bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐470: Beam Performance of the Radiance 330 Proton Therapy System
Authors: Nazaryan H , Nazaryan V , Flanz J , Alexandrov V , Wang F
Published: July 2014

Purpose:

The ProTom Radiance 330 proton radiotherapy system is a fully functional, compact proton radiotherapy system that provides advanced proton delivery capabilities. It supports three‐dimensional beam scanning with energy and intensity modulation. A series of measurements have been conducted to characterize the beam performance of the first installation of the system at the McLaren Proton Therapy Center in Flint, Michigan. These measurements were part of the technical commissioning of the system. Select measurements and results are presented.

Methods:

The Radiance 330 proton beam energy range is 70–250 MeV for treatment, and up to 330 MeV for proton tomography and radiography. Its 3‐D scanning capability, together with a small beam emittance and momentum spread, provides a highly efficient beam delivery. During the technical commissioning, treatment plans were created to deliver uniform maps at various energies to perform Gamma Index analysis. EBT3 Gafchromic films were irradiated using the Planned irradiation maps. Bragg Peak chamber was used to test the dynamic range during a scan in one layer for high (250 MeV) and Low (70 MeV) energies. The maximum and minimum range, range adjustment and modulation, distal dose falloff (80%–20%), pencil beam spot size, spot placement accuracy were also measured. The accuracy testing included acquiring images, image registration, receiving correction vectors and applying the corrections to the robotic patient positioner.

Results:

Gamma Index analysis of the Treatment Planning System (TPS) data vs. Measured data showed more than 90% of points within (3%, 3mm) for the maps created by the TPS. At Isocenter Beam Size (One sigma) < 3mm at highest energy (250 MeV) in air. Beam delivery was within 0.6 mm of the intended target at the entrance and the exit of the beam, through the phantom.

Conclusion:

The Radiance 330 Beam Performance Measurements have confirmed that the system operates as designed with excellent clinical performance specifications.

Hovakim Nazaryan, Vahagn Nazaryan and Fuhua Wang are employees of ProTom International, Inc. who contributed to the development and completed the technical commissioning of the Radiance 330 proton therapy delivery system manufactured by ProTom International.
SU‐E‐T‐471: Small Field Jaw/MLC Reference Data
Authors: Kerns J , Alvarez P , Followill D , Lowenstein J , Molineu A , Summers P , Kry S
Published: July 2014

Purpose:

In recent years the need for small field data of MLCs has increased due to the use of intensity‐modulated radiation (IMRT), but moreover the use of stereotactic body radiation (SBRT) has increased, which uses not simply small field sizes, but small jaw and field sizes together. Having reference data for these small fields that is reliable would be invaluable to the physics community. Our study has gathered these values and the data distributions from the Radiological Physics Center's (RPC) site visits between 1990 and the present.

Methods:

For all measurements, the RPC used a 25 × 25 × 25cm water phantom placed at 100cm SSD. All measurements were made with an Exradin A16 cylindrical ion chamber at an effective depth of 10 cm. A total of 42 Varian machine measurements were used to compose the data for a 6 MV beam and 5 TrueBeam 6 MV flattening filter free (FFF) beams were used for FFF data.

Results:

Jaw/MLC fields were measured for both 6 MV and 6 MF FFF beams with the jaws and MLCs both at the following field sizes: 6×6, 4×4, 3×3, and 2×2cm. Measurements were normalized to the 10×10 field readings (defined by the jaws and MLC). Spread in the data was minimal and demonstrates a high level of accuracy of acquired data.

Conclusion:

Small field Jaw/MLC reference data for Varian 6MV and 6 MV FFF beams has been analyzed and presented here, composed of the aggregation of numerous RPC site visits. Obtaining reliable small field data remains difficult, however the RPC has collected high fidelity small field Jaw/MLC data. The data are presented as a reference along with their distributions, in such a way that the physicist can act based upon their own desired agreement with the reference data.
SU‐E‐T‐472: A Multi‐Dimensional Measurements Comparison to Analyze a 3D Patient Specific QA Tool
Authors: Ashmeg S , Jackson J , Zhang Y , Oldham M , Yin F , Ren L
Published: July 2014

Purpose:

To quantitatively evaluate a 3D patient specific QA tool using 2D film and 3D Presage dosimetry.

Methods:

A brain IMRT case was delivered to Delta4, EBT2 film and Presage plastic dosimeter. The film was inserted in the solid water slabs at 7.5cm depth for measurement. The Presage dosimeter was inserted into a head phantom for 3D dose measurement. Delta4's Anatomy software was used to calculate the corresponding dose to the film in solid water slabs and to Presage in the head phantom. The results from Anatomy were compared to both calculated results from Eclipse and measured dose from film and Presage to evaluate its accuracy. Using RIT software, we compared the “Anatomy” dose to the EBT2 film measurement and the film measurement to ECLIPSE calculation. For 3D analysis, DICOM file of “Anatomy” was extracted and imported to CERR software, which was used to compare the Presage dose to both “Anatomy” calculation and ECLIPSE calculation. Gamma criteria of 3% – 3mm and 5% – 5mm was used for comparison.

Results:

Gamma passing rates of film vs “Anatomy”, “Anatomy” vs ECLIPSE and film vs ECLIPSE were 82.8%, 70.9% and 87.6% respectively when 3% – 3mm criteria is used. When the criteria is changed to 5% – 5mm, the passing rates became 87.8%, 76.3% and 90.8% respectively. For 3D analysis, Anatomy vs ECLIPSE showed gamma passing rate of 86.4% and 93.3% for 3% – 3mm and 5% – 5mm respectively. The rate is 77.0% for Presage vs ECLIPSE analysis. The Anatomy vs ECLIPSE were absolute dose comparison. However, film and Presage analysis were relative comparison

Conclusion:

The results show higher passing rate in 3D than 2D in “Anatomy” software. This could be due to the higher degrees of freedom in 3D than in 2D for gamma analysis.
SU‐E‐T‐473: A Patient‐Specific QC Paradigm Based On Trajectory Log Files and DICOM Plan Files
Authors: DeMarco J , McCloskey S , Moran J , Low D
Published: July 2014

Purpose:

To evaluate a remote QC tool for monitoring treatment machine parameters and treatment workflow.

Methods:

The Varian TrueBeamTM linear accelerator is a digital machine that records machine axis parameters and MLC leaf positions as a function of delivered monitor unit or control point. This information is saved to a binary trajectory log file for every treatment or imaging field in the patient treatment session. A MATLAB analysis routine was developed to parse the trajectory log files for a given patient, compare the expected versus actual machine and MLC positions as well as perform a cross‐comparison with the DICOM‐RT plan file exported from the treatment planning system. The parsing routine sorts the trajectory log files based on the time and date stamp and generates a sequential report file listing treatment parameters and provides a match relative to the DICOM‐RT plan file.

Results:

The trajectory log parsing‐routine was compared against a standard record and verify listing for patients undergoing initial IMRT dosimetry verification and weekly and final chart QC. The complete treatment course was independently verified for 10 patients of varying treatment site and a total of 1267 treatment fields were evaluated including pre‐treatment imaging fields where applicable. In the context of IMRT plan verification, eight prostate SBRT plans with 4‐arcs per plan were evaluated based on expected versus actual machine axis parameters. The average value for the maximum RMS MLC error was 0.067±0.001mm and 0.066±0.002mm for leaf bank A and B respectively.

Conclusion:

A real‐time QC analysis program was tested using trajectory log files and DICOM‐RT plan files. The parsing routine is efficient and able to evaluate all relevant machine axis parameters during a patient treatment course including MLC leaf positions and table positions at time of image acquisition and during treatment.
SU‐E‐T‐474: IMRT Verification Using the On‐Board EPID
Authors: Dormer J , Witztum A , Ding X , Jin P , Zhu T
Published: July 2014

Purpose:

To verify IMRT and Rapid Arc (RA) plan's agreement with treatment delivery for radiation therapy using an on‐board EPID compared to MapCHECK2 and ArcCHECK.

Methods:

On‐board EPID (Exact arm) is commissioned using manufacturer's Preconfigured Data Input Package (PDIP). Portal dose calculation engine for comparison with measurement was commissioned with PDIP. The absolute dosimetric calibration of the EPID is performed using 10×10cm field size at 105cm source to image detector distance with 90.7 CU in the integrated mode. The dark and flood field of EPID were also calibrated in the integrated mode for all energies and dose rates. The output dose‐response data from the manufacturer was verified. The improved gamma test method was used for EPID data analysis. Gamma test were used for MapCHECK2 (or ArcCHECK). The sensitivity of the method was tested using collimator rotation at 3 degree and 5 degree. Student T‐test was used to distinguish the difference among the groups.

Results:

IMRT: The average of Gamma passing rate using EPID and MapCHECK2 is 98.9±1.6% and 98.7±2.0% (p = 0.342). There is no statistical difference between two groups.RA: The average of Gamma passing rate using EPID and ArcCHECK is 97.2±2.3% and 93.2±4.1%. (p = 0.002). EPID significantly improved the RapidARC plan passing rate compared to the ArcCHECK. 5% dose change typically causes between 3 – 55% change in Gamma.

Conclusion:

Using the EPID, we were able to perform QA verification on IMRT plans comparable to MapCHECK2 (p=0.342) and superior to that of ArcCHECK (p=0.002) using Gamma 3%, 3mm criteria. The sensitivity of EPID was found to be comparable to that of the MapCHECK2 and ArcCHECK. EPID dosimetry is faster (4.3 mins vs. 10 mins) due to easier setup and integrated data processing.
SU‐E‐T‐475: An Accurate Linear Model of Tomotherapy MLC‐Detector System for Patient Specific Delivery QA
Authors: Chen Y , Mo X , Chen M , Olivera G , Reeher M , Parnell D , Key S , Galmarini D , Lu W
Published: July 2014

Purpose:

An accurate leaf fluence model can be used in applications such as patient specific delivery QA and in‐vivo dosimetry for TomoTherapy systems. It is known that the total fluence is not a linear combination of individual leaf fluence due to leakage‐transmission, tongue‐and‐groove, and source occlusion effect. Here we propose a method to model the nonlinear effects as linear terms thus making the MLC‐detector system a linear system.

Methods:

A leaf pattern basis (LPB) consisting of no‐leaf‐open, single‐leaf‐open, double‐leaf‐open and triple‐leaf‐open patterns are chosen to represent linear and major nonlinear effects of leaf fluence as a linear system. An arbitrary leaf pattern can be expressed as (or decomposed to) a linear combination of the LPB either pulse by pulse or weighted by dwelling time. The exit detector responses to the LPB are obtained by processing returned detector signals resulting from the predefined leaf patterns for each jaw setting. Through forward transformation, detector signal can be predicted given a delivery plan. An equivalent leaf open time (LOT) sinogram containing output variation information can also be inversely calculated from the measured detector signals. Twelve patient plans were delivered in air. The equivalent LOT sinograms were compared with their planned sinograms.

Results:

The whole calibration process was done in 20 minutes. For two randomly generated leaf patterns, 98.5% of the active channels showed differences within 0.5% of the local maximum between the predicted and measured signals. Averaged over the twelve plans, 90% of LOT errors were within +/−10 ms. The LOT systematic error increases and shows an oscillating pattern when LOT is shorter than 50 ms.

Conclusion:

The LPB method models the MLC‐detector response accurately, which improves patient specific delivery QA and in‐vivo dosimetry for TomoTherapy systems. It is sensitive enough to detect systematic LOT errors as small as 10 ms.
SU‐E‐T‐476: Quality Assurance for Gamma Knife Perfexion Using the Exradin W1 Plastic Scintillation Detector
Authors: Pino R , Therriault‐Proulx F , Yang J , Beddar S
Published: July 2014

Purpose:

To perform dose profile and output factor measurements for the Exradin W1 plastic scintillation detector (PSD) for the Gamma Knife Perfexion (GKP) collimators in a Lucy phantom and to compare these values to an Exradin A16 ion chamber, EBT3 radiochromic film and treatment planning system (TPS) data.

Methods:

We used the Exradin W1 PSD which has a small volume, near‐water equivalent sensitive element. It has also been shown to be energy independent. This new detector is manufactured and distributed by Standard Imaging, Inc. Measurements were performed for all three collimators (4 mm, 8 mm and 16 mm) for the GKP. The Lucy phantom with the PSD inserted was moved in small steps to acquire profiles in all three directions. EBT3 film was inserted in the Lucy phantom and exposed to a single shot for each collimator. Relative output factors were measured using the three detectors while profiles acquired with the PSD were compared to the ones measured with EBT3 radiochromic film.

Results:

Measured output factors relative to the largest collimator are as followsCollimator PS EBT3 A1616mm 1.000 1.000 1.0008mm 0.892 0.881 0.8834mm 0.795 0.793 0.727 The nominal (vendor) OFs for GKP are 1.000, 0.900, and 0.814, for collimators 16 mm, 8 mm and 4 mm, respectively. There is excellent agreement between all profiles measured with the PSD and EBT3 as well as with the TPS data provided by the vendor.

Conclusion:

Output factors measured with the W1 were consistent with the ones measured with EBT3 and A16 ion chamber. Measured profiles are in excellent agreement. The W1 detector seems well suited for beam QA for Gamma Knife due to its dosimetric characteristics.

Sam Beddar would like to disclose a NIH/NCI SBIR Phase II grant (2R44CA153824‐02A1) with Standard Imaging, Title: “Water‐Equivalent Plastic Scintillation Detectors for Small Field Radiotherapy”
SU‐E‐T‐477: An Efficient Dose Correction Algorithm Accounting for Tissue Heterogeneities in LDR Brachytherapy
Authors: Mashouf S , Lai P , Karotki A , Keller B , Beachey D , Pignol J
Published: July 2014

Purpose:

Seed brachytherapy is currently used for adjuvant radiotherapy of early stage prostate and breast cancer patients. The current standard for calculation of dose surrounding the brachytherapy seeds is based on American Association of Physicist in Medicine Task Group No. 43 (TG‐43 formalism) which generates the dose in homogeneous water medium. Recently, AAPM Task Group No. 186 emphasized the importance of accounting for tissue heterogeneities. This can be done using Monte Carlo (MC) methods, but it requires knowing the source structure and tissue atomic composition accurately. In this work we describe an efficient analytical dose inhomogeneity correction algorithm implemented using MIM Symphony treatment planning platform to calculate dose distributions in heterogeneous media.

Methods:

An Inhomogeneity Correction Factor (ICF) is introduced as the ratio of absorbed dose in tissue to that in water medium. ICF is a function of tissue properties and independent of source structure. The ICF is extracted using CT images and the absorbed dose in tissue can then be calculated by multiplying the dose as calculated by the TG‐43 formalism times ICF. To evaluate the methodology, we compared our results with Monte Carlo simulations as well as experiments in phantoms with known density and atomic compositions.

Results:

The dose distributions obtained through applying ICF to TG‐43 protocol agreed very well with those of Monte Carlo simulations as well as experiments in all phantoms. In all cases, the mean relative error was reduced by at least 50% when ICF correction factor was applied to the TG‐43 protocol.

Conclusion:

We have developed a new analytical dose calculation method which enables personalized dose calculations in heterogeneous media. The advantages over stochastic methods are computational efficiency and the ease of integration into clinical setting as detailed source structure and tissue segmentation are not needed.

University of Toronto, Natural Sciences and Engineering Research Council of Canada
SU‐E‐T‐478: Sliding Window Multi‐Criteria IMRT Optimization
Authors: Craft D , Bokrantz R , Papp D , Unkelbach J
Published: July 2014

Purpose:

To demonstrate a method for what‐you‐see‐is‐what‐you‐get multi‐criteria Pareto surface navigation for step and shoot IMRT treatment planning.

Methods:

We show mathematically how multiple sliding window treatment plans can be averaged to yield a single plan whose dose distribution is the dosimetric average of the averaged plans. This is incorporated into the Pareto surface navigation based approach to treatment planning in such a way that as the user navigates the surface, the plans he/she is viewing are ready to be delivered (i.e. there is no extra ‘segment the plans’ step that often leads to unacceptable plan degradation in step and shoot Pareto surface navigation). We also describe how the technique can be applied to VMAT. Briefly, sliding window VMAT plans are created such that MLC leaves paint out fluence maps every 15 degrees or so. These fluence map leaf trajectories are averaged in the same way the static beam IMRT ones are.

Results:

We show mathematically that fluence maps are exactly averaged using our leaf sweep averaging algorithm. Leaf transmission and output factor corrections effects, which are ignored in this work, can lead to small errors in terms of the dose distributions not being exactly averaged even though the fluence maps are. However, our demonstrations show that the dose distributions are almost exactly averaged as well. We demonstrate the technique both for IMRT and VMAT.

Conclusions:

By turning to sliding window delivery, we show that the problem of losing plan fidelity during the conversion of an idealized fluence map plan into a deliverable plan is remedied. This will allow for multicriteria optimization that avoids the pitfall that the planning has to be redone after the conversion into MLC segments due to plan quality decline.

David Craft partially funded by RaySearch Laboratories.
SU‐E‐T‐479: Development and Validation of Analytical Models Predicting Secondary Neutron Radiation in Proton Therapy Applications
Authors: Farah J , Bonfrate A , De Olivera A , Delacroix S , Donadille L , Herault J , Martinetti F , Piau S , Trompier F , Vabre I , Clairand I
Published: July 2014

Purpose:

Test and validation of analytical models predicting leakage neutron exposure in passively scattered proton therapy.

Methods:

Taking inspiration from the literature, this work attempts to build an analytical model predicting neutron ambient dose equivalents, H*(10), within the local 75 MeV ocular proton therapy facility. MC simulations were first used to model H*(10) in the beam axis plane while considering a closed final collimator and pristine Bragg peak delivery. Next, MC‐based analytical model was tested against simulation results and experimental measurements. The model was also expended in the vertical direction to enable a full 3D mapping of H*(10) inside the treatment room. Finally, the work focused on upgrading the literature model to clinically relevant configurations considering modulated beams, open collimators, patient‐induced neutron fluctuations, etc.

Results:

The MC‐based analytical model efficiently reproduced simulated H*(10) values with a maximum difference below 10%. In addition, it succeeded in predicting measured H*(10) values with differences <40%. The highest differences were registered at the closest and farthest positions from isocenter where the analytical model failed to faithfully reproduce the high neutron fluence and energy variations. The differences remains however acceptable taking into account the high measurement/simulation uncertainties and the end use of this model, i.e. radiation protection. Moreover, the model was successfully (differences < 20% on simulations and < 45% on measurements) extended to predict neutrons in the vertical direction with respect to the beam line as patients are in the upright seated position during ocular treatments. Accounting for the impact of beam modulation, collimation and the present of a patient in the beam path is far more challenging and conversion coefficients are currently being defined to predict stray neutrons in clinically representative treatment configurations.

Conclusion:

Analytical models predicting secondary neutrons in proton therapy represent a promising solution that substitute for time‐consuming MC calculations.
SU‐E‐T‐480: Radiobiological Dose Comparison of Single Fraction SRS, Multi‐Fraction SRT and Multi‐Stage SRS of Large Target Volumes Using the Linear‐Quadratic Formula
Authors: Ding C , Hrycushko B , Jiang S , Meyer J , Timmerman R
Published: July 2014

Purpose:

To compare the radiobiological effect on large tumors and surrounding normal tissues from single fraction SRS, multi‐fractionated SRT, and multi‐staged SRS treatment.

Methods:

An anthropomorphic head phantom with a centrally located large volume target (18.2 cm3) was scanned using a 16 slice large bore CT simulator. Scans were imported to the Multiplan treatment planning system where a total prescription dose of 20Gy was used for a single, three staged and three fractionated treatment. Cyber Knife treatment plans were inversely optimized for the target volume to achieve at least 95% coverage of the prescription dose. For the multistage plan, the target was segmented into three subtargets having similar volume and shape. Staged plans for individual subtargets were generated based on a planning technique where the beam MUs of the original plan on the total target volume are changed by weighting the MUs based on projected beam lengths within each subtarget. Dose matrices for each plan were export in DICOM format and used to calculate equivalent dose distributions in 2Gy fractions using an alpha beta ratio of 10 for the target and 3 for normal tissue.

Results:

Singe fraction SRS, multi‐stage plan and multi‐fractionated SRT plans had an average 2Gy dose equivalent to the target of 62.89Gy, 37.91Gy and 33.68Gy, respectively. The normal tissue within 12Gy physical dose region had an average 2Gy dose equivalent of 29.55Gy, 16.08Gy and 13.93Gy, respectively.

Conclusion:

The single fraction SRS plan had the largest predicted biological effect for the target and the surrounding normal tissue. The multi‐stage treatment provided for a more potent biologically effect on target compared to the multi‐fraction SRT treatments with less biological normal tissue than single‐fraction SRS treatment.
SU‐E‐T‐481: Dosimetric Comparison of Acuros XB and Anisotropic Analytic Algorithm with Commercial Monte Carlo Based Dose Calculation Algorithm for Stereotactic Body Radiation Therapy of Lung Cancer
Authors: Cao M , Tenn S , Lee C , Yang Y , Lamb J , Agazaryan N , Lee P , Low D
Published: July 2014

Purpose:

To evaluate performance of three commercially available treatment planning systems for stereotactic body radiation therapy (SBRT) of lung cancer using the following algorithms: Boltzmann transport equation based algorithm (AcurosXB AXB), convolution based algorithm Anisotropic Analytic Algorithm (AAA); and Monte Carlo based algorithm (XVMC).

Methods:

A total of 10 patients with early stage non‐small cell peripheral lung cancer were included. The initial clinical plans were generated using the XVMC based treatment planning system with a prescription of 54Gy in 3 fractions following RTOG0613 protocol. The plans were recalculated with the same beam parameters and monitor units using AAA and AXB algorithms. A calculation grid size of 2mm was used for all algorithms. The dose distribution, conformity, and dosimetric parameters for the targets and organs at risk (OAR) are compared between the algorithms.

Results:

The average PTV volume was 19.6mL (range 4.2–47.2mL). The volume of PTV covered by the prescribed dose (PTV‐V100) were 93.97±2.00%, 95.07±2.07% and 95.10±2.97% for XVMC, AXB and AAA algorithms, respectively. There was no significant difference in high dose conformity index; however, XVMC predicted slightly higher values (p=0.04) for the ratio of 50% prescription isodose volume to PTV (R50%). The percentage volume of total lungs receiving dose >20Gy (LungV20Gy) were 4.03±2.26%, 3.86±2.22% and 3.85±2.21% for XVMC, AXB and AAA algorithms. Examination of dose volume histograms (DVH) revealed small differences in targets and OARs for most patients. However, the AAA algorithm was found to predict considerable higher PTV coverage compared with AXB and XVMC algorithms in two cases. The dose difference was found to be primarily located at the periphery region of the target.

Conclusion:

For clinical SBRT lung treatment planning, the dosimetric differences between three commercially available algorithms are generally small except at target periphery. XVMC and AXB algorithms are recommended for accurate dose estimation at tissue boundaries.
SU‐E‐T‐482: Development and Systematic Testing of Dose Analysis Engine for Research and Clinical Applications Using API Interface of Varian Eclipse Treatment Planning System
Authors: Fatyga M , Gao F , Wu T , Liu W
Published: July 2014

Purpose:

To validate standalone software that provides dose analysis capabilities of a treatment planning system. The intended use of this software is in research and in clinical applications where commercial solutions are not yet available.

Methods:

We used Application Programmer Interface (API) of the Eclipse Treatment Planning System (Varian,Inc), to extract dosimetric information from treatment plans. We used dose volume histogram (DVH) object to extract standard dose volume histogram data. We used two API functions to construct 3D representation of anatomy (a bitmap) and compute dose values at all voxels that belong to a structure. We wrote a C++ package which achieves the same reconstruction based on stored contour data and a dose volume. For this work we compared structure volumes and simple dose statistics on dose buffers (minimum, mean, maximum and standard deviation). We used data from 6 Head and Neck patients and examined a total of 102 structures.

Results:

The API based reconstruction of 3D anatomy systematically overestimates structure volumes when compared to volumes reported by the API DVH module. The discrepancy is largest for small structures, and can exceed 20%. Volume estimates obtained by the C++ package show better agreement with the DVH module if partial volume corrections are applied to surface voxels. Among four dosimetric variables, largest discrepancies are observed for the minimum dose. While we observe better than 2% agreement in most cases, we find outliers with discrepancies reaching over 20%, even when we compare the two API based methods.

Conclusion:

We find that good validation of a standalone dose analysis package requires testing on a large series of structures obtained from multiple patients. Disagreements between two API based methods show that vendor algorithms have hidden features which may affect dosimetric analysis.
SU‐E‐T‐483: Treatment Planning Study of Volumetric Modulated Arc Therapy for Left‐Sided Breast and Chestwall Cancers
Authors: Xu H
Published: July 2014

Purpose:

To perform the comparison of dose distributions and dosevolume‐ histograms generated by VMAT and conventional field‐in‐field technique for left‐sided breast and chestwall cancers; to determine whether VMAT offers more dosimetric benefits than does the field‐in‐field technique.

Methods:

All VMAT and field‐in‐filed plans were produced in Eclipse(version 10). Five plans were generated for left‐sided breast and leftsided chestwall with supraclavicular nodes, respectively. A clockwise arc (CW) and a counter‐clockwise arc (CCW) were used with start and stop angles being 310o±10o and 140o±10o. Collimator angles were 30o for CW and 330o for CCW. The conformity index (CI) is the ratio of V95% over PTV. The homogeneity index (HI) is the ratio of the difference between D2% and D98% over the prescribed dose. The V5, as an indicator of low dose bath to organs‐at‐risk, was used for ipsilateral lung, heart, contralateral lung, and contralateral breast. The V20, as an indicator of radiation pneumonitis, was used for ipsilateral lung.

Results:

Breast/chestwall VMAT delivers much higher low dose bath to ipsilateral lung, contralateral lung and contralateral breast/chestwall for both intact breast and chestwall with nodes. V5 for heart is increased in VMAT plans. V20 for ipsilateral lung is lower in VMAT plans. PTV coverage is similar for both techniques. For one particular chestwall patient with supraclavicular and internal mammary nodes, VMAT offers superior dose coverage of PTVs with slightly more low‐dose‐wash to heart, contralateral lung and contralateral breast.

Conclusion:

This study indicates that there is generally no benefit using VMAT for left‐sided intact breast, due to large low‐dose‐bath (5Gy) to normal tissues with insignificant improvement in PTV coverage. Dosimetric benefits will be seen in VMAT plans for some chestwall patients with large size, and/or internal mammary nodes, etc. Whether a chestwall patient is treated with VMAT should be carefully analyzed on an individual basis.
SU‐E‐T‐516: Measurement of the Absorbed Dose Rate in Water Under Reference Conditions in a CyberKnife Unit
Authors: Aragon‐Martinez N , Gomez‐Munoz A , Hernandez‐Guzman A , Massillon‐JL G
Published: July 2014

Purpose:

This paper aims to measure the absorbed‐dose‐rate in a CyberKnife unit reference‐field (6cm diameter) using three ionization chambers (IC) following the new IAEA/AAPM formalism and Gafchromic film (MD‐V3‐55 and EBT3) protocol according to our work reported previously.

Methods:

The absorbed‐dose‐rates were measured at 90cm and 70cm SSD in a 10cmx10cm field and at 70cm SSD in a 5.4cmx5.4cm equivalent to 6cm diameter field using a linac Varian iX. All measurements were performed at 10cm depth in water. The correction factors that account for the difference between the IC response on the reference field and the CyberKnife reference field, k_(Q_msr,Q)^(f_msr,f_ref), were evaluated and Gafchromic film were calibrated using the results obtained above. Under the CyberKnife reference conditions, the factors were used to measure the absorbed‐dose‐rate with IC according to the new formalism and the calibrated film was irradiated in water. The film calibration curve was used to evaluate the absorbed‐dose‐rate in the CyberKnife unit.

Results:

Difference up to 2.56% is observed between dose‐rate measured with IC in the reference 10cmx10cm field, depending where the chamber was calibrated, which was not reflected in the correction factor k_(Q_msr,Q)^(f_msr,f_ref) where variations of ~0.15%‐0.5% were obtained. Within measurements uncertainties, maximum difference of 1.8% on the absorbed‐dose‐rate in the CyberKnife reference field is observed between all IC and the films

Conclusion:

Absorbed‐dose‐rate to water was measured in a CyberKnife reference field with acceptable accuracy (combined uncertainties ~1.32%‐1.73%, k=1) using three IC and films. The MD‐V3‐55 film as well as the new IAEA/AAPM formalism can be considered as a suitable dosimetric method to measure absorbed‐dose‐rate to water in small and non‐standard CyberKnife fields used in clinical treatments However, the EBT3 film is not appropriated due to the high uncertainty provided (combined uncertainty ~9%, k=1)

This work is partially supported by Conacyt grant 127409 and PAPIITUNAM grant IN10581
SU‐E‐QI‐03: Compartment Modeling of Dynamic Brain PET – The Effect of Scatter and Random Corrections On Parameter Errors
Authors: Häggström I , Schmidtlein C , Karlsson M , Larsson A
Published: July 2014

Purpose:

To investigate the effects of corrections for random and scattered coincidences on kinetic parameters in brain tumors, by using ten Monte Carlo (MC) simulated dynamic FLT‐PET brain scans.

Methods:

The GATE MC software was used to simulate ten repetitions of a 1 hour dynamic FLT‐PET scan of a voxelized head phantom. The phantom comprised six normal head tissues, plus inserted regions for blood and tumor tissue. Different time‐activity‐curves (TACs) for all eight tissue types were used in the simulation and were generated in Matlab using a 2‐tissue model with preset parameter values (K1,k2,k3,k4,Va,Ki). The PET data was reconstructed into 28 frames by both ordered‐subset expectation maximization (OSEM) and 3D filtered back‐projection (3DFBP). Five image sets were reconstructed, all with normalization and different additional corrections C (A=attenuation, R=random, S=scatter): Trues (AC), trues+randoms (ARC), trues+scatters (ASC), total counts (ARSC) and total counts (AC). Corrections for randoms and scatters were based on real random and scatter sinograms that were back‐projected, blurred and then forward projected and scaled to match the real counts. Weighted non‐linearleast‐ squares fitting of TACs from the blood and tumor regions was used to obtain parameter estimates.

Results:

The bias was not significantly different for trues (AC), trues+randoms (ARC), trues+scatters (ASC) and total counts (ARSC) for either 3DFBP or OSEM (p<0.05). Total counts with only AC stood out however, with an up to 160% larger bias. In general, there was no difference in bias found between 3DFBP and OSEM, except in parameter Va and Ki.

Conclusion:

According to our results, the methodology of correcting the PET data for randoms and scatters performed well for the dynamic images where frames have much lower counts compared to static images. Generally, no bias was introduced by the corrections and their importance was emphasized since omitting them increased bias extensively.
SU‐E‐QI‐05: Denoising Intravoxel Incoherent Motion Magnetic Resonance Images Using Non‐Local Mean Technique for Oropharyngeal Cancer Study
Authors: Ding Y , Fuller C , Mohamed A , He R , Wang J , Frank S , Rosenthal D , Colen R , Hazle J
Published: July 2014

Purpose:

Intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) normally shows a low signal to noise ratio (SNR) due to the presence of noise which complicates and biases the estimation of quantitative diffusion parameters. In this study, a Non‐local Means (NLM) approach was applied to remove the noise in oropharyngeal cancer IVIMMRI images.

Methods:

Eight male patients with squamous cell carcinoma of the oropharynx were included in this study under an approved IRB protocol. IVIM‐MRI was carried out on a 3.0‐T GE MRI. NLM denoising technique was performed using the MIPAV (V7, NIH). IVIM parameters (D, pure diffusion coefficient; f, perfusion fraction; D*, pseudodiffusion coefficient) were calculated on a pixel‐by‐pixel basis using a bi‐exponential model implemented within ImageJ (V1.47, NIH) with ten b‐values ranging from 0 – 800 s/mm2. SNR with and without denoising processing was calculated and compared in tumor regions. The agreements of IVIM‐MRI parameters estimated between with and without NLM processing in tumor region were assessed by Bland‐Altman plots.

Results:

Examples of IVIM images (b=800 s/mm2) and parametric maps (D, D* and f) with and without NLM applied are illustrated in Fig. 1 for an oropharynx cancer patient. Results of SNR and IVIM diffusion parameters between two different processing, as mean and standard deviation on 8 patients, are reported in Table 1. Bland‐Altman plots (Fig. 2) between the two approaches show better concordance for D (0.22% ± 1.42%) and f (0.56% ± 3.49%), whereas larger discrepancies were found for D* (0.86% ± 6.25%).

Conclusion:

NLM approach gives better SNR and quantitative data quality, also shows a good agreement between the IVIM parameters processed with and without NLM approaches. Therefore, NLM denoising technique can be applied to improve performance in terms of denoising quality and estimation of IVIM parameter as a post‐processing step without increasing the scanning time.
SU‐E‐QI‐06: Design and Initial Validation of a Precise Capillary Phantom to Test Perfusion Systems
Authors: Wood R , Iacobucci G , Khobragade P , Ying L , Snyder K , Wack D , Rudin S , Ionita C
Published: July 2014

Purpose:

To design a precise perfusion phantom mimicking capillaries of the brain vasculature which could be used to test various perfusion protocols and algorithms which generate perfusion maps.

Methods:

A perfusion phantom was designed in Solidworks and built using additive manufacturing. The phantom was an overall cylindrical shape of diameter and height 20mm and containing capillaries of 200μm or 300μm which were parallel and in contact making up the inside volume where flow was allowed. We created a flow loop using a peristaltic pump and contrast agent was injected manually. Digital Subtraction Angiographic images and low contrast images with cone beam CT were acquired after the contrast was injected. These images were analyzed by our own code in LabVIEW software and Time‐Density Curve, MTT and TTP was calculated.

Results:

Perfused area was visible in the cone beam CT images; however, individual capillaries were not distinguishable. The Time‐Density Curve acquired was accurate, sensitive and repeatable. The parameters MTT, and TTP offered by the phantom were very sensitive to slight changes in the TDC shape.

Conclusion:

We have created a robust calibrating model for evaluation of existing perfusion data analysis systems. This approach is extremely sensitive to changes in the flow due to the high temporal resolution and could be used as a golden standard to assist developers in calibrating and testing of imaging perfusion systems and software algorithms.

Supported by NIH Grant: 2R01EB002873 and an equipment grant from Toshiba Medical Systems Corporation
SU‐E‐QI‐07: Early Evaluation of Tumor Response to Therapy Via More Accurate Apparent Diffusion Coefficient Maps
Authors: Ma B , Li X , Kuang Y
Published: July 2014

Purpose:

We investigated the impact of more accurately computed apparent diffusion coefficient (ADC) maps, generated by registration of high‐b‐value and low‐b‐value diffusion weighted MR volumes, on early evaluation of tumor response to therapy.

Methods:

As in previous work, voxel‐by‐voxel ADC changes in diffusion MR exams during the course of cancer treatment have been shown to be capable of predicting therapeutic response earlier and more accurately than conventional methods. Here we further improved the prediction accuracy using better estimated ADC values. Due to the different susceptibility effects of the different b‐field acquisitions, the low‐ and high‐b‐value diffusion weighted MR volumes can be markedly out of alignment. Nonlinear registration was employed to align these two volumes and more accurate ADC values were produced. Therapeutic efficacy was then evaluated using the voxel‐by‐voxel ADC change analysis on the registered pre‐ and post‐treatment ADC maps.

Results:

We have applied the described method to 14 sets of pre‐ and post‐treatment diffusion MRI volumes of breast cancer patients. The post‐treatment exams were acquired in average five weeks after the initiation of treatment. Voxel‐by‐voxel ADC change analysis with logistic regression (p=0.009) demonstrated that the probability of a responsive treatment is significantly associated with increased ADC values. There were 2 false positives and 1 false negative (sensitivity=80%, specificity=75%). Using more accurate ADC values estimated with nonlinear registration, ADC change analysis yielded 1 false positive and 1 false negative for a sensitivity of 90% and a specificity of 75%.

Conclusion:

The study suggests registration of high‐b‐value and low‐b‐value diffusion weighted MR volumes ensures their voxel correspondence and the subsequent estimation of ADC values are more accurate than ADC computation without registration. The improved ADC maps could increase the accuracy of voxelby‐ voxel ADC change analysis of registered interval exams in early assessment of treatment response.

NIH/NIGMS U54 GM104944, Lincy Endowed Assistant Professorship
SU‐E‐QI‐08: Fourier Properties of Cone Beam CT Projection
Authors: Bai T , Yan H , Jia X , Jiang Steve B. , Mou X
Published: July 2014

Purpose:

To explore the Fourier properties of cone beam CT (CBCT) projections and apply the property to directly estimate noise level of CBCT projections without any prior information.

Methods:

By utilizing the property of Bessel function, we derivate the Fourier properties of the CBCT projections for an arbitrary point object. It is found that there exists a double‐wedge shaped region in the Fourier space where the intensity is approximately zero. We further derivate the Fourier properties of independent noise added to CBCT projections. The expectation of the square of the module in any point of the Fourier space is constant and the value approximately equals to noise energy. We further validate the theory in numerical simulations for both a delta function object and a NCAT phantom with different levels of noise added.

Results:

Our simulation confirmed the existence of the double‐wedge shaped region in Fourier domain for the x‐ray projection image. The boundary locations of this region agree well with theoretical predictions. In the experiments of estimating noise level, the mean relative error between the theory estimation and the ground truth values is 2.697%.

Conclusion:

A novel theory on the Fourier properties of CBCT projections has been discovered. Accurate noise level estimation can be achieved by applying this theory directly to the measured CBCT projections.

This work was supported in part by NIH(1R01CA154747‐01), NSFC((No. 61172163), Research Fund for the Doctoral Program of Higher Education of China (No. 20110201110011) and China Scholarship Council.
SU‐E‐QI‐09: In Vivo Monitoring of Fluorinated Inhalational Anesthetics Using 19F MRI: A Pilot Study
Authors: Bednarz B , Ludwig K , Fain S
Published: July 2014

Purpose:

Despite the widespread use of fluorinated hydrocarbons for inhalational anesthesia very little is known about the role of these anesthetics in postoperative cognitive impairment. There is a compelling need for safe and effective quantitative and qualitative imaging techniques to monitor the spatial distribution of inhalational anesthetics in vivo to appropriately assess this role. Herein we present a pilot study on the use of 1 9F MRI to image fluorinated anesthetics in vivo.

Methods:

The spatial distribution of isoflurane in a healthy C57BL/6 mouse subject to a constant flow rate of gas was image using a 4.7T small animal MRI system (Aligent Technologies, Santa Clara, CA). Multiple coronal 19F 2 mm slice images were acquired using a volumetric quadrature coil tunable to 1 9F frequency (187.9 MHz) averaging over 4 different time points (30, 35, 60 and 75 minutes). 1 9F images were overlaid onto T2‐weighted fast echo multi‐slice (FSEMS) 1H images of soft tissue anatomy.

Results:

An average over the 4 collection time points clearly demonstrates the distribution of isoflurane in vivo with peak uptake in muscle and fatty tissue as well as in the frontal lobe of the mouse brain. A time resolved imaging sequence demonstrates the increasing uptake of isoflurane in each of these compartments.

Conclusion:

A novel technique to image fluorinated gas anesthetics in vivo has been demonstrated. To the best of our knowledge, this is the first time isoflurane has been imaged in vivo using MRI.
SU‐E‐QI‐10: Intravoxel Incoherent Motion Imaging for MR‐Guided Cryoablation
Authors: Yung J , Ahrar K , Hazle J , Stafford R
Published: July 2014

Purpose:

Percutaneous renal cryoablation for renal tumors has been shown to be nephron sparing and have low morbidity. Post‐treatment verification of the ablated tissue often utilizes contrast‐enhanced MR imaging (ce‐MRI) to assess the region of altered perfusion. However, particularly within this population, some patients are contraindicated for contrast injection. Intravoxel incoherent motion (IVIM) MRI is a technique that measures diffusion and perfusion characteristics from the measured diffusion signals of multiple b values. In this study, IVIM MRI is evaluated versus ce‐MRI to assess its feasibility for differentiating normal and ablated tissue.

Methods:

Under real‐time MR guidance, 3 cryoprobes were introduced to a patient with renal cell carcinoma in the right kidney. Two cycles of cryoablation were performed with each cycle consisting of 12 minutes and a thaw cycle of 10 minutes. Dynamic ce‐MRI was performed following the last thaw cycle and diffusion‐weighted imaging. IVIM MRI was obtained using a respiratory navigator triggered single‐shot echo planar imaging sequence on a 1.5T clinical scanner. The diffusion coefficient D and the perfusion f parameters were estimated by fitting the diffusion for b values higher and lower than 200 sec/mm2 signal, respectively, using the IVIM model. Regions of interest (ROI) were manually placed in non‐enhancing and enhancing regions according to the post‐treatment contrast‐enhanced images and compared to one another.

Results:

The perfusion fraction and diffusion coefficient values decreased in the ablated tissue (5.51 ± 7.28 and 0.94 ± .30) compared to the normal kidney tissue (13.13 ± 10.37 and 1.68 ± 0.22). The perfusion fraction and diffusion coefficient maps demonstrate good agreement with the contrast‐enhanced images.

Conclusion:

In these preliminary results, the use of IVIM parameters could help verify treatment without the use of contrast. In the future, more patients undergoing MRguided cryoablation will be analyzed to determine the accuracy of these damage predictions.
SU‐E‐QI‐11: Measurement of Renal Pyruvate‐To‐Lactate Exchange with Hyperpolarized 13C MRI
Authors: Adamson E , Gordon J , Johnson K , Fain S
Published: July 2014

Purpose:

Previous work [1] modeling the metabolic flux between hyperpolarized [1‐13C]pyruvate and [1‐13C]lactate in magnetic resonance spectroscopic imaging (MRSI) experiments failed to account for vascular signal artifacts. Here, we investigate a method to minimize the vascular signal and its impact on the fidelity of metabolic modeling.

Methods:

MRSI was simulated for renal metabolism in MATLAB both with and without bipolar gradients. The resulting data were fit to a two‐site exchange model [1], and the effects of vascular partial volume artifacts on kinetic modeling were assessed. Bipolar gradients were then incorporated into a gradient echo sequence to validate the simulations experimentally. The degree of diffusion weighting (b = 32 s/mm2) was determined empirically from 1H imaging of murine renal vascular signal. The method was then tested in vivo using MRSI with bipolar gradients following injection of hyperpolarized [1‐13C]pyruvate (∼80 mM at 20% polarization).

Results:

In simulations, vascular signal contaminated the renal metabolic signal at resolutions as high as 2 × 2 mm2 due to partial volume effects. The apparent exchange rate from pyruvate to lactate (kp) was underestimated in the presence of these artifacts due to contaminating pyruvate signal. Incorporation of bipolar gradients suppressed vascular signal and improved the accuracy of kp estimation. Experimentally, the in vivo results supported the ability of bipolar gradients to suppress vascular signal. The in vivo exchange rate increased, as predicted in simulations, from kp = 0.012 s‐1 to kp = 0.020‐1 after vascular signal suppression.

Conclusion:

We have demonstrated the limited accuracy of the two‐site exchange model in the presence of vascular partial volume artifacts. The addition of bipolar gradients suppressed vascular signal and improved model accuracy in simulations. Bipolar gradients largely affected kp estimation in vivo. Currently, slow‐flowing spins in small vessels and capillaries are only partially suppressed, so further improvement is possible.

Funding support: Seed Grant from the Radiological Society of North America, GE Healthcare, University of Wisconsin Graduate School