bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐74: A Dosimeter for In Vivo Real Time Verification of Intensity Modulated Radiation Therapy
Authors: Price S , Silvius A A , Izaguirre E W
Published: November 2011

Purpose: To study the feasibility of implementing a low cost, high speed in vivo real time dosimeter based on scintillating fiber arrays to verify intensity modulated radiation therapy (IMRT) to enhance treatment safety and delivered dose verification. Methods: Detector construction is performed by mounting linear scintillating fiber sensors in a water equivalent plastic support to form a homogenous water equivalent array. The fibers are aligned to match each MLC leaf pair and the detector is placed in the accessory tray of a clinical LINAC for beam output determination. Each fiber is coupled to a high speed photodetector and front end amplifier to process the detector output which is digitized and analyzed using in house developed software to compute the beam fluence, dose rate, and MLC opening. Results: The detector response correlates linearly with the LINAC beam intensity and MLC positions. The sensor and front end amplifier has a time response of 0.2 usec, thus every 2 usec LINAC pulse is recorded to determine the beam fluence with a precision better than 1%. The array offers a minimum beam attenuation of 2.4%, allowing the use of this technology as an in vivo transmission detector. We determined that the detector is capable of measuring the MLC opening with a precision of 2 mm per leaf. Conclusions: We have proven the feasibility of constructing a scintillating fiber sensor array for in vivo real time dosimetry to enhance patient safety during IMRT treatment and measure actual dose delivered to the patient. The technical highlight of this detector is based on the high speed of the linear sensors and front end amplifier which allows real time verification of the IMRT fluence output, dose rate, and leaf opening with a minimum of perturbation or absorption of the delivered beam.
SU‐E‐J‐75: Clinical Commissioning and Quality Assurance Procedures for a Wide Bore MRI Unit Configured for Radiation Therapy Planning
Authors: Hammoud R , Perkins G , Paloor S , Celik A , Al‐Hammadi N
Published: November 2011

Purpose: To develop a comprehensive protocol for the acceptance testing and clinical commissioning a wide bore (70cm) MRI‐Simulator for radiotherapy localization and planning.Methods: A GE 1.5T Optima 450W MR scanner was installed in our department in 2010. Standards derived from the ACR MRI Accreditation Program were used as reference for acceptance testing and commissioning. Commercially available phantoms were used to characterize magnetic field homogeneity, image intensity uniformity, high contrast spatial resolution, slice thickness, position accuracy and geometric accuracy. For 2D SE, GRE and 3D CUBE imaging sequences, in plane and through plane distortion and distortion correction accuracy with and without the GradWarp distortion algorithm provided the software was assessed. The test was performed using multi ROI at different locations off center with multiple slices using the Magphan® phantom. Couch position, couch load and laser system accuracy were also assessed. Daily QA procedures were developed for SNR, RF, isocenter position and the gradient linearity. Parameters derived from commissioning were utilized as baseline reference values for a comprehensive QA program. Results: For clinical commissioning, the MR scanner met the criteria established by the ACR MRI Accreditation Program .The results from ACR phantom showed that image quality specifications were met. The highest spatial frequencies were 9 lp/cm; visualized. The results from the monthly QA demonstrate that variations are within 1% of the commissioning data illustrating good self consistency as regards MRI simulator performance. In‐plane distortion measurements show that the distortion correction algorithm reduced the error to within acceptable (< 1mm at 30mm sup/inf to isocentre and within 2 mm at 120 mm off center) Conclusions: Analysis of the test results indicates consistent and reproducible operation of the wide bore MRI‐SIM unit. A comprehensive commissioning and QA protocol has been developed for use in the radiation oncology setting.
SU‐E‐J‐83: Feasiblity of Real Time Tumour Tracking in Low Field MRI ‐ A Phantom Study
Authors: Yip E , Yun J , Wachowicz K , Rathee S , Fallone B
Published: November 2011

Purpose: Real time adaptive radiotherapy of lung tumours is a promising application of the proposed hybrid Linac‐MR system. Several linac‐MR designs use low magnetic field strength (0.2T and 0.5T) imaging. Rapid real time imaging is potentially challenging due to the limited available contrast to noise ratio (CNR), especially at low MR fields. The goal of this phantom study is to quantitatively evaluate our in‐house tumour tracking algorithm with images of a moving lung tumour model with CNR equivalent to those obtained at 0.2T and 0.5T.Methods: A chest phantom with a moving lung compartment capable of 1D programmable motion is built. The lung compartment is loaded with mixtures containing MnCl2 and CuSO4 that simulates lung tumour/ healthy lung tissue by mimicking their relaxation properties at 0.2Tand 0.5T in the available 3T scanner. CNR of the acquired images is scaled down to 0.2T and 0.5T by addition of Gaussian noise. Dynamic bSSFP images (4 frames/s) are acquired with the lung compartment undergoing a series of pre‐programmed motion pattern based on patient data. An optical encoder is used to provide an independent reference measurement of phantom position while the lung compartment undergoes motion. In‐house automatic tumour tracking software is used to contour the tumour off‐line. The automatic contours are compared against user defined contours by evaluation of the centroid position error, and the Dice coefficient.Results: The average RMS errors of the contour centroids are < 0.5 mm and < 0.8 mm in all of our motion patterns in 0.5T CNR and 0.2T CNR images, respectively. Agreement with the user defined contours is excellent, with a dice coefficient of > 0.9 at both CNR levels Conclusions: Our auto‐contouring algorithm is able to accurately track a moving tumour with the limited CNR available from real time, low field MR sequences.
SU‐E‐J‐84: Radiation Induced Currents in RF Coil Conductors: Measurements and Simulations
Authors: Ghila A , Burke B , Fallone B , Rathee S
Published: November 2011

Purpose: The integration of a medical linac with magnetic resonance imaging (MRI) has the potential to provide exquisite soft tissue contrast and real time imaging during the radiation treatment. However, during a real time treatment‐imaging session, the direct irradiation of MRIˈs radiofrequency (RF) coil by the pulsed x‐ray beam induces a current in the conductor of the RF coil due to the release of Compton electrons. This radiation induced current (RIC) can potentially degrade the SNR in acquired MRI images. The present work investigates methods of minimizing this RIC both experimentally and through Monte Carlo simulations.Methods: Copper and aluminum metal plates emulating the conductors used in RF coils were connected to an amplifier and placed in an RF cage. The plates (i.e. “detector”) were irradiated by the linacˈs pulsed 6 MV beam through the RF cage. The induced signal was measured by an oscilloscope and recorded using a PC. Various materials were used as buildup in an attempt to establish electronic equilibrium in the “detectors” ‐ thus removing the undesired RIC. A Monte Carlo script was written which counts the amount of charge entering and leaving a specified “detector volume”, and determines the net change in charge per primary history as a measure of RIC. The simulation geometry mimics the experimental setup.Results: It has been clearly demonstrated by both measurements and simulations that buildup of the same material as the conductor will reestablish electronic equilibrium and remove the RIC. Also, using a polymer with a density close to that of the conductor (i.e. Teflon with aluminum) for buildup will reduce the RIC to negligible amplitude Conclusions: With the proper combination of coil conductor and buildup, the RIC can be reduced to negligible amplitudes. Future work will assess the importance of RIC for the SNR in MRI images.
SU‐E‐J‐86: Comparing Regional Perfusion Loss in Lung Cancer Patients Treated with 3D Conformal Radiation Therapy and Stereotactic Body Radiation Therapy
Authors: Yin L , Liu M , Wu J , Shcherbinin S , Celler A , Duzenli C , Moiseenko V
Published: November 2011

Purpose: To compare correlations between radiation and perfusion damage in lung cancer patients treated with 3D‐CRT (both radical and palliative intent) and SBRT. Methods: Eleven (3 palliative 3D‐CRT, 5 radical 3D‐CRT, 3 SBRT) non‐small cell lung cancer patients receiving radiation therapy were included in this study. 99mTc SPECT scans were performed before RT and 2∼3 months after RT. Perfusion images were reconstructed with quantitative attenuation and scatter corrections. These reconstructions were used to assess the change in lung perfusion, i.e. blood flow, as an effect of radiation on the normal lung during RT. Dose and corresponding percentage reduction in the SPECT intensity were used to establish dose‐response curve. Results: 1): No dose‐response was observed in the palliative patient group possibly due to tumor regression and reperfusion. The threshold dose of compensation (increased perfusion in low dose region) could not be found, although increased perfusion in either low dose or high dose volume was common. 2) A consistent pattern of compensation and reduction of perfusion was observed in four patients. D50, dose causing 50% reduction in perfusion ranged from 39 to 54Gy. Reperfusion was observed in one of the five patients in the radical patient group. 3) In the SBRT patient group, a consistent pattern of decreased perfusion was observed in two patients. Compared to patients treated with radical 3D‐CRT, the reduction in perfusion caused by high grade dose (>30Gy) is much smaller in SBRT patients (25% reduction at 45Gy compared to 35% in radical 3D‐CRT group). Conclusions: A strong correlation of radiation dose and perfusion change was found in patients treated with 3D‐CRT with a radical intent, but not palliative intent. Interestingly, perfusion loss in SBRT is smaller than 3D‐CRT, suggesting that normal lung in SBRT eligible patients is more capable of preserving lung function.
SU‐E‐J‐87: Imaging Biomarkers of Treatment Response: A Roadmap to Validation
Authors: Scully P , Jallow N , Vanderhoek M , Jeraj R
Published: November 2011

Purpose: Quantitative imaging measures are essential for assessment of tumor response to therapy; however, systematic validation is required before imaging biomarkers can be successfully implemented. We performed preliminary validation of the optimal image reconstruction parameters to maximize the accuracy of PET‐based imaging biomarkers. Methods: Optimal PET reconstruction parameters were determined using four spheres of various sizes (10–22mm) containing 168 kBq/cc of [18F]FDG. Spheres were placed inside a NEMA IEC body phantom. Scans were acquired on a GE VCT PET/CT scanner in both 2D and 3D mode. Multiple images were reconstructed using OSEM by varying matrix dimensions, iteration number, and post‐filtration. For each sphere, the recovery coefficient (RC) was used to measure quantitative image accuracy. Robustness of reconstruction parameters to sphere size changes was measured as the coefficient of variation (CV) of the RCs of the individual spheres within an image. Optimal reconstruction parameters were those which resulted in the highest average RC and lowest CV. Results: RC averaged over all four spheres ranged from 0.72 – 0.95 for the image reconstructions investigated. Higher RCs were observed for 2D acquisition mode than 3D (0.91 vs. 0.80), and for 22mm spheres than 10mm spheres (0.99 vs. 0.74). No such trends were observed for CVs. CV values varied by a factor of two across the reconstructions investigated, ranging from 9% to 17%. Image accuracy and robustness to lesion size changes were highest for 2D acquisition, 256×256 matrix, 2 iterations, and 3mm post‐filtration, yielding an RC of 0.92 and CV of ±9%. Conclusions: We successfully optimized image reconstruction parameters to maximize quantitative imaging accuracy, which will increase reproducibility of biomarkers. Future work will include test‐retest imaging of biomarkers in patients to quantify remaining uncertainties. This study represents a critical first step towards validation of imaging biomarkers of treatment response.
SU‐E‐J‐104: Is It Necessary to Do 4D‐CT for Chest Wall EBRT? A Motion Analysis
Authors: Xu Y , Ingram G , Lam S , Chong L
Published: November 2011

Purpose: To examine and quantify the chest wall motion for patients under EBRT for chest wall lesions using 4D‐CT, determine the necessity of 4D‐CT simulation for planning; and evaluate the requirement of respiration gated treatment for chest wall treatments. Methods: 4D‐CT is currently performed for all chest wall/breast patients in our clinic to assess the motion of the target volume for EBRT treatment. GE LightSpeed® 16‐Slice scanner and Varian PRM® system are combined to acquire the images, with the infrared reflector placed on patientˈs abdominal region where the most up‐and‐down motion is found. Patients are setup in supine position, with Wingboard® and Vac‐Bag® for immobilization. The raw 4D images were binned into ten phases (0–90%) using GE advantage 4D® application and then transferred to MIM Vista® for reviewing. To determine the largest shift of the chest wall/breast during a respiratory cycle, the highest point (on patientˈs skin) among all phases was selected. Then the distance between its highest and lowest position among all phases was recorded. Results: Ten chest wall/breast patients were initially selected. The average maximum shift was 0.18 cm, which is insignificant amount of movement even for IMRT treatment. Eight (five of which are male) lung tumor patients (with similar simulation setup) were added to the study, the focus was still on the motion of the chest wall/breast region (not treatment volume). The average maximum shift was 0.23 cm for all eighteen patients. Conclusions: It is believed that the patientˈs setup in this study greatly increases the diaphragmatic breathing. As a result, the chest wall/breast motion was found to be negligible in view of combined uncertainty of mechanical alignment and clinically relevant accuracy. Utilizing 4D‐CT for treatment planning and respiration‐gating for chest wall treatment seems unnecessary.
SU‐E‐J‐111: Skin Entrance Dose Estimation for the Radiographic Image Guidance at the Various Anatomic Regions of the CyberKnife Radiation Treatment
Authors: Kim J , Lee S , North D , Curran B , Sternick E
Published: November 2011

Purpose: The patient treatment data were collected, and skin entrance doses were estimated retrospectively using the preliminary exposure measurements. Methods: Forty‐one brain cases, 21 thorax cases, 16 spine cases, and 13 abdomen/pelvis cases were treated by CyberKnife irradiation from July, 2009, to February, 2011. The preliminary exposure measurements were performed with a 6 cc RadCal ion chamber at the iso‐center, whose distance was 230 cm from the focal spot of each X‐ray tube. Exposure measurements were made over ranges of 80 kV to 150 kV, 50 mA to 320 mA, and 50 msec to 640 msec. The total number of X‐ray images associated with each CyberKnife treatment was retrieved. Then, the skin entrance doses from imaging were estimated to the different anatomic treatment regions, such as brain, thorax, spine, and abdomen/pelvis, using the exposure measurements. Results: The average skin entrance dose for the brain region treatment was 17cGy (range of 3cGy to 53 cGy); for the thorax region treatment, 53cGy (range of 23 cGy to 112 cGy); for the abdomen and pelvis region treatment, 41cGy (range of 17 cGy to 111 cGy); and for the spine region treatment, 28cGy (range of 6 cGy to 68 cGy). Conclusions: The estimated average additional skin entrance dose from imaging delivered to the patients was 1.2% of the prescription treatment dose (range 0.2% to 4.6%).
SU‐E‐J‐115: A Study of Tumor Volume Parameters in Lung Cancer Patients and the Possible Effects on Tumor Motion
Authors: Elguindi S , Ewell L , Hepler C , Nguyen N
Published: November 2011

Purpose: To study volume parameters and how they might affect tumor motion in lung cancer patients. Methods: Nine patients with lung lesions were imaged with a Philips Brilliance Big Bore 4D CT scanner before and after receiving radiation therapy treatment. A single board certified radiation oncologist contoured all patient tumors in zero (maximum inhalation) and fifty percent (full exhalation) phases. Images were ported to the treatment planning system Pinnacle© 9.0. Volume measurements of the lesions were automatically obtained from these contours. Maximal tumor dimensions were obtained manually in the saggital, coronal, and transverse planes. Tumor motion was assessed from the centroid tumor locations (obtained automatically) between respiratory phases. Centroid distance to the diaphragm was also measured. Results: A comparison of the difference from the spherical equivalent volume (SV) based upon the maximal tumor dimension and the volume measurements from Pinnacle© were compared. A linear correlation (R̂2 = 0.972) was noted. A correlation using a power law fit was determined between tumor motion and distance from the diaphragm for the initial scan and subsequent rescan (R̂2 = 0.251 and R̂2 = 0.249 respectively). Tumor motion was separated based upon which planar view the maximal tumor dimension was found to be in. Tumors with the largest sagittal dimensions (5 scans) had an average and standard deviation in tumor motion of 0.47 +/− 0.61 cm, coronal (5 scans) had 1.29 +/− 0.43 cm, and transverse (8 scans) had 0.61 +/− 0.31 cm. Conclusions: The data suggests a correlation to estimate spherical equivalent volume (SV) and thus the maximal dimension of the lesion. Also, if this maximal dimension was found in the coronal view, those tumors exhibited approximately twice as much tumor motion between respiratory phases as compared with tumors with maximal dimensions found in the other planar views.
SU‐E‐J‐117: 4D‐CT: Low Pitch Helical. How Low Should You Go?
Authors: Klahr P , Dhanantwari A
Published: November 2011

Purpose: A basic tenet of 4D‐CT in helical mode is that each voxel at each position must be illuminated for the entire breathing cycle. This gives rise to the oft quoted equation pitch factor (PF) < BPM/RPM (breaths per minute divided by revolutions per minute). For cine axial mode, the equivalent requirement is the cine time (TC) > breathing period. The objective of this study is to demonstrate that these formulae are incorrect for helical scans and will require overlapped scans in cine axial mode. The PF adjustment and overlap percent are dependent on scanner geometry and reconstructed field of view (FOV). Methods: With wide detector scanners, it cannot be assumed that the x‐ray beam is parallel. Therefore, in calculating the total illumination time of any voxel, beam divergence must be addressed. It can be shown analytically that the FOV and source to isocenter distance will have significant impact on the time each voxel remains in the view of the multi‐detector rings. Results: Based on these calculations, PF is inversely dependent on FOV with a larger FOV requiring a lower pitch. In cine axial mode, the overlap percent increases with FOV. This overlap percent means that each couch increment will be less than the full detector collimation Conclusions: The commonly used approach for estimating PF or TC based on BPM is incorrect because it ignores the effects of beam divergence. For a geometrically accurate 4D‐CT scan, a new formula was developed and it is dependent on FOV and source to CT isocenter distance. A method to account for beam divergence in axial scans was also described.

Authors are employees of Philips Healthcare
SU‐E‐J‐118: Impact of Reference CT for Daily Localization of Mobile Lung Tumors
Authors: Glide‐Hurst C , Chetty I
Published: November 2011

Purpose: To systematically evaluate, in phantom and patient, differences obtained between using free‐breathing CT (FBCT) and average CT (AVGCT) as the reference dataset for daily treatment localization with cone‐beam CT (CBCT). Methods: Five displacement curves generated from Varianˈs RPM patient data were inputted into motion platform varied amplitudes and irregularities. FBCTs and 4DCTs were acquired under programmed motion conditions. CBCTs were acquired for phantom on Trilogy equipped with cone‐beam CT. Beam‐on information from RPM isolated appropriate platform motion for each curve studied. Manual registrations between FBCT/CBCT and AVGCT/CBCT were performed in Eclipseˈs Registration Workspace. Volumes and registration results were compared. Seven early‐stage lung cancer patients (mean ITV volume = 21.5 +/−22.4 cc) were studied. CBCTs (2–4/patient, n=26) were registered to both AVGCT and FBCT, evaluating 52 registrations overall. Results: In phantom, mean differences between using AVGCT and FBCT for CBCT localization were 0.01 +/− 0.24 mm, 0.24 +/− 0.23 mm, and 1.55 +/− 6.12 mm in lateral (LAT), anterior‐posterior (A‐P), and superior‐inferior (S‐I) directions, respectively. In one case, FBCT registration was 1.2 cm superior to that of the AVG‐CT. Over 52 patient registrations, mean differences between using AVG‐CT and FBCT as reference for CBCT registration were 0.4 +/− 1.3 mm, 0.2 +/− 2.0 mm, and 1.6 +/− 2.0 mm LAT, A‐P, and S‐I directions, respectively. Largest discrepancy between registrations was for small mobile tumor (6.2 mm S‐I) with FBCT at end‐exhale. Another case revealed 6.2 mm anterior shift between AVGCT and FBCT, which corresponded to obvious CT intensity differences. Conclusions: CBCT registration differences between the AVG‐CT and FBCT can be marked. FBCT as the reference image for daily CBCT on‐line image guidance, especially for SBRT, should be exercised with caution, and should be verified to ensure it is not representative of an extreme phase of patient breathing.
SU‐E‐J‐126: CT Simulation Uncertainties in Patients with Metallic Implants: Impact on 3D Conformal and IMPT Proton Therapy
Authors: Verburg J , Kooy H , Madden T , Seco J
Published: November 2011

Purpose: To correct for errors due to metallic implants in CT‐based patient simulation imaging. To quantify the impact of these imaging errors on treatment planning for 3D conformal and intensity modulated proton therapy (IMPT). Methods: Several methods were developed to correct for imaging errors in treatment plans for patients with metallic implants. CT metal artifact reduction methods were applied, the implant sizes were verified using CT‐based radiographs instead of reconstructed images, and implant‐specific CT to proton stopping‐power conversion curves were designed using an extended CT number range. 3D conformal proton therapy plans for chordoma patients with various implants were studied in retrospect. IMPT plans were designed in addition based on the original clinical prescriptions. After applying the corrections, all dose distributions were recalculated and compared to the original plans. Results: High‐density implants such as platinum coiling introduced significant errors in both 3D conformal proton therapy and IMPT. Proton range shifts > 1 cm were observed due to errors in the originally estimated size and material of the implant. CT artifacts resulted in range shifts of ∼ 5 mm. Treatment planning for patients with titanium implants was mainly affected by CT artifacts. Range shifts in the IMPT plans were again on the order of 5 mm. The impact of titanium on 3D conformal therapy was limited. Conclusions: Metallic implants result in uncertainty in CT simulation imaging for proton therapy planning and may compromise the accuracy and precision of treatment. The impact depends on the implant material and the proton delivery method. IMPT is more sensitive to these issues as compared to 3D conformal proton therapy. Implants with higher density also result in larger errors. Novel CT reconstruction and segmentation methods provide a significant reduction of errors.
SU‐E‐J‐127: Uncertainties in Planned Dose Due to the Limited Voxel Size of the Planning CT When Treating Lung Tumors with Proton Therapy
Authors: España S , Paganetti H
Published: November 2011

Purpose: Dose calculation for lung tumors can be challenging due to the low density and the fine structure of the geometry. The latter is not fully considered in the CT image resolution used in treatment planning causing the prediction of a more homogeneous tissue distribution. In proton therapy, this could result in predicting an unrealistically sharp distal dose falloff, i.e. an underestimation of the distal dose falloff degradation. The goal of this work was the quantification of such effects. Methods: Two computational phantoms, resembling a two‐dimensional heterogeneous random lung geometry and a swine lung were considered applying a variety of voxel sizes for dose calculation. Monte Carlo simulations were used to compare the dose distributions predicted with the voxel size typically used for the treatment planning procedure with those expected to be delivered using the finest resolution. Results: The results show, for example, distal falloff position differences of up to 4 mm between planned and expected dose at the 90% level for the heterogeneous random lung (assuming treatment plan on a 2×2×2.5 mm3 grid). For the swine lung, differences of up to 38 mm were seen when airways are present in the beam path when the treatment plan was done on a 0.8×0.8×2.4 mm3 grid.Conclusion: The two‐dimensional heterogeneous random lung phantom apparently does not describe the impact of the geometry adequately because of the lack of heterogeneities in the axial direction. The differences observed in the swine lung between planned and expected dose are presumably due to the poor axial resolution of the CT images used in clinical routine. In conclusion, when assigning margins for treatment planning for lung cancer, proton range uncertainties due to the heterogeneous lung geometry and CT image resolution need to be considered.
SU‐E‐J‐131: Safety of 131I‐Rituximab Outpatient Radioimmunotherapy of Non‐Hodgkin Lymphoma
Authors: Calais P.J. , Turner J.H.
Published: November 2011

Purpose: Establish the safety of outpatient 131I‐rituximab radioimmunotherapy (RIT) by determining prospective individual radiation absorbed dose to critical normal organs in patients and by calculating the radiation exposure to hospital staff, carers, and members of the public. Determine environmental impact of radioactive urine. Methods: Two hundred consecutive outpatients treated with 131I‐rituximab radioimmunotherapy for non‐Hodgkin Lymphoma with therapeutic activities between 1000 and 4500 MBq (mean 2290 MBq), predicated upon whole body radiation absorbed dose of 0.75 Gy, were studied. Their 292 family members/carers and 432 visitors wore TLD badges for the week during which the patients were confined to their home and contact with children and pregnant women was avoided. The entire urine output of the first 100 patients was collected for that week and measured. Results: All patients received 131I‐rituximab activities according to the prescribed dose of 0.75 Gy to whole body. Toxicity was limited to hematological grade 4 neutropenia in 10% of patients and thrombocytopenia in 10%. There were no episodes of bleeding or infection. The objective response rate (ORR) of 50 first‐line RIT was 98% with complete remission (CR) in 78%. The ORR for 142 consecutive patients with relapsed, refractory disease was 67% with CR in 50%. From 200 consecutive patients, radiation exposure to adult carers ranged from <0.01 mSv to 3.67 mSv (mean 0.48 mSv), to other co‐residing family members was <0.01 mSv to 1.2 mSv (mean 0.23 mSv), and to visitors sharing badges was <0.01 to 0.73 mSv (mean 0.17 mSv). Excreted urinary activity was typically <25% of administered activity. Conclusions: Outpatient 131I‐rituximab radioimmunotherapy of non‐ Hodgkin Lymphoma is safe and effective. The median radiation exposure of carers is within the range permitted by international guidelines. Release dose rates of less than 25 uSv/h at 1 m were attained within one week of therapy.
SU‐E‐J‐134: Effect of Reproducibility of the Deep Inspiration Breath Hold in Left Breast Cancer Radiotherapy
Authors: Harry T , Rahn D , Gu X , Jiang S , Yashar C , Cerviño L
Published: November 2011

Purpose: To evaluate the dosimetric impact of variable reproducibility of the Deep Inspiration Breath Hold (DIBH) level for left breast cancer external beam radiotherapy. Methods: Left breast cancer patients went through CT scans at FB and DIBH prior to external beam treatment. Deformable registration between the two data sets was performed using the demons algorithm on a GPU developed by Gu et al. PMB 55(1). With an in‐house program using Matlab, the vectors were verified for accuracy and applied to the FB image at 75%, 90% and 110% magnitude, in order to simulate fictional anatomical configurations with different breath hold levels . The new images were saved as DICOM files. These new images represent variable reproducibility of a patientsˈ DIBH level. The new DICOM Files were imported into the treatment planning system (TPS). The DIBH scan and the 75%, 90%, 110% fictitious scans were registered in the TPS based on the breast/chest surface. A treatment plan was created on the DIBH CT scan, and was copied to the registered breath hold images. Dose to the heart was calculated and compared for all the inspiration levels to determine the effect of the reproducibility of DIBH levels on the dose to the heart. Results: Preliminary results show that there is a significant effect on the location of the heart from FB to the various inspiration levels. Normal tissue complication probability decreases greatly from the FB to the breath hold scans, although it is patient dependent. Variation amongst the breath hold levels is less severe. Conclusions: We have developed a tool to quantify the effect of reproducibility of the DIBH level on dose to the heart in left breast cancer radiation treatments. Preliminary results show that the effect of DIBH reproducibility is less severe than the change from FB to DIBH.
SU‐E‐J‐135: Clinical Efficacy of Using KV‐CBCT Imaging Guided 6D Robotic Couch in Lung SBRT
Authors: Shang C Y , Williams T R , Kasper M
Published: November 2011

Purpose: To evaluate the clinical efficacy of 6D Robotic couch‐top in CBCT image‐guided stereotactic body radiotherapy (SBRT) for lung cancer. Methods: A total 94 analyzable setup cases for Lung SBRT using 6D robotic couch‐top were evaluated. The 6D robotic couch‐top, furnished by Protura (via Civco Medical Solutions™), can be mounted to the table pedestal of the Varianˈs TX accelerator. In addition to the original 4D corrections (3 linear motions and Yaw) offered by the Varian table pedestal, the 6D robotic apparatus allows two additional freedoms ‐ Pitch and Roll, which were investigated in this study. During setup, the patient anatomy from planning CT was first aligned to the kV‐CBCT in Varianˈs 4DTC 3D matching program. The 6D movements were then executed from the treatment console. Results: Concerning the values of Pitch and Roll corrections in the 94 setups using the 6D robotics, the mean absolute values of both adjustments were 0.86 ± 0.33 degree and 0.61 ± 0.31 degree respectively (p = 0.007). Greater than 0.5 degree angular corrections were observed in 69.1% cases for Pitch and in 51.1% cases for Roll, collectively accounting for 90.4% cases. Corrections for one degree or more in either Pitch or Roll consisted 51.1% of cases. However, the average raw adjustments in those were 0.07 ±1.03 degree and −0.11 ± 0.82 degree respectively. Conclusions: Comprehensive correction of high precision alignment for kV‐CBCT imaging guided lung cancer SBRT requires adjustments in all six dimensions, including unconventional Pitch and Roll rotations. About 51% of patients require at least one degree corrections in either Pitch or Roll. Less than 10% of cases Pitch or Roll correction were insignificant or smaller than 0.5 degree. Relative to the manual corrections, the automated 6D robotic process increased the efficiency of alignment when Pitch and Roll corrections were warranted.
SU‐E‐J‐137: Blurring Correction of Portal Images by 2D‐Deconvolution, Providing Enhanced Accuracy of Radiotherapy Patient Positioning Verification
Authors: Looe H K , Harder D , Poppe B
Published: November 2011

Purpose: To characterize and correct for the physical and geometrical effects impairing the quality of electronic portal image devices (EPIDs). Methods: EPID image blurring is due to: a) lateral transport of secondary electrons within the EPID, and its pixel size, b) geometric penumbra, c) scattering of photons in the patientˈs body. At an ARTISTE accelerator (Siemens) a) ‐ c) were characterized via the edge‐spread‐function (ESF). Assuming that the line‐spread function (LSF) takes the form of a Lorentz function 1/(1+x̂2/lambdâ2), each blurring component can be characterized by parameter lambda. For blurring correction the acquired raw image I(x,y), the convolution product of the true image I0(x,y) and the two dimensional convolution kernel K(x,y), is iteratively deconvolved. The iteration algorithm consists in a sequence of approximations I0,n(x,y), each of which is numerically convolved with K(x,y), resulting in an approximation In(x,y) to the blurred image. The next approximation I0,n+1(x,y) is derived by adding to I0,n(x,y) the difference I(x,y) − In(x,y). The iteration converges towards the desired I0(x,y) and is terminated using a X̂2‐criterion. Results : Geometrical penumbra and secondary electron transport plus pixel size in the EPID are the major contributors to image blurring. The lambda‐values of the combined effects amount to 0.5 mm for 6 MV and 0.65 mm for 15 MV. The evaluation of a line‐pairs phantom revealed that, after the deconvolution, the relative modulation transfer function (RMTF) of the system is approaching the one of an ideal detector. Clinical portal images show enhancement of contrast and sharpness, allowing for easier identification of anatomical landmarks. Conclusions: The blurring effects of EPIDs were characterized and corrected by an iterative deconvolution algorithm. The fast algorithm accomplishes corrections in real‐time, allowing routine patient positioning verification to be performed with increased accuracy.
SU‐E‐J‐152: Improving 4D CBCT Image Quality by Using Tumor Trajectory Based Rebinning with Orthogonal Dual Source KV Imaging of the Novel VERO System
Authors: Poels K , Depuydt T , Gevaert T , Reynders T , Tournel K , Duchateau M , Boussaer M , Verellen D , De Ridder M
Published: November 2011

Purpose: To improve image quality of 4D CBCT FDK reconstructions by rebinning using 3D tumor trajectories acquired with orthogonal dual source kV imaging. Methods: The Shepp‐Logan in‐silico phantom was used to generate artificial single and dual source projection images during 4D CBCT acquisition. The Shepp‐Logan phantom was modified by adding a 3 cm tissue equivalent sphere inside an air cavity. The sphere was moved inside the phantom by applying six minutes of tumor motion retrieved from a Cyberknife treatment. Images were generated with frame rates of 12 fps and an acquisition speed of 1 degree per second. Through detection of a marker inserted in the moving sphere, the 3D tumor motion trajectory was extracted from the projection data. The projection images were binned either based on the 1D marker motion in the cranial‐caudal direction for 8 phases or based on the 3D marker position using orthogonal images. The 1D rebinning technique was used for both the single and dual source acquisition. The dual source marker projections formed a 3D point cloud representing the tumor track. The track based rebinning used the 175 most proximal marker locations corresponding to 350 projections with minimal intra‐bin residual motion. Results: Differences between single and dual source CBCT images were small, although dual source CBCT used less breathing cycles. The contrast‐to‐noise ratio for the track based reconstruction was significantly higher compared to 1D rebinned reconstructions. An intra‐bin motion of 2.0 ±1.4 mm was found for 1D rebinned dual source images and 1.2 ± 0.4 mm for track based rebinning. Maximum intra‐bin motion after track rebinning was found to be 2.2 ±0.8 mm. Conclusions: Using track‐based rebinning for 4D CBCT in dual source acquisition, intra‐bin residual motion is reduced and image quality was improved for reconstructions with projection images from irregular breathing.
SU‐E‐J‐165: Unobtrusive Optical Fiber Rectal Balloon Deformation Sensor for Real‐Time Prostate Motion Monitoring
Authors: Zhao D , Campos D , Yan Y , Kissick M
Published: November 2011

Purpose: To design and develop an innovative prostate therapy motion sensor that applies an optical fiber based sensing technique to measure the deformation of a rectal balloon in order to measure real‐time prostate motion for radiation therapy. Methods: Based on the absorption spectraˈs high‐sensitivity to curvature in a long period grating (LPG) written in an optical fiber, a LPG based fiber sensor is utilized to monitor prostate motion by being attached to rectal balloon. To mimic very realistic prostate motion, we use an anthropomorphic prostate phantom modified by Kyoto Kagaku, Inc. with a large hole for the insertion of a sphere of realistic prostate size. It moves with a rigid bent arm attached to the Washington University 4D Motion Phantom. An inserted water tank allows for water to be around the prostate at all times as it moves. The rectal balloon, with fiber sensing head attached, is inserted into the phantom and placed adjacent to the prostate sphere. To detect the sensing signal, a broadband light source and an optical spectrum analyzer are used to complete the whole sensing system. Results: The prostate sphere movement results in curvature change of the fiber, and consequently spectral change of the LPG. The experimental results reveal that the spectral response of the LPG is linearly dependent on the degree of the curvature. Consequently, any position change of prostate is detected by monitoring the spectral change of the LPG‐based optical fiber sensing system. Since the sensorˈs sensitivities to curvature is up to 6.87 nm/m‐1, high displacement resolution of less than 0.1 mm is obtained. Conclusions: We have demonstrated a prototype of a novel real‐time prostate motion monitoring system based on optical fiber sensing techniques to measure rectal balloon deformation. Experimental results suggest the potential to improve radiation prostate treatment by monitoring prostate movement, when a balloon is used.
SU‐E‐J‐166: An Assessment of Single‐Fiducial versus Multiple‐Fiducial Prostate Positioning Accuracy
Authors: de Kruijf W , Verstraete J , van den Bergh L , Hol S , Davits R , Wijsman B , Neustadter D , Corn B , Poortmans P , Haustermans K
Published: November 2011

Purpose: Implanted fiducial markers are commonly used for high accuracy positioning of the prostate in radiation therapy. One source of error in fiducial‐based patient positioning is the rotation and deformation of the prostate. The sensitivity of fiducial‐based positioning to rotation and deformation depends upon the location of the center of mass (COM) of the fiducials relative to the COM of the prostate and on the stability of this geometric relationship throughout the treatment. This work assesses the geometric stability within the prostate of a single implanted trackable fiducial marker (Tracer, Navotek Medical Ltd.) relative to the COM of 4 gold seeds. Methods: In a multi‐site ethics committee approved clinical trial, 20 prostate radiation therapy patients were implanted with 4 gold seeds and one Tracer. CBCT imaging was performed during 5 treatment sessions to measure the locations of the implants. The locations of the Tracer and the COM of the gold seeds were compared in each treatment session, and the stability of the Tracer relative to the COM of the gold seeds from treatment to treatment was assessed. Results: The mean change in position of the Tracer relative to the COM of the gold seeds was 2mm +/− 1mm (mean +/− std) and increased with the distance between the Tracer and the COM of the gold seeds and with the amount of rotation of the prostate as estimated based on the positions of the gold seeds, as expected. Conclusions: The stability of the Tracer relative to the COM of the gold seeds was found to be similar in magnitude to the differences in positioning between any two highly accurate positioning methods. These results support the assertion that a single fiducial, placed near the COM of the prostate, can provide positioning accuracy comparable to multiple fiducials distributed around the prostate.

This research was funded by Navotek Medical Ltd.
SU‐E‐J‐172: The Effect of MVCT Image Quality Parameters on Dose Recalculation for Tomotherapy
Authors: Tournel K , Duchateau M , Reynders T , Gevaert T , Depuydt T , Boussaer M , Leysen K , Poels K , Verellen D , De Ridder M
Published: November 2011

Purpose: The tomotherapy MVCT images should in theory allow offline adaptive treatment monitoring by recalculation of the dose on each dayˈs image and summation over the entire treatment course. However, Instabilities in the MVCT‐beam can cause shifts in the calculated doses because of shifts in the HU‐calibration (Duchateau et al,2010 Phys. Med. Biol. 55). However, the significance of these shifts can only be established by performing the recalculation again using a newly acquired hu‐calibration curve using a density phantom or patient specific datapoints. This work aims in defining a clear threshold using simple image parameters such as mean HU shift and noise level on the image. This also allows to devise a strict QA program for the MVCT beam based on image quality, which can be accessed in a simple manner, as opposed to beam characteristics, which require service interventions. Methods: Simple spherical phantom‐images were created in dicom‐format with a mean HU‐value representing air, bone, fat, lung and muscle with no superposed noise (baseline set). This set was altered by a)shifting the mean HU and b)superimposing Gaussian noise‐levels of up to 30% (clinical observation). The dose was planned on the baseline set and recalculated on the other sets using the tomotherapy DQA‐ software. Results: Results show a deviation of 2% in dose for a 30HU‐shift in the water‐like region (fat, muscle) and a much lower sensitivity for the high and low densities(air,bone, lung) of about 0.5%. Noise levels had no influence on the center of the sphere when levels were below 20%. Conclusions: It is possible to predict changes in dose from the mean HU and noise level on MVCT images. To derive a clear threshold and a QA protocol, the measurements will be repeated using multiple HU‐images and finally on patients.
SU‐E‐J‐175: An Analysis of Localization Methods for SRS Using CBCT
Authors: Sudhyadhom A , Jhaveri J , Juneja B , Bova F
Published: November 2011

Purpose: To evaluate multiple methods of localization for stereotactic radiosurgery (SRS) for spatial accuracy and time required for each procedure. Methods: Multiple phantoms were imaged using a helical diagnostic computed tomography (CT) scanner (Toshiba™ Aquilion) and a linear accelerator mounted cone‐beam computed tomography (CBCT). Scans (for both machines) were acquired with a matrix of 512×512 at a field of view of 340 mm. A Varian Medical Systems™ absolute position phantom, in‐house created uniformity phantom, LUCY™ phantom, and Catphan phantom were each imaged to compare spatial homogeneity, linearity, spatial resolution, contrast, and uniformity. A final test of localization accuracy was completed by localizing a phantom using three different Methods: headring localization using helical CT, headring localization using CBCT, and “anatomical” localization using on‐board CBCT. Results: Average spatial localization errors from absolute phantom spheres were similar for the helical CT scanner (∼0.37 mm) compared with the on‐board CBCT (∼0.35 mm). R2 values for a line fit to the spatial position of the rods in the uniformity phantom scanned with CBCT were > 0.99. Spatial resolution of CBCT and CT were found to be similar using the CTP528 insert of the Catphan phantom (0.071 line pairs/cm). Spatial accuracy of localization by headring for CT and CBCT were similar but “anatomical” localization with CBCT may be less consistent. Conclusions: The spatial accuracy and linearity of CBCT may be adequate for stereotactic localization using a headring for SRS. Loss of low contrast resolution in CBCT may affect localization and position by CBCT alone. Headring localization using CBCT results in overall time savings without significant loss of spatial information. Localization by CBCT alone may result in increased spatial inaccuracies due to loss of contrast and potential MV radiation and on‐board imager isocenter mismatches.
SU‐E‐T‐25: A Learning Method for Assessing Margin Definition from Daily Image Deformations
Authors: Apte A , Mansur D , El Naqa I
Published: November 2011

Purpose: To investigate a new tool for quantification of deformations and optimal margin estimation from daily images using learning algorithms based on swarm intelligence. Methods: Swarm intelligence methods, specifically Ant Colony Optimization (ACO) are used to provide an efficient estimate of the optimal margin extent in each direction. ACO can provide global optimal solutions in highly nonlinear problems such as margin estimation. The proposed method is demonstrated using cases from stomach lymphoma with daily TomoTherapy megavoltage CT (MVCT) contours. Results: The process consists of two main steps that involve deriving organ motion probability and estimating the optimal margin. For motion probability, we used methods based on rigid registration. The estimation of the optimal margin was carried out using swarm intelligence based on the ACO algorithm. Preliminary results using Dice similarity index are promising. In order to achieve 95% coverage, the ACO ran for 25 nest relocations and converged in about 10 iterations with an optimal Dice metric of 0.88. It is expected that the proposed method will be helpful for guiding future margin estimation protocols. Conclusions: In this work, we have presented a new software tool and an algorithm for estimating organ motion margins from daily images. Our results indicate that the developed tool can provide improved visualization and quantification of daily deformations for estimating isotropic and anisotropic margins for radiotherapy treatment plans in cases where organ motion is an issue such as the presented example of stomach lymphoma, or in cases of lung and prostate cancers.