bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐J‐179: Commissioning Dosimetric Data of a New 2.5 Megavoltage Imaging Beam from a TrueBeam Linear
Authors: Ding G
Published: July 2016

Purpose:

Recently a new 2.5 megavoltage imaging beam has become available in a TrueBeam linear accelerator for image guidance. There is limited information available related to the beam characteristics. Commissioning dosimetric data of the new imaging is necessary for configuration of the beam in a treatment planning system in order to calculate imaging doses to patients resulting from this new imaging beam. The purpose of this study is to provide measured commissioning data recommended for a beam configuration in a treatment planning system.

Methods:

A recently installed TrueBeam linear accelerator is equipped with a new low energy photon beam with a nominal energy of 2.5 MV which provides better image quality in addition to other therapeutic megavoltage beams. Dosimetric characteristics of the 2.5 MV are measured for commissioning. An ionization chamber was used to measure dosimetric data including depth‐dose curves and dose profiles at different depths for field sizes ranging from 5×5 cm2 to 40×40 cm2.

Results:

Although the new 2.5 MV beam is a flattening‐filter‐free (FFF) beam, its dose profiles are much flatter compared to a 6 MV FFF beam. The dose decrease at 20 cm away from the central axis is less than 30% for a 40×40 cm2 field. This moderately lower dose at off‐axis distances benefits the imaging quality. The values of percentage depth‐dose (PDD) curves are 53% and 63% for 10×10 cm2 and 40×40 cm2 fields respectively. The measured beam output is 0.85 cGy/MU for a reference field size at depth 5 cm obtained according to the AAPM TG‐51 protocol.

Conclusion:

This systematically measured commissioning data is useful for configuring the new imaging beam in a treatment planning system for patient imaging dose calculations resulting from the application of this 2.5 MV beam which is commonly set as a default in imaging procedures.
SU‐F‐J‐180: A Reference Data Set for Testing Two Dimension Registration Algorithms
Authors: Dankwa A , Castillo E , Guerrero T
Published: July 2016

Purpose:

To create and characterize a reference data set for testing image registration algorithms that transform portal image (PI) to digitally reconstructed radiograph (DRR).

Methods:

Anterior‐posterior (AP) and Lateral (LAT) projection and DRR image pairs from nine cases representing four different anatomical sites (head and neck, thoracic, abdominal, and pelvis) were selected for this study. Five experts will perform manual registration by placing landmarks points (LMPs) on the DRR and finding their corresponding points on the PI using computer assisted manual point selection tool (CAMPST), a custom‐made MATLAB software tool developed in house. The landmark selection process will be repeated on both the PI and the DRR in order to characterize inter‐ and ‐intra observer variations associated with the point selection process. Inter and an intra observer variation in LMPs was done using Bland‐Altman (B&A) analysis and one‐way analysis of variance. We set our limit such that the absolute value of the mean difference between the readings should not exceed 3mm. Later on in this project we will test different two dimension (2D) image registration algorithms and quantify the uncertainty associated with their registration.

Results:

Using one‐way analysis of variance (ANOVA) there was no variations within the readers. When Bland‐Altman analysis was used the variation within the readers was acceptable. The variation was higher in the PI compared to the DRR.ConclusionThe variation seen for the PI is because although the PI has a much better spatial resolution the poor resolution on the DRR makes it difficult to locate the actual corresponding anatomical feature on the PI. We hope this becomes more evident when all the readers complete the point selection. The reason for quantifying inter‐ and ‐intra observer variation tells us to what degree of accuracy a manual registration can be done.

Research supported by William Beaumont Hospital Research Start Up Fund.
SU‐F‐J‐184: Proton Computed Tomography Using 1D Silicon Diode Array
Authors: Wang P , Cammin J , Bisello F , Solberg T , McDonough J , Zhu T , Menichelli D , Teo B
Published: July 2016

Purpose:

Proton radiography and proton computed tomography (PCT) can be used to measure proton stopping power directly. However, practical and cost effective proton imaging detectors are not widely available. In this study, the authors investigated the feasibility of proton imaging using a silicon diode array.

Methods:

A one‐dimensional silicon‐diode detector array (1DSDA) was aligned with the central axis (CAX) of the proton beam. Polymethyl methacrylate (PMMA) slabs were used to find the correspondence between the water equivalent thickness (WET) and 1DSDA channel number. 2D proton radiographs (PR) were obtained by translation and rotation of a phantom relative to CAX while the proton nozzle and 1DSDA were kept stationary. A PCT image of one slice of the phantom was reconstructed using filtered backprojection.

Results:

PR and PCT images of the PMMA cube were successfully acquired using the 1DSDA. The WET of the phantom was measured using PR data with an accuracy of 4.2% or better. Structures down to 1 mm in size could be resolved. Reconstruction of a PCT image showed very good agreement with simulation. Limitations in spatial resolution are attributed to limited spatial sampling, beam collimation, and proton scatter.

Conclusion:

The results demonstrate the feasibility of using silicon diode arrays for proton imaging. Such a device can potentially offer fast image acquisition, high spatial and energy resolution for PR and PCT.
SU‐F‐J‐190: Time Resolved Range Measurement System Using Scintillator and CCD Camera for the Slow Beam Extraction
Authors: Saotome N , Furukawa T , Mizushima K , Takeshita E , Hara Y , Saraya Y , Tansho R , Shirai T , Noda K
Published: July 2016

Purpose:

To investigate the time structure of the range, we have verified the rang shift due to the betatron tune shift with several synchrotron parameters.

Methods:

A cylindrical plastic scintillator block and a CCD camera were installed on the black box. Using image processing, the range was determined the 80 percent of distal dose of the depth light distribution. The root mean square error of the range measurement using the scintillator and CCD system is about 0.2 mm. Range measurement was performed at interval of 170 msec. The chromaticity of the synchrotron was changed in the range of plus or minus 1% from reference chromaticity in this study. All of the particle inside the synchrotron ring were extracted with the output beam intensity 1.8×108 and 5.0×107 particle per sec.

Results:

The time strictures of the range were changed by changing of the chromaticity. The reproducibility of the measurement was sufficient to observe the time structures of the range. The range shift was depending on the number of the residual particle inside the synchrotron ring.

Conclusion:

In slow beam extraction for scanned carbon‐ion therapy, the range shift is undesirable because it causes the dose uncertainty in the target. We introduced the time‐resolved range measurement using scintillator and CCD system. The scintillator and CCD system have enabled to verify the range shift with sufficient spatial resolution and reproducibility.
SU‐F‐J‐195: On the Performance of Four Dual Energy CT Formalisms for Extracting Proton Stopping Powers
Authors: Baer E , Lalonde A , Royle G , Bouchard H
Published: July 2016

Purpose:

Dual energy CT can predict stopping power ratios (SPR) for ion therapy treatment planning. Several approaches have been proposed recently, however accuracy and practicability in a clinical workflow are unaddressed. The aim of this work is to provide a fair comparison of available approaches in a human‐like phantom to find the optimal method for tissue characterization in a clinical situation.

Methods:

The SPR determination accuracy is investigated using simulated DECT images. A virtual human‐like phantom is created containing 14 different standard human tissues. SECT (120 kV) and DECT images (100 kV and 140 kV Sn) are simulated using the software ImaSim. The single energy CT (SECT) stoichiometric calibration method and four recently published calibration‐based DECT methods are implemented and used to predict the SPRs from simulated images. The difference between SPR predictions and theoretical SPR are compared pixelwize. Mean, standard deviation and skewness of the SPR difference distributions are used as measures for bias, dispersion and symmetry.

Results:

The average SPR differences and standard deviations are (0.22 ± 1.27)% for SECT, and A) (−0.26 ± 1.30)%, B) (0.08 ± 1.12)%, C) (0.06 ± 1.15)% and D) (−0.05 ± 1.05)% for the four DECT methods. While SPR prediction using SECT is showing a systematic error on SPR, the DECT methods B, C and D are unbiased. The skewness of the SECT distribution is 0.57%, and A) −0.19%, B) −0.56%, C) −0.29% and D) −0.07% for DECT methods respectively.

Conclusion:

The here presented DECT methods B, C and D outperform the commonly used SECT stoichiometric calibration. These methods predict SPR accurately without a bias and within ± 1.2% (68th percentile). This indicates that DECT potentially improves accuracy of range predictions in proton therapy. A validation of these findings using clinical CT images of real tissues is necessary.
SU‐F‐J‐197: A Novel Intra‐Beam Range Detection and Adaptation Strategy for Particle Therapy
Authors: Chen M , Jiang S , Shao Y , Lu W
Published: July 2016

Purpose:

In‐vivo range detection/verification is crucial in particle therapy for effective and safe delivery. The state‐of‐art techniques are not sufficient for in‐vivo on‐line range verification due to conflicts among patient dose, signal statistics and imaging time. We propose a novel intra‐beam range detection and adaptation strategy for particle therapy.

Methods:

This strategy uses the planned mid‐range spots as probing beams without adding extra radiation to patients. Such choice of probing beams ensures the Bragg peaks to remain inside the tumor even with significant range variation from the plan. It offers sufficient signal statistics for in‐beam positron emission tomography (PET) due to high positron activity of therapeutic dose. The probing beam signal can be acquired and reconstructed using in‐beam PET that allows for delineation of the Bragg peaks and detection of range shift with ease of detection enabled by single‐layered spots. If the detected range shift is within a pre‐defined tolerance, the remaining spots will be delivered as the original plan. Otherwise, a fast re‐optimization using range‐shifted beamlets and accounting for the probing beam dose is applied to consider the tradeoffs posed by the online anatomy. Simulated planning and delivery studies were used to demonstrate the effectiveness of the proposed techniques.

Results:

Simulations with online range variations due to shifts of various foreign objects into the beam path showed successful delineation of the Bragg peaks as a result of delivering probing beams. Without on‐line delivery adaptation, dose distribution was significantly distorted. In contrast, delivery adaptation incorporating detected range shift recovered well the planned dose.

Conclusion:

The proposed intra‐beam range detection and adaptation utilizing the planned mid‐range spots as probing beams, which illuminate the beam range with strong and accurate PET signals, is a safe, practical, yet effective approach to address range uncertainty issues in particle therapy.
SU‐F‐J‐200: An Improved Method for Event Selection in Compton Camera Imaging for Particle Therapy
Authors: Mackin D , Beddar S , Polf J , Peterson S , Draeger E
Published: July 2016

Purpose:

The uncertainty in the beam range in particle therapy limits the conformality of the dose distributions. Compton scatter cameras (CC), which measure the prompt gamma rays produced by nuclear interactions in the patient tissue, can reduce this uncertainty by producing 3D images confirming the particle beam range and dose delivery. However, the high intensity and short time windows of the particle beams limit the number of gammas detected. We attempt to address this problem by developing a method for filtering gamma ray scattering events from the background by applying the known gamma ray spectrum.

Methods:

We used a 4 stage Compton camera to record in list mode the energy deposition and scatter positions of gammas from a Co‐60 source. Each CC stage contained a 4×4 array of CdZnTe crystal. To produce images, we used a back‐projection algorithm and four filtering

Methods:

basic, energy windowing, delta energy (ΔE), or delta scattering angle (Δθ). Basic filtering requires events to be physically consistent. Energy windowing requires event energy to fall within a defined range. ΔE filtering selects events with the minimum difference between the measured and a known gamma energy (1.17 and 1.33 MeV for Co‐60). Δθ filtering selects events with the minimum difference between the measured scattering angle and the angle corresponding to a known gamma energy.

Results:

Energy window filtering reduced the FWHM from 197.8 mm for basic filtering to 78.3 mm. ΔE and Δθ filtering achieved the best results, FWHMs of 64.3 and 55.6 mm, respectively. In general, Δθ filtering selected events with scattering angles < 40°, while ΔE filtering selected events with angles > 60°.

Conclusion:

Filtering CC events improved the quality and resolution of the corresponding images. ΔE and Δθ filtering produced similar results but each favored different events.
SU‐F‐J‐202: Secondary Radiation Measurements for Charged Particle Therapy Monitoring: Fragmentation of Therapeutic He, C and O Ion Beams Impinging On a PMMA Target
Authors: Rucinski A , Battistoni G , Collamati F , Collini F , De Lucia E , Faccini R , Frallicciardi P , Mancini‐Terracciano C , Marafini M , Muraro S , Paramatti R , Patera V , Piersanti L , Pinci D , Russomando A , Sarti A , Sciubba A , Camillocci E Solfaroli , Toppi M , Traini G , Voena C
Published: July 2016

Purpose:

In Charged Particle Therapy (CPT), besides protons, there has been recently a growing interest in 4He, 12C and 16O beams. The secondary radiation produced in the interaction of those beams with a patient could be potentially used for on‐line monitoring of range uncertainties in order to fully exploit the advantages of those light ions resulting from increased Radio Biological Effectiveness, reduced multiple scattering and Oxygen Enhancement Ratio. The study and precise characterization of secondary radiation (beta+, prompt gamma, charged fragments) is the cornerstone of any R&D activity aiming for online monitoring development and purpose of the analysis presented here.

Methods:

We present the measurements of the secondary radiation generated by He, C and O beams impinging on a beam stopping PMMA target. The data has been collected at the Heidelberg Ionbeam Therapy center (HIT), where several millions of collisions were recorded at different energies, relevant for therapeutical applications.

Results:

The experimental setup, as well as the analysis strategies will be reviewed. The detected particle fluxes as a function of the primary beam energy and the emission angle with respect to the beam direction will be presented and compared to the results of other available measurements. In addition, the energy spectra and emission shapes of charged secondary particles will be shown and discussed in the context of the primary beam range monitoring technique that is being developed by the ARPG collaboration, within the INSIDE project funded by the Italian research ministry. The implications for dose monitoring applications will be discussed, in the context of the current (or planned) state‐of‐ the‐art detector solutions.

Conclusion:

The characterization of the radiation produced by 12C, 4He and 16O beams fully supports the feasibility of on‐line range monitoring in the clinical practice of CPT by means of secondary particles detection.
SU‐F‐J‐203: Retrospective Assessment of Delivered Proton Dose in Prostate Cancer Patients Based On Daily In‐Room CT Imaging
Authors: Stuetzer K , Paessler T , Valentini C , Exner F , Thiele J , Hoelscher T , Krause M , Richter C
Published: July 2016

Purpose:

Retrospective calculation of the delivered proton dose in prostate cancer patients based on a unique dataset of daily CT images.

Methods:

Inter‐fractional motion in prostate cancer patients treated at our proton facility is counteracted by water‐filled endorectal ballon and bladder filling protocol. Typical plans (XiO, Elekta Instruments AB, Stockholm) for 74 Gy(RBE) sequential boost treatment in 37 fractions include two series of opposing lateral double‐scattered proton beams covering the respective iCTV. Stability of fiducial markers and anatomy were checked in 12 patients by daily scheduled in‐room control CT (cCT) after immobilization and positioning according to bony anatomy utilizing orthogonal X‐ray. In RayStation 4.6 (RaySearch Laboritories AB, Stockholm), all cCTs are delineated retrospectively and the treatment plans were recalculated on the planning CT and the registered cCTs. All fraction doses were accumulated on the planning CT after deformable registration. Parameters of delivered dose to iCTV (D98%>95%, D2%<107%), bladder (V75Gy<15%, V70Gy<25%, V65Gy<30%), rectum (V70Gy<10%, V50Gy<40%) and femoral heads (V50Gy<5%) are compared to those in the treatment plan. Intra‐therapy variation is represented in DVH bands.

Results:

No alarming differences were observed between planned and retrospectively accumulated dose: iCTV constraints were met, except for one patient (D98%=94.6% in non‐boosted iCTV). Considered bladder and femoral head values were below the limits. Rectum V70Gy was slightly exceeded (<11.3%) in two patients. First intra‐therapy variability analysis in 4 patients showed no timedependent parameter drift, revealed strongest variability for bladder dose. In some fractions, iCTV coverage (D98%) and rectum V70Gy was missed.

Conclusion:

Double scattered proton plans are accurately delivered to prostate cancer patients due to fractionation effects and the applied precise positioning and immobilization protocols. As a result of rare interventions after daily 3D imaging of the first 12 patients, in‐room CT frequency for prostate cancer patients was reduced. The presented study supports this decision.

The authors acknowledge the German Federal Ministry for Education and Research for funding the High Precision Radiotherapy Group at the OncoRay ‐ National Center for Radiation Research in Oncology (BMBF‐ 03Z1N51).
SU‐F‐J‐204: Carbon Digitally Reconstructed Radiography (CDRR): A GPU Based Tool for Fast and Versatile Carbonimaging Simulation
Authors: Dias M F , Seco J , Baroni G , Riboldi M
Published: July 2016

Purpose:

Research in carbon imaging has been growing over the past years, as a way to increase treatment accuracy and patient positioning in carbon therapy. The purpose of this tool is to allow a fast and flexible way to generate CDRR data without the need to use Monte Carlo (MC) simulations. It can also be used to predict future clinically measured data.

Methods:

A python interface has been developed, which uses information from CT or 4DCT and thetreatment calibration curve to compute the Water Equivalent Path Length (WEPL) of carbon ions. A GPU based ray tracing algorithm computes the WEPL of each individual carbon traveling through the CT voxels. A multiple peak detection method to estimate high contrast margin positioning has been implemented (described elsewhere). MC simulations have been used to simulate carbons depth dose curves in order to simulate the response of a range detector.

Results:

The tool allows the upload of CT or 4DCT images. The user has the possibility to selectphase/slice of interested as well as position, angle…). The WEPL is represented as a range detector which can be used to assess range dilution and multiple peak detection effects. The tool also provides knowledge of the minimum energy that should be considered for imaging purposes. The multiple peak detection method has been used in a lung tumor case, showing an accuracy of 1mm in determine the exact interface position.

Conclusion:

The tool offers an easy and fast way to simulate carbon imaging data. It can be used for educational and for clinical purposes, allowing the user to test beam energies and angles before real acquisition. An analysis add‐on is being developed, where the used will have the opportunity to select different reconstruction methods and detector types (range or energy).

Fundacao para a Ciencia e a Tecnologia (FCT), PhD Grant number SFRH/BD/85749/2012
SU‐F‐J‐206: Systematic Evaluation of the Minimum Detectable Shift Using a Range‐ Finding Camera
Authors: Platt M , Platt M , Lamba M , Mascia A , Huang K
Published: July 2016

Purpose:

The robotic table used for patient alignment in proton therapy is calibrated only at commissioning under well‐defined conditions and table shifts may vary over time and with differing conditions. The purpose of this study is to systematically investigate minimum detectable shifts using a time‐of‐flight (TOF) range‐finding camera for table position feedback.

Methods:

A TOF camera was used to acquire one hundred 424 × 512 range images from a flat surface before and after known shifts. Range was assigned by averaging central regions of the image across multiple images. Depth resolution was determined by evaluating the difference between the actual shift of the surface and the measured shift. Depth resolution was evaluated for number of images averaged, area of sensor over which depth was averaged, distance from camera to surface, central versus peripheral image regions, and angle of surface relative to camera.

Results:

For one to one thousand images with a shift of one millimeter the range in error was 0.852 ± 0.27 mm to 0.004 ± 0.01 mm (95% C.I.). For varying regions of the camera sensor the range in error was 0.02 ± 0.05 mm to 0.47 ± 0.04 mm. The following results are for 10 image averages. For areas ranging from one pixel to 9 × 9 pixels the range in error was 0.15 ± 0.09 to 0.29 ± 0.15 mm (1σ). For distances ranging from two to four meters the range in error was 0.15 ± 0.09 to 0.28 ± 0.15 mm. For an angle of incidence between thirty degrees and ninety degrees the average range in error was 0.11 ± 0.08 to 0.17 ± 0.09 mm.

Conclusion:

It is feasible to use a TOF camera for measuring shifts in flat surfaces under clinically relevant conditions with submillimeter precision.
SU‐F‐J‐208: Prompt Gamma Imaging‐Based Prediction of Bragg Peak Position for Realistic Treatment Error Scenarios
Authors: Xing Y , Macq B , Janssens G , Bondar L
Published: July 2016

Purpose:

To quantify the accuracy in predicting the Bragg peak position using simulated in‐room measurements of prompt gamma (PG) emissions for realistic treatment error scenarios that combine several sources of errors.

Methods:

Prompt gamma measurements by a knife‐edge slit camera were simulated using an experimentally validated analytical simulation tool. Simulations were performed, for 143 treatment error scenarios, on an anthropomorphic phantom and a pencil beam scanning plan for nasal cavity. Three types of errors were considered: translation along each axis, rotation around each axis, and CT‐calibration errors with magnitude ranging respectively, between −3 and 3 mm, −5 and 5 degrees, and between −5 and +5%. We investigated the correlation between the Bragg peak (BP) shift and the horizontal shift of PG profiles. The shifts were calculated between the planned (reference) position and the position by the error scenario. The prediction error for one spot was calculated as the absolute difference between the PG profile shift and the BP shift.

Results:

The PG shift was significantly and strongly correlated with the BP shift for 92% of the cases (p<0.0001, Pearson correlation coefficient R>0.8). Moderate but significant correlations were obtained for all cases that considered only CT‐calibration errors and for 1 case that combined translation and CT‐errors (p<0.0001, R ranged between 0.61 and 0.8). The average prediction errors for the simulated scenarios ranged between 0.08±0.07 and 1.67±1.3 mm (grand mean 0.66±0.76 mm). The prediction error was moderately correlated with the value of the BP shift (p=0, R=0.64). For the simulated scenarios the average BP shift ranged between −8±6.5 mm and 3±1.1 mm. Scenarios that considered combinations of the largest treatment errors were associated with large BP shifts.

Conclusion:

Simulations of in‐room measurements demonstrate that prompt gamma profiles provide reliable estimation of the Bragg peak position for complex error scenarios.

Yafei Xing and Luiza Bondar are funded by BEWARE grants from the Walloon Region.

The work presents simulations results for a prompt gamma camera prototype developed by IBA.
SU‐F‐J‐210: A Preliminary Study On the Dosimetric Impact of Detector Based Spectral Ct On Proton Therapy Treatment Planning
Authors: Cheng C , Lee S , Muzic R , Wessels B , Jesseph F , Ellis R , Mansur D , Dhanantwari A
Published: July 2016

Purpose:

To compare the difference in Hounsfield unit‐relative stopping power and evaluate the dosimetric impact of spectral vs. conventional CT on proton therapy treatment plans.

Method:

The Philips prototype (IQon), a detector‐based, spectral CT system (spectral) was used to scan calibration and Rando phantoms. Data were reconstructed with and without energy decomposition to produce monoenergetic 70 keV, 140 keV, and the Zeff images. Relative stopping power (RSP) in the head and lung regions were evaluated as a function of HU in order to compare spectral and conventional CT. Treatment plans for the Rando phantom were also generated and used to produce DVHs of fictitious target volume and organ‐at‐risk contoured on the head and lung.

Results:

Agreement of the Zeff of the tissue‐substitute materials determined using spectral CT agrees to within 1 to 5% of the Zeff of the known phantom composition. The discrepancy is primarily attributed to non‐uniformity in the phantom. Differences between the HU‐RSP curves obtained using spectral and conventional CT were small except for in the lung curve at HU>1000. The large difference in planned doses using Spectral vs. conventional CT occurred in a low‐dose brain region (1.7mm between the locations of the 100 cGy lines and 3 mm for 50 cGy lines).

Conclusion:

Conventionally, a single HU‐RSP from CT scanner is used in proton treatment planning. Spectral CT allows site‐specific HU‐RSP for each patient. Spectral and conventional HU‐RSP may result in different distributions as shown here. Additional study is required to evaluate the impact of Spectral CT in proton treatment planning.

This study is part of a research agreement between Philips and University Hospitals/Case Medical Center.
SU‐F‐J‐212: Enabling Conventional Cone Beam CT with the Capability of Dual Energy Imaging Using a Simple Add‐On Beam Modifier
Authors: Vinke R , Takao S , Umegaki K , Shirato H , Peng H , Xing L
Published: July 2016

Purpose:

In searching for a robust, efficient and cost‐effective dual energy cone beam CT (DECBCT) solution for various radiation oncology applications, in particularly for improved proton dose planning/replanning accuracy and DE‐CBCT guided radiation therapy, we investigate a novel energy modulation scheme using a beam modifier placed between the source and patient and optimize its geometric configuration for routine clinical use.

Methods:

The study was performed using a Hitachi CBCT scanner and the tube voltage was set at 125 kVp. The higher energy beam was obtained by filtering the incident utilizing a beam modulation layer (material: copper, thickness: 1.8 mm). To avoid the need for double scans (one with and one without the energy modulator), the modulation layer was configured to cover only the half of the X‐ray beam so that two sets of sinograms corresponding low and high energies were collected after a single gantry rotation of 360 deg. The average high energy and low energy HU numbers (HUhigh and HUlow) were derived for pixels in a defined region‐of‐interest, respectively.

Results:

The beam modifier increased the threshold of the energy spectrum from ∼20 keV up to ∼50 keV. Two complete sets of images were obtained with good alignment between the high energy and low‐energy cases without any artifact observed (Fig. 2). The HUlow/HUhigh is ∼0/0 (water), ∼394/238 (brain), ∼1283/1085 (cortical bone) and ∼3000/1800 (titanium).

Conclusion:

The feasibility of the proposed DECT implementation using a beam modifier has been demonstrated. Compared to the existing DECT solutions, the proposed scheme is much more cost‐effective and requires minimum hardware modification. The work lays foundation for us to study the quantification of HU values to derive material density images and atomic number (and electron density) of substances.
SU‐F‐J‐214: Dose Reduction by Spatially Optimized Image Quality Via Fluence Modulated Proton CT (FMpCT)
Authors: De Angelis L , Landry G , Hansen D , Rit S , Belka C , Dedes G , Parodi K
Published: July 2016

Purpose:

Proton CT (pCT) is a promising imaging modality for reducing range uncertainty in image‐guided proton therapy. Range uncertainties partially originate from X‐ray CT number conversion to stopping power ratio (SPR) and are limiting the exploitation of the full potential of proton therapy. In this study we explore the concept of spatially dependent fluence modulated proton CT (FMpCT), for achieving optimal image quality in a clinical region of interest (ROI), while reducing significantly the imaging dose to the patient.

Methods:

The study was based on simulated ideal pCT using pencil beam (PB) scanning. A set of 250 MeV protons PBs was used to create 360 projections of a cylindrical water phantom and a head and neck cancer patient. The tomographic images were reconstructed using a filtered backprojection (FBP) as well as an iterative algorithm (ITR). Different fluence modulation levels were investigated and their impact on the image was quantified in terms of SPR accuracy as well as noise within and outside selected ROIs, as a function of imaging dose. The unmodulated image served as reference.

Results:

Both FBP reconstruction and ITR without total variation (TV) yielded image quality in the ROIs similar to the reference images, for modulation down to 0.1 of the full proton fluence. The average dose was reduced by 75% for the water phantom and by 40% for the patient. FMpCT does not improve the noise for ITR with TV and modulation 0.1.

Conclusion:

This is the first work proposing and investigating FMpCT for producing optimal image quality for treatment planning and image guidance, while simultaneously reducing imaging dose. Future work will address spatial resolution effects and the impact of FMpCT on the quality of proton treatment plans for a prototype pCT scanner capable of list mode data acquisition. Acknowledgement: DFG‐MAP

DFG ‐ Munich‐Centre for Advanced Photonics (MAP)
SU‐F‐J‐215: Non‐Thermal Pulsed High Intensity Focused Ultrasound Therapy Combined with 5‐Aminolevulinic Acid: An in Vivo Pilot Study
Authors: Wang B , He W , Cvetkovic D , Chen L , Ma C
Published: July 2016

Purpose:

It has recently been shown that non‐thermal pulsed high intensity focused ultrasound (pHIFU) has a cell‐killing effect. The purpose of the study is to investigate the sonosensitizing effect of 5‐Aminolevulinic Acid (5‐ALA) in non‐thermal pHIFU cancer therapy.

Methods:

FaDu human head and neck squamous cell carcinoma cells were injected subcutaneously in the flanks of nude mice. After one to two weeks, the tumors reached the volume of 112 ± 8 mm3 and were assigned randomly into a non‐thermal pHIFU group (n=9) and a non‐thermal sonodynamic therapy (pHIFU after 5‐ALA administration) group (n=7). The pHIFU treatments (parameters: 1 MHz frequency; 25 W acoustic power; 0.1 duty cycle; 60 seconds duration) were delivered using an InSightec ExAblate 2000 system with a GE Signa 1.5T MR scanner. The mice in the non‐thermal sonodynamic group received 5‐ALA tail‐vein injection 4 hours prior to the pHIFU treatment. The tumor growth was monitored using the CT scanner on a Sofie‐Biosciences G8 PET/CT system.

Results:

The tumors in this study grew very aggressively and about 60% of the tumors in this study developed ulcerations at various stages. Tumor growth delay after treatments was observed by comparing the treated (n=9 in pHIFU group; n=7 in sonodynamic group) and untreated tumors (n=17). However, no statistically significant differences were found between the non‐thermal pHIFU and non‐thermal sonodynamic group. The mean normalized tumor volume of the untreated tumors on Day 7 after their first CT scans was 7.05 ± 0.54, while the normalized volume of the treated tumors on Day 7 after treatment was 5.89 ± 0.79 and 6.27 ± 0.47 for the sonodynamic group and pHIFU group, respectively.

Conclusion:

In this study, no significant sonosensitizing effects of 5‐ALA were obtained on aggressive FaDu tumors despite apparent tumor growth delay in some mice treated with non‐thermal sonodynamic therapy.
SU‐F‐J‐217: Accurate Dose Volume Parameters Calculation for Revealing Rectum Dose‐Toxicity Effect Using Deformable Registration in Cervical Cancer Brachytherapy: A Pilot Study
Authors: Zhen X , Chen H , Liao Y , Zhou L , Hrycushko B , Albuquerque K , Gu X
Published: July 2016

Purpose:

To study the feasibility of employing deformable registration methods for accurate rectum dose volume parameters calculation and their potentials in revealing rectum dose‐toxicity between complication and non‐complication cervical cancer patients with brachytherapy treatment.

Method and Materials:

Data from 60 patients treated with BT including planning images, treatment plans, and follow‐up clinical exam were retrospectively collected. Among them, 12 patients complained about hematochezia were further examined with colonoscopy and scored as Grade 1–3 complication (CP). Meanwhile, another 12 non‐complication (NCP) patients were selected as a reference group. To seek for potential gains in rectum toxicity prediction when fractional anatomical deformations are account for, the rectum dose volume parameters D0.1/1/2cc of the selected patients were retrospectively computed by three different approaches: the simple “worstcase scenario” (WS) addition method, an intensity‐based deformable image registration (DIR) algorithm‐Demons, and a more accurate, recent developed local topology preserved non‐rigid point matching algorithm (TOP). Statistical significance of the differences between rectum doses of the CP group and the NCP group were tested by a two‐tailed t‐test and results were considered to be statistically significant if p < 0.05.

Results:

For the D0.1cc, no statistical differences are found between the CP and NCP group in all three methods. For the D1cc, dose difference is not detected by the WS method, however, statistical differences between the two groups are observed by both Demons and TOP, and more evident in TOP. For the D2cc, the CP and NCP cases are statistically significance of the difference for all three methods but more pronounced with TOP.

Conclusion:

In this study, we calculated the rectum D0.1/1/2cc by simple WS addition and two DIR methods and seek for gains in rectum toxicity prediction. The results favor the claim that accurate dose deformation and summation tend to be more sensitive in unveiling the dose‐toxicity relationship.

This work is supported in part by grant from VARIAN MEDICAL SYSTEMS INC, the National Natural Science Foundation of China (no 81428019 and no 81301940), the Guangdong Natural Science Foundation (2015A030313302)and the 2015 Pearl River S&T Nova Program of Guangzhou (201506010096).
SU‐F‐J‐223: Patterns of Failure for Laryngeal Cancer Patients Treated with Definitive IMRT: Comparing Two Different Methods for Determining the Origin of Recurrence From Follow‐Up PET/CT Scans
Authors: Brodin P , Kabarriti R , Vogelius I , Guha C , Kalnicki S , Garg M , Tome W
Published: July 2016

Purpose:

To determine patterns of failure in laryngeal cancer treated with definitive IMRT by comparing two different methods for identifying the recurrence epicenter on follow‐up PET/CT.

Methods:

We identified 20 patients treated for laryngeal squamous cell carcinoma with definitive IMRT who had loco‐regional recurrence diagnosed on PET/CT. Recurrence PET/CT scans were co‐registered with the original treatment planning CT using deformable image registration with the VoxAlign deformation engine in MIM Software. Recurrence volumes were delineated on co‐registered follow‐up scans using a semi‐automatic PETedge tool and two separate methods were used to identify the recurrence point of origin: a) Finding the point within the recurrence volume for which the maximum distance to the surface of the surrounding recurrence volume is smaller than for any other point. b) Finding the point within the recurrence volume with the maximum standardized uptake value (SUVmax), without geometric restrictions.For each method the failure pattern was determined as whether the recurrence origin fell within the original high‐dose target volumes GTV70, CTV70, PTV70 (receiving 70Gy), intermediate‐risk PTV59 (receiving 59.4Gy) or low‐risk PTV54 (receiving 54.1Gy), in the original treatment planning CT.

Results:

23 primary/nodal recurrences from the 20 patients were analyzed. The three‐dimensional distance between the two different origins was on average 10.5mm (std.dev. 10mm). Most recurrences originated in the high‐dose target volumes for both methods with 13 (57%) and 11 (48%) in the GTV70 and 20 (87%) and 20 (87%) in the PTV70 for method a) and b), respectively. There was good agreement between the two methods in classifying the origin target volumes with 69% concordance for GTV70, 89% for CTV70 and 100% for PTV70.

Conclusion:

With strong agreement in patterns of failure between two separate methods for determining recurrence origin, we conclude that most recurrences occurred within the high‐dose treatment region, which influences potential risk‐adaptive treatment strategies.
SU‐F‐J‐224: Impact of 4D PET/CT On PERCIST Classification of Lung and Liver Metastases in NSLC and Colorectal Cancer
Authors: Meier J , Lopez B , Mawlawi O
Published: July 2016

Purpose:

To quantify the impact of 4D PET/CT on PERCIST metrics in lung and liver tumors in NSCLC and colorectal cancer patients.

Methods:

32 patients presenting lung or liver tumors of 1–3 cm size affected by respiratory motion were scanned on a GE Discovery 690 PET/CT. The bed position with lesion(s) affected by motion was acquired in a 12 minute PET LIST mode and unlisted into 8 bins with respiratory gating. Three different CT maps were used for attenuation correction: a clinical helical CT (CT_clin), an average CT (CT_ave), and an 8‐phase 4D CINE CT (CT_cine). All reconstructions were 3D OSEM, 2 iterations, 24 subsets, 6.4 Gaussian filtration, 192×192 matrix, non‐TOF, and non‐PSF. Reconstructions using CT_clin and CT_ave used only 3 out of the 12 minutes of the data (clinical protocol); all 12 minutes were used for the CT_cine reconstruction. The percent change of SUVbw_peak and SUVbw_max was calculated between PET_CTclin and PET_CTave. The same percent change was also calculated between PET_CTclin and PET_CTcine in each of the 8 bins and in the average of all bins. A 30% difference from PET_CTclin classified lesions as progressive metabolic disease (PMD) using maximum bin value and the average of eight bin values.

Results:

30 lesions in 25 patients were evaluated. Using the bin with maximum SUVbw_peak and SUVbw_max difference, 4 and 13 lesions were classified as PMD, respectively. Using the average bin values for SUVbw_peak and SUVbw_max, 3 and 6 lesions were classified as PMD, respectively. Using PET_CTave values for SUVbw_peak and SUVbw_max, 4 and 3 lesions were classified as PMD, respectively.

Conclusion:

These results suggest that response evaluation in 4D PET/CT is dependent on SUV measurement (SUVpeak vs. SUVmax), number of bins (single or average), and the CT map used for attenuation correction.
SU‐F‐J‐225: Histology Study of MR Guided Pulsed Focused Ultrasound On Treatment of Prostate Cancer in Vivo
Authors: Chen L , Cvetkovic D , Chen X , Wang B , Gupta R , Ma C
Published: July 2016

Purpose:

Our previous study demonstrated significant tumor growth delay in the mice treated with pulsed high intensity focused ultrasound (pHIFU). The purpose of this study is to understand the cell killing mechanisms of pHIFU.

Methods:

Prostate cancer cells (LNCaP), were grown orthotopically in 17 nude mice. Tumor‐bearing mice were treated using pHIFU with an acoustic power of 25W, pulse width 100msec and 300 pulses in one sonication under MR guidance. Mutiple sonications were used to cover the whole tumor volume. The temperature (less than 40 degree centigrade in the focal spot) was monitored using MR thermometry. Animals were euthanized at pre‐determined time points (n=2) after treatment: 0 hours; 6 hrs; 24 hrs; 48 hrs; 4 days and 7 days. Two tumorbearing mice were used as control. Three tumor‐bearing mice were treated with radiation (RT, 2 Gy) using 6 MV photon beams. RT treated mice were euthanized at 0 hr, 6 hrs and 24 hrs. The tumors were processed for immunohistochemical (IHC) staining for PARP (a surrogate of apoptosis). A multispectral imaging analysis system was used to quantify the expression of PARP staining. Cell apoptosis was calculated based on the PARP expression level using the DAB analysis software.

Results:

Our data showed that PARP related apoptosis peaked at 48 hrs and 7 days in pHIFU treated mice, which is comparable to that for the RT group at 24 hrs. The preliminary results from this study were consistent with our previous study on tumor growth delay using pHIFU.

Conclusion:

Our results demonstrated that non‐thermal pHIFU increased apoptotic tumor cell death through the PARP related pathway. MR guided pHIFU may have a great potential as a safe, noninvasive treatment modality for cancer therapy. This treatment modality may synergize with PARP inhibitors to achieve better therapeutic result.
SU‐F‐T‐02: Estimation of Radiobiological Doses (BED and EQD2) of Single Fraction Electronic Brachytherapy That Equivalent to I‐125 Eye Plaque: By Using Linear‐Quadratic and Universal Survival Curve Models
Authors: Kim Y , Waldron T , Pennington E
Published: July 2016

Purpose:

To test the radiobiological impact of hypofractionated choroidal melanoma brachytherapy, we calculated single fraction equivalent doses (SFED) of the tumor that equivalent to 85 Gy of I125‐BT for 20 patients. Corresponding organs‐at‐risks (OARs) doses were estimated.

Methods:

Twenty patients treated with I125‐BT were retrospectively examined. The tumor SFED values were calculated from tumor BED using a conventional linear‐quadratic (L‐Q) model and an universal survival curve (USC). The opposite retina (α/β = 2.58), macula (2.58), optic disc (1.75), and lens (1.2) were examined. The % doses of OARs over tumor doses were assumed to be the same as for a single fraction delivery. The OAR SFED values were converted into BED and equivalent dose in 2 Gy fraction (EQD2) by using both L‐Q and USC models, then compared to I125‐BT.

Results:

The USC‐based BED and EQD2 doses of the macula, optic disc, and the lens were on average 118 ± 46% (p < 0.0527), 126 ± 43% (p < 0.0354), and 112 ± 32% (p < 0.0265) higher than those of I125‐BT, respectively. The BED and EQD2 doses of the opposite retina were 52 ± 9% lower than I125‐BT. The tumor SFED values were 25.2 ± 3.3 Gy and 29.1 ± 2.5 Gy when using USC and LQ models which can be delivered within 1 hour. All BED and EQD2 values using L‐Q model were significantly larger when compared to the USC model (p < 0.0274) due to its large single fraction size (> 14 Gy).

Conclusion:

The estimated single fraction doses were feasible to be delivered within 1 hour using a high dose rate source such as electronic brachytherapy (eBT). However, the estimated OAR doses using eBT were 112 ∼ 118% higher than when using the I125‐BT technique. Continued exploration of alternative dose rate or fractionation schedules should be followed.
SU‐F‐T‐03: Radiobiological Evaluation of a Directional Brachytherapy Device Surgically Implanted Following EBRT
Authors: Rivard MJ , Emrich JG , Poli J
Published: July 2016

Purpose:

Preceding surgical implantation following external‐beam radiotherapy (EBRT) delivery, a radiobiological evaluation was performed for a new LDR Pd‐103 directional brachytherapy device (CivaSheet). As this was the first case with the device used in combination with EBRT, there was concern to determine the appropriate prescription dose.

Methods:

The radiobiological model of Dale (1985, 1989) was used for a permanent LDR implant including radioactive decay. The biological effective dose (BED) was converted to the equivalent dose in 2 Gy fractions (EQD2) for comparison with EBRT prescription expectations. Given IMRT delivery of 50.4 Gy, an LDR brachytherapy dose of approximately 15–20 Gy EQD2 was desired. To be specific to the treatment site (leiomyosarcoma T2bN0M0, grade 2 with R1 surgical margin), the radiobiological model required several radiobiological parameters with values taken from the literature. A sensitivity analysis was performed to determine their relative importance on the calculated BED and subsequent EQD2. The Pd‐103 decay constant (λ=0.0017 h−1) was also used. DVHs were prepared for pre‐ and post‐surgical geometries to glean the possible and realized implant geometric configuration. DVHs prepared in VariSeed9 were converted to BEDVHs and subsequently EQD2 values for each volume‐element.

Results:

For a physical dose of 28 Gy to a 0.5 cm depth, BED=21.7 Gy and EQD2=17.6 Gy, which was near the center of the desired EQD2 range. Tumor bed (CTV=4 cm3) coverage was 99.2% with 48 sources implanted. In order of decreasing importance from the sensitivity analysis, the radiobiological parameters were α=0.25 Gy−1, TPOT=23 days, α/β=8.6 Gy, and T=1.5 h. Percentage variations in these values produced EQD2 variations of 40%, 20%, 18%, and 1%, respectively.

Conclusion:

This radiobiological evaluation indicated that prescription dose may be determined for comparison with the desired EQD2, and that radiobiologicalparameter uncertainties produce smaller EQD2 differences than had physical dose been simply added to EBRT dose.

Research support provided in part by CivaTech Oncology, Inc. for Dr. Rivard.