bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐J‐64: Robustness of a Gantry‐Mounted Radioactive Tracking System in a Clinical Radiation Therapy Environment
Authors: Alezra D , Schifter D , Shchory T , Kurtzhand M , Lifshitz I , Pfeffer R , Corn B
Published: April 2010

Purpose: To examine the robustness of a gantry mounted radioactive tracking system in 6MV and 10MV clinical radiation therapy environments. Method and Materials: The gantry‐mounted tracking system was installed in several radiation therapy treatment rooms. Total dose equivalent to 20 treatment sessions was delivered at 6MV or 10MV in a few fractions (within 1 hour) to a phantom containing a radioactive marker (Ir192). During irradiation the tracking system was operating and system parameters were recorded before, during and immediately after irradiation. Recorded data was analyzed to assess system performance and the accumulated effects of radiation on the system. The radioactive marker location measured by the tracking system was monitored during and after irradiation to test for accuracy and stability. The spectra of the signals from the radioactive marker before and after irradiation were compared to see if any shift in spectrum is observed. After 10MV irradiation, background signal level was monitored to analyze the halflives of the isotopes resulting from neutron activation. Results: There was no significant change in signal spectrum after irradiation and no cumulative influence on system performance was observed. Tracking is temporarily interrupted during 10MV irradiation and is resumed within a few seconds after irradiation despite the increased background noise resulting from neutron activation which decays with a half life of approximately 105 seconds. At 6MV, the system maintains tracking accuracy and performance throughout irradiation despite an increased background noise level. The system adjusts to the changes in background noise level at the beginning and end of irradiation in under 3 seconds. Conclusion: The radioactive tracking system is robust in the radiation environment. There is no observable effect or malfunction after exposure to radiation. The system is capable of tracking a radioactive marker during irradiation at 6MV. Conflict of Interest: Research sponsored by Navotek Medical Ltd.
SU‐FF‐J‐65: Coherent Bremsstrahlung in Image Guided Radiotherapy
Authors: Koenig T , Oelfke U
Published: April 2010

Purpose: To determine the suitability of coherent bremsstrahlung (CB) from monocrystalline targets for improving the quality of megavoltage imaging in radiotherapy by selectively enhancing the amount of photons in the energy range useful for diagnostic applications. Method and Materials: A theoretical investigation of CB was carried out in first‐order Born approximation. The interaction cross‐sections derived allow to study features of CB particularly at electron energies in the low MeV regime as used by common clinical linear accelerators. Special emphasis was placed on the comparison with incoherent bremsstrahlung, arising simultaneously. Photon energy distributions were calculated for electron beams hitting various monocrystalline targets at different angles with respect to major crystal axes. The suitability of various elemental crystals for creating low energy photons from megavoltage electrons was determined. Results: Examination of the cross‐sections identified diamond and tungsten crystals to be capable of significantly reducing average photon energies when used as bremsstrahlung targets. The mentioned effect is especially pronounced at electron energies between 10 and 20 MeV and, on a cross‐section level, outperforms ordinary bremsstrahlung produced with 5 MeV electron beams. In case of tungsten a further enhancement can be achieved by cooling the target. Conclusion: Monocrystalline targets carry the potential of creating considerably softer photon spectra than common amorphous or polycrystalline materials. They also offer the possibility of tuning the photon energy distributions by rotating the crystal with respect to the direction of the incident electron beam. Experimental realization, however, appears challenging as the emitted x‐rays are mainly concentrated in the forward direction, thus being unable to illuminate fields of view large enough for IGRT. An array of differently oriented crystals hit by a divergent electron beam is thought to circumvent this limitation.
SU‐FF‐J‐66: Deriving Correlation of External Surface and Internal Tumor Motion Using 4D‐CT Images
Authors: Jiang Y , Cerviño L , Li R , Lewis J , Jiang S
Published: April 2010

Purpose: To quantify the correlation between patient surface motion and internal tumor motion. Method and Materials: Thoracic 4D‐CT scans are used for the study. The CT image at the end of inhale is set as the target image. On each CT slice of the target image, 201 points are evenly placed on the skin contour (excluding the patient's back). The other nine CT images, corresponding to nine different respiratory phases, are set as moving images. An optical flow deformable image registration algorithm is used to map the moving images to the target image. Then the surface points in the target image are transferred to the moving images using the deformation vector field. The motion trajectory of each surface point is quantified for the ten respiratory phases, and the correlation between each surface point motion and internal tumor movement in the superior‐inferior direction is computed. Results: Color maps of the surface point motion amplitude and correlation with internal tumor motion have been derived for each patient. Color maps highlight the high‐correlation and high‐amplitude motion regions on the surface. It has been observed that 88% of body surface has a correlation of 0.9 or higher with internal tumor motion in the SI direction but only 17% of surface points have motion amplitude bigger than 2mm. Conclusion: Color maps of the surface point motion amplitude and correlation with internal tumor motion have been derived for each patient from a 4D‐CT scan. These color maps can be used to identify patient specific surface regions of interest to be used as surrogates for external gating.
SU‐FF‐J‐67: Marker‐Less Verification of Respiratory‐Gated Radiotherapy for Lung Cancer
Authors: Berbeco R , Aristophanous M , Rottmann J , Park S
Published: April 2010

Purpose: To maximize the potential benefit of respiratory gating for lung tumors, a method of image‐guided verification is necessary. We propose using the MV EPID in cine mode during respiratory‐gated radiotherapy to verify the location of the tumor without the aid of implanted fiducials. Method and Materials: The verification procedure to be studied is as follows: prior to each fraction of gated radiation therapy, a gated radiograph is acquired for each of the therapy beam angles. This reference image is then compared to cine EPID images acquired during respiratory‐gated radiotherapy. The target can be visualized in the images and the deviation from the reference position calculated. Phantom studies were performed using a dynamic phantom and internal respiratory traces derived from patients undergoing lung SBRT treatments. Setup images were taken when the external surrogate signal was in the reference (exhale) position and gated radiotherapy was simulated using clinically realistic fields. The reference and treatment images were loaded into offline research software and the location of the target relative to the reference was calculated using a template matching algorithm. Clinical patient data has also been used to demonstrate the feasibility of the technique for an oblique treatment beam. Results: Preliminary phantom and clinical studies demonstrate that the target can be tracked through a series of MV cine EPID images. From both studies, accuracy was assessed to be better than 1 mm. Conclusion: A procedure for confirming the target location during lung cancer respiratory‐gated radiotherapy without the aid of internal fiducials has been defined. Although the proposed procedure is demonstrated retrospectively, in principle, in could be performed in real‐time.

Conflict of interest: Research funded, in part, by Varian Medical Systems, Inc.
SU‐FF‐J‐69: Dosimetric Impact of Gold Fiducial Markers in Patients Undergoing External Beam Radiation Therapy
Authors: Vassiliev O , Kudchadker R , Kuban D , Lee A
Published: April 2010

Purpose: Gold fiducial markers are widely used in image guided radiation therapy to correct for setup error and organ movement. These gold fiducial markers could cause dose perturbations in the target volume for patients undergoing external beam radiation therapy. The objective of this study was to determine the dosimetric impact of gold fiducial markers in patients receiving photon radiation therapy. Method and Materials: Monte Carlo simulations were performed using a newly developed user code for EGSnrcMP. The gold fiducial marker was 3 mm long and 1.2 mm in diameter. Singe field and parallel opposed, 6 MV and 18 MV photon beams, were tested with the marker in different orientations. Radiochromic film measurements confirmed the accuracy of the Monte Carlo model. Results: Monte Carlo simulations indicated that dose perturbation depended on marker size, orientation, and beam energy of the incident beam. Maximum dose perturbation were found for single 6 MV beam. In that case, dose increase reached a factor of 1.52 near the upstream surface of the marker due to electron backscatter. At the downstream surface the dose dropped to 0.72 of the dose at the same point without the marker. For 18 MV the respective values were 1.46 and 0.91. In parallel‐opposed beams, the dose reduction was within only 5% and 2% at 6 MV and 18, respectively. Dose enhancement, however, remained significant reaching factors of 1.15 and 1.30 for the two energies. Conclusion: Dose perturbations from the gold fiducial marker exceeded 50%. The dose reduction effect can be alleviated with multiple beams incident from various directions, whereas the dose enhancement can be optimized to achieve elevated dose around the markers placed inside a lesion. Markers of different sizes and/or materials (carbon, for example) will be further investigated for their potential for improving dose distributions.
SU‐FF‐J‐74: Validation of Bony Anatomy Based (2D‐2D) Image Registration
Authors: Palaniswaamy G , Goddu S , Mamalui‐Hunter M , Low D
Published: April 2010

Purpose: Image‐guided daily localization is becoming standard of care in radiation therapy. The purpose of this work is to validate the accuracy of bony landmarks based image‐registration of the Acculoc software, Isoloc's (v7.0). This provides daily patient localization ability on linear accelerators which don't have on‐board kV‐imager for 2D‐2D matching or cone‐beam CT. Methods and materials: The image‐registration accuracy can be compromised by the image quality. In order to test the bony anatomy based image‐registration accuracy, a blind study was conducted with two individuals; first person to off‐set the anthropomorphic phantom and the second person for alignments. Anthropomorphic phantoms representing head‐and‐neck, thorax and pelvis were used in this study. All three phantoms were CT‐scanned and treatment plans were generated using Pinnacle (v8.0). Orthogonal {anterior‐posterior (AP) and right‐lateral (RLAT)} setup beams were added for each isocenter and digitally reconstructed radiographs (DRRs) were generated for each beam. At the treatment machine, both AP and RLAT portal images were obtained using Portal‐Vision software. Portal images and their respective DRRs were imported into the Isoloc software for the alignments. Several blind translational off‐sets followed by the image‐registration were made for each site. Furthermore, in order to simulate obese patients, the pelvic phantom was wrapped with around 10 cm bolus and checked the accuracy of the software to align the phantom based on bony landmarks. Results: The image quality was acceptable for all three sites and we were able to align the head and neck phantom with ±2 mm accuracy in each direction. Accuracy for aligning thorax and pelvis phantoms were within ±3 mm. Conclusion: 2D image‐registration based on bony landmarks using Isoloc 7.0 software has been validated and the image‐registration accuracy was found to be within ±3 mm.
SU‐FF‐J‐75: Real‐Time MR Tumour Tracking and Dose Adaptation
Authors: Yun J , Robinson D , MacKenzie M , Rathee S , Murray B , Fallone B
Published: April 2010

Purpose: To develop a real‐time (while the patient is being irradiated) tumour tracking and dose adaptation algorithm that can operate within a novel Linear accelerator‐Magnetic Resonance imaging (Linac‐MR) system. Current emphasis is given to lung tumour, which shows the most extensive and abrupt motion. Method and Materials: The auto‐contouring algorithm to automatically identify the shape of the tumour from each MR image is comprised of an autocorrelation technique for image matching, and Histogram Shifting (HS) algorithm for edge detection. A MR compatible motion phantom was built to simulate the motion of tumours (ex: lung tumours) and to perform various dosimetric measurements. The 4D MR images of this phantom and volunteers were used to evaluate the auto‐contouring algorithm. To conform the radiation beam, a Multi‐Leaf Collimator (MLC) controller is being developed using Field Programmable Gate Array (FPGA) based electronics. To compensate for the time delay between MR imaging and irradiating instances, a motion prediction algorithm was developed using a Kalman filter. Results: The auto‐contouring algorithm showed successful tumour tracking and contouring capabilities in the 4D MR images of thoracic region and phantom. The motion prediction algorithm was evaluated by using a modified cosine model, motion phantoms, and fluoroscopic patient data. In most cases, the algorithm predicted the position of tumour correctly more than 95% of the total treatment time. The FPGA based electronics demonstrated its real‐time MLC controlling capability. Various 1‐D lung tumour motions were simulated by the MR motion phantom, which was used to evaluate our algorithms. Conclusion: This work indicates the potential of Linac‐MR system for (1) auto‐contouring capability of tumours in real‐time MR image (more than 4 frames per second) (2) radiation beam conformity to the shape of tumours (3) accurate tumour tracking ability by developing motion prediction algorithm (4) beam intensity modification.
SU‐FF‐J‐76: Radio Frequency Noise From Clinical Linear Accelerators
Authors: Lamey M , Burke B , Rathee S , Murray B , Fallone B
Published: April 2010

Purpose: Several groups are actively pursuing the integration of an MRI with a megavoltage teletherapy treatment unit. Our system will use a 0.2 Tesla magnet for imaging and a 6MV linear accelerator (linac) for treatment. An important scientific aspect of this project is the possible radio frequency (RF) noise interference between the MRI and linac. The purpose of this work is to report on the measurement of the RF emissions in the treatment room of a clinical linac. Method and Materials: The electric (E) and magnetic (H) field components of the RF noise from a clinical linac were measured using commercially available field probes. Measurements were taken on a Varian 600C linac. The time response of the signal induced in the probes was captured by an appropriate oscilloscope. The discrete Fourier transforms of these time domain measurements were calculated to obtain the measured power as a function of frequency. A second set of measurements were taken to study the dependence of field strength on the location within the vault. Results: Our measurements indicate that the E field strength is on the order of V/m, around 8.5 MHz, and that most of the signal in the H field in concentrated at frequencies below 5 MHz. Besides a few peaks, in general toward higher frequencies both the E and H field strengths drop. We measured a power density of 14.6 μW/m2 at 8.5 MHz for a Varian 600C linac. Our measurements show that the measured field strength has little dependency on the measurement position within a treatment vault. Conclusion: Since an MRI coil receives power on the order of μWs during imaging, it will be important to properly shield or otherwise reduce this extraneous RF power in the linac‐MR unit.
SU‐FF‐J‐144: Stability Assessment of MVCT Imaging for Dose Calculation Purposes
Authors: Duchateau M , Tournel K , Verellen D , Reynders T , Linthout N , Gevaert T , Storme G
Published: April 2010

Background and purpose: Using Helical Tomotherapy (HT) it is possible to acquire MVCT images of the patient prior to treatment to position the patient. Previous studies have shown that it is possible to use these images for dose calculation, given the exact Image‐value‐to‐density conversion table (IVDT). However, in a clinical setting the image quality is susceptible to changing noise levels, base‐line shifts with output changes and beam spectrum changes, which also have an influence on the IVDT. The aim of this study is to investigate the stability of these images when used for dose calculation in function of varying machine output, beam energy and component changes, and to develop and test a rigid and fast QA protocol that can be used in clinical routine for these images. Material and Methods: The effect of output and energy changes on the IVDT was measured for clinically observed output and energy changes, and the effect on the dose calculation was measured using phantom calculations. Measurements on image characteristics were also performed before and after magnetron and target changes. To be able to build a QA protocol output/energy effects were linked to image quality and noise levels. Results: Clinical variations in output and energy of the beam lead to variations in the IVDT of up to 5% and differences in dose calculation on phantom of up to 3%. Measurements show the noise level of the images can be used as test for changes in the IVDT and that changing a magnetron or target can completely alter the IVDT characteristics. A QA schedule of acquiring one IVDT every week is proposed. Conclusion: Even though studies have shown that dose calculation on tomotherapy‐MVCT images is feasible, the use of this in clinical routine is only possible when combined with a strict imaging‐QA‐protocol.
SU‐FF‐J‐148: Comparison of the Intratumoral Distribution of Targeted and Non‐Targeted Cu‐67‐Carrying Composite Nanodevices (CNDs)
Authors: Nazareth D , Rigual D , Kasturirangan V , Kariapper M , Tran T , Sablauer A , Lesniak W , Roberson P , Balogh L , Khan M
Published: April 2010

Purpose: To investigate the tumor distribution of angiogenic microvascular targeted and non‐targeted beta‐emitting Cu‐67‐carrying composite nanodevices (CNDs) using an in vivo mouse tumor model. Method and Materials: Composite nanodevices (CNDs) are third‐generation “smart” nanoparticles synthesized from nanomaterials. We synthesized gold/dendrimer CND's (cRGD‐AuCND) with certain peptides molecules, which target the proteins expressed in tumor microvasculature. The same constructs, but without targeting molecules (AuCND) were used as control. Labeling was achieved by complexing known activities of the beta emitter Cu‐67 ions with the targeting and non‐targeting CNDs in solution. The solutions were introduced into a group of subcutaneous prostate‐tumor‐bearing mice via tail‐vein injections. Sections of the tumors were resected and exposed on autoradiographic film. Autoradiographs were also produced of an agarose gel standard containing various concentrations of the same Cu‐67 sample. These calibration films were digitized and analyzed using a threshold technique, and provided 32 regions of interest. Average pixel values of these regions were plotted versus the calculated number of beta events, and fit to a power law, to produce a sensitometric curve. Results: The regions of interest of the calibration films varied between a high signal of 57 and a low signal of 177, based on 8‐bit digital images. Images of tumor sections containing the targeted and non‐targeted CND were analyzed using the sensitometric curve. The average relative activity of beta decays corresponding to the targeted cRGD‐AuCND was 3.4 times higher than that of the non‐targeted AuCND. Conclusion: Based on analysis of autoradiographs, we have shown that targeted CND's are preferentially deposited in tumors. The relative activity of Cu‐67 in tumor tissue was a factor of 3–4 greater for the targeted cRGD‐AuCND than the non‐targeted AuCND. In combination with other tumor image analysis techniques, these results will permit detailed quantitative intratumoral biodistribution and then microdosimetry of the nanodevices.
SU‐FF‐J‐161: Feasibility Analysis On Converting Conventional Orthovoltage Biological Irradiator to a Micro‐Beam Array for Small Animal/cell Irradiation
Authors: Huang K , Yan K , Podder T , Hu Y , Yu Y
Published: April 2010

Purpose: To evaluate the feasibility and restrictions in converting an X‐ray orthovoltage biological irradiator, PXI‐X‐RAD‐320, to a micro‐beam array using Geant4 Monte Carlo Simulation. Two important aspects of the beam, the peak‐to‐valley ratio (PVR) and beam flux, were evaluated quantitatively. Method and Materials: X‐ray tube used in the irradiator (MXR‐321) was simulated to generate the angular dependent X‐ray spectrum. With this spectrum, X‐ray beams impinged onto a plate with micro‐grids (micro‐beam plate) or a control plate (normal‐beam plate), with photons collected by detectors underneath at spatial resolution of 0.02mm. The impact of such factors as source‐to‐plate distance, plate‐to‐detector distance, with/without blocking, and the diameter of blocking on the beam profiles and flux was evaluated. Kodak EDR2 films were analyzed by VIDAR‐Dosimetrypro‐Advantage scanner. Results: PVR increased and beam flux decreased with decreasing plate‐to‐detector distance. For instance, keeping the source‐to‐plate distance at 345mm from source, a decrease of the plate‐to‐detector distance from 5cm to 1mm led to PVR increase from 1.3 to 687.3 and beam flux increase from 1.16% to 1.27%. The relative low resolution of scanner caused micro‐beam doses being averaged within vicinity area. It was showed that a PVR of 1.916 got from film was consistent with 1.843 from average of the simulation data for 1mm plate‐to‐detector distance. As the source‐to‐plate distance became larger at constant plate‐to‐detector distance, PVR increased whereas beam flux decreased. In situations where a larger plate‐to‐target distance is desired, a blocking with small orifice must be used. While providing an outstanding PVR at orifice diameter of 0.65mm, this method resulted in an extremely low beam flux. Conclusion: A conventional x‐ray irradiator can be converted to a micro‐beam array but with limitations. The primary restriction is caused by machine's large irradiation angular coverage. Advanced method should be developed to evaluate micro‐beam dose from film.
SU‐FF‐J‐164: A Calibration Method for Positioning Small Animal Radiotherapy Subjects Using MicroCT
Authors: Rodriguez M , Nelson G , Zhou H , Keall P , Graves E
Published: April 2010

Purpose: To establish an accurate positioning protocol to deliver dose to internal organs of mice using a microCT/RT system. This protocol employs microCT images acquired with the system as a guide to place a desired target at the scanner isocenter. Methods and Materials: A 6×6×1.5 cm3 solid water phantom with a superficial iron ring and a gafchromic EBT film sandwiched at 3 mm from the front face was placed at the isocenter of a microCT/RT system so that the film was parallel to the plane of gantry rotation. The phantom was imaged using 400 70 kVp x‐ray beams from directions equally spaced over 360°. The film in the phantom was irradiated with a 6 mm diameter beam from 8 different angles. The film was also irradiated perpendicular to the beam in the ring axis direction. Analysis of the film image, images from the microCT detector, and reconstructed CT data were used to determine the isocenter projection on the detector and in the three‐dimensional image obtained from the reconstructed data. Results: The coordinates of the central pixel of the detector image are (437, 238) but analysis of the CT detector images demonstrated that the coordinates of the pixel that represents the isocenter are (449, 245). The reconstructed volumetric CT images revealed that the isocenter of the microCT is located at the geometric center of the images obtained from the microCT scan. Conclusion: Using external markers and film and detector images, targets in mice can be accurately positioned on the beam axis for irradiation. The reconstructed data from a brief microCT scan provides the information to place an arbitrary anatomic location at the scanner isocenter for dose delivery. In general, the microCT images capabilities can be used as a guide to precisely perform radiation treatments on internal targets in mice.
SU‐FF‐J‐167: MRI‐To‐CT Deformable Registration for Treatment Planning of Breast Irradiation
Authors: Godley A , Ahunbay E , Paulson E , White J , Li X
Published: April 2010

Purpose: Breast MRI provides enhanced tissue differentiation and physiological information that greatly improves the delineation of targets for breast cancer radiotherapy. MRI needs to be registered with CT as the CT provides the electron density information for dose calculation and alignment in IGRT. We are developing a technique to deformably register MRI to CT, allowing for the transfer of the MRI‐defined structures to the CT for dose calculation, and the dose distribution from CT to MRI for outcome analysis. Method and Materials: An MRI data series was acquired, using a breast coil on a large bore 3T scanner (Verio, Siemens), with prone patient position using multiple sequences including T1, T1 fat saturation (FS), T2, T2FS, and T1FS with contrast. A CT was taken shortly after MRI acquisition. The multi‐form MRIs were rigidly registered to the CT. Anisotropic (edge preserving) noise filtering is applied to the images. A deformable image registration program developed using ITK then registers the MRIs individually to the CT using B‐Spline with Mattes mutual information as a metric and LBFGSB as the optimizer. MRI‐defined structures were overlaid on the CT for treatment planning, and the dose distribution transferred from CT to MRIs for analysis of radiation response based on multi‐form MRIs, using the deformation field obtained. Results: Multi‐form MRIs for prone breast were successfully registered to CT as gauged by high mutual information. Registration amongst the MRI modalities showed negligible deformation between them. T1FS registered best with the CT. Consequently its deformation field was used to deform the other MRIs. This improved the agreement between these MRIs and the CT over their individual registration. The deformation field was used for dose overlay on multi‐form MRIs. Conclusion: The deformable image registration tool developed successfully registers multi‐form MRIs to CT for treatment planning of prone breast radiotherapy.
SU‐FF‐J‐168: Evaluation of a Commercial Software Package for Incorporating Biological MRI Into Treatment Planning of Gliomas
Authors: Chang J , Duckworth T , Narayana A , DeWyngaert J
Published: April 2010

Purpose: To investigate the feasibility of incorporating biological imaging information into the treatment planning of gliomas using Prism View™, a commercially available medical imaging application for processing anatomical and functional/physiologic brain imaging data. Method and Materials: The patient first underwent whole brain axial fluid‐attenuated‐inversion‐recovery (FLAIR) MRI, followed by three‐dimensional magnetic resonant spectroscopy imaging (MRSI) measurements and perfusion MRI. All three MR image sets were loaded into the Prism View™ software and the MRSI and perfusion MRI overlaid on the FLARI MRI. Contrast of MRSI was adjusted so that only two levels (high and low) of Cho/Cr ratios were shown. The fused images were then converted to a grayscale image set, exported in DICOM format and imported into the Eclipse treatment planning system. Two planning target volume (PTVs) were contoured on the FLAIR images: PTV1 corresponded to the FLAIR enhancement and the low Cho/Cr region plus 15mm margin, and PTV2 represented the high Cho/Cr area plus 5mm margin. The fused MR image set were then co‐registered with the simulation CT images, and an IMRT dose‐painting plan was generated that simultaneously delivers two different dose levels (59.4 Gy and 66 Gy) to PTV1 and PTV2, respectively. Results: The above treatment planning process was performed for one patient. Fusion of FLAIR, MRSI and perfusion MRI was successfully performed with the Prism View™ software. Import of the fused DICOM MR images into the Eclipse treatment system was smooth and didn't encounter any problems. Dose‐painting IMRT plans were also generated with good coverage (at least 95% volume received 95% prescription dose) for both PTVs. Conclusion: It is feasible to incorporate biological imaging data into the treatment planning of gliomas with Prism View™ software. However, this software lacks the ability to display absolute metabolite ratios, making it difficult to determine tumor severity from MRSI.
SU‐FF‐J‐170: Impact of 4D Cone Beam CT View‐Aliasing Artifact On Nonrigid Registration Accuracy
Authors: Hugo G , Lu J , Sleeman W , Williamson J
Published: April 2010

Purpose: To evaluate the effect of 4D cone beam CT view‐aliasing artifact on nonrigid registration accuracy. Method and Materials: End exhalation (EE) and end inhalation (EI) volumes from a 4D multi‐slice CT image (4DCT) of a research subject were registered using a small deformation inverse consistent linear elastic (SICLE) registration algorithm to produce a reference displacement vector field (DVF) between the two images. Artificial cone beam CT projections were generated for the EE and EI volumes at several different angular sampling patterns, mimicking 4D cone beam CT (4DCBCT) acquisition in a free‐breathing patient. The projections were reconstructed into EE and EI 4DCBCT phase images containing view‐aliasing artifact due to angular undersampling, but without CBCT scatter and beam hardening artifacts. The EE and EI 4DCBCT images were registered using the SICLE algorithm to produce a test DVF. Test DVFs were generated at a range of angular frequencies from 0.17 projections per degree to 1.83 projections per degree (full angular sampling on a commercial cone beam CT system). The norm of the voxel by voxel vector difference between the test DVF and reference DVF within the patient's delineated lung volume was calculated. Results: The mean absolute error was significantly associated with the projection angular frequency (p < 0.05, exponential regression, R2=0.996). The median error was below 0.2 cm and 90% of the error was below 0.3 cm for the lowest frequency evaluated here of 60 projections per phase. However, above a sampling frequency of 0.33 projections per degree (120 projections per phase), 90% of the error was less than 0.1 cm in relation to the 4DCT registration. Conclusion: Using at least 120 projections per phase, view‐aliasing artifact had a minimal effect on the registration accuracy for the SICLE algorithm due to inherent elastic and smoothing constraints in the algorithm.
SU‐FF‐J‐175: Segmentation of Moving Targets in PET: Threshold Dependence On Lesion Size, Motion Extent, and Signal‐To‐Background
Authors: Riegel A , Bucci MK , Ahmad M , Sun X , Chandler A , Mawlawi O , Pan T
Published: April 2010

Purpose: To determine optimal PET activity concentration thresholds for lung lesions as a function of lesion size, motion extent, and signal‐to‐background ratio. Method and Materials: The background tank of the NEMA IEC phantom was filled with water and the 6 spheres were kept empty. The phantom was placed on a motion platform positioned on the PET/CT scanner bed. The platform moves sinusoidally at 0, 1, 2, and 3 cm amplitudes and a 4‐second period. Cine CT scans were taken at each amplitude and minimum intensity projections were formed to determine the “motion envelope” of the empty spheres. This volume served as the reference volume. The 6 spheres and background tank were filled with activity to create two signal‐to‐background ratios (SBR): Infinite (no background) and 10:1. At each motion extent and SBR, the phantom was scanned for 6 minutes in 3‐D mode. Thresholds of varying percentages of maximum activity concentration were applied to the PET images to determine which threshold best fit the reference CT contour for each motion condition, sphere size, and SBR. Optimization was performed by minimizing the separation between the CT and PET threshold surfaces. Results: For all spheres in the “no background” condition, the optimal threshold dropped substantially to less than 15% of maximum activity concentration beyond 1 cm of motion. For SBR of 10:1, thresholds for all spheres and all motion extents increased, especially for smaller spheres where the maximum value was degraded due to motion. Conclusion: Though motion and size had a measurable impact on the optimal threshold, SBR seemed to be the dominant factor in optimal threshold determination. Additional analysis will include scans at finer motion amplitudes (every 0.5 cm), repeated PET imaging at each amplitude, and optimal threshold analysis for over 30 patient studies.
SU‐FF‐T‐04: Permanent Brachytherapy Seed Localization Via Iterative Forward Projection Matching (IFPM) Algorithm Using Intraoperative Cone‐Beam CT Sinogram Projections
Authors: Pokhrel D , Murphy M , Todor D , Lazos D , Weiss E , Motai Y , Williamson J
Published: April 2010

Purpose: To experimentally validate a new algorithm for reconstructing the 3D positions of implanted brachytherapy seeds from intraoperatively acquired 2D cone‐beam CT sinogram projections. Methods and materials: The iterative forward projection matching (IFPM) algorithm consists of finding the 3D‐seed geometry that minimizes the sum‐of‐squared‐intensity differences between computed projections of the candidate seed array positions and experimentally acquired auto‐segmented projections of the implanted seeds. Starting with clinically reasonable initial‐estimate of the seed configuration, e.g., the ultrasound pre‐plan, IFPM iteratively refines the 3D‐seed coordinates and the imaging view‐points until the computed and measured projections match. Four post‐implant patients were scanned using an Acuity digital‐simulator with a full 660 projections conebeam‐CT(CBCT) for post‐implant dosimetry. 3–10 x‐ray images were selected from the CBCT sinogram and were preprocessed to create the binary seed‐only images. 2D Gaussian functions centered at each binary image centroid were used to create gray scale images. The Gaussian width was reduced when IFPM converged. To quantify IFPM accuracy, the reconstructed seed positions were forward projected and overlaid with the measured seed images and found the nearest‐neighbor‐distance between computed and measured seed positions for each image‐pair. Results: For all example cases, the mean registration error was found to be about 1.2mm; the IFPM converged in 16–21 iterations and in 4–7 iterations following reduction of Gaussian blurring function width with computation time of about 1.9–2.3 minutes/iteration on a 2 GHz processor. Discussion: The IFPM algorithm avoids the need for matching corresponding seeds images on each projection as required by standard back‐projection methods. Also it has a potential to accommodate incomplete data by iteratively recreating the overlap seeds on the matching computed projections. Our preliminary results of the patient's studies demonstrated that ∼1mm accuracy in reconstructing the 3D‐positions of brachytherapy seeds from the measured 2D projections.

Supported by Varian‐Medical‐Systems
SU‐FF‐T‐06: Analytic Expression and Functional Fitting for the COMS Eye Plaque Dosimetry Data
Authors: Chiu‐Tsao S
Published: April 2010

Purpose: We developed an analytic expression and functional fitting scheme for the COMS eye plaque dosimetry data generated from Monte Carlo calculations which incorporated the heterogeneity effects of the COMS plaque assembly (gold alloy backing and silastic insert). Method and Materials: For each plaque size and a specific radionuclide and seed model, I‐125 (model 6711) or Pd‐103 (model 200), the 2D dosimetry data in a central plane, D(x=0,y,z), generated from Thomson's Monte Carlo calculations1 were expressed as a product of three functions, F0(z), F1(y,z) and F2(y,z). F0(z) was a fitting rational function of z for the central axis depth doses, D(x=0,y=0,z). The off‐axis ratio, OAR(x=0,y,z) = D(x=0,y,z)/D(x=0,y=0,z), was expressed as the product of F1(y,z) and F2(y,z). F1(y,z) described the dose profile in the primary field. F2(y,z) was a sigmoid function, describing the collimating effect of the plaque. Using TableCurve2D v5.01.05, we obtained the fitting parameters for the functions, F0(z), F1(y,z) and F2(y,z). Results: We obtained the following equations for F0, F1 and F2. , where a1 through a5 were fitting parameters. . . For each plaque size and radionuclide, the parameters, h, p, b, c, and d, were further fitted to various functions of z with up to 4 parameters each. Along the central axis, all the fitted dose values were within ±2% of the Monte Carlo generated doses. For the majority (>95 %) of the off‐axis points in the eye, the fitted dose values were within ±2% of the Monte Carlo generated doses. Conclusion: An analytic expression and functional fitting scheme for the COMS eye plaque dosimetry data in a central plane was developed to facilitate the routine treatment planning calculations for eye plaque cases, with the heterogeneity effects of the plaque assembly taken into account.
SU‐FF‐T‐11: Measurements of Dose Discrepancies Due to Inhomogenieties and Radiographic Contrast in Balloon Catheter Brachytherpay
Authors: Oh S , Scott J , Shin D , Suh T , Kim S
Published: April 2010

Purpose: Recently, a device called MammoSite consisting of balloon and catheter was developed to perform partial breast irradiation using high‐dose‐rate (HDR) brachytherapy unit with ease and reproducibility. However, the actual dose to the skin does not agree well with the calculated dose by the treatment planning system because of the difference between the calculation condition and the real treatment condition (i.e., homogeneous water and full scatter condition vs. contrast existing and lack of full scatter condition). In this study, we experimentally estimated dose discrepancies due to contrast and lack of full scatter in breast HDR brachytherapy with MammoSite. Method and Materials: Using MOSFET detectors and a breast simulating phantom, the dose discrepancies between calculation and treatment condition were measured according to contrast concentration (10 and 20% volume ratio), balloon size (35 cc and 60 cc), and source to detector distance (SDD) ranging from 25 to 50 mm. The source was Ir‐192 isotope from Nucletron HDR unit. To correct the energy dependency of MOSFET detectors, the mean energy of each measured condition was obtained using Monte Carlo simulation with simplified geometry. For uncertainty analysis, the 80% confidence level of measurements was assessed by Student's t distribution. Results: The dose discrepancies from calculation condition due to both contrast and lack of full scatter combined ranged from about −1.4% to −18.2% in studied cases. Conclusion: In all cases, the effect of lack of full scatter was dominant to that of contrast. Significant dose discrepancies existed between the calculation and the real treatment condition due to contrast and lack of full scatter. Therefore, actual skin dose is expected to be less than calculated.
SU‐FF‐T‐17: Impact of Applicator and Dummy Pellets On the TG 43 Parameters of Selectron Cs‐137 Source
Authors: Sina S , Faghihi R , Mosleh‐Shirazi M , Mehdizadeh S , Meigooni A , Zehtabian M
Published: April 2010

Introduction In this study, dose rate distribution around a spherical pellet source, from a low dose rate (LDR) Selectron remote afterloading system, have been determined using Experimental and Monte Carlo Simulation techniques. Materials and Methods: Monte Carlo simulations were performed using MCNP4C code, for a single pellet source in water medium and Plexiglas and measurements were performed in Plexiglas phantom material using LiF TLD chips. Absolute dose rate distribution and the TG‐43 dosimetric parameters such as dose rate constant, radial dose functions and anisotropy functions were obtained for a single pellet source. In order to investigate the effect of the applicator, and surrounding pellets on dosimetric parameters of the source, the simulations were repeated for 6 different arrangements with a single active source and five non‐active pellets inside central metallic tubing of a vaginal cylindrical applicator. In commercial treatment planning systems (TPS) the attenuation effects of the applicator and inactive spacers on total dose are neglected. Results The results indicate that this effect could lead to overestimation of the calculated anisotropy function by up to 7% along the longitudinal axis of the applicator especially beyond the applicator tip. The radial dose function and anisotropy function of the new source design have been tabulated for each configuration. Conclusions Impact of the Applicator and Dummy Pellets on the TG‐43 Parameters of Selectron Cs‐137 Source has been determined using TLD and Monte Carlo calculations. The results indicate neglecting the applicator and dummy pellets could cause significant errors in F(r, θ).
SU‐FF‐T‐19: Accelerated Partial Breast Irradiation With Shielded MammoSite‐Type Applicator
Authors: Govindarajan N , Nazaryan V , Keppel C , Gueye P
Published: April 2010

Purpose: We propose a method to improve delivery of APBI and therefore improve patient access to BCT. Method and Materials: BCT in conjunction with accelerated partial breast irradiation (APBI), using for instance the Hologic MammoSite applicator, is becoming popular due to the good dose distribution, and relatively short five day treatment procedure. Brachytherapy‐based APBI procedures typically work by implanting a double lumen balloon catheter in the lumpectomy cavity of breast following surgery. The balloon is inflated with an iodine‐based material mixed with saline. If the skin to balloon distance is less than 7mm, the procedure may not be recommended due to adverse skin reactions leading to poor cosmesis. This problem could be avoided by partially shielding the radiation dose to the skin by introducing a thin layer of high density material (high Z powder) inside the balloon catheter. In this case, the metal powders may be controlled by a relatively weak external magnetic field applied externally to the patient to form an internal shielding layer inside the balloon in the region of concern, thus avoiding radiation damage to the skin. Results: Our preliminary results indicate that if, for example, the skin‐to‐balloon spacing is only 4 mm, when about 2 mm thin layer of iron powders arranged internally under that segment of surface of the MammoSite balloon will decrease the skin dose to an acceptable level. Our laboratory tests show that only a slight magnetic filed is required to bring such a small amount of ferrous powders to controllable configuration. Conclusion: The suggested approach will improve cosmetic outcome for all APBI patients treated, in addition to increasing survival expectancy and minimizing negative side effects.
SU‐FF‐T‐28: Localizing Differences in 131Cs Intraoperative and Postoperative Prostate Seed Brachytherapy Plans
Authors: Treas J , Dean D , Jones A
Published: April 2010

Purpose: Relative shifts in isodose curves were noted between post‐operative and intra‐operative prostate seed plans. This study examines the dose differences between intra‐operative and post‐operative plans and evaluates regions of prostate to determine the direction of the shift. Materials and Methods: 103 patient plans done with seed implants were examined. Each intra‐operative plan was derived in realtime via TRUS. Loose seeds (mean activity of 2.1U) were implanted to deliver a peripheral dose of 115Gy. Post‐operative studies were evaluated via CT at 4 weeks post implant. Intra‐operative and post‐operative prostate D90, D100 and V100 were compared. 50 patients were randomly selected and had two additional volumes contoured, Anterior‐Prostate (AP) and Posterior‐Prostate (PP). D90, D100 and V100 values for these additional regions were also compared. Results: Comparing intra‐operative and post‐operative plans, significant differences (p<0.0001) were noted in D90, D100 and V100 prostate values. From the intra‐operative to the post‐operative plan, 91.3% of plans showed a reduction in D90. Post‐operative D100 values dropped >= 10% in 73.8% of patients. V100 prostate quantities dipped in post‐operative plans >= 4% in 64.1% patients. For the additional regions contoured, intra‐operative AP D90, D100 and V100 values were >=10% higher than their corresponding post‐operative values in 74.0%, 64.0% and 68.0% of patients, respectively. Intra‐operative to post‐operative dose reductions of at least 5% to the PP D90 and D100 values were noted for 56% and 64% of patients. Conversely, 62% experienced increased post‐operative PP V100 values of at least 5%. Conclusion: These findings confirm significant prostate dose discrepancies between intra‐operative and post‐operative plans. Specifically, the dose to anterior prostate was consistently overestimated in intra‐operative plans. Discrepancies are believed to be due to the probe deforming the prostate during the implant. However, further evaluation is needed to provide conclusive results.
SU‐FF‐T‐30: Commissioning the Ring & Tandem Combination Applicator Set — CT & MR Compatible, for Clinical Use with the VariSource™ HDR Unit
Authors: Waid D , Morrison J , Glennie G
Published: April 2010

Purpose: Ring applicators always present a challenge for source wire positioning in HDR brachytherapy. X‐ray and autoradiograph imaging of applicators may indicate that without commissioning, a delivered dwell position may be different than planned. The reason for these differences may be attributed to the fact that the inner diameter of the ring has to be larger than the wire diameter to accommodate it within the applicator. This work reports on a method to develop correction offsets in the treatment plan to deliver the intended dwell positions. Method & Materials: Imaging of HDR applicators is commonly used for the commissioning process. In addition to taking x‐ray images with a static marker wire inserted, we describe imaging of dwell positions using the dummy and/or active wire to show the physical location of the HDR source for a given dwell position with respect to the ring applicator. Coupled with autoradiography, it is possible to determine the delivered dwell position by viewing the active source footprints on film. Delivered dwell positions can be compared to the planned dwell positions for comparison. Depending on the magnitude and location of the variations, one correction method is to apply a positional offset table for a given ring, where the offset depends on the planned dwell position. Additional imaging is used to verify that the dwell position modifications are appropriate. Results: We found differences between planned position and treatment position of up to 5 millimeters. Such a difference may be of clinical significance. Using the described dwell position offset method; we applied correction offsets for improved source position accuracy. Conclusion: Using standard radiation therapy equipment, we have shown a straightforward method to determine potential differences between planned and delivered treatment source positions in an HDR ring applicator, and illustrated a straightforward method to correct for positional variation.