bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐J‐114: Reduction of Respiratory Motion Using Diaphragm Compression and Gating for Hypofractionated Radiotherapy of Lung and Liver Cancer
Authors: Shen S , Duan J , Spencer S , Fiveash J , Ye S , Wu X , Popple R , Pareek P , Brezovich I
Published: July 2006

Purpose: Hypofractionated radiotherapy for lung and liver cancer has received great attention recently because of possible improved efficacy and convenient treatment length. Respiratory motion presents a special challenge, as hypofractionated radiotherapy requires a high level of confidence in image targeting and delivery. This study evaluates reduction of respiratory motion using combined diaphragm compression and gating. Method and Materials: Patients received either 45 or 60 Gy in 3 fractions. Patients were immobilized with customized Alpha Cradles body cast and a vac bag on abdomen and pelvis. The vac bag served for diaphragm compression and position immobilization. Gated CT data were first acquired at the end‐of‐expiration and then at the end‐of‐inspiration 30 minutes later using a commercial gating system. These two CT data sets were registered and positional changes in target were evaluated to estimate residual target motion during gating using scaling factor derived from external marker motion track and gating amplitude. Portal images were acquired for each fraction using manual gating at the end‐of‐expiration with the guide of the gating system. Results: In this ongoing study, we have treated 3 lung cancer and 2 liver cancer patients. The mean difference in CT lung volume between end‐of‐expiration and end‐of‐inspiration was 10.5% (range 7.7– 15.5%). The mean differences in position of GTV mass center was 1.5 (range 0.2–2.9 mm) in lateral, 3.3 (range 1.3–7.4 mm) in anterior‐posterior, 3.5 (range 0.4–9.0 mm) in superior‐inferior. The residual target motion during gating was 0.5 (range 0.1–1.0 mm) in lateral, 1.1 (range 0.4–2.4 mm) in anterior‐posterior, 1.1 (range 0.2–3.0 mm) in superior‐inferior. For tumors visualized in portal images, target‐to‐lung positions were reproducible in 2 mm. Conclusion: Combined with diaphragm compression and gating and daily imaging, respiratory motion has been effectively reduced to a minimal residual motion during gating, suggesting that CTV‐PTV margin reduction may be feasible.
SU‐FF‐J‐115: Registering the Planning CT to the Treatment Geometry in IGRT, Using a Limited Reconstructed Volume Derived From Planar Images
Authors: Zaini M , Forest G , Mosentine W
Published: July 2006

A set of megavoltage (MV) and kilovoltage (kV) images are obtained during a patient's image‐guided radiotherapy treatment (IGRT). The kV images are acquired prior to treating the fields using an on‐board x‐ray imager. However, The MV images can be acquired both prior and during the actual treatments. Fan‐beam reconstruction of back‐projected kV images obtained at four or more gantry angles can be used to orient the planning CT to match the treatment geometry. Registering the planning CT to the treatment geometry is necessary if one is to perform dose reconstruction using the multi‐planar images and the planning CT, in the absence of a cone beam CT. The MV and kV images provide the exit fluence information for 3D dose reconstruction. Using these 2D treatment images along with the 3D planning CT volume provides adequate information about the treatment anatomy that is needed for the dose reconstruction process. This system might alleviate the need for cone beam CT for patient positioning and/or dose reconstruction. The planar treatment images provide adequately sampled sinogram planes in the spatial dimension, but not in the radial direction. Nonetheless, there is enough data in the sinogram space for registering the treatment geometry to the planning CT. Canny edge finding method is used to decipher anatomical structure in the limited reconstructed volume as well as in the CT volume. This technique can detect both strong and weak edges; and it is less likely than the other edge finding techniques to be fooled by noise. The resulting edge maps are registered to each other by affine transformations. The transformation matrices are then applied to the CT volume in order to register it to the treatment geometry.
SU‐FF‐J‐116: Registration of X‐Ray Portal Images with 4DCT DRRs for Patient Setup Verification
Authors: Xu Q , He Z , Hamilton R , Xing L
Published: July 2006

Purpose: To provide a noninvasive method for both setup verification of 4DCT treatment planning and isocenter positioning shifts for treatment delivery. Method and Materials: A ten phase 4DCT treatment planning study of the patient was acquired using a respiratory gating system. When the patient was on the treatment couch, multiple on board x‐ray images were taken in the anterior‐posterior (AP) and lateral directions. An intensity based rigid registration algorithm was applied to obtain optimal shifts in the x, y and z directions. First, a digitally reconstructed radiograph (DRR) using ray‐casting algorithm was computed from one of the ten phases of the 4DCT. The correlation coefficient (CC) between the DRR and the x‐ray image was then calculated. The 4DCT volume was shifted and new DRRs were generated until the maximum CC value was reached through an optimization process. This procedure was repeated for all ten 4DCT phases. Results: Registration of each phase of the 4DCT with the x‐ray image provided ten maximum CC values. These values exhibited a single maximum at the phase corresponding to the breathing phase when the x‐ray image was taken. The corresponding isocenter positioning shifts for treatment delivery were also obtained. The robustness of our algorithm was demonstrated by registering x‐ray images taken at five random phases to 4DCT. The resulting isocenter shifts were consistent between all phases. The standard deviations of the shifts determined for the AP x‐rays were 2 mm (lateral), 5 mm (anterior‐posterior), and 2 mm (superior‐inferior). Conclusion: Using only the RPM system, one cannot be certain that the internal anatomy is consistent between 4DCT acquisition and any particular treatment day. Our noninvasive method accounts for internal organ motion and may be used for daily 4DCT treatment setup verification and isocenter positioning.
SU‐FF‐J‐117: Respiration Monitoring Using Radiotherapy Treatment Beam
Authors: Chen Q , Lu W , Chen M , Ruchala K , Olivera G
Published: July 2006

Purpose: Real‐time monitoring intra‐fraction motion is essential for four‐dimensional (4D) radiotherapy. Surrogate‐based and internal‐fiducial‐based methods may suffer from drawbacks such as false correlations, being invasive, delivering extra patient radiation, or require additional hardware. We developed a non‐surrogate, non‐invasive method to real time monitor respiratory motion during radiotherapy treatments. This method directly utilizes the treatment beam and thus imposes no extra radiation to the patient. Method and Materials: The method requires a real time detector system and a 4DCT image. The basic idea is to correlate the real‐time measured detector signal from the treatment beam with the pre‐calculated signals assuming that beam passed through the different phase of 4DCT image. The on‐line processes only involve detector signal readout, and 1D correlation of the measured signal with the pre‐calculated signals. The respiration phase is determined as the position of peak correlation. The method was tested with extensive simulations based on a 4DCT of a lung cancer patient. Three different IMRT delivery fluence maps were used. Three arbitrary breathing patterns and two dose levels, 2Gy/fraction and 2cGy/fraction, were used to study the robustness of this method against detector quantum noise. Results: For the 2Gy/fraction simulations, the respiration phases were accurately determined in real‐time for most projections of the treatment, except for a few projections in which beam intensities were extremely low. At 2cGy/fraction dose level, the method can still determine the respiration phase very well with only about 5% of projections having errors greater than 1 phase (0.5 second). Conclusion: It is demonstrated that our method can monitor the respiratory motion within +/−1 phase in real time. This method can be easily implemented in any radiotherapy machine with high speed detector system. The motion information obtained can be used to either verify or correct the treatment delivery in real‐time.
SU‐FF‐J‐118: Respiration Phase‐Based Cone‐Beam Computed Tomography (CBCT) Reconstruction
Authors: Yan H , Godfrey D , Yin F
Published: July 2006

Purpose: To develop a method to reconstruct CBCT data based on projection data acquired at a specific respiration phase. Methods and Materials: The original projection data were acquired using an on‐board imager (OBI) (Varian Medical Systems) over scanning angles from 0° to 360° with 0.5° interval. During the retrospective process, the diaphragm location on each projection image was identified by contrasting the surrounding anatomies. Based on the location of the diaphragm in different respiration phases, the projection data were categorized into respective subsets. Subsequently, the CBCT was reconstructed from the projection data in each subset, using a Feldkamp CBCT reconstruction algorithm. Results: The CBCT was reconstructed based on a subset of projection data (single sampling) acquired at the end point of exhalation, which shows the least motion of the diaphragm. In addition, as an extension, the neighboring 1 or 2 projections were also included in the reconstruction scheme (multiple sampling). The preliminary results show that with a single sampling scheme, the reconstructed CBCT image quality is coarse but the implanted staple and bony structures are clearer. When multiple sampling schemes were used, the image quality is better but with increased blurring effect and motion artifact. Conclusion: Compared with CBCT conventionally reconstructed for full scan images, the phase‐based CBCT provided a sub‐optimal option for clinical use. Although the image were imperfectly reconstructed due to the substantially decreased number of projections, a significant reduction of radiation exposure, improvement on blurring and motion artifacts is achieved. In the future, the synchronized respiratory signal (such as RPM signal) could be used to sort the projections for this purpose. This study is partially supported by Varian research grant.
SU‐FF‐J‐119: Respiratory Gating with Gantry Mounted Fluoroscopic Imaging
Authors: Sharp G , Jeung A , Tang X , Mostafavi H , Chen G , Jiang S
Published: July 2006

Purpose: To perform respiratory‐gated treatment based on the position of implanted markers in fluoroscopy using a gantry mounted x‐ray imaging system. Method and Material: We have designed hardware and software capable of gated treatment using the position of implanted markers. The system tracks the position of the marker in real‐time using fluoroscopic imaging. Tracking can be done in a single image, for 2D position information, or can be done simultaneously in a pair of orthogonal images, for 3D position information. When the marker is in the treatment window, the linear accelerator is signaled to deliver the beam. A live display of the fluoroscopy is used to initiate tracking, and to verify tracking and gating operation. Results: Gated treatment was performed on a moving phantom, with 3 cm peak‐to‐peak motion and a 4 mm gating window for internal motion. Fluoroscopy was acquired at a rate of 7.5 frames per second. The system latency from image acquisition to gating was roughly estimated to be approximately 50 ms. Gating operation was tested by delivering 4×4 cm open fields, and tracking the position of a 2mm steel marker in fluoroscopy. This initial position of the marker was assigned interactively. Treatment was delivered successfully for each field, despite some image degradation due to scatter from the MV treatment beam. The dosimetry of the gated treatment was measured in film, and compares well with the non‐gated treatment of a static phantom. Conflict of Interest: Research sponsored by Varian Medical Systems.
SU‐FF‐J‐121: Retrospective Analysis of Prostate Cancer Patients with Fiducial Gold Markers Using a Real‐Time Tumor Tracking System
Authors: Oita M , Osaka Y , Onimaru R , Onodera S , Fujita K , Saito E , Shirato H
Published: July 2006

Purpose: The aim of this study was to measure interfraction and intrafraction motion of the prostate during the course of radiation treatment using a real‐time tumor tracking system (RTRT‐system) and gold fiducial markers. Method and Materials: Fifty‐five patients underwent implantation with three 2‐mm gold markers in the prostate before IMRT treatment planning CT scans. Using a RTRT‐system, fluoroscopic images were taken after a) skin‐based patient's positioning and b) translational repositioning by moving a couch after a calculation of actual and planned positions of three gold markers. Intrafraction as well as interfraction translation and rotations were analyzed along the three axes (right‐left[RL], cranio‐caudal[CC], antero‐posterior[AP]). Systematic and random errors were computed for these translations and rotations in (a)conventional setup and (b)RTRT setup. To determine adequate margins for these setup, van Herks's formula of were used. Results: Without consideration of interfraction errors, prostate treatment would have required average margin of 9.8, 14.3 and 12.5mm (n=1466) about the right‐left(RL), craniao‐caudal(CC), and antero‐posterior(AP) directions, respectively for skin‐based patient's positioning. Interfractional random rotation error was 5.9°(systematic error, 8.6°) around RL axis, 3.1°(systematic error, 5.5°) around CC axis, and 5.1°(systematic error, 5.4°) around AP axis. Inclusion of intrafraction movement increases these margins to 11.0, 15.3, and 13.1mm, respectively (n=2905). Intrafractional and inter‐beam adjustment further reduced margins to an average of 2.1, 2.5 and 2.3mm, respectively, based on a threshold of 3mm for each direction. Conclusion: Monitoring and correction of the intrafraction movement for prostate treatment using this system, significant reduction of margins would have achieved. However, the interfraction as well as intrafraction rotations of the prostate should be taken into account for the additional margins because their magnitudes are not negligible. Conflict of Interest: The authors indicated no potential conflicts of interest.
SU‐FF‐J‐124: The Hounsfield Unit (HU) Accuracy in Varian's Cone‐Beam CT (CBCT) and Its Effect On Dosimetric Verification
Authors: Dong H , Hammoud R , Li S , Chen Q , Guan H
Published: July 2006

Purpose: To evaluate the HU accuracy of Varian's on board CBCT and its effect on the accuracy of dose calculation for dosimetric verification. Methods and Materials: A mini CT QC phantom (15cm diameter, 2cm thickness) with different inserts (2cm diameter) of known electron densities was embedded into an IMRT QA phantom to form a body phantom and scanned using CBCT. The scan was acquired in half‐fan and pulsed‐fluoro mode with a half bowtie mounted. A technical setting of 125kV, 80mA and 25ms was used. The HU for each insert was measured and the HU‐ED curve for CBCT was obtained. After that, a Rando pelvic phantom was scanned with both CBCT and SIM‐CT using nearly the same KV. The two sets of CT were fused so that SSD at any beam direction agree to 1mm. In this way, the structures drawn in SIM‐CT (to simulate prostate treatment) can be exactly transferred to CBCT. Without inhomgeneity correction; the two sets of CT generate exactly the same plan. With inhomogeneity correction, the dosimetric difference was mainly from the HU difference. Results: The average HU difference between CBCT and SIM‐CT is ∼50 but the standard deviation of HU in CBCT is 3–4 times higher. Due to higher beam hardening effect in CBCT, the HU at phantom center is 60–80 higher than that at edges. There is also a ring artifact of 20cm diameter and 1.5cm broad in which the HU is 200 lower. Even though, the dosimetric difference with inhomogeneity correction is relatively small. The minimum dose, maximum dose and mean dose etc. for any structure generally agrees within ∼2–5% between the CBCT plan and the SIM‐CT plan. The CBCT plan is ∼2% hotter at the phantom center. Conclusions: Dosimetric difference between CBCT and SIM‐CT is ∼2–5% due to the inaccurate HU in CBCT.
SU‐FF‐J‐125: Therapy Assessment Using a Full Time Point (fTP) Pharmacokinetic Analysis of Dynamic Contrast‐Enhanced Magnetic Resonance Imaging (DCE‐MRI): Role of Region of Interest (ROI) Selection in Three Tumor Sites
Authors: Craciunescu O , Raidy T , Brizel D , Blackwell K , Vujaskovic Z , Wong T , Jones E , Larrier N , MacFall J , Dewhirst M
Published: July 2006

Background: DCE‐MRI has great potential to provide routine assessment of cancer treatment response. The contrast agent preferentially accumulates in tumors due to increased tumor vascular permeability. The MR based parameters that can be used for treatment assessment (permeability and leakage space) can be averaged over the whole tumor or over a maximum enhancement ROI. The optimal method of analysis is controversial. Material and Methods: DCE‐MR images of selective head and neck, breast and extremity sarcoma patients were acquired on a 1.5T GE Signa Exite scanner before and after different therapy regimens (concurrent chemoradiation for head and neck, neoadjuvant and hyperthermia for breast, and radiation and hyperthermia for extremity sarcomas). The images were analyzed using an fTP pharmacokinetic analysis implemented by CAD Sciences® (White Plains, NY) that determines the tumor's permeability (PERM) and extracellular volume fraction (EVF). ROIs were defined over the entire extent of the tumor (Tumor ROI) and over areas that show maximum enhancement (MaxEnhROI). For head and neck cases, MaxEnhROI were carefully selected not to include fast enhancing arteries which can bias the averaging. Results: For all three tumor types, the trends of PERM and EVF change are the same, but the absolute changes are not. Larger differences are seen in tumors that have peripheral enhancement and large necrotic areas (found often in head and neck and extremity sarcomas). As expected, for homogeneous enhancing tumors (rarely encountered), the differences are not significant. Conclusions: Preliminary results show that ROI selection is important in MR parameter averaging, particularly if the quantitative analysis is used for therapy assessment. This statement is true for all the three sites considered. Although DCE‐MRI has great potential to provide routine assessment of cancer treatment response, its widespread application should be standardized for clinical use. Supported in part by grant NCI CA42745.
SU‐FF‐J‐126: Treatment of Moving Targets with Scanned Ion Beams: A Comparison of Different Strategies
Authors: Bert C , Rietzel E , Haberer T , Chen G , Kraft G
Published: July 2006

Purpose: To compare internal target volume (ITV), gating, rescanning, and motion compensation (tracking) for treating moving targets with a scanned carbon ion beam based on time‐resolved computed tomography (4DCT) data for 4 patients. Method and Materials: The GSI treatment planning system TRiP has been extended to calculate dose distributions in the presence of motion. Calculations are based on 4DCT data and corresponding deformation maps. To account for respiratory target motion and time dependent irradiation with a scanned carbon ion pencil beam, the treatment plan is temporally divided into sub‐plans. Treatment plans were generated for 4 lung‐tumor patients. Each plan consists of 1 field to the CTV with margins appropriate for tumor motion. For each patient and technique, 12 combinations of respiratory period and initial breathing phase were studied. Total dose distributions under respiratory motion were compared to a reference treatment plan at end‐exhale (without motion) by dose volume histograms and mean lung doses. Results: The ITV concept showed severe misdosage caused by interplay between target motion and scanned ion beam. Gating, rescanning (30×), and motion compensation resulted in adequate target coverage for all patients. In comparison to the reference, mean lung dose was similar for motion compensation, but increased by 10–15% for gating, and by ∼40% for rescanning. Conclusion: An ITV treatment strategy results in severe under‐ and over‐dosage of moving targets. Gating, rescanning, and motion compensation assure target coverage. Mean lung dose is increased for gating and rescanning.
SU‐FF‐J‐127: Two‐Dimesional Analysis of Patient Cervical Spine Movement Pattern During Radiation Therapy
Authors: Zhou X , Zhu T
Published: July 2006

Purpose: To characterize the two dimensional movement pattern of cervical spine during head and neck radiation treatment with the aim to adaptively modify the treatment. Method and Materials: An intensity based algorithm was used to extract the vertebrae contours in both diagnosis CT and treatment planning CT images. Vertebrae movement variables were characterized by superimposing segmented sagital CT images using a localized linear conformal registration. The correlation coefficient was used as a method of measuring the similarity for registration. Relative 2‐D motion of cervical spine were characterized by a transformation matrix representing motion relative to the adjacent vertebrae with 3 degrees of freedom by rigid body Euler angle and translations of orthogonal coordinate system. Results: We demonstrated that an intensity‐based local linear conformal registration can be used accurately co‐registered cervical spine in the treatment planning CT images acquired before the treatment and in the diagnosis CT images. A large variation was observed in the transformation matrix. The mean absolute Euler rotation of vertebrae were 25.4° for C2, 18.9° for C3, 13.7° for C4, 11.3° for C5, 5.3° for C6 and 7.6° for C7. Conclusion: We have quantitatively analyzed the intervertebral motions of the cervical spine during the radiation treatment. We have documented the first accurate depictions of cervical spine coupled motion. This information can be used for treatment planning in an adaptive CT‐guided radiation therapy.
SU‐FF‐J‐128: Uncertainties in Target Volume Surrogates in Image Guided External Beam Partial Breast Irradiation
Authors: Gierga DP , Turcotte JC , Sharp GC , Riboldi M , Franke A , Jiang SB , Chen GTY
Published: July 2006

Purpose: Two methods of image guidance for external beam partial breast irradiation (PBI) are under investigation: kilovoltage (kV) imaging and video‐based three‐dimensional (3D) surface imaging. Kilovoltage imaging utilizes implanted clips as surrogates for the target volume (seroma). Surface imaging uses the breast surface as a surrogate for the target volume. This study investigates the uncertainties present when utilizing such surrogates in image‐guided external beam PBI. Method and Materials: Patients were treated on a linear accelerator with dual gantry‐mounted kV imagers. Patients were initially aligned using lasers, and simultaneous orthogonal kV images were taken prior to each fraction to correct the setup. Setup corrections were calculated using software that registered the clips in the daily images with their corresponding positions in digitally reconstructed radiographs. Clip migration was examined by quantifying variations in the position of individual clips relative to the center of mass of all clips. Surface video images were also taken for each treatment. The breast surface from each treatment position was registered to the reference surface. Surface deformations were quantified by calculating the distribution of position differences for each vertex on the 3D surface. Results: The standard deviation in individual clip positions ranged from less than 1 mm to as much as 2 mm. For the surface deformation, the mean difference between surface vertices was 0.6 mm (range 0.4 to 1.0 mm). The standard deviation of the distribution of surface differences, used as a measure of the distribution width, ranged from 0.5 mm to 1.2 mm. The amount of deformation of the breast did correlate with breast size. Conclusion: The uncertainties in target volume surrogates for both clip‐based kV imaging and video‐based surface matching are small, typically on the order of a few mm. The precision of these surrogates indicates that they can reliably be used for image‐guided treatment.
SU‐FF‐J‐129: Using Cone Beam CT to Investigate the Local Geometrical Uncertainties During Head and Neck Radiation Therapy
Authors: Zeng G , Breen S , Jaffray D , Bayley A , White E , Keller H
Published: July 2006

Purpose: To develop a model to quantify the local displacements, rotations and deformations in head and neck during the treatment course using Cone Beam CT (CBCT). Methods: Five patients underwent weekly CBCTs, immobilized in head and shoulder thermoplastic masks (MedTech®, Orange City, USA). CBCT images were registered to the planning CT by matching the clivus and occipital bone. Eight points located at visibly distinguishable bony landmarks in the head were identified on all images. The displacements of the CBCT points relative to the CT were computed. Head rotation was calculated from the angular change of a plane constituted by three rigid bony points. The spinal canal was contoured in all the image sets and the geometrical centroid line was used as the cord surrogate. The cord deformation relative to the CT was quantified by the variation of the centroid lines.

Results: The means of the inter‐fraction displacements, varied between −0.3 and 0.3 cm (standard deviations range from 0.02 to 0.3 cm), for all bony landmark points of each patient. Centrally located points have smaller displacements (mean between −0.1 to 0.1 cm) than circumferential points. The inter‐fraction average head spin (rotation in axial plane) was 2 degrees, while the rotations in the saggital and coronal planes were 4 degrees on average. Cord deformation was minimal superiorly (mean ranged over −0.1 to 0.1 cm) and increased inferiorly to the range of −0.3 to 0.4 cm (standard deviation, 0.3 cm). The deformation was larger in the sagittal plane than in the coronal plane. Conclusion: Sequential CBCTs enable the analysis of the spatial displacements in the head and neck. This method can be used to develop localized treatment margins for this patient population and immobilization technique.
SU‐FF‐J‐130: Validation of Non‐Linear Image Registration‐Based Correction Method for Motion Artifacts in 4D‐CT
Authors: Heath E , Keall P , Collins L , DeBlois F , Seuntjens J
Published: July 2006

Purpose: Motion artifacts in CT can be reduced by using 4D‐CT acquisition techniques where image slices are retrospectively binned according to breathing phase as determined by a breathing trace. However, motion artifacts may still occur due to breathing irregularities. Such artifacts affect organ delineation and lead to complications when using 4D CT data for dose calculation and accumulation. We propose a method for correcting such artifacts by temporal interpolation using non‐linear image registration. Method and Materials: The ANIMAL non‐linear image registration algorithm was used to determine the transformation between artifact‐free phases adjacent to the phase containing the motion artifacts. The weighting factor which, when applied to the transformation, most closely reconstructs the anatomy at the phase to be corrected was determined. CT values in regions of the image containing the artifacts were then replaced with the corresponding CT values from the reconstructed image. The accuracy of the temporal interpolation method was evaluated by simulating motion artifacts resulting from different breathing amplitudes using the NCAT numerical breathing phantom for which the artifact‐free image is available by definition. The reconstructed image was compared to the artifact‐free image. The temporal interpolation method was applied to correct motion artifacts in patient 4D CT data and the corrected images were compared to physician‐delineated contours. Results: Correlation between the NCAT phantom images with and without artifacts was improved from 0.971 to 0.992 after correction of the artifacts by temporal interpolation. The quality of the patient 4D CT data was improved after temporal interpolation and the reconstructed anatomy was consistent with manual contours. Conclusion: We have developed a method for reconstructing anatomy on 4D CT images in the presence of motion artifacts. The temporal interpolation method was demonstrated to reduce the appearance of these artifacts and therefore improve the accuracy of organ delineation and dose calculation.
SU‐FF‐J‐131: Is There a Relationship Between Body Mass Index, Treatment Set‐Up Errors, and the Development of Myocardial Perfusion Defects Following Radiation Therapy for Left‐Sided Breast Cancer?
Authors: Evans E , Yu X , Prosnitz R , Zhou S , Wong T , Light K , Hardenbergh P , Blazing M , Marks L
Published: July 2006

Purpose: To assess whether body mass index (BMI) affects the rate of “deep” set‐up errors (i.e. those that increase the volume of heart irradiated), resulting in an increased risk of RT‐induced myocardial perfusion defects (PD) 6–60 months post‐RT. Materials and Methods: For 87 patients receiving RT for left‐sided breast cancer, treatment set‐up accuracy was determined by measuring the height of the lung shadow seen at the level of the central axis on simulation and serial medial tangent portal films. SPECT nuclear medicine scans were performed serially pre‐ and post‐RT to assess for cardiac PD. The interaction among BMI, set‐up error frequency, and the rate of PD was compared using a 1‐tailed Fisher's Exact Test. Results: The rates of deep set‐up deviations were 9/32 vs. 24/51 in patients with BMI<25 kg/m2 and ⩾25 kg/m2, respectively (p=0.068) (Fig 1). When patients were stratified by volume of left ventricle (% LV) in the RT field, set‐up deviations had an impact on the rate of PD in patients with >0% but ⩽1% LV in the field (i.e. patients who are generally predicted to be at very low risk for RT‐induced cardiac dysfunction). The rates of PD in these patients with deep vs. “shallow” set‐up errors (i.e. those that decrease the volume of heart irradiated) were 5/6 vs. 3/10 (p=0.059) (Fig 2). Conclusions: Patients with BMI⩾25 kg/m2 tend to have a higher incidence of deep set‐up errors, causing more heart to be irradiated than intended. In patients with very small volumes of heart in the RT field, those with deep set‐up errors are more likely to have PD post‐RT. Accurate patient set‐up on the treatment machine is critical to minimize the risk of RT‐induced cardiac injury, particularly in overweight and obese patients. Supported by grants 17‐98‐1‐8071 and BC010663 from the DOD.
SU‐FF‐T‐03: 3‐D Dosimetric Evaluation On Isocenter Positioning Error in the Dynamic Arc Stereotactic Radiotherapy Based On Optical CT Based Polymer Gel Dosimetry
Authors: Wuu C , Xu Y , Lo Y
Published: July 2006

Purpose: Accurate isocenter positioning is very important for patient setup in the treatment of stereotactic radiosurgery. In this study, the effect of positioning error of the planned isocenter on the 3‐D dose distribution was evaluated for brain lesions treated with Novalis dynamic arc stereotactic radiotherapy, using an optical CT based polymer gel dosimeter. Method and Materials: Recent developments in mechanic accuracy of gantry and couch rotation and IGRT devices have shown that the patient setup can be corrected with sub‐millimeter shift along the three vertical axes. This leads to an important question: What is the impact on the dose‐volume‐histogram for both target and critical organs, if the isocenter positioning error is not corrected. To assess this impact, two plastic cylinders filled with BANG® polymer gel (MGS Research, Inc) were used for dose measurements. One gel was irradiated with an adjustment on the isocenter shift due to couch rotation between couch positions. One gel was irradiated without any correction for isocenter shift. The irradiated gels were then scanned with 1 mm resolution using an optical CT scanner, OCTOPUS™ (MGS Research, Inc). Dose distributions and DVHs from two gel measurements and the treatment planning calculation were compared. Results: Comparison of dose distributions between the gel measurement and the treatment planning calculation showed that the agreement was within 2% in dose or 2 mm in distance. The DVH obtained from the gel measurement without any correction for isocenter shift showed smaller dose coverage at the target volume and a larger volume at the low dose (50%–80% isodose). Conclusion: Polymer gel dosimeter can provide a method of acquiring 3‐D dose distribution for a complex treatment modality. The clinical impact of sub‐millimeter error in isocenter positioning depends on disease site, target size, and other clinical information. Conflict of Interest: Research sponsored by MGS Research, Inc.
SU‐FF‐T‐08: A Comparison Between the New Stereotactic‐Mode 6 MV Beam and the Standard 6 MV Beam of Varian Trilogy Accelerators
Authors: Poffenbarger B
Published: July 2006

Purpose: Recently, a new high dose‐rate radiation beam has been offered by Varian to reduce radiosurgery treatment times. The stereotactic‐mode 6 MV beam (SRS‐6X) operates at a dose rate of 1000 MU/min. To achieve this dose rate, the flattening filter of the standard 6 MV beam (STD‐6X) was redesigned to be significantly thinner. Comparisons between the SRS‐ 6X and STD‐6X beams has been performed. Method and Materials: Profiles and Percentage Depth Doses (PDDs) were measured for a 3×3, 10×10, and 15×15 cm (maximum) field size. The profiles were acquired at depths: 1.6, 10 and 20 cm. Total Scatter Factors (Scp) were measured for various field sizes. All measurements were repeated for the SRS‐6X and STD‐6X beams on three Varian linacs. The PDD and Scp measurements were averaged over the linacs. The profile data was not averaged. Results: At a given depth, SRS‐6X PDD curves exhibit a greater slope then that of STD‐6X PDD curves. The depth 20 cm to 10 cm ionization ratio of the SRS‐6X beam was 1.0% ±0.4% lower than that of the STD‐6X beam. These results show that the SRS‐6X beam has a lower mean energy. Excluding the tail region, the 1.6 cm depth profiles agreed to within 0.8% or 0.4 mm or better for all field sizes and the 15×15 cm profiles agreed to within 1.4% or 0.2 mm at each depth. In the tail region, the SRS‐6X profiles exhibited a higher dose, indicating that the SRS‐6X beam has a larger component of scattered radiation. The SRS‐6X beam Scp values were 1% to 2% larger than those of the STD‐6X beam. The difference increased with decreasing field size. Conclusion: Clinically significant differences exist between the Trilogy SRS‐6X and STD‐6X beams. The beam data should not be interchanged. Conflict of Interest: Research sponsored by Varian.
SU‐FF‐T‐09: A Comparison of MatriXX, MapCHECK and Film for IMRT QA: Limitations of 2D Electronic Systems
Authors: Heintz B , Hammond D , Cavanaugh D , Rosencranz D
Published: July 2006

Purpose: Evaluation and comparison of 2D electronic systems versus film/ion chamber based dosimetry for IMRT QA using MapCHECK and MatriXX. Method and Materials: All IMRT plans were generated with Eclipse/Helios 7.3.10 treatment planning software (Varian). Treatments were delivered on a Varian 21EX linear accelerator (6MV) with 120 leaf Millenium MLC for delivery of sliding window IMRT. The film measurements were first compared to the Eclipse dose plane. Secondly, the electronic measurements were compared to the Eclipse dose plane. Thirdly, the film measurements were compared to the electronic measurements. The film, Eclipse dose plane and MatriXX (Scanditronix) were analyzed using the OmniPro IMRT software (Scanditronix). The film, Eclipse dose plane and MapCHECK (SunNuclear) were analyzed using the MapCHECK software. Analysis was based on distance to agreement (DTA), Gamma, profile comparisons, measured dose (relative/absolute) and visual comparison. Results: Film and ion chamber comparisons were in good agreement as well as comparisons between electronic and ion chamber measurements. However, in some instances, electronic system measurements did not agree with film due to MLC leaf failure. Advantages and disadvantages of MatriXX and MapCheck for IMRT QA as well as specific MLC leaf failure instances will be discussed further. Conclusion: With many clinics implementing electronic IMRT QA devices, a careful understanding of the limitations of the MLC system and the electronic IMRT QA device is needed. We are investigating the resolution capabilities of each QA system. The MLC failure was caught before treatment began. A major disadvantage in implementing 2D electronic systems for IMRT QA is the limited resolution, resulting in limited sensitivity to MLC failures. Primary advantages of 2D electronic systems include: 1) time, 2) efficiency, 3) ease of use, and 4) overall simplification of IMRT QA.
SU‐FF‐T‐81: Adaptive Differencing Schemes with Parallel Computing for Detailed SN Solutions of a Co‐60 Radiotherapy Unit
Authors: Al‐Basheer A , Sjoden G E
Published: July 2006

Purpose: To apply deterministic techniques to provide a numerical solution for the 3‐D integro‐differential form of the Boltzmann transport equation using the discrete ordinates (SN) method for a radiotherapy unit. Method and Materials: Comparisons were made between deterministic and Monte Carlo simulations considering angular quadrature, spatial discretization (also spatial differencing), and cross section library selection. In order to assess these issues, we simulated the 60Co beam from a standard Eldorado radiotherapy unit. In addition, we simulated the gantry, air gaps, and a water phantom. A 3‐D spatial distribution was generated to yield a 24 ‘z‐level’ model of 150,000 fine mesh cells. To accurately compare our deterministic results with Monte Carlo, we considered an equivalent MCNP5 model with ENDF/B‐VI cross‐section data libraries and volumetric flux (F4) tallies along the central axis of the model. Results: Overall, deterministic SN results yielded good agreement with Monte Carlo results within the Monte Carlo stochastic error for the reference case. At the same time, the parallel SN model provided a full 3D‐scalar flux distribution over the entire geometry within an acceptable running time. To accurately represent the radiation transport, a quadrature level of at least S24 was required with an added ordinate splitting refinement of 6 directions of interest. These results where obtained when the Directional Theta‐Weighted (DTW) differencing scheme was locked for the regions with low density material (air regions), and the adaptive differencing scheme with upgrades up to the Exponential‐Directional Weighted (EDW) differencing scheme was prescribed for higher density regions. Conclusions: The discrete ordinates (SN) method provides a viable alternative to the Monte Carlo method for solving the Boltzmann transport equation. With the proper discretization, an adaptive differencing scheme, and suitable quadratures with ordinate splitting, the SN method is a useful tool in determining the resulting radiation transport throughout a radiotherapy unit.
SU‐FF‐T‐85: An Alternative Technique for Breast Tumor Bed Boost: MammoSite HDR Brachytherapy
Authors: Lee J , Sadeghi A , Prestidge B
Published: July 2006

Purpose: The use of the MammoSite applicator as an alternative technique for delivering the tumor bed boost is analyzed. The equivalent fraction size in MammoSite boost is estimated based on the LQ model. Method and Materials: 42 patients treated with MammoSite brachytherapy were investigated. Two electron fields were setup for each patient: based on the scar and based on the seroma shown on the pre‐scan CT. The electron energy was determined depending on maximum depth of the tumor bed on the CT scan. Isodose distributions were generated for each electron plan and compared with those from the MammoSite plan. Employing the concept of BED and EUD, the fraction dose for the MammoSite boost (2 fractions, bid. α/β=10Gy, Tp=15 days, α=0.3 cGy) was estimated to match the electron treatment scheme (10Gy in 5 fractions). The late toxicity was estimated as well. Results: V100 for the electron boost plan based on the scar were 39.7% and 69.2% based on the seroma location. The coverage was improved to 92.1% when the MammoSite applicator was used. There were no statistically significant differences for the V50 of normal breast tissue, lung V30, and maximum dose of the heart between the electron plan based on the seroma location and MammoSite boost plan. Contralateral breast received higher dose for the MammoSite plan. The estimated fraction size with and without considering the tumor proliferation were 3.04∼3.15Gy×2 fraction and 3.21∼3.32Gy×2 fraction, respectively. The late toxicity based on the calculated prescribed dose was comparable between the Mammosite and electron boost. Conclusion: Applying the MammoSite brachytherapy to deliver a boost dose to the primary tumor bed appears to be more precise relative to the conventional electron boost technique. The benefit of dose better localized to the target is expected to result in better local control.
SU‐FF‐T‐88: An Experimental Evaluation of the Impact of Setup Uncertainty On Dose Near the Surface for IMRT Plans Where the Skin Is Considered a Sensitive Structure and Is Excluded From the PTV
Authors: Court L , Tishler R
Published: July 2006

Purpose: (1) To investigate the impact of setup uncertainty on doses near the surface for IMRT plans where the skin is considered a sensitive structure and is excluded from the PTV. (2) To evaluate the impact of PTV design (how close to the skin the PTV is allowed) and number of gantry angles. Method and Materials: Effects of setup uncertainty were investigated experimentally using a semi‐cylindrical phantom with MOSFET dosimeters positioned at depths of 3, 6, 9 and 12mm. A CT image was taken of the phantom, and a node‐like CTV was drawn near the surface. Two PTVs were created by uniformly expanding the CTV by 5mm, and then pulling back 3 and 5mm from the body contour (PTV(3mm) and PTV(5mm), respectively). A 2mm skin structure was contoured. Seven and nine‐field IMRT plans were created using Eclipse for each PTV with the following guidelines: 99% of PTV volume to receive 90–93% of prescribed dose, maximum 105% hotspot, and minimize dose to skin structure. The phantom was then positioned at isocenter, the planned treatments delivered using a Varian 21Ex, and doses delivered to the build‐up region were measured. Setup uncertainty was simulated by shifting the phantom laterally in a range ±5mm, and the experiment repeated. Results: The number of beams did not significantly affect the results. For PTV(5mm), setup errors of 3 and 5mm reduced dose at 6mm depth by an average of 8% and 17%, respectively. For PTV(3mm), this was reduced to 4% and 12%, respectively. Corresponding numbers for 3mm depth were 8% and 12% for PTV(5mm), and 4% and 9% for PTV(3mm). Conclusion: To avoid daily dose to the surface nodes being reduced by more than 5%, the PTV should not be pulled back more than 3mm from the body contour, and setup uncertainty should be kept below 3mm.
SU‐FF‐T‐89: An Exploration of New Formulations for PRESAGETM 3D Dosimetry
Authors: Manzoor A , Guo P , Adamovics J , Oldham M
Published: July 2006

Purpose: Presage is a new radiochromic material with substantial promise as a practical and convenient 3D dosimeter. Here we investigate new formulations of PRESAGETM to determine formulations that have high sensitivity, high stability, and/or are amenable to repeat measurements. Method and Materials: PRESAGETM formulations were manufactured in 2 mL glass vial samples and were irradiated in a 6MV photon beam to a dose of 5 Gy. Fifteen formulations were studied, eight of which were variations containing leucomalachite green (LMG) and seven variations containing leuco crystal violet (LCV). The transmission spectra (500–700 nm) were measured in a spectrophotometer for each sample pre‐irradiation and then approximately one hour post‐irradiation. Subsequent spectrum acquisitions were recorded at 2, 24, 48, and 72 hours post‐irradiation to ascertain the stability of optical density changes. Results: Overall, the LCV formulations show greater sensitivity than the formulations containing LMG. The most promising LCV formulations exhibit a 15 – 33 % increase in post‐irradiation absorption relative to pre‐irradiation. The LCV formulations had minimal post‐irradiation color bleaching from 2 to 72 hours, while the LMG formulations varied widely in stability post‐irradiation. A number of the LMG samples returned to their pre‐irradiation optical density, suggesting the possibility of a formulation which could be reusable. In addition, two of the formulations which contained polymeric acrylates along with the leuco dyes increased transmission relative to pre‐irradiation, illustrating the intriguing potential of an ‘inverse radiochromic dosimeter’ (i.e. a dosimeter that becomes clearer after irradiation). Conclusions: Absorption changes post‐irradiation identified LCV formulations with the initial response and stability for application in 3D dosimetry. In addition, LMG formulations were identified that may permit the unique potential for ‘inverse radiochromic dosimetry’ and reusability.
SU‐FF‐T‐96: Analyzing Tertiary Multileaf Collimators Position Effect On the Dose Distribution in Irradiated Field Edge
Authors: Su M , Szal M , Li T
Published: July 2006

Purpose: To study the varying of dose distribution at the irradiated field edge (IFE) affected by the relative position between jaw and MLC setting. Method and Materials: Varian 21EX linear accelerator with 80 MLC was used for this study. The dose distribution was measured with a 2D‐array Seven29 (PTW) ion chamber with 6 and 18 MV photon beam and field sizes (FS) 5×6, 10×10, 15×16 and 20×20cm2. Ion chamber array was set perpendicular to the central axis beam and placed at 100 cm SAD at Dmax. Dmax was built with a solid water phantom. Measurements were taken at following four field setting: (1) MLC aligned up with jaw, (2) MLC 1cm larger than the jaw setting, and (3) MLC 2cm larger than the jaw setting, and (4) MLC fully retracted. Dose comparison was done between the field setting (1) and the others at x‐axis and y‐axis IFE separately. To minimize the measurement device inaccuracy, dose was measured at 0° and 90° collimator angles with FS 10×10cm2 for the verification. To limit the setup error, each set data was measured at same setup. Results: There was not significant dose different observed from x‐axis direction. However, there were 2.8, 4.3, 6.3 and 7% lower dose observed from y‐axis direction with four measured FS from 18 MV beam, respectively. A similar result was observed from 6 MV beam. The difference amount other three settings was less than 1%. Conclusions: Relative jaw and MLC location affects a dose distribution significant at y‐axis IFE and this effect increased with the off central axis distance. We recommended that for a linac commissioning with jaws alone, when a tertiary MLC is used to shape an irradiated field, a 1cm extra distance should be provide from MLC at y‐axis direction to avoid the low dose at IFE.