bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐J‐135: Exploring the Neuroprotective Effects of Bee Venom in a Mouse Parkinson Model with Immunohistochemistry, Magnetization Transfer Ratio Imaging and Spectroscopy
Authors: Yoon M , Doo A , Park H , Kim S , Jung J , Kim H
Published: August 2010

Purpose: Neuroprotective therapeutics stop or slowdown the degeneration process in animal models of Parkinson's disease (PD). In the present study, we investigated the anti‐inflammatory effect of bee venom (BV) on lipopolysaccharide (LPS)‐stimulated microglia. Method and Materials: To investigate whether MR techniques have added value in neuroprotection research in the MPTP mouse model, both MRI and MRS were applied to investigate the neuroprotective effects of BV. BV is suggested to stimulate anti‐inflammatory processing indirectly via DA‐dependent mechanisms or γ‐aminobutyric acid (GABA) and glutamate release. Magnetization transfer ratio (MTR) and 1H‐MRS studies were performed on control mice, MPTP‐intoxicated mice and BV treatment mice. The successfully induced lesions were verified by tyrosine hydroxylase immunolabelling on the substantia nigra (SN) and striatum (ST) performed on perchloric extracts of mice brains, after the control mice and the MPTP‐intoxicated mice were killed. All the MTR and 1H‐MRS experiments were performed on a 9.4 T MRI/MRS system using a standard head coil. Outer volume suppression combined with the ultra‐short echo‐time stimulated echo acquisition mode was used for the localized 1H‐MRS. The quantitative analysis of metabolites was determined using jMRUI from the 1H spectra obtained in vivo on the striatum. Results: The peak height of the MTR histograms in the PD model group was significantly lower than that in the BV treatment group (P<0.05). The present study revealed that the peak height of the MTR histogram was significantly decreased in the ST and SN, and a significant increase of the Glx/Cr ratio was found in the striatum of the PD group, as compared with that of the BV treatment group. Conclusion: These results demonstrate that BV possess a potent suppressive effect on proinflammatory responses of microglia and suggest that these compounds may offer substantial therapeutic potential for treatment of neurodegenerative diseases that are accompanied by microglial activation.
SU‐GG‐J‐136: High Fidelity, Low Distortion Diffusion‐Weighted MRI for Head and Neck Cancer Radiotherapy Planning
Authors: Paulson E , Ahunbay E , Li X
Published: August 2010

Purpose: Diffusion‐weighted (DW) MRI can provide information to improve target delineation in radiation treatment planning. However, acquisition of DW images in head and neck presents several challenges, including tissues with short T2s and off‐resonance effects arising from air‐tissue/air‐bone interfaces. We implemented a multi‐shot, variable density spiral (VDS) acquisition method and demonstrate that it is capable of generating low distortion, high fidelity DW images of head and neck cancer patients suitable for radiation treatment planning. Method and Materials: A multi‐shot, VDS sequence of our own design with Stejkal and Tanner diffusion encoding gradients was implemented on a 3.0T Siemens Verio scanner. Multi‐shot, DW images were acquired on three head and neck cancer patients (FOV: 220mm2, matrix: 1282, interleaves: 16, TE: 67 msec, TR: 3500 msec, TH: 3 mm, b=0, 600 s/mm2, scan time: 3.7 minutes). Custom reconstruction software was written to exploit the self‐navigating capabilities of the VDS readout gradients, which facilitated correction of each spiral interleaf for eddy current‐ and motion‐induced phase errors encoded by the diffusion gradients. Results: In terms of signal‐to‐noise ratio, short T2s impose an upper limit on echo times and, thus, the maximum achievable degree of diffusion weighting in head and neck regions. The use of the Stejkal and Tanner diffusion encoding scheme permits a reduction in minimum echo time, relative to the widely used twice‐refocused spin‐echo, which facilitates acquisition of DW images in tissues with short T2s. In addition, the combination of VDS readout gradients and the custom reconstruction algorithm permit effective correction of both eddy current and motion‐induced phase errors, thereby facilitating acquisition of high fidelity, low distortion DW images in the head and neck. Conclusions: High‐fidelity, low distortion diffusion‐weighted MR imaging of the head and neck useful for radiation treatment planning is achievable using multi‐shot, variable‐density spiral acquisitions. Research supported by Siemens Healthcare
SU‐GG‐J‐138: Effect of RF Pulse Dwell Time on Eddy Current and Motion Compensation in Multi‐Shot Diffusion‐Weighted MRI
Authors: Paulson E , Ahunbay E , Li X
Published: August 2010

Purpose: Diffusion‐weighted (DW) MRI can provide information to improve target delineation in radiation treatment planning. The widely used twice‐refocused spin‐echo (TRSE) sequence is optimized to diminish eddy current‐induced geometric distortions. However, the TRSE sequence imposes a longer minimum echo time, which precludes its use in acquiring DW images in tissues with short T2s. We found that radiofrequency (RF) pulse dwell times can also affect DW image quality, and demonstrate that high‐fidelity, multi‐shot DW images can be obtained using the non‐optimized Stejkal and Tanner (ST) sequence when short RF pulse dwell times are employed. Method and Materials: A pulse sequence of our own design was implemented to acquire DW images using ST and TRSE diffusion‐encoding schemes with 25 usec and 2 usec RF pulse dwell times. Single‐ and multi‐shot spiral DW images (b=0, 1000 s/mm2) of phantom and healthy volunteer were acquired on a 3.0T Siemens Verio scanner. Images were reconstructed offline using custom software developed at our Institution. Results: Single‐ and multi‐shot non‐DW images did not exhibit a dependence on RF pulse dwell time. Furthermore, single‐shot DW images acquired with the TRSE method did not exhibit a dependence on RF pulse dwell time. However, multi‐shot DW images exhibited significant artifacts at long RF pulse dwell times, even for the optimized TRSE method. Reducing the RF pulse dwell time improved the inherent immunity of the sequences to eddy current and motion‐induced artifacts, permitting acquisition of high‐fidelity, multi‐shot DW images even with the non‐optimized ST method. Conclusions: Compensation of eddy current and motion‐induced artifacts in multi‐shot DW imaging can be affected by choice of RF pulse dwell time. High‐fidelity, multi‐shot DW images of short T2 tissues can be obtained using the non‐optimized, traditional ST method so long as the RF pulse dwell time is kept short. Research supported by Siemens Healthcare
SU‐GG‐J‐143: Automatic Region‐Of‐Interest Delineation of Cone‐Beam CT Images for Adapting Treatment and Assessing Response in Head‐And‐Neck Cancer
Authors: Hou J , Chen W , Guerrero M , D'Souza W
Published: August 2010

Purpose: As the use of image guided therapy becomes more common, cone‐beam CT images taken during treatment are now often available. These images can potentially be used for on‐line adaptive radiation therapy if automatic ROI delineation can be implemented. We have developed an automatic region‐of‐interest delineation method based on deformable image registration of cone‐beam CT images for adaptive treatment and assessing response in head‐and‐neck cancer. Method and Materials: Six head‐and‐neck cancer patients were initially imaged with conventional CT and daily/weekly CBCT during 5–7 week treatment period. Contours of regions‐of‐interest on the CT images obtained from a commercial planning system was used as atlas and mapped onto the reference daily/weekly CBCT images via deformable image registration. The deformable image registration is based on Thirion's ‘demons’ method and was implemented with multiple resolution strategy. For each of six patients, three daily/weekly CBCT images were delineated by this method. Manually drawn contours on the CBCT images were used as reference to evaluate the performance of this automatic delineation method. Results: Examination of the difference image between the reference CBCT image and the registered CT image validated the feasibility of the deformable image registration method. For the 18 CBCT images collected from 6 patients, the overlap index (defined as the ratio of A∩B/AUB, where A represents automatically delineated GTV volume and B represents manually drawn GTV volume) has a mean value of 0.303 with standard deviation of 0.086. For the left neck nodes, the overlapping index has a mean value of 0.163 with standard deviation of 0.1133. For the right neck nodes, the overlapping index has a mean value of 0.105 with standard deviation of 0.09. Conclusion: Automatic atlas based ROI delineation was demonstrated as a promising tool for on‐line adaptive treatment of head and neck patients using daily/weekly cone‐beam CT images.
SU‐GG‐J‐147: Quantification of Tumor Response in Serial PET Imaging Using Level Set Clustering
Authors: Schreibmann E , Fox T
Published: August 2010

Purpose: Simple comparison tools and measures such as the maximum standardized uptake value (SUV) are currently used to gauge treatment response with PET imaging. In reality, the tumor and its response are heterogeneous and metabolic changes should be characterized by local measures. This study presents a tumor response algorithm that corrects for anatomical changes and robustly identifies local changes in serial PET images through a clustering algorithm. Materials and Methods: A two‐step analysis was performed for this study. First, pre and post‐treatment images are rigorously aligned using a deformable registration to correct for posture and soft tissue changes. The detailed mapping is modeled by free form deformations B‐spline optimized using the limited memory BFGS algorithm. A clustering algorithm further detects voxel changes in proximity to the user‐delineated structures. The level set clustering is an advanced approach that combines the advantages of pixel‐based and distance‐based techniques to classify the dataset into regions of both signal enhancement and reduction. The enhancing regions, where the treatment failed, are correlated with the RT Dose and Structure Set objects from the treatment plan. While enhancing regions inside the tumor receiving a high dose are associated with poor biological response, enhancing regions near tumor margins are associated with geometrical misses due to setup errors or targeting inaccuracies. Results: Results of the level‐set based clustering algorithm are presented to the user as colorwash displays overlaid over the original anatomy. The technique was instrumental in detecting geometrical and segmentation misses on actual clinical cases and provided an indispensable tool for accurate, outcome‐based quality assurance of the radiation treatment process. Conclusions: Patient studies have indicated that the method is reliable and provides a valuable tool to integrate imaging information into treatment assessment for image guided radiation therapy.
SU‐GG‐J‐150: Analyses of Multiple Q‐Sampled Diffusion Tensor Amplitudes for Pseudoprogressive GBM
Authors: Chu A , Knisely J , Constable R , Fulbright R , Nath R
Published: August 2010

Motivation: The current temozolomide (TMZ) concomitant with radiotherapy, can lead to earlier disruption of the blood‐brain barrier (BBB) than the conventional radiotherapy alone. 1∼2 months after concomitant radio‐chemotherapy, the BBB disruption from the therapeutic response may be radiologically evidenced as an apparently progressive (i.e. pseudoprogressive) lesion. There are few convincing functional imaging studies, e.g. perfusion MRI, F‐18 PET, that can clearly differentiate true tumor from pseudoprogressive one. The multiple‐q‐sampled diffusion tensor imaging (DTT) analyses, i.e. multiple “diffusion weighted echo‐amplitudes” analyzed in q‐space along the resolved diffusion characterized directions, can associate a certain diffusion population with diffusion spectral function of “q”. The hypotheses of this study: (1) large diffusive displacements with dispersive characteristic directions correspond to the BBB or edema area; (2) the range of anisotropic displacement becoming larger reflects deteriorating white matter (WM) glioma infiltration. Method: Each of 10 q‐sampled‐amplitudes (q: 0∼380cm−1) with 6 DTI‐sensitized‐directions is analyzed by 3D‐ellipsoidal diffusion model. Then Eigen‐values and Eigenvectors for each of amplitudes sampled with various q‐values are resolved by tensor diagonalization processes. Results: The DTI data sampled by q‐value lower than 180cm−1 illustrates the averaged population over a wider diffusive range without anisotropic enhancement and the one higher q‐value (e.g. q>250cm−1) excluding larger displacement spectrum shows anisotropic specification. As scanned by conventional T2‐weighted imaging or apparent‐diffusion‐coefficient mapping, GBM‐brain images are overwhelmingly dominated by larger diffusive components and incapable of differentiating BBB from infiltrated WM. Our preliminary results show the multiple q‐sampled DTI analyses can distinguish the regions of increasing diffusive displacements with dispersive diffusive directions (assuming BBB or edema) from the increasing secretion along WM fibers (assuming infiltrating WM). Conclusion: The spectrum of diffusive displacement are possibly differentiated by multiple q‐sampled DTI, and this technique can be utilized for a better diagnosis and prognosis for GBM treatment studies or WM diseases.
SU‐GG‐J‐151: Intra‐Patient Response Heterogeneity Using FLT PET during Chemotherapy in Canine Subjects with Lymphoma
Authors: Vanderhoek M , Lawrence J , Vail D , Jeraj R
Published: August 2010

Purpose: PET is routinely used for treatment response assessment in lymphoma after the completion of therapy. However, characterization of lymph node response heterogeneity during therapy could result in treatment modification to improve outcome. We used PET during chemotherapy to assess intra‐patient response heterogeneity in canine subjects with lymphoma. Method and Materials: Nine dogs with lymphoma were treated with GS‐9219, a novel antineoplastic agent preferentially targeting proliferative lymphoid cells. Using the cellular proliferation marker [18F]FLT, whole‐body PET/CT scans were acquired pre‐treatment and after 1, 3, and 5 chemotherapy cycles. Lymph nodes (∼16/dog) were segmented on CT images and these contours were applied to PET images to extract mean and maximum SUV for each node. Lymph node response was defined as relative change in SUV. For each dog, nodal responses and baseline values were normalized to their respective means. Heterogeneity was measured using the coefficient of variation (CV) and range of nodal responses and baseline values. Results: Intra‐patient heterogeneity of lymph node baseline values and responses were substantial. Within each dog, the average variation of mean SUV baseline values (CV: 30%) was slightly less than that of response (CV: 40%). Similar heterogeneities were measured using maximum SUV. There was no significant correlation between heterogeneities of baseline uptake and response (p=0.3). Individual dogs responded differently to treatment as some responses were very heterogeneous (most heterogeneous, CV: 115%) while others were quite uniform (least heterogeneous, CV: 5%). Response heterogeneity increased throughout therapy with CV of 35% after 1 chemotherapy cycle, 55% after 3 cycles, and 60% after 5 cycles. Heterogeneity trends measured using CV and ranges were consistent. Conclusions: During chemotherapy, there was substantial intra‐patient response heterogeneity (∼40%) in dogs with lymphoma. Early PET assessment of nodal response heterogeneity may identify poorly responding lymph nodes, permit early intervention, and improve outcomes in lymphoma patients.
SU‐GG‐J‐152: Assessment of Normal Tissue Response to Therapy Using FLT PET
Authors: Scully P , Perlman S , Liu G , Jeraj R
Published: August 2010

Purpose: In treatment of disease, dosing of drugs is often limited by normal tissue toxicities. The feasibility of [18F]‐fluoro‐3′‐deoxy‐3′‐L‐fluorothymidine (FLT) PET to assess changes in normal tissue physiology over the course of therapy was investigated. Methods: Sixteen cancer patients representing a variety of disease pathologies received sunitinib, a multi‐targeted receptor tyrosine kinase inhibitor with anti‐angiogenic and anti‐proliferative effects. Doses of 50mg/kg/day were administered in two schemes: Cohort A (n = 8) used a 4/2 (four weeks on/two weeks off) schedule; Cohort B (n = 6) used a 2/1 schedule. FLT‐PET images were acquired at baseline, peak drug exposure, and the end of the first planned treatment break. Regions of interest in liver, spleen, and marrow were segmented, and the mean standardized uptake value (SUVmean) was compared across the three scans. Two patients with liver métastases were excluded from analysis. Results: At peak exposure, both cohorts exhibited similar trends; SUVmean, was elevated relative to baseline in liver (30% ± 9%) and spleen (15% ± 10%), and reduced in marrow (−10% ± 7%). During treatment break, SUVmean in all tissues approached pre‐treatment levels for Cohort A, decreased in liver (13% ± 6%) and spleen (10% ± 9%) and increased in marrow (5% ± 2%). For Cohort B, SUVmean approached pre‐treatment levels in spleen (3% ± 10%), but remained near peak exposure levels in liver (29% ± 14%) and marrow (−10% ± 9%). This suggests a one‐week break may not allow sufficient time for normal tissue recovery. Large standard errors reflect a high degree of inter‐patient variability. Conclusions: Significant changes in FLT uptake during sunitinib treatment were observed in liver, marrow, and spleen. A high degree of inter‐patient variability was noted. FLT‐PET may provide a unique tool to monitor physiological changes prior to the development of dose‐limiting toxicities. Research sponsored by Pfizer corporation.
SU‐GG‐J‐154: Developing Multimodality Image Analysis Software for Target Definition and Therapy Response Assessment
Authors: Hua C , Zhang Y , Glenn G , Krasin M
Published: August 2010

Purpose: Multimodality functional imaging in cancer chemo‐radiotherapy holds promise for improved determination of tumor involvement in tissues and quantification of spatial and temporal changes in tumor pathophysiology in response to therapy. To address urgent needs for efficient analysis tools, we have developed an integrated software suite for retrospective research, prospectively evaluating the efficacy of functional imaging and facilitating streamlined data analysis for large‐scale clinical trials. Methods: Our software was developed using the MATLAB programming language version 7.6. The software runs on a Dell computer server with a 3‐GHz Intel Quad Core Xeon processor and 16‐gigabytes of memory. The software was designed to allow data exchange either directly with a patient image database or via a file system that organizes the data files hierarchically by institutional protocol, patient medical record number, imaging modality, study date, and series description. The spatial transformation matrix files generated in Siemens image registration applications can be read into our system and applied to image datasets in their original format. Results: This software allows simultaneous visualization of spatially registered images and derived parametric maps from various functional and anatomic imaging modalities at multiple time points. DICOM‐RT structure and dose files imported from treatment planning systems can be related to these multimodality images. Quantitative tools were implemented to perform image segmentation, histogram analysis of volumes of interest, and voxel‐wise correlation across modalities. Image and dosimetry data from example patients were processed to illustrate the clinical applicability of the software. Conclusion: We present an efficient image analysis software suite capable of simultaneously analyzing longitudinal patient images and radiation dose map with user‐defined volumes of interest or structures previously drawn for treatment planning. We hope this study illustrates well the unique needs of multimodality imaging in radiation therapy practice and encourages collaborative research between medical imaging sciences and radiation oncology.
SU‐GG‐J‐155: Impact of Deformable‐Registration‐Based Contour Propagation on PET Based Treatment Response Assessment
Authors: Yip S , Vanderhoek M , Jeraj R
Published: August 2010

Purpose: Contour propagation reduces effects of physician variability as well as the workload associated with manual contouring. However, its effect on PET based treatment response assessment is unknown. We compared the effects of manual contouring and deformable‐registration‐based contour propagation on treatment response assessment. Method and Materials: Ten adult patients with various tumors underwent one pre‐treatment and two follow‐up whole body PET/CT scans [18F]FLT, a cellular proliferation marker. Most tumors were in proximity of highly deformable tissues, such as abdomen and lung. Manual contours of tumors were drawn on PET images by a nuclear medicine physician. Pre‐treatment contours were chosen as the reference. Pre‐treatment CT was deformably registered to follow‐up CT using the fast‐free‐form deformable registration. Deformation fields resulting from the registration were used to propagate the reference to follow‐up contours. A Matching index () was used to quantify the overlapped volume of manual and propagated contours. Treatment responses using manual and propagated contours were then evaluated by calculating the relative change of SUVmean (ΔSUVmean) and SUVmax (ΔSUVmax) between pre‐treatment and follow‐up scans. Results: The average matching index was 35% and ranged from 5% to 70%. This mismatch led to differences in treatment response assessment between manual contouring and contour propagation. The average difference in ΔSUVmean was 15% and ranged from 5% to 35%. While ΔSUVmax had similar average difference and range, treatment responses using ΔSUVmax of four patients were found to be insensitive to contouring methods. However, differences in ΔSUVmean always occurred. Conclusion: The study showed that the treatment response was quite sensitive to different contouring methods. Fast‐free‐form deformable registration of tumor anatomy was insufficient to capture the change of tumor. Assistance of manual contour adjustment or other deformable registration is needed to fully capture the organ deformation on highly deformable tissues.
SU‐GG‐J‐156: Optimizing a 3‐Stage Compton Camera for Imaging Prompt Gammas during Proton Irradiation
Authors: Peterson S , Robertson D , Polf J
Published: August 2010

Purpose: Due to the intrinsic range uncertainties in proton therapy and its potential impact on the dose delivery, secondary prompt gamma ray emitted during proton treatment delivery is being explored as a dose verification tool. In this work, we investigate the use of a 3‐stage Compton camera to measure secondary prompt gamma emission. The purpose of this study was: (1) to develop an optimal 3‐stage Compton camera specifically designed to measure prompt gamma rays from tissue and (2) to determine the feasibility of using this 3‐stage Compton camera to measure and image prompt gammas emitted from irradiated tissues during proton beam irradiation. Method and Materials: The 3‐stage Compton camera was modeled in Geant4 as three high‐purity germanium detectors arranged in parallel‐plane geometry. Initially, an isotropic gamma source ranging from 0.1 to 15 MeV was used to determine the detector dimensions (width and thickness) that provided the optimal detection efficiency. Then, the gamma source was replaced by a proton beam irradiating a tissue phantom to calculate the overall efficiency of the optimized camera during proton beam irradiation. Results: Using the isotropic gamma source, the optimal dimensions chosen for the 3‐stage Compton camera were 3 cm thick by 10 cm wide for the first detector, 3 cm thick by 10 cm wide for the second, and 10 cm thick by 10 cm wide for the third. The overall efficiency of the 3‐stage Compton camera varied from 2.4 to 10.5 × 10−6 prompt gammas detected per starting proton over the range of proton energies. Conclusion: Based on the overall efficiency results and the typical number of protons emitted during a treatment (about 1 × 1011 protons), the 3‐stage Compton camera should detect a sufficient number of prompt gammas to allow for image reconstruction of the dose deposition within the tissue phantom.
SU‐GG‐J‐157: Evaluation of Volumetric Losses during Radiation Therapy Using Image Guidance of Electronic Portal Imaging Device
Authors: Senick S , Chang Z
Published: August 2010

Purpose: Changes in patient volume, due to tumor shrinkage, dehydration, dysphagia and atrophy, could present issues in the accuracy of dosimetry throughout the course of treatment. The aim of this work is to study the dosimetric impacts of the volumetric changes during IMRT and to investigate the feasibilities of electronic portal imaging device (EPID) in predicting the impacts. Materials and Methods: An anthropomorphic head and neck phantom was used to represent two scenarios: symmetric and asymmetric volume loss. The phantom was simulated and planned according to the head and neck protocols used in our clinic. Dose volume histograms (DVH) were generated for each set up scenario, comparing the dose expected at the coincident volume of the phantom. During treatment delivery, the EPID captured exit fluence of each beam at each level of bolus thickness. These images were quantitatively analyzed using gamma analysis with criteria of 3% and 3mm dose difference and distance‐to‐agreement respectively. Results: Comparing maximum to minimum volume in the symmetric situation with DVH generated in Eclipse show fluctuations in dose. Maximum dose to the planning target volume (PTV) increased by 9.3%. In addition, increases to organs at risk ranged from ∼4% to 7.3%. The asymmetric volume change predicted dose fluctuations that were less significant with the largest dose increase < 4% in the PTV. As for gamma analysis, a quantitative evaluation showed extreme variability in the images with five layers of bolus when compared to images with no bolus. Less significant variation was shown in layers of closer thicknesses, as expected. Conclusions: The phantom study indicates that volume loss could contribute to clinically considerable changes in the dose delivered to target and organs at risk. The proposed technique using EPID could provide valuable information about the variation of dose due to volumetric changes and might be potentially useful.
SU‐GG‐J‐161: Dosimetric Variations Due to the Photon Beam Energy in Monte Carlo Dose Calculation Using Sub‐Millimeter Voxels
Authors: Chow J
Published: August 2010

Purpose: This study investigates dosimetric variations in Monte Carlo calculation using sub‐millimeter voxels due to the photon beam energy and presence of inhomogeneity. The bone dose enhancement due to the photoelectric effect for the kilovoltage (kV) photon beams was evaluated using Monte Carlo simulation. Methods and Materials: Three Monte Carlo phantoms namely, inhomogeneous, homogeneous and bone homogeneous using the same mouse CT image set were used. These phantoms were generated by overriding the relative electron density of no voxel (inhomogeneous), all voxel (homogeneous) and the bone voxel (bone homogeneous) to one. The 360 deg photon arcs with beam energies of 50, 100, 150, 200, 250, 300 and 1250 keV were used in the dose calculations. Doses in the above phantoms were calculated using the EGSnrc‐based DOSXYZnrc code through DOSCTP. Results: For the inhomogeneous mouse phantom, increasing the photon beam energy from 50 keV to 1250 keV increased seven times the dose deposited at the isocenter based on the same number of history in Monte Carlo simulations. For the bone dose enhancement, the mean dose was 2.7 times higher when the bone inhomogeneity was not neglected using the 50 keV photon beams. However, the effect of the presence of the lung inhomogeneity on the variation of the mean dose was only within ±5% for the photon beams with energies in the range of 50 – 1250 keV. Conclusions: Bone dose enhancement affecting the mean dose in the mouse irradiation can be found in the photon beams with energy range of 50 – 200 keV, and the dose enhancement decreases with an increase of the beam energy. When keV photon beam is used in the dose calculation, the increase of the mean dose due to the bone dose enhancement may be a dosimetric concern.
SU‐GG‐T‐157: Accurate Modeling of Calypso KVue Couch for Pinnacle SmartArc Based Elekta VMAT Prostate Treatments
Authors: Wu C , Tunnicliff C , Asche D
Published: August 2010

Purpose: To accurately model the attenuation effect of Calypso kVue couch insert for Pinnacle SmartArc based Elekta VMAT treatments Method and Materials: A Calypso kVue couch insert set was provided by the manufacturer. The set includes a Calypso kVue couch top and two underneath support rails. On our Philips Brilliance Big Bore CT scanner, the couch set was positioned to duplicate the typical treatment configuration where two support rails were expanded at their widest separation under the couch top. The couch set was CT scanned and DICOM exported to Pinnacle 8.0m TPS. In Pinnacle, two regions of interests (ROI) were carefully created — one for the couch top and one for the two support bars. The couch top ROI is assigned with a physical density of 0.16 g/cm3 and the support rails density of 1.17 g/cm3, based on manufacture specification and actual CT numbers. Then the two ROIs were saved as 2D meshes in Pinnacle organ library. In volumetric modulated radiotherapy (VMAT) planning, the above couch model is loaded from the Pinnacle organ library and moved to proper position under patient CT image in order to take the actual couch attenuation effect into consideration. Ion chamber and 2D diode arrays were used to measure and compare with Pinnacle computed point doses to evaluate the accuracy of the couch model. Results and conclusion: This in‐house developed model for Calypso couch insert was proven to work well in our routine VMAT planning and QA practice. The attenuation effect of the Calypso couch is found to be around 1% for prostate PTV mean dose for typical prostate VMAT cases.
SU‐GG‐T‐159: Beam Angle Optimization for IMRT Plans
Authors: Nguyen TB , Nguyen VH , Fong W
Published: August 2010

Purpose: Selecting good beam orientations is an important step in the IMRT planning process that is usually completed by the planner based on their experience. In this study, we proposed a method for determining the minimum number of beams needed and the beam orientation for IMRT plans. Materials and Methods: The beam angle selection begins with a search of the best “one‐beam” plan. For this purpose, 36 single‐beam plans with the beam gantry angle from 0° to 350° every 10° degrees were optimized using Prowess Panther TPS. The two beam orientations with lowest dose to OARs and satisfying the plan constraints are selected. The next step, which applies for the remainder of selected beam orientations applies a different criterion ‐ a beam orientation is selected if it maximizes the conformality index while keeping the OARs does within tolerance. For example, for the third beam orientation, thirty‐four “three beam” plans in which two fixed beams are from previous step and third beam's gantry varying from 0° to 350° and not at the same beam angles previously selected was optimized. This step was repeated for next beam until the plan achieved a reasonable conformity. Results: It takes about 2h to running beam angle optimization. For the selected brain case, it has been shown that our selected 5 beam plan results in a better target conformity, 0.81 compared to 0.76, with similar OARs doses compared to 7 equispaced beam plans. Both of these plans satisfy dose constraints for OARs. Conclusions: We concluded that using fewer, well placed beams than equispaced beam has capacity of achieving as good plans in term of conformity and dose to OARs. This will enable a fully automatic IMRT planning process without going through a time consuming trial and error beam selection process.
SU‐GG‐T‐160: Multi‐Objective Optimization of Beam Orientation and Apertures in Intensity Modulated Radiation Therapy (IMRT)
Authors: Cao R , Pei X , Wu Y
Published: August 2010

Purpose: The intensity modulated radiation therapy requires to determinate the beam orientation and its apertures (the leave positions of the multi‐leaf collimator (MLC)). Inverse planning optimization is a multi‐objective optimization problem whose solution is known as Pareto solution set. According to the multi‐objective character of inverse planning in IMRT, the multi‐objective optimization of beam orientation and its apertures based on Pareto solution set was studied. Method and Materials: The clinical requirements for a treatment plan were transformed into a multi‐objective optimization problem with multiple constraints, in which the parameters are beam orientation and its apertures. And then the fast and elitist multi‐objective Non‐dominated Sorting Genetic Algorithm (NSGA‐II) was introduced to optimize the problem. For each region of interest ‐ target volume or organ at risk, this study used a “physical” objective function in which the dose delivered to each region in the patient's body was compared directly with a dose distribution prescribed by the physician, or a dose‐volume (DV) constraint which typically require that no more than/no less than a specified fraction of volume of a given region receives a dose of higher/Lower than a certain specified level. The aim of NSGA‐II based optimization algorithm was to provide a representative set of non‐dominated solutions for problems where many conflicting objectives and many constraints need to be considered simultaneously instead of a single solution. Results: A clinical example was tested with this method. The results showed that a set of non‐dominated solutions that were obtained distributed uniformly, and the corresponding dose distribution of each solution not only approached to the expected dose distribution but also met the dose‐volume constraints. Conclusions: It was indicated that the clinical requirements were better satisfied by the method and planner could select the optimal treatment plan from the non‐dominated solution set.
SU‐GG‐T‐163: Implications of 120‐MLC Plans Treated on an 80‐MLC Linear Accelerator
Authors: Esquivel C , Wang X , Calvo O , Stathakis S , Corona I , Mihailidis D , Papanikolaou N
Published: August 2010

Methods and Materials: This study reviews nine head‐and‐neck IMRT plans created on Pinnacle3 Treatment Planning System for a Varian 120‐Millenium MLC linac. Using the Varian MLC Shaper application, each field was reconfigured for an 80‐Millenium MLC machine. The reconfigured fields were exported to RadCalc and were replaced with the new MLC configurations before being exported to Pinnacle. Each plan was recalculated to deliver the same dose to the same target volume using the same number of monitor units for the same number of fractions. Isodose distributions and dose volume histograms were compared. In addition, a 2D‐array system was used for absolute dose verification of each plan delivered on the 120‐MLC machine and on the 80‐MLC machine. Isodose distributions, histogram and the gamma fluence were evaluated for each delivery. Results: The MLC Shaper averages two adjacent leaves to form a single leaf which may significantly affect the dose delivery. The isodose distributions and comparative DVHs of the same plan delivered show adequate sparing of normal tissues and other surrounding structures for low isodose regions. However, structures close to or adjacent to the target region may receive higher doses. Both the planning and dose validation confirm that there are larger high‐isodose regions with higher hotspots for the 80‐MLC plan. Conclusion: The results indicated that delivery of a 120‐MLC IMRT head‐and‐neck plan after undergoing MLC shaping can be delivered on an 80‐MLC linac. In cases were a patient is transferred from a 120‐MLC machine to an 80‐MLC linac for a small number of fractions of the total dose regime, there may be insignificant changes in dose distribution. However, investigation of each individual plan must be evaluated, either through the treatment planning system or dose validation for extended treatments.
SU‐GG‐T‐165: Evaluation of the Effect of the Head Holder Base Plate on Head/Neck RapidArc Plans
Authors: Wang L , Veltchev I , Fan J , Jin L , Price R , Ma C‐M
Published: August 2010

Purpose: Unlike conventional IMRT head and neck (H&N) treatment planning, attenuation due to the head‐holder base plate t cannot be accounted for manually in RapidArc planning due to the dynamic arc beams used. While precisely taking into account head‐holder plate attenuation is not trivial in routine clinical practice, it is necessary to evaluate this effect on dose calculation and delivery in order to provide a quantitative basis for clinical decision‐making. Materials & Methods: In order to quantitatively account for the head‐holder attenuation in RapidArc planning, we contoured the entire head holder and included it as part of the patient external structure. This is not trivial for routine treatment planning. RapidArc treatment planning was performed with the head‐holder base plate in place. We then created a verification plan using the original leaf sequence and MUs and the original image set that does not contain the head‐holder plate. We further verified the calculation results with Iba MatriXX phantom measurements, with and without the head‐holder plate. Results: The difference in the dose‐volume‐histogram between the plan with the head‐holder plate and the verification plan without the head‐holder plate is generally within 0.6% for all of the structures. The mean dose to the PTV differed only by ∼0.5%. The difference in the measured dose for the treatment plans with and without the head‐holder plate is also small, up 0.7% in the plateau region. The points of largest gamma show a 2.0% dose difference in the high dose region, while all measurement points pass our 3 mm/3% acceptance criteria. Conclusions: Our calculation and experimental results demonstrate that the dose difference with and without the head‐holder base plate is well within our clinical quality assurance criteria. It is therefore acceptable to omit the head‐holder plate in H&N RapidArc treatment planning for convenience.
SU‐GG‐T‐166: Patient Characteristics That Predict the Need for Breast IMRT
Authors: Harrington C , Lyatskaya Y , Czerminska M , Harris J , Cormack R
Published: August 2010

Purpose: Dose inhomogeneities in RT of the breast have been associated with increased acute and late toxicity. IMRT can reduce dose inhomogeneities, but is associated with increased costs, requires additional department resources and not all patients require IMRT. This work seeks patient variables that predict the need for IMRT to achieve dose homogeneity. Method and Materials: 100 patients were planned with an algorithmic forward planning technique. Subfields were added to initial open fields to reduce dose inhomogeneity. Characteristics, including separation, size, breast volume and maximum open field dose and number of subfields, were recorded. Receiver operator characteristic analysis evaluated the ability of binary classifiers of patient characteristics to predict the number of subfields. Results: Variable values were (median [min‐max]) will be presented. One third of patients required seven or more subfields to achieve the planning method's dose homogeneity goal. No single variable predicted the number of subfields with a zero rate of false positives or false negatives. A composite index, created from separation, size and volume, selected roughly 2/3 of these patients but with only a 5% false positive rate. Conclusion: The majority of tangent breast cases did not require IMRT to attain the desired dosimetric outcome. Neither geometric measures nor composite measures could select all patients requiring a large number of fields without including a greater number of patients that require fewer fields. Dosimetric evaluation of the patient at the time of simulation offers the highest specificity with a sensitivity of 1 for a large number of fields. Dose cutoff of 120% predicts necessity for 8 or more subfields with high specificity and selectivity. Including relatively simple dosimetric calculations in the simulation process may be in the effort to optimize use of department resources.
SU‐GG‐T‐168: Comparison of Target Coverage and Organs at Risk Dose between Simultaneous Integrated Boost Whole Field IMRT and a Junctioned IMRT with Conventional Radiotherapy Field in Treatment of Nasopharyngeal Carcinoma
Authors: Chung J , Lee J , Kim J , Kim I , Choe B , Suh T
Published: August 2010

We have retrospectively investigated 20 nasopharyngeal carcinoma patients treated in our institution between March 2007 and August 2009 was reviewed. We used simultaneous integrated boost whole field intensity modulated radiotherapy to treat the entire planning target volume in the head and neck cancer. For comparison with the jounctioned intensity modulated radiotherapy technique, treatment plans were each replanned using jounctioned intensity modulated radiotherapy technique at 6 MV. The effect on target coverage and sparing of organs at risk, including laryngeal sparing in the optimal whole field intensity modulated radiotherapy plan was compared with that achieved using a jounctioned intensity modulated radiotherapy technique. The mean larynx dose was 25.2 Gy in the whole sis intensity modulated radiotherapy. and 19.8 ar in the jounctioned intensity modulated radiotherapy. With comparison between whole field intensity modulated radiotherapy and jounctioned intensity modulated radiotherapy technique, it demonstrated that larynx dose in the whole field intensity modulated radiotherapy technique was increased to that achieved with jounctioned intensity modulated radiotherapy and conventional anterior neck field. However, if applying strong dose constraint on larynx and using the pseudo volume to enforce a steep dose fall‐off immediately outside the target, the simultaneous integrated boost whole field intensity modulated radiotherapy technique led to larynx dose comparable to that achieved with jounctioned intensity modulated radiotherapy. Therefore, in our current practice we use the simultaneous integrated boost whole field intensity modulated radiotherapy technique which does not have the problem of setup error at match line for treatment of nasopharyngeal carcinoma.
SU‐GG‐T‐169: The Utility of Off‐Cord Arc Beams in RapidArc Planning for Head/Neck Cancers
Authors: Zhang J
Published: August 2010

Purpose To utilize off‐cord arc beams in RapidArc planning for head/neck cancers. Methods and Materials: Five patients with head/neck cancer were planned with RapidArc technique. Three RapidArc plans were generated for each patient, including a “2+1” plan, a “1+2” plan, and a “0+3” plan. The first number indicates the number of off‐cord arcs with the inner x‐jaw closed at 5mm away from the spinal cord. The second number indicates the number of arc beams with open jaws. The three arcs were placed with the same isocenter. Field size and collimator angle were manually set for off‐cord arcs and automatically optimized in Eclipse for open‐jaw arcs. Same dose constraints and priority weights were used for all three plans. No MU constraints were set. The plans were normalized to the same PTV coverage criterion. MU numbers were compared to evaluate the degree of MLC modulation. Dose volume histograms were compared for PTVs and the spinal cord plus a 5 mm margin. Results: With the same optimization setting, the “0+3” plan has the lowest MU number. The “2+1” plan has the highest MU number, 1.3±0.1 times of the “0+3” plan. The “1+2” plan h the second highest MU number, 1.3±0.1 times of the “0+3” plan. With more MLC modulation, the “1+2” and “2+1” plans outperform the “0+3” plan in terms of cord protection and PTV coverage for all five patients. However the “2+1” plan is not guaranteed to be the best even though it has the highest MU number. Conclusions: Utilizing off‐cord arc beams causes higher MU number and more MLC modulation in head/neck planning.
SU‐GG‐T‐170: Evaluation of Tradeoffs between Delivery Efficiency and Clinical Plan Quality Arising from Optimizer and MLC Sequencer Compromises
Authors: Wilkie J , Feng M , Matuszak M , Moran J , Fraass B
Published: August 2010

Purpose: Delivery efficiency is an important consideration for IMRT treatment plans. IMRT planning and MLC sequencing schemes can be modified to generate more efficient treatment delivery, but the effect those modifications have on plan quality is often difficult to determine. In this work, we evaluate tradeoffs between delivery efficiency and clinical plan quality which arise from MLC sequencer‐related compromises. Method and Materials: Treatment plans for a series of prostate and head and neck patients were studied. Optimization was performed for the original plans using an unlimited number of intensity levels. Baseline delivery times were determined with the clinical MLC sequencer, which uses >100 segments, assuring delivered intensities are within 1% of the optimized intensity pattern. To evaluate compromises which MLC sequencers or optimizers make as they limit the number of intensity levels (or segments), each patient's plan was further optimized with successively fewer intensity levels (50, 20, 10, 5). Delivery time was calculated for all plans, and direct evaluation of the tradeoffs between delivery time and plan degradation was performed. Plan degradation was evaluated by a physician using predetermined acceptability tolerances for relevant clinical plan metrics associated with the plan optimization strategy. Results: The range of clinical plan degradation present in the plans depends dramatically on the clinical plan criteria and site: prostate plans were much more easily accomplished with fewer intensity levels (and faster delivery) than more complex head and neck cases. The methodology could be tuned to allow physician and planner to make delivery‐time‐driven compromises with direct quantitative knowledge of the effect on relevant clinical metrics. Conclusion: A quantitative assessment of the tradeoffs in plan quality and delivery time can help make possible the most efficient treatment delivery while maintaining the desired plan metrics with the physician's desired tolerances. This work supported in part by NCI grant P01‐CA59827.