bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐90: Medical Physicists' Implication in Diagnostic CT in Switzerland: Results of After One Year of Experience
Authors: Ryckx N. , Elandoy C. , Bize J. , Verdun F.R.
Published: July 2014

Purpose:

Since January 1st 2008, the Swiss ordinance on radiation protection requires the involvement of a medical physicist to support the optimization process of medical imaging techniques using ionizing radiation. After a long process of implementation, this requirement is satisfied all over the country since the beginning of 2013. The goal of this contribution is to summarize the main results obtained in this first year of experience in CT.

Methods:

We assessed the output and clinical use of 45 CT units using a three‐pronged approach. First, we assessed the output of the device (CTDIvol, primary beam collimation and HU in water at different tube tensions). Secondly, we characterized the local chest and abdomen acquisition and reconstruction protocols using the Catphan 600 phantom. Lastly, we assessed the clinical use of the machine by analyzing an extract of a dozen clinical examinations per unit.

Results:

9 out of 45 units had incorrect collimator settings, e.g. 4mm instead of 1mm. We witnessed also a large spread in reconstruction parameters, especially for reconstructed slice thickness, thus showing notable variations in low contrast detectability performances. Clinical practice is also clearly spread out. For example, estimated patient effective dose per abdomen examination lies at 18.7+/−12.7mSv (min: 2.0mSv — max: 112.0mSv). Chest and brain scans have a narrower dispersion, but patient effective dose is also spread by about a factor of 10 to 20.

Conclusion:

The spread in clinical practice being fairly large, it appears of crucial importance to collaborate more closely with radiologists and technologists to assess it. The lack of statistical precision will imply that we analyze clinical practice according to a specific medical demand rather than an anatomical region. Furthermore, low contrast sensitivity (LCD) being a crucial parameter, an objective method using a model observer will be used to assess LCD.
SU‐E‐I‐91: Reproducibility in Prescribed Dose in AEC CT Scans Due to Table Height, Patient Size, and Localizer Acquisition Order
Authors: Winslow J , Hurwitz L , Christianson O , Samei E
Published: July 2014

Purpose:

In CT scanners, the automatic exposure control (AEC) tube current prescription depends on the acquired prescan localizer image(s). The purpose of this study was to quantify the effect that table height, patient size, and localizer acquisition order may have on the reproducibility in prescribed dose.

Methods:

Three phantoms were used for this study: the Mercury Phantom (comprises three tapered and four uniform regions of polyethylene 16, 23, 30, and 37 cm in diameter), acrylic sheets, and an adult anthropomorphic phantom. Phantoms were positioned per clinical protocol by our chief CT technologist or broader symmetry. Using a GE Discovery CT750HD scanner, a lateral (LAT) and posterior‐anterior (PA) localizer was acquired for each phantom at different table heights. AEC scan acquisitions were prescribed for each combination of phantom, localizer orientation, and table height; the displayed volume CTDI was recorded for each. Results were analyzed versus table height.

Results:

For the two largest Mercury Phantom section scans based on the PA localizer, the percent change in volume CTDI from ideal were at least 20% lower and 35% greater for table heights 4 cm above and 4 cm below proper centering, respectively. For scans based on the LAT localizer, the percent change in volume CTDI from ideal were no greater than 12% different for 4 cm differences in table height. The properly centered PA and LAT localizer‐based volume CTDI values were within 13% of each other.

Conclusion:

Since uncertainty in vertical patient positioning is inherently greater than lateral positioning and because the variability in dose exceeds any dose penalties incurred, the LAT localizer should be used to precisely and reproducibly deliver the intended amount of radiation prescribed by CT protocols. CT protocols can be adjusted to minimize the expected change in average patient dose.
SU‐E‐I‐93: Improved Imaging Quality for Multislice Helical CT Via Sparsity Regularized Iterative Image Reconstruction Method Based On Tensor Framelet
Authors: Nam H , Guo M , Lee K , Li R , Xing L , Gao H
Published: July 2014

Purpose:

Inspired by compressive sensing, sparsity regularized iterative reconstruction method has been extensively studied. However, its utility pertinent to multislice helical 4D CT for radiotherapy with respect to imaging quality, dose, and time has not been thoroughly addressed. As the beginning of such an investigation, this work carries out the initial comparison of reconstructed imaging quality between sparsity regularized iterative method and analytic method through static phantom studies using a state‐of‐art 128‐channel multi‐slice Siemens helical CT scanner.

Methods:

In our iterative method, tensor framelet (TF) is chosen as the regularization method for its superior performance from total variation regularization in terms of reduced piecewise‐constant artifacts and improved imaging quality that has been demonstrated in our prior work. On the other hand, X‐ray transforms and its adjoints are computed on‐the‐fly through GPU implementation using our previous developed fast parallel algorithms with O(1) complexity per computing thread. For comparison, both FDK (approximate analytic method) and Katsevich algorithm (exact analytic method) are used for multislice helical CT image reconstruction.

Results:

The phantom experimental data with different imaging doses were acquired using a state‐of‐art 128‐channel multi‐slice Siemens helical CT scanner. The reconstructed image quality was compared between TF‐based iterative method, FDK and Katsevich algorithm with the quantitative analysis for characterizing signal‐to‐noise ratio, image contrast, and spatial resolution of high‐contrast and low‐contrast objects.

Conclusion:

The experimental results suggest that our tensor framelet regularized iterative reconstruction algorithm improves the helical CT imaging quality from FDK and Katsevich algorithm for static experimental phantom studies that have been performed.
SU‐E‐I‐98: Dose Comparison for Pulmonary Embolism CT Studies: Single Energy Vs. Dual Energy
Authors: Mahmood U , Erdi Y
Published: July 2014

Purpose:

The purpose of this study was to assess and compare the size specific dose estimate (SSDE), dose length product (DLP) and noise relationship for pulmonary embolism studies evaluated by single source dual energy computed tomography (DECT) against conventional CT (CCT) studies in a busy cancer center and to determine the dose savings provided by DECT.

Methods:

An IRB‐approved retrospective study was performed to determine the CTDIvol and DLP from a subset of patients scanned with both DECT and CCT over the past five years. We were able to identify 30 breast cancer patients (6 male, 24 female, age range 24 to 81) who had both DECT and CCT studies performed. DECT scans were performed with a GE HD 750 scanner (140/80 kVp, 480 mAs and 40 mm) and CCT scans were performed with a GE Lightspeed 16 slice scanner (120 kVp, 352 mAs, 20 mm). Image noise was measured by placing an ROI and recording the standard deviation of the mean HU along the descending aorta.

Results:

The average DECT patient size specific dose estimate was to be 14.2 ± 1.7 mGy as compared to 22.4 ± 2.7 mGy from CCT PE studies, which is a 37% reduction in the SSDE. The average DECT DLP was 721.8 ± 84.6 mGy‐cm as compared to 981.8 ± 106.1 mGy‐cm for CCT, which is a 26% decrease. Compared to CCT the image noise was found to decrease by 19% when using DECT for PE studies.

Conclusion:

DECT SSDE and DLP measurements indicate dose savings and image noise reduction when compared to CCT. In an environment that heavily debates CT patient doses, this study confirms the effectiveness of DECT in PE imaging.
SU‐E‐I‐99: Estimation of Effective Charge Distribution by Dual‐Energy CT Reconstruction
Authors: Sakata D , Kida S , Nakano M , Masutani Y , Nakagawa K , Haga A
Published: July 2014

Purpose:

Computed Tomography (CT) is a method to produce slice image of specific volume from the scanned x‐ray projection images. The contrast of CT image is correlated with the attenuation coefficients of the x‐ray in the object. The attenuation coefficient is strongly dependent on the x‐ray energy and the effective charge of the material. The purpose of this presentation is to show the effective charge distribution predicted by CT images reconstructed with kilovoltage(kV) and megavoltage(MV) x‐ray energy.

Methods:

The attenuation coefficients of x‐ray can be characterized by cross section of photoionization and Compton scattering for the specific xray energy. In particular, the photoionization cross section is strongly correlated with the effective charge of the object. Hence we can calculate effective charge by solving the coupled equation between the attenuation coefficient and the theoretical cross section. For this study, we use the megavoltage (MV) and kilovoltage (kV) x‐rays of Elekta Synergy as the dual source x‐ray, and CT image of the Phantom Laboratory CatPhan is reconstructed by the filtered back projection (FBP) and iterative algorithm for cone‐beam CT (CBCT).

Results:

We report attenuation coefficients of each component of the CatPhan specified by each x‐ray source. Also the effective charge distribution is evaluated by the MV and kV dual x‐ray sources. The predicted effective charges are comparable with the nominal ones.

Conclusion:

We developed the MV and kV dual‐source CBCT reconstruction to yield the effective charge distribution. For more accuracy, it is critical to remove an effect of the scattering photon in the CBCT reconstruction algorithm. The finding will be fine reference of the effective charge of tissue and lead to the more realistic absorbed‐dose calculation.

This work was partly supported by the JSPS Core‐to‐Core Program(No. 23003), and this work was partly supported by JSPS KAKENHI 24234567.
SU‐E‐J‐07: A Functional MR Protocol for the Pancreatic Tumor Delineation
Authors: Andreychenko A , Heerkens H , Meijer G , van Vulpen M , Lagendijk J , van den Berg C
Published: July 2014

Purpose:

Pancreatic cancer is one of the cancers with the poorest survival prognosis. At the time of diagnosis most of pancreatic cancers are unresectable and those patients can be treated by radiotherapy. Radiotherapy for pancreatic cancer is limited due to uncertainties in CT‐based delineations. MRI provides an excellent soft tissue contrast. Here, an MR protocol is developed to improve delineations for radiotherapy treatment of pancreatic cancer. In a later stage this protocol can also be used for on‐line visualization of the pancreas during MRI guided treatments.

Methods:

Nine pancreatic cancer patients were included. The MR protocol included T2 weighted(T2w), T1 weighted(T1w), diffusion weighted(DWI) and dynamic contrast enhanced(DCE) techniques. The tumor was delineated on T2w and T1w MRI by an experienced radiation oncologist. Healthy pancreas or pancreatitis (assigned by the oncologist based on T2w) areas were also delineated. Apparent diffusion coefficient(ADC), and area under the curve(AUC)/time to peak(TTP) maps were obtained from DWI and DCE scans, respectively.

Results:

A clear demarcation of tumor area was visible on b800 DWI images in 5 patients. ADC maps of those patients characterized tumor as an area with restricted water diffusion. Tumor delineations based on solely DCE were possible in 7 patients. In 6 of those patients AUC maps demonstrated tumor heterogeneity: a hypointense area with a hyperintense ring. TTP values clearly discriminated the tumor and the healthy pancreas but could not distinguish tumor and the pancreatitis accurately.

Conclusion:

MR imaging results in a more pronounced tumor contrast than contrast enhanced CT. The addition of quantitative, functional MRI provides valuable, additional information to the radiation oncologist on the spatial tumor extent by discriminating tumor from the healthy pancreas(TTP, DWI) and characterizing the tumor(ADC). Our findings indicate that tumor delineation in pancreatic cancer can greatly benefit from the addition of MRI and especially functional MR techniques.
SU‐E‐J‐08: A Hybrid Three Dimensional Registration Framework for Image‐Guided Accurate Radiotherapy System ARTS‐IGRT
Authors: Wu Q , Pei X , Cao R , Hu L , Wu Y
Published: July 2014

Purpose:

The purpose of this work was to develop a registration framework and method based on the software platform of ARTS‐IGRT and implement in C++ based on ITK libraries to register CT images and CBCT images. ARTS‐IGRT was a part of our self‐developed accurate radiation planning system ARTS.

Methods:

Mutual information (MI) registration treated each voxel equally. Actually, different voxels even having same intensity should be treated differently in the registration procedure. According to their importance values calculated from self‐information, a similarity measure was proposed which combined the spatial importance of a voxel with MI (S‐MI). For lung registration, Firstly, a global alignment method was adopted to minimize the margin error and achieve the alignment of these two images on the whole. The result obtained at the low resolution level was then interpolated to become the initial conditions for the higher resolution computation. Secondly, a new similarity measurement S‐MI was established to quantify how close the two input image volumes were to each other. Finally, Demons model was applied to compute the deformable map.

Results:

Registration tools were tested for head‐neck and lung images and the average region was 128*128*49. The rigid registration took approximately 2 min and converged 10% faster than traditional MI algorithm, the accuracy reached 1mm for head‐neck images. For lung images, the improved symmetric Demons registration process was completed in an average of 5 min using a 2.4GHz dual core CPU.

Conclusion:

A registration framework was developed to correct patient's setup according to register the planning CT volume data and the daily reconstructed 3D CBCT data. The experiments showed that the spatial MI algorithm can be adopted for head‐neck images. The improved Demons deformable registration was more suitable to lung images, and rigid alignment should be applied before deformable registration to get more accurate result.

Supported by National Natural Science Foundation of China (NO.81101132) and Natural Science Foundation of Anhui Province (NO.11040606Q55)
SU‐E‐J‐13: A New Variable for Plan Quality Evaluation Based On Normal Tissue Sparing
Authors: Zhang Q , Lei Y , Zheng D , Morgan B , Driewer J , Zhang M , Li S , Zhou S , Zhen W , Thompson R , Lin C , Wahl A , Enke C
Published: July 2014

Purpose:

The dose dropping speed (DDS) in normal tissue was proposed to assess plan quality. It was tested in stereotactic radiosurgery (SRS) cases.

Methods:

The DDS was tested with a total 40 plans for 8 SRS cases. Dynamic conformal arc plans were generated for each case, with prescription dose to isodose levels (IDL) ranging from 50% to 90% with 10% increment to cover the PTV. Forty non‐overlapping rind structures of 1mm thickness were created layer by layer from each PTV surface. The average dose in each rind was calculated and fitted with a double exponential function (DEF) of the distance from the PTV surface, which models the steep and moderate portions of the average dose curve in normal tissue. The parameter charactering the steep portion of the average dose curve in the DEF quantifies the DDS in the normal tissue receiving high dose. Provided that the prescription dose covers the whole PTV, a greater DDS indicates better normal tissue sparing.

Results:

Among all plans, the DDS was found to be the smallest for prescription of 90% IDL and reached a higher plateau region for prescription to 60% or 70%. The ratio of the highest slope to that of 90% prescription was 1.68±0.35. Analyzed with ANOVA, the DDS difference between the plans with prescription to 60% or 70% IDLS and those with prescription to 90% IDL were found significant (p<0.01). This can be attributed to the field size and penumbra slope change with different prescription levels. The trend became less pronounced with increasing PTV size due to less change of field profile for larger field size.

Conclusion:

A method was proposed to estimate dose dropping speed as a measure of plan quality. Based on this measure, prescriptions to 60% and 70% IDLs were found to provide best normal tissue sparing.
SU‐E‐J‐17: A Study of Accelerator‐Induced Cerenkov Radiation as a Beam Diagnostic and Dosimetry Tool
Authors: Bateman F , Tosh R
Published: July 2014

Purpose:

To investigate accelerator‐induced Cerenkov radiation imaging as a possible beam diagnostic and medical dosimetry tool.

Methods:

Cerenkov emission produced by clinical accelerator beams in a water phantom was imaged using a camera system comprised of a high‐sensitivity thermoelectrically‐cooled CCD camera coupled to a large aperture (f/0.75) objective lens with 16:1 magnification. This large format lens allows a significant amount of the available Cerenkov light to be collected and focused onto the CCD camera to form the image. Preliminary images, obtained with 6 MV photon beams, used an unshielded camera mounted horizontally with the beam normal to the water surface, and confirmed the detection of Cerenkov radiation. Several improvements were subsequently made including the addition of radiation shielding around the camera, and altering of the beam and camera angles to give a more favorable geometry for Cerenkov light collection. A detailed study was then undertaken over a range of electron and photon beam energies and dose rates to investigate the possibility of using this technique for beam diagnostics and dosimetry.

Results:

A series of images were obtained at a fixed dose rate over a range of electron energies from 6 to 20 MeV. The location of maximum intensity was found to vary linearly with the energy of the beam. A linear relationship was also found between the light observed from a fixed point on the central axis and the dose rate for both photon and electron beams.

Conclusion:

We have found that the analysis of images of beam‐induced Cerenkov light in a water phantom has potential for use as a beam diagnostic and medical dosimetry tool. Our future goals include the calibration of the light output in terms of radiation dose and development of a tomographic system for 3D Cerenkov imaging in water phantoms and other media.
SU‐E‐J‐18: A Thermal Simulation Model and Validation for Percutaneous Cancer Ablation
Authors: Deshazer G , Dupuy D , Merck D
Published: July 2014

Purpose:

Image‐guided percutaneous ablation is an effective, inexpensive, and accessible treatment for liver, lung, and kidney cancers. However, because of its relatively high recurrence rate, percutaneous ablation is usually considered to be palliative only. We hypothesize that the high recurrence rate is due in part to poor margin control resulting from inaccurate treatment models in procedure planning. To address this shortcoming, we are developing a thermal simulation model for percutaneous cancer ablation from first principles.

Methods:

Our model uses finite element methods to solve Penne's Heat Equation and Maxwell's equations for electromagnetic energy transfer in matter over time. The simulation accounts for applicator geometry and materials as taken from actual clinical devices, and incorporates appropriate density, thermal conductivity properties, dielectric properties, power dissipation, and the relative water content for a homogeneous liver tissue domain.

Results:

The solution generated is a continuous 3D thermal profile over time. The simulated 60 degree Celsius isotherm at 60 watts for 10 minutes in homogenous liver tissue is accurate to within approximately 5% (i.e., an average 2mm variance from a 36mm expected width) of the vendor specification and within 12% (5mm) of our own ex vivo ablation procedures as measured by 4D CT and visual inspection of the coagulation zone. Simulations at other input settings give similar results within 5%–15% of expected and empirically observed results.

Conclusion:

This promising initial model forms the basis of ongoing work in principled thermal simulation for ablation planning. Our next goals are to incorporate heterogeneous tissue types and heat sinks in the solution domain and validate the resulting simulation against our ongoing clinical data collection.
SU‐E‐J‐19: Accuracy of Dual‐Energy CT‐Derived Relative Electron Density for Proton Therapy Dose Calculation
Authors: Mullins J , Bues M , Duan X , Kruse J , Herman M
Published: July 2014

Purpose:

To determine the suitability of dual‐energy CT (DECT) to calculate relative electron density (RED) of tissues for accurate proton therapy dose calculation.

Methods:

DECT images of RED tissue surrogates were acquired at 80 and 140 kVp. Samples (RED=0.19−2.41) were imaged in a water‐equivalent phantom in a variety of configurations. REDs were calculated using the DECT numbers and inputs of the high and low energy spectral weightings. DECT‐derived RED was compared between geometric configurations and for variations in the spectral inputs to assess the sensitivity of RED accuracy versus expected values.

Results:

RED accuracy was dependent on accurate spectral input influenced by phantom thickness and radius from the phantom center. Material samples located at the center of the phantom generally showed the best agreement to reference RED values, but only when attenuation of the surrounding phantom thickness was accounted for in the calculation spectra. Calculated RED changed by up to 10% for some materials when the sample was located at an 11 cm radius from the phantom center. Calculated REDs under the best conditions still differed from reference values by up to 5% in bone and 14% in lung.

Conclusion:

DECT has previously been used to differentiate tissue types based on RED and Z for binary tissue‐type segmentation. To improve upon the current standard of empirical conversion of CT number to RED for treatment planning dose calculation, DECT methods must be able to calculate RED to better than 3% accuracy throughout the image. The DECT method is sensitive to the accuracy of spectral inputs used for calculation, as well as to spatial position in the anatomy. Effort to address adjustments to the spectral calculation inputs based on position and phantom attenuation will be required before DECT‐determined RED can achieve a consistent level of accuracy for application in dose calculation.
SU‐E‐J‐22: Alternative Method for Evaluating the Need for Replanning in Patient's with Significant Anatomical Changes
Authors: Myers P , Tran D , Liu T , Rodriguez‐Rivera E
Published: July 2014

Purpose:

The use of IGRT is highlighting the issue of anatomical patient changes during treatment due to weight loss and/or tumor shrinkage. A means of quickly reviewing the need to replan is important to maximize efficiency and review the necessity of modifying treatment planning. The goal of this project is to use an alternative method of evaluation for replanning that does not involve extra patient scanning or specific deformable registration software.

Methods:

Five patients that had undergone daily CBCT imaging during treatment and were noted to have considerable changes in anatomy due to weight loss or tumor shrinkage were evaluated with two methods. First, CBCT external volumes were subtracted from original planning CT to obtain a “change‐in‐volume” contour. The density of this contour was overridden to that of air and original plan recalculated. Second, the original plan was recalculated on a new CT scan taken the same day as the CBCT for comparison. The contours remained unchanged from the original planning scan.

Results:

So far 1 patient has been evaluated using both methods. The DVH comparison shows similar results between each method for the target tissues (CTV and PTV) as well as critical structures (right parotid and spinal cord). Using the CBCT method mean doses for each structure examined were within 3.2% of those calculated with a new CT scan. The remaining four patients will be evaluated similarly after a new CT scan is obtained.

Conclusion:

By using the patient's daily CBCT scan from setup prior to treatment, a quick method for evaluating anatomical changes and the need to replan a patient during the course of treatment was demonstrated. This method prevents the need to rescan the patient initially and allows a quick visualization of possible dose differences caused by a significant change in body habitus.
SU‐E‐J‐25: Analysis of Commercial 4DCT Flaws and the Potential Benefits of a New Technique for Irregular Breathing Patients
Authors: Dou T , Thomas D , Lamb J , Low D
Published: July 2014

Purpose:

To determine the distribution of inhalation to exhalation breathing amplitudes as measured using a commercial 4DCT and a proposed 4DCT protocol for irregular breathing patients.

Methods:

External breathing surrogate signals correlating with lung tidal volume were collected using an abdominal bellows for a set of 50 patients. Breathing traces over 5‐minute durations were evaluated and the peak inhalation and exhalation peaks identified. An arbitrary time point was identified and the nearest exhalation peak located within a ±180° gantry rotation period. The times at which the follow‐up inhalation scans occurred were correlated with the couch velocity to determine whether the tumor would be within 180° of that specific peak inhalation given the CT scanner coverage, pitch, rotation period, tumor size, and tumor motion amplitude (defined in units of centimeters per bellows signal). The imaged tumor motion amplitude was based on which inhalation peak would be imaged and the couch location at that time relative to the exhalation peak. This analysis provided a series of measured breathing motion amplitudes, which were compared against the 85th percentile motion, consistent with the proposed 4DCT protocol. Because the 4DCT scans would yield a single amplitude determination for each patient, errors in the amplitude measurement were considered systematic. Therefore, the largest 5% and smallest 5% of the measured amplitudes were selected to identify over‐and under‐determined motion amplitudes.

Results:

30% of the patients exhibited breathing amplitude overestimations of at least 27%, while 30% showed underestimations of at least 34%.

Conclusion:

For the majority of patients, the current system provided a high probability of correct breathing motion amplitude measurements. 30% had a significant chance of a systematic over‐ or under‐estimation of tumor motion. The proposed protocol will be immune to such irregularities because the entire breathing trace is used for breathing motion amplitude assessments.
SU‐E‐J‐34: Clinical Evaluation of Targeting Accuracy and Tractogrphy Delineation of Radiosurgery
Authors: Juh R , Suh T , Kim Y , Han J , Kim C , Oh C , Kim D
Published: July 2014

Purpose:

Focal radiosurgery is a common treatment modality for trigeminal neuralgia (TN), a neuropathic facial pain condition. Assessment of treatment effectiveness is primarily clinical, given the paucity of investigational tools to assess trigeminal nerve changes. The efficiency of radiosurgery is related to its highly precise targeting. We assessed clinically the targeting accuracy of radiosurgery with Gamma knife. We hypothesized that trigeminal tractography provides more information than 2D‐MR imaging, allowing detection of unique, focal changes in the target area after radiosurgery.

Methods:

Sixteen TN patients (2 females, 4 male, average age 65.3 years) treated with Gamma Knife radiosurgery, 40 Gy/50% isodose line underwent 1.5Tesla MR trigeminal nerve . Target accuracy was assessed from deviation of the coordinates of the target compared with the center of enhancement on post MRI. Radiation dose delivered at the borders of contrast enhancement was evaluated

Results:

The median deviation of the coordinates between the intended target and the center of contrast enhancement was within 1mm. The radiation doses fitting within the borders of the contrast enhancement the target ranged from 37.5 to 40 Gy. Trigeminal tractography accurately detected the radiosurgical target. Radiosurgery resulted in 47% drop in FA values at the target with no significant change in FA outside the target, suggesting that radiosurgery primarily affects myelin. Tractography was more sensitive, since FA changes were detected regardless of trigeminal nerve enhancement

Conclusion:

The median deviation found in clinical assessment of gamma knife treatment for TN Is low and compatible with its high rate of efficiency. DTI parameters accurately detect the effects of focal radiosurgery on the trigeminal nerve, serving as an in vivo imaging tool to study TN. This study is a proof of principle for further assessment of DTI parameters to understand the pathophysiology of TN and treatment effects
SU‐E‐J‐73: Generation of Volumetric Images with a Respiratory Motion Model Based On An External Surrogate Signal
Authors: Hurwitz M , Williams C , Mishra P , Dhou S , Lewis J
Published: July 2014

Purpose:

Respiratory motion during radiotherapy treatment can differ significantly from motion observed during imaging for treatment planning. Our goal is to use an initial 4DCT scan and the trace of an external surrogate marker to generate 3D images of patient anatomy during treatment.

Methods:

Deformable image registration is performed on images from an initial 4DCT scan. The deformation vectors are used to develop a patient‐specific linear relationship between the motion of each voxel and the trajectory of an external surrogate signal. Correlations in motion are taken into account with principal component analysis, reducing the number of free parameters. This model is tested with digital phantoms reproducing the breathing patterns of ten measured patient tumor trajectories, using five seconds of data to develop the model and the subsequent thirty seconds to test its predictions. The model is also tested with a breathing physical anthropomorphic phantom programmed to reproduce a patient breathing pattern.

Results:

The error (mean absolute, 95th percentile) over 30 seconds in the predicted tumor centroid position ranged from (0.8, 1.3) mm to (2.2, 4.3) mm for the ten patient breathing patterns. The model reproduced changes in both phase and amplitude of the breathing pattern. Agreement between prediction and truth over the entire image was confirmed by assessing the global voxel intensity RMS error. In the physical phantom, the error in the tumor centroid position was less than 1 mm for all images.

Conclusion:

We are able to reconstruct 3D images of patient anatomy with a model correlating internal respiratory motion with motion of an external surrogate marker, reproducing the expected tumor centroid position with an average accuracy of 1.4 mm. The images generated by this model could be used to improve dose calculations for treatment planning and delivered dose estimates.

This work was partially funded by a research grant from Varian Medical Systems.
SU‐E‐J‐78: Internal Target Volume Delineation for Lung Tumors in Patients Treated with Robotic Radiosurgery
Authors: Descovich M , Pinnaduwage D , Kirby N , Gottschalk A , Yom S , Pouliot J , Braunstein S
Published: July 2014

Purpose:

To compare different approaches for Internal Target Volume (ITV) delineation for patients treated with fiducial‐free robotic radiosurgery for primary and metastatic lung tumors.

Methods:

Ten patients undergoing Lung‐Optimized Treatment (LOT) for robotic radiosurgery were imaged with inhale and exhale breath‐hold CT scans and 8‐phase 4DCT scan. We evaluated the differences in internal target volume (ITV) delineated using three approaches: 1) maximum intensity projection (MIP) images reconstructed from 4DCT scan (ITV‐MIP); 2) linear interpolation of Gross Tumor Volumes (GTV) segmented on inhale and exhale breath‐hold scans (ITV‐BH); 3) linear interpolation of GTV segmented on inhale and exhale phases of 4DCT scan (ITV‐2Phase). All contours were independently generated by the same radiation oncologist using lung window settings. Patients had ITV‐MIP volumes ranging from 1.5 to 146.9 cc (mean 36.8 cc) located in various parts of the lung. Volume overlap and matching index (MI) were calculated and compared. The MI between two volumes was defined as the ratio of their intersection to their union. MI of 1 indicates the volumes are identical; MI of 0 indicates that there is no overlap.

Results:

The three approaches generated very different results. The average (SD) MI for ITV‐MIP and ITV‐BH was 0.52 (0.24); for ITV‐MIP and ITV‐2Phase it was 0.69 (0.13); and for ITV‐BH and ITV‐2Phase was 0.57 (0.21), (ANOVA, p=0.16). Relative to the ITV‐MIP, the percentage of volume overlap was 72% (26%) and 90% (7%) for ITV‐BH and ITV‐2Phase, respectively (t‐test, p=0.05).

Conclusion:

Differences between ITV‐BH and ITV‐MIP are due to inconsistent lung filling at breath‐hold and nonlinear tumor motion. Therefore, methods to check breath‐hold scanning against regular patient breathing patterns should be developed. Whenever possible, ITV‐BH generated by the LOT workflow should be verified by 4DCT data.
SU‐E‐J‐80: Interplay Effect Between VMAT Intensity Modulation and Tumor Motion in Hypofractioned Lung Treatment, Investigated with 3D Pressage Dosimeter
Authors: Touch M , Wu Q , Oldham M
Published: July 2014

Purpose:

To demonstrate an embedded tissue equivalent presage dosimeter for measuring 3D doses in moving tumors and to study the interplay effect between the tumor motion and intensity modulation in hypofractioned Volumetric Modulated Arc Therapy(VMAT) lung treatment.

Methods:

Motion experiments were performed using cylindrical Presage dosimeters (5cm diameter by 7cm length) mounted inside the lung insert of a CIRS thorax phantom. Two different VMAT treatment plans were created and delivered in three different scenarios with the same prescribed dose of 18 Gy. Plan1, containing a 2 centimeter spherical CTV with an additional 2mm setup margin, was delivered on a stationary phantom. Plan2 used the same CTV except expanded by 1 cm in the Sup‐Inf direction to generate ITV and PTV respectively. The dosimeters were irradiated in static and variable motion scenarios on a Truebeam system. After irradiation, high resolution 3D dosimetry was performed using the Duke Large Field‐of‐view Optical‐CT Scanner, and compared to the calculated dose from Eclipse.

Results:

In the control case (no motion), good agreement was observed between the planned and delivered dose distributions as indicated by 100% 3D Gamma (3% of maximum planned dose and 3mm DTA) passing rates in the CTV. In motion cases gamma passing rates was 99% in CTV. DVH comparisons also showed good agreement between the planned and delivered dose in CTV for both control and motion cases. However, differences of 15% and 5% in dose to PTV were observed in the motion and control cases respectively.

Conclusion:

With very high dose nature of a hypofraction treatment, significant effect was observed only motion is introduced to the target. This can be resulted from the motion of the moving target and the modulation of the MLC. 3D optical dosimetry can be of great advantage in hypofraction treatment dose validation studies.
SU‐E‐J‐85: Leave‐One‐Out Perturbation (LOOP) Fitting Algorithm for Absolute Dose Film Calibration
Authors: Chu A , Feng W , Ahmad M , Chen Z , Nath R
Published: July 2014

Purpose:

To introduce an outliers‐recognition fitting routine for film dosimetry. It cannot only be flexible with any linear and non‐linear regression but also can provide information for the minimal number of sampling points, critical sampling distributions and evaluating analytical functions for absolute film‐dose calibration.

Methods:

The technique, leave‐one‐out (LOO) cross validation, is often used for statistical analyses on model performance. We used LOO analyses with perturbed bootstrap fitting called leave‐one‐out perturbation (LOOP) for film‐dose calibration . Given a threshold, the LOO process detects unfit points (“outliers”) compared to other cohorts, and a bootstrap fitting process follows to seek any possibilities of using perturbations for further improvement. After that outliers were reconfirmed by a traditional t‐test statistics and eliminated, then another LOOP feedback resulted in the final. An over‐sampled film‐dose‐ calibration dataset was collected as a reference (dose range: 0‐800cGy), and various simulated conditions for outliers and sampling distributions were derived from the reference. Comparisons over the various conditions were made, and the performance of fitting functions, polynomial and rational functions, were evaluated.

Results:

(1) LOOP can prove its sensitive outlier‐recognition by its statistical correlation to an exceptional better goodness‐of‐fit as outliers being left‐out. (2) With sufficient statistical information, the LOOP can correct outliers under some low‐sampling conditions that other “robust fits”, e.g. Least Absolute Residuals, cannot. (3) Complete cross‐validated analyses of LOOP indicate that the function of rational type demonstrates a much superior performance compared to the polynomial. Even with 5 data points including one outlier, using LOOP with rational function can restore more than a 95% value back to its reference values, while the polynomial fitting completely failed under the same conditions.

Conclusion:

LOOP can cooperate with any fitting routine functioning as a “robust fit”. In addition, it can be set as a benchmark for film‐dose calibration fitting performance.
SU‐E‐J‐86: Lobar Lung Function Quantification by PET Galligas and CT Ventilation Imaging in Lung Cancer Patients
Authors: Eslick E , Bailey D , Bailey E , Kipritidis J , Keall P
Published: July 2014

Purpose:

The purpose of this study was to quantify the lobar lung function using the novel PET Galligas ([68Ga]‐carbon nanoparticle) ventilation imaging and the investigational CT ventilation imaging in lung cancer patients pre‐treatment.

Methods:

We present results on our first three lung cancer patients (2 male, mean age 78 years) as part of an ongoing ethics approved study. For each patient a PET Galligas ventilation (PET‐V) image and a pair of breath hold CT images (end‐exhale and end‐inhale tidal volumes) were acquired using a Siemens Biograph PET CT. CT‐ventilation (CT‐V) images were created from the pair of CT images using deformable image registration (DIR) algorithms and the Hounsfield Unit (HU) ventilation metric. A comparison of ventilation quantification from each modality was done on the lobar level and the voxel level. A Bland‐Altman plot was used to assess the difference in mean percentage contribution of each lobe to the total lung function between the two modalities. For each patient, a voxel‐wise Spearmans correlation was calculated for the whole lungs between the two modalities.

Results:

The Bland‐Altman plot demonstrated strong agreement between PET‐V and CT‐V for assessment of lobar function (r=0.99, p<0.001; range mean difference: −5.5 to 3.0). The correlation between PET‐V and CT‐V at the voxel level was moderate(r=0.60, p<0.001).

Conclusion:

This preliminary study on the three patients data sets demonstrated strong agreement between PET and CT ventilation imaging for the assessment of pre‐treatment lung function at the lobar level. Agreement was only moderate at the level of voxel correlations. These results indicate that CT ventilation imaging has potential for assessing pre‐treatment lobar lung function in lung cancer patients.
SU‐E‐J‐89: Motion Effects On Organ Dose in Respiratory Gated Stereotactic Body Radiation Therapy
Authors: Wang T , Khan M , Landry J , Rajpara R , Hawk N , Zhu L
Published: July 2014

Purpose:

Existing reports on gated radiation therapy focus mainly on optimizing dose delivery to the target structure. This work investigates the motion effects on radiation dose delivered to organs at risk (OAR) in respiratory gated stereotactic body radiation therapy (SBRT). A new algorithmic tool of dose analysis is developed to evaluate the optimality of gating phase for dose sparing on OARs while ensuring adequate target coverage.

Methods:

Eight patients with pancreatic cancer were treated on a phase I prospective study employing 4DCT‐based SBRT. For each patient, 4DCT scans are acquired and sorted into 10 respiratory phases (inhale‐exhale‐ inhale). Treatment planning is performed on the average CT image. The average CT is spatially registered to other phases. The resultant displacement field is then applied on the plan dose map to estimate the actual dose map for each phase. Dose values of each voxel are fitted to a sinusoidal function. Fitting parameters of dose variation, mean delivered dose and optimal gating phase for each voxel over respiration cycle are mapped on the dose volume.

Results:

The sinusoidal function accurately models the dose change during respiratory motion (mean fitting error 4.6%). In the eight patients, mean dose variation is 3.3 Gy on OARs with maximum of 13.7 Gy. Two patients have about 100cm3 volumes covered by more than 5 Gy deviation. The mean delivered dose maps are similar to plan dose with slight deformation. The optimal gating phase highly varies across the patient, with phase 5 or 6 on about 60% of the volume, and phase 0 on most of the rest.

Conclusion:

A new algorithmic tool is developed to conveniently quantify dose deviation on OARs from plan dose during the respiratory cycle. The proposed software facilitates the treatment planning process by providing the optimal respiratory gating phase for dose sparing on each OAR.
SU‐E‐J‐94: Positioning Errors Resulting From Using Bony Anatomy Alignment for Treating SBRT Lung Tumor
Authors: Frame C , Ding G
Published: July 2014

Purpose:

To quantify patient setups errors based on bony anatomy registration rather than 3D tumor alignment for SBRT lung treatments.

Method:

A retrospective study was performed for patients treated with lung SBRT and imaged with kV cone beam computed tomography (kV‐CBCT) image‐guidance. Daily CBCT images were registered to treatment planning CTs based on bony anatomy alignment and then inter‐fraction tumor movement was evaluated by comparing shift in the tumor center in the medial‐lateral, anterior‐posterior, and superior‐inferior directions. The PTV V100% was evaluated for each patient based on the average daily tumor displacement to assess the impact of the positioning error on the target coverage when the registrations were based on bony anatomy. Of the 35 patients studied, 15 were free‐breathing treatments, 10 used abdominal compression with a stereotactic body frame, and the remaining 10 were performed with BodyFIX vacuum bags.

Results:

For free‐breathing treatments, the range of tumor displacement error is between 1–6 mm in the medial‐lateral, 1–13 mm in the anterior‐posterior, and 1–7 mm in the superior‐inferior directions. These positioning errors lead to 6–22% underdose coverage for PTV – V100% . Patients treated with abdominal compression immobilization showed positional errors of 0–4mm mediallaterally, 0–3mm anterior‐posteriorly, and 0–2 mm inferior‐superiorly with PTV – V100% underdose ranging between 6–17%. For patients immobilized with the vacuum bags, the positional errors were found to be 0–1 mm medial‐laterally, 0–1mm anterior‐posteriorly, and 0–2 mm inferior‐superiorly with PTV – V100% under dose ranging between 5–6% only.

Conclusion:

It is necessary to align the tumor target by using 3D image guidance to ensure adequate tumor coverage before performing SBRT lung treatments. The BodyFIX vacuum bag immobilization method has the least positioning errors among the three methods studied when bony anatomy is used for registration.
SU‐E‐J‐101: Retroactive Calculation of TLD and Film Dose in Anthropomorphic Phantom as Assessment of Updated TPS Performance
Authors: Alkhatib H , Oves S
Published: July 2014

Purpose:

To demonstrate a quick and comprehensive method verifying the accuracy of the updated dose model by recalculating dose distribution in an anthropomorphic phantom with a new version of the TPS and comparing the results to measured values.

Methods:

CT images and IMRT plan of an RPC anthropomorphic head phantom, previously calculated by Pinnacle 9.0, was re‐computed using Pinnacle 9.2 and 9.6. The dosimeters within the phantom include four TLD capsules representing a primary PTV, two TLD capsules representing a secondary PTV, and two TLD capsules representing an organ at risk. Also included were three sheets of Gafchromic film. Performance of the updated TPS version was assessed by recalculating point doses and dose profiles corresponding to TLD and film position respectively and then comparing the results to reported values by the RPC.

Results:

Comparing calculated doses to reported measured doses from the RPC yielded an average disagreement of 1.48%, 2.04% and 2.10% for versions 9.0, 9.2, 9.6 respectively. Computed doses points all meet the RPC's passing criteria with the exception of the point representing the superior organ at risk in version 9.6. However, qualitative analysis of the recalculated dose profiles showed improved agreement with those of the RPC, especially in the penumbra region.

Conclusion:

This work has demonstrated the calculation results of Pinnacle 9.2 and 9.6 vs 9.0 version. Additionally, this study illustrates a method for the user to gain confidence upgrade to a newer version of the treatment planning system.
SU‐E‐J‐104: Single Photon Image From PET with Insertable SPECT Collimator for Boron Neutron Capture Therapy: A Feasibility Study
Authors: Jung J , Yoon D , Hong K , Suh T
Published: July 2014

Purpose:

The aim of our proposed system is to confirm the feasibility of extraction of two types of images from one positron emission tomography (PET) module with an insertable collimator for brain tumor treatment during the BNCT.

Methods:

Data from the PET module, neutron source, and collimator was entered in the Monte Carlo n‐particle extended (MCNPX) source code. The coincidence events were first compiled on the PET detector, and then, the events of the prompt gamma ray were collected after neutron emission by using a single photon emission computed tomography (SPECT) collimator on the PET. The obtaining of full width at half maximum (FWHM) values from the energy spectrum was performed to collect effective events for reconstructed image. In order to evaluate the images easily, five boron regions in a brain phantom were used. The image profiles were extracted from the region of interest (ROI) of a phantom. The image was reconstructed using the ordered subsets expectation maximization (OSEM) reconstruction algorithm. The image profiles and the receiver operating characteristic (ROC) curve were compiled for quantitative analysis from the two kinds of reconstructed image.

Results:

The prompt gamma ray energy peak of 478 keV appeared in the energy spectrum with a FWHM of 41 keV (6.4%). On the basis of the ROC curve in Region A to Region E, the differences in the area under the curve (AUC) of the PET and SPECT images were found to be 10.2%, 11.7%, 8.2% (center, Region C), 12.6%, and 10.5%, respectively.

Conclusion:

We attempted to acquire the PET and SPECT images simultaneously using only PET without an additional isotope. Single photon images were acquired using an insertable collimator on a PET detector.

This research was supported by the Leading Foreign Research Institute Recruitment Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, Information and Communication Technologies (ICT) & Future Planning (MSIP)(Grant No.2009 00420) and the Radiation Technology R&D program (Grant No.2013M2A2A7043498), Republic of Korea.