgas T, Flampouri S, Santanam L, Moore JA, Purdie TG, M Tags: Int J Radiat Oncol Biol Phys Source Type: research

Improving Quality and Consistency in NRG  Oncology Radiation Therapy Oncology Group 0631 for Spine Radiosurgery via Knowledge-Based Planning.
CONCLUSION: Incorporation of KBP models into the clinical trial setting may have a profound impact on the quality of trial results, owing to the increase in consistency and standardization of planning, especially for treatment sites or techniques that are nonstandard. PMID: 29485048 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 28, 2018 Category: Physics Authors: Younge KC, Marsh RB, Owen D, Geng H, Xiao Y, Spratt DE, Foy J, Suresh K, Wu QJ, Yin FF, Ryu S, Matuszak MM Tags: Int J Radiat Oncol Biol Phys Source Type: research

Comparison of Stereotactic Body Radiation Therapy and Radiofrequency Ablation in the Treatment of Intrahepatic Metastases.
Abstract PURPOSE: Stereotactic body radiation therapy (SBRT) and radiofrequency ablation (RFA) are widely used therapies for the treatment of intrahepatic metastases; however, direct comparisons are lacking. We sought to compare outcomes for these 2 modalities. METHODS AND MATERIALS: From 2000 to 2015, 161 patients with 282 pathologically diagnosed unresectable liver metastases were treated with RFA (n = 112) or SBRT (n = 170) at a single institution. The primary outcome was freedom from local progression (FFLP). The effect of treatment and covariates on FFLP was modeled using a mixed-effects Cox model w...
Source: Physics in Medicine and Biology - February 28, 2018 Category: Physics Authors: Jackson WC, Tao Y, Mendiratta-Lala M, Bazzi L, Wahl DR, Schipper MJ, Feng M, Cuneo KC, Lawrence TS, Owen D Tags: Int J Radiat Oncol Biol Phys Source Type: research

Development of a Radiation Oncology Resident Continuity Clinic to Improve Clinical Competency and Patient Compliance.
PMID: 29413269 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 8, 2018 Category: Physics Authors: Yoo SK, Bian SX, Lin E, Batth SS, Ng LW, Andrade J, Williams PA, Pham AH, Ragab OM, Schechter NR, Chang EL, Jennelle RLS Tags: Int J Radiat Oncol Biol Phys Source Type: research

Impact of event positioning algorithm on performance of a whole-body PET scanner using one-to-one coupled detectors.
Abstract The advent of silicon photomultipliers (SiPMs) has introduced the possibility of increased detector performance in commercial whole-body PET scanners. The primary advantage of these photodetectors is the ability to couple a single SiPM channel directly to a single pixel of PET scintillator that is typically 4 mm wide (one-to-one coupled detector design). We performed simulation studies to evaluate the impact of three different event positioning algorithms in such detectors: i) a weighted energy centroid positioning (Anger logic), ii) identifying the crystal with maximum energy deposition (1&lt;sup&...
Source: Physics in Medicine and Biology - February 7, 2018 Category: Physics Authors: Surti S, Karp JS Tags: Phys Med Biol Source Type: research

Average stopping powers for electron and photon sources for radiobiological modeling and microdosimetric applications.
This study concerns calculation of the average electronic stopping power for photon and electron sources. It addresses two problems that have not yet been fully resolved. The first is defining the electron spectrum used for averaging in a way that is most suitable for radiobiological modeling. We define it as the spectrum of electrons entering the sensitive to radiation volume (SV) within the cell nucleus, at the moment they enter the SV. For this spectrum we derive a formula that combines linearly the fluence spectrum and the source spectrum. The latter is the distribution of initial energies of electrons produced by a so...
Source: Physics in Medicine and Biology - February 7, 2018 Category: Physics Authors: Vassiliev ON, Kry SF, Grosshans DR, Mohan R Tags: Phys Med Biol Source Type: research

Accuracy and precision of patient positioning for pelvic MR-only radiation therapy using digitally reconstructed radiographs.
Conclusions The MRCAT pseudo-CT method provides clinically acceptable accuracy and precision for patient positioning for pelvic radiation therapy based on planar DRR images. Furthermore, due to the reduction of geometric uncertainty, compared to dual-modality workflow, the approach is likely to improve the total geometric accuracy of pelvic radiation therapy. PMID: 29405121 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 6, 2018 Category: Physics Authors: Kemppainen R, Vaara T, Joensuu T, Kiljunen T Tags: Phys Med Biol Source Type: research

Experimental validation of a deforming grid 4D dose calculation for PBS proton therapy.
Abstract The aim of this study was to verify the temporal accuracy of the estimated dose distribution by a 4D dose calculation (4DDC) in comparison to measurements. A single-field plan (0.6Gy), optimised for a liver patient case (CTV volume: 403cc), was delivered to a homogeneous PMMA phantom and measured by a high resolution scintillating-CCD system at two water equivalent depths. Various motion scenarios (no motion and motions with amplitude of 10mm and two periods: 3.7s and 4.4s) were simulated using a 4D Quasar phantom and logged by an optical tracking system in real-time. Three motion mitigation approaches (s...
Source: Physics in Medicine and Biology - February 6, 2018 Category: Physics Authors: Krieger M, Klimpki G, Fattori GF, Hrbacek J, Oxley D, Safai S, Weber DC, Lomax AJ, Zhang Y Tags: Phys Med Biol Source Type: research

Prototype volumetric ultrasound tomography image guidance system for prone stereotactic partial breast irradiation: proof-of-concept.
Abstract Accurate dose delivery in Stereotactic partial breast irradiation (S-PBI) is challenging because of the target position uncertainty caused by breast deformation, the target volume changes caused by lumpectomy cavity shrinkage, and target delineation uncertainty on simulation computed tomography (CT) images caused by poor soft tissue contrast. We have developed a volumetric ultrasound tomography (UST) image guidance system for prone position S-PBI. The system is composed of a novel 3D printed rotation water tank, a patient-specific resin breast immobilization cup, and a 1D array ultrasound transducer. Coro...
Source: Physics in Medicine and Biology - February 6, 2018 Category: Physics Authors: Chiu TD, Parsons D, Zhang Y, Hrycushko B, Zhao B, Chopra R, Kim N, Spangler A, Rahimi A, Timmerman RD, Jiang SB, Lu W, Gu X Tags: Phys Med Biol Source Type: research

Performance of a new accelerating-electrode-equipped fast-time-response PMT coupled with fast LGSO.
In this study, we measured the performance of a newly developed Hamamatsu Photonics R13478 photomultiplier tube (PMT) and compared the results with those for an existing R9800 PMT. In R13478, an accelerating electrode is placed between the focusing electrode and first dynode for time resolution improvement through reduced transit time jitter. We investigated the time resolution dependence on the supply voltage and time pickoff method for R13478 and R9800 PMTs, each coupled with a 2.9 × 2.9 × 20 mm3 fast LGSO:Ce (0.025 mol%) crystal. In addition, we measured the PMT time resolutions coupled with the crystals in ...
Source: Physics in Medicine and Biology - February 6, 2018 Category: Physics Authors: Lee S, Lee MS, Won JY, Lee JS Tags: Phys Med Biol Source Type: research

Evaluation of the UF/NCI hybrid computational phantoms for use in organ dosimetry of pediatric patients undergoing fluoroscopically guided cardiac procedures.
In this study, two types of simulations were modeled. A dose assessment was performed on 29 patient-specific voxel phantoms (taken as representing the patient's true anatomy), height/weight-matched hybrid library phantoms, and age-matched reference phantoms. Two exposure studies were conducted for each phantom type. First, a parametric study was constructed by the attending pediatric interventional cardiologist at the University of Florida to model the range of parameters seen clinically. Second, four clinical cardiac procedures were simulated based upon internal logfiles captured by a Toshiba Infinix-i Cardiac Bi-Plane fl...
Source: Physics in Medicine and Biology - February 6, 2018 Category: Physics Authors: Marshall EL, Borrego D, Tran T, Fudge JC, Bolch WE Tags: Phys Med Biol Source Type: research

PET attenuation correction for rigid MR Tx/Rx coils from 176Lu background activity.
We present a straightforward method to measure the attenuation of Tx/Rx coils in simultaneous MR-PET imaging based on the natural 176Lu background contained in the scintillator of the PET detector without the requirement of an external CT scanner or PET scanner with transmission source. The method was evaluated on a prototype 3T MR-BrainPET produced by Siemens Healthcare GmbH, both with phantom studies and with true emission images from patient/volunteer examinations. Furthermore, the count rate stability of the PET scanner and the x-ray properties of the Tx/Rx head coil were investigated. Even without energy extrapolation...
Source: Physics in Medicine and Biology - February 6, 2018 Category: Physics Authors: Lerche CW, Kaltsas T, Caldeira L, Scheins J, Rota Kops E, Tellmann L, Pietrzyk U, Herzog H, Shah NJ Tags: Phys Med Biol Source Type: research

Development of real time abdominal compression force monitoring and visual biofeedback system.
In this study, we developed and evaluated a system that could monitor abdominal compression force (ACF) in real time and provide a surrogating signal, even under abdominal compression. The system could also provide visual-biofeedback (VBF). The real-time ACF monitoring system developed consists of an abdominal compression device, an ACF monitoring unit and a control system including an in-house ACF management program. We anticipated that ACF variation information caused by respiratory abdominal motion could be used as a respiratory surrogate signal. Four volunteers participated in this test to obtain correlation coef...
Source: Physics in Medicine and Biology - February 2, 2018 Category: Physics Authors: Kim TH, Kim S, Kim DS, Kang SH, Cho MS, Kim KH, Shin DS, Suh TS Tags: Phys Med Biol Source Type: research

Investigating the effect of a magnetic field on dose distributions at phantom-air interfaces using PRESAGE ® 3D dosimeter and Monte Carlo simulations.
Investigating the effect of a magnetic field on dose distributions at phantom-air interfaces using PRESAGE® 3D dosimeter and Monte Carlo simulations. Phys Med Biol. 2018 Feb 02;: Authors: Costa F, Doran SJ, Hanson IM, Nill S, Billas I, Shipley DR, Duane S, Adamovics J, Oelfke U Abstract Dosimetric quality assurance (QA) of the new Elekta Unity (MR-linac) will differ from the QA performed of a conventional linac due to the constant magnetic field, which creates an electron return effect (ERE). In this work we aim to validate PRESAGE(R) dosimetry in a transverse magnetic field, and assess its use to...
Source: Physics in Medicine and Biology - February 2, 2018 Category: Physics Authors: Costa F, Doran SJ, Hanson IM, Nill S, Billas I, Shipley DR, Duane S, Adamovics J, Oelfke U Tags: Phys Med Biol Source Type: research

MRI-only treatment planning: benefits and challenges.
Abstract Over the past decade, the application of magnetic resonance imaging (MRI) has increased, and there is growing evidence to suggest that improvements in the accuracy of target delineation in MRI-guided radiation therapy may improve clinical outcomes in a variety of cancer types. However, some considerations should be recognized including patient motion during image acquisition and geometric accuracy of images. Moreover, MR-compatible immobilization devices need to be used when acquiring images in the treatment position while minimizing patient motion during the scan time. Finally, synthetic CT images (i.e. ...
Source: Physics in Medicine and Biology - February 2, 2018 Category: Physics Authors: Owrangi AM, Greer PB, Glide-Hurst CK Tags: Phys Med Biol Source Type: research

A novel method to remove the background from x-ray diffraction signal.
Abstract The first step that is required to extract the correct information from a two-dimensional (2D) diffraction signature is to remove the background accurately. However, direct background subtraction inevitably overcorrects the signal as it does not take into account the attenuation by the sample. Other traditional background removal methods, such as the rolling ball technique, can separate sharp diffraction peaks of crystalline materials from their background. These methods are unsuitable for biological tissue, which is amorphous and does not have sharp diffraction peaks. This technical note proposes a novel...
Source: Physics in Medicine and Biology - February 2, 2018 Category: Physics Authors: Zheng Y, Speller R, Griffiths J Tags: Phys Med Biol Source Type: research

Modeling of Normal Tissue Complications Using Imaging and Biomarkers After Radiation Therapy for Hepatocellular Carcinoma.
CONCLUSIONS: The incorporation of imaging findings and biological markers into NTCP modeling of liver toxicity improved the estimates of expected NTCP risk compared with using dose-only models. In addition, such generalized NTCP models should contribute to a better understanding of the normal tissue response in HCC SBRT patients and facilitate personalized treatment. PMID: 29353652 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - January 23, 2018 Category: Physics Authors: El Naqa I, Johansson A, Owen D, Cuneo K, Cao Y, Matuszak M, Bazzi L, Lawrence TS, Ten Haken RK Tags: Int J Radiat Oncol Biol Phys Source Type: research

Intraoperative Electron Radiation Therapy in  Retroperitoneal Sarcoma.
CONCLUSIONS: Treatment with surgery, IORT, and EBRT is feasible and resulted in good LC and OS, with acceptable morbidity in this unfavorable patient cohort. Incomplete resection and recurrent status resulted in clearly inferior outcomes. Reasonable efforts should be made during primary treatment to prevent the onset of a local recurrence. PMID: 29353660 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - January 23, 2018 Category: Physics Authors: Roeder F, Alldinger I, Uhl M, Saleh-Ebrahimi L, Schimmack S, Mechtersheimer G, Büchler MW, Debus J, Krempien R, Ulrich A Tags: Int J Radiat Oncol Biol Phys Source Type: research

A prospective gating method to acquire a diverse set of free-breathing CT images for model-based 4DCT.
Abstract Breathing motion modeling requires observation of tissues at sufficiently distinct respiratory states for proper 4D characterization. This work proposes a method to improve sampling of the breathing cycle with limited imaging dose. We designed and tested a prospective free-breathing acquisition protocol with a simulation using datasets from 5 patients imaged with a model-based 4DCT technique. Each dataset contained 25 free-breathing fast helical CT scans with simultaneous breathing surrogate measurements. Tissue displacements were measured using deformable image registration. A correspondence model ...
Source: Physics in Medicine and Biology - January 19, 2018 Category: Physics Authors: O'Connell D, Ruan D, Thomas DH, Dou TH, Lewis JH, Santhanam AP, Lee PP, Low DA Tags: Phys Med Biol Source Type: research

Estimation and correction of produced light from prompt gamma photons on luminescence imaging of water for proton therapy dosimetry.
Abstract Although the luminescence images of water during proton-beam irradiation using a cooled charge-coupled device (CCD) camera showed almost the same ranges of proton beams as those measured by an ionization chamber, the depth profiles showed lower Bragg peak intensities than those measured by an ionization chamber. In addition, a broad optical baseline signal was observed in depths that exceed the depth of Bragg peak. We hypothesize that this broad baseline signal originates from interaction of proton-induced prompt gamma photons with water. These prompt gamma photons interact with water to form high-energy ...
Source: Physics in Medicine and Biology - January 19, 2018 Category: Physics Authors: Yabe T, Komori M, Toshito T, Yamaguchi M, Kawachi N, Yamamoto S Tags: Phys Med Biol Source Type: research

A three-dimensional correction method for predicting the readings of a PinPoint chamber on the CyberKnife < sup > ® < /sup > M6 ™ machine.
Conclusion: These results demonstrate the existence and efficiency of the novel 3D correction method for small field dosimetry. The 3D correction method provides an access to evaluate the clinical measurement data and can be applied to non-standard composite fields IMRT point dose verification. . PMID: 29350197 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - January 19, 2018 Category: Physics Authors: Zhang Y, Brandner E, Ozhasoglu C, Lalonde R, Heron DE, Huq MS Tags: Phys Med Biol Source Type: research

A depth-encoding PET detector using light sharing and single-ended readout with SiPMs.
Abstract Detectors with depth encoding capability and good timing resolution are required to develop a high-performance whole-body or total-body PET scanner. In this work, depth-encoding PET detectors using light sharing between two discrete crystals and single-ended readout with SiPMs were manufactured and evaluated. The detectors consisted of two unpolished LYSO crystals of 3×3×20 mm3 with different coupling materials between them and were read out by Hamamatsu 3×3 mm2 SiPMs with one-to-one coupling. The ratio of the energy of one SiPM to the total energy of two SiPMs is used to measure the dep...
Source: Physics in Medicine and Biology - January 19, 2018 Category: Physics Authors: Kuang Z, Yang Q, Wang X, Fu X, Ren N, Sang Z, Wu S, Zheng Y, Zhang X, Hu Z, Du J, Liang D, Liu X, Zheng H, Yang Y Tags: Phys Med Biol Source Type: research

Fraction-variant beam orientation optimization for non-coplanar IMRT.
Abstract Conventional beam orientation optimization (BOO) algorithms for IMRT assume that the same set of beam angles is used for all treatment fractions. In this paper we present a BOO formulation based on group sparsity that simultaneously optimizes non-coplanar beam angles for all fractions, yielding a fraction-variant (FV) treatment plan. Beam angles are selected by solving a multi-fraction fluence map optimization problem involving 500-700 candidate beams per fraction, with an additional group sparsity term that encourages most candidate beams to be inactive. The optimization problem is solved using the Fast ...
Source: Physics in Medicine and Biology - January 19, 2018 Category: Physics Authors: O'Connor D, Yu V, Nguyen D, Ruan D, Sheng K Tags: Phys Med Biol Source Type: research

Joint estimation of activity and attenuation for PET using pragmatic MR-based prior: application to clinical TOF PET/MR whole-body data for FDG and non-FDG tracers.
Abstract Accurate and robust attenuation correction remains challenging in hybrid PET/MR particularly for torsos because it is difficult to segment bones, lungs and internal air in MR images. Additionally, MR suffers from susceptibility artifacts when a metallic implant is present. Recently, joint estimation (JE) of activity and attenuation based on PET data, also known as maximum likelihood reconstruction of activity and attenuation (MLAA), has gained considerable interest because of (1) its promise to address the challenges in MR-based attenuation correction (MRAC), and (2) recent advances in time-of-flight (TOF...
Source: Physics in Medicine and Biology - January 18, 2018 Category: Physics Authors: Ahn S, Cheng L, Shanbhag DD, Qian H, Kaushik SS, Jansen FP, Wiesinger F Tags: Phys Med Biol Source Type: research

Accelerating acquisition strategies for low-frequency conductivity imaging using MREIT.
Abstract We sought to improve efficiency of Magnetic Resonance Electrical Impedance Tomography data acquisition so that fast conductivity changes or electric field variations could be monitored. Undersampling of k-space was used to decrease acquisition times in spin-echo-based sequences by a factor of two. Full MREIT data were reconstructed using continuity assumptions and preliminary scans gathered without current. We found that phase data were reconstructed faithfully from undersampled data. Conductivity reconstructions of phantom data were also possible. Therefore, undersampled k-space methods can potentia...
Source: Physics in Medicine and Biology - January 18, 2018 Category: Physics Authors: Song Y, Seo JK, Chauhan M, Indahlastari A, Ashok Kumar N, Sadleir R Tags: Phys Med Biol Source Type: research

4D computed tomography scans for conformal thoracic treatment planning: is a single scan sufficient to capture thoracic tumor motion?
Abstract Four dimensional computed tomography (4DCT) scans are routinely used in radiation therapy to determine the internal treatment volume for targets that are moving (e.g. lung tumors). The use of these studies has allowed clinicians to create target volumes based upon the motion of the tumor during the imaging study. The purpose of this work is to determine if a target volume based on a single 4DCT scan at simulation is sufficient to capture thoracic motion. Phantom studies were performed to determine expected differences between volumes contoured on 4DCT scans and those on the evaluation CT scans (slow scans...
Source: Physics in Medicine and Biology - January 18, 2018 Category: Physics Authors: Tseng YD, Wootton L, Nyflot M, Apisarnthanarax S, Rengan R, Bloch C, Sandison G, St James S Tags: Phys Med Biol Source Type: research

Bone surface enhancement in ultrasound images using a new Doppler-based acquisition/processing method.
The objective of this technique is to facilitate US-based bone segmentation methods and improve the accuracy of their outcomes. The newly proposed technique is tested both in in vitro and in vivo experiments. The results of these preliminary experiments suggest that the use of the proposed technique has the potential to significantly enhance the detectability of bone surfaces in noisy ultrasound images. PMID: 29339568 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - January 17, 2018 Category: Physics Authors: Yang X, Tang S, Tasciotti E, Righetti R Tags: Phys Med Biol Source Type: research

Comparison of Monte Carlo and Analytical Dose Computations for Intensity Modulated Proton Therapy.
Conclusion: This analysis concludes that for a fraction of the patients studied, differences TPS may overestimate the dose in the target by as much as 10%, while for some OARs the dose could be underestimated by as much as 10 Gy. Monte Carlo dose calculations may be needed to ensure more accurate dose computations to improve target coverage and sparing of OARs in proton therapy. . PMID: 29339570 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - January 17, 2018 Category: Physics Authors: Yepes PP, Adair AH, Grosshans DR, Mirkovic D, Poenisch F, Titt U, Wang Q, Mohan R Tags: Phys Med Biol Source Type: research

Dynamic PET image reconstruction integrating temporal regularization associated with respiratory motion correction for applications in oncology.
Abstract Respiratory motion reduces both the qualitative and quantitative accuracy of PET images in oncology. This impact is more significant for quantitative applications based on kinetic modeling, where dynamic acquisitions are associated with limited statistics due to the necessity of enhanced temporal resolution. The aim of this study is to address these drawbacks by combining within a unique reconstruction algorithm in dynamic PET imaging, a respiratory motion correction approach, as well as a temporal regularization. Elastic transformation parameters for the motion correction are estimated from th...
Source: Physics in Medicine and Biology - January 17, 2018 Category: Physics Authors: Merlin T, Visvikis D, Fernandez P, Lamare F Tags: Phys Med Biol Source Type: research

Optimizing highly noncoplanar VMAT trajectories: the NoVo method.
Abstract We introduce a new method called NoVo (Noncoplanar VMAT Optimization) to produce volumetric modulated arc therapy (VMAT) treatment plans with noncoplanar trajectories. While the use of noncoplanar beam arrangements for intensity modulated radiation therapy (IMRT), and in particular high fraction stereotactic radiosurgery (SRS), is common, noncoplanar beam trajectories for VMAT are less common as the availability of treatment machines handling these is limited. For both IMRT and VMAT, the beam angle selection problem is highly nonconvex in nature, which is why automated beam angle selection procedures have...
Source: Physics in Medicine and Biology - January 16, 2018 Category: Physics Authors: Langhans M, Unkelbach J, Bortfeld T, Craft D Tags: Phys Med Biol Source Type: research

An analytical poroelastic model for ultrasound elastography imaging of tumors.
Abstract The mechanical behavior of biological tissues has been studied using a number of mechanical models. Due to the relatively high fluid content and mobility, many biological tissues have been modeled as poroelastic materials. Diseases such as cancers are known to alter the poroelastic response of a tissue. Tissue poroelastic properties such as compressibility, interstitial permeability and fluid pressure also play a key role for the assessment of cancer treatments and for improved therapies. At the present time, however, a limited number of poroelastic models for soft tissues are retrievable in the literatur...
Source: Physics in Medicine and Biology - January 16, 2018 Category: Physics Authors: Islam MT, Chaudhry A, Unnikrishnan G, Reddy JN, Righetti R Tags: Phys Med Biol Source Type: research

Comparison of acrylic polymer adhesive tapes and silicone optical grease in light sharing detectors for positron emission tomography.
Abstract Optical coupling is an important factor in detector design as it improves optical photon transmission by mitigating internal reflections at light-sharing boundaries. In this work we compare optical coupling materials, namely double-sided acrylic polymer tapes and silicone optical grease (SiG), in the context of positron emission tomography (PET). Four double-sided tapes from 3M of varying thicknesses (0.229mm-1.016mm) and adhesive materials ('100MP', adhesive 100 'A100', 'VHB') were characterized with spectrophotometer measurements and photopeak amplitude and energy resolution measurements using lutetium-...
Source: Physics in Medicine and Biology - January 16, 2018 Category: Physics Authors: Van Elburg DJ, Noble SD, Hagey S, Goertzen AL Tags: Phys Med Biol Source Type: research

High PRF ultrafast sliding compound doppler imaging: fully qualitative and quantitative analysis of blood flow.
Abstract Ultrafast compound Doppler imaging based on plane-wave excitation (UCDI) can be used to evaluate cardiovascular diseases using high frame rates. In particular, it provides a fully quantifiable flow analysis over a large region of interest with high spatio-temporal resolution. However, the pulse-repetition frequency (PRF) in the UCDI method is limited for high-velocity flow imaging since it leverages between the number of plane-wave angles (&lt;i&gt;N&lt;/i&gt;) and acquisition time. In this paper, we present high PRF ultrafast sliding compound Doppler imaging method (HUSDI) to improve quan...
Source: Physics in Medicine and Biology - January 15, 2018 Category: Physics Authors: Kang J, Jang WS, Yoo Y Tags: Phys Med Biol Source Type: research

First heating measurements of endovascular stents in magnetic particle imaging.
Abstract Magnetic Particle Imaging (MPI) is a three-dimensional imaging method which visualizes the spatial distribution of Superparamagnetic Iron Oxide Nanoparticles (SPIOs) with oscillating and static magnetic fields. It is a quantitative method as the intensity of its signal is proportional to the concentration of the SPIOs. Due to its quantitativeness, high temporal resolution and kidney-safe tracers it is proposed to be a very promising noninvasive method for cardiovascular imaging. In this regard MPI in the presence of endovascular stents and assessment of stent patency with MPI has to be evaluated. The purp...
Source: Physics in Medicine and Biology - January 15, 2018 Category: Physics Authors: Wegner F, Friedrich T, Panagiotopoulos N, Vaalma S, Goltz JP, Vogt FM, Koch MA, Buzug TM, Barkhausen J, Haegele J Tags: Phys Med Biol Source Type: research

Global spectral graph wavelet signature for surface analysis of carpal bones.
Abstract Quantitative shape comparison is a fundamental problem in computer vision, geometry processing and medical imaging. In this paper, we present a spectral graph wavelet approach for shape analysis of carpal bones of the human wrist. We employ spectral graph wavelets to represent the cortical surface of a carpal bone via the spectral geometric analysis of the Laplace-Beltrami operator in the discrete domain. We propose global spectral graph wavelet (GSGW) descriptor that is isometric invariant, efficient to compute, and combines the advantages of both low-pass and band-pass filters. ...
Source: Physics in Medicine and Biology - January 12, 2018 Category: Physics Authors: Masoumi M, Rezaei M, Ben Hamza A Tags: Phys Med Biol Source Type: research

A PET reconstruction formulation that enforces non-negativity in projection space for bias reduction in Y-90 imaging.
Abstract Most existing PET image reconstruction methods impose a nonnegativity constraint in the image domain that is natural physically, but can lead to biased reconstructions. This bias is particularly problematic for Y-90 PET because of the low probability positron production and high random coincidence fraction. This paper investigates a new PET reconstruction formulation that enforces nonnegativity of the projections instead of the voxel values. This formulation allows some negative voxel values, thereby potentially reducing bias. Unlike the previously reported NEG-ML approach that modifies the Poisson log-li...
Source: Physics in Medicine and Biology - January 12, 2018 Category: Physics Authors: Lim H, Dewaraja YK, Fessler JA Tags: Phys Med Biol Source Type: research

Direct determination of < i > k < /i > < sub > Q < /sub > factors for cylindrical and plane-parallel ionization chambers in high-energy electron beams from 6 MeV to 20 MeV.
Direct determination of kQ factors for cylindrical and plane-parallel ionization chambers in high-energy electron beams from 6 MeV to 20 MeV. Phys Med Biol. 2018 Jan 12;: Authors: Krauss A, Kapsch RP Abstract For the ionometric determination of the absorbed dose to water, Dw, in high-energy electron beams from a clinical accelerator, beam quality dependent correction factors, kQ, are required. By using a water calorimeter, these factors can be determined experimentally and potentially with lower standard uncertainties than those of the calculated kQ factors, which are tabulated in various dosimetry pr...
Source: Physics in Medicine and Biology - January 12, 2018 Category: Physics Authors: Krauss A, Kapsch RP Tags: Phys Med Biol Source Type: research

Spatiotemporal radiotherapy planning using a global optimization approach.
Abstract This paper aims at quantifying the extent of potential therapeutic gain, measured using biologically effective dose (BED), that can be achieved by altering the radiation dose distribution over treatment sessions in fractionated radiotherapy. To that end, a spatiotemporally integrated planning approach is developed, where the spatial and temporal dose modulations are optimized simultaneously. The concept of equivalent uniform BED (EUBED) is used to quantify and compare the clinical quality of spatiotemporally heterogeneous dose distributions in target and critical structures. This gives rise to a large-sca...
Source: Physics in Medicine and Biology - January 12, 2018 Category: Physics Authors: Adibi A, Salari E Tags: Phys Med Biol Source Type: research