bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐180: A CT‐Based On‐Line Radiotherapy Treatment for Urgent Treatment Delivery
Authors: Held M , Morin O , Pouliot J
Published: July 2013

Purpose: To implement a new CT‐based on‐line radiotherapy treatment workflow (CTORT) to rapidly simulate, plan and deliver emergency radiation treatments (ERTs), while the patients are on the treatment couch. Our specific objective was to treat in under 15 minutes with dose calculation accuracy better than 5%. A key component was to investigate the effect of cone‐beam CT (CBCT) image quality on dose calculation accuracy. Methods: Artificial and clinical megavoltage and kilovoltage CBCT phantom and patient images were used for simulation and dose calculation. Electron density‐to‐Hounsfield unit (HU) calibrations were acquired for the CBCT systems and integrated in the planning system. A specialized treatment planning interface (ERT module ‐ Prowess) was developed to streamline the dose prediction process. Image degradations (noise, reduced contrast, scatter artifact, non‐uniformity, etc.) observed on CBCT images were applied to CT images to quantify the respective reduction in dose calculation accuracy. Dose distribution comparisons provide a direct method to predict achievable dose calculation accuracy of specific clinical sites using MV and kV CBCT images. The complete workflow was tested off‐line on an array of emergency and palliative radiotherapy cases. Results: A MVCBCT specific electron density calibration allows for dose calculation accuracy better than 5% for all cases in presence of heterogeneity. Based on digital phantom analysis, CBCT non‐uniformity is the biggest contributor to reduction in dose calculation accuracy. The complete workflow was tested on simple cases to show simulation, planning and treatment delivery performed within 15 minutes. Conclusion: CBCT image quality is satisfying for simple dose calculation as used for urgent radiotherapy. CTORT presents a workflow of imaging, dose planning, treatment delivery and quality assurance that allows for fast radiotherapy. This approach may reduce patient pain, improve dose planning and delivery accuracy and provide new possibilities for simple radiotherapy treatments when CT simulation is not feasible. Siemens OCS; Prowess Inc.
SU‐E‐J‐186: Automated SPECT‐Based Segmentation for Quality Assurance of CT‐Delineated Tumor Volumes for 131I Tositumomab Therapy of Non‐Hodgkins Lymphoma
Authors: Thorwarth R , Dewaraja Y , Wilderman S , Kaminski M , Avram A , Roberson P
Published: July 2013

Purpose: CT segmentation of tumor volumes suffers from many error sources which can impact the calculation of absorbed dose and 4D bio‐effect modeling. Determination of gross tumor volumes from SPECT scans of anti‐CD20 monoclonal antibody uptake was explored as a quality assurance step. Investigated were two count threshold methods (optimal and constant threshold) and one edge detection method. Methods: Patient data were selected from a dataset of refractory non‐Hodgkins lymphoma studies of 131I radioimmunotherapy. The calibration phantom geometry consisted of seven (1 mL to 95 mL) spheres in an elliptical tank. The background activity was 5 mCi with sphere activities adjusted for an approximate 6:1 concentration ratio. Phantom scans were repeated with no background activity. The patient and calibration sphere data were collected on a Siemens Symbia TruePoint SPECT/CT scanner and reconstructed with in‐house OS‐EM software. The optimal threshold technique used a calibration of threshold vs volume. The constant threshold method (40% and 60% thresholds explored) used a calibration of volume correction factor vs volume. The edge detection method used the Canny algorithm to map edges and determine an edge correction factor. Results: Challenges included 1) resolving tumor volume from nearby significant uptake objects (organs, vessels or other tumors) and 2) identifying volume for large tumors with significantly non‐uniform activity. A constant threshold of 60% with background and volume correction performed best. The determined volumes from patient data were 0.70–0.73 (>12mL) or 0.44‐0.69 (<12mL) of the CT‐delineated volumes. The lower than unity values were attributed to non‐sharp activity boundaries. A priori volume estimates were required for object radii less than the scanner resolution (i.e. <12mL). Conclusion: The constant threshold method can be used to check the validity of CT‐delineated tumor volumes. An additional volume correction factor is required to account for non‐sharp tumor edges. Dr M Kaminski receives research support from GlaxoSmithKline and royalties from Bexxar.
SU‐E‐J‐187: Single‐Cell Dosimetric Simulation and Evaluation of Sb‐119 for Use as Auger Emitting Nuclide in Targeted Radiotherapy
Authors: Graves S , Cox B , Weisse N , Hoffman S , Nickles RJ
Published: July 2013

Purpose: Auger electrons have strong potential for targeted radiotherapy applications because of their relatively short ranged dose profile. 119Sb in particular shows promise as a radioisotope for this application because of its electron emissions with energies near 20 keV. A stochastic characterization of 119Sb and comparison to other auger emitting nuclides has been made to demonstrate this advantage. Methods: A Monte Carlo electron transport code has been written in Python to model the dose to a single cell for activity distributions within the cell membrane, cellular cytoplasm, and nuclear cytoplasm. A spherical geometry has been used, where energy is deposited in shells about the cell center. An extrapolated power fit has been used to model low‐energy electron stopping powers under a continual slowing down approximation. S‐values for dose to the nucleus were calculated from simulation results and were compared to previous analytic results (Thisgaard et. al., Med. Phys. 35, 2008). Finally, the results from this code were compared to other auger electron transport Monte Carlo codes for dosimetric verification. Results: For a cell and nucleus of radius 8μm and 6μm respectively, calculated 119Sb S‐values for activity distributions were 4.10E‐4 Gy/(s Bq) in the cell membrane, 5.93E‐4 Gy/(s Bq) in the cytoplasm, and 2.06E‐3 Gy/(s Bq) within the nucleus. These values are within 13% of S‐values calculated analytically. An explanation for this difference is the omission of CK electrons from this simulation. S‐values calculated for 123I compared with other auger electron transport codes typically agree within a 10% margin. Conclusion: Simulated 119Sb dose distributions have been shown to agree with analytic calculations. The ability of Auger electrons to localize dose to a single cell may lead to a significant dose reduction in healthy tissue. With the development of proper production and chelation techniques, 119Sb shows promise as a radiotherapeutic nuclide. This research was supported by the US Department of Energy: DE‐FG02‐12ER41882
SU‐E‐J‐190: 4DCBCT Detection of Lung Compliance Change in Irradiated Rats: A Validation Study
Authors: Ding K , Deng J , Chen Q , Larner J , Wong J , Kazanzides P
Published: July 2013

Purpose: The lung is often included in the radiation field in the treatment of malignant tumors in the thoracic region and is often the dose‐limiting normal tissue. Different interventions, such as fractionation design, lung radioprotector and tumor radiosensitizer drugs are increasingly common in human clinical trials. We propose a 4DCBCT based small animal lung compliance imaging technique on small animal research platform (SARRP) to facilitate testing of the radiation induced lung injuries and the interventions in animal models. Methods: The end of inhale and end of exhale phases of 4DCBCT are first registered. The compliance at each voxel is derived from the regional expansion calculated from tissue volume preserved deformable image registration and the lung pressure monitored from the pressure sensor. Two lab rats were used in this study. One was irradiated with the 60 Gy using 3 × 9 mm cone to the left lower lung and the other served as the control. Compliance maps were acquired with the pressure triggered 4DCBCT on SARRP seven months after radiation. Both the control and the test rat were perfused with normal saline and the whole lung was taken out for post‐fixation overnight. Results: Significant compliance difference is found after seven month of radiation between the irradiated rat left lower lung (0.57±0.08) and the counter part of the right lower lung (0.75±0.06). Significant compliance difference is also found between the irradiated rat left lower lung and the counter part of the control rat (0.79±0.06). The low compliance region was confirmed from the scar as indicated by digital pictures from post‐fixation lung. Conclusion: We proposed a method that uses 4DCBCT based compliance imaging and compared the irradiated animal seven months after radiation with the control animal. Our study validated the compliance measurement by the anatomical change observed from post‐fixation. This study is supported in part by UVa George Amorino Pilot Grant.
SU‐E‐J‐192: A Method For Estimating Delivered Dose To Head‐And‐Neck Cancer Patients Treated With IMRT
Authors: Wolf E , Kumar N , Huth B , Lamba M , Elson H
Published: July 2013

Purpose: To evaluate one method for estimating the delivered dose to H&N IMRT patients through the analysis of weekly CBCT data. Methods: The planning CT (pCT) and weekly kv‐CBCT images were imported into the treatment planning system from the oncology information system. The treatment plan was applied incorporating the shifts resulting from the CBCT and the dose was calculated for each data set. The CT images with dose information were exported to the image fusion and analysis software. Using deformable registration, each weekly CBCT image and accompanying dose was deformed to the pCT. A dose accumulation of the weekly CBCT dose was used to obtain the “delivered” dose to the patient. The “delivered” dose was compared to the “planned” dose through DVH analysis of target volumes and OARs. Data was analyzed for 5 H&N cancer patients treated with IMRT using a simultaneous‐integrated‐boost (SIB) technique. Results: For the PTV70, the D95 decreased by an average of 1.3%. For OARs, the dose to the parotids, spinal cord, brainstem, and larynx were considered. The maximum doses to the spinal cord did not exceed 107% of the planned dose. The mean dose to the brainstem was within 2 Gy of the planned dose and the larynx was within 5 Gy of the planned dose. The mean dose to the parotid (spared) was 25.3 Gy compared with the planned mean dose of 24.3 Gy. Conclusion: When assuming that the weekly CBCT data is representative of daily alignment for this cohort of head‐and‐neck patients, the PTV70 dose agreed within 1.3% and the OAR within 11% of the planned dose.
SU‐E‐J‐195: Comparison of Dose Difference of Heart Based On KV‐CBCT and Planning CT in the Stereotactic Body Radiotherapy (SBRT) of Early Stage Non‐Small Cell Lung Cancer (NSCLC)
Authors: Yin Y , Chen J
Published: July 2013

Purpose: To compare the difference in evaluating the heart irradiation dose based on different heart rang contoured on KV‐CBCT and planning CT images in the stereotactic body radiotherapy (SBRT) of early stage non‐small cell lung cancer (NSCLC). Methods: 15 early non‐small cell lung cancer (NSCLC) patients accepted radiotherapy in our hospital were selected. For every case, KV‐CBCT scan was achieved before every fraction treatment to correct the setup error, and the first 10 serious CBCT images were used to research. Contour the heart rang on CBCT and planning CT images, analyze the volume and dose‐volume indices differences. Results: (1)The heart volume on first CBCT (717±103 cm3) was larger than planning CT (588±90 cm3) with statistical difference (p<0.05). (2) The relative dose‐volume indices obtained on CBCT images were larger than planning CT with statistical difference(p<0.05): V10Gy‐R(18.9±11.7%vs17.4±11.8%), V15Gy‐R(14.4±10.2%vs 2.8±10.4%), V20Gy‐R(10.5±9.0%vs9.0±8.9%), V25Gy‐R(6.6±2.8%vs4.5±2.3%), V30Gy‐R(4.2±2.2%vs2.5±1.6%), V35Gy‐R(3.2±1.8%vs1.7±1.3%), expect for V5Gy‐R(47.7±16.4% vs 49.0±16.0%,P>0.05); (3)The absolute dose‐volume indices obtained on CBCT images were larger than planning CT: V5Gy‐A (333±78.4vs 282±61.7cm3), V10Gy‐A (133±68.6 vs 246±68.4 cm3), V15Gy‐A (102±62.6 vs101±59.0 cm3), V20Gy‐A (74±55.8vs 52.5±46.4 cm3), V25Gy‐A (46±16.9 vs 27±12.0 cm3), V30Gy‐A (30±14.4 vs 15±8.7 cm3), V35Gy‐A (24±12.0 vs 10±7.0 cm3), and all differences were statistical significant (P<0.05). (4) The dose of certain heart volume Dmean, Dmax based on CBCT imageswere larger than CT images and differed statistically significantly: D50cm3(19.9±7.7vs17.1±6.3 Gy), D100cm3 (15.3±6.2vs12.8±5.7Gy), D150cm3 (11.8±5.5 vs 9.2±3.4Gy), D200cm3 (8.2±2.0 vs 6.8±1.5), D250cm3 (6.4±1.7 vs5.2±2.0Gy), Dmean(7.0±2.8vs 6.5±2.4Gy) and Dmax(45.7±13.1vs 45.1±13.5Gy) . Conclusion: The more accurate and objective dose‐volume indices could be obtained applying KV‐CBCT in SBRT of NSCLC.
SU‐E‐J‐197: Tracking Tumor Response Over Treatment Course in IMRT and Proton Patients
Authors: Williamson R , Court L , Zhang L , Liao Z , Mohan R , Chen Y , Balter P
Published: July 2013

Purpose: To assess the changes in tumor mass and volume for NSCLC patients treated with either protons or IMRT. Methods: Analyses were done on the T50 phase from weekly 4DCTs of patients with stage 3 NSCCLC treated on an IRB approved trial comparing IMRT with passively scattered protons. Patients received either 74 GY or 66 Gy in 2 Gy fractions with concurrent chemotherapy. We performed deformable registration to segment the GTV on each CT. The deformable registration process was 1) rigid registration to determine the region of the GTV 2) deformation of the contours from the planning CT 3) thresholding to account for cavities formed inside the GTV. The resultant contours were used to determine volume and mass, as determined from the TPSs CT‐to‐density curve, change over course of treatment. Results: We analyzed 48 patients 30 were treated with IMRT and 18 with protons. The ratio of GTV volume and mass between the final week CT and planning CT were 0.80 ± .21 % and 0.77 ± 0.25% for IMRT and 0.71 ± 0.21% and 0.66 ± 0.24% for protons. Conclusion: We found that tumors shrank 20‐30% when treated with concurrent chemo‐radiotherapy at 2 Gy/fraction. In addition we noted that the remaining tumor, on average, had a lower density at the end of treatment. A difference was noted between protons and IMRT but was not statistically significant. This work was, in part, funded by the National Cancer Institute.
SU‐E‐J‐200: Impact of FDG‐PET/CT Reconstruction Parameters On PET Variability and Treatment Response Assessment
Authors: Rankine L , Bowsher J , Brizel D , Yin F , Das S
Published: July 2013

Purpose: To examine the effect of PET image reconstruction parameters on baseline and early‐treatment FDG‐PET/CT quantitative imaging. Early‐treatment changes in tumor metabolism in primary tumor and nodes can potentially determine if the patient is responding to therapy, but this assessment can change based on the reconstruction parameters. We investigate the effect of the following reconstruction parameters: number of Ordered‐Subset‐Expectation‐Maximization (OSEM) iterations, post‐reconstruction smoothing, and quantitative metrics (SUV‐max, SUV‐mean, SUV‐peak). Methods: 11 patients on an IRB‐approved study underwent 2 baseline PET scans (mean‐separation=11 days) prior to chemoradiotherapy (70Gy,2Gy/fraction). An intra‐treatment PET scan was performed early in the course of therapy (10‐20Gy,mean=14Gy). The images were reconstructed with varying OSEM iterations (1–12) and Gaussian filtering (1–7mm). For each combination of iterations and smoothing, Bland‐Altman analysis was applied to quantitative metrics (SUV‐max, SUV‐mean, SUV‐peak) from the baseline scans to evaluate metabolic variability (repeatability=1.96σ). The number and extent of early treatment changes that were significant, i.e. exceeding repeatability, was assessed. Results: Repeatability improved with increasing smoothing and decreasing iterations from SUV=3.9 (iterations=12,smoothing=1mm) to SUV=2.1 (iterations=1,smoothing=7mm). The average number of cases exceeding repeatability averaged over all metrics (SUV‐max, SUV‐mean, SUV‐peak) and all structures (primary, nodes) improved with increasing smoothing and decreasing iterations from 3.3 cases (ΔSUVgt;repeatability=17%) for iterations=12 and smoothing=1mm to 3.9 cases (ΔSUVgt;repeatability=19%) for iterations=1 and smoothing=5.5mm. Smoothing beyond 5.5mm deteriorated results. Practically, several combinations provided comparable performance (low repeatability,high number/extent of intra‐treatment cases exceeding repeatability): 1 iteration with 1–5.5 mm smoothing, 2 iterations with 2–5.5 mm smoothing, 4 iterations with 4–5.5 mm smoothing. In general, increasing iterations increased the lower limit of filter size required. Conclusion: Images reconstructed for quantitative analysis may benefit from a low number of OSEM iterations (1–2). Some post‐reconstruction smoothing was beneficial, however, oversmoothing for the sake of more qualitatively appealing images may prove detrimental to quantitative response assessment analysis.
SU‐E‐J‐202: Design and Study of In‐House Gantry Couch Anti‐Collision Device for External Bam Radiotherapy Machines
Authors: Senthilkumar S , Karthik S
Published: July 2013

Purpose: The main purpose of this study was to develop a low cost in‐house anti‐collision device for external radiotherapy machines. All radiotherapy machines have moving parts, needs some safety measures to maintain the accuracy and safety of the patients. The moving parts of radiotherapy machines may cause collision between the treatment head and the table, which affects the machine accuracy and sometimes a replacement of affected parts. If a patient interferes, it results in severe injuries. So, every radiotherapy machine should have a safety feature to overcome the problem of collision. Methods: The anti‐collision device consists of an IR(infrared) emitter, an IR receiver, an Acrylic holding device, a magnetic support, computer based micro controller circuits, a threshold selector, an LCD display, an LED light source and an alarming device. This device is fixed in the lower surface of the gantry head. The threshold distance can be varied when adjusting the threshold selector. When the fixed pre threshold limit is exceeded, the LED will glow; at the same time the alarming device produces sound. On hearing the sound the technologist can stop the movement of the machine. If the output device is connected with the RT machine, the device can stop the movement automatically when the fixed pre threshold limit is exceeded. Results : We used this device to monitor the movement during the radiotherapy using phantoms and patients. Our method correctly confirmed clearance between the patient/treatment table and the gantry. This device is easy to handle, inexpensive, alert the radiation technologist as well as it stops the machine movement when the gantry and the couch come nearer to each other. Anti‐collision device improves the performance of the machine and most importantly reduces the chance of collision.
SU‐E‐J‐203: Texture Analysis of 3D and 4D PET/CT Images of Lung Cancer
Authors: Oliver J , Budzevich M , Zhang G , Latifi K , Kuykendall C , Hoffe S , Montilla‐Soler J , Eikman E , Moros E
Published: July 2013

Purpose: Texture/feature analysis of PET/CT images has great potential for predicting/monitoring tumor/normal tissue response to therapy, quantifying tumor spatiotemporal heterogeneity and radiosensitivity, and as indicators for adaptive therapy schemes. The objective of this study was to define a baseline and determine candidate texture/feature parameters. To this end, we performed image analysis on three dimensional (3D) and four dimensional (4D) PET/CT images of non‐small cell lung cancer patients. The ultimate goal is the development of radiomics tools for application in radiotherapy. Methods: All 4D‐PET data were reconstructed in 10 bins using the corresponding phases in 4D‐CT for attenuation correction. Co‐occurrence matrices of the tumor volumes were generated based on 3D and 4D PET images for 8 lung cancer patients. The texture parameters that were extracted from the original images or the co‐occurrence matrices included: entropy, local homogeneity, contrast, energy, V10‐V90, V80, V70, V40, I10‐I90, I30, Coefficient Variation, SD, Mean Intensity, Maximum Intensity, Minimum Intensity, and number of voxels. Texture comparisons between 3D and 4D PET and CT images and between various phases of 4D scans were performed. Results: A weak dependency of all the tested texture parameters on respiration phase was found for the 4D‐PET data for all patients, while large differences in some textures were found between the 3D‐PET or CT and one of the phases of the corresponding 4D data set, with larger percentage differences for the CT images. The differences for PET varied from 25% to 900%. Conclusion: Motion due to breathing altered statistical information obtained from intensity distributions from PET images, consequently 4D‐PET features were significantly different than 3D‐PET features. Texture parameters show minimal dependency on phase. PET images from one of the phases of a 4D‐PET with its corresponding 4D‐CT for attenuation correction are useful for texture analysis.
SU‐E‐J‐204: Experimental Validation of Dose Warping Accuracy From Deformable Image Registration
Authors: Varadhan  , Hui S
Published: July 2013

Purpose: The purpose of this work is to verify accuracy of deformable dose arising from deformable image registration (DIR) algorithms where the mass and density of tissue is conserved. This was done by using custom built deformable phantom mimicking bladder geometry with implanted MOSFETs that can be positioned in multiple locations thereby enabling direct measurement of dose delivered in different deformation states. Methods: The phantom was made using viscoelastic polymer which is nearly tissue equivalent with high tensile strength and elasticity. The phantom was deformed by positioning it with in a compression plate. 5 parallel air canals that run along the organ were used for positioning MOSFET detectors at multiple locations. Dose calculation was performed in undeformed geometry with varying degree of dose gradients. DIR was performed using both B‐Splines algorithm using 3D Slicer and commercial MimVista platform which uses intensity based free form algorithm. The resultant DVF was applied to the original dose distribution and compared with directly measured dose in deformed geometry at multiple locations. For IMRT fields the accuracy of dose warp was also validated by recalculating the original fluence map on the deformed data set and comparing the resultant dose distribution with the deformed dose from DIR. Results: For non IMRT type fields, both B‐Splines and MimVista yielded excellent point dose agreement to directly measured dose (within 2 cGy or 2%). For IMRT fields with large modulation since the inherent uncertainty in MOSFET measurement is 4.6%, agreement was less satisfactory. However comparison between IMRT doses recalculated in the deformed geometry with deformed dose from DIR yielded γ3%/3mm greater than 90%. Conclusion: We have verified that DIR based dose warping can yield accurate results for the algorithms studied. The magnitude of deformation and degree of dose modulation has the greatest impact on accuracy of dose warp.
SU‐E‐J‐209: Dosimetric Benefits of Replanning for IMRT Treatment of Head and Neck Cancer
Authors: Poon E , Shenouda G , Parker W
Published: July 2013

Purpose: To evaluate the dosimetric benefit of replanning during the course of intensity modulated radiotherapy (IMRT) for head‐and‐neck cancer patients. Methods: The study included 30 patients who had at least one replan due to weight loss, tumor growth, swelling, or positioning issues. They were prescribed to receive between 60 and 70 Gy with simultaneous integrated boost using multiple‐field IMRT or volumetric modulated arc therapy. The original plan of each patient was recalculated on the computed tomography (CT) set acquired for replanning. MIM Software (Cleveland, OH) was used to rigidly align the original and the new CT to the same coordinate system, matching the high‐dose clinical target volume (CTV). These recalculations represent the scenario where the treatment continues with a new setup but the same treatment plan is used. Results: Without replanning, the mean near maximum dose (D2%) to the high‐dose CTV was increased by 2.0%. The mean near minimum (D98%) doses to the high, intermediate, and low‐dose CTVs were decreased by 5.1%, 4.0%, and 3.1% respectively. One patient could not meet the brainstem maximum dose (Dmax) constraint of 54 Gy. The mean parotid dose was increased by 1.8%. There was a weak correlation between the parotid dose and the change in parotid volume (correlation coefficient=−0.323, p=0.016). Setup variations between CT simulations caused 46% of the plans to exceed the spinal cord Dmax constraint of 45 Gy, and 22% of the plans to have hot spots exceeding 120% of the prescription dose. The replans were comparable to the original plans in target dose coverage, homogeneity, and critical structure doses. Replanning reduced the mean parotid dose by <0.7%. Conclusion: Replanning is important when the patient setup is notably different than the original simulation. When done in conjunction with image guidance before treatment delivery, it helps to ensure dosimetric objectives can be maintained.
SU‐E‐J‐212: Tracking Dosimetric Changes Due to Lung Patient Physical Changes During Proton Therapy Treatment
Authors: Bennett M , Hoppe B , Li Z , Flampouri S
Published: July 2013

Purpose: It is normal for the bodies of lung cancer patients to change during treatment due to tumor shrinkage, pleural effusion and other treatment related physical changes. The purpose of this study is to determine the differences between the original planned radiation therapy dose and the actual delivered dose given to patients with initially unresectable stage III non‐small cell lung cancer (IRB approved study) and to ensure that protocol dosimetric constraints are not violated. Methods: Target and critical structures are contoured on the original time averaged simulation CT. Patients receive weekly 4DCT scans during the course of treatment. These scans are snapshots of the patients changing bodies. The dose to tumor and anatomical structures actually delivered during that week based on the original plan is determined based on the weekly scan. Approximately 25% of the patients required plan modifications during the course of treatment. MIMvista deformable registration is used to deform the actual dose given each week back to the original planned dose. Dose volume histograms are used to compare the actual dose delivered to the critical structures based on the changing patient body to that given based on the original plan. Results: Results are analyzed for 20 patients, including 5 patients with plan modifications. The mean change for all structures is 1.5% +/− 0.8%, suggesting insignificant dosimetric effects due to the changing patient body. Maximum changes of 6.8% for the contralateral lung dose and upto 9.2Gy for the maximum absolute dose to the spinal cord occurred, but these were still within dosimetric constraint goals. Conclusion: Proton lung patients in our institution are imaged weekly and their treatments are adapted when necessary. All of the patients delivered dose accumulated from the weekly scans using deformable registration did not differ significantly from the planned dose and no critical constraints were violated.
SU‐E‐J‐214: Assessment of Rotational Lung Tumor Motion and Its Influence On Treatment Margins for Stereotactic Body Radiosurgery (SBRT)
Authors: Xu Q , Fan J , LaCouture T , Chen Y
Published: July 2013

Purpose: To quantify rotational motion of lung tumors under radiotherapy based on fiducial imaging. Tumor rotational motion in lung has not been well understood due to difficulties of imaging and target delineation. In this study the rotational motion of fiducial clusters were measured for assessing the treatment margins necessary for adequate dose coverage to CTV. Methods: 25 patients who underwent CyberKnife based SBRT were recruited. Three to five fiducials were implanted in or near the tumor. The reference fiducial locations were determined using a breath‐hold CT. Orthogonal X‐ray image pairs were acquired for modeling and tumor tracking during treatment. These images were used to reconstruct the fiducial locations in 3D. A rigid‐body registration was derived between the measured and reference fiducial locations. The mean distance between the corresponding fiducial pairs was used to evaluate the registration. 2796 pairs of images in 106 fractions of treatment were analyzed. The rotational motion of fiducial clusters was used to simulate the tumor rotational motion for assessing the adequacy of the PTV margins. A margin of 3mm was used to expand the upper lobe (UL) target and 5 mm for lower lobe (LL) target. Additional tracking errors were included in the analysis for tumor coverage under alignment of the rotated CTV with the PTV. Results: The tumor rotational angles in LL and UL were 0.25°±5.7° vs 0.40°±2.1° in roll, — 0.21°±7.3° vs 0.05°±1.8° in pitch, and 0.23°±5.3° vs. 0.1°±2.1° in yaw, respectively. In 94.4% (LL) and 97.1% (UL) of the total imaged tumor locations, the CTV was 100% covered by the corresponding PTV. The mean missing coverage of the CTV for the rest locations were of 4.4% and 1%, respectively. Conclusion: The reported angles were highly correlated to the distance to the diaphragm. Appropriate margins need to be applied for different lobes to ensure CTV coverage.
SU‐E‐J‐217: To Determine the Gross Tumor Volume with CT Scan in End Expiration, Inspiration and All Phases of Respiration in Carcinoma Lung Patients
Authors: Srivastava R , Sharma PK , Sharma P , Munshi A , Chomal M , Laishram S , Saini G
Published: July 2013

Purpose: The aim of this study was to compare the delineation and treatment planning of two phase‐based (the end‐expiration and the endinspiration phases) IGTV (Internal Gross Tumor Volume) with ten‐phase based (4D) IGTV. Methods: Two patients with lung tumors at different sites were selected for the study.The location of the tumor in Patient A was at the upper lobe(attached to the chest wall) of the left lung.In patient B the location was the middle lobe of right lung.We contoured the GTV on each of the ten respiratory phases of the 4D‐CT data set.The combination of these GTVs produced the IGTV .GTV was also generated on the extreme respiratory phases 0% phase = peak inhalation, 50% phase = peak exhalation).The combination of these two GTVs produced IGTV <2Phases>.Treatment planning was done and dose to OARs were compared in both end expiration inspiration(EEI) and 4DCT study set. Results: IGTV <2Phases> (175cc)and IGTV  (180 cc) for Patient A were nearly same. But for Patient B, IGTV <2Phases> (80cc) was smaller than the IGTV  (181 cc).C.I.(Conformity Index) was found better in EEI and 4DCT in Patient A than in Patient B due to the limitation of the AAA algorithm in the low density region.Lung‐GTV doses were less in EEI scan than in 4DCT for Patient B whereas it was the same for EEI and 4DCT in Patient A. Conclusion: The study shows the patients with tumor in upper lobe have no difference in tumor coverage and OARs sparing in the EEI and 4DCT. However,tumors in middle lobe have a greater excursion during respiration and hence greater all phase IGTV.We suggest performing a 4D scan and EEI scan both,for these categories of patients in order to include the tumor excursion due to breathing. Conflict of Interest: Nil; Funding Support: Required if possible
SU‐E‐T‐01: Comparison of Head Scatters in Flattening‐Filter‐Free and Flattened Photon Beams
Authors: Chen Y , Shih R , Afghan M , Gopal A , Chen H
Published: July 2013

Purpose: To decouple and quantify scatter contributions in air and in phantom for flattening‐filter‐free (FFF) photon beams in comparison with those for flattened beams from a medical linac in radiotherapy. Methods: The 7 UF FFF beam on a Siemens Artiste linac shows equivalent depth dose distribution as the 6 MV flat beam. An ionization chamber was used to measure doses along central axis in air (with a 3 cm diameter buildup cap) and in phantom (SSD = 100 cm and depth = 1.5 cm) for both beams in a range of field size, yielding head scatter factors (Sc) and output factors (Scp). A third‐order polynomial function was used to fit the data within the fields of 3×3 to 12×12 cm2 for each Sc or Scp distribution. An extrapolation of the fitted function to 0×0 field yielded the dose component due to primary radiation. Scatter components for different field sizes can be derived by subtracting this primary component from measured total doses. Results: A primary FFF beam produces only 5% scatters in 10× 10 cm2 field through the linac head while 43% scatters are produced by a flat primary beam, resulting in a reduction of scatter contributions by a factor of 6 in the measured doses in air. Comparable scatter contributions (∼10% in 10× 10 field) produced in the phantom at the same depth were observed for both primary beams as expected. Overall, the significantly reduced head scatter for the FFF beam leads to a total scatter reduction of 60% in phantom at 1.5 cm depth (14% and 34% scatter contributions in 10× 10 field for the FFF and flat beams, respectively). Conclusion: Our method works well in decoupling scatter components from measured total doses. The significant reduction of head scatters for FFF beams would provide dosimetric benefits to patients with reduced shallow‐dose. This work is supported in part by a Siemens research fund.
SU‐E‐T‐03: A Comparison of HDR Near Source Dosimetry Using a Treatment Planning System, Monte Carlo Simulation, and Radiochromic Film
Authors: Amoush A , Luckstead M , Lamba M , Elson H
Published: July 2013

Purpose: This study aimed to investigate the high dose rate (HDR) 192Ir brachytherapy, including near source dosimetry, of a catheter‐based applicator from 0.5 mm to 1 cm along the transverse axis. Methods: Radiochromic film and Monte Carlo (MC) simulation were used to generate absolute dose for the catheter‐based applicator. Results from radiochromic film and MC simulation were compared directly to the treatment planning system (TPS) based on the AAPM Updated Task Group 43 (TG‐43U1) dose calculation formalism. Results: Difference between dose measured using radiochromic film along the transverse plane at 0.5 mm from the surface and the predicted dose by the TPS was 24%±13%. Dose difference between the MC simulation along the transverse plane at 0.5 mm from the surface and the predicted dose by the TPS was 22.1%±3%. For distances from 1.5 mm to 1 cm from the surface, radiochromic film and MC simulation agreed with TPS within an uncertainty of 3%. Conclusion: The TPS under‐predicts the dose at the surface of the applicator, i.e., 0.5 mm from the catheter surface, as compared to the measured and MC simulation predicted dose. MC simulation results demonstrated that 15% of this error is due to neglecting the beta particles and discrete electrons emanating from the sources and not considered by the TPS and 7% of the difference was due to the photon alone, potentially due to the differences in MC dose modeling, photon spectrum, scoring techniques, and effect of the presence of the catheter and the air gap. Beyond 1mm from the surface, the TPS dose algorithm agrees with the experimental and MC data within 3%.
SU‐E‐T‐05: The Effect of Leaf Corner Details in Sliding Windows Distributions, Implementation of Corrections in a Commercial Planning System
Authors: Dumont J , Schupp N , Kristupaitis D , Krivosheev O
Published: July 2013

Purpose: The dosimetric effect of leaf tip corner details in sliding window dose distributions has been studied, a solution to account for this corner leakage has been designed and implemented. Methods: The dosimetric effect of leaf tip corner deviations from perfect 90 degree borders between the front face and leaf side, was analyzed for sliding window IMRT beams. The study was carried out using film, EPID and diode arrays on Elekta Linacs fitted with MLCi and MLCi2 MLC models. Although the effect is general and does not depend on a particular MLC model, the magnitude and distribution is dependent on MLC model. The study consisted of simple fields designed to de‐couple the combined effects of the leaf properties (transmission, interleaf leakage, tongue and grove, corner leakage), such that corner leakage could be quantified. An enhancement to the transmission filter of a commercial Monte Carlo treatment planning system (Monaco, Elekta AB) was implemented to account for this effect, allowing the user to model the corner leakage for individual leaf tip corners. Results: The analysis of test beams indicates that corner leakage will introduce additional fluence in sliding window IMRT distributions. Of the two mlc models studied, this effect is more important for MLCi, but is also present for MLCi2. Generally, corner leakage will be present in every mlc in which the corner is not perfectly cut at 90 degrees. In this light, small manufacturing differences give rise to small but visible effects on the dose distribution. Correct modeling of these small effects is increasingly important as users seek improved patient specific QA results, in particular using local gamma. Conclusion: In this work we study the effect of mlc leaf corner leakage in sliding window distributions, presenting a software implementation to model this effect in a Monte Carlo‐based Treatment Planning system. This work was funded by Elekta Inc.
SU‐E‐T‐06: Comparison of Different Commercial MU Verification Software in Terms of Accuracy and Performance
Authors: McKinsey R , Qiu Y , Stathakis S , Esquivel C , Papanikolaou N , Mavroidis P
Published: July 2013

Purpose: All radiation therapy departments have a need for a quick and accurate verification of their treatment plans ranging from conventional, brachytherapy, to IMRT. The aim of this study is to perform an inter‐comparison of different commercially available Monitor Unit (MU) secondary/independent software. Methods: In this study, four independent MU verification software were examined (IMSure, DIAMOND, MuCheck, and Radcalc) as quality assurance tools for RTP systems. An inter‐comparison of the treatment plans of 13 patients was performed using those MU verification software. All the plans were generated using the Pinnacle v9.2 treatment planning system. The treatment techniques include VMAT, MLC‐based step‐and‐shoot IMRT and Conventional Conformal plans for different treatment sites (breast, head and neck, chest, pelvis, abdomen, and brain). The parameters that had to be adjusted after importing the treatment plans into the different software were the average SSD and effective depth. Results: The average percent differences between the MUs provided by the Pinnacle and the RadCalc, ImSure and DIAMOND software were found to be −1.7%, −1.9% and 3.4%, respectively. The variation of the percent differences among the individual patients were 2.9% (−7.2 − 2.5), 3.7% (−7.2 − 3.7) and 7.0% (−9.9 – 16.2) for RadCalc, ImSure and DIAMOND, respectively. Conclusion: Importing the files from the Pinnacle RTP system was equally easy for all the software. It was found that Radcalc was the software that required the minimum changes/interventions when inserting the average SSD and effective depth. However, the Radcalc was the slower among the examined software in computing the MUs of the different beams for the VMAT technique. Overall, the variation of the MU calculations between the examined software was found to be very similar indicating that their ability to be used as quality assurance tools of the calculations provided by the RTP systems is equivalent.
SU‐E‐T‐08: How Much Dose to the Eyelid Is Reduced by the Backscatter Cap of the Eye Shield From Electron Beam Radiation Therapy?
Authors: Bond J , Song H
Published: July 2013

Purpose: The eye shield set (tungsten (W) shells of 2 and 3 mm thick and various diameters) that is manufactured by RPD, Albertville, MN is supplied with aluminum backscatter caps of 0.5 and 1 mm thickness. However, existing backscatter reduction data (Weaver et al 1998, IJROBP, 41.1. pg.233) are not sufficient. This study attempts to quantify eyelid dose vs backscatter cap thickness using MCNP5. Methods: The electron source in MCNP is simplified to be monoenergetic. The simulated PDD is first validated to measured PDD. The eyelid, Al backscatter cap, tungsten shield, and eyeball are stacked along the electron beam direction. Additional cap thickness of 1.5 mm and 2 mm are simulated to increase the thickness range. For comparison, 3 mm thick lead (Pb) shield is simulated. All dose values are normalized to the dose at dmax without the eye shield. Results: Without any Al cap, the eyelid dose is 123%, 123%, 126% for 2 mm W, 3 mm W, and 3 mm Pb shields. With a 1 mm Al cap, the eyelid dose is 112%, 112%, and 114% respectively. With a 2 mm Al cap, the eyelid dose falls to 105% for all three shields. The backscattered photon dose component is <1% for all simulation scenarios so the backscatter dose is dominated by electrons. The transmission through the shield is <0.8%, suggesting the shield thickness can be reduced for 6 MeV electrons. Further study is needed for higher electron energy beams. Conclusion: Of practical guidance value: If 110% or less hot spot is desired for eyelid, the 0.5 mm Al cap is not sufficient for 6 MeV. The 1 mm cap or 1.5 mm (0.5+1 mm) should be considered (while factoring in patient discomfort in using a thick cap).
SU‐E‐T‐11: Quantitative Validation of a New Algorithm TMR10 by Comparison with Clinically Applied TMR Classic Dose Plans Using Gamma Knife Perfexion for Gamma Knife Radiosurgery
Authors: Pokhrel D , Gopalakrishnan M , Lee P , Sathiaseelan V
Published: July 2013

Purpose: To quantitatively validate and clinically implement a new algorithm, TMR10 for the LGK radiosurgery for brain cancer patients.Materials and Methods: Using actual patient MRI images, three individual plans were generated for 4, 8, and 16 mm cones by using TMR Classic. Plans with a single isocenter using same prescription, dose rate, grid size and shot location; were re‐computed using TMR10. Also, fifteen patients datasets that contained multiple isocenters (shots ranged from 1 to 65), who underwent GK radiosurgery using TMR Classic were retrospectively recalculated using TMR10. For these studies, the difference in total treatment time, treated volume under 50% and 90% isodose lines (50%, 90%IDV) were pairwise compared to TMR Classic plans. Also, for single isocenter studies, OAR points are defined 2cm away from the isocenter in three directions and point doses were calculated. Whereas qualitative assessment of 50% and 90%IDL were perform for the patient cases. Results: For the single isocenter studies, the largest difference was for the 8mm cone size in which total treatment time was increased by 3%, whereas 50% and 90%IDV were 8% and 27%, respectively. OAR doses were up to 12% higher when using TMR10. For the patient cases, with TMR10, total treatment time increased by 3.5%, whereas 50% and 90%IDV were 4% and 18%, respectively, in an average and maximum 90%IDV was up to 53%. Visual inspection of 50% and 90%IDL for both algorithms was similar, but, an effective prescription dose was decreased by nearly 3.5% when applying TMR10.Discussion: Dosimetric differences between the two algorithms were the characteristics of the more accurate Monte Carlo estimate of the new beam profiles, depth dose modeling, and output factors used by TMR10. TMR10 showed longer treatment time, higher OAR doses, and larger 50% and 90%IDV, but, 3.5% lower dose than the equivalent TMR classic.
SU‐E‐T‐13: An Evaluation of RadCal Software in Its Monitor Unit Calculation Accuracy for Small Dynamic Fields Using HDMLC
Authors: Morales‐Paliza M , Ding G
Published: July 2013

Purpose: To investigate the accuracy of an independent monitor unit (MU) verification program for small fields used in dynamically modulated highdefinition multileaf‐collimator (HDMLC)‐based stereotatic radiosurgery (SRS). Methods: HDMLC‐SRS patient‐treatment plans were calculated using the BrainLab‐pencil beam dose‐calculation algorithm implemented in the BrainLab‐iPlan treatment planning system (TPS) (v.4.1.2) for the Novalis‐TX 6X‐SRS beam. Percent depth doses, beam profiles and output tables from this clinical beam were utilized to commission the RadCalc software (v.6.2) for independent MU verification. The MU difference between the MU calculation of the treatment planning system and the independent MU verification program for 187 dynamic arcs and 44 intensity modulated beams corresponding to 41 intracranial lesions from 35 patients was calculated. Field sizes of the arcs and beams studied ranged from 15 to 34 mm in their longest extension. Results: The average difference in the MUs with one standard deviation was −0.1% +/− 1.0% for the dynamic arcs and −0.0%+/− 2.7% for the intensity‐modulated beams. The intensity modulated beams verifications showed a much higher spread in the difference compared to the non‐modulated dynamic arcs; however, the average results can be considered clinically acceptable. The MU difference correlated inversely with the lesion size, indicating the limitation of the TPS algorithm with smaller field sizes. Conclusion: Use of the RadCalc software as an independent monitor unit verification system for both modulated and non‐modulated small fields based on high‐definition multileaf collimation is adequate to independently validate the point dose calculation accuracy. The system can be utilized as a part of the SRS quality assurance program.
SU‐E‐T‐14: Validation of Electron Monte Carlo(eMC) Algorithm in Heterogenous Conditions Using Imatrixx 2D Array Chamber Detectors
Authors: Babu A Ananda Giri , Ganesh KM , Prasad B Durga , Murthy K Krishna , Kaviarasu K
Published: July 2013

Purpose: To validate the eMC dose calculation algorithm in eclipse TPS in various heterogeneous conditions using Imatrixx chamber 2D‐array system, by comparing the dose planes. Methods: Clinac‐iX Linear Accelerator with 6,9,12,16 and 20MeV electron energies with 6× 6,10× 10,15× 15 and 20× 20 electron applicators and Eclipse TPS eMC algorithm is used in this study. Dose planes are calculated with different heterogeneous media like SP‐34(solid water) slabs, Gel Bolus, Perspex and airgap placing them on Imatrixx. In TPS, Calculation grid size was kept 0.15 and 3D‐Gaussian smoothing done. All calculations are normalized to 100% and the plans are delivered on Imatrixx heterogeneous setup for measurements. Initially, Imatrixx is calibrated for all electron energies with SP‐34 slabs as per protocol of Omnipro‐IMRT software and it is verified for homogenous medium. For all heterogeneous setup,1cm thickness of heterogeneity in study was kept above the Imatrixx surface and on top to heterogeneity, 1cm SP‐34 slab was kept facing the beam entry. Hence detector array plane was at 2.3cm depth from the surface and all dose plane comparisons are made at this depth. Since 6MeV beam will not contribute higher dose at this depth, setup changed only for 6MeV as 5mm SP34 and 5mm heterogeneous medium and dose plane at 1.3cm depth is studied. Results: For 9 and 12MeV all the applicators and all the heterogeneous media the pass percentage between TPS and measured is above 96% even for 1% & 1mm Gamma Criteria. For 16 and 20MeV, smaller applicators (6× 6 and 10× 10), Perspex gave less pass percentage for 2% & 2mm and others passed well. For 6MeV, near applicator edges fail points were more, hence pass percentage is less. Conclusion: Hence above 9MeV accuracy of eMC is good with all heterogeneities and 6MeV should be evaluated carefully in clinical plans.