bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐DD‐A3‐04: Analysis of Prostate Patient Setup Error and Organ Motion Error Using Calypso Setup Shift and Tracking Data
Authors: Su Z , Farukhi Y , Murphy M , Williamson J 
Published: July 2008

Purpose: To evaluate the prostate patient setup and intra‐fraction organ motion error distributions by analyzing initial setup shift and target tracking data obtained from the Calypso system. Method and Materials: The spatial coordinates of the centroid of three implanted markers implanted in the prostates of 13 patients were monitored by our Calypso system with 10Hz sampling frequency. Patients were initially setup to tattoos and then shifted to the Calypso localized locations. Measurements were performed for average 32 fractions of average time about 8 minutes each. For each patient, the systematic setup correction and standard‐deviation (SD) over all fractions was obtained for the left‐right (LR), anterior‐posterior (AP) and superior‐inferior (SI) axes. Systematic setup error was obtained as the SD of the systematic setup errors of all patients. Similarly, the systematic and random components of prostate intra‐fractional motion were obtained from the tracking data. For all patients, correlation coefficients were calculated among the three axes of tracking data; the cumulative probability of total 3D displacement from initial setup was also calculated. Results: The systematic and random components of the initial setup errors for LR, AP and SI axes are 2.4mm, 2.6mm and 3.2mm, respectively and 3.6mm, 2.7mm and 3.3mm. The corresponding systematic and random components of prostate intra‐fractional motion errors are 0.3mm, 0.5mm and 0.6mm, and 0.6mm, 1.1mm and 1.0mm, respectively. The correlation between AP and SI motion was significant. The 3D displacement data indicates that 11 of 13 patients have 94.4% or higher probability of prostate motion within 5mm from the Calypso setup positions. However, one patient showed 28.7% probability of motion beyond 5mm. Conclusion: In our patient population, residual systematic and random error due to intra‐fraction prostate motion is small, once inter‐fraction setup‐organ motion errors have been eliminated by Calypso‐guided online setup.Supported in part by grant P01 CA 116162.
SU‐GG‐I‐31: Comparison of Breast‐Centered and Volume‐Of‐Interest (VOI)‐Centered VOI Cone Beam CT Techniques — Dose and Scatter Considerations with Monte Carlo Simulation
Authors: Chen L , Lai C , Han T , Liu X , Shen Y , Wang T , Shaw C 
Published: July 2008

Purpose: To evaluate and compare dose saving and scatter reduction properties of VOI‐centered and breast‐centered approaches to VOI cone beam CT with Monte Carlo simulation. Method and Materials: To implement the VOI scanning technique, a mask with an opening is inserted between the x‐ray source and the patient to deliver higher exposures inside the VOI and lower exposures outside the VOI during the scan. There are two approaches to implement this technique. One is to center the breast with the rotation axis and move the VOI mask to track the VOI. The other is to center the VOI with the rotation axis, thus keeping the VOI mask fixed during the scan. A cylindrical breast model with a VOI close to the breast boundary was constructed to evaluate and compare the two approaches with Geant4 based Monte Carlo simulation. Dose distribution in the breast and scatter‐to‐primary ratios (SPRs) at the detector input were evaluated and compared to those estimated for full field cone beam CT. Results: Both VOI scanning techniques significantly reduce the radiation doses and scatter intensities both inside and outside the VOI. However, dose saving with the breast‐centered approach was approximately twice as much as that with the VOI‐centered approach both inside and outside the VOI. SPRs inside the VOI were similar for the two approaches and varied little with rotation degree. Conclusion: The breast‐centered scan appears to be the preferred approach to VOI cone beam CT because it resulted in substantially better dose saving while similar scatter reduction as compared to the VOI centered approach. Effort to implement this technique is underway to demonstrate this technique and to validate the simulation results.Acknowledgement: This work was supported in part by grants CA104759 and CA124585 from NIH‐NCI, a grant EB00117 from NIH‐NIBIB, and a subcontract from NIST‐ATP.
SU‐GG‐I‐35: Geometric Accuracy of High Contrast Region Visualization On 4D X‐Ray CT Imaging Using Sinogram Binning
Authors: Rosu M , Weiss E , Wiesmeyer M , Brady A , Williamson J 
Published: July 2008

Purpose: To assess geometric errors in delineating high‐contrast structures from 4DCT‐acquired images undergoing simulated motion of various amplitudes. The broader goal is to formulate margin‐design guidelines that account for imperfections in 4D target imaging for a range of tumor sizes and motion amplitudes. Method and Materials: Three spherical objects with different diameters were placed on a moving platform adjusted to provide sinusoidal, one‐dimensional motions of various excursions (range: 0.5–4 cm) along the longitudinal axis of a Philips Brilliance scanner. Repeated scans were performed for three pitch values (0.15, 0.11, 0.075). Sinogram data were sorted into 10 different breathing phase bins. In addition, time‐averaged and maximum intensity projection (MIP) image sets were reconstructed. Data analysis included qualitative inspection of the shape of scanned objects, comparisons of contoured volumes for the static and moving targets, and centroid motion assessment. Results: The accuracy of reconstructed objects generally improves with decreasing amplitude and pitch. For large excursions and phases intermediate between exhale and inhale, large deviations from the spherical shape are observed; amplitude and volume deviations are as large as 10 mm and 30%. The observed centroid excursion is always less than the actual bin midpoint excursion. Smaller pitch does not always guarantee better results. The MIP centroid lines up closely with the centroid from time‐averaged datasets, but its actual position is underestimated by 3–4 mm as well. There is a tendency for deviations to be larger for datasets reconstructed during inhalation. Conclusion: The accuracy of 4D‐acquired datasets depends on motion characteristics and protocol acquisition parameters. The evaluation of the associated uncertainties is necessary for a more accurate margin design during treatment planning when either one or multiple 4D‐derived datasets are used for treatment planning. More studies are required to investigate the clinical significance of such errors.Supported in part by NIH P01 CA116602.
SU‐GG‐I‐114: Detector Characterization of a New Flat‐Panel Imager: Prospects for Image Quality Improvement in Fluoroscopy and Cone‐Beam CT
Authors: Mail N , Moseley D , Siewerdsen J , Jaffray D 
Published: July 2008

Purpose: To characterize the imaging performance of a new flat‐panel‐imager (FPI) with respect to metrics such as detector gain, linearity, lag, modulation transfer function (MTF), noise‐power spectrum (NPS), and detective quantum efficiency (DQE) and to evaluate its potential application in fluoroscopy and cone‐beam CT for radiation therapy guidance. Method and Materials: The detector examined was a Trixell (Pixium 4343RF) indirect‐ FPI with a 2881×2880 array of 0.143×0.143 mm2 pixels, 43×43 cm2 FOV and a 0.06 mm thick CsI:Tl x‐ray converter. The FPI was operated at a frame rate 3 fps. Gain, linearity and NPS were calculated using gain‐corrected flood images. MTF was measured using an edge‐spread function method. DQE was calculated from the measured MTF and NPS. Image lag was characterized as a function of incident exposure. NPS, MTF, DQE and lag were compared with a FPI design (Perkin Elmer RID1640) currently employed in image‐guided radiotherapy. Results: The dark current stabilizes after 30 minutes. The detector has high gain and linearity with R2∼1. The 50% MTF was achieved at 1.51 and 0.91 lp/mm at 120 kVp for Trixel and Perkin Elmer (PE) FPI, respectively. The spatial resolution was limited by the focal spot size. The NPS(f) is found lower than the PE at 120 kVp for the same pixel saturation. The DQE is calculated 55 and 34% at 1.25 lp/mm for Trixel and PE, respectively. The first frame lag is 7 times lower than Perkin Elmer for the same pixel saturation at 120 kVp. Radiographic images of a head phantom show high contrast and spatial resolution. Conclusion: Imaging performance metrics (in particular, the high linearity, low lag, and high DQE(f)) suggest a significant improvement for the Trixell FPI and strongly support potential application of this detector for fluoroscopy and cone‐beam CT.Research sponsored by Elekta.
SU‐GG‐J‐91: Fast, Low‐Dose Patient Localization On TomoTherapy Via Topogram Registration
Authors: Moore KL , Goddu SM , Chaudhari S , Kintzel EJ , Low DA 
Published: July 2008

Purpose: We present a protocol to efficiently localize patients on TomoTherapy by using a scout imaging (topogram) mode that can be used instead of or in conjunction with 3D MVCT imaging. Method and Materials: To show the feasibility of this method, we scanned anthropomorphic head, thorax, and pelvis phantoms on a kilovoltage CT simulator and subsequently generated digitally reconstructed topograms (DRTs) in the native geometry of the TomoTherapy source/imaging array. The same phantoms were scanned in the imaging mode of the TomoTherapy unit with a moving couch and fixed gantry of 0° and 270°. The raw detector data were read out at the end of these respective “anterior‐posterior” and “right‐lateral” scans, which in turn were compared against DRTs to evaluate the ability of computing shifts and rotations using these images. Results: Using the helical MVCT beam parameters, the time needed to acquire a quality topogram was 12.5 sec for a 50 cm long field. The minimum acquisition time was limited by the maximum couch speed of 4.0 cm/sec. The topogram dose was <1% of that incurred by a MVCT scan. Conclusion: Using topogram images may dramatically reduce the time required to localize the patient for treatment sites that require only bony anatomy imaging. Topograms can be used alternately with MVCT imaging for cases where topograms are useful for positioning, while MVCT is used for monitoring soft tissue response. Where topograms alone can suffice, our protocol boasts a 30‐fold reduction in time and 100‐fold reduction in dose to standard MVCT patient localization.This work is supported by a grant from TomoTherapy, Inc.
SU‐GG‐J‐161: Radiofrequency Interference Between a Linac and MRI
Authors: Carlone M , Burke B , Lamey M , Rathee S , Fallone B 
Published: July 2008

Purpose: Modern radiotherapy relies heavily on 3‐D image based guidance to reduce treatment margins and to conform the dose distribution to the target shape. Due to the poor soft‐tissue contrast and non‐real‐time nature of x‐ray and ultrasound based image guidance, several groups are integrating an MRI and linear accelerator. One of several unresolved technical issues is RF interference between the two devices. The purpose of this presentation is to show that LINAC RF correlates with the operation of certain components of its pulsed power modulator (PPM). Method and Materials: Electric (E) and magnetic (H) field temporal patterns (RF signals) were measured using separate E‐field and H‐field probes on three medical LINAC configurations: klystron and PPM in the same room; klystron and PPM in different rooms; and magnetron and PPM in the same room. Time resolved high voltage power supply (HVPS) current, pulse forming network (PFN) voltage, klystron current and klystron voltage, and magnetron current were all measured coinciding with the RF signals. All measured signals were compared in time and frequency domains.Results: For a klystron powered LINAC, correlation between the HVPS current, and E and H field signals were observed in both the time and frequency domains. No correlation was observed between RF signals and the klystron current pulse. For a magnetron powered LINAC, correlation among HVPS current, magnetron current and RF signals was observed. RF signals coincided in time with the magnetron current, but the frequency spectrum were dissimilar. Conclusion: The results suggest that charging of the PFN by the HVPS current is a mechanism of RF noise generation in the klystron based LINAC operation. For magnetron based PPMs the results further suggest the magnetron current pulse generates RF noise, however dissimilar frequency spectrum indicates an indirect and more complicateds mechanism requiring further investigation.
SU‐GG‐J‐171: Stability and Visibility of a Novel Non‐Migrating Radiographic/radioactive Fiducial Marker: Implications for External Beam Treatment of Prostate Cancer
Authors: Neustadter D , Tune M , Zaretsky A , Shofti R , Kushnir A , Corn B 
Published: July 2008

Purpose: A novel Platinum/Iridium implantable soft tissue marker is being developed for radiographic and/or radioactive target localization to optimize external beam radiation therapy. In this study, non‐radioactive and radioactive versions of the marker were implanted in the prostate of 1 dog and the liver of 19 rabbits to assess marker stability and visibility. Method and Materials: In the canine prostate and each rabbit liver, 3–4 markers were implanted. A total of 34 non‐radioactive markers and 35 radioactive markers were implanted. Stability was assessed by measuring intermarker distance (IMD) variation relative to IMDs measured at the time of implantation. IMDs were measured on a weekly basis for 3 months in the dog and a biweekly basis for 2–4 weeks in the rabbits. Ultrasound and X‐ray imaging were performed on all subjects. CT and MRI were performed on the dog. Results: No differences in marker migration or visibility were found between non‐radioactive and radioactive versions of the marker. A total of 139 IMD variation measurements made in 1 dog and 16 rabbits had a mean absolute variation (+/− SD) of 1.1 +/− 1.1mm. These IMD variations are consistent with those reported in the literature due to random organ deformation. The markers were visible, identifiable, and induced minimal or no image artifacts in all tested imaging modalities. Conclusion: The observed stability of the markers from the time of implantation suggests that these markers may allow the immediate onset of treatment without the 1–2 week post‐implantation stabilization period required with most implanted fiducials. The markers were found to be compatible with all common medical imaging modalities. With respect to marker stability and visibility these implanted fiducials are appropriate for target positioning in the radiation treatment of cancers of the prostate and other mobile organs.Conflict of Interest: Research sponsored by Navotek Medical Ltd.
SU‐GG‐T‐148: Quantification of IMRT Patient Dose Deviations Due to Daily MLC‐Leaf Positional Variations
Authors: Dogan N , Saleh H , Fatyga M , Bartee C , Siebers J 
Published: July 2008

Purpose: To develop a tool utilizing MLC‐log files and Monte Carlo (MC) dose recalculation that will allow cumulative deviations of IMRT patient plans to be assessed over the treatment course by taking into account the possible inaccuracy in the IMRT delivery. Method and Materials: Prostate, head and neck and lung IMRT patients were selected. The delivered MLC positions during the IMRT delivery were recorded in the form of MLC‐log files which were converted to MLC leaf‐sequence files. These files were then transferred back to the TPS and were attached to the original planned IMRT fields to regenerate the delivered dose distribution. Delivered fractional dose to each patient was then re‐produced using MC calculation. The recalculated fractional doses calculated via MC, which utilized the delivered MLC leaf‐sequences, were then combined to produce correct cumulative dose distribution received by the patient during treatment. Both delivered fractional and cumulative dose distributions and corresponding Dose‐Volume statistics were then compared with the ones obtained from the original IMRT plan. Results: For H&N IMRT case, the fractional changes in delivered dose‐volume indices were <1%. The changes in critical structure doses were negligible. For lung IMRT case, the differences in all dose‐volume parameters with MC re‐calculation using the delivered MLC‐sequences and the original planned MC dose calculation were less than 1.1% for PTV and all critical structures, except for the esophagus where differences in D30 were 2.4%. The similar results have been obtained for the prostate case in the study. Conclusion: The utilization of Monte Carlo for the recalculation of actual fractional doses delivered to the patients using the delivered MLC leaf sequence files for each IMRT field provides a powerful tool for offline QA of IMRT patients and can also be utilized for the verification of adaptive radiotherapy.This work supported by NIH grant P01CA11602.
SU‐GG‐T‐176: Helical Tomotherapy Room Shielding: Leakage Radiation Levels and Tenth Value Layer Measurements Around Tomotherapy Machine
Authors: Goddu S , Ramirez J Garcia , Kintzel E , Mutic S , Chaudhari S , Klein E , Rangaraj D , Low D 
Published: July 2008

Purpose: The objectives of this study were to measure the leakage radiation levels surrounding the tomotherapy machine and to determine the tenth value layers (TVL) for concrete. Method and Materials: A custom designed shield was fabricated with Cerrobend to shield a 1000cc spherical ionization‐chamber used in these measurements. Measurements were performed inside the treatment room at the height of the axis of rotation (AOR). Leakage measurements were performed for rotational delivery with the field size of 5×40cm2 and all the MLC leaves were closed. For TVL measurements, concrete slabs of 2.2g/cc were used. Measurements were repeated with full scattering conditions of a 30cm diameter phantom. Results and Discussion: The results indicate that our measured leakage values are 2–4 times lower than the vendor's data. This difference is attributed to the low energy scatter bouncing off the walls. The results also revealed that, for distances >3m, the leakage radiation followed the inverse square relationship within ±10%. Under full scattering conditions radiation levels are approximately 2.5–4 times higher for locations in the front of the gantry. This increase is higher along the AOR. For points that are behind the gantry and away from the AOR, measured phantom scatter component is much lower due to attenuation by the hardware of the machine. TVL measurements for the tomotherapy machine were found to be 21cm for Leakage radiation. These results are in agreement with the published literature2. When the phantom scatter is included in the measurements TVL dropped to 11cm. This is due to higher attenuation for the low energy scatter. Conclusion: Measured leakage levels around the tomotherapy unit were found to be 2–4 times lower than the values reported. The tenth value layer (TVL) for the tomotherapy beam was found to be 21cm of concrete.This work is supported in part by Tomotherapy Inc.
SU‐GG‐T‐303: Evaluation of An Implantable MOSFET Dosimeter for Use with Hypo‐Fractionated External Beam Treatments
Authors: Beyer GP , Kry S , Rini C , Baum E , Mann G , Espenhahn E 
Published: July 2008

Purpose: Evaluate the performance of an implantable MOSFET dosimeter designed for hypo‐fractionated protocols. Method and Materials: The DVS® implantable dosimeter has been developed for use with external beam radiotherapy. A new version is currently under development for use with hypo‐fractionated protocols (DVS‐HFT*). This dosimeter is pre‐calibrated for use at body temperature in a dose per fraction range of 340–1200 cGy. The dosimeter response was evaluated in a water phantom at 37°C to validate the accuracy as a function of dose. Since delivery times for high dose fractions can vary, a study of the response as a function of treatment time was performed. In addition, dose rate dependency for high doses was evaluated. Final dosimeter accuracy was validated by delivering simulated hypo‐fractionated treatments on a body phantom at 37 °C. Two dosimeters each (total six) were irradiated inside the phantom with a breast BID plan at 340 cGy per fraction (10 fx), two prostate IMRT plans at 700 cGy per fraction (5 fx) using 6 MV and 18 MV. Results: The dosimeter had minimum dependency on dose fraction size from 340 to 1200 cGy. Phantom testing found a response accuracy of <6% for 50 dosimeters tested with different doses and fractionation schemes. Dose rate dependence measurements in the range of 300 to 600 MU/min showed <0.6% variability. The dosimeter was found to have a slight dose response fall off as a function of fraction number for irradiation times larger than 1 hour. Simulated clinical treatments on six dosimeters resulted in an overall accuracy of −0.65% (σ=1.9%). Conclusion: Hypo‐fractionated treatments have fewer fractions requiring increased treatment accuracy. Phantom testing suggests that the DVS‐HFT could be used to measure the dose per fraction delivered helping optimize hypo‐fractionated treatments.*Not FDA cleared for use in the USResearch sponsored by Sicel Technologies, Inc.
SU‐GG‐T‐349: Large‐Field Sensitivity Analysis of a Non‐Cylindrically Symmetric Monte Carlo Beam Model of a Varian Electron Accelerator
Authors: Schreiber E , Sawkey D , Faddegon B 
Published: July 2008

Purpose: To facilitate the development and commissioning of radiotherapy electron beam models by studying the dosimetric response of a Varian Trilogy electron accelerator to variations of the geometric and electron beam parameters of the treatment head, including lateral offsets of linac components and lateral and angular offsets of the incident electron beam. Method and Materials: We have performed a sensitivity study examining the effect of varying beam and geometric parameters of a Monte Carlo model of a Varian Trilogy accelerator. The accelerator was modeled using a modified BEAMnrc package that included asymmetric accelerator and beam models. The dose output was modeled using DOSXYZnrc. Electron beams were modeled for 40×40 cm2 fields with applicators removed. Profiles at dmax and in the bremsstrahlung region were calculated for 4, 12, and 20 MeV configurations. Results: The dose distributions were evaluated for flatness, symmetry, and OAR. Scattering foil thickness had a negligible effect on dmax profiles, but increased the bremsstrahlung production rate. A 3 mm shift in the interfoil distance had a 5% effect on the OAR at 12 cm, but only 2% at 5 cm radius. Profiles in the bremsstrahlung region help differentiate between similar dmax behavior for changes in incident electron angle and lateral secondary scattering foil position. A 4 mm variation in the electron spot size had a negligible effect on the 4 MeV dose distribution, but varied the flatness of the 12 and 20 MeV beams by 2% and 5%, respectively. Conclusion: Lateral and angular offsets of beam and accelerator components have strong effects on dose distributions, and need to be included in any high‐accuracy electron beam model. Large fields without applicators and bremsstrahlung profiles can give additional insight into how parameters should be adjusted when commissioning a Monte Carlo beam model.Support from NIH R01 CA104777‐01A2.