bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐I‐09: Minimizing Scatter Artifact in Cone‐Beam CT Reconstruction Using Both Kilovoltage and Megavoltage Beams
Authors: Zhang J , Yin F
Published: July 2006

Purpose: To study the effect of imaging orientations on image quality of aggregated conebeam CT and to develop a strategy to minimize scatter artifact. Method and Materials: Orthogonal kilovoltage (kV) and megavoltage (MV) beam projections were acquired and used to reconstruct kV/MV aggregated CT images. With a $15$‐degree fan‐beam angle, only $105$‐degree gantry rotation s needed to obtain a minimal scan coverage. Besides its short scanning time, the new scan technique has the advantage of getting high soft‐tissue contrast from kV beams and low scatter artifacts from MV beams. The kV and MV projection images were obtained by using a kV on‐board imager and MV portal imager mounted orthogonally on a Varian‐21EX LINAC. A linear model was established to fit the kV and MV attenuation values over the 15‐degree overlap region. MV projections were then converted into kV‐equivalent ones. Aggregated CT images were reconstructed from both kV and converted MV projections jointly, using the filter‐back projection method. Results: Using 8 different kV/MV orientations, we reconstructed 16 aggregated CT images for two phantoms, eight for each one. Each image was registered to its corresponding simulator‐CT image from a GE LightSpeed‐RT simulator. The reconstructed images show good contrast for both bones and soft‐tissue. However some of them have relatively severe scatter artifacts. We calculated the normalized mutual information (NMI) between the aggregated CT and simulator CT images. The NMI exhibits a sinusoidal oscillation when plotted against the gantry start angle. The two maximums correspond to the two imaging orientations with kV (or MV) beams through the thinner (or thicker) side views of the phantoms, indicating that scatter from kV beams has more impact on image quality than MV beams. Conclusion: A strategy has been developed to determine the optimal imaging orientation for aggregated kV/MV CBCT.
SU‐FF‐I‐12: Validation of Geant4's Predictions On X‐Ray Scatter and Glandular Dose in Pendant‐Geometry Cone‐Beam Breast CT
Authors: Sechopoulos I , Vedantham S , Suryanarayanan S , Karellas A
Published: July 2006

Purpose: The Geant4 toolkit is a freely available, widely supported base package for the simulation of particles through matter. This study aimed to test Geant4's accuracy by comparing its predictions for glandular dose and x‐ray scatter in pendant‐geometry cone‐beam breast CT against previously published experimental and simulated data. Method and Materials: We performed Monte Carlo simulations using the Geant4 package [Agostinelli et al, Nucl Instrum Meth A 506: 250–303, 2003] to recreate the conditions of three previously published papers on breast CT dose and scatter. Geant4's scatter simulations are compared against experimental data [Kwan et al, Med Phys 32(9): 2967–2975, 2005], while the dose results are compared against Monte Carlo simulations based on other codes [Boone et al, Med Phys 31(2): 226–235, 2004; Thacker et al, Phys Med Biol 49: 5433–5444, 2004]. The compared scatter results include scatter‐to‐primary ratio profiles for breasts of different sizes, glandularity and incident x‐ray spectra. For the dose comparisons, we compared Geant4's monochromatic results with the monochromatic results reported by the two previously published papers. Results: Geant4 matches the reported experimental SPR profiles to an accuracy of 1.6–16.7% (μ=9.2%, σ=5.4%). The sources for observed deviations include inexact re‐creation of the experimental setup and lack of specific information on the x‐ray spectra used in the experiments. The dose results agree with Boone's published results within 0.7–12.3% (μ=5.3%, σ=4.2%) and with Thacker's to within 1.2–22.3% (μ=10.8%, σ=8.8%). Conclusion: The data comparison suggests that Geant4 can be used to predict x‐ray scatter and dose deposition in low energy experiments such as dedicated breast CT. Given the availability, support and flexibility of the Geant4 toolkit, the use of this package for simulation of breast CT studies can be very useful to researchers in the field. Research supported in part by: NIH‐NIBIB Grant RO1‐EB002123 and the Georgia Cancer Coalition.
SU‐FF‐I‐15: Effects, Detection and Removal of Zingers From Scattered X‐Rays in CCD Based Cone Beam CT
Authors: Meng Y , Shaw C , Liu X , Lai C , Tu S , Altunbas M , Chen L , Wang T
Published: July 2006

Purpose: Zingers are tiny spurious white dots that appear randomly in CCD images. In order to improve the quality of CCD based cone beam CT technique, a new technique for the detection and removal of zingers is described and evaluated. Method and Materials: A bench top CCD based cone beam CT system was used to measure and investigate the presence of zingers. The cause and effects of zingers were studied. A new technique was developed to detect and correct the zingers. With this technique, the statistical behavior of pixel values in a projection image was first analyzed to identify candidates for zingers. Pixel values at the detected zinger locations were then compared in two consecutive projection views to eliminate false detections. To investigate and evaluate this technique, zingers were simulated by increasing the pixel values at randomly selected locations in projection data computed for a modified Shepp‐Logan phantom. The simulated data were then detected and corrected for zingers and used for reconstruction. The resulting reconstructed image was compared with the image reconstructed from zinger free data and with images reconstructed from data corrected using three other zinger removal techniques. Results: Our measurement indicated that zingers may have resulted from scattered x‐rays. They were found to generate visible artifacts and degrade the quality of reconstructed images. It was shown that zingers detection by comparing two identically acquired projections could be highly effective but impractical in CT imaging. Detection by comparing two consecutive projection views was equally effective but may be subject image blurring. Detection by analyzing signal fluctuations could result in a large number of faulty detections. The proposed new detection technique was found to be practical and effective without resulting in image blurring or faulty detections.

This work was supported in part by a research grant CA104759 from NIHNCI.
SU‐FF‐I‐33: A Graphical and Quantitative Procedure for Amplitude‐Gated Treatment Planned Using Phase‐Based 4DCT Using the Varian RPM System
Authors: Hubenschmidt J , Santanam L , Goddu S , Parikh P , Mutic S , Low D
Published: July 2006

Purpose: A graphical and quantitative procedure for amplitude‐gated treatment planned using phase based 4DCT of free breathing patients using the Varian RPM gating system has been developed as a part of the study of phase and amplitude based imaging and treatment. There are several phase‐based CT scanning systems that produce phase‐based images for gated treatments, but for free breathing phase may not be a reliable predictor of tumor location. Good correlation has been shown between abdomen height and diaphragm position, making it a promising treatment modality. Method and Materials: A phase‐based retrospective CT scan from a Philips large bore 16 slice CT scanner is obtained and the phase markers are adjusted to delineate actual breaths. A gating window that is a subset of the whole CT scan is set and a visual representation of gated motion called a MIP(maximum intensity projection) is created to visualize any anatomical excursions. The Varian RPM data is then compared with the scan data to quantify the actual marker block motion(or chest height) during the gating window as well as for an entire phase. The scan data is then presented not only as a percentage of an average breath, but as a chest height range within the total. This information is checked on treatment days and adjusted if necessary. The gating signal and fluoroscopy are compared to a 4D DRR generated from the MIP to check for geographic as well as systematic misses. Before treatment a gated port film (gated over several breaths and dose limited) can be captured to verify gating of the treatment beam. Results: For phantom based studies of regular breathing the method is robust. The model converts phase to amplitude of abdomen height. Conclusion: This method can validate a gated treatment using different imaging modalities.
SU‐FF‐I‐60: 3D Wavelet Packet Denoising of Arterial Spin Labeled MR Perfusion Images
Authors: Maleki N , Roberts T
Published: July 2006

Purpose: To develop a 3D denoising approach based on wavelet packet decomposition for denoising MRI brain perfusion weighted images acquired with Flow‐sensitive Alternating Inversion Recovery (FAIR) arterial spin labeling technique. Method and Materials: A 3D multi‐resolution wavelet packet decomposition approach was developed that takes advantage of both spatial and temporal correlation between multiple consecutive slice selective and non‐selective inversion recovery images acquired with FAIR technique. Single shot spin‐echo EPI‐FAIR imaging was performed on 5 healthy volunteers on a 1.5T GE scanner using FAIR inversion time of 1200ms. Other imaging parameters were 64×64 matrix, TE/TR=20/2000ms, and 20 image pairs. To find the best wavelet base, different bases with different levels of decomposition were tested. Then using the best filter and 2D wavelet transform each image was first decomposed and then for each image a threshold was estimated for noise coefficients and wavelet coefficients below that threshold were removed and the image was reconstructed from the remaining coefficients (Spatial denoising). Then these images were fed into the second step of processing in which each pixel's time course along all of the selective and nonselective images was considered as an one‐dimensional signal and decomposed again using wavelet packets and denoised based on a separate threshold estimated for each signal (Temporal denoising). Then each image was reconstructed again. Results: Among different wavelet packets that were tested Coiflet wavelet packet with 5 vanishing moments, 4 level of decomposition with Shannon entropy and soft SURE threshold (for smoothness and preservation of the edges) criteria resulted the best performance in terms of PSNR and minimal distortion after reconstruction. The mean PSNR of the denoised images was 22.29 ± 4.2. Conclusion: Denoising based on our proposed method in general significantly improves the acquired FAIR perfusion‐weighted images. This improvement is associated with blurring of the edges in the image.
SU‐FF‐I‐61: A New Gel Phantom for MRI
Authors: Pfeiffer D , Zerhouni M
Published: July 2006

Purpose: To develop a gel‐based quality control phantom for MRI that does not suffer from flow artifacts seen in liquid‐based phantoms. Method and Materials: We have developed a gel based phantom incorporating NiCl and NaCl that does not suffer from flow artifacts. The phantom was evaluated for accuracy of the stated T1 and T2 values, uniformity and dehydration properties. The T1 relaxation time was measured using a spin echo sequence with TR = 1000 mS and TE varied between 10 mS and 350 mS. The T2 relaxation time was measured through a fast spin echo inversion recovery sequence with TR = 1000 mS, TE = 50 mS and TI varied between 50 and 983 mS. All measurements and images were made on a GE Signa 1.5T MRI scanner. Results: Measured T1 and T2 values were within 1.3% of the nominal values of 260.3 mS for T1 and 234.1 mS for T2. Uniformity was measured using the ACR T1 sequence of TR = 500 mS, TE = 20 mS. The gel phantom demonstrated a uniformity of 86.5% over its volume in a dedicated head coil, compared to 87.2% for a still liquid phantom in an identical container. The measured mass of 4691 grams did not change over a 6 month period. Conclusion: This new gel phantom shows promise as a replacement for liquid MRI phantoms. Future efforts will focus on adapting the gel to other container geometries and modifying the formulation for more tissue equivalent relaxation times and to match the ACR MRI accreditation program phantom. Conflict of Interest: Research sponsored by Computerized Imaging Reference Systems, Inc.
SU‐FF‐T‐263: Imaging with Brachytherapy Sources
Authors: Song H , Wu Q , Bowsher J , Yin F
Published: July 2006

Purpose: To demonstrate the concept of 2D projection and 3D volumetric imaging using brachytherapy treatment sources in patient prior to or during treatment. Method and Materials: As shown Figure 1, an Ir‐192 HDR catheter is placed at 15 cm depth (a reasonable value for pelvic site) in a solid water phantom. XV films are placed on top of the phantom to capture 2D projection images. Vertebra‐like structures serving as anatomical landmarks are placed at mid distance between the catheter and film. Results: The structures are clearly shown on the projection film with a dwell time of 600 seconds. Projection image acquisition time on the order of seconds or less is achievable with more sensitive (100 times more) detectors such as silicone flat panels and detectors used in SPECT cameras. The projection of the landmark coincides with the reference mark when the source is at the correct dwell position and is off the mark when the HDR source is away from the correct dwell position, as shown in Figure 1b and 1c. Thus a “port film” approach can be developed to verify the source position prior to treatment. With the possibility of verifying one dwell position against its reference mark, all other dwell positions can be verified against its own the reference mark. This provides a way of dynamically tracking the dwell positions of a multiple dwell position treatment plan. With projections taken at multiple angles with sensitive detectors at a fraction of a typical therapeutic dwell time, it will be possible and useful to obtain volume images of the treatment sources superimposed on anatomy, using tomographic (CT, SPECT, tomosynthesis) reconstruction methods. Conclusion: Three dimensional volume imaging with a HDR treatment source has been demonstrated. The concept applies to other brachytherapy modalities, e.g., SPECT for permanent prostate implants, LDRs.
SU‐FF‐T‐266: Impact of MLC Leaf Size On the Quality of IMRT Plan
Authors: Cheng C , Das I
Published: July 2006

Objective: For a given set of constraints, IMRT optimization searches for a minimum of the cost function to within the user specified convergence limit. The efficacy of segmentation and subsequent delivery may be dependent on the design and the leaf width of the MLC. The objective of the present study is to investigate if leaf resolution affects the quality of the treatment plan. Materials & Methods: Two accelerators with different MLC leaf resolution (10mm and 5 mm) are chosen in this study for three different cases (prostate, lung and head and neck). The dosimetry of the two machines are identical to within ±1%. With identical beam angles and dose grid (2 mm), IMRT plans are generated for the same set of constraints for both machines. The DVHs of the PTV and the relevant organs‐at‐risk (OAR) are compared. Results: Figure 1(a, b, c) shows the DVH for prostate, lung, and head and neck. There are very little differences between PTV coverage and OARs except for small structures (<2 cm3) for which the differences are appreciable. Conclusions: For treatment sites which involve small structures (volume< 2 cm3), the use of 5 mm MLC is more beneficial as demonstrated in this study in the head‐and‐neck IMRT. For IMRT treatments with reasonable size OARs, MLC resolution does not appear to be a significant factor for all practical purpose. Thus in general, IMRT optimization and segmentation is relatively insensitive to the leaf width.
SU‐FF‐T‐285: Independent Monitor Unit Verification with the RadCalc® Program of Serial Tomotherapy IMRT Treatment Delivery
Authors: Workie D , Sehgal V , He B , Al‐Ghazi M
Published: July 2006

Purpose: To present our initial experience with the implementation of commercially available independent monitor unit (MU) verification calculation software (RadCalc®) for dose verification for patients undergoing IMRT (serial tomotherapy) treatments planned using a commercially available IMRT planning system (CORVUS® 6.0) and delivered using the multileaf intensity modulating collimator (MIMiC) delivery device. Method and Materials: As a first step we defined a separate machine within the RadCalc® software to facilitate the dose verification process. At our facility, serial tomotherapy is used to deliver IMRT treatments. This is accomplished using the MIMiC delivery device attached to a Varian 600C linear accelerator producing a 6 MV photon beam. Dosimetric data for this treatment machine which included collimator and phantom scatter factors (Sc and Sp) and leaf transmission for the MIMiC were also incorporated in the RadCalc® Software. After the treatment plans are approved for treatment by the radiation oncologist a hybrid QA (quality assurance) plan is generated and delivered to an ion chamber and film placed in a rectangular solid water phantom of dimensions 30 cm × 30 cm × 22 cm. The phantom geometry was also defined in the RadCalc® software to facilitate dose calculation and comparison with the dose determined from ion‐chamber measurements. In this preliminary study a total of 13 patients undergoing IMRT treatment with the MIMiC were analyzed. Results: Initial results indicate a good agreement (within ±5%) between dose calculated from the hybrid plan, ion chamber measurements, and the dose calculated by the RadCalc® program. Conclusion: Based on initial results presented here we have set an action level of ±5% which will be reviewed and revised as necessary as we continue to acquire and analyze additional patient data.
SU‐FF‐T‐286: Inhomogeneity Correction in Brachytherapy
Authors: Das I , Both S , Cheng C
Published: July 2006

Purpose: Dose calculation accuracy at interfaces and in medium with inhomogeneities is still not well established in brachytherapy. Commercial planning systems do not account for the presence of inhomogeneity, while theoretical calculations in inhomogeneities have poor agreement with measurements. The wide use of brachytherapy for breast, prostate, brain and lung treatment in recent development necessitates the need for improvement in brachytherapy dose calculations. In this study, we present an experimental approach to investigate the effect of inhomogeneity for Ir‐192 and Cs‐137. Method and Materials: To study the effect of lung in brachytherapy dose calculation, measurements are performed in a polystyrene phantom embedded with cork sheets of density 0.25 g/cm3. Radioactive source used in the study are Ir‐192 (HDR source) and Cs‐137 tube. Two conditions are studied, one mimics the partial breast treatment with the Mammosite technique, and the other brachytherapy in lung after wedge resection. Dose is measured with a small volume parallel plate ion chamber, embedded in polystyrene or in cork by varying the position of the chamber from the source. Inhomogeneity correction factor (ICF), defined as dose in inhomogenerity / dose in water at the same distance (Di/Dw) is calculated. Results: The calculated ICF values qualitatively agree with our measured values. However there are significant differences that could be due to inaccuracies in build up factors and other assumptions made in the calculations. The dose in medium falls exponentially with distance. The measured ICF is strongly dependent on the position and energy. For example, at 2 cm, ICF for the full inhomogeneity condition is approximately 3.5 and 8.5 for Cs‐137 and Ir‐192 respectively. Conclusions: The magnitude of correction is significantly dependent on the distance and energy as well as the condition of partial or full inhomogeneity. TPS vendors should provide ICF for all commonly used brachytherapy sources.
SU‐FF‐T‐294: Interference of I‐125 Dose Distributions by Neighboring Seeds in Dense Packing Configurations: A Radiochromic Film Study
Authors: Chiu‐Tsao S , Ennis R , Shasha D , Harrison L
Published: July 2006

Purpose: To study the interference effect on the I‐125 seed dose distributions by neighboring seeds in dense packing configuration using radiochromic EBT film dosimetry. Method and Materials: Radiochromic EBT films (lot #35076) were used to measure the dose distributions around I‐125 seed (Implant Sciences model 3500) with neighboring dummy seeds in dense packing configurations in solid water phantom. The types of dummy seeds studied included model 6714 (dummy of 6711), xenated dummies with and without sliver marker. Four dummy seeds of the same type were positioned parallel to the active seed, two on the left and two on the right, with center‐to‐center spacing of 1mm (B), 2mm (C) or 3mm (D). The single seed (A) configuration was also done for comparison. EBT films were located at contact geometry, 2mm or 5 mm distance from the plane of seed/s. After exposure, all the experimental and calibrations films were scanned using PeC CCD100 densitometer with 0.2mm spatial resolution. Conversion from optical density to dose was achieved based on the established calibration curve. The dose distributions for configurations B, C and D were compared with those of A. The ratios of B/A, C/A and D/A were also plotted against the radial distance from the active seed center. Results: Compared with configuration A, we found major dose reduction up to 80% in the contact film for configuration B. The extent of dose reduction was progressively less; but remains significant, for configurations C and D, and for 2mm and 5 mm distances. Conclusion: We have observed major dose reduction (up to 80%) around an I‐125 seed with neighboring seeds in dense packing configurations. Such interference may be clinically significant for prostate implants and eye plaque treatment when the interseed distances are small. Acknowledgement: Implant Sciences Corporation, model 3500 I‐125 seeds.
SU‐FF‐T‐295: Intermediate Energy Photon Dramatically Improves Penumbra, Dose Distribution Homogeneity and Conformality for Small Field Radiosurgery
Authors: Pignol J , O'Malley L , Keller B , Beachey D , Presutti J , Sharpe M
Published: July 2006

Purpose: Stereotactic radiosurgery ensures highly conformal treatment of small volumes. When treating lesions with no microscopic extension and with efficient immobilisation, the PTV (Planned Target Volume) closely overlaps the GTV (Gross Tumour Volume). When using dedicated beam collimation devices, the radiological penumbra accounts for an additional 2 to 3mm dose gradient extending within the normal tissue. We hypothesized that, for small radiosurgery field sizes, intermediate energy photons (IEP, above orthovoltage and below megavoltage) will dramatically reduce the radiological penumbra. Material and Methods: Monte Carlo simulation was used to investigate the dose distribution characteristics and the radiological penumbra of monoenergetic photons (100 keV to 1 MeV) in a water phantom and for various field sizes (0.5×0.5 to 4×4cm2). A virtual unit based on a simulated optimised IEP spectrum was described in the Pinnacle3 TPS using an extended kernel library in the kilovoltage range. Results: Radiological penumbra below 300μm are generated for field sizes below 2×2 cm2 at all depth and for monoenergetic photons between 200 to 400keV. The depth dose curve is steeper with a 50% relative dose at 6.5 cm depth, the dose homogeneity in the target is dramatically increased, and the dose to the bone is not increased. An 800 kV beam generated in a 0.5mm tungsten target maximizes the photon intensity in this range. Using six coincidental IEP generators allow a dose rate of 1.5Gy per minutes at 5 cm depth. Pinnacle3 confirms the dramatic reduction in penumbra size, and the superiority of IEP over megavoltage beams for radiosurgery applications regarding dose distribution homogeneity and conformality. Conclusions: The reduction of radiological penumbra is linked to the reduced photon scattering using small field sizes and the reduced secondary electron range using IEP. This is the first report of the use of IEP for radiosurgery.
SU‐FF‐T‐308: ITC Assists Developers of ATC Compliant DICOM Export for Clinical Trials
Authors: Matthews J , Bosch W , Straube W , Purdy J
Published: July 2006

Purpose: The Image‐guided Therapy QA Center (ITC) as part of the Advanced Technology QA Consortium (ATC) has played a key role in assisting treatment planning system (TPS) developers in verifying that their DICOM implementations (CT, RT Structure Set, RT Dose, RT Plan, and RT Image) match ATC's conformance statement. This presentation will review lessons learned in this important effort. Methods and Materials: ITC hosted a series of DICOM Implementers' Workshops to assist TPS vendors in implementing RT objects needed for clinical trials. A system of software (“ATC Method 1”) developed at ITC to receive, process, and review volumetric treatment planning data for advanced technology clinical trials was used to assist vendors in their implementation of DICOM export. ATC's DICOM conformance statement specifies requirements for using DICOM RT objects in these clinical trials. ITC's DICOM fileset reader converts incoming data to an internal format for efficient display and review using the ITC web‐based Remote Review Tool (RRT). The RRT was used by TPS developers to visualize/compare submitted images, structure sets, and dose distributions, thus greatly facilitating their DICOM implementations. Results: Interactions with developers have exposed several problems in interpretation and implementation of the DICOM standard resulting from the complexity of DICOM RT objects and differences in design/capabilities of TPSs. Examples of problems seen include CT/Structure/Dose miss‐registration and DVH‐calculation discrepancies. To date, 6 TPSs have released ATC‐compliant DICOM export software. ITC has received DICOM data matching the ATC conformance statement from a total of 15 TPSs. ITC has worked with 8 additional TPS developers. Conclusions: The ITC web‐based Remote Review Tool has proven to be of great help to vendors in developing and verifying implementations. More effort is needed by vendors to make digital data submission for clinical trials a simpler process. Support: NIH U24 CA81647.
SU‐FF‐T‐315: Mammosite Balloon Type Vs. Integral Dose to the Skin
Authors: Deore S , Casey W , DaConceicao A
Published: July 2006

Purpose: The purpose of this study was to investigate the influence of different Mammosite applicators (Spherical vs. Ellipsoidal) on integral dose to the skin. Introduction: In early 2005, Mammosite introduced a new balloon in ellipsoidal shape. Ellipsoidal balloon has typical five dwell positions with 10 mm dwell spacing, and different weightings to each dwell position compared to the single dwell position for spherical balloon. The dose prescription for both balloons is identical. However, the influence of different dwell positions & dwell time on integral dose to the skin is not well documented. Dose distributions were reviewed retroactively in 12 mammosite cases to establish the relationship for integral dose to skin vs. balloon type. Methods and Materials: Dosimetry plans (*Nucletron, V14.26) for twelve mammosite patients were reviewed. Nine patients were treated with spherical balloon and remaining three patients received treatment with ellipsoidal balloon. The dose prescription, for all the patients was 34 Gy in 10 fractions at 10 mm from balloon surface. In order to eliminate the influence of skin distance from the balloon center on integral dose, each plan was re‐run using both types of dwell configurations. Entire skin surface (thickness 5 mm) above the balloon was contoured. Dose volume histograms (DVH) were generated for the skin. Results: The DVH analysis indicated consistently higher skin dose with Ellipsoidal balloon compared to the spherical balloon technique. The difference was more pronounced for shorter skin distance (7–10 mm) from the balloon surface. On average the integral skin dose was higher by 11% with ellipsoidal balloon for skin distance of ⩾ 7 mm. While for skin distance of ⩾ 13mm, the integral dose was higher by 6.5% for ellipsoidal balloon. Conclusions: Ellipsoidal balloon technique of mammosite delivers higher integral skin dose. It is too early to indicate any clinical significance of these findings.
SU‐FF‐T‐398: Study of Inhomogeneous Dose Distribution in a Cell Box Due to the X‐Ray Scattering Effect
Authors: Yoon M , Shin J , Shin D , Lee S , Park S , Lee D , Kim J , Pyo H , Shin K , Cho K
Published: July 2006

Purpose: The ratio of hypoxic to aerated doses needed to achieve the same biological effects, called the oxygen enhancement ratio (OER), is very important factor in radiotherapy since none produces such a dramatic effect and no other agent has such obvious practical implication. Although it is usually assumed that the dose distribution in a cell box is uniform, the absorbed dose to the tumor cells could be very different according to the locations of the cells within a cell box, which affects the cell survival curves. We have studied the inhomogeneous dose distribution in a cell box due to the scattering of x‐rays with the cover and side‐walls of cell box. Method and Materials: Three different sizes of cubical cell boxes, whose side lengths are 10, 15, 20 cm, were designed and irradiated by 6 and 15 MV x‐rays using Varian 2100CD linear accelerator. Results: The differences of the absorbed doses at the center between 10×10×10 cm3 box and 20×20×20 cm3 box were less than 2 % for 6 MV and 15 MV x‐ray irradiation, which indicates that the scattering effect depending on the size of cell box is not significant for the absolute absorbed dose at the center of box. However, the relative dose distribution within the cell box shows very different behavior revealing distinct heterogeneous dose distribution in a cell box. For example, the percentage showing more than 10 % dose difference within the cell box was ∼ 40 % for 20×20×20 cm3 box with 15 MV x‐ray irradiation. Conclusion: While the dose inhomogeneity for 15 MV x‐ray irradiation increases as the size of cell box increases, the dose inhomogeneity for 6 MV x‐ray doesn't show any size dependency. Our experimental evidence suggests that the dose inhomogeneity within the cell box is not negligible.
SU‐FF‐T‐419: The Impact of Gating On the Reduction of Heart Doses for Left Sided Breast Cancer Irradiation
Authors: Cossmann PH , Nguyen L , von Briel C
Published: July 2006

Purpose: Because there are indications for an increased risk of cardiovascular diseases after radiotherapy of the left chest wall the dose to the heart should be reduced as far as possible. With respiratory gating technique irradiation can be restricted only to the inspiratory plateau phase. We investigated in all patients with left sided breast cancer dose reduction to the heart when treated only in the inspiration phase compared with not gated treatments. Materials and Methods: Between Sept 2004 and Feb 2006 107 patients with left sided breast cancer were treated with respiratory gating technique based on a retrospective 4D CT scan. We performed for all of these patients a normal and a respiratory gated planning CT. Planning was done with the same treatment parameters in both CT. DVH for the entire heart and the anterior left ventricle wall were calculated. All patients were treated with 2 Gy single dose to a total dose of 50 Gy to the entire left breast/chest wall. 68 patients received an additional boost of 10 Gy. Results: The mean dose to the entire heart was 0.7 Gy without and 0.6 Gy with respiratory gating (p=0.04) whereas the mean maximal dose was 40.2 Gy without and 11.7 Gy with respiratory gating (p=0.0003). The anterior heart wall receives 2.4 Gy without and 1.2 Gy with respiratory gating (p=0.0001) with a mean maximal dose of 39.6 Gy without and 10.1 Gy with respiratory gating (p=0.0004). Conclusion: 4D analysis has shown that the distance between the PTV and the heart is influenced by two separate parameters. Besides the movements of the chest wall the heart is pushed into the irradiated volume also by the diaphragm. Respiratory gating and irradiation only in the inspiratory phase significantly reduces radiation doses to the heart and especially to the anterior heart wall.
SU‐FF‐T‐430: The Use of Fricke Solutions to Assess Light Dose in Photodynamic Therapy
Authors: Austerlitz C , Mota H , Souza V , Campos D , Bagnato V , Allison R , Sibata C
Published: July 2006

Purpose: To study the response of a Fricke solution doped with Photogem® to laser beams and light emitting diodes due to reactive radicals produced in Photodynamic Therapy (PDT). Method and Materials: The Fricke solution was prepared with 0.392 g of ferrous ammonium sulphate, 0.060 g of sodium chloride, 22 mL of sulphuric acid and made up to a volumetric flask of 1,000 mL with Milli‐Q water. The Photogem®‐doped Fricke solution was prepared by adding 0.0015 g of Photogem® to 1 liter of Fricke solution obtaining a concentration equivalent to what is employed for photodynamic therapy of tumors (4 mg/l). The solution was irradiated with laser beams and light emitting diode using radiant exposures up to 1300 Jcm−2. The effect of laser irradiation on the solutions was evaluated by spectrophotometric technique. Results: Examination of spectrometric data have shown that Fricke solutions doped with Photogem® present a linear increase in their optical density at 304 nm as a function of the radiant exposure of light sources which ranged between 514 and 640 nm. The efficiency of producing Fe3+ is dependent on the wavelength of the laser, being higher at 514 nm where this photosensitizer has the highest absorbance. Conclusions: The results obtained in this work indicate that Photogem®‐doped Fricke solution may be used in PDT quality assurance to verify the consistency of the light sources and the photosensitizer solution used in a given treatment. The use of this method to quantify the combined effect of the interaction of light beams with photosensitizers in different protocols is discussed. It is hypothesized that a possible relation exists between the efficacy of PDT to the concentration of ferric ions formed in the Fricke system.
SU‐FF‐T‐438: Treatment Planning Study of Prostate Cancer IMRT with a Flattening Filter Free Accelerator
Authors: Kry S , Vassiliev O , Kuban D , Poenisch F , Salehpour M , Gillin M , Mohan R , Titt U
Published: July 2006

Purpose: IMRT is a common treatment modality for prostate radiotherapy. With IMRT, the optimization of the fluence map renders the flattening filter unnecessary. Flattening‐filter free therapy for IMRT has been investigated recently, but clinical evaluations have not been conducted. In this study we compare IMRT treatment plans for prostate therapy generated with and without a flattening filter. Methods and Materials: IMRT plans were generated at 6MV for 4 early stage prostate patients using clinical dose prescriptions. Plans were generated with Eclipse 8.0 (Varian Medical Systems), which we commissioned with beam data measured on a Clinac 21EX operated with and without the flattening filter. For each patient two plans were generated, one with and one without the flattening filter. The plan DVHs were normalized so 98% of the PTV received 75.6 Gy. Results: Plans using the unflattened beam required 2 times fewer monitor units (on average) than plans using the flattened beam. Treatment plans using the unflattened beam had more homogeneous PTV coverage. The average maximum dose was 81.0 (0.6) Gy for the unflattened beam and 84.2 (0.6) Gy for the flattened beam. The average minimum dose was 70.5 (0.8) Gy for the unflattened beam and 71.2 (0.8) Gy for the flattened beam. DVHs showed nearly identical doses to critical structures between flattened and unflattened treatments. Conclusion: Clinically acceptable IMRT plans for prostate cancer can be developed with unflattened beams. They require substantially fewer monitor units than comparable treatments with conventional flattened beams while generating more homogenous PTV coverage. Conflict of Interest: Research sponsored by Varian Medical Systems.
SU‐FF‐T‐443: Use of Minimum Intensity Projection for Target Volume Delineation in 4D‐CT Using Contrast for Liver Cancer
Authors: Tsunashima Y , Beddar A , Briere T , Krishnan S , Tolani N , Starkschall G , Gillin M , Mohan R
Published: July 2006

Purpose: To investigate the use of the minimum intensity projection (minIP) methodology for the accurate and rapid generation of internal target volumes (ITVs) in four‐dimensional CT (4D‐CT) scans using IV contrast for Liver Cancer. Single (4D‐CT) scans reliably capture intrafractional tumor mobility for radiotherapy planning, but generating the ITVs requires the contouring of gross tumor volumes (GTVs) in up to 10 respiratory phases. The use of maximum intensity projection (MIP) protocols for the generation of ITVs in Lung has been recently shown to be reliable, but cannot be used for Liver due to the use of contrast agents. Method and Materials: We obtained the 10‐phase ITVs using the 4D‐CT data sets contoured by one physician using Pinnacle. The ITVs generated from the minIP volume data sets were determined by automatic contouring. Comparison of the ITVs was performed by focusing on the tumor volumes and voxel positions. Results: The results showed that the differences in the tumor volumes were slight in the lower lobe of the liver. In the upper lobe of the liver, however, we observed a significant difference in tumor volumes between the ITVs. This is because the minIP algorithm systematically chooses the lowest CT value in each 10‐phase voxel set, which leads to a preferential selection of lung tissue over liver tissue in the diaphragm region. In the lower lobe of the liver, the tissue is basically liver or tumor, and so tissue selection should generally not be as complex. Conclusion: The minIP algorithm has not been shown to be robust for the delineation of liver tumors located near the top of the diaphragm. In the rare occasion where there is bowel including gas is located near the liver tumor, we predict the minIP may also be inadequate for the tumor delineation.
SU‐FF‐T‐444: Use of the Gamma Index to Evaluate the Dosimetric Characteristics of X‐Rays Beams in Radiotherapy: Implementation to a LINAC Monte Carlo Simulation
Authors: Blazy L , Beaumont S , Bordy JM
Published: July 2006

Purpose: From IEC 976 and 977, the dose distributions quality for x‐rays beams from LINAC gets through the fulfilment of four parameters. This work is aimed at replacing these dosimetric tests by one parameter (gamma index) and using this concept to validate Monte Carlo simulated beams. Method and Materials: From measurements of a 12 MV beam of a medical LINAC, analytical functions have been set to fit reference depth‐dose and profile distributions. Then, those 1D distributions have been altered to reach the admissible limits of the IEC standard criteria. The peculiar tolerance criteria of the gamma index have been determined by comparing altered and reference distributions. This 12 MV beam have been simulated with the Monte Carlo code PENELOPE for different incident electron configurations at the target. The simulations have been fitted with polynomial functions to get better resolution before being compared to measurements using the gamma index to avoid false positives or false negatives due to a lack of spatial resolution in these simulations. Results: The tolerance criteria for the gamma index have been determined experimentally by comparison with the IEC standard requirements. They are more restrictive by nature than the IEC criteria. This unified concept of dosimetric tests by the systematic use of the gamma index enabled us to select effectively the parameters for the beam simulation. Conclusion: This work shows the possibility of using only one test for all the measurements required for x‐rays beam QA and its Monte Carlo simulations. In the future, this work will lead to the implementation of a set of simulations in order to replace measurements required for the quality control of the Treatment Planning System. Evaluation tests should be based on the calculation of the 3D gamma index to simplify test processes.
SU‐FF‐T‐454: Video‐Coaching as a Biofeedback Tool to Improve Gated Treatments
Authors: Cossmann PH , Stuessi A , von Briel C
Published: July 2006

Purpose: Gated treatments using the Varian RPM—gating™ System include in a standard configuration a coaching tool based on voice commands (“breathe‐in”/“breathe‐out”) called audio‐coaching. As this configuration does not include feedback information like amplitude and breathing period, there are limitations concerning respiration depth and breathing pattern. The aim of this study was to evaluate the impact of video‐coaching as biofeedback to improve gated treatments of breast cancer. Method and Materials: Varian RPM‐gating system is used for acquisition of the CT‐Scan (4D‐CT) as well as the treatments; for the latter it manages the controlled switching of the radiation beam during a pre‐selected specific phase of the respiratory cycle. 100 patients with gated treatments have been analyzed, whereas 50 were only audio‐coached and 50 audio‐coached with video‐feedback. We evaluated periodicity and amplitude changes as well as compliance with regard to the theoretically calculated duty cycle and determined the dependency of the parameters on the coaching type. Results: For the CT acquisition several changes has been observed, i.e. amplitude fluctuations are significantly smaller (p=0.005) and the breathing curves are smoother. This leads to an increased compliance during the treatment course: almost all video‐coached patients reached in average their theoretical duty cycle, whereas 60% of the patients with audio‐coaching only had more than 25% longer treatment times due to inappropriate amplitudes. Periodicity is not dependent on the kind of coaching (p=0.01). Conclusion: Video‐coaching is suitable to significantly improve the quality of 4D scans and allows optimizing the treatment time due to better compliance. In a next step we are currently implementing this feedback technology combined with deep inspiration breath hold technique thus allowing the patient to control the treatment themselves in a direct way. Preliminary results indicate that this approach could suit the individual patient need in a better way.
MO‐B‐230A‐01: AAPM TG‐43 Update for 2004 and Beyond
Authors: Rivard MJ , Butler WM , DeWerd LA , Huq MS , Ibbott GS , Melhus CS , Mitch MG , Nath R , Williamson JF
Published: July 2006

Since publication of the 2004 update to the American Association of Physicists in Medicine (AAPM) Task Group No. 43 Report (AAPM TG‐ 43U1), several new low‐energy photon‐emitting brachytherapy sources have become available. Many of these sources have satisfied the AAPM prerequisites for routine clinical use as of January 10th, 2005, and are posted on the Joint AAPM/RPC Brachytherapy Seed Registry. Consequently, the AAPM has prepared this supplement to the 2004 AAPM TG‐43 update. This paper presents the AAPM‐approved consensus datasets for these sources, and includes the following 125I sources: Amersham model 6733, Draximage model LS‐1, Implant Sciences model 3500, IBt model 1251L, IsoAid model IAI‐125A, Mentor model SL‐125/SH‐125, and SourceTech Medical model STM1251. The Best Medical model 2335 103Pd source is also included. While the methodology used to determine these datasets is identical to that published in the AAPM TG‐ 43U1 report, additional information and discussion are presented here on some questions that arose since the publication of the TG‐43U1 report. Specifically details of interpolation and extrapolation methods are described further. Despite these small changes, additions, and clarifications, the overall methodology, the procedures for developing consensus datasets and the dose calculation formalism remain the same as in the TG‐43U1 report. Thus, the AAPM recommends that the consensus datasets and resultant source‐specific dose‐rate distributions included in this supplement be adopted by all end users for clinical treatment planning of low‐energy photon‐emitting brachytherapy sources. Adoption of these recommendations may result in changes to patient dose calculations, and these changes should be carefully evaluated and reviewed with the radiation oncologist prior to implementation of the current protocol.
MO‐D‐330A‐04: Exploitation of Data Redundancy in a Reduced Fan‐Beam Scan
Authors: Xia D , Zou Y , Yu L , Pan X
Published: July 2006

Purpose: We aim to devise new weighting schemes to improve the signalto‐noise ratio (SNR) in images reconstructed from data acquired in reduced fan‐beam scans by fully utilizing the redundant information. Method and Materials: Recently, we have developed a backprojection‐filtration (BPF) algorithm, which can reconstruct ROI‐images from the transversely truncated data in a reduced‐scan with a scanning angular range less than that in a short‐scan. However, the measured data in a practical reduced scan contain some redundant information. In this work, we devised two weighting schemes to appropriately incorporate the redundant data. Applying the weighting schemes to the BPF algorithm, we derived two new algorithms, derivative of weighted BPF (WD‐BPF) and weighted‐derivative BPF (DW‐BPF) algorithms. Both of these two algorithms can be used to improve the SNR in reconstructed images. Results: The ROI‐images are reconstructed from the truncated projection data in a short‐scan and a reduced‐scan, respectively. For the reduced‐scan, some shading artifacts appear in the images reconstructed by use of the WD‐BPF algorithm. This is caused by the numerical error in the derivative of the discontinuous weighting function. In contrast, artifact‐free images can be obtained by use of the DW‐BPF algorithm. For the short‐scan, both algorithms can obtain artifact‐free images, because the weighting function is smooth. The results in the noise study show that image noise obtained by use of WD‐BPF and DW‐BPF algorithms are similar within the ROI. Conclusion: We propose two weighting schemes for handling the data redundancy in reduced‐scan fan‐beam CT. Our results demonstrate that the proposed two algorithms can utilize the redundant data to improve the signal‐noise ratio. Moreover, the noise properties of these two algorithms are similar to each other.