bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐322: The Evaluation of the Gafchromic EBT3 Film in Low Dose 6 MV X‐Ray Beams with Different Scanning Modes
Authors: Lee H , Kim D , Chung W , Sung J , Yoon M
Published: July 2014

Purpose:

We have evaluated the response of the Gafchromic EBT3 film in low dose for 6 MV x‐ray beams with two scanning modes, the reflection scanning mode and the transmission scanning mode.

Methods:

We irradiated the Gafcromic EBT3 film using a 60 degree enhanced dynamic wedge (EDW) with 6 MV x‐ray beams from Clinac iX Linear accelerator (Varian Medical Systems, Palo Alto, CA). The irradiated Gafchromic EBT3 film was scanned with different scanning modes, the reflection scanning mode and the transmission scanning mode. The scanned Gafchromic EBT3 film was analyzed with MATLAB.

Results:

When 7.2 cGy was irradiated to the Gafchromic EBT3 film, the uncertainty was 0.54 cGy with reflection scanning mode and was 0.88 cGy with transmission scanning mode. When 24 cGy was irradiated to the Gafchromic EBT3 film, the uncertainty was similar to the case of 7.2 cGy irradiation showing 0.51 cGy of uncertainty with reflection scanning mode and 0.87 cGy of uncertainty with transmission scanning mode. The result suggests that the reflection mode should be used in Gafchromic EBT3 film for low irradiation.

Conclusion:

The result suggests that the reflection mode should be used in Gafchromic EBT3 film for low irradiation.
SU‐E‐T‐325: The New Evaluation Method of the VMAT Plan Delivery Using Varian DynaLog Files and Modulation Complexity Score (MCS)
Authors: Tateoka K , Fujimomo K , Saitou Y , Nakazawa T , Abe T , Nakata A , Yano M , Hareyama M
Published: July 2014

Purpose:

The aim of the study is to evaluate the use of Varian DynaLog files to verify VMAT plans delivery and modulation complexity score (MCS) of VMAT.

Methods:

Delivery accuracy of machine performance was quantified by multileaf collimator (MLC) position errors, gantry angle errors and fluence delivery accuracy for volumetric modulated arc therapy (VMAT). The relationship between machine performance and plan complexity were also investigated using the modulation complexity score (MCS). Plan and Actual MLC positions, gantry angles and delivered fraction of monitor units were extracted from Varian DynaLog files. These factors were taken from the record and verify system of MLC control file. Planned and delivered beam data were compared to determine leaf position errors and gantry angle errors. Analysis was also performed on planned and actual fluence maps reconstructed from those of the DynaLog files. This analysis was performed for all treatment fractions of 5 prostate VMAT plans. The analysis of DynaLog files have been carried out by in‐house programming in Visual C++.

Results:

The root mean square of leaf position and gantry angle errors were about 0.12 and 0.15, respectively. The Gamma of planned and actual fluence maps at 3%/3 mm criterion was about 99.21. The gamma of the leaf position errors were not directly related to plan complexity as determined by the MCS. Therefore, the gamma of the gantry angle errors were directly related to plan complexity as determined by the MCS.

Conclusion:

This study shows Varian dynalog files for VMAT plan can be diagnosed delivery errors not possible with phantom based quality assurance. Furthermore, the MCS of VMAT plan can evaluate delivery accuracy for patients receiving of VMAT. Machine performance was found to be directly related to plan complexity but this is not the dominant determinant of delivery accuracy.
SU‐E‐T‐326: The Oxygen Saturation (SO2) and Breath‐Holding Time Variation Applied Active Breathing Control (ABC)
Authors: Gong G , Yin Y
Published: July 2014

Purpose:

To study the oxygen saturation (SO2) and breath‐holding time variation applied active breathing control (ABC) in radiotherapy of tumor.

Methods:

24 volunteers were involved in our trials, and they all did breath‐holding motion assisted by ELEKTA Active Breathing Coordinator 2.0 for 10 times respectively. And the patient monitor was used to observe the oxygen saturation (SO2) variation. The variation of SO2, and length of breath‐holding time and the time for recovering to the initial value of SO2 were recorded and analyzed.

Results:

(1) The volunteers were divided into two groups according to the SO2 variation in breath‐holding: A group, 14 cases whose SO2 reduction were more than 2% (initial value was 97% to 99%, while termination value was 91% to 96%); B group, 10 cases were less than 2% in breath‐holding without inhaling oxygen. (2) The interfraction breath holding time varied from 8 to 20s for A group compared to the first breath‐holding time, and for B group varied from 4 to 14s. (3) The breathing holding time of B group prolonged mean 8s, compared to A group. (4) The time for restoring to the initial value of SO2 was from 10s to 30s. And the breath‐holding time shortened obviously for patients whose SO2 did not recover to normal.

Conclusion:

It is very obvious that the SO2 reduction in breath‐holding associated with ABC for partial people. It is necessary to check the SO2 variation in breath training, and enough time should be given to recover SO2.
SU‐E‐T‐327: The Update of a XML Composing Tool for TrueBeam Developer Mode
Authors: Yan Y , Mao W , Jiang S
Published: July 2014

Purpose:

To introduce a major upgrade of a novel XML beam composing tool to scientists and engineers who strive to translate certain capabilities of TrueBeam Developer Mode to future clinical benefits of radiation therapy.

Methods:

TrueBeam Developer Mode provides the users with a test bed for unconventional plans utilizing certain unique features not accessible at the clinical mode. To access the full set of capabilities, a XML beam definition file accommodating all parameters including kV/MV imaging triggers in the plan can be locally loaded at this mode, however it is difficult and laborious to compose one in a text editor. In this study, a stand‐along interactive XML beam composing application, TrueBeam TeachMod, was developed on Windows platforms to assist users in making their unique plans in a WYSWYG manner. A conventional plan can be imported in a DICOM RT object as the start of the beam editing process in which trajectories of all axes of a TrueBeam machine can be modified to the intended values at any control point. TeachMod also includes libraries of predefined imaging and treatment procedures to further expedite the process.

Results:

The TeachMod application is a major of the TeachMod module within DICOManTX. It fully supports TrueBeam 2.0. Trajectories of all axes including all MLC leaves can be graphically rendered and edited as needed. The time for XML beam composing has been reduced to a negligible amount regardless the complexity of the plan. A good understanding of XML language and TrueBeam schema is not required though preferred.

Conclusion:

Creating XML beams manually in a text editor will be a lengthy error‐prone process for sophisticated plans. A XML beam composing tool is highly desirable for R&D activities. It will bridge the gap between scopes of TrueBeam capabilities and their clinical application potentials.
SU‐F‐BRF‐07: Impact of Different Patient Setup Strategies in Adaptive Radiation Therapy with Simultaneous Integrated Volume‐Adapted Boost of NSCLC
Authors: Balik S , Weiss E , Dogan N , fatyga m , Sleeman W , Wu Y , Hugo G
Published: July 2014

Purpose:

To evaluate the potential impact of several setup error correction strategies on a proposed image‐guided adaptive radiotherapy strategy for locally advanced lung cancer.

Methods:

Daily 4D cone‐beam CT and weekly 4D fan‐beam CT images were acquired from 9 lung cancer patients undergoing concurrent chemoradiation therapy. Initial planning CT was deformably registered to daily CBCT images to generate synthetic treatment courses. An adaptive radiation therapy course was simulated using the weekly CT images with replanning twice and a hypofractionated, simultaneous integrated boost to a total dose of 66 Gy to the original PTV and either a 66 Gy (no boost) or 82 Gy (boost) dose to the boost PTV (ITV + 3mm) in 33 fractions with IMRT or VMAT. Lymph nodes (LN) were not boosted (prescribed to 66 Gy in both plans). Synthetic images were rigidly, bony (BN) or tumor and carina (TC), registered to the corresponding plan CT, dose was computed on these from adaptive replans (PLAN) and deformably accumulated back to the original planning CT. Cumulative D98% of CTV of PT (ITV for 82Gy) and LN, and normal tissue dose changes were analyzed.

Results:

Two patients were removed from the study due to large registration errors. For the remaining 7 patients, D98% for CTV‐PT (ITV‐PT for 82 Gy) and CTV‐LN was within 1 Gy of PLAN for both 66 Gy and 82 Gy plans with both setup techniques. Overall, TC based setup provided better results, especially for LN coverage (p = 0.1 for 66Gy plan and p = 0.2 for 82 Gy plan, comparison of BN and TC), though not significant. Normal tissue dose constraints violated for some patients if constraint was barely achieved in PLAN.

Conclusion:

The hypofractionated adaptive strategy appears to be deliverable with soft tissue alignment for the evaluated margins and planning parameters.

Research was supported by NIH P01CA116602
SU‐F‐BRF‐08: Conformal Mapping‐Based 3D Surface Matching and Registration
Authors: Song Y , Zeng W , Liu C , Gu X
Published: July 2014

Purpose:

Recently, non‐rigid 3D surface matching and registration has been used extensively in engineering and medicine. However, matching 3D surfaces undergoing non‐rigid deformation accurately is still a challenging mathematical problem. In this study, we present a novel algorithm to address this issue by introducing intrinsic symmetry to the registration

Methods:

Our computational algorithm for symmetric conformal mapping is divided into three major steps: 1) Finding the symmetric plane; 2) Finding feature points; and 3) Performing cross registration. The key strategy is to preserve the symmetry during the conformal mapping, such that the image on the parameter domain is symmetric and the area distortion factor on the parameter image is also symmetric. Several novel algorithms were developed using different conformal geometric tools. One was based on solving Riemann‐Cauchy equation and the other one employed curvature flow

Results:

Our algorithm was implemented using generic C++ on Windows XP and used conjugate gradient search optimization for acceleration. The human face 3D surface images were acquired using a high speed 3D scanner based on the phase‐shifting method. The scanning speed was 30 frames/sec. The image resolution for each frame was 640 × 480. For 3D human face surfaces with different expressions, postures, and boundaries, our algorithms were able to produce consistent result on the texture pattern on the overlapping region

Conclusion:

We proposed a novel algorithm to improve the robustness of conformal geometric methods by incorporating the symmetric information into the mapping process. To objectively evaluate its performance, we compared it with most existing techniques. Experimental results indicated that our method outperformed all the others in terms of robustness. The technique has a great potential in real‐time patient monitoring and tracking in image‐guided radiation therapy
SU‐F‐BRF‐09: A Non‐Rigid Point Matching Method for Accurate Bladder Dose Summation in Cervical Cancer HDR Brachytherapy
Authors: Chen H , Zhen X , Zhong Z , Pompos A , Yan H , Zhou L , Jiang S , Gu X
Published: July 2014

Purpose:

To propose and validate a deformable point matching scheme for surface deformation to facilitate accurate bladder dose summation for fractionated HDR cervical cancer treatment.

Method:

A deformable point matching scheme based on the thin plate spline robust point matching (TPSRPM) algorithm is proposed for bladder surface registration. The surface of bladders segmented from fractional CT images is extracted and discretized with triangular surface mesh. Deformation between the two bladder surfaces are obtained by matching the two meshes' vertices via the TPS‐RPM algorithm, and the deformation vector fields (DVFs) characteristic of this deformation is estimated by B‐spline approximation. Numerically, the algorithm is quantitatively compared with the Demons algorithm using five clinical cervical cancer cases by several metrics: vertex‐to‐vertex distance (VVD), Hausdorff distance (HD), percent error (PE), and conformity index (CI). Experimentally, the algorithm is validated on a balloon phantom with 12 surface fiducial markers. The balloon is inflated with different amount of water, and the displacement of fiducial markers is benchmarked as ground truth to study TPS‐RPM calculated DVFs' accuracy.

Results:

In numerical evaluation, the mean VVD is 3.7(±2.0) mm after Demons, and 1.3(±0.9) mm after TPS‐RPM. The mean HD is 14.4 mm after Demons, and 5.3mm after TPS‐RPM. The mean PE is 101.7% after Demons and decreases to 18.7% after TPS‐RPM. The mean CI is 0.63 after Demons, and increases to 0.90 after TPS‐RPM. In the phantom study, the mean Euclidean distance of the fiducials is 7.4±3.0mm and 4.2±1.8mm after Demons and TPS‐RPM, respectively.

Conclusions:

The bladder wall deformation is more accurate using the feature‐based TPS‐RPM algorithm than the intensity‐based Demons algorithm, indicating that TPS‐RPM has the potential for accurate bladder dose deformation and dose summation for multi‐fractional cervical HDR brachytherapy.

This work is supported in part by the National Natural ScienceFoundation of China (no 30970866 and no 81301940).
SU‐F‐BRF‐13: Investigating the Feasibility of Accurate Dose Measurement in a Deforming Radiochromic Dosimeter
Authors: Juang T , Adamovics J , Oldham M
Published: July 2014

Purpose:

Presage‐Def, a deformable radiochromic 3D dosimeter, has been previously shown to have potential for validating deformable image registration algorithms. This work extends this effort to investigate the feasibility of using Presage‐Def to validate dose‐accumulation algorithms in deforming structures.

Methods:

Two cylindrical Presage‐Def dosimeters (8cm diameter, 4.5cm length) were irradiated in a water‐bath with a simple 4‐field box treatment. Isocentric dose was 20Gy. One dosimeter served as control (no deformation) while the other was laterally compressed during irradiation by 21%. Both dosimeters were imaged before and after irradiation with a fast (∼10 minutes for 1mm isotropic resolution), broad beam, high resolution optical‐CT scanner. Measured dose distributions were compared to corresponding distributions calculated by a commissioned Eclipse planning system. Accuracy in the control was evaluated with 3D gamma (3%/3mm). The dose distribution calculated for the compressed dosimeter in the irradiation geometry cannot be directly compared via profiles or 3D gamma to the measured distribution, which deforms with release from compression. Thus, accuracy under deformation was determined by comparing integral dose within the high dose region of the deformed dosimeter distribution versus calculated dose. Dose profiles were used to study temporal stability of measured dose distributions.

Results:

Good dose agreement was demonstrated in the control with a 3D gamma passing rate of 96.6%. For the dosimeter irradiated under compression, the measured integral dose in the high dose region (518.0Gy*cm3) was within 6% of the Eclipse‐calculated integral dose (549.4Gy*cm3). Elevated signal was noted on the dosimeter edge in the direction of compression. Change in dosimeter signal over 1.5 hours was ≤2.7%, and the relative dose distribution remained stable over this period of time.

Conclusion:

Presage‐Def is promising as a 3D dosimeter capable of accurately measuring dose in a deforming structure, and warrants further study to quantify comprehensive accuracy at different levels of deformation.

This work was supported by NIH R01CA100835.

John Adamovics is the president of Heuris Inc., which commercializes PRESAGE.
SU‐F‐BRF‐15: Interfractional Dose Variations in Parotid and Submandibular Glands in IG‐IMRT for Head and Neck Cancer
Authors: Chen X , Botros M , Ahunbay E , Wang D , Schultz C , Li X
Published: July 2014

Purpose:

To quantify interfractional anatomic changes and the dosimetric variations in the parotid and submandibular glands in image‐guided IMRT for head and neck cancer.

Methods:

Daily diagnostic‐quality CTs acquired during daily IGRT using an in‐room CT (CTVision, Siemens) for 16 head and neck cancer patients treated with IMRT were analyzed. The contours of parotid glands and submandibular glands on dialy CTs were generated using an auto‐segmentation tool (ABAS, Elekta) with manual editing by a single physician. The volumetric changes were measured and the center of mass (COM) of each gland was obtained. The positional changes of the glands were characterized by inter‐parotid and inter‐submandibular gland distances. The original plan was applied to each fraction CT with isocenter shifts based on the alignment of the tumor. The DVHs and commonly used dose volume parameters from daily plans were compared to the original plans.

Results:

From fraction 1 to fraction 31, the average volume reduction was roughly 25% for all glands. The changes of inter‐parotid and inter‐submandibular gland distances were significant, with these distances decreased by 1.7±4.3 mm and 1.4±2.7 mm in average from fraction 1 to fraction 31. The average distance changes between the glands to the isocenter were from 0.4 to 3.3 mm. The mean dose changes for the four glands were from 109 cGy to 265 cGy.

Conclusion:

Significant decreases in the volume, inter‐gland distance were found during IG‐IMRT for head and neck cancer. These changes result in significant variations in doses to these glands, indicating the need of adaptive replanning.
SU‐F‐18C‐03: Loss of Image Sharpness in CT Bone Imaging Due to Positioning Within the Scan Field of View – Possible Solutions
Authors: Ranallo F , Szczykutowicz T
Published: July 2014

Purpose:

To demonstrate how both the positioning of an object in the scan field of view (SFOV) and the size of the reconstructed field of view (RFOV) can both significantly affect and degrade the image sharpness.

Methods:

Clinical CT scans of the shoulders and elbows were inspected for image sharpness. GE scanners were used for the imaging with a “Bone Plus” reconstruction algorithm. In all scans the anatomy of interest was significantly displaced from the center of the SFOV (away from the scanner iso‐center). Radial and azimuthal image sharpness measurements using the Modulation Transfer Function (MTF) were made using the same RFOV at the center of the SFOV and at varying distances from the center. These MTF measurements were also made with varying values of the RFOV.

Results:

Clinical images with the bone anatomy of interest positioned farther from the center of the SFOV showed increasing image softness occasionally to the point of being non‐diagnostic. The MTF measurements showed that the resolution degraded significantly, by more than a factor of 2, moving from the center toward the periphery of the SFOV: from 12 cycles/cm to less than 6 cycles/cm at distances of 15 cm or more from the center of the SFOV. Increasing the RFOV beyond 20 cm also degraded the resolution, though less significantly.

Conclusion:

When preservation of bone detail is important one must not only use the proper bone reconstruction algorithm, but also must keep the body part as close to the center of the SFOV as possible. Though this may be difficult with some imaging tasks, such as imaging of the shoulder and elbow, every effort should be made to this end. For the best resolution, the RFOV should also be kept small, ideally to 20 cm or less.

Partial research funding from GE HealthCare.
SU‐F‐18C‐05: Characterization of a Silicon Strip Photon‐Counting Detector in the Presence of Compton Scatter: A Simulation Study
Authors: Ziemer B , Ding H , Cho H
Published: July 2014

Purpose:

To investigate the effect of Compton scatter on detection efficiency and charge‐sharing for a Si strip photon‐counting detector as a function of pixel pitch, slice thickness and total pixel length.

Methods:

A CT imaging system employing a silicon photon‐counting detector was implemented using the GATE Monte Carlo package. A focal spot size of 300 µm, magnification of 1.33, and pixel pitches of 0.1 and 0.5mm were initially investigated. A 60 kVp spectrum with 3 mm Al filter was used and energy spectral degradation based on a prototype detector was simulated. To study charge‐sharing, a single pixel was illuminated, and the detector response in neighboring pixels was investigated. A longitudinally semiinfinite detector was simulated to optimize the quantum detection efficiency of the imaging system as a function of pixel pitch, slice thickness and depth of interaction. A 2.5 mm thick tungsten plate with a 0.01 mm by 1.5 mm slit was implemented to calculate the modulation transfer function (MTF) from projection‐based images. A threshold of 15 keV was implemented in the detector simulation. The preliminary charge sharing investigation results considered only scattering effects and the detector electronics related factors were neglected.

Results:

Using a 15 keV threshold, 1% of the pixel charge migrated into neighboring pixels with a pixel size of 0.1×0.1 mm2. The quantum detection efficiency was 77%, 84%, 87% and 89% for 15 mm, 22.5 mm, 30 mm, and 45 mm length silicon detector pixels, respectively. For a pixel pitch of 0.1 mm, the spatial frequency at 10% of the maximum MTF was found to be 5.2 lp/mm. This agreed with an experimental MTF measurement of 5.3 lp/mm with a similar detector configuration.

Conclusion:

Using optimized design parameters, Si strip photon‐counting detectors can offer high detection efficiency and spatial resolution even in the presence of Compton scatter.
SU‐F‐18C‐10: Clinical Implementation of Radiochromic Film Based CTDI Measurements
Authors: Quintero C , Tomic N , DeBlois F , Seuntjens J , Devic S
Published: July 2014

Purpose:

To evaluate accuracy and reproducibility of a radiochromic film‐based protocol to measure computer tomography dose index (CTDI) as a part of annual QA on CT scanners and kV CBCT systems attached to linear accelerators.

Methods:

Energy dependence of Gafchromic XR‐QA2(R) film model was tested over imaging beam qualities (50 – 140 kVp). Film pieces were irradiated in air to known values of air kerma in air (up to 10 cGy). Change in film reflectance was determined with an in‐house written code using images produced by a flatbed document scanner. Calibration curves for each beam quality were created, and film responses for same air‐kerma values were compared.Sets of film strips were placed into holes of a CTDI phantom and irradiated for several clinical scanning protocols on CT‐simulators and CBCT systems. Film reflectance change was converted into dose to water and used to calculate CTDIvol values. Measured CTDIvol values were compared to tabulated CTDIvol values.

Results:

Average variations of ±5.2% in the mean film reflectance change were observed in the energy range of 80 to 140 keV, and 11.1% between 50 and 140 keV. The averaged measured CTDI values presented a mean variation for the same machine and protocol of 2.6%. However, measured CTDI values were in average 10% lower than tabulated CTDI values for CT‐simulators, and 44% higher for CBCT systems.

Conclusion:

We found that in relatively broad range of beam qualities used in diagnostic radiology variation of film response is within ±5% resulting in ±15% systematic error in dose estimates if a single calibration curve is used. Relatively large discrepancy between measured and tabulated CTDI values for different protocols and imaging systems used within radiotherapy department strongly support the trend towards replacing CTDI value with equilibrium dose measurement in the center of cylindrical phantom as suggested by TG‐111.

This work was supported by the Natural Sciences and Engineering Research Council of Canada, Contract No. 386009; Partial support by CREATE, Medical Physics Research Training Network grant of the Natural Science and Engineering Research Council, Contract No. 432290.
SU‐F‐18C‐14: Hessian‐Based Norm Penalty for Weighted Least‐Square CBCT Reconstruction
Authors: Sun T , Sun N , Wang J , Tan S
Published: July 2014

Purpose:

To develop a Hessian‐based norm penalty for cone‐beam CT (CBCT) reconstruction that has a similar ability in suppressing noise as the total variation (TV) penalty while avoiding the staircase effect and better preserving low‐contrast objects.

Methods:

We extended the TV penalty to a Hessian‐based norm penalty based on the Frobenius norm of the Hessian matrix of an image for CBCT reconstruction. The objective function was constructed using the penalized weighted least‐square (PWLS) principle. An effective algorithm was developed to minimize the objective function using a majorization‐minimization (MM) approach. We evaluated and compared the proposed penalty with the TV penalty on a CatPhan 600 phantom and an anthropomorphic head phantom, each acquired at a low‐dose protocol (10mA/10ms) and a high‐dose protocol (80mA/12ms). For both penalties, contrast‐to‐noise (CNR) in four low‐contrast regions‐of‐interest (ROIs) and the full‐width‐at‐half‐maximum (FWHM) of two point‐like objects in constructed images were calculated and compared.

Results:

In the experiment of CatPhan 600 phantom, the Hessian‐based norm penalty has slightly higher CNRs and approximately equivalent FWHM values compared with the TV penalty. In the experiment of the anthropomorphic head phantom at the low‐dose protocol, the TV penalty result has several artificial piece‐wise constant areas known as the staircase effect while in the Hessian‐based norm penalty the image appears smoother and more similar to that of the FDK result using the high‐dose protocol.

Conclusion:

The proposed Hessian‐based norm penalty has a similar performance in suppressing noise to the TV penalty, but has a potential advantage in suppressing the staircase effect and preserving low‐contrast objects.

This work was supported in part by National Natural Science Foundation of China (NNSFC), under Grant Nos. 60971112 and 61375018, and Fundamental Research Funds for the Central Universities, under Grant No. 2012QN086.
MO‐A‐19A‐01: Interview Like Your Job Depended On It!
Authors: Miller R , Meineke M
Published: July 2014

The purpose of our talk is to provide a relaxed and fun session for those seeking to improve their interviewing skills. You got your foot in the door, they liked your resume, and thought you looked interesting enough to bring out to meet face to face. How do you showcase your skills, while simultaneously showing them how well you would mesh with their current team? How do you respond to these newly popular questions that seem more interested in your feelings than in your technical skills? How do you pick up on the details that might clue you in that this potential employer isn' t right for you? Our session will give you concrete advice with examples to give you the tools you need to be successful in your next interview.

Learning Objectives:

Review some basic interviewing skills in terms of behavioral questions, common etiquette and human interactions

Demonstrate a good interview

Review some basic negotiating tactics
MO‐A‐BRD‐03: Quantifying 19F‐Labeled Human Natural Killer Cell‐Trafficking with MRI
Authors: Ludwig KD , Bouchlaka MN , Gordon JW , Bednarz BP , Capitini CM , Fain SB
Published: July 2014

Purpose:

To determine 19F‐labeling efficiency in ex vivo MRI of cultured human Natural Killer (hNK) cells and to quantify 19F‐labeled NK cell trafficking in vivo in naive mice and in mice bearing pediatric cancers with MRI.

Methods:

One immunodeficient and one neuroblastoma tumorbearing mouse were anesthetized with ketamine and xylazine. The hNK and mouse NK cells isolated from healthy donor peripheral blood mononuclear cells or spleens were expanded and incubated for 24 hours in a commercially available perfluoropolyether (PFPE) tracer. NMR was performed on a 9.4T spectrometer to verify successful uptake of PFPE agent into NK cells. Imaging was performed on a 4.7T small animal MRI system using a 19F volume quadrature coil. 19F images were acquired using a spinecho sequence (1.1×1.1×2.0mm3 resolution, ∼42 minutes scan time). A 19F reference vial was placed contralateral to the tumor/injection site for in vivo quantification.

Results:

A dose‐dependent response of 19F signal was shown in mouse NK cells labeled with increasing concentrations of PFPE. NMR spectra of the separated cells and supernatant confirmed that 19F signal originated from within the hNK cells. In vitro signal from 19F‐labeled hNK cells was quantified as a function of cell concentration. About 1.6×106 hNK cells was determined to be the minimum cell concentration detectabilty for a 1.1×1.1×2.0mm3 voxel at the 42 minute scan time. 19F‐labeled hNK cells were injected into the flank or tumor directly. 19F signal stayed localized in flank or within the neuroblastoma tumor for at least 48 hours.

Conclusion:

19F‐labeling of NK cells has been confirmed in vitro, both with imaging and spectroscopic analysis. hNK injection into a neuroblastoma tumor‐bearing mouse showed that hNK cells can be successfully detected and tracked longitudinally in vivo. Improving sensitivity for quantification of trafficking patterns within the tumor is ongoing.
MO‐A‐BRD‐06: In Vivo Cherenkov Video Imaging to Verify Whole Breast Irradiation Treatment
Authors: Zhang R , Jarvis L , Gladstone D , Andreozzi J , Hitchcock W , Glaser A , Pogue B
Published: July 2014

Purpose:

To show in vivo video imaging of Cherenkov emission (Cherenkoscopy) can be acquired in the clinical treatment room without affecting the normal process of external beam radiation therapy (EBRT). Applications of Cherenkoscopy, such as patient positioning, movement tracking, treatment monitoring and superficial dose estimation, were examined.

Methods:

In a phase 1 clinical trial, including 12 patients undergoing post‐lumpectomy whole breast irradiation, Cherenkov emission was imaged with a time‐gated ICCD camera synchronized to the radiation pulses, during 10 fractions of the treatment. Images from different treatment days were compared by calculating the 2‐D correlations corresponding to the averaged image. An edge detection algorithm was utilized to highlight biological features, such as the blood vessels. Superficial dose deposited at the sampling depth were derived from the Eclipse treatment planning system (TPS) and compared with the Cherenkov images. Skin reactions were graded weekly according to the Common Toxicity Criteria and digital photographs were obtained for comparison.

Results:

Real time (fps = 4.8) imaging of Cherenkov emission was feasible and feasibility tests indicated that it could be improved to video rate (fps = 30) with system improvements. Dynamic field changes due to fast MLC motion were imaged in real time. The average 2‐D correlation was about 0.99, suggesting the stability of this imaging technique and repeatability of patient positioning was outstanding. Edge enhanced images of blood vessels were observed, and could serve as unique biological markers for patient positioning and movement tracking (breathing). Small discrepancies exists between the Cherenkov images and the superficial dose predicted from the TPS but the former agreed better with actual skin reactions than did the latter.

Conclusion:

Real time Cherenkoscopy imaging during EBRT is a novel imaging tool that could be utilized for patient positioning, movement tracking, treatment monitoring, superficial dose and skin reaction estimation and prediction.
MO‐A‐BRD‐08: Radiosurgery Beyond Cancer: Real‐Time Target Localization and Treatment Planning for Cardiac Radiosurgery Under MRI Guidance
Authors: Ipsen S , Blanck O , Oborn B , Bode F , Liney G , Keall P
Published: July 2014

Purpose:

Atrial fibrillation (AF) is the most common cardiac arrhythmia, affecting >2.5M Americans and >4.5M Europeans. AF is usually treated with minimally‐invasive, time consuming catheter ablation techniques. Radiosurgery of the pulmonary veins (PV) has been proposed for AF treatment, however is challenging due to the complex respiratory and cardiac motion patterns. We hypothesize that an MRI‐linac could solve the difficult real‐time targeting and adaptation problem. In this study we quantified target motion ranges on cardiac MRI and analyzed the dosimetric benefits of margin reduction assuming real‐time MRI tracking was applied.

Methods:

For the motion study, four human subjects underwent real‐time cardiac MRI under free breathing. The target motion on coronal and axial cine planes was analyzed using a template matching algorithm. For the planning study, an ablation line at each PV antrum was defined as target on an AF patient scheduled for catheter ablation. Various safety margins ranging from 0mm (perfect tracking) to 8mm (untracked motion) were added to the target defining the PTV. 30Gy single fraction IMRT plans were then generated. Finally, the influence of a 1T magnetic field on treatment beam delivery was calculated using the Geant4 Monte Carlo algorithm to simulate the dosimetric impact of MRI guidance.

Results:

The motion study showed the mean respiratory motion of the target area on MRI was 8.4mm (SI), 1.7mm (AP) and 0.3mm (LR). Cardiac motion was small (<2mm). The planning study showed that with increasing safety margins to encompass untracked motion, dose tolerances for OARs such as the esophagus and airways were exceeded by >100%. The magnetic field had little impact on the dose distribution.

Conclusion:

Our results indicate that real‐time MRI tracking of the PVs seems feasible. Accurate image guidance for high‐dose AF radiosurgery is essential since safety margins covering untracked target motion will result in unacceptable treatment plans.
MO‐A‐BRD‐09: A Data‐Mining Algorithm for Large Scale Analysis of Dose‐Outcome Relationships in a Database of Irradiated Head‐And‐Neck (HN) Cancer Patients
Authors: Robertson SP , Quon H , Kiess AP , Moore JA , Yang W , Cheng Z , Sharabi A , McNutt TR
Published: July 2014

Purpose:

To develop a framework for automatic extraction of clinically meaningful dosimetric‐outcome relationships from an in‐house, analytic oncology database.

Methods:

Dose‐volume histograms (DVH) and clinical outcome‐related structured data elements have been routinely stored to our database for 513 HN cancer patients treated from 2007 to 2014. SQL queries were developed to extract outcomes that had been assessed for at least 100 patients, as well as DVH curves for organs‐at‐risk (OAR) that were contoured for at least 100 patients. DVH curves for paired OAR (e.g., left and right parotids) were automatically combined and included as additional structures for analysis. For each OAR‐outcome combination, DVH dose points, D(Vt), at a series of normalized volume thresholds, Vt=[0.01,0.99], were stratified into two groups based on outcomes after treatment completion. The probability, P[D(Vt)], of an outcome was modeled at each Vt by logistic regression. Notable combinations, defined as having P[D(Vt)] increase by at least 5% per Gy (p<0.05), were further evaluated for clinical relevance using a custom graphical interface.

Results:

A total of 57 individual and combined structures and 115 outcomes were queried, resulting in over 6,500 combinations for analysis. Of these, 528 combinations met the 5%/Gy requirement, with further manual inspection revealing a number of reasonable models based on either reported literature or proximity between neighboring OAR. The data mining algorithm confirmed the following well‐known toxicity/outcome relationships: dysphagia/larynx, voice changes/larynx, esophagitis/esophagus, xerostomia/combined parotids, and mucositis/oral mucosa. Other notable relationships included dysphagia/pharyngeal constrictors, nausea/brainstem, nausea/spinal cord, weight‐loss/mandible, and weight‐loss/combined parotids.

Conclusion:

Our database platform has enabled large‐scale analysis of dose‐outcome relationships. The current data‐mining framework revealed both known and novel dosimetric and clinical relationships, underscoring the potential utility of this analytic approach. Multivariate models may be necessary to further evaluate the complex relationship between neighboring OARs and observed outcomes.

This research was supported through collaborations with Elekta, Philips, and Toshiba.
MO‐A‐BRD‐10: A Fast and Accurate GPU‐Based Proton Transport Monte Carlo Simulation for Validating Proton Therapy Treatment Plans
Authors: Wan Chan Tseung H , Ma J , Beltran C
Published: July 2014

Purpose:

To build a GPU‐based Monte Carlo (MC) simulation of proton transport with detailed modeling of elastic and non‐elastic (NE) protonnucleus interactions, for use in a very fast and cost‐effective proton therapy treatment plan verification system.

Methods:

Using the CUDA framework, we implemented kernels for the following tasks: (1) Simulation of beam spots from our possible scanning nozzle configurations, (2) Proton propagation through CT geometry, taking into account nuclear elastic and multiple scattering, as well as energy straggling, (3) Bertini‐style modeling of the intranuclear cascade stage of NE interactions, and (4) Simulation of nuclear evaporation. To validate our MC, we performed: (1) Secondary particle yield calculations in NE collisions with therapeutically‐relevant nuclei, (2) Pencil‐beam dose calculations in homogeneous phantoms, (3) A large number of treatment plan dose recalculations, and compared with Geant4.9.6p2/TOPAS. A workflow was devised for calculating plans from a commercially available treatment planning system, with scripts for reading DICOM files and generating inputs for our MC.

Results:

Yields, energy and angular distributions of secondaries from NE collisions on various nuclei are in good agreement with the Geant4.9.6p2 Bertini and Binary cascade models. The 3D‐gamma pass rate at 2%–2mm for 70–230 MeV pencil‐beam dose distributions in water, soft tissue, bone and Ti phantoms is 100%. The pass rate at 2%–2mm for treatment plan calculations is typically above 98%. The net computational time on a NVIDIA GTX680 card, including all CPU‐GPU data transfers, is around 20s for 1×107 proton histories.

Conclusion:

Our GPU‐based proton transport MC is the first of its kind to include a detailed nuclear model to handle NE interactions on any nucleus. Dosimetric calculations demonstrate very good agreement with Geant4.9.6p2/TOPAS. Our MC is being integrated into a framework to perform fast routine clinical QA of pencil‐beam treatment plans. Hardware for such a system will cost under $5000.

This work was funded in part by a grant from Varian Medical Systems, Inc.
MO‐C‐BRD‐01: SBRT I: Overview of Simulation, Planning, and Delivery
Authors: Cai J , Wijesooriya K , Benedict S
Published: July 2014

SBRT is having a dramatic impact on radiation therapy of early‐stage, locally advanced cancers. Treatment planning of SBRT is characterized by precise target volume delineation, highly conformal dose distribution, sharp dose gradient outside the target volume, and meticulous tumor motion management. Stringent dose volume constraints of SBRT require the treatment planning to be highly personalized. Not only the complete patient's medical information (anatomy, tumor size/shape/location/motion, breathing pattern, health status) should be taken into consideration during planning, but also a wide range of factors including imaging techniques (imaging modality, breathing control, immobilization, patient position, etc.), treatment planning techniques (3D‐conformal, dynamic conformal arcs, IMRT, VMAT, etc.), image guidance techniques (CBCT, orthogonal X‐Ray, fiducial marker tracking, fluoroscopy, etc.), and delivery techniques (FFF, gating, tracking, etc.). In addition, potential pitfalls may exist in SBRT techniques and processes, such as target volume error in 4DCT and image registration error in image guidance. How to manage these affecting factors to achieve optimal, personalized SBRT treatment plans remains a great challenge. In this proposal, we will review technologies, share experiences, and discuss strategies concerning SBRT simulation, planning, and delivery.

Learning Objectives:

Understand requirements and challenges of SBRT treatment planning

Discuss information‐driven strategies of developing optimal SBRT plans

Discuss practical considerations and potential pitfalls of SBRT treatment planning
MO‐C‐17A‐02: A Novel Method for Evaluating Hepatic Stiffness Based On 4D‐MRI and Deformable Image Registration
Authors: Cui T , Liang X , Czito B , Palta M , Bashir M , Yin F , Cai J
Published: July 2014

Purpose:

Quantitative imaging of hepatic stiffness has significant potential in radiation therapy, ranging from treatment planning to response assessment. This study aims to develop a novel, noninvasive method to quantify liver stiffness with 3D strains liver maps using 4D‐MRI and deformable image registration (DIR).

Methods:

Five patients with liver cancer were imaged with an institutionally developed 4D‐MRI technique under an IRB‐approved protocol. Displacement vector fields (DVFs) across the liver were generated via DIR of different phases of 4D‐MRI. Strain tensor at each voxel of interest (VOI) was computed from the relative displacements between the VOI and each of the six adjacent voxels. Three principal strains (E1, E2 and E3) of the VOI were derived as the eigenvalue of the strain tensor, which represent the magnitudes of the maximum and minimum stretches. Strain tensors for two regions of interest (ROIs) were calculated and compared for each patient, one within the tumor (ROI1) and the other in normal liver distant from the heart (ROI2).

Results:

3D strain maps were successfully generated fort each respiratory phase of 4D‐MRI for all patients. Liver deformations induced by both respiration and cardiac motion were observed. Differences in strain values adjacent to the distant from the heart indicate significant deformation caused by cardiac expansion during diastole. The large E1/E2 (∼2) and E1/E2 (∼10) ratios reflect the predominance of liver deformation in the superior‐inferior direction. The mean E1 in ROI1 (0.12±0.10) was smaller than in ROI2 (0.15±0.12), reflecting a higher degree of stiffness of the cirrhotic tumor.

Conclusion:

We have successfully developed a novel method for quantitatively evaluating regional hepatic stiffness based on DIR of 4D‐MRI. Our initial findings indicate that liver strain is heterogeneous, and liver tumors may have lower principal strain values than normal liver. Thorough validation of our method is warranted in future studies.

NIH (1R21CA165384‐01A1)
MO‐C‐17A‐08: Evaluation of Lung Deformation Using Three Dimensional Strain Maps
Authors: Cui T , Huang Q , Miller W , Zhong X , Yin F , Cai J
Published: July 2014

Purpose:

To develop a systematic approach to generate three dimensional (3D) strain maps of lung using the displacement vector field (DVF) during the respiratory deformation, and to demonstrate its application in evaluating deformable image registration (DIR).

Methods:

A DVF based strain tensor at each voxel of interest (VOI) was calculated from the relative displacements between the VOI and each of the six nearest neighbors. The maximum and minimum stretches of a VOI can be determined by the principal strains (E1, E2 and E3), which are the eigenvalues and the corresponding strain tensors. Two healthy volunteers enrolled in this study under IRB‐approved protocol, each was scanned using 3D Hyperpolarized He‐3 tagging‐MRI and 3D proton‐MRI with TrueFISP sequence at the endof‐ inhalation (EOI) and the end‐of‐exhalation (EOE) phases. 3D DVFs of tagging‐ and proton‐MRI were obtained by the direct measurements of the tagging grid trajectory and by the DIR method implemented in commercial software.

Results:

3D strain maps were successfully generated for all DVFs. The principal strain E1s were calculated as 0.43±0.05 and 0.17±0.25 for tagging‐MRI and proton‐MRI, respectively. The large values of E1 indicate the predominant lung motion in the superior‐inferior (SI) direction. Given that the DVFs from the tagging images are considered as the ground truth, the discrepancies in the DIR‐based strain maps suggest the inaccuracy of the DIR algorithm. In the E1 maps of tagging‐MRI for subject 1, the fissures were distinguishable by the larger values (0.49±0.02) from the adjacent tissues (0.41±0.03) due to the larger relative displacement between the lung lobes.

Conclusion:

We have successfully developed a methodology to generate DVF‐based 3D strain maps of lung. It can potentially enable us to better understand the pulmonary biomechanics and to evaluate and improve the DIR algorithms for the lung deformation. We are currently studying more subjects to evaluate this tool.
MO‐C‐17A‐13: Uncertainty Evaluation of CT Image Deformable Registration for H&N Cancer Adaptive Radiotherapy
Authors: Qin A , Yan D
Published: July 2014

Purpose:

To evaluate uncertainties of organ specific Deformable Image Registration (DIR) for H&N cancer Adaptive Radiation Therapy (ART).

Methods:

A commercial DIR evaluation tool, which includes a digital phantom library of 8 patients, and the corresponding “Ground truth Deformable Vector Field” (GT‐DVF), was used in the study. Each patient in the phantom library includes the GT‐DVF created from a pair of CT images acquired prior to and at the end of the treatment course. Five DIR tools, including 2 commercial tools (CMT1, CMT2), 2 in‐house (IH_FFD1, IH_FFD2), and a classic DEMON algorithms, were applied on the patient images. The resulting DVF was compared to the GT‐DVF voxel by voxel. Organ specific DVF uncertainty was calculated for 10 ROIs: Whole Body, Brain, Brain Stem, Cord, Lips, Mandible, Parotid, Esophagus and Submandibular Gland. Registration error‐volume histogram was constructed for comparison.

Results:

The uncertainty is relatively small for brain stem, cord and lips, while large in parotid and submandibular gland. CMT1 achieved best overall accuracy (on whole body, mean vector error of 8 patients: 0.98±0.29 mm). For brain, mandible, parotid right, parotid left and submandibular glad, the classic Demon algorithm got the lowest uncertainty (0.49±0.09, 0.51±0.16, 0.46±0.11, 0.50±0.11 and 0.69±0.47 mm respectively). For brain stem, cord and lips, the DVF from CMT1 has the best accuracy (0.28±0.07, 0.22±0.08 and 0.27±0.12 mm respectively). All algorithms have largest right parotid uncertainty on patient#7, which has image artifact caused by tooth implantation.

Conclusion:

Uncertainty of deformable CT image registration highly depends on the registration algorithm, and organ specific. Large uncertainty most likely appears at the location of soft‐tissue organs far from the bony structures. Among all 5 DIR methods, the classic DEMON and CMT1 seem to be the best to limit the uncertainty within 2mm for all OARs.

Partially supported by research grant from Elekta.