bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐G‐TeP3‐01: A New Approach for Calculating Variable Relative Biological Effectiveness in IMPT Optimization
Authors: Cao W , Randeniya K , Yepes P , Grosshans D , Mohan R
Published: July 2016

Purpose:

To investigate the impact of a new approach for calculating relative biological effectiveness (RBE) in intensity‐modulated proton therapy (IMPT) optimization on RBE‐weighted dose distributions. This approach includes the nonlinear RBE for the high linear energy transfer (LET) region, which was revealed by recent experiments at our institution. In addition, this approach utilizes RBE data as a function of LET without using dose‐averaged LET in calculating RBE values.

Methods:

We used a two‐piece function for calculating RBE from LET. Within the Bragg peak, RBE is linearly correlated to LET. Beyond the Bragg peak, we use a nonlinear (quadratic) RBE function of LET based on our experimental. The IMPT optimization was devised to incorporate variable RBE by maximizing biological effect (based on the Linear Quadratic model) in tumor and minimizing biological effect in normal tissues. Three glioblastoma patients were retrospectively selected from our institution in this study. For each patient, three optimized IMPT plans were created based on three RBE resolutions, i.e., fixed RBE of 1.1 (RBE‐1.1), variable RBE based on linear RBE and LET relationship (RBE‐L), and variable RBE based on linear and quadratic relationship (RBE‐LQ). The RBE weighted dose distributions of each optimized plan were evaluated in terms of different RBE values, i.e., RBE‐1.1, RBE‐L and RBE‐LQ.

Results:

The RBE weighted doses recalculated from RBE‐1.1 based optimized plans demonstrated an increasing pattern from using RBE‐1.1, RBE‐L to RBE‐LQ consistently for all three patients. The variable RBE (RBE‐L and RBE‐LQ) weighted dose distributions recalculated from RBE‐L and RBE‐LQ based optimization were more homogenous within the targets and better spared in the critical structures than the ones recalculated from RBE‐1.1 based optimization.

Conclusion:

We implemented a new approach for RBE calculation and optimization and demonstrated potential benefits of improving tumor coverage and normal sparing in IMPT planning.
SU‐G‐TeP3‐02: Determination of Geometry‐Specific Backscatter Factors for Radiobiology Studies
Authors: Viscariello N , Culberson W , Lawless M , Kunugi K , DeWerd L
Published: July 2016

Purpose:

Radiation biology research relies on an accurate radiation dose delivered to the biological target. Large field irradiations in a cabinet irradiator may use the AAPM TG‐61 protocol. This relies on an air‐kerma measurement and conversion to absorbed dose to water (Dw) on the surface of a water phantom using provided backscatter factors. Cell or small animal studies differ significantly from this reference geometry. This study aims to determine the impact of the lack of full scatter conditions in four representative geometries that may be used in radiobiology studies.

Methods:

MCNP6 was used to model the Dw on the surface of a full scatter phantom in a validated orthovoltage x‐ray reference beam. Dw in a cylindrical mouse, 100 mm Petri dish, 6‐well and 96‐well cell culture dishes was simulated and compared to this full scatter geometry. A reference dose rate was measured using the TG‐61 protocol in a cabinet irradiator. This nominal dose rate was used to irradiate TLDs in each phantom to a given dose. Doses were obtained based on TLDs calibrated in a NIST‐traceable beam.

Results:

Compared to the full scattering conditions, the simulated dose to water in the representative geometries were found to be underestimated by 12‐26%. The discrepancy was smallest with the cylindrical mouse geometry, which most closely approximates adequate lateral‐ and backscatter. TLDs irradiated in the mouse and petri dish phantoms using the TG‐61 determined dose rate showed similarly lower values of Dw. When corrected for this discrepancy, they agreed with the predicted Dw within 5%.

Conclusion:

Using the TG‐61 in‐air protocol and given backscatter factors to determine a reference dose rate in a biological irradiator may not be appropriate given the difference in scattering conditions between irradiation and calibration. Without accounting for this, the dose rate is overestimated and is dependent on irradiation geometry.
SU‐G‐TeP3‐06: Nanoparticle‐Aided External Beam Radiotherapy Leveraging the Cerenkov Effect
Authors: Ouyang Z , Liu B , Yasmin‐Karim S , Sajo E , Ngwa W
Published: July 2016

Purpose:

This study investigates the feasibility of exploiting the Cerenkov radiation (CR) present during external beam radiotherapy (EBRT) for significant therapeutic gain, using titanium dioxide nanoparticles (titania) delivered via a new design of radiotherapy biomaterials.

Methods:

Recently published work has shown that CR generated by radionuclides during PET imaging could substantially enhance damage to cancer cells in the presence of 0.625 µg/g titania. We hypothesize that equal or greater damage can be achieved during EBRT. To test this hypothesis, Monte Carlo simulation was done using GEANT4 in order to get the total CR yield inside a tumor volume during EBRT compared to that of the radionuclides. We considered a novel approach where a sufficiently potent concentration of the titania was delivered directly into the tumor using radiotherapy biomaterials (e.g. fiducials) loaded with the titania. The intra‐tumor distribution/diffusion of titania released from the fiducials was calculated. An in‐vitro MTS assay experiment was also carried out to establish the relative non‐toxicity of titania for concentrations of up to 1 µg/g.

Results:

For a radiotherapy biomaterial loaded with 15 µg/g of 2‐nm titania, at least 0.625 µg/g could be delivered through out a tumor sub‐volume of 2‐cm diameter after 14 days. This concentration level could inflict substantial damage to tumor cells during EBRT. The Monte Carlo results showed the CR yield in tumor by 6 MV radiation was higher than the radionuclides and hence potentially greater damage may be obtained during EBRT. No significant cell viability change was observed for 1 µg/g titania.

Conclusion:

Altogether, these preliminary findings demonstrate a potential new approach that can be used to take advantage of the CR present during megavoltage EBRT to boost damage to tumor cells. The results provide significant impetus for further experimental studies towards development of nanoparticle‐aided EBRT powered by the Cerenkov effect.
SU‐G‐TeP3‐08: Pre‐Clinical Radionuclide Therapy Dosimetry in Several Pediatric Cancer Xenografts
Authors: Marsh I , Otto M , Weichert J , Baiu D , Bednarz B
Published: July 2016

Purpose:

The focus of this work is to perform Monte Carlo‐based dosimetry for several pediatric cancer xenografts in mice treated with a novel radiopharmaceutical 131I‐CLR1404.

Methods:

Four mice for each tumor cell line were injected with 8–13 µCi/g of the 124124I‐CLR1404. PET/CT images of each individual mouse were acquired at 5–6 time points over the span of 96–170 hours post‐injection. Following acquisition, the images were co‐registered, resampled, rescaled, corrected for partial volume effects (PVE), and masked. For this work the pre‐treatment PET images of 124I‐CLR1404 were used to predict therapeutic doses from 131I‐CLR1404 at each time point by assuming the same injection activity and accounting for the difference in physical decay rates. Tumors and normal tissues were manually contoured using anatomical and functional images. The CT and the PET images were used in the Geant4 (v9.6) Monte Carlo simulation to define the geometry and source distribution, respectively. The total cumulated absorbed dose was calculated by numerically integrating the dose‐rate at each time point over all time on a voxel‐by‐voxel basis.

Results:

Spatial distributions of the absorbed dose rates and dose volume histograms as well as mean, minimum, maximum, and total dose values for each ROI were generated for each time point.

Conclusion:

This work demonstrates how mouse‐specific MC‐based dosimetry could potentially provide more accurate characterization of efficacy of novel radiopharmaceuticals in radionuclide therapy.

This work is partially funded by NIH grant CA198392.
SU‐G‐TeP3‐09: Proton Minibeam Radiation Therapy Increases Normal Tissue Resistance
Authors: Prezado Y , Gonzalez‐Infantes W , Heinrich S , Labiod D , Juchaux M , Martinez‐Rovira I , Nauraye C , Patriarca A , Peucelle C , Sebrie C
Published: July 2016

Purpose:

The dose tolerances of normal tissues continue being the main limitation in radiotherapy. To overcome it, we recently proposed a novel concept: proton minibeam radiation therapy (pMBRT) [1]. It allies the physical advantages of protons with the normal tissue preservation observed when irradiated with submillimetric spatially fractionated beams (minibeam radiation therapy) [2]. The dose distributions are such that the tumor receives a homogeneous dose distribution, while normal tissues benefit from the spatial fractionation of the dose. The objective of our work was to implement this promising technique at a clinical center (Proton therapy center in Orsay) in order to evaluate the potential gain in tissue sparing.

Methods:

Dose distributions were measured by means of gafchromic films and a PTW microdiamond detector (60019). Once the dosimetry was established, the whole brain of 7 weeks old male Fischer 344 rats was irradiated. Half of the animals received conventional seamless proton irradiation (25 Gy in one fraction). The other rats were irradiated with pMBRT (58 Gy peak dose in one fraction). The average dose deposited in the same targeted volume was in both cases 25 Gy.

Results:

The first complete set of dosimetric data in such small proton field sizes was obtained [3]. Rats treated with conventional proton irradiation exhibited severe moist desquamation and permanent epilation afterwards. The minibeam group, on the other hand, exhibited no skin damage and no clinical symptoms. MRI imaging and histological analysis are planned at 6 months after irradiation.

Conclusion:

Our preliminary results indicate that pMBRT leads to an increase in tissue resistance. This can open the door to an efficient treatment of very radioresistant tumours. [1] Prezado et al. Med. Phys. 40, 031712, 1–8 (2013).[2] Prezado et al., Rad. Research. 184, 314‐21 (2015). [3] Peucelle et al., Med. Phys. 42 7108‐13 (2015).
SU‐G‐TeP3‐13: The Role of Nanoscale Energy Deposition in the Development of Gold Nanoparticle‐Enhanced Radiotherapy
Authors: Kirkby C , Koger B , Suchowerska N , McKenzie D
Published: July 2016

Purpose:

Gold nanoparticles (GNPs) can enhance radiotherapy effects. The high photoelectric cross section of gold relative to tissue, particularly at lower energies, leads to localized dose enhancement. However in a clinical context, photon energies must also be sufficient to reach a target volume at a given depth. These properties must be balanced to optimize such a therapy. Given that nanoscale energy deposition patterns around GNPs play a role in determining biological outcomes, in this work we seek to establish their role in this optimization process.

Methods:

The PENELOPE Monte Carlo code was used to generate spherical dose deposition kernels in 1000 nm diameter spheres around 50 nm diameter GNPs in response to monoenergetic photons incident on the GNP. Induced “lesions” were estimated by either a local effect model (LEM) or a mean dose model (MDM). The ratio of these estimates was examined for a range of photon energies (10 keV to 2 MeV), for three sets of linear‐quadratic parameters.

Results:

The models produce distinct differences in expected lesion values, the lower the alpha‐beta ratio, the greater the difference. The ratio of expected lesion values remained constant within 5% for energies of 40 keV and above across all parameter sets and rose to a difference of 35% for lower energies only for the lowest alpha‐beta ratio.

Conclusion:

Consistent with other work, these calculations suggest nanoscale energy deposition patterns matter in predicting biological response to GNP‐enhanced radiotherapy. However the ratio of expected lesions between the different models is largely independent of energy, indicating that GNP‐enhanced radiotherapy scenarios can be optimized in photon energy without consideration of the nanoscale patterns. Special attention may be warranted for energies of 20 keV or below and low alpha‐beta ratios.
SU‐G‐TeP3‐15: Radiation Dose Enhancement by Anatase TiO2NPs
Authors: Youkhana E , Geso M , Feltis B
Published: July 2016

Purpose:

This work investigates radiation dose enhancement caused by TiO2 nanoparticles covering entire X‐ray energy ranges used in radiation therapy.

Methods:

Anatase TiO2NPs crystal were synthesised and modified as hydrophilic and hydrophobic to disperse in culture‐medium and halocarbons (PRESAGE chemical composition) respectively. TiO2NPs were characterised using TEM, XPS, XRD, TGA and FTIR. Various Concentrations have been utilised for determination of radiation‐dose enhancement. This investigation is carried out in two ways; one using PRESAGE dosimeter/phantom and the other is radiobiological and based on in vitro study using two types of cell lines, Human Keratinocyte (HaCaT) and prostate cancer cell lines. The x‐ray used are both kilovoltage and megavoltage separately. The prepared PRESAGE dosimeters were scanned using optical CT scanner. Clonogenic and MTS assays were employed for cell cytotoxicity and viability measurements for determination of the levels of dose enhancement.

Results:

Significant about (50%, 45%) dose enhancement by TiO2‐NPs for kV x‐rays is measured in both ways (Presage and Cells study). Slightly more is detected with the cells. However, the dose enhancement with megavoltage beams was insignificant using Presage and under same conditions the cells survival curves indicates around 20% which is relatively high. This difference can only be attributed to some biochemical effects. Such as generation of reactive oxygen species (ROS), this can affect the cells while it can't be detected by Presage. Elevation of hydroxyl radicals (•OH) of many orders is observed with the inclusion of TiO2‐NPs in cells‐medium.

Conclusion:

Dose enhancement inflicted by TiO2‐NPs is proven to be significant with megavoltage beams and minimal with kV. The high dose enhancements obtained can be attributed to higher levels of ROS generated. Since MV beams are most commonly used, this research proves potential value for more efficient beam delivery. This has potential to be applied in future clinical radiotherapy applications

The research is supported and funded by RMIT university‐Melbourne/Australia
SU‐G‐IeP4‐09: Method of Human Eye Aberration Measurement Using Plenoptic Camera Over Large Field of View
Authors: Lv Yang , Wang Ruixing , Ma Haotong , Zhang Xuanzhe , Ning Yu , Xu Xiaojun
Published: July 2016

Purpose:

The measurement based on Shack‐Hartmann wave‐front sensor(WFS), obtaining both the high and low order wave‐front aberrations simultaneously and accurately, has been applied in the detection of human eyes aberration in recent years. However, Its application is limited by the small field of view (FOV), slight eye movement leads the optical bacon image exceeds the lenslet array which result in uncertain detection error. To overcome difficulties of precise eye location, the capacity of detecting eye wave‐front aberration over FOV much larger than simply a single conjugate Hartmann WFS accurately and simultaneously is demanded.

Methods:

Plenoptic camera's lenslet array subdivides the aperture light‐field in spatial frequency domain, capture the 4‐D light‐field information. Data recorded by plenoptic cameras can be used to extract the wave‐front phases associated to the eyes aberration. The corresponding theoretical model and simulation system is built up in this article to discuss wave‐front measurement performance when utilizing plenoptic camera as wave‐front sensor.

Results:

The simulation results indicate that the plenoptic wave‐front method can obtain both the high and low order eyes wave‐front aberration with the same accuracy as conventional system in single visual angle detectionand over FOV much larger than simply a single conjugate Hartmann systems. Meanwhile, simulation results show that detection of eye aberrations wave‐front in different visual angle can be achieved effectively and simultaneously by plenoptic method, by both point and extended optical beacon from the eye.

Conclusion:

Plenoptic wave‐front method possesses the feasibility in eye aberrations wave‐front detection. With larger FOV, the method can effectively reduce the detection error brought by imprecise eye location and simplify the eye aberrations wave‐front detection system comparing with which based on Shack‐Hartmann WFS. Unique advantage of the plenoptic method lies in obtaining wave‐front in different visual angle simultaneously, which provides an approach in building up 3‐D model of eye refractor tomographically.

Funded by the key Laboratory of High Power Laser and Physics, CAS Research Project of National University of Defense Technology No. JC13‐07‐01; National Natural Science Foundation of China No. 61205144
SU‐G‐IeP4‐10: Microimaging for Different Degrees of Human Cavernous Hemangioma of Liver by Using In‐Line Phase‐Contrast Imaging CT
Authors: Duan J
Published: July 2016

Purpose:

Cavernous hemangioma of the liver (CHL) is the most common benign solid tumor of the liver. In this study, we quantitative assessment the different degrees of CHL from microscopic viewpoint by using in‐line phase‐contrast imaging CT (ILPCI‐CT).

Methods:

The experiments were performed at x‐ray imaging and biomedical application beamline (BL13W1) of Shanghai Synchrotron Radiation Facility (SSRF) in China. Three typical specimens at different stages, i.e., mild, moderate and severe human CHL were imaged using ILPCI‐CT at 16keV without contrast agents. The 3D visualization of different degrees of CHL samples were presented using ILPCI‐CT. Additionally, quantitative evaluation of the CHL features, such as the range of hepatic sinusoid equivalent diameters in different degrees of CHL samples, the ratio of the hepatic sinusoid to the CHL tissue, were measured.

Results:

The planar image clearly displayed the dilated hepatic sinusoids in microns. There was no normal hepatic vascular found in the all CHL samples. Different stages of CHL samples were presented with vivid shapes and stereoscopic effects by using 3D visualization. The equivalent diameters of hepatic sinusoids in three degrees CHL were different. The equivalent diameters of the hepatic sinusoids in mild CHL, range from 60 to 120 µm. The equivalent diameters of the hepatic sinusoids in moderate CHL, range from 65 to 190 µm. The equivalent diameters of the hepatic sinusoids in severe CHL, range from 95 to 215 µm. The ratio of the hepatic sinusoid to the mild, moderate and severe CHL tissue were 3%, 16% and 21%, respectively.

Conclusion:

The results show that the high degree of sensitivity of the ILPCI‐CT technique and demonstrate the feasibility of accurate visualization of different stage human CHL. ILPCI‐CT may offers a potential use in non‐invasive study and analysis of CHL.
SU‐G‐IeP4‐13: PET Image Noise Variability and Its Consequences for Quantifying Tumor Hypoxia
Authors: Kueng R , Manser P , Fix M K , Driscoll B , Stampanoni M F M , Keller H
Published: July 2016

Purpose:

The values in a PET image which represent activity concentrations of a radioactive tracer are influenced by a large number of parameters including patient conditions as well as image acquisition and reconstruction. This work investigates noise characteristics in PET images for various image acquisition and image reconstruction parameters.

Methods:

Different phantoms with homogeneous activity distributions were scanned using several acquisition parameters and reconstructed with numerous sets of reconstruction parameters. Images from six PET scanners from different vendors were analyzed and compared with respect to quantitative noise characteristics. Local noise metrics, which give rise to a threshold value defining the metric of hypoxic fraction, as well as global noise measures in terms of noise power spectra (NPS) were computed. In addition to variability due to different reconstruction parameters, spatial variability of activity distribution and its noise metrics were investigated. Patient data from clinical trials were mapped onto phantom scans to explore the impact of the scanner's intrinsic noise variability on quantitative clinical analysis.

Results:

Local noise metrics showed substantial variability up to an order of magnitude for different reconstruction parameters. Investigations of corresponding NPS revealed reconstruction dependent structural noise characteristics. For the acquisition parameters, noise metrics were guided by Poisson statistics. Large spatial non‐uniformity of the noise was observed in both axial and radial direction of a PET image. In addition, activity concentrations in PET images of homogeneous phantom scans showed intriguing spatial fluctuations for most scanners. The clinical metric of the hypoxic fraction was shown to be considerably influenced by the PET scanner's spatial noise characteristics.

Conclusion:

We showed that a hypoxic fraction metric based on noise characteristics requires careful consideration of the various dependencies in order to justify its quantitative validity. This work may result in recommendations for harmonizing QA of PET imaging for multi‐institutional clinical trials.
SU‐G‐JeP4‐03: Anomaly Detection of Respiratory Motion by Use of Singular Spectrum Analysis
Authors: Kotoku J , Kumagai S , Nakabayashi S , Haga A , Kobayashi T
Published: July 2016

Purpose:

The implementation and realization of automatic anomaly detection of respiratory motion is a very important technique to prevent accidental damage during radiation therapy. Here, we propose an automatic anomaly detection method using singular value decomposition analysis.

Methods:

The anomaly detection procedure consists of four parts:1) measurement of normal respiratory motion data of a patient2) calculation of a trajectory matrix representing normal time‐series feature3) real‐time monitoring and calculation of a trajectory matrix of real‐time data.4) calculation of an anomaly score from the similarity of the two feature matrices. Patient motion was observed by a marker‐less tracking system using a depth camera.

Results:

Two types of motion e.g. cough and sudden stop of breathing were successfully detected in our real‐time application.

Conclusion:

Automatic anomaly detection of respiratory motion using singular spectrum analysis was successful in the cough and sudden stop of breathing. The clinical use of this algorithm will be very hopeful.

This work was supported by JSPS KAKENHI Grant Number 15K08703.
SU‐G‐JeP4‐05: Effects of Irregular Respiratory Motion On the Positioning Accuracy of Moving Target with Free Breathing Cone‐Beam Computerized Tomography
Authors: Li X , Yang G , Ma R , Yorke E , Mageras G , Tang X , Xiong W , Chan M , Reyngold M , Gewanter R , Wu A , Deasy J , Hunt M
Published: July 2016

Purpose:

Average or maximum intensity projection (AIP or MIP) images derived from 4DCT images are often used as a reference image for target alignment when free breathing Cone‐beam CT (FBCBCT) is used for positioning a moving target at treatment. This method can be highly accurate if the patient has stable respiratory motion. However, a patient's breathing pattern often varies irregularly. The purpose of this study is to investigate the effect of irregular respiration on the positioning accuracy of a moving target with FBCBCT.

Methods:

Eight patients’ respiratory motion curves were selected to drive a Quasar phantom with embedded cubic and spherical targets. A 4DCT of the moving phantom was acquired on a CT scanner (Philips Brilliance 16) equipped with a Varian RPM system. The phase binned 4DCT images and the corresponding MIP and AIP images were transferred into Eclipse for analysis. CBCTs of the phantom driven by the same breathing curves were acquired on a Varian TrueBeam and fused such that the zero positions of moving targets are the same on both CBCT and AIP images. The sphere and cube volumes and centrioid differences (alignment error) determined by MIP, AIP and FBCBCT images were compared.

Results:

Compared to the volume determined by FBCBCT, the volumes of cube and sphere in MIP images were 22.4%±8.8% and 34.2%±6.2% larger while the volumes in AIP images were 7.1%±6.2% and 2.7%±15.3% larger, respectively. The alignment errors for the cube and sphere with center‐center matches between MIP and FBCBCT were 3.5±3.1mm and 3.2±2.3mm, and the alignment errors between AIP and FBCBCT were 2.1±2.6mm and 2.1±1.7mm, respectively.

Conclusion:

AIP images appear to be superior reference images than MIP images. However, irregular respiratory motions could compromise the positioning accuracy of a moving target if the target center‐center match is used to align FBCBCT and AIP images.
MO‐A‐BRC‐02: TG167 Report ‐ Detailed Description
Authors: Rivard M.
Published: July 2016

Although a multicenter, Phase III, prospective, randomized trial is the gold standard for evidence‐based medicine, it is rarely used to evaluate innovative radiotherapy devices because of many practical and ethical reasons. It is usually sufficient to compare the dose distributions and dose rates for determining equivalence of the innovative device to an existing one. Thus, quantitative evaluation of the dosimetric characteristics of an innovative brachytherapy device or application is a critical part in which physicists are actively involved. The physicist's role, along with physician colleagues, in this process is highlighted for innovative products or applications and includes evaluation of 1) dosimetric considerations for clinical implementation (including calibrations, dose calculations, and radiobiological aspects) to comply with existing societal dosimetric prerequisites for sources in routine clinical use, 2) risks and benefits from regulatory and safety perspectives, and 3) resource assessment and preparedness. Further, calibration methods should be traceable to a primary standards dosimetry laboratory such as NIST in the U.S. or to other primary standards dosimetry laboratory located elsewhere. Clinical users should follow standards as approved by their country's regulatory agencies that approved such a brachytherapy device. Integration of this system into the medical source calibration infrastructure of secondary standard dosimetry laboratories such as the ADCLs is encouraged before a source is introduced into widespread routine clinical use. The AAPM and GEC‐ESTRO have developed guidelines for the safe and consistent application of brachytherapy using innovative brachytherapy devices and applications. The current report covers regulatory approvals, calibration, dose calculations, radiobiological issues, and overall safety concerns that should be addressed during the commissioning stage preceding clinical use. These guidelines are based on review of requirements of the U.S. NRC, FDA, Department of Transportation, International Electrotechnical Commission Medical Electrical Equipment Standard 60601, European Commission for CE Marking, and institutional review boards and radiation safety committees.

Learning Objectives:

Understand the necessary dosimetric considerations for clinical implementation (including calibrations, dose calculations, and radiobiological aspects) to comply with existing societal dosimetric prerequisites for sources in routine clinical use.

Evaluate risks and benefits from regulatory and safety perspectives.

Identify necessary resources and create a plan for clinical introduction of innovative brachytherapy device or applications.

Consultant for Theragenics Corp.; R. Nath, Consultant to Theragenics Corp.
MO‐AB‐BRA‐01: A Global Level Set Based Formulation for Volumetric Modulated Arc Therapy
Authors: Nguyen D , Lyu Q , Ruan D , O'Connor D , Low D , Sheng K
Published: July 2016

Purpose:

The current clinical Volumetric Modulated Arc Therapy (VMAT) optimization is formulated as a non‐convex problem and various greedy heuristics have been employed for an empirical solution, jeopardizing plan consistency and quality. We introduce a novel global direct aperture optimization method for VMAT to overcome these limitations.

Methods:

The global VMAT (gVMAT) planning was formulated as an optimization problem with an L2‐norm fidelity term and an anisotropic total variation term. A level set function was used to describe the aperture shapes and adjacent aperture shapes were penalized to control MLC motion range. An alternating optimization strategy was implemented to solve the fluence intensity and aperture shapes simultaneously. Single arc gVMAT plans, utilizing 180 beams with 2° angular resolution, were generated for a glioblastoma multiforme (GBM), lung (LNG), and 2 head and neck cases—one with 3 PTVs (H&N3PTV) and one with 4 PTVs (H&N4PTV). The plans were compared against the clinical VMAT (cVMAT) plans utilizing two overlapping coplanar arcs.

Results:

The optimization of the gVMAT plans had converged within 600 iterations. gVMAT reduced the average max and mean OAR dose by 6.59% and 7.45% of the prescription dose. Reductions in max dose and mean dose were as high as 14.5 Gy in the LNG case and 15.3 Gy in the H&N3PTV case. PTV coverages (D95, D98, D99) were within 0.25% of the prescription dose. By globally considering all beams, the gVMAT optimizer allowed some beams to deliver higher intensities, yielding a dose distribution that resembles a static beam IMRT plan with beam orientation optimization.

Conclusions:

The novel VMAT approach allows for the search of an optimal plan in the global solution space and generates deliverable apertures directly. The single arc VMAT approach fully utilizes the digital linacs’ capability in dose rate and gantry rotation speed modulation.

Varian Medical Systems, NIH grant R01CA188300, NIH grant R43CA183390.
MO‐AB‐BRA‐02: Modeling Nanoparticle‐Eluting Spacer Degradation During Brachytherapy Application with in Situ Dose‐Painting
Authors: Boateng F , Ngwa W
Published: July 2016

Purpose:

Brachytherapy application with in situ dose‐painting using gold nanoparticles (GNP) released from GNP‐loaded brachytherapy spacers has been proposed as an innovative approach to increase therapeutic efficacy during brachytherapy. This work investigates the dosimetric impact of slow versus burst release of GNP from next generation biodegradable spacers.

Methods:

Mathematical models were developed based on experimental data to study the release of GNP from a spacer designed with FDA approved poly(lactic‐co‐glycolic acid) (PLGA) polymer. The diffusion controlled released process and PLGA polymer degradation kinetics was incorporated in the calculations for the first time. An in vivo determined diffusion coefficient was used for determining the concentration profiles and corresponding dose enhancement based on initial GNP‐loading concentrations of 7 mg/g.

Results:

The results showed that there is significant delay before the concentration profile of GNP diffusion in the tumor is similar to that when burst release is assumed as in previous studies. For example, in the case of burst release after spacer administration, it took up to 25 days for all the GNP to be released from the spacer using diffusion controlled release process only. However, it took up to 45 days when a combined model for both diffusion and polymer degradation processes was used. Based on the tumor concentration profiles, a significant dose enhancement factor (DEF >20%), could be attained at a tumor distances of 5 mm from a spacer loaded with 10 nm GNP sizes.

Conclusion:

The results highlight the need to take the slow release of GNP from spacers and factors such as biodegradation of polymers into account in research development of GNP‐eluting spacers for brachytherapy applications with in‐situ dose‐painting using gold nanoparticles. The findings suggest that I‐125 may be the more appropriate for such applications given the relatively longer half‐live compared to other radioisotopes like Pd‐103 and Cs‐131.
MO‐AB‐BRA‐06: Dynamic FLT PET for Investigating Potential Synergistic Therapeutic Targets During Anti‐Angiogenic Treatment
Authors: Scarpelli M , Simoncic U , Perlman S , Liu G , Jeraj R
Published: July 2016

Purpose:

Novel treatment strategies for metastatic cancer patients involve synergistically combining treatments with the hope of improving outcomes. This study investigated changes in tumor proliferative and vascular characteristics derived from dynamic [F‐18]FLT PET during antiangiogenic treatment with the goal of identifying synergistic treatment opportunities.

Methods:

Patients with various solid cancers underwent continuous three‐week cycles of anti‐angiogenic treatment with intermittent dosing (two‐weeks‐on/one‐week‐off). Patients received up to six dynamic FLT PET/CT scans (days 0, 14, and 21 of cycle 1 (C1) and cycle 3 (C3)). Tumor proliferative (Kflt, net uptake rate) and vascular parameters (K1 blood‐to‐tissue transfer; Vb, vascular fraction) were calculated using a two‐tissue compartment four‐rate parameter kinetic model. Relative changes in these parameters, from day 0 to 14 (TxResp) and day 14 to 21 (offTxResp), were calculated. Significant differences were tested using Wilcoxon signed‐rank test and significant correlations were tested using Spearman correlation.

Results:

Thirty patients were evaluable for C1 offTxResp with median values for Kflt, K1, and Vb of +30%, +35% and +30%, respectively. The fractions of patients with positive C1 offTxResp were: 21/30 for Ki, 24/30 for K1, 21/30 for Vb, and 12/30 had positive offTxResp for all three kinetic parameters. The offTxResp in C3 was not significantly different from C1 for any of the kinetic parameters. Significant correlations were found between TxResp and offTxResp in C1 for Kflt (ρ=‐0.52, p=0.014), K1 (ρ=−0.61, p=0.003) and Vb (ρ=−0.80, p<0.001). Similar correlations were found for Kflt (ρ=‐1, p=0.017) and K1 (ρ=−1, p=0.017) for the five patients evaluable in C3.

Conclusion:

Dynamic FLT PET showed evidence of distinct vascular and proliferative increases during off treatment weeks that could potentially be targeted with synergistic therapy. Early changes in kinetic parameters were correlated with later changes suggesting potential for early prediction of vascular and proliferative changes during off treatment weeks.
MO‐AB‐BRA‐08: A Modular Multi‐Source X‐Ray Tube for Novel Computed Tomography Applications
Authors: Walker B , Radtke J , Petry G , Swader R , Chen G , Eliceiri K , Mackie T
Published: July 2016

Purpose:

To develop and build a practical implementation of an x‐ray line source for the rapidly increasing number of multi‐source imaging applications in CT.

Methods:

An innovative x‐ray tube was designed using CST Particle Studio, ANSYS, and SolidWorks. A slowly varying magnetic field is synchronized with microsecond gating of multiple thermionic electron sources. Electrostatic simulations were run to optimize the geometry of the optics and prevent electrode arcing. Magnetostatic simulations were used for beam deflection studies and solenoid design. Particle beam trajectories were explored with an emphasis on focusing, acceleration, deflection, and space charge effects. Thermal constraints were analyzed for both transient and steady‐state regimes. Electromagnetic simulations informed the design of a prototype unit under construction.

Results:

Particle tracking simulations for a benchtop system demonstrate that three 80 keV electron beams are able to be finely controlled and laterally swept a combined distance of 15 cm over a stationary target with an oscillating magnetic field in the hundreds of gauss. The beams are pulsed according to scanning sequences developed for implementation in a mock stationary CT scanner capable of a 30 ms temporal resolution. Beam spot diameters are approximately 1 mm for 30 mA beams and the stationary target stays well within thermal limits. The relevant hardware and control circuits were developed for incorporation into a physical prototype.

Conclusion:

A new multi‐source x‐ray tube was designed in a modular form factor to push the barriers of high‐speed CT and spur growth in emerging imaging applications. This technology can be used as the basis for a stationary high‐speed CT scanner, a system for generating a virtual fan‐beam for dose reduction, or for reducing scatter radiation in cone‐beam CT utilizing a tetrahedron beam CT geometry. A 2.4 kW benchtop system is currently being built to show proof of concept for the tube.

Support for this research was provided by the University of Wisconsin Madison, Office of the Vice Chancellor for Research and Graduate Education with funding from the Wisconsin Alumni Research Foundation.
MO‐AB‐206‐00: Nuclear Medicine Physics and Testing
Authors: White Sharon
Published: July 2016

This education session will cover the physics and operation principles of gamma cameras and PET scanners.

The first talk will focus on PET imaging. An overview of the principles of PET imaging will be provided, including positron decay physics, and the transition from 2D to 3D imaging. More recent advances in hardware and software will be discussed, such as time‐of‐flight imaging, and improvements in reconstruction algorithms that provide for options such as depth‐of‐interaction corrections. Quantitative applications of PET will be discussed, as well as the requirements for doing accurate quantitation. Relevant performance tests will also be described.

Learning Objectives:

Be able to describe basic physics principles of PET and operation of PET scanners.

Learn about recent advances in PET scanner hardware technology.

Be able to describe advances in reconstruction techniques and improvements

Be able to list relevant performance tests.

The second talk will focus on gamma cameras. The Nuclear Medicine subcommittee has charged a task group (TG177) to develop a report on the current state of physics testing of gamma cameras, SPECT, and SPECT/CT systems. The report makes recommendations for performance tests to be done for routine quality assurance, annual physics testing, and acceptance tests, and identifies those needed satisfy the ACR accreditation program and The Joint Commission imaging standards. The report is also intended to be used as a manual with detailed instructions on how to perform tests under widely varying conditions.

Learning Objectives:

At the end of the presentation members of the audience will:

Be familiar with the tests recommended for routine quality assurance, annual physics testing, and acceptance tests of gamma cameras for planar imaging.

Be familiar with the tests recommended for routine quality assurance, annual physics testing, and acceptance tests of SPECT systems.

Be familiar with the tests of a SPECT/CT system that include the CT images for SPECT reconstructions.

Become knowledgeable of items to be included in annual acceptance testing reports including CT dosimetry and PACS monitor measurements.

T. Turkington, GE Healthcare
MO‐A‐209‐03: A Look Ahead: Stewarding the Financial Future of AAPM Journals
Authors: Svatos M.
Published: July 2016

Scientific publishing is a major endeavor of the AAPM. Although publishing requires substantial resources, it has the potential to generate both reputation and revenue to further the missions of our society. The AAPM owns and publishes two journals: Medical Physics and the Journal of Applied Clinical Medical Physics (JACMP). Medical Physics, with the tagline “The international journal of medical physics research and practice,” publishes research concerned with the application of physics and mathematics to the solution of problems in medicine and human biology, with an emphasis on theoretical and experimental approaches. The JACMP is an applied journal that publishes papers designed to help clinical medical physicists perform their responsibilities more effectively and efficiently for the greater benefit of patients. The two journals reflect two different missions, reach two different (yet often overlapping) audiences, engage two different publication approaches, and operate under two different financial models. A journal must serve both “producers” (authors who submit manuscripts to – and ultimately have their work published in – the journal) and “consumers” (readers – either individuals who access journal content or subscribing institutions that make the journal's content available to its members). Any viable publication model and cost‐recovery structure must satisfy the interests of both groups without sacrificing the needs of the scientific community. The purpose of this symposium is to explore the roles of the AAPM's two journals in advancing the scientific and clinical missions of the society and to understand the complex interplay of economic factors that impact financial decisions governing the journals and the returns they bring to the AAPM.

Learning Objectives:

Appreciate the complementary roles of Medical Physics and JACMP in advancing the scientific and clinical missions of the AAPM.

Understand AAPM resources committed to the two journals and the return on these investments.

Understand the role of the AAPM's Journals Business Management Committee in the financial stability of the two journals.

Explore the potential benefits and pitfalls of various economic and publication models for the two journals.

J. Bourland, Member, Journals Business Management Committee, AAPM.
MO‐A‐207B‐00: Segmentation & Feature Extraction Techniques
Authors: Veeraraghavan Harini
Published: July 2016

Image segmentation is one of the core problems for applying radiomics‐based analysis to images. However, achieving repeatable and accurate segmentations for large datasets is challenging. The choice of segmentation method, the metrics used to evaluate the quality of such segmentations all depend on the specific clinical problem. This course will introduce three approaches, namely, fully automatic, interactive, and semi‐automatic methods for generating segmentations. The pros and cons of each approach and when to choose a specific method will be discussed. Evaluation and assessment of the quality of a segmentation method is essential before it can be deployed for high‐throughput analysis such as radiomics. This course will present some of the metrics that can be used for assessing quality of segmentations and highlight their advantages and deficiencies.

Another important issue with respect to generating high quality segmentations and ultimately extracting robust radiomics features is image pre‐processing. A few pre‐processing techniques that can be used to improve the robustness of the analysis for MR and CT images will be presented.

Learning Objectives:

Understand the difference and applicability of various segmentation methods.

Understand how pre‐processing can be used to improve the robustness of feature extraction and segmentation

Understand some basics of evaluating the quality of segmentations and the relevance of such metrics for clinical problems.
MO‐B‐BRC‐01: Introduction
Authors: Prisciandaro J.
Published: July 2016

Brachytherapy has proven to be an effective treatment option for prostate cancer. Initially, prostate brachytherapy was delivered through permanently implanted low dose rate (LDR) radioactive sources; however, high dose rate (HDR) temporary brachytherapy for prostate cancer is gaining popularity. Needle insertion during prostate brachytherapy is most commonly performed under ultrasound (U/S) guidance; however, treatment planning may be performed utilizing several imaging modalities either in an intra‐ or post‐operative setting. During intra‐operative prostate HDR, the needles are imaged during implantation, and planning may be performed in real time. At present, the most common imaging modality utilized for intra‐operative prostate HDR is U/S. Alternatively, in the post‐operative setting, following needle implantation, patients may be simulated with computed tomography (CT) or magnetic resonance imaging (MRI). Each imaging modality and workflow provides its share of benefits and limitations.

Prostate HDR has been adopted in a number of cancer centers across the nation. In this educational session, we will explore the role of U/S, CT, and MRI in HDR prostate brachytherapy. Example workflows and operational details will be shared, and we will discuss how to establish a prostate HDR program in a clinical setting.

Learning Objectives:

Review prostate HDR techniques based on the imaging modality

Discuss the challenges and pitfalls introduced by the three imagebased options for prostate HDR brachytherapy

Review the QA process and learn about the development of clinical workflows for these imaging options at different institutions
MO‐B‐209‐00: Certificate Extension Process for DBT and the Medical Physicist's Role
Authors: Reiser Ingrid
Published: July 2016

This presentation will describe the role of medical physicists during FDA's certificate extension process (CE). The presentation will outline FDA's CE process, with detailed discussions on training, MEE, and requirements for continued QA for the facility, vis‐a‐vis medical physicist's responsibilities. A few important tests will be discussed that need special emphasis for each of the DBT systems currently approved by FDA. What can be accepted as additional didactic and hands on training in fulfilling modality related training will be explained.

Learning Objectives:

Understand the certificate extension process

Understand medical physicist's responsibility in performing QC tests following the QC manual

Learn about proper presentation of data in reporting and generating soft copy phantom image

Understand on‐going responsibilities in monitoring QC technologists’ tests
MO‐B‐207B‐01: Harmonization & Robustness in Radiomics
Authors: Court L.
Published: July 2016

Feature extraction for radiomics studies typically comprises the following stages: Imaging, segmentation, image processing, and feature extraction. Each of these stages has associated uncertainties that can affect the quality of a radiomics model created using the resulting image features. For example, the imaging device manufacturer and model have been shown to impact the values of image features, as have pixel size and imaging protocol parameters. Image processing, such as low‐pass filtering to reduce noise, also changes calculated image features and should be designed to optimize the information content of the resulting features. The details of certain feature algorithms, such as co‐occurrence matrix bin sizes, are also important, and should be optimized for specific radiomics tasks. The volume of the region of interest should be considered as image features can be related to volume and can give unanticipated results when the volumes are too small. In this session we will describe approaches to quantify the variabilities in radiomics studies, including the most recent results quantifying these variabilities for CT, MRI and PET imaging. We will discuss methods to optimize image processing and feature extraction in order to maximize the information content of the image features. Finally, we will describe work to harmonize imaging protocols and feature calculations to help minimize uncertainties in radiomics studies.

Learning Objectives:

At the end of this session, participants will be able to:

Identify the sources of uncertainty in radiomics studies (CT, PET, and MRI imaging)

Describe methods for quantifying the magnitude of uncertainties

Describe approaches for mitigating the effects of the uncertainties on radiomics models

Funding from NIH, CPRIT, Varian, Elekta; L. Court, NCI, CPRIT, Varian, Elekta