bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐P‐40: Dosimetric Characteristics of Field Aperture Margin Design in Stereotactic Body Radiation Therapy (SBRT)
Authors: Zhu J 
Published: June 2015

Purpose:To characterize the dosimetric effects of field aperture margin design in Stereotactic Body Radiation Therapy (SBRT).Methods:Three artificial spherical PTVs, with diameter of 10mm, 20mm and 30mm, were created on CT images of a human body thoracic phantom. Seven non_coplanar isocentric fields were used for treatment planning. For each PTV, treatment plans with margins 0mm, 1mm, 2mm and 3mm were planned. Dosimetric comparison among plans was done considering the following parameters: prescribed isodose line for target coverage, maximum dose, mean dose as well as dose spillages of V80, V50, and V20.Results:Corresponding to aperture margins of 0mm, 1mm,2m and 3mm used in the treatment planning, the percentage of isodose line chosen for dose prescription increases from 65% to 93% for 10mm PTV, 70% to 92% for 20mm PTV, and 75% to 92% for 30mm PTV. The maximum dose decrease accordingly from 155.7% to 109.5% for 10mm PTV, 145% to 111.6% for 20mm PTV, 137% to 112.2% for 30mm PTV. The mean dose decrease from 138.% to 104.4% for 10mm PTV, 122.8% to 106.1% for 20mm PTV, 121.3% to 106% for 30mm PTV. Dose spillages (mm3) increase (V80−2.6 to 4.02, V50−4.55 to 9.3, V20–87.86 to 101.71) for 10 mm PTV, (V80−6.78 to 9.89, V50–13.46 to 20.4, V20‐119.16 to 219.1) for 20 mm PTV, (V80–22.01 to 28.59, V50–41.56 to 52.66, V20‐532.71 to 551.84) for 30 mm PTV.Conclusion:In SBRT treatment planning, tight field aperture margin requires prescribing dose to lower isodose line that leading to higher dose inhomogeneity and higher mean dose to PTV. Loose margin allows prescribing dose to higher isodose line, therefore improves the dose homogeneity. However, it increases dose spillages. Clinician could try different margins according to the PTV size and location of surrounding critical organs to optimize the dose delivered to the patient.
SU‐E‐P‐45: An Analytical Formula for Deriving Mechanical Iso‐Center of Rotational Gantry Treatment Unit Rotational Gantry Treatment Unit
Authors: Ding X , Bues M 
Published: June 2015

Purpose:To present an analytical formula for deriving mechanical isocenter (MIC) of a rotational gantry treatment unit. The input data to the formula is obtained by a custom‐made device. The formula has been implemented and used in an operational proton therapy facility since 2005.Methods:The custom made device consisted of 3 mutually perpendicular dial indicators and 5 clinometers, to obtain displacement data and gantry angle data simultaneously. During measurement, a steel sphere was affixed to the patient couch, and the device was attached to the snout rotating with the gantry. The displacement data and angle data were obtained simultaneously at angular increments of less than 1 degree. The analytical formula took the displacement and angle as input and derived the positions of dial indicator tips (DIT) position in room‐fixed coordinate system. The formula derivation presupposes trigonometry and 3‐dimentional coordinate transformations. Due to the symmetry properties of the defining equations, the DIT position can be solved for analytically without using mathematical approximations. We define the mean of all points in the DIT trajectory as the MIC. The formula was implemented in computer code, which has been employed during acceptance test, commissioning, as well as routine QA practice in an operational proton facility since 2005.Results:It took one minute for the custom‐made device to acquire the measurement data for a full gantry rotation. The DIT trajectory and MIS are instantaneously available after the measurement. The MIC Result agrees well with vendor's Result, which came from a different measurement setup, as well as different data analysis algorithm.Conclusion:An analytical formula for deriving mechanical isocenter was developed and validated. The formula is considered to be absolutely accurate mathematically. Be analyzing measured data of radial displacements as function of gantry angle, the formula calculates the MI position in room coordinate.
SU‐E‐P‐54: Evaluation of the Accuracy and Precision of IGPS‐O X‐Ray Image‐Guided Positioning System by Comparison with On‐Board Imager Cone‐Beam Computed Tomography
Authors: Zhang D , Wang W , Jiang B , Fu D 
Published: June 2015

Purpose:The purpose of this study is to assess the positioning accuracy and precision of IGPS‐O system which is a novel radiographic kilo‐voltage x‐ray image‐guided positioning system developed for clinical IGRT applications.Methods:IGPS‐O x‐ray image‐guided positioning system consists of two oblique sets of radiographic kilo‐voltage x‐ray projecting and imaging devices which were equiped on the ground and ceiling of treatment room. This system can determine the positioning error in the form of three translations and three rotations according to the registration of two X‐ray images acquired online and the planning CT image. An anthropomorphic head phantom and an anthropomorphic thorax phantom were used for this study. The phantom was set up on the treatment table with correct position and various “planned” setup errors. Both IGPS‐O x‐ray image‐guided positioning system and the commercial On‐board Imager Cone‐beam Computed Tomography (OBI CBCT) were used to obtain the setup errors of the phantom. Difference of the Result between the two image‐guided positioning systems were computed and analyzed.Results:The setup errors measured by IGPS‐O x‐ray image‐guided positioning system and the OBI CBCT system showed a general agreement, the means and standard errors of the discrepancies between the two systems in the left‐right, anterior‐posterior, superior‐inferior directions were −0.13±0.09mm, 0.03±0.25mm, 0.04±0.31mm, respectively. The maximum difference was only 0.51mm in all the directions and the angular discrepancy was 0.3±0.5° between the two systems.Conclusion:The spatial and angular discrepancies between IGPS‐O system and OBI CBCT for setup error correction was minimal. There is a general agreement between the two positioning system. IGPS‐O x‐ray image‐guided positioning system can achieve as good accuracy as CBCT and can be used in the clinical IGRT applications.
SU‐E‐I‐16: Scan Length Dependency of the Radial Dose Distribution in a Long Polyethylene Cylinder
Authors: Bakalyar D , Feng W , McKenney S 
Published: June 2015

Purpose:The area‐averaged dose in the central plane of a long cylinder following a CT scan depends upon the radial dose distribution and the length of the scan. The ICRU/TG200 phantom, a polyethylene cylinder 30 cm in diameter and 60 cm long, was the subject of this study. The purpose was to develop an analytic function that could determine the dose for a scan length L at any point in the central plane of this phantom.Methods:Monte Carlo calculations were performed on a simulated ICRU/TG200 phantom under conditions of cylindrically symmetric conditions of irradiation. Thus, the radial dose distribution function must be an even function that accounts for two competing effects: The direct beam makes its weakest contribution at the center while the scatter begins abruptly at the outer radius and grows as the center is approached. The scatter contribution also increases with scan length with the increase approaching its limiting value at the periphery faster than along the central axis. An analytic function was developed that fit the data and possessed these features.Results:Symmetry and continuity dictate a local extremum at the center which is a minimum for the ICRU/TG200 phantom. The relative depth of the minimum decreases as the scan length grows and an absolute maximum can occur between the center and outer edge of the cylinders. As the scan length grows, the relative dip in the center decreases so that for very long scan lengths, the dose profile is relatively flat.Conclusion:An analytic function characterizes the radial and scan length dependency of dose for long cylindrical phantoms. The function can be integrated with the results expressed in closed form. One use for this is to help determine average dose distribution over the central cylinder plane for any scan length.
SU‐E‐J‐138: On the Ion Beam Range and Dose Verification in Hadron Therapy Using Sound Waves
Authors: Fourkal E , Veltchev I , Gayou O , Nahirnyak V 
Published: June 2015

Purpose:Accurate range verification is of great importance to fully exploit the potential benefits of ion beam therapies. Current research efforts on this topic include the use of PET imaging of induced activity, detection of emerging prompt gamma rays or secondary particles. It has also been suggested recently to detect the ultrasound waves emitted through the ion energy absorption process. The energy absorbed in a medium is dissipated as heat, followed by thermal expansion that leads to generation of acoustic waves. By using an array of ultrasound transducers the precise spatial location of the Bragg peak can be obtained. The shape and intensity of the emitted ultrasound pulse depend on several variables including the absorbed energy and the pulse length. The main objective of this work is to understand how the ultrasound wave amplitude and shape depend on the initial ion energy and intensity. This would help guide future experiments in ionoacoustic imaging.Methods:The absorbed energy density for protons and carbon ions of different energy and field sizes were obtained using Fluka Monte Carlo code. Subsequently, the system of coupled equations for temperature and pressure is solved for different ion pulse intensities and lengths to obtain the pressure wave shape, amplitude and spectral distribution.Results:The proposed calculations show that the excited pressure wave amplitude is proportional to the absorbed energy density and for longer ion pulses inversely proportional to the ion pulse duration. It is also shown that the resulting ionoacoustic pressure distribution depends on both ion pulse duration and time between the pulses.Conclusion:The Bragg peak localization using ionoacoustic signal may eventually lead to the development of an alternative imaging method with sub‐millimeter resolution. It may also open a way for in‐vivo dose verification from the measured acoustic signal.
SU‐E‐J‐176: Characterization of Inter‐Fraction Breast Variability and the Implications On Delivered Dose
Authors: Sudhoff M , Lamba M , Kumar N , Ward A , Elson H 
Published: June 2015

Purpose:To systematically characterize inter‐fraction breast variability and determine implications on delivered dose.Methods:Weekly port films were used to characterize breast setup variability. Five evenly spaced representative positions across the contour of each breast were chosen on the electronic port film in reference to graticule, and window and level was set such that the skin surface of the breast was visible. Measurements from the skin surface to treatment field edge were taken on each port film at each position and compared to the planning DRR, quantifying the variability. The systematic measurement technique was repeated for all port films for 20 recently treated breast cancer patients. Measured setup variability for each patient was modeled as a normal distribution. The distribution was randomly sampled from the model and applied as isocentric shifts in the treatment planning computer, representing setup variability for each fraction. Dose was calculated for each shifted fraction and summed to obtain DVHs and BEDs that modeled the dose with daily setup variability. Patients were categorized in to relevant groupings that were chosen to investigate the rigorousness of immobilization types, treatment techniques, and inherent anatomical difficulties. Mean position differences and dosimetric differences were evaluated between planned and delivered doses.Results:The setup variability was found to follow a normal distribution with mean position differences between the DRR and port film between − 8.6–3.5 mm with sigma range of 5.3–9.8 mm. Setup position was not found to be significantly different than zero. The mean seroma or whole breast PTV dosimetric difference, calculated as BED, ranged from a −0.23 to +1.13Gy.Conclusion:A systematic technique to quantify and model setup variability was used to calculate the dose in 20 breast cancer patients including variable setup. No statistically significant PTV or OAR BED differences were found between immobilization, treatment or anatomical differences investigated.
SU‐E‐J‐183: Quantification of Motion During Hypo‐Fractionated Prostate Cancer Radiation Therapy
Authors: Ravindranath B , Zhang P , Xiong J , Mageras G , Hunt M 
Published: June 2015

Purpose:To quantify patient motion during hypo‐fractionated prostate cancer treatment as tracked by Calypso™ 4D localization system.Methods:50 prostate cancer patients with implanted Calypso beacons underwent hypofractionated IMRT treatment. Typical fraction size was 5 with doses of 5–8 Gy/fraction. 213 traces from the 50 patients were analyzed to quantify the probability of motion vs time starting from beam‐on. Couch corrections applied by therapists were undone to obtain the natural course of patient motion. The Calypso data was used to identify vector displacements greater than 2 mm from the starting position. The direction of this vector was classified into one of the 26 directions (combinations of L/R, A/P, S/I). The probability of motion >2mm was estimated by computing the fraction of traces that exceed the 2mm threshold at each time point. The violating motion points were also binned by direction in order to identify specific directions that were more prone to movement.Results:The overall probability of motion greater than 2 mm at 5 and 10 minutes from beam‐on were 27 % and 50% respectively. The primary directions in which motion occurred were Posterior‐Inferior (PI) and Inferior (I) with a probability of 8.5% and 4% at 5 minutes and 10% for both at 10 minutes. Motion was classified into the following bins: 0–2, 2–3, 3–4, 4–5, 5–6, 6–7, 7–8 and greater than 8 mm. It is observed that motion < 2mm decreases from the first 5 minutes to the next while the higher magnitude components increase with time.Conclusion:The probability of prostate motion increases with time. The trend seen in the PI and I directions can be attributed to physiological factors like bladder filling. This probability can be factored in for scheduling intrafraction imaging and used to compare dosimetric impact of VMAT vs. IMRT plans.This work is supported in part by Varian Medical Systems
SU‐E‐J‐184: Volumetric Indices to Aid Definition of Respiratory Gates with Particular Reference to Lung Stereotactic Body Radiotherapy (SBRT)
Authors: Malhotra H , Gomez J 
Published: June 2015

Purpose:Conventional definition of respiratory gates relies on tumor motion determination in limited planes. We are proposing a new method to define the RPM gates in a consistent manner ensuring that the tumor motion is restricted to 4 mm in 3D for lung SBRT patients. The method relies on studying the ratio of volumes obtained by GTVnn intersection with GTV50+2mm margin and GTVnn where GTVnn is the GTV volume in phase nn (=0,10,30.) while GTV50+2mm is a pseudo structure created by adding an isotropic margin of 2mm to GTV50. If for any phase nn, above ratio equals 1, it ensures that the tumor motion is ≤ ±2 mm in 3D from GTV50.Methods:This method was tested for 50 patients (14‐Central, 36‐peripheral) to determine the RPM gates which were then compared with the gates used clinically. The minimum cut‐off value of the above coefficient for its inclusion of a phase in RPM gate was taken as 0.97 for central and 0.95 for peripheral tumors.Results:15 (30%) of the patients did not require any change in the RPM gates w.r.t. gates defined using conventional motion assessment methods. In 15(30%) cases, the RPM gates could have been smaller while in remaining 20 patients, gates could have been larger. 5(/14) patient's central tumors and 10 (/36) peripheral tumors did not need any gate change. 8(/50) patients could have RPM gate change of 30% while 10(/50) could have a gate change of up to 20%. 10, 20 & 30% RPM gate change could have happened for 11, 10 & 9 patients, respectively.Conclusion:Proposed volumetric indices based method allows a consistent, scientific and objective method to decide optimal RPM gates which is free from any inter or intra person variability and satisfies the tumor motion limits as defined by AAPM TG‐76 in totality.
SU‐E‐J‐192: Comparative Effect of Different Respiratory Motion Management Systems
Authors: Nakajima Y , Kadoya N , Kida S , Ito K , Kanai T , Kishi K , Sato K , Dobashi S , Takeda K , Jingu K 
Published: June 2015

Purpose:Irregular breathing can influence the outcome of four‐dimensional computed tomography imaging for causing artifacts. Audio‐visual biofeedback systems associated with patient‐specific guiding waveform are known to reduce respiratory irregularities. In Japan, abdomen and chest motion self‐control devices (Abches), representing simpler visual coaching techniques without guiding waveform are used instead; however, no studies have compared these two systems to date. Here, we evaluate the effectiveness of respiratory coaching to reduce respiratory irregularities by comparing two respiratory management systems.Methods:We collected data from eleven healthy volunteers. Bar and wave models were used as audio‐visual biofeedback systems. Abches consisted of a respiratory indicator indicating the end of each expiration and inspiration motion. Respiratory variations were quantified as root mean squared error (RMSE) of displacement and period of breathing cycles.Results:All coaching techniques improved respiratory variation, compared to free breathing. Displacement RMSEs were 1.43 ± 0.84, 1.22 ± 1.13, 1.21 ± 0.86, and 0.98 ± 0.47 mm for free breathing, Abches, bar model, and wave model, respectively. Free breathing and wave model differed significantly (p < 0.05). Period RMSEs were 0.48 ± 0.42, 0.33 ± 0.31, 0.23 ± 0.18, and 0.17 ± 0.05 s for free breathing, Abches, bar model, and wave model, respectively. Free breathing and all coaching techniques differed significantly (p < 0.05). For variation in both displacement and period, wave model was superior to free breathing, bar model, and Abches. The average reduction in displacement and period RMSE compared with wave model were 27% and 47%, respectively.Conclusion:The efficacy of audio‐visual biofeedback to reduce respiratory irregularity compared with Abches. Our results showed that audio‐visual biofeedback combined with a wave model can potentially provide clinical benefits in respiratory management, although all techniques could reduce respiratory irregularities.
SU‐E‐J‐194: Continuous Patient Surface Monitoring and Motion Analysis During Lung SBRT
Authors: Chung E , Rioux A , Benedict S , Yamamoto T 
Published: June 2015

Purpose:Continuous monitoring of the SBRT lung patient motion during delivery is critical for ensuring adequate target volume margins in stereotactic body radiotherapy (SBRT). This work assesses the deviation of the patient surface motion using a real‐time surface tracking system throughout treatment delivery.Methods:Our SBRT protocol employs abdominal compression to reduce the diaphragm movement to within 1 cm, and this is confirmed daily with fluoroscopy. Most patients are prescribed 3–5 fractions, and on treatment day a repeat motion analysis with fluoroscopy is performed, followed by a kV CBCT is aligned with the original planning CT image for 3D setup confirmation. During this entire process a patient surface data restricted to whole chest or the sternum at the middle of the breathing cycle was captured using AlignRT optical surface tracking system and defined as a reference surface. For 10 patients, the deviation of the patient position from the reference surface was recorded during the SBRT delivery in the anterior‐posterior (AP) direction at 3–6 measurements per second.Results:On average, the patient position deviated from the reference surface more than 4 mm, 3 mm and 2 mm in the AP direction for 0.95%, 3.7% and 11.1% of the total treatment time, respectively. Only one of the 10 patients showed that the maximum deviation of the patient surface during the SBRT delivery was greater than 1 cm. The average deviation of the patient surface from the reference surface during the SBRT delivery was not greater than 1.6 mm for any patient.Conclusion:This investigation indicates that AP motion can be significant even though the frequency is low. Continuous monitoring during SBRT has demonstrated value in monitoring patient motion ensuring that margins selected for SBRT are appropriate, and the use of non‐ionizing and high‐frequency imaging can provide useful indicators of motion during treatment.
SU‐E‐J‐203: Investigation of 1.5T Magnetic Field Dose Effects On Organs of Different Density
Authors: Lee H , Rubinstein A , Ibbott G 
Published: June 2015

Purpose:For the combined 1.5T/6MV MRI‐linac system, the perpendicular magnetic field to the radiation beam results in altered radiation dose distributions. This Monte Carlo study investigates the change in dose at interfaces for common organs neighboring soft tissue.Methods:MCNP6 was used to simulate the effects of a 1.5T magnetic field when irradiating tissues with a 6 MV beam. The geometries used in this study were not necessarily anatomically representative in size in order to directly compare quantitative dose effects for each tissue at the same depths. For this purpose, a 512 cm3 cubic material was positioned at the center of a 2744 cm3 cubic soft tissue material phantom. The following tissue materials and their densities were used in this study: lung (0.296 g/cm3), fat (0.95), spinal cord (1.038), soft tissue (1.04), muscle (1.05), eye (1.076), trabecular bone (1.40), and cortical bone (1.85).Results:The addition of a 1.5T magnetic field caused dose changes of +46.5%, +2.4%, −0.9%, −0.8%, −1.5%, −6.5%, and −8.8% at the entrance interface between soft tissue and lung, fat, spinal cord, muscle, eye, trabecular bone, and cortical bone tissues respectively. Dose changes of −39.4%, −4.1%, −0.8%, −0.8%, +0.5%, +6.7%, and +10.9% were observed at the second interface between the same tissues respectively and soft tissue. On average, the build‐up distance was reduced by 0.6 cm, and a dose increase of 62.7% was observed at the exit interface between soft tissue and air of the entire phantom.Conclusion:The greatest changes in dose were observed at interfaces containing lung and bone tissues. Due to the prevalence and proximity of bony anatomy to soft tissues throughout the human body, these results encourage further examination of these tissues with anatomically representative geometries using multiple beam configurations for safe treatment using the MRI‐linac system.NSF GRFP Grant Award #LH‐102SPS