bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐J‐95: MLC Tracking of Respiration‐Induced Target Motion
Authors: Zhang G , Ha J , Yi B , Nazareth D , Van Liew S , D'Souza W , Jiang Z , Yu C
Published: July 2006

Purpose: Respiration induced target motion is a challenge in achieving both target dose coverage and normal tissue sparing in external radiation therapy. This study is to develop a new technique to dynamically track the moving target when delivering either three‐dimensional (3D) conformal therapy or intensity modulated radiation therapy (IMRT) for whose patients who can reproduce their recorded breathing pattern under audio/video guidance. Method and Materials: 4D‐CT scanning is triggered by respiration signal and CT images are sorted into eight respiration phases. After the physician contours the GTVs of the eight CT data sets, the GTVs' centroid positions are measured and the trajectories in the beam's eye‐view (BEV) can be calculated. A treatment plan can be generated based on a reference phase CT image with the MLC's travel direction set to the target moving direction. The step‐and‐shoot MLC segments of the static plan are converted into dynamic segments based on the motion trajectories in the BEV. During the delivery, the beam is turned on at the reference phase and remains on as long as the dynamic MLC segments are in sync with breathing. Results: Breathing patterns were successfully deduced from 4D CT images and the motion amplitudes were found varying with the patient and tumor position. A sinusoidal motion pattern was used in the segment conversion for verification purpose. Three films were placed on a phantom moving sinusoidally and were irradiated for the static, tracking, and no‐tracking cases, and the film dosimetric study was conducted. As an indication of the dose coverage, Gamma index was measured and found to be 91.1% and 67.9% for the tracking and no‐tracking cases, respectively. Conclusions: The MLC tracking significantly improves the dose coverage. This technique provides a potential to improve dose conformity when considering the target motion induced by respiration.
SU‐FF‐J‐98: Motion Encoded Beamlets for Optimization and Evaluation in Four‐Dimensional (4D) Radiotherapy
Authors: Lu W , Olivera G , Chen Q , Chen M , Pan Y , Schnarr E , Ruchala K
Published: July 2006

Purpose: To develop a simple model that fully utilizes the information of 4DCT and accurately incorporates a priori knowledge of patient motion into plan optimization and evaluation in 4D radiotherapy. Methods and Materials: We model the IMRT optimization as two independent schemes, the beamlet dose calculation scheme and the beamlet weights updating scheme. All motion information is encoded in the beamlet dose calculation scheme. A 4DCT is used to calculate beamlet dose associated with each phase. Deformable registration determines the voxel‐to‐voxel map from the arbitrary phase to the reference phase, which is used to map beamlet dose of the arbitrary phase to the reference phase. A priori knowledge of respiration is modeled as (time‐dependant) probability density function of respiration phases. The motion encoded beamlet (MEB) is the probability‐weighted summation of the deformed beamlet of the arbitrary phase. Dose calculation and plan evaluation is always in the reference phase. Beamlet weights updating scheme is same as static optimization. We studied different optimization and delivery schemes in 4D radiotherapy. These studies include static optimization with various margins, free breathing delivery (FBD), gating deliveries (GD) with uncertainty and breathing synchronized delivery (BSD) with uncertainty. Results: As for the FBD considered, optimization using MEB show superior DVHs with reduced OAR dose than the margin‐based optimization. GD is better than the FBD if proper gating phase is chosen and gating uncertainty is low. BSD is superior to FBD if synchronization is enforced during delivery. On the other hand, FBD shows greater tolerance to delivery uncertainty than GD and BSD method. Conclusions: Motion encoding through probability‐weighted summation of beamlets is a flexible and powerful technique to incorporate arbitrary patient motion into optimization and evaluation. Through MEB, evaluations of different delivery schemes in 4D radiotherapy can be done in the same framework.
SU‐FF‐J‐100: Normal Tissue Dose in Abdomen Under Dynamic Beam Tracking
Authors: Yi B , Feng Y , Yu C
Published: July 2006

Purpose: Dynamic beam tracking has been proposed for moving targets. Since planning systems consider all structures stationary, the tracking delivery is purposely different from the plan. This study evaluated the dosimetric differences in normal tissue between the stationary beam plan and the dynamic beam delivery. Method and Materials: IMRT plans for abdominal cancers were generated without considering organ motion. A margin of 1 cm, rather than the conventional 1.5 to 2cm, was used. The resulting MLC sequences were converted to dynamic sequences to track a hypothetical sinusoidal target motion of ±2cm in superior/inferior direction and ±1.5 cm in anterior/posterior direction. A 4‐second respiration cycle and 400 MU/minute dose rate were also assumed. To assess the worst‐case scenario of normal tissue dose difference, all normal structures including liver, kidneys, small bowel and spinal cord were assumed stationary. Doses recalculated using the dynamic sequences were compared with that of the original IMRT plan. Results: As expected, dynamic beam tracking maintained target dose coverage while substantially reduced doses to surrounding normal structures. The differences in normal tissue dose between the stationary beam plan and the moving beam plan were small. The low‐dose volume was increased while the high‐dose volume was decreased slightly in normal tissue with dynamic beam tracking. No degradation of normal structure sparing was observed although the structures were not moving with the target. Conclusion: Contrary to our intuitions, dynamic beam tracking does not significantly alter the normal tissue dose in the abdomen as compared with optimized plans using stationary beams. Unsynchronized motion between the target and normal structures did not cause higher doses to the normal structures when tracking is focused on the target. MLC sequences of the optimized stationary plans can be used for dynamic beam tracking using a simple conversion into dynamic sequences that follows tumor motion.
SU‐FF‐J‐102: Patient Breathing Motion Synchronized IMAT: A New Technique for Compensating Intra‐Fraction Organ Motions
Authors: Luan S , Wang C , Cao D , Chen D , D'Souza W , Yu C
Published: July 2006

Purpose: To develop an image‐guided radiotherapy technique for compensating intra‐fraction organ motions by taking full advantage of 4‐D CT and motion tracking. Methods and Material: We have developed a new image‐guided radiotherapy technique called patient breathing motion‐synchronized intensity‐modulated arc therapy (IMAT) based on the following observations. (1) If the LINAC gantry rotates x degrees in one breathing cycle during an IMAT arc delivery, then the beam source “sees” the same breathing phase at beam angles spaced x degrees apart. (2) If each breathing cycle is divided into k breathing phases, then we can partition all discrete beam angles used for planning an IMAT treatment into k groups, with each group “seeing” a particular breathing phase. If one can first calculate an intensity map for each group of beam angles using their corresponding snapshot in the 4D CT image set as a gantry‐fixed IMRT plan, then the resulting k groups of intensity maps can be combined and converted into a final set of IMAT treatment arcs. As long as the patient can reproduce his/her own pre‐recorded breathing patterns, the IMAT plan can be delivered and is optimal in 4‐D. (3) To ensure that the patient's breathing is always at the correct breathing phase at the start of the irradiation of each IMAT arc, the beam is not turned on after pressing the “Beam‐On” button until the breathing pattern reaches the predetermined phase through motion tracking. Results: We applied the motion‐synchronized IMAT technique to the dynamic phantom from CIRS Inc., which can simulate patient breathing motions. Our experimental study indicated that this technique can deliver optimal treatments under motions. Conclusion: We have developed a new image‐guided radiotherapy technique called patient breathing motion‐synchronized IMAT. Our prototype study has demonstrated the feasibility and advantage of this novel method that warrants further investigation.
SU‐FF‐J‐104: Performance of the Philips Gemini GXL PET/CT Simulator
Authors: Goulet P , Martel C , Albaret C , Béliveau‐Nadeau D , Blais D , Bouchard H , Michalowski S
Published: July 2006

Purpose: To present results obtained during the acceptance of the Gemini GXL PET/CT Simulator system. Method and Materials: A flat radiotherapy tabletop is permanently installed on our system. CT Simulator acceptance was performed using the TG‐66 Tables II and III as templates. Two 60‐cm long CT Sim phantoms were used. The relative electron density (RED) to HU relationship was measured with the RMI 465 and Catphan 600 phantoms and analysed using the stoichiometric method of Schneider et al. HU uniformity was measured with a 20‐cm water phantom and contrast‐to‐noise (CNR) performance measured with the Catphan. PET performance was measured using the NEMA 2‐2001 standard at the factory before shipment and after installation. Results: Table sag was measured to be +/− 4 mm over a 1200 mm scan range with loads of 0 to 282 lbs. During longitudinal table displacements, a 2–3 mm shift occurs over a 300 mm range and makes it impractical to use the head‐end of the table in some applications. The slice sensitivity profiles for the 0.75 and 1.5 mm nominal slice thickness were measured to be 1.1 and 1.8 mm. From the RMI 465 and Catphan measurements, a RED‐HU relationship applicable to biological tissues at 120 and 140 kVp was developed. HU uniformity for water was measured to be +10 HU to −12 HU for clinical protocols. Image quality is evaluated by quantifying the CNR for a 15 mm object. PET peak true count rate and peak NEC rate performance measured at the factory and at installation are below manufacturer published specifications: (191, 182 vs 203 kcps) and (61, 56 vs 70 kcps). Conclusion: Future work will involve evaluating PET spatial resolution at 20 cm off‐axis positions, quantifying the impact of table load on PET/CT fusion accuracy and developing tools to permit clinical PET/CT simulation.
SU‐FF‐J‐109: Preliminary Study of Deformable Image Registration Using ALE Mesh
Authors: Li J , Zhu T , Finlay J
Published: July 2006

Purpose: It is desirable to preserve mass and topology at every element during deformable image registration. We present some preliminary results using an ALE mesh for deformable image registration of head and neck tumors. Method and Materials: Arbitrary Lagrangian‐Eulerian (ALE) moving mesh is a finite‐element based technique that preserves mass and topology during deformation. The displacement of the moving boundary can propagate to the interior nodes throughout the domain. A smooth mesh deformation can be obtained by solving partial‐differential equations (PDEs) for the mesh displacements. We adopted this technique in deformable image registration. The idea of our image registration, currently contour‐based, is to generate ALE mesh in a reference image, move the external boundary (or surface) to match the boundary in a target image, and track the contours of the interior organs or tumors, which are deformed by the ALE mesh movement. The software COMSOL Multiphysics (Comsol, Inc., MA) was used. Results: The image registration was tested with two‐dimensional images, using structure contours of head and neck tumors. Two sets of CT images and structure contours taken before and after chemotherapy, respectively, were used. The external contour obtained before the chemotherapy was moved to match the external contour obtained after the chemotherapy. Displacement vectors of the domain enclosed by the external contour were derived from the moving mesh, which were then examined with the deformation of gross target volume (GTV) contour. A warped GTV contour was obtained by applying the displacement vectors to the GTV obtained before the chemotherapy. The result showed that the warped GTV nearly agreed with the GTV obtained after the chemotherapy, except a small part. Conclusion: The preliminary study shows promising application of deformed mesh in image registration. Further studies in three dimensions and comparing the agreements between our methods and elastic‐mechanical modeling will be included.
SU‐FF‐J‐113: Real Time Tracking of Respiratory Tumor Motion Based On External Respiratory Output
Authors: Zhang J , Wu Y , Stepaniak C , Liu W , Gore E , Li X
Published: July 2006

Purpose: Inability to effectively predict respiratory motion in real‐time is a major challenge to account for respiratory motion during radiotherapy. This work aims to develop a novel technique for real‐time predicting (tracking) 3D respiratory motion (tumor position and shape change) from external respiratory output (ERO). Method and Material: A non‐invasive technique, based on the framework known as optimal recursive estimation in signal processing, was developed. Given an optimal filtering algorithm, such as the Kalman filter or the particle filter, the solution of motion tracking is converted to developing proper state and observation models. The state model is a probability density characterizing tumor's motion dynamics. Two types of state model, a conventional motion model and a periodic motion model, were investigated. The observation model is a probability density characterizing the relationship between tumor motion and ERO which can be acquired using a pressure sensor (Anzai) or optical markers (RPM/Varian) place at abdomen. We used the ERO as observation and a conditional Gaussian density as the observation model. The 4DCT datasets of a motion phantom and patients were used to validate the technique. Results: The efficacy of our technique was investigated with the phantom and patient data. For each case, state and observation models were constructed by using the “training” 4DCT containing tumor position and shape and corresponding ERO. These models are then applied to “testing data” that contain only ERO to estimate tumor position and shape. Our experimental results showed that the estimated tumor position and shape were consistent with the true position and shape based on the 4DCT acquired with the testing ERO. Conclusion: The present technique is capable of effectively tracking 3D respiratory motion in real time. By changing the state and observation models, the technique can be used for a variety of internal motions and real‐time external outputs.
SU‐FF‐J‐120: Results of a Multi‐Institutional Benchmark Test for Cranial CT/MR Image Registration
Authors: Ulin K , Urie M
Published: July 2006

Purpose: To assess variability in CT/MR image registration results using a benchmark case developed by the Quality Assurance Review Center. The benchmark was developed to credential institutions for participation in Children's Oncology Group Protocol ACNS0221 for treatment of low‐grade glioma. Method and Materials: Two DICOM image sets were provided. The MR scan had a small target in the posterior occipital lobe that was readily visible on two slices. The lesion was not visible on the CT scan, which was obtained with the patient in a BRW head frame. Each institution was asked to register the two scans using whatever software system and method it would ordinarily use for such a case, to outline the target volume on the two MR slices, and to report the coordinates of the center of the target in the CT coordinate system. To establish a common reference point, the coordinates of the center of the largest BRW rod on the most inferior CT slice were to be reported. Acceptability criteria are based on results from the first 17 submissions. The average of all submissions was used to determine the “true” center of the target. Results: Results are reported from 31 submissions representing 26 institutions and 10 software systems. One standard deviation in the position of the center of the target is 1.9 mm. The least variation is in the lateral direction. There was no correlation of deviation with method of registration, i.e. automatic, manual, or match points. Conclusion: When MR and CT scans of the head are registered with currently available software, there is inherent uncertainty. This uncertainty of approximately 2mm should be accounted for when defining the PTVs and the PRVs for organs at risk on registered image sets. This work was supported by NCI‐H Grant 5U10CA02951.
SU‐FF‐J‐122: Systematic Study of Inter‐Fractional Variations for Anatomic Sites From Head to Feet
Authors: Li X , Qi X , Mueller K , Jursinic P , Erickson B , Wang D , Schultz C , Firat S , Wilson J
Published: July 2006

Purpose: Inter‐fractional variations in patient set‐up and anatomic changes are usually site specific. This work aims to systematically study these inter‐fractional variations for anatomic sites from head to feet based on the daily MV CT images collected using helical tomotherapy. Methods and Materials: A total of first 51 patients treated at various anatomic sites using a helical tomotherapy system (Hi‐Art, Tomotherapy Inc.) were analyzed. Daily Tomotherapy MV CT acquired prior to each treatment were used to correct for daily setup error online. A total of 6120 translational shifts and rotational corrections were performed for the 51 patients. The daily serial MV CT and the planning CT were also used to determine inter‐fractional anatomic changes off‐line. The data for three representative patient cases, pancreas, uterus, and soft tissue sarcoma, are presented. Results: Inter‐fractional set up errors in skull, brain, and head and neck are significantly smaller than those in chest, abdomen/pelvic, and extremity. The translational shifts are mostly within 3 mm in skull, brain, and head and neck, while they are within 6 mm for other sites. The inter‐fractional anatomic changes were significant. For example, during the course of treatment, the pancreas moved up to ±20 mm, and volumes of the uterus and sarcoma varied up to 30% and 100%, respectively. Conclusions: The inter‐fractional variations in patient setup and in shapes, sizes and positions of both targets and normal structures can be significant and are site specific. The helical Tomotherapy technology has the capability of quantifying and addressing these variations. The data presented in this work dealing with several anatomic sites may be useful in developing adaptive radiotherapy.
SU‐FF‐J‐123: The Effect of Respiratory Motion On Two Breast Radiotherapy Techniques: A Phantom Study
Authors: Menon G , Pudney D , Smith W , Dunscombe P
Published: July 2006

Purpose: Many centers are looking beyond conventional wedged tangential fields for the treatment of breast cancer by using intensity modulation techniques for improvements in the dose distribution, reduced late tissue toxicity, and improved cosmesis. The improvement in dose uniformity may be mitigated in the presence of respiratory motion. We have compared a forward planned intensity modulated technique with a conventional wedged tangent approach for irradiation of the whole breast. The purpose of this study was to compare these techniques under both static and dynamic conditions to simulate the effect of respiratory motion. Method and Materials: We planned these two techniques (conventional wedged tangents and forward planned intensity modulated) on a stationary beeswax breast phantom containing a cork lung insert, using a CT acquired 3D dataset. Treatments were performed with the phantom stationary, and mounted on a moving platform having a sinusoidal waveform. The resulting dose distributions were measured using radiographic film in the anterior‐posterior (AP) and medial‐lateral (ML) directions. The amplitude of motion and angle of tilt of the breast, representing the relative contributions of the cranio‐caudal (CC) and AP components of breathing motion, were varied. Results: The dose distributions for the conventional and forward planned techniques were not significantly affected by motion in both the CC and ML directions, for 1cm and 2cm amplitude, and tilt angles of 15, 30 or 45 degrees. This can be explained as the majority of dose is delivered through open fields, with only a small modulation component using MLCs for forward planning. Conclusion: This study demonstrates negligible differences in dose distribution with conventional and simple forward‐planned IMRT techniques. The dosimetric benefits of forward planned 3D compensated breast radiotherapy are not adversely affected by respiratory motion.
SU‐FF‐T‐01: A Delivery Transfer Function (DTF) Analysis of Helical Tomotherapy
Authors: Kissick M , Mackie T , Jeraj R
Published: July 2006

Purpose: Explore the delivery resolution (blurring) for any given beamlet for a helical tomotherapy unit. Based on this analysis, then to determine how the optimization procedure can be further improved to account for the source motion blurring inherent to the unique intensity modulation method used. Also, organ motion blurring effects can be evaluated in this context. Method and Materials: We rely upon and expand previous theoretical work of the “Delivery Transfer Function (DTF)” [K. Otto, et al., Med. Phys. 29, 1823 (2002)] to include the unique intensity modulation method of helical tomotherapy. In addition to the collimation of each beamlet, and the Gaussian convolution spreading of the dose that other radiotherapy units have, helical tomotherapy used small arcs of varying lengths to adjust the intensity. The blurring from these arcs are not taken into account in the current Hi‐ART® TomoTherapy device. Results: Near the isocenter, the transverse (to a given beam direction) blurring is small but at larger radii, the source blurring dominates over leaf size. The longitudinal blurring is dominated by the jaw width, and organ motion blurring less than this width will not be noticed. When a large number of angles are averaged together and with the varying intensities of a real sinogram, the average blurring is very close to the leaf width value >∼ 6.5 mm for typical parameters — even well off‐axis where source motion blurring will be larger. Conclusion: The treatment planning which does not include this source motion can be improved by adding a penalty to beamlets that give large blurring at a particular voxel. Organ motion blurring effects may not seem as deleterious in the context. The averaging effects of many beam directions and many leaf intensities reduces the overall transverse blurring to a very low level for typical situations.
SU‐FF‐T‐02: Comparison of the Dosimetric Properties of Standard MOSFET and MicroMOSFET with Home Made Phantom
Authors: Chung J , Lee J , Lee D , Kim Y , Choi K , Oh S , Kim J , Hong S , Suh T
Published: July 2006

Purpose: To evaluate dosimetric properties of a standard MOSFET in comparison with a microMOSFET Method and Materials: We developed the phantoms to perform a calibration and to analyze characteristics of standard MOSFET and microMOSFET. The phantoms are made of polystyrene, which have the shape of semi‐sphere with 10cm diameters and flat slab of 30×30cm2 with 1cm thickness. The slab phantom was used for calibration and characterization measurements such as reproducibility, linearity and dose rate dependence. The semi‐sphere phantom was used for angular and directional dependence on the types of MOSFETs. The measurements were conducted at a depth of 1.5cm under 10×10cm2 fields at 100cm SSD for reproducibility, linearity, and dose rate dependence. For calibration and reproducibility, five standard MOSFETs and microMOSFETs were repeatedly irradiated by 200cGy three times. Dose linearity was evaluated in the range of 10 to 600cGy. The effect of dose rate was also investigated by 200cGy from 100 to 600MU/min. For angular and directional dependence, the measurements were performed between 0° and 90° gantry angles, while MOSFETs were placed at the center of semi‐sphere phantom. The 50cGy was irradiated repeatedly three times under same setup. Results: The average calibration factor was 1.1±0.95 for standard MOSFETs and 1.09±0.50 for microMOSFETs. The response of reproducibility in the two types of MOSFETs was found to be maximum 0.5% variation. In linearity, the results showed good linear response with R2 value of 0.997 and 0.999. The angular and directional dependence was found to be within ±2∼5% and ±7∼8%. Conclusion: Standard MOSFET and microMOSFET were compared by the dosimetric characteristics with the home‐made phantom. For linearity, reproducibility and calibration factor, two types of MOSFETs showed similar results. On the other hand, standard MOSFET and microMOSFET were found to be remarkable difference due to its detection area size in angular and directional dependence.
SU‐FF‐T‐04: 3D Intensity Modulated Proton Therapy with Minimal Beam Number
Authors: Li H , Fox C , Romeijn H , Dempsey J
Published: July 2006

Purpose: We investigate the influence of beam number on the quality of intensity modulated proton therapy (IMPT) treatment planning with 3‐dimension (3D) modulation. Getting a good quality IMPT plan with the least beam number is critical to reduce delivery time. We seek the minimal beam number required to meet the treatment plan criteria. Method and Materials: An IMPT treatment‐planning study was run employing an in‐house treatment planning system that applied a density‐scaled finite proton pencil beam dose model. The dose model ray traced to every voxel in each beamlet with an isotropic 2.5 mm voxel grid (Shannon‐Nyquist limited). A 3D fluence modulation algorithm was employed using 1 × 1 cm2 beamlets with mono‐energetic ranges having 2.5 mm steps between Bragg peaks along the range of the beamlet where it intersects the targets. Plans where run for 23 head and neck cases with 1 to 4 manually placed beams. The beams angles were selected to avoid critical structures if possible. We started with 4 beams then decreased the beam number while manually adjusting the beam angles for each case until we were unable to meet the planning criteria. Plans were compared with 7 beam 6 MV photon IMRT plans. Results: Out of 23 cases: 1 beam was sufficient for 3 cases, 2 beams were sufficient for 12 cases, 3 beams were required for 6 cases, and the 2 most difficult cases needed 4 beams. Plan quality for IMPT and IMRT were comparable with IMPT having less dose to normal tissues. Conclusion: The beam number required for an IMPT plan with 3D modulation can be reduced to a small number by using manual beam angle adjustment. This result indicates that beam angle optimization should be very valuable for IMPT. This work was supported in part by Florida DOH Grant 04‐NIR03.
SU‐FF‐T‐05: A Biological Model‐Based 4‐D Lung IMRT Plan Optimization Algorithm
Authors: Li X , Zhang P , Kutcher G , Yue N , Yang Y , Heron D , Huq M
Published: July 2006

Purpose: To spare the normal lung we developed a novel lung IMRT plan optimization algorithm that incorporates both biological model and respiratory motion. Method and Materials: We implemented a novel IMRT optimization algorithm on an in‐house IMRT planning system that interfaces with an Eclipse® workstation (Varian, Palo Alto, CA). The IMRT objective function is a combination of the normal lung tissue complication probability (NTCP), the equivalent uniform dose (EUD), and a penalty on tumor dose in‐homogeneity. A series of 4‐D CT scans were taken at different breath phases and a deformable registration was applied to trace voxel‐to‐voxel correspondence at each snapshot. The time averaged (4‐D) dose was utilized to calculate the NTCP and EUD in the optimization process. The proposed method was compared with the gated IMRT approach, which allowed a residual respiratory motion of 3mm and used a PTV defined as the union of the tumors at different phases within the gating window. The performance of the two approaches was evaluated via comparison of DVH at the exhale phase of the breathing cycle and quantitative parameters such as V20, V10, and the mean lung dose. Results: Five‐field 6MV IMRT beams were setup to deliver a total dose of 63Gy in 35 fractions. Each plan was renormalized such that the prescribed dose covers 95% of the tumor volume. Comparing with the gated IMRT plan, our proposed method resulted in a reduction of 4.3%, 4.4%, 2.2Gy and 11.2%, in terms of V10, V20, the mean dose and NTCP, respectively. Meanwhile, the EUD obtained by our method was 65.6Gy, slightly higher than 64.5Gy obtained by the gated IMRT approach. Conclusion: Compared with the gated lung IMRT approach, the proposed biological model‐based 4‐D lung IMRT plan optimization algorithm is able to further spare the healthy lung tissue while maintaining relatively homogeneous tumor coverage.
SU‐FF‐T‐06: A Biomedical Patient Data Driven Approach for the Prediction of Tumor
Authors: Klinginsmith J , Mahoui M , Wu H , Wu Y
Published: July 2006

Purpose: IGRT is a recent advancement in the treatment of cancer that presents a great potential to increase the efficiency of treatment of tumor in the lower abdomen and lungs. However, the efficacy of treating tumors with radiation in these locations is often degraded by tumor respiratory motion. Therefore, the characterization and prediction of tumor motion aids in the precision of radiotherapy treatment. We hereby propose a knowledge discovery solution based on the correlation of the patient biomedical data and the tumor motion data for accurate tumor motion characterization and prediction. Method and Materials: For the analysis of biomedical data, we worked through the main steps involved in a typical knowledge discovery analysis. An important phase includes the analysis of a large spectrum of biomedical data falling into several categories such as tumor description data, and patient treatment data in order to select the set of features to be considered for the mining process. We used clustering techniques such as K‐means clustering to group patients based on a selected set of biomedical data attributes. Results: Comprehensive preprocessing of the raw clinical data and several experiments were performed to identify stable patient clustering. The clustering results were graphically represented using the tumor location of patients for further analysis, which clearly demonstrate certain consistency among the grouping of patients based on their biomedical information. We have compared our clustering results with the current tumor location representation based on bronchopulmonary segments. Conclusion: Patient biomedical data is a rich set of information that has the great potential in tumor characterization and predication especially for the treatment of patients with little or no tumor motion data. Combining the biomedical information and tumor motion data to explore the correlation among them will yield more accurate tumor motion predication. Conflict of Interest:
SU‐FF‐T‐07: A Comparison Between Intensity Modulated Arc Therapy (IMAT) and Tomotherapy
Authors: Cao D , Earl M , Holmes T , Shepard D
Published: July 2006

Purpose: Intensity Modulated Arc Therapy (IMAT) has been proposed as an alternative to helical tomotherapy. IMAT can be delivered on a conventional linear accelerator and uses overlapping arcs to deliver a modulated intensity pattern from each beam direction. In this study, IMAT treatment plans were developed for ten patients previously treated with helical tomotherapy. The goal was to determine if IMAT could match the dosimetric capabilities of tomotherapy. Method and Materials: The IMAT planning process begins with an IMRT optimization performed using the Pinnacle3 planning system. In Pinnacle3, beams are placed at 10° increments along each arc path. After the optimization, an arc‐sequencing algorithm is applied to the optimized fluence maps to create a deliverable IMAT plan. The treatment sites in this study included lung, prostate, pancreas, brain, and head‐and‐neck. The IMAT plans were created under the assumption that the dose rate can vary from one beam angle to the next in each IMAT arc. Results: For coplanar delivery, the plan comparisons reveal that IMAT can generally provide equivalent plan quality as compared with tomotherapy. An average of 5 arcs and 692 MUs were used for these cases. In some cases improved critical structure sparing was observed in the IMAT plans at the expense of target dose uniformity. For three cases, noncoplanar IMAT plans were developed. The results demonstrate that for select cases the ability to incorporate noncoplanar arcs serves as a distinct advantage for IMAT. For example, in one case IMAT reduced the brainstem mean dose from 1866 to 606 cGy and the mean dose to the optic nerve from 388 to 95 cGy. Conclusion: When only axial coplaner arcs are used, IMAT plan can achieve as conformal dose distributions as tomotherapy plan. The IMAT plan, however, can provide a much better sparing to critical structures with non‐coplaner arcs.
SU‐FF‐T‐79: Accurate and Efficient Monte Carlo Dose Calculation for Electron Beams
Authors: Sheu R , Chui C , LoSasso T , Lim S , Kirov A
Published: July 2006

Purpose: To develop a Monte Carlo dose calculation engine for electron beams that is feasible for routine clinical treatment planning. Method and Materials: The dose calculation engine consists of a description of the clinical beams and a dose calculation module. A 12‐component multi‐source model was used to characterize the phase‐space of clinical beams. There are 6 components each for electrons and photons, corresponding to the 3 scrapers, x‐jaws, y‐jaws, and the direct component respectively. In addition, we have developed a method to account for the presence of an arbitrary shaped cutout by modifying the last component of the standard beam model. For the dose calculation module, implementation of the Super‐Monte Carlo method accelerates the calculation by using electron and photon tracks pre‐calculated in water to avoid the computationally intensive sampling processes. These tracks are replayed in the patient computer model as defined by CT. To account for inhomogeneities, the step size and scattering angle were adjusted according to the CT voxel values and material indexes. The dose calculation engine was verified by comparing with film measurements in several different geometries. Results: The results agreed with film measurements to within 2–5% percent both in homogeneous and heterogeneous phantoms. Our method is faster than the analog Monte Carlo calculation by a factor of 6 to 10 and is comparable in performance to a commercial system. The modified beam models for arbitrary cutouts can be derived in a few seconds. The disk storage for pre‐calculated tracks is about 5.5 GB and 125 MB for the standard beam models. Conclusion: The developed Monte Carlo calculation engine is accurate and efficient. The disk space and computational time required are well within clinical acceptability. It is a highly promising dose calculation tool for routine clinical applications. This work supported in part by NCI grant P01‐CA59017.
SU‐FF‐T‐80: Acute Skin Toxicity for Woman Receiving Radiation for Breast Cancer in Relation to the Skin Dose
Authors: Li JS , Freedman G , Stathakis S , Anderson P , Ma C‐M
Published: July 2006

Purpose: To investigate the relationship of clinically observed incidence and severity of acute skin toxicity and the skin dose received by the patient after intensity‐modulated radiotherapy (IMRT) or conventional radiotherapy of breast cancer. Method and Materials: The study population consists of 133 women with early stage breast cancer treated with breast‐conserving surgery and radiation therapy. Seventy three patients have been treated using IMRT and the rest 60 were treated using conventional techniques. The dose distributions were calculated retrospectively with the Monte Carlo method for all the patients. Beam phase space was used for dose calculation and the Monte Carlo results were validated by comparing with measurements. The smallest voxel size (0.9×0.9×2.7mm3) converted from patient CT scan is used for Monte Carlo dose calculation. Dose to the skin epidermis which is less than 0.1mm thick can be estimated from the dose of the 0.9mm thick voxel based on the experience established from Monte Carlo simulations in a fine layered water phantom for beams with different incidence angle and ultra thin TLD measurements. Results: There was no desquamation in 42% of IMRT patients while 37% developed dry desquamation and 21% developed moist desquamation. The degree of desquamation was greater for conventional patients compared to IMRT patients — 52% grade 0, 10% grade 1 and 38% grade 2 (p=0.001). The IMRT dose distributions were more uniform compared with conventional treatments; 24% of the breast volume received dose more than 105% of the prescription dose for conventional treatment but only 7% for IMRT. Results show that a strong correlation exists between the area of skin receiving high dose and the severity of acute skin reaction. Conclusion: IMRT is associated with a decrease in severity of acute desquamation compared with conventional radiotherapy. Significant correlation is observed between the acute skin toxicity and the skin dose.
SU‐FF‐T‐83: Algorithm for Optimizing Beam Angles in IMRT Treatment Planning
Authors: Pesola K , Alakuijala J , Helminen H , Siljamäki S
Published: July 2006

Purpose: The goal of beam angle optimization in external radiation therapy treatment planning is to find field directions which shall result in an optimal treatment plan. In this work, a beam angle optimization algorithm to be used in Intensity Modulated Radiation Therapy (IMRT) treatment planning has been developed. Method and Materials: The plan optimality is defined by constraints set on the Dose‐Volume Histogram (DVH) of the target(s) and of the critical organs. The same constraints may be applied both in beam angle and in beam profile (beamlet) optimization. In beam angle optimization, either a co‐planar or a non‐coplanar initial search space may be used. The search space is covered with a preset number of uniformly distributed fields. Thereafter, a few beamlet optimization iterations are calculated in order to produce optimal beam profiles. Each field is then removed from the plan, and the corresponding value of the objective function is calculated. The fields with a low importance value are thereafter removed. The process is continued until the desired number of fields in the plan has been reached. Results: The optimized plans have been compared with equispaced beams, class solution —based plans and manually made plans. Beam angle optimization has been found to decrease the OF value typically to 20–80 % of the original value calculated with reference plans. The improvement has been clearly visible also in the shape of the DVH curves. The algorithm has been designed to execute fast (less than 30 minutes) in order to be applicable in routine use for patient‐specific planning. Conclusion: The new beam angle optimization algorithm has been able to produce IMRT plans with superior quality to class solution or manually made plans. Conflict of Interest: This work has been funded by Varian Medical Systems Inc.
SU‐FF‐T‐87: An Empirical Method for the Determination of Wall Perturbation Factors for Parallel‐Plate Chambers in High Energy Electron Beams
Authors: McEwen M , Williams A , Palmans H
Published: July 2006

Purpose: The National Physical Laboratory operates an absorbed dose calibration service for therapy‐level electron beam ionization chambers. The service is based on a primary standard graphite calorimeter and uses cavity theory to obtain absorbed dose to water calibration coefficients. The dose transfer process requires knowledge of the ratio of perturbation factors in graphite and water phantoms for the NACP reference ionization chamber type used. A value of unity at present is assumed for this perturbation ratio but data published in recent years indicates that this assumption may be in error by as much as 1%. Method and Materials: Using chamber backscatter data an empirical model was developed to calculate the perturbation due to the rear wall, pwall, of a well‐guarded ion chamber in a high‐energy electron beam. The overall uncertainty in this method is estimated to be 0.22%, which is the lowest reported to date. Results: The model reproduces measured data at the 0.1% level or better and indicates that the NACP ion chamber has a non‐zero perturbation factor in electron beams due to backscatter from the rear wall. The effect is small (< 0.5%) at high energies (R50 > 4 cm, E0 > 10 MeV) but becomes large at low energies — up to 1.0% at E0 = 4 MeV (R50 = 1.2 cm). The model indicates that there is a non‐zero correction for the NACP chamber in both a graphite and water phantom and that material adjacent to the air cavity has a significant effect on the measured ionization. Conclusion: These values are consistent with previous measurements and recent Monte Carlo calculations. The model is simple to apply and could be used in the design of ion chambers and also in the estimation of corrections for non‐homogeneous systems, especially in the absence of accurate Monte‐Carlo simulations.
SU‐FF‐T‐91: An IMRT Planning Technique for Head‐And‐Neck Cancers That Utilizes Direct Aperture Optimization
Authors: Earl M , Shepard D , Jiang Z , Houser T , Oh M
Published: July 2006

Purpose: IMRT can play an important role in the irradiation of head and neck tumors traditionally treated by lateral fields matched with an anterior supraclivicular field. However, due to the complex PTV geometry, these IMRT plans result in large numbers of segments leading to inefficient deliveries. We have developed an alternative IMRT planning technique utilizing Direct Aperture Optimization (DAO) to streamline the planning process and provide significant efficiency gains. Method and Materials: The process begins with the placement of traditional 3D conformal fields (laterals and anerior superclavicular). Next, the dose is calculated with this beam arrangement. The 90% isodose line is converted into a PTV with surrounding critical structures (e.g. spinal cord, parotid glands, posterior medial neck region) excluded from the PTV definition. The resulting PTV serves as the target for IMRT planning. For our planning technique, we have used the DAO algorithm in the Prowess Panther planning system. DAO plans generally result in significantly fewer segments as compared with those generated by traditional IMRT planning techniques. This is of critical importance since traditional IMRT plans for these cases have excessively long treatment times. Using DAO allows practical treatment times without sacrificing plan quality. Results: Fifteen patients were planned and treated with this technique. Seven equispaced beams were used in each. The objectives were PTV dose conformity and low dose to any avoidance regions. The spinal cord limit was 40Gy. For the DAO plans, treatment times ranged from 9 to 17 minutes on an Elekta SL20 acclerator. For corresponding plans produced using Pinnacle3, treatment times ranged from 30 to 45 minutes. Conclusions: An IMRT treatment technique for head and neck cancer has been devised. This technique removes field matching and allows the initial 50Gy to be delivered with a single plan. Using DAO provides significant reductions in treatment times.
SU‐FF‐T‐92: An Investigation of the Effect of IMRTwith Large Jaw Defined Back‐Up Fields On the Accuracy of Dose Calculations
Authors: Yu M K , Gladstone DJ
Published: July 2006

Purpose: To investigate the effect of IMRT with large photon‐jaw defined back‐up fields on the accuracy of dose calculations by analyzing the deviation between calculated and measured dose, DV, for 19 IMRT cases with various jaw defined field sizes. Method and Materials: Suppose that Dc is the point dose calculated from a Pinnacle treatment planning system (TPS), and Dm is the dose measured at the same point in IMRT‐QA. The DV is defined as (Dm‐Dc)/Dm. Each IMRT case in this work had two PTVs, PTV1 and PTV2. For every case, the average equivalent field size (AEFS) of jaw defined fields for PTV1 was considerably larger (at least 3.5 cm larger) than that for PTV2 of the same case. The point at which the dose was measured and calculated was the same for PTV1 and PTV2 for each case. We compared the DV for PTV1 with that for PTV2. The beam energy used was 10 or 18‐MV. A 0.3cc ion chamber placed in solid water was used for measurements. Results: The AEFS of jaw defined fields for PTV1 ranged from 12.8 to 16.3 cm, and for PTV2 from 7.2 to 9.9 cm. The DV for PTV1 was from 2.7 to 8.9%, and for PTV2 from −2.1 to 3.3%. For 17 of 19 cases, the DV for PTV1 was much larger than that for PTV2. The average DV for PTV1 and PTV2 were 6.1 and 1.8% respectively. Conclusion: The results indicate that significant deviation between calculated and measured dose could be associated with IMRT using large jaw defined fields. It is possibly because the TPS doesn't fully account for radiation transmission and leakage through MLC and interleaf for large jaw defined fields. We believe that, to increase dose accuracy, MU corrections are necessary for IMRT with large jaw defined fields.
SU‐FF‐T‐93: Analysis of the Impact of Skull Scaling Deviations in Gamma Knife Radiosurgery
Authors: Cernica G , de Boer S , Malhotra H , Podgorsak M
Published: July 2006

Purpose: To investigate the impact of variations in skull scaling measurements in Gamma Knife radiosurgery. Method and Materials: We developed an in‐house planning algorithm able to calculate the boundary of the skull directly from an image set. We imported 11 patient plans and obtained the skull contours from the image set. We then manually replicated GammaPlan's skull scaling interpolation directly into our algorithm, and noted the change in times and isodose line distribution produced by such changes. Results: Dipstick measurements on average deviated from our skull measurements on average 8 mm. Prescription isodose lines were not visibly affected by the differences in skull scaling. Time calculations were affected by skull scaling differences; in multi‐shot plans, shot times differed from 0.6% to 2.9%. Prescription isodose lines did not shift significantly despite significant differences in skull scaling. Differences were similar regardless of lesion location. For single shots, times differed depending on the proximity of the shot to large differences in skull boundary; thus shots placed in the frontal region demonstrated discrepancies of approximately 5%, whereas shots placed superiorly (where the interpolation tends to be successful) and centrally (far from skull boundaries) showed differences of less than 1%. Conclusion: For most lesions, skull scaling will not affect the treatment times by more than 3%. Single shots placed near a defective skull interpolation will be the most strongly affected, with discrepancies in time calculations of 5%. It is important to consider the quality of the skull interpolation surrounding the lesion to be treated, as the quality of the treatment could be impacted.