bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐J‐14: Failure Mode and Effect Analysis (FMEA)‐Based Quality Assurance for Dynamic MLC Tracking Systems
Authors: Sawant A , Dieterich S , Svatos M , Keall P
Published: August 2010

Purpose: Effective QA for newly introduced radiotherapy technology has received increased attention within the radiotherapy community and the general public. This work aims to develop and implement a FMEA‐based quality management (QM) framework for dynamic MLC (DMLC) tumor tracking systems. Methods: A systematic FMEA was performed for a prototype tumor tracking system that uses the Calypso system for position monitoring and a DMLC for real‐time beam adaptation. A process tree of DMLC tracking delivery was mapped and potential failure modes were identified. For each failure mode, a risk probability number (RPN 1:1000) was calculated from the product of the probability of occurrence, severity of effect and detectability of failure. Based on the insights obtained from FMEA, commissioning and QA procedures were developed to check (i) coordinate transformation, (ii) system latency, (iii) delivery accuracy, (iv) delivery efficiency and (v) system response to error conditions. Results: Failures modes with RPN ≥ 20 were: delivery accuracy, efficiency and data communication integrity. These were recommended to be tested monthly. Failure modes with RPN < 20 were: coordinate transformation, latency error and target out‐of‐range error. These were recommended only during comprehensive testing e.g., commissioning, annual testing and after major software/hardware upgrades. The total time taken for monthly QA was ∼35 minutes while that taken for comprehensive testing was ∼3.5 hours. Conclusion: FMEA proved to be a powerful and flexible tool to develop a QM framework for DMLC tracking. We conclude that the use of FMEA ensures efficient allocation of valuable clinical resources because the most critical failure modes receive the most attention. Finally, consistent with the goals of FMEA, this framework can serve as the basis of a dynamic QM program that is continuously updated with increasing intra‐ and inter‐institutional experience.

Conflict of interest: This work was partially supported by Varian and Calypso
SU‐GG‐J‐17: Technical Aspects of a Simple and Effective Method to Perform Stereotactic Body Radiation Therapy (SBRT) in Lung Cancer Patients without 4D‐Ct and Gating
Authors: Jani S , Glazebrook S , Volpp B , Weinstein G
Published: August 2010

Purpose: In recent years, there has been considerable debate about the necessity of using respiratory gating and 4D ‐CT to perform SBRT, a fast‐growing practice with high risk to patients. Here, we describe the technical aspects of a method to perform SBRT in lung patients without the use of respiratory gating and 4D‐CT. Methods and Materials: After two years of slow dose escalation, we launched our SBRT program in 4/2009 and have enrolled 10 patients (11 lesions) so far. Each patient underwent a CT‐guided placement of a Visicoil marker. Patients were immobilized with a homegrown method utilizing a Vac‐loc and Aquaplast body cast; then underwent a fluoroscopic exam with a C‐Arm to determine tumor motion. Normal tissues dose limits were set using RTOG/ M.D. Anderson guidelines on lung SBRT. About two‐third of lesions (7/11) were treated with 50 Gy in 4–5 fractions, the remainder with >5 fractions due to increased risk of complications. Treatments were carried out at a BrainLab Novalis system with ExacTrac image guidance. Prior to treatment, a series of x‐rays were taken with the patient in “breath‐in and hold” and “breath‐out and hold” positions. The mid‐point of tumor motion was established and used to determine the treatment isocenter. Results: Average target dimensions were 19cc (GTV) and 73cc (PTV). The lung DVH (V‐20), based on whole lung‐GTV, ranged from 3.1% to 11% with an average of 7.8%. Tumor motion observed at the treatment machine using ExacTrac x rays matched to within 3 mm of the fluoroscopic value. Patient follow‐up (9/10) showed no evidence of Grade III toxicity and no progression of disease in any patient. Conclusions: Respiratory gating and 4D‐CT are not essential components of SBRT. As pointed out by recent ASTRO/ACR guidelines, the truly critical aspect is rigurous QA of each process.
SU‐GG‐J‐18: Robust Tracking of Fiducials and Interventional Tools during Image‐Guided Interventions
Authors: Siddique S , Fiume E , Jaffray D
Published: August 2010

Purpose: The purpose of image‐guidance during clinical interventions is to provide information on the location of objects of interest, often relative to other anatomical structures. Robust methods for real‐time tracking of such objects are necessary to provide quantitative information to the interventionalist. Most tracking algorithms fail when the assumptions of the algorithm are not met or when cases are encountered that are unaccounted for by the model used. This study highlights some of the challenges involved in tracking objects in 2D image sequences, particularly in X‐ray fluoroscopy, and proposes methods to address them. Method and Materials: Experiments are conducted by simulating three fundamental cases of noise, occlusion and unexpected dynamics in X‐ray fluoroscopic images. An extension to particle filters is developed and is used to track objects under these challenging conditions. The proposed extension to particle filters (i) adapts the number of particles used during tracking in response to noise in the image, (ii) modulates the resolution of particles for robustness to occlusion, and (iii) adjusts to unexpected dynamics or ‘surprises’ in motion exhibited by the object of interest. The performance of this algorithm is contrasted with a conventional particle filter using the mean squared error (M.S.E.) as a metric. Results: When compared to a conventional particle filter, a reduction in the M.S.E is observed for the proposed particle filter in all three fundamental cases evaluated. Conclusion: The proposed adaptive particle filter offers an improvement in robustness to factors unaccounted for in the dynamic and observation models that constitute the tracking algorithm. This method would be valuable in image‐guided interventions as it can provide real‐time feedback that can improve the performance of a surgeon, control robotics, and optimize imaging parameters.
SU‐GG‐J‐20: Methods for Improvement of Clip Localization in CBTS for Breast Cancer Patients Setup Verification
Authors: Ng SK , Zygmanski P , Buehler A , Stsepankou D , Hesser J , Bellon J , Lyatskaya Y
Published: August 2010

Purpose: To establish clip localization procedures for setup verification of breast cancer patients based on Cone‐Beam Tomosynthesis (CBTS). To develop an automatic clips registration algorithm and characterize its accuracy and efficiency versus the manual procedure. Furthermore, to determine potential benefits of 80°CBTS over 40°CBTS. Method and Materials: CBTS and CBCT images were reconstructed for 7 breast cancer patients with surgical clips implanted around the tumor cavity. Known shifts of patient anatomy were introduced and registration of clips was carried between the reference and treatment reconstructions using two methods: manual and automatic. Manual method relied on matching of clips in CBTS with clip contours drawn in the reference CT. An automatic clip localization method consisted of two image processing steps: auto‐segmentation using multi‐level thresholding and prior knowledge about clip size and locations followed by auto‐registration of the segmented clips. Results: The automatic method was developed and demonstrated to accurately localize clips with Hounsfield Units > 460 with an accuracy of better than 2.5mm. Accuracy of manual method registration was slightly better (accuracy <1.5 mm). However, time efficiency of manual method was up to a few minutes depending on the spatial distribution of the clips, their HU, CBTS‐specific artifacts and experience level of the users. Performance of the automatic method is user independent and fast. Conclusion: Surgical clips can be accurately localized in CBTS images used for breast cancer patient setup using both methods. The manual clip localization is user dependent and generally inefficient. In order to improve the efficiency of the setup procedure, automatic clip registration is recommended. The automatic algorithm based on multi‐level thresholding is straightforward to implement on linac‐mounted CBCT systems with estimated time of clip localization of up to a few seconds. Conflict of Interest: This research was funded by Kaye Scholars Grant.
SU‐GG‐J‐26: Comparison of Intrafractional Motion between Supine and Prone Patient Positions during Radiation Therapy of Pelvic Malignancies Using a 3D Surface Imaging System
Authors: Zhao H , Wang B , Rassiah‐Szegedi P , Huang Y , Sarkar V , Szegedi M , Salter B
Published: August 2010

Purpose: To compare intrafractional motion between supine and prone positions during radiation therapy of pelvic malignancies using a 3D surface imaging system. Method and Materials: Five patients with pelvic malignancies treated with radiation therapy were enrolled, three treated in supine and two in prone position. For each patient, both supine and prone position simulation CTs were performed. Body surfaces were generated from simulation CT and then exported to AlignRT as reference images. AlignRT motion tracking was performed for both supine and prone position for each patient once per week for five weeks. The length of the tracking record was between 1.5 to 2 minutes. The maximum and the standard deviation of patient displacement were calculated and compared along the vertical, longitudinal and lateral directions for both positions. Results: A fairly strong correlation was observed between the intrafractional displacement and the BMI. Generally, the displacements were smaller in prone position for patients with a normal BMI in both vertical and longitudinal directions. This is reasonable as the magnitude of the respiratory induced motion is compressed to be smaller in prone position. This phenomenon was reversed for the obese patient with a large BMI value of 30, where the intrafractional displacement was smaller in supine position. For obese patients, it is more difficult to hold still on their large belly with regular respiratory motion. In lateral direction, however, the intrafractional motion did not have statistically difference between supine and prone positions for all the patients. Conclusion: The intrafractional motion between supine and prone position during radiation therapy of pelvic malignancies depends on patient's BMI. Normal BMI patients have a smaller intrafractional motion in prone position in vertical and longitudinal directions, while obese patients have a smaller motion in supine position.
SU‐GG‐J‐27: Assessment of Patient Setup Corrections in External Beam Radiotherapy Using On‐Line Kilo‐Voltage Imaging
Authors: Cao M , Hanns L , Lengerich N , Anderson C , King K , Das I
Published: August 2010

Purpose: Image‐Guided Radiation therapy (IGRT) has evolved as a new and better tool for accurate patient setup in radiation therapy. The purpose of this study was to assess patient setup corrections in external beam radiotherapy for head‐and‐neck, breast and prostate tumors by using on‐line kilovoltage (kV) imaging. Method and Materials: Patient position corrected values resulted from on‐line orthogonal kV image matching with DRR were retrospectively collected for three different treatment sites: head‐and‐neck (H&N) (n=19), prostate (n=14) and breast (n=10). The systematic and random setup corrections for each individual patient and the groups were calculated and compared between different treatment sites. Results: For H&N patients, the overall systematic and random setup errors were 0.6±3.0, 0.1±3.6 and −1.2±3.8 mm in the left‐right (LR), anterior‐posterior (AP) and superior‐inferior (SI) directions, respectively. Individual systematic errors greater than 5mm were observed in only 1 of 19 (5.2%) H&N patients. Compared with H&N patients, prostate patients showed similar overall systematic and random errors (0.1±6.4, 0.3±3.9 and 0.6±3.6 mm in the LR, AP and SI directions, respectively). However, a relatively larger fraction (21.4%) of prostate patients had individual systematic offsets greater than 5mm. The overall systematic errors (1.3mm in LR, −2.7mm in AP and 0.6mm in SI) in breast patients were similar to the other two sites. However, significantly larger random setup errors (6.9mm in LR, 4.5mm in AP and 5.7mm in SI) were observed in breast patients. Conclusion: Our study showed that the systematic errors for all anatomic sites are all smaller than 3mm. However, relatively large systematic errors were observed in some individual patients. The random setup errors were found larger in breast patients than other two anatomic sites. These observations support that IGRT is an important and necessary tool in improving the patient setup accuracy.
SU‐GG‐J‐29: Feasibility of Improving Cone Beam CT Number Consistency with a Scatter‐Correction Algorithm
Authors: Li J , Yao W , Xiao Y , Yu Y
Published: August 2010

Purpose: To explore the feasibility of improving Elekta cone beam CT (CBCT) number consistency using a scatter‐correction algorithm, with the aim of using CBCT images for treatment planning with heterogeneity correction. Method and Materials: A Gammex tissue phantom was scanned with and without a 1‐cm bolus on an Elekta XVI cone beam CT. A scatter‐correction algorithm was applied to process the projection images, where the first order scatter fluence was expressed as a function of the primary photon fluence, and iterations were performed to estimate primary and scatter fluences from the projections, assuming higher‐order scatter fluence was constant or proportional to the first order scatter fluence. Volumetric images were reconstructed with the projection images. CBCT numbers of the insert rods of the Gammex phantom were compared between images with and without bolus, and with and without scatter‐correction processing. Single field treatment plans with heterogeneity correction were generated using CBCT‐to‐electron‐density conversions obtained in the images without the bolus, which were compared with the plans generated using CT images. Results: CBCT numbers of the same insert rods were different in the images with and without bolus. Without the scatter‐correction processing, the maximum, mean, and minimum differences of the CBCT numbers between bolus and no‐bolus images were 485, 128, and 40, respectively. After the processing, the corresponding differences were reduced to 349, 80, and 4, respectively. The CBCT plans which were based on the processed images, show better dose agreement with the CT plans: for example, in the bolus plans, without the processing, the difference of the dose at isocenter was 7.1%; after the processing, the difference was reduced to 0.8%. Conclusion: CBCT number consistency was improved by use of the scatter‐correction algorithm. It is expected that with further improvement, the algorithm can be used in clinical applications.
SU‐GG‐J‐32: Evaluation of a Thinner‐Slice MVCT Scan Mode across Several Systems
Authors: Chao E , Lucas D , Ruchala K , Olivera G
Published: August 2010

Purpose: To evaluate the system‐to‐system variation in TomoTherapySM MVCT slice profiles using the existing (J4) jaw setting and a thinner (J1) jaw setting. Method and Materials: The MVCT image slice sensitivity profile is measured using a thin, metallic disc to approximate a delta impulse function in the longitudinal direction. At each jaw setting, the slice profiles are measured for the three available couch speeds: 4mm/rotation, 8mm/rotation, and 12mm/rotation, corresponding to the Fine, Normal, and Coarse scan modes. These measurements are then repeated on 10 systems. Results: With the current TomoTherapy factory settings for the jaw (J4), the Fine, Normal, and Coarse scan modes yield images with a full‐width at half‐maximum of 6.17±0.38mm, 6.89±0.29mm, and 8.02±0.21mm (mean ± standard deviation). Using a thinner (J1) jaw setting but the same couch speeds yields slice thicknesses of 3.85±0.09mm, 5.27±0.18mm, and 7.14±0.10mm. The thinner slice profiles reduce partial volume effects and increase the contrast of the thin, metallic disc. The average contrast of the disc using the existing (J4) jaw setting is 167, 148, and 115HU for the Fine, Normal, and Coarse scan modes, respectively. Using the thinner (J1) jaw setting, the average contrast increases to 282, 192, and 137HU. Conclusion: The thinner (J1) jaw setting consistently and significantly reduces the MVCT slice thicknesses for all three scan modes (Fine, Normal, and Coarse). The system‐to‐system variation is substantially smaller than the average improvement. Corresponding to the reduced slice thickness, the contrast of thin objects in the transverse plane is substantially improved. By adjusting the beam output to keep dose per pulse constant, these improvements to longitudinal resolution are achieved with no change in other imaging properties (noise, artifact, average dose).
SU‐GG‐J‐34: Comprehensive Clinical Commissioning and Quality Assurance Procedures of a Big Bore CT Simulator in a Radiation Oncology Department
Authors: Zhang J , Sehgal V , Roa D , He Q , Martin M , Al‐Ghazi M
Published: August 2010

Purpose: To perform acceptance testing and clinical commissioning of a 16‐slice big bore CT‐simulator (85 cm) and comprehensive quality assurance (QA) procedures for radiation treatment planning using several phantoms. Method and Materials: This study focused on the performance evaluation of this CT simulator in a radiation oncology environment through the acceptance testing and commissioning for clinical use. Parameters derived from commissioning were used as reference values for a comprehensive QA program. Several phantoms were used in this project to evaluate the CT simulator image quality, like ACR phantom, Vendor (Philips) provided phantom and CATPHAN 504. CTDI phantom was used to evaluate the radiation dose to patients during scans. RMI phantom was used to evaluate the CT number linearity for use in the treatment planning system for density correction. Results: For clinical commissioning, the radiation dose reported in this study is lower compared to published data based on CTDI measurements. The results from ACR phantom showed that image quality specifications were met. The highest spatial frequency for two parts of the ACR phantom; abdomen and chest, there were 8 and 9 lp/cm; respectively visualized. The manufacture specification is 5 lp/cm. CT number linearity and low contrast resolution tests were also within acceptance requirements. Image quality evaluation parameters from different phantoms were compared. These showed good self consistency using this CT simulator. Conclusion: A comprehensive analysis of the test results indicates consistent and reproducible operation of the big bore CT‐simulator. This big bore CT simulator is well suited for use in a radiation oncology setting.
SU‐GG‐J‐39: Beam‐Centric Algorithm for Pretreatment Patient Position Correction in External Beam Radiation Therapy
Authors: Bose S , Shukla H , Maltz J
Published: August 2010

Purpose: In image‐guided pretreatment patient position adjustment methods, image registration is used to determine alignment parameters. Since most positioning hardware lacks the full six degrees of freedom (DsOF), accuracy is compromised. We present an algorithm for determining optimal realizable adjustments and demonstrate that such compromises are often unnecessary when planned treatment beams are modelled as part of the adjustment calculation. Method: Our beam shape model is based on the polygonal intersection of each beam segment with the plane in pretreatment image volume that passes through machine isocenter, perpendicular to the central axis of the beam. Under a virtual 6‐DOF correction, ideal positions of these polygon vertices are computed. The proposed method determines the couch, gantry and collimator adjustments that minimize the total mismatch of all vertices over all segments with respect to their ideal positions. Using this geometric error metric as a function of the number of available DsOF, the user may select the most desirable correction regime. Results: For a simulated plan consisting of three equally weighted coplanar fixed beams, we achieve a 7% residual geometric error (with respect to the ideal correction, considered 0% error) by applying gantry rotation as well as translation and isocentric rotation of the couch. For a clinical head‐and‐neck IMRT plan with 7 beams and 5 segments per beam, the corresponding error is 6%. Correction involving only couch translation (typical clinical practice) leads to a much larger 18% mismatch. After adjustment, dose volume histograms demonstrate clinically significance of geometric error reduction. Conclusion: Suggested algorithm improves delivery accuracy using standard delivery hardware without significantly increasing total treatment session duration. It encourages parsimonious utilization of all available DsOF. Finally, in certain cases, it obviates the need of a 6‐DOF robotic couch for pre‐treatment position adjusment. Conflict of Interest: Research sponsored by Siemens Medical Solutions.
SU‐GG‐J‐41: Treatment Beam's‐Eye‐View Speed‐Modulated CBCT Imaging Used in a Triple Imaging Modality to Track Moving Tumors during Treatment Delivery
Authors: Ionascu D , Zhuang L , Liang J , Yan D
Published: August 2010

Purpose: To track the target trajectory during the treatment based on the pre‐treatment CBCT projection images when the gantry is selectively slowed down at the treatment angles, the synchronized 3D surface imaging and the EPID in movie mode. Methods and Materials: A gantry‐speed device slows down the CBCT gantry speed (2min/360degrees) by half for a 6 degrees arc centered on the MV treatment beam, allowing us acquire twice as many frames within the treatment arc (22frames/5.5fps). The treatment arc is chosen to accommodate a typical full breathing period (4s). A CBCT kV beam‐on trigger is used to acquire 3D surface images using the AlignRT cameras. Phantom experiments were performed using a programmable respiratory motion platform. During the treatment delivery, MV imaging was performed in movie mode (3fps) while the surface cameras tracked the chest‐wall component. A mutual information algorithm was employed to compare the kV an MV images. Results: CBCT reconstruction was performed using every other frame when in the slow treatment arc for correct reconstruction. The longer scanning times were translated in ∼10–15% additional CBCT dose when 4 beams were used. For simple trajectory, the kV and MV images were phase correlated ∼98% of the time for the high contrast tumor and ∼92% for the low contrast tumor. Phase knowledge provided by the surface cameras increased the later kV‐MV correlation to ∼97%. Patient‐like trajectories were tested where the most irregular trace (3mm baseline‐shift) showed a moderate kV‐MV correlation, enabling one to interrupt the treatment for a second on‐line baseline correction. Conclusion: The selective beams‐eye‐view slow‐arc CBCT technique in conjunction with surface cameras and MV imaging has been demonstrated to be an effective tool for tumor tracking due to its treatment time immediacy and minimal impact on treatment flow.
SU‐GG‐J‐43: Accumulating Delivered Doses Based on Daily CT in Head and Neck Cancer Radiotherapy
Authors: Hu B , Godley A , Ahunbay E , Wang K , Li X
Published: August 2010

Purpose: To accumulate actually delivered dose based on daily CTs to evaluate patient repositioning techniques and adaptive strategies for head and neck cancer radiotherapy. Methods: Daily CTs acquired for 28 Head and Neck cancer patients using a CT‐on‐Rails (CTVision, Siemens) were analyzed. These patients were treated with IMRT plans, designed with a 5 mm CTV to PTV margin with prescription in the range of 60–70Gy. Daily plans were reconstructed using a planning system (XiO, CMS) based on daily CTs with iso‐center shifted according to three clinically used alignment techniques: skin markers (BB), soft‐tissue and bone. The daily dose distributions were then deformed using an in‐house deformable registration tool and mapped on to the planning CTs. The cumulative delivered dose distributions with three alignment techniques were compared with planning doses. Results: Although patient repositioning shifts are different between three alignment methods, the accumulated doses for GTV and PTV are comparable. The differences in PTV mean doses between the delivered (accumulative) and the planned values are within 2% for all three alignment methods. However, the accumulated mean doses for parotid glands and salivary glands are different by as much as 20% from their planned values. The soft‐tissue alignment leads to smaller differences. Conclusion: The actual delivered doses for head and neck radiotherapy are calculated by deforming daily CTs to the planning CT for three clinically used patient alignment techniques. While the delivered accumulative doses in targets are similar to the planned doses, the delivered doses to critical structures are different and these differences depend on the alignment rection.
SU‐GG‐J‐49: Interfractional Breast Shape Variation and Dosimetric Consequences in Whole Breast Irradiation
Authors: Morrow N , Carver M , Ahunbay E , White J , Wilson J , Li X
Published: August 2010

Purpose: This work aims to quantify interfractional variations in breast shape and their dosimetric consequences for conformal whole breast irradiation (WBI). Materials/Methods: Daily CT data acquired for 10 breast cancer patients during IGRT were analyzed. Patients were setup supine and daily pre‐treatment CTs were acquired using CT‐on‐Rails (CTVision, Siemens). Contours of breast and critical structures on daily CTs were generated using a tool (ABAS, CMS) based on deformable image registration. Interfractional changes of breast shape and volume were measured by using Dice's Coefficient. For each patient, two commonly‐used WBI plans with tangential beams based on the planning CT, one using wedges and another using field‐in‐field (FiF) technique, were developed. Each daily CT was registered with corresponding planning CT to obtain repositioning shifts. Plans were applied to the daily CTs. Dosimetric variations were measured by a series of dose‐volume parameters. Results: Breast volume variations were generally small. Interfractional shifts can be significant and breast shape varies modestly. The average overlap between planning and daily breast volumes was 88–93%. The daily values of D95 and D50 (dose received by 95% and 50% of treated breast volume) varied by 1–2% from their planning values for both plans. For D98, the variation was upto 5%. These variations were not significantly different between the wedge and FIF plans. Daily global maximum was on average increased by 2–4% for the FiF plans as compared to the wedge plans. The interfractional variation of V52.5 (volume receiving 52.5 Gy) was significantly higher for FiF plans compared to the corresponding wedge plans. Conclusion: Interfractional variations in patient positioning result in modest breast shape changes which can lead to dosimetric variations during the course of treatment and cannot be fully corrected for by patient repositioning. FiF plans are more sensitive to the breast shape change than wedge plans.
SU‐GG‐J‐53: A Novel Dose Reconstruction Method for Four‐Dimensional Treatment Planning
Authors: Zhong H , Kim J , Glide‐Hurst C , Chetty I
Published: August 2010

Purpose: To present a novel dose mapping algorithm that takes into account heterogeneity effects of radiation energy distribution in 4D planning, and compare it with two well‐established dose calculation strategies. Method and Materials: A 4DCT dataset was imported into Eclipse and the end‐inhalation image (EI) was used to develop a free‐breathing lung cancer radiotherapy treatment plan. The EI was registered to the end‐exhalation image (EE, reference) using a B‐Spline deformable registration algorithm. The resultant displacement map Φ, defined from EE to EI, was iteratively reversed to generate a self‐inverse consistent map ΦR. With the Eclipse Advanced Planning‐Interface (API, Varian Medical Systems), the mass density matrix of EI was derived from the treatment plan and mapped to EE using ΦR. The dose was calculated on the EI using the AAA algorithm and multiplied by the mass density matrix of EI to generate the deposited energy. The energy was then mapped to the image EE again using ΦR. The warped dose D on the EE image was calculated as the ratio of the mapped energy and mass (REM). For comparison, two additional approaches were used that warped the dose on EI with Φ: center of mass (COM) and trilinear dose interpolation (TRI). The three dose reconstruction strategies were then compared on the reference image (EE). Results: The average spatial difference between the composition of Φ and ΦR and the identity map was approximately 0.0 mm. On average, the dose to 95% of the ITV (D95) was 70.2%, 67.5%, and 64.3% for the REM, TRI, and COM methods, respectively. The dose difference between COM and REM was up to 14.5% at the high gradient beam edges. Conclusion: The independent mappings of mass and energy may help minimize heterogeneity‐induced dose interpolation errors, thereby improving dose mapping accuracy in 4D treatment planning.
SU‐GG‐J‐57: Image‐Guided Extended‐Field Radiation Therapy for Functional Bone Marrow Sparing in Cervical Cancer Patients with Positive Para‐Aortic Lymphnodes
Authors: Liang Y
Published: August 2010

Purpose: To assess the feasibility of image guided radiation therapy to reduce functional bone marrow (FBM) dose for cervical cancer patients with positive para‐aortic lymph nodes undergoing extended field intensity modulated radiotherapy (EF‐IMRT). Method and Materials: Three patients were enrolled on a prospective study to test image‐guided FBM‐sparing EF‐IMRT (IG‐EF‐IMRT). Patients underwent CT simulation plus (1) whole body 18F‐FDG‐PET and (2) quantitative MRI using iterative decomposition of water and fat with echo asymmetry and least‐squares estimation (MRI‐IDEAL). Regions of high standardized uptake value (SUV) (increased glucose metabolism) on PET and low fat fraction (high cellularity) on MRI‐IDEAL indicated higher FBM concentrations. The PET and MRI‐IDEAL were registered with the simulation CT. FBM was segmented based on the patient's individual mean SUV and fat fraction within lumbosacral spine and pelvis. For each patient, 2 plans were compared: non‐IG‐EF‐IMRT(CT defined BM as the sparing objective) vs. IG‐EF‐IMRT(FBM as the sparing objective). Results: The mean FBM volume, as a proportion of lumbosacral spine and pelvis, was 23% (s.d. 0.6%). IG‐EF‐IMRT significantly reduced the volume of FBM receiving ≥ 10 Gy and ≥ 20 Gy (V10 and V20) compared to non‐IG‐EF‐IMRT. With PET and MRI‐IDEAL guidance, the mean FBM V10 was reduced from 94% to 89%, mean FBM V20 was reduced from 86% to 73%. IG‐IMRT plans did not compromise target coverage or increase dose to normal organs. One patient was treated with IG‐EF‐IMRT, with FBM V10 and V20 of 82% and 70%, respectively. She received all 5 cycles of weekly cisplatin (40 mg/m2) and had grade 2 HT during CRT. The other two patients were treated with non‐IG‐EF‐IMRT and planned with IG‐EF‐IMRT. Conclusion: IGRT for FBM sparing is clinically feasible and significantly reduces FBM dose compared to standard IMRT. This novel technique may reduce HT and is being tested in a clinical trial.
SU‐GG‐J‐58: Stereotactic Body Radiotherapy: Computer‐Assisted Verification of a Lung Tumor Region Using EPID without Implanted Markers
Authors: Arimura H , Shioyama Y , Nakamura K , Yoshitake T , Anai S , Nomoto S , Honda H , Toyofuku F , Higashida Y , Onizuka Y , Terashima H , Hirata H
Published: August 2010

Purpose: Our purpose of this study was to develop a computer‐assisted verification method for lung tumor regions using a Gaussian image enhancement based on second derivatives of Gaussian functions in cine images on an EPID without implanted markers during SBRT. Method and Materials: The localization for a lung tumor was based on a template matching technique between a “tumor template” image obtained from a first EPID cine image and the subsequent image. The irradiation field region was cropped from an original EPID cine image by analyzing the histogram of this image. The “tumor template” image was segmented from the first EPID cine image, i.e., reference portal image, by using a Gaussian image enhancement based on second derivatives of Gaussian functions and a region growing technique. The tumor region was determined within the irradiation field as the position where the tumor template image took the maximum cross‐correlation value within each subsequent cine image. For performance evaluation of the proposed method, we applied the proposed method to EPID images acquired from twelve cases (age: 51–83 years old, mean: 72) with a non‐small cell lung cancer, and calculated the following two values: (1) the location error, i.e., the Euclidean distance from “tumor” point to the candidate point and (2) the overlap measure between the target candidate regions obtained by the manual method and our automated segmentation method. Results: The average location deviation between tumor center points obtained by the proposed method and the manual method was 1.80 ± 0.73 mm. The average overlap measure was 66.0 ± 10.0% for 12 cases. Conclusion: The results of this study suggest that the proposed method based on the tumor template matching technique might be feasible for localization of a lung tumor without implanted markers in SBRT.
SU‐GG‐J‐59: Variation of Target Position Determined by Gold Fiducial Markers for Radiotherapy of Pancreatic Cancers
Authors: Shen S , Jacob R , Steward J , Duan J , Varadarajulu S
Published: August 2010

Purpose: To determine daily positional variations of the target relative to skeleton during pancreatic IMRT. To assess the dosimetric impact of these variation to target and critical organ. Methods: Eight patients with pancreatic cancer underwent placement of at least 3 gold fiducials by endoscopic ultrasound guidance. Patients were immobilized using alpha‐cradle for gated CT simulation and gated IMRT. Gated CT images were acquired with either prospective gating or retrospective gating (4D‐CT). IMRT was planned and treated at end of expiration. A gated on‐board kilovoltage (kv) image was acquired daily in the treatment position prior to IMRT. The gated kV image was registered with a DRR from the gated CT based on skeletal anatomy. The deviation in fiducial position in anterior‐posterior, superior‐inferior and left‐right directions were recorded. IMRT plans were calculated to estimate change of DVH when patient was shifted with mean daily deviation for each patient. Results: The mean (and range) daily (n=25 fractions) deviation for 8 patients between images based on skeletal fusion and fiducial location were 0.2 cm (0.1–1.0 cm), 0.5 cm (0.2–1.5 cm) and 0.4 cm (0.2–2.0 cm) in the anterior‐posterior, superior‐inferior and left‐right directions. The dose coverage at 95% target volume would decrease by 3.7% (median, ranged 1.5–6.2%; n=8) when patient daily position was not adjusted. The cord max dose would increase by 5.8% (median, range 0.1–26.6%, n=8) when patient daily position was adjusted. The cord dose would not change (median 0% range −1.2–5.1%, n=8) when patient daily position was adjusted only in the S‐I direction. Conclusions: The daily soft‐tissue set‐up variations of target in the treatment of pancreatic cancer were measured. An additional margin is needed around the target when IMRT is delivered using skeletal registration without fiducials. Without real‐time re‐optimization, position adjustment using daily image‐guidance might need compromise between tumor and critical organs.
SU‐GG‐J‐61: The Optimal Frame Rate for Cine EPID Images
Authors: Liao Y , Turian J , Zhou J , Templeton A , Chu J
Published: August 2010

Purpose: To determine the patient‐specific optimal cine EPID image acquisition parameters for intra‐fraction organ/tumor motion monitoring. Method and Materials: EPID images acquired in cine mode can provide verification of patient‐setup and monitor internal organ motion during actual treatment without additional dose to the patient. This is especially useful when respiratory motion is of concern. The acquired EPID images are analyzed retrospectively with each image given equal weight for delivered dose estimation, thus it is important that they accurately represent the tumor locations throughout the treatment. 100 MU's were delivered to a phantom simulating patient breathing at 15 breaths‐per‐minute (BPM). Respiratory motion is in superior‐inferior(SI) direction, and its position is recorded at intervals of 0.1, 0.5, 0.8, 1, 1.3, and 2 seconds, corresponding to 40 frames‐per‐breath(FPB), 8FPB, 5FPB, 4FPB, 3FPB, and 2FPB, respectively. Counts of recorded positions are plotted against the relative excursion (i.e. position divided by the amplitude of waveform) at bin size of 0.25. The histogram does not vary significantly with phase delay at high frame rate. A frame rate of 10Hz (40FPB) is the intrinsic maximum limit of the device and is impractical due to processing speed and storage space limitations but provides a reference case. The optimal frame rate mimics the average excursion of the reference case and is independent of phase delay.Results: Results from 5FPB generated the average excursion closest to 40FPB case and are less dependent on the phase, hence more preferable. Interestingly, at 2FPB, when the EPID images are acquired in sync with patient breathing, only the center position is recorded and the entire excursion is missed. Conclusions: Cautions need to be taken when choosing the frame rate of EPID images so they represent the excursion of the tumor throughout the treatment. It is recommended to acquire images at a minimum of 5FPB.
SU‐GG‐J‐65: CBCT Image Guidance for Head and Neck IMRT Radiation Therapy—A Study on the Tumor Coverage and Critical Structure Avoidance
Authors: Tang X , Lawrence M , Chang S
Published: August 2010

Purpose: Cone beam computed tomography (CBCT) is becoming more prevalently used for image‐guided radiation therapy (IGRT). The ideal CBCT frequency and protocol will limit patient imaging dose, while insuring the accuracy of the radiation therapy (RT). We herein examine the effects of a possible CBCT imaging protocol on the delivered RT. Methods and Materials: The intensity modulated radiation therapy (IMRT) plans for 6 head and neck cancer patients undergoing IGRT with CBCT were retrospectively studied. The CBCT protocol called for daily IGRT for the first treatment week, followed by twice‐weekly imaging for the remaining RT fractions. The statistics of the IGRT patient set‐up shifts throughout the treatment course was used to create the treatment dose for non‐IGRT days using our in‐house TPS PlanUNC. The cumulative dose from the entire treatment course is the sum of the non‐IGRT daily doses and the planned daily doses for IGRT days. The resulting cumulative doses to the clinical target volume (CTV) and critical structures were examined.Results: The delivered treatment plans maintained the CTV treatment planning goals for 6 patients. Incorporating the IGRT shift statistics caused the CTV of one patient to be under dosed. The hotspots for the optic chiasm, cord, and brainstem were all within the treatment goals, and the absolute doses were within 5% of the planned RT. The dose constraints for the larynx and parotids were all maintained in the delivered treatment plans.Conclusions: The proposed CBCT protocol is sufficient for accurate RT delivery to the target volumes and critical structures of head and neck IMRT patients.
SU‐GG‐J‐66: A Single Phantom Study for the Evaluation of Accuracy of Three IGRT Techniques
Authors: Djemil T , Gajdos S , Ouzidane M , Tendulkar R , Khan M , Xia P
Published: August 2010

Purpose: Ultrasound, CBCT, and Electro‐Magnetic image‐guided radiotherapy (IGRT) techniques are widely used in prostate localization. Using a single phantom, our aim is to investigate the accuracy of these technologies. Method and Materials: A CT scan (1 mm slice) of an ultrasound phantom with three implanted transponders was acquired for this study. Ten treatment plans with 10 different isocenters within a range of 5 cm from the origin of the phantom were created. The contoured cavity and coordinates of the isocenters were exported to the three systems. The origin of the phantom was aligned to the lasers and the isocenters were localized by the three techniques. During the 30 localization experiments, the phantom was not moved. The measured shifts from each localization method were compared with the known shifts from the treatment plans. The differences between these shifts were analyzed. Results: The mean vector differences are 2.7 ± 0.5 mm, 0.9 ± 0.3 mm and 0.3 ± 0.1 mm for Clarity, CBCT, and Calypso system, respectively. Specifically, the mean differences in the lateral direction are 2.1 ± 0.4 mm, 0.3 ± 0.3 mm, and −0.17 ± 0.09 mm, respectively. In the longitudinal direction, the mean differences are −1.6 ± 0.2 mm, 0.6 ± 0.2 mm, and −0.1 ±0.1 mm, respectively inthe 0.4 ± 0.2 mm, 0.6 ± 0.2 mm, and −0.1 ±0.1 mm, respectively in the vertical direction. The maximum deviation from the known shifts is 3.1 mm for Clarity, followed by 0.9 mm for CBCT, and 0.3 mm for Calypso. These shifts are independent of the distances from each isocenter to the origin of the phantom. Conclusion: The three IGRT systems achieve different accuracy and it is important to understand the limitation of each system. Further studies for the impact of rotation on localization are warranted.
SU‐GG‐J‐69: Management of Inter‐ and Intra‐Fractional Variations in Abdominal Irradiation Using Gated In‐Room CT
Authors: Tai A , Peng C , Erickson B , Li X
Published: August 2010

Purpose: Images with high soft‐tissue contrast are desirable in the management of inter‐ and intra‐fraction variations for many anatomic sites, such as abdomen. We present a strategy of using a gated in‐room CT to guide gated treatment delivery for the management of interfraction (setup errors and anatomy changes) and intrafraction (respiration) variations in abdominal irradiation. Method and Materials:. The process started with a 4DCT scan acquired and sorted into 10 phases. The 3 sets of images (40%, 50% and 60%) corresponding to the 3 phases around the end of exhale were fused in the treatment planning system. The target was delineated on all 3 sets of images separately and the internal tumor volume (ITV) was generated by tracing the 3 target contours with no margin. A 5 mm margin was added to ITV to generate the PTV. All the contours of organs at risk (OAR) were drawn on the 50%‐phase CT. An IMRT plan was generated using a planning system (Prowess Inc). Prior to each delivery, a gated CT scan at the end of exhale was acquired using a CT‐on‐Rails (CTVision, Siemens). This gated treatment CT was registered with the planning CT starting with bony anatomy alignment, then fine tuned to soft‐tissue alignment to calculate shifts. The gated IMRT were delivered after patient repositioning. Results:. The registration of the treatment and planning CTs was accurate due to the high soft tissue contrast and the breathing synchronized acquisition for the two CT sets. The ITV volume was reduced due to the gated delivery by 20% on average. Doses to OARs were substantially reduced due to the reduced PTV margin. Delivery times were extended by 2–3 minutes by gating. Conclusion: The gated IMRT with gated CT‐on‐Rails guidance is an effective approach to manage inter‐ and intra‐fraction variations in abdominal irradiation.
SU‐GG‐J‐70: Prostate Bed Localization in Post‐Prostatectomy Image‐Guided Radiation Therapy
Authors: Zeng G , Do A , Lawrence K , Wang Y , McGowan T , MacPherson M
Published: August 2010

Purpose: Recent RTOG trials recommended CTV definition for post‐prostatectomy radiation therapy. Part of CTV anterior border has fixed relationship to pubic symphysis and other part of the CTV doesn't adjacent to bone and is affected by the movement of rectum and bladder. Either pelvic bones or surgical clips alignment is commonly practiced in IGRT, because either indicates part of CTV position. In this study we are investigating the differences between these two setups, since clips movement relative to bone may imply target deformation. Material and methods: 20 patients' verification images during prostate bed IMRT will be analyzed. The data of 6 patients who finished more than half of treatment are presented in this submission. 2D KV orthogonal images in Varian OBI system is used for patient setup. Pubic arch match in AP images is applied for Sup‐Inf and Rt‐Lt while symphysis match in lateral images for Ant‐Post setup. CBCT is performed for the first 3 fractions and weekly thereafter to check rectum and bladder preparations. After the treatment, surgical clips are retrospectively matched in Offline Review of Varian Aria system. The differences between bony and clips alignment are recorded. Results: The differences between bony and clips matches over 6 patients are 0.0±0.1cm, 0.0±0.2 cm and 0.2±0.4cm in Rt‐Lt, Sup‐Inf and Ant‐Post directions, respectively. The largest differences are found in Ant‐Post direction with 0.7±0.4 cm being recorded for one patient. Sup‐Inf and Rt‐Lt show random variations with smaller magnitudes. CBCT images indicate the rectum preparations cause CTV posterior border deformation and subsequently clips shifts relative to bone. Bladder fillings contribute to CTV Sup‐Inf variations. Conclusions: Initial data suggest larger CTV deformation in Ant‐Post than other directions due to soft tissue movement. Statistically sufficient data will be needed for asymmetric PTV margins to account for this deformation in IGRT.
SU‐GG‐J‐71: Cone Beam CT Hounsfield Unit to Electron Density Calibration and Its Impact on Dose Calculation Accuracy
Authors: Zhang L , Williamson J
Published: August 2010

Purpose: Accuracy of direct dose calculation on CBCT datasets is compromised by inaccuracy of reconstructed Hounsfield unit (HU) numbers in CBCT. Establishing HU to electron density (ED) calibration curves for CBCT can improve dose calculation accuracy on CBCT images. The goal of this study is to investigate effects of phantom volume and radial positions of inserting materials on HU‐to‐ED calibration for CBCT and evaluate impact of the calibration on dose calculation accuracy on CBCT datasets. Method and Materials: Catphan 600 and Gammex RMI 467 phantoms were used to characterize HU‐to‐ED calibration curves for both FBCT and CBCT. The effect of scatter volume on the HU‐to‐ED calibration was evaluated using the Catphan phantom fitted with annuli and the Gammex phantom in water. The CBCT HU‐to‐ED calibration was conducted by varying the radial positions of inserts in the Gammex phantom. The determined calibration curves were input into the Pinnacle TPS to calculate dose for an anthropomorphic pelvis phantom. Results: The scatter volume has negligible effects on the HU‐to‐ED calibration for FBCT. The CBCT HU‐to‐ED calibration curves vary significantly with the scatter volume and differ largely from that of FBCT. Large deviations of 330 HU and 700 HU in high density materials are observed for CBCT with the use of the modified Catphan and Gammex phantoms. In comparison to FBCT, the HU numbers on the CBCT HU‐to‐ED calibration curves are larger and smaller for materials less dense and denser than water, respectively. Radial position variations of inserts can cause HU number to change by up to 200 HU. The doses computed based on FBCT and CBCT of the pelvis phantom agree to within 3%. Conclusion: The CBCT and FBCT HU‐to‐ED calibration curves differ significantly. A fairly good dose calculation accuracy can be achieved using a single CBCT HU‐to‐ED calibration curve.