bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐EE‐A1‐02: Feasibility Study of Helical Tomotherapy for Total Body and Total Marrow Irradiation
Authors: Hui S , Gerbi B , Kapatoes J , Olivera G , Henderson D , Manon R , Mackie T , Welsh J , Fowler J
Published: June 2005

Purpose: Total body radiation (TBI) has been used for many years as a pre‐conditioning agent before bone marrow transplantation. Many side effects still plague its use. To assess the feasibility of using Helical Tomotherapy, we investigated various parameters and treatment techniques. Method and Materials: We studied variations in pitch, field width, and modulation on total body and total marrow helical tomotherapy treatments. We varied these parameters to provide a uniform dose along with a treatment times similar to conventional TBI (15–30 min.). We also investigated using limited total body mega‐voltage CT (MVCT) scanning rather than total body MVCT scanning to shorten the time per treatment fraction. Thermoluminescent detectors (TLDs) were placed inside a Rando phantom and we measured dose at seven anatomical sites including the lungs. Whole body MVCT and limited MVCT (head, chest, and pelvis) scanning were used for 3‐D set up verification. Results: TBI simulation showed homogeneous dose coverage to the whole body. Doses to the sensitive organs were reduced by 35–70 % of the target dose. In the TMI study, dose was mainly conformal to the bone marrow only. TBI and TMI treatment delivery time was reduced (by 50%) by increasing the field width from 2.5 cm to 5.0 cm in the inferior‐superior direction. TLD measurements on Rando showed accurate dose delivery to the target and critical organs. A limited MVCT reduced the target localization time significantly compared to whole body MVCT. Conclusion: This study showed that Helical Tomotherapy can deliver uniform dose to the total body and total marrow by a judicious selection of pitch, modulation, and field size. A limited MVCT also can be used in place of whole body MVCT. Details of this investigation will be presented. Conflict of Interest: The authors associated with TomoTherapy Inc. have a financial interest in that company.
SU‐FF‐I‐07: Respiratory Correlated CT: Acceptance and Clinical Introduction
Authors: Dekker A , Bosmans G , Öllers M , Boersma L , De Ruysscher D , Minken A , Lambin P
Published: June 2005

Purpose: Respiratory correlated CT (RC‐CT) has the potential to enable individual margins and prevent geometrical miss in radiotherapy for lung cancer patients. The objective of this study was to develop a procedure for acceptance and clinical introduction of RC‐CT. Method and Materials: RC‐CT was performed with a modified Siemens Sensation 10 and Biograph PET/CT with extremely low pitch (0.1) in combination with a respiratory signal obtained by a pressure sensor in a chest belt. Two phantoms were used for acceptance: Phantom 1: A ventilator (12 and 20bpm) and balloon, on which metal markers and the chest belt were positioned. This phantom was used to test the accuracy of the system. Phantom 2: A sphere moving 34mm(A‐P), 6mm(L‐R) and 34mm(Cr‐Ca) at 18bpm was used to evaluate distortion. Clinical introduction: In 16 NSCLC RT patients an RC‐CT was performed and tumor movement was measured. The volume within which the visible tumor moved(IGTV), was delineated and projected onto the regular CT/PET used for treatment planning. Results: Phantom 1: Correlation between reconstructed and true displacement of the markers with respiration was excellent (R=.992 p<.001 for the vector movement). The relation between true and reconstructed displacement was not significantly different from identity. Phantom 2: The distortion was minimal, in each of the ten respiration phases the sphere volume (65cm3) was accurately reconstructed within 4cm3. Patients: In all patients, RC‐CT could be successfully performed without coaching. The duration of the scan was always less than 90 seconds, with the whole procedure completed within 10 minutes. An RC‐CT delivered an estimated dose of 20cGy (CTDI). Mean and range of movement was 2.5±1.6,0–6mm(A‐P), 1.4±1.7,0–5mm(L‐R) and 4.4±4.5,0–15mm(Cr‐Ca). Conclusion: A procedure for acceptance and clinical introduction of RC‐CT has been developed. The results of the tested RC‐CT system were satisfactory and the system is now in clinical use.
SU‐FF‐I‐10: Evaluation of a Micro‐CT Scanner Applied to the Characterization of Pulmonary Architecture in the Rat
Authors: Yang K , Miller D , Plopper C , Lee D , Wexler A , Boone J
Published: June 2005

Purpose: With the rapid demographic shift towards urbanization worldwide, increasing numbers of children are exposed to ozone and particulate pollutants as a result of closer proximity to transportation corridors. To quantify the effect that ozone has on mammals, a rat‐lung cast model was developed and micro‐CT techniques were used to image the lung casts at high spatial resolution. Method and Materials: A normal rat lung was characterized. At sacrifice, the trachea was cannulated, and a RTV silicone compound was injected by syringe into the airways and allowed to harden. The rat tissues were decomposed using acid bath, so that a cast of the respiratory tree of each rat remained. A custom designed micro‐CT scanner was used to evaluate the lung casts. The system used a 70 micrometer focal spot tungsten anode, a rotating stage, and a 2048 × 1024 CMOS based indirect detector. Results: CT scans were acquired using the full resolution of the detector, and using between 300 and 1000 projection images. A cone beam reconstruction developed in house was used to generate high resolution volume data sets (eg. 1024 × 1024 × 512) of the lung casts. Conclusion: The micro‐CT scanner was able to accurately characterize the pulmonary structure of the rat from the lungs casts, and this approach was necessary to characterize the complex three dimensional pulmonary structures. This application of small animal imaging technology has enabled computer modeling and quantitative analysis of the biological issues surrounding ozone exposure using the rat model.
SU‐FF‐I‐17: Study On MOSFET Sensitivity Characteristics as a Function of Frame Rate in Modern Interventional Digital Pulsed Angiography/Fluoroscopy
Authors: Toncheva G , Yoshizumi T , Nguyen G , Frush D , Racadio J , Luckau N , Hallil A , Stueve D
Published: June 2005

Purpose: Application of MOSFET technology in modern interventional pulsed digital angiography/fluoroscopy presents a new opportunity to measure organ dose in real‐time using anthropomorphic phantoms. The purpose of this paper was to study MOSFET response characteristics to a series of short pulses (10 msec pulse width) at various frame rates. To the best of our knowledge, no data have been published on the response characteristics of high sensitivity diagnostic MOSFET using modern interventional pulsed fluoroscopy system. Method and Materials: High sensitivity MOSFET detectors (model TN‐1002RD, Thomson‐Nielson, Ottawa, Canada) and an ion chamber (model 10×5–6 ion chamber and model 9015 monitor, Radcal, Monrovia, CA) were exposed to a series of pulsed x‐ray beams (pulse width 10 msec) at different frame rates and MOSFET response characteristics were studied as a function of frame rate. To simulate patient, aluminum plate (total thickness 1.5″) was placed between the patient table and a flat panel detector. Philips Integris Allura 3‐D rotational angiography system was employed. The frame rate was varied as follows: 0.5/s, 1/s, 2/s, 3/s, 7.5/s, 15/s, and 30/s. These frame rates cover entire spectrum of clinical applications; from interventional radiological procedures to cardiac catheterization applications. Results: Normalized MOSFET responses (mV/Roentgen) were plotted as a function of frame rate and MOSFET responses were constant as a function of the frame rate. Conclusion: Using state‐of‐the‐art interventional radiology x‐ray system, we observed that response characteristics of the MOSFET remained constant as a function of frame rate. This suggests that MOSFET technology may be used for interventional angiography and cardiac catheterization dosimetry.
SU‐FF‐I‐20: Improved Image Quality And Dose Efficiency with a Next‐Generation Interventional Cardiac Digital Flat Panel (DFP) System
Authors: Belanger B , Nicolas F , Desponds L , Betraoui F , Dubroeucq G , Gopinath P
Published: June 2005

Purpose: Cardiologists are treating smaller coronary vessels using stents with less metal content and smaller micro strut thicknesses designed to reduce in‐stent restenosis rates. We present the image quality and dose measurements of a next‐generation digital flat panel (DFP) cardiovascular angiography system optimized to meet the needs of these demanding interventional procedures. Specific improvements include a detector with higher DQE at fluoroscopic (73% at 1 μR) and record (79%) doses, optimized xray exposure factors based on a neural‐net patient thickness estimation, and an xray source with higher fluoro power and increased range of spectral filtration. Performance improvements are demonstrated in a controlled comparison with the most widely installed state‐of‐the art DFP system. Method and Materials: Measurements of image quality and dose were made using the standard cardiovascular benchmarking SCAI‐NEMA phantom on a state‐of‐the‐art Innova®2000 and the new DFP system. Low contrast iodine visibility and phantom entrance dose were measured for simulated medium and large patient sizes using 20 and 30 cm thicknesses of polymethlymethacrylate (PMMA), respectively. Other measurements included limiting resolution, dynamic range and moving guide wire visibility, using the standard 20 cm phantom configuration. Measurements were obtained using normal mode, 30 frames per second (fps) fluoroscopy over all fields of view. Results: The new DFP system demonstrated significant improvement (p<=0.05) in low contrast iodine detectability, at equal or lower doses, and in moving wire visibility. Working thickness (dynamic range) was improved. Spatial resolution limits were comparable. Conclusions: The SCAI‐NEMA measurements strongly suggest that, compared to the current state‐of‐the‐art DFP system, the new interventional cardiovascular DFP system will provide better dose efficiency with a significant improvement in device and vessel visibility in a cardiac environment marked by anatomical motion. Images and data demonstrating stent visualization improvements will also be presented. Conflict of Interest: Authors are employees of a medical imaging equipment manufacturer.
SU‐FF‐I‐28: A Novel Simulated Method of Quantifying Susceptibilities in Objects: The First Step Toward Quantitative Diagnosis in MRI
Authors: Hsieh C , Cheng Y , Liu Q , Haacke E
Published: June 2005

Quantifying tissue susceptibilities in‐vivo is important because certain tissue susceptibilities may reflect health conditions of an individual. Many researchers have accurately measured susceptibilities of different materials using the least‐square‐fit method when the object sizes occupy at least 50 pixels on MRI. In this abstract we have developed a new approach to measure susceptibilities of small objects from MRI. We first simulated a disk with a radius of 16 pixels on 4096×4096 magnitude and phase images. The disk was a cross section of an infinite tube, perpendicular to the main magnetic field in MRI. The magnitude inside the disk was zero but unity outside the disk. The echo time and the field strength were chosen as 5ms and 1.5T. The phase was then simulated according to the well‐known physics laws in magnetostatics, with a −9ppm susceptibility difference inside and outside the tube. Through a low‐pass k‐space filter, the sizes of images were then converted to 256×256 such that the radius of the disk became roughly 1 pixel. The 256×256 magnitude and phase images would be almost identical to images acquired from a 1.5T MR system, with an air tube of radius 1mm perpendicular to the magnetic field and surrounded by water. Our images were simulated with different tube radii as well as with and without Gaussian noises. Two circles around the disk were drawn on images. The centers of these two circles were coincided with the center of the disk. With each circle, the complex signal was summed. We were able to solve the susceptibility from an inverse approach, based on the known disk sizes, the comparisons of the obtained complex sums, and a theoretical model. Without the presence of noise, the solved susceptibilities were within 1% accuracy compared to −9ppm. With the presence of noise, the results are more complicated.
SU‐FF‐I‐40: Image Registration and Voxel Based Analysis for the Differential Diagnosis of Corticobasal Degeneration and Progressive Supranuclear Palsy
Authors: Juh R , Suh T , Choe B , Lee C
Published: June 2005

Purpose: This study measured the cerebral glucose metabolism in patients suffering from corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP). PSP and CBD are neurodegenerative disorders that may be accompanied by dementia and parkinsonism as clinical symptoms. The aim was to determine if there was a different metabolic pattern using 18F‐labeled 2‐deoxyglucose (18F‐FDG) positron emission tomography (PET). Method and Materials: The regional cerebral glucose metabolism was examined in 8 patients with a clinical diagnosis of CBD (mean age 69.6 ± 7.8 y; male/female: 5/3), 8 patients with probable PSP (mean age 67.8 ± 4.5 y; male/female: 4/4) and 22 healthy controls. Statistical parametric mapping (SPM) using a voxel by voxel approach (p<0.001, 200 voxel‐level) was used to compare the regional cerebral glucose metabolism between the 3 groups. Results: Compared with the normal controls, asymmetry in the regional glucose metabolism was observed in the parietal, frontal and cingulate in CBD patients. In the PSP patients, the glucose metabolism was lower in the orbitofrontal, middle frontal, cingulated, thalamus and mid brain than their age matched normal controls. A comparison of the two patient groups demonstrated relative hypometabolism in the thalamus, the mid brain in PSP and the parietal lobe in CBD patients. Conclusion: These results suggest that when making a differential diagnosis of CBD and PSP, voxel based analysis of the 18F‐FDG PET images using SPM might be a useful adjunct tool in clinical examinations.
SU‐FF‐I‐49: The Effects of Magnetic Field On Energy Resolution and Linearity in SPECT System
Authors: Rasaneh S , Rajabi H , Farsinejad M
Published: June 2005

Purpose: Inside a Photomultiplier tube (PMT) electrons are accelerated. When directions of electron are perpendicular to earth magnetic field, Lorenz force could be equivalent to 10V cross voltage applied to PMT. Such force divers electrons and considerably change the electron multiplication, hence the gain of PMTs. In this study, we evaluated the effects of magnetic field in photo peak, energy resolution and line spread shifting in three SPECT systems when the heads rotate in different angles. Method and Materials: Three SPECT system available in our department were examined. One Pointe source including 5 mCi of 99mTc were fixed on the face of collimators (LEHR). The peak and FWHM of energy spectrum were determined. Then two Line sources of 5 cm long including 150 μCi of 99mTc were fixed on the face of collimators (LEHR). The linearity were determined. The procedure was repeated while heads rotate in different angles. One air conditioner was placed at 3‐meter distance from the camera gantries and the whole procedures were repeated . Results: In all three systems the maximum variations observed in energy photo peak, peak of LSF and linearity are statistically significant (p<0.01) when the heads rotate in earth magnetic field. when the air conditioner was functioning, the height of energy spectrum peak was less than when the AC was off. In one of the system variation were much more prominent than the two other systems. This most probably was due to orientation of the system not to intrinsic construction. Conclusion: When the heads of SPECT systems rotate, the magnetic field can vary energy resolution and linearity of systems. It is suggested that when SPECT systems are installing, the setting orientation be noted more accurately.
SU‐FF‐J‐66: Iso‐NTCP Dose Escalation with Image‐Guided Adaptive Radiation Therapy (IGART) for Localized Carcinoma of the Prostate
Authors: Song W , Schaly B , Bauman G , Battista J , Van Dyk J
Published: June 2005

Purpose: To evaluate the efficacy of various image‐guided target localization techniques to assist in the safe dose escalation for prostate cancer radiation therapy in the presence of geometric uncertainties. Method and Materials: Five prostate cancer patients were analyzed, retrospectively. All patients were planned with an 18MV six‐field conformal technique with a 10 mm margin and an initial prescription dose of 70 Gy in 35 fractions. For the dose escalation study, the prescription dose was increased from 50 Gy in 2 Gy increments until the rectum normal tissue complication probability (NTCP) reached the level equal to that of the plan NTCP (i.e., iso‐NTCP). The target localization techniques simulated were (1) laser alignment to external tattoo marks, (2) alignment to bony landmarks with daily portal images, and (3) alignment to the clinical target volume (CTV) with daily CT imaging. Techniques (1) and (3) were re‐simulated with a reduced margin of 5 mm to investigate further dose escalation. Results: The selection of the target localization technique was less critical on the treatment outcome when 10 mm margin was used. Reducing the margin size from 10 to 5 mm effectively decreased the NTCP by ∼60 % for all patients. For iso‐NTCP dose escalation, to our surprise, the average dose and TCP gain for the five patients were largest with the external tattoo technique (6.4 Gy and 7.5 %, respectively) followed by the daily CTV and the bony landmarks. The variability in gain across the five patients, however, was also largest with the tattoo registration technique and smallest with the daily CTV technique. Conclusion: Based on these data, the best dose escalation strategy is to combine margin reduction (for increased normal tissue sparing) with the use of the daily CTV technique to localize the target volume (for consistent dosimetric coverage and escalation).
SU‐FF‐J‐70: Respiratory Gated Radiation Therapy Directly Using Patient's Fluoroscopic Images Instead of External Or Internal Markers
Authors: Guan H , Yan H , Yin F , Kim J , Keall P , Vedam S , Movsas B
Published: June 2005

Purpose: To develop a respiratory gated radiation therapy (RGRT) technique by directly matching the patient's anatomical structures acquired during the imaging cycles to that in a reference image. Method and Materials: Studies showed that the external markers and the internal treatment volume are not always well correlated during the RGRT. Here we propose to measure the correlations of a reference image to the fluoroscopic images acquired during the breathing cycles. Such correlation measurement can be the surrogate for the external markers. A threshold of the correlation can be used to trigger the linear accelerator (Linac) for RGRT. With the capability of acquiring fluoroscopic images from the on‐board imaging (OBI) device developed by Varian, this approach becomes available. In this study, we measured the correlation coefficient (cc) and the root mean square (rms) error of the reference image to the on‐line fluoroscopic images. Results: In order to do efficient gating, the calculation of the correlation of one image to the reference should be 1–10ms and this can be easily achieved in our preliminary study. Also, the correlation can be better calculated by sparsely sampling the calculation pixels around the treatment volume rather than using a local ROI inside the volume. In the former, we found that both the cc and the rms demonstrated good periodicity. As we expected, the external marker locations recorded by the RPM software not always correlate well with the cc and rms. Conclusion: We demonstrated that RGRT by matching the patient's anatomical structures is highly feasible. The reference image can be the one from a gated fluoroscopic image or DRR from a gated CT scan. This technique will allow both gating and tracking and can be significant for high dose high‐precision radiation therapy with reduced margins for moving targets.
SU‐FF‐J‐78: Evaluation of Setup Accuracy for Hypofractionated Radiotherapy of Liver Using Portal Imaging and On‐Line KV Fluoroscopy
Authors: Bissonnette J‐P , Hawkins M , Moseley D , Eccles C , Siewerdsen J , Jaffray D , Dawson L
Published: June 2005

Purpose: To compare image‐guided accuracy for stereotactic radiotherapy of the liver in terms of reproducibility and targeting confidence. Method and Materials: The study involved eight patients treated for inoperable liver metastases or hepatobiliary carcinoma. Each treatment fraction, these patients were imaged and repositioned using orthogonal portal images acquired in AP and lateral views. Repositioning occurred when the measured offset exceed 3mm in any of the cranio‐caudal (CC), anterior‐posterior (AP), and medio‐lateral (ML) directions. A second pair of orthogonal images assessed the residual setup accuracy. Orthogonal fluoroscopy sessions, each lasting 30 s, were acquired; some prior, but most after radiotherapy delivery. All images were acquired with the patient under active breathing control. All treatments were performed using a conventional medical linear accelerator equipped with a kilovoltage x‐ray source and flat‐panel detector mounted at 90 degrees from the linac beam central axis. The right diaphragm was used as a surrogate for the liver position. The reproducibility and stability of the diaphragm was thus analysed for a total of 48 fractions. Results: After initial setup and repositioning, the residual setup error determined from portal images was 2.6 (CC), 3.0 (AP), and 2.6 mm (ML); conversely, the residual setup error measured from the kilovoltage fluoroscopy sessions was 3.2 (CC), 3.1 (AP), and 2.1 mm (ML). Conclusion: Daily portal imaging and repositioning based on these images improves setup accuracy. Similar accuracy is shown from kilovoltage fluoroscopy analysis. On‐line fluoroscopy can potentially assess patient position prior and after delivery of radiation therapy, and provide a baseline for cone‐beam CT analysis. Conflict of Interest:: This work is supported, in part, by Elekta Radiation Oncology. LD is supported by an ASCO career development award.
SU‐FF‐J‐95: Comparison of a Center‐Of‐Volume Contour‐Based Alignment and a CT Image‐Based Automatic Alignment of Prostate Target in CT‐Guided Radiotherapy
Authors: Zhang L , de Crevoisier R , Bonnen M , Kuban D , Mohan R , Dong L
Published: June 2005

Purpose: Due to organ deformation, the validity of using center‐of‐volume (COV) for prostate alignment has not been evaluated against other approaches and vice versa. The goal of this study was to compare two methods of prostate target alignment: one used manually delineated contours and the other used a combination of automatic and manual image registration method. Method and Materials: In an IRB‐approved protocol for repeat CT imaging using a CT‐on‐rails system, 15 patients received 3 CT scans per week over a period about 8 weeks. For each of the 353 CT images, the prostate was manually contoured by two radiation oncologists and checked by one of them. The center of volume (COV) was computed based on the gravity center of the contour containing the prostate. A CT‐Assisted Targeting (CAT) software was also developed in‐house for on‐line CT image‐guided radiotherapy. The registration algorithm consisted of cost functions that were designed to provide accurate, robust and automatic detection of the prostate. The daily position of the prostate was calculated using both the COV method and the CAT software. For the later, the results were also reviewed in every CT images and adjusted when necessary. Results: The mean differences (±1SD) between COV and CAT alignments were −0.2±0.9 mm, −0.4±1.5 mm, and 0.7±2.4 mm in lateral(RL), anterior‐posterior(AP), and superior‐inferior(SI) directions, respectively. The results of alignments were highly correlated (p<0.0001) in all directions. Although large differences are few, an outlier analysis showed that large differences were due to (1) inter‐observer variation in contouring the reference CT and the daily CT (61%), (2) large deformations of anatomy (65%), and (3) the combination of both (45%). Conclusion: We found that both the COV method and the CAT alignment agreed well to within 2mm in RL, 3mm in AP, and 5mm in SI for 95% of alignments.
SU‐FF‐T‐40: Monte Carlo Calculation of Pd‐103 Prostate Implant Treatment Plan
Authors: Napolitano M , Butler W
Published: June 2005

Purpose: A TheraSeed® Model 200 prostate implant treatment plan calculation based on TG‐43 formalism will be compared to a Monte Carlo (MCNPX) simulation of the treatment plan complete with detailed seed geometry. Dose contour lines as well as specific dose points will be compared. Method and Materials: Co‐ordinates from typical pre‐plan treatment plans were used to set up 3‐D Monte Carlo simulations of a small prostate (84 seeds) and a medium prostate (107 seeds). The seeds were modeled in full geometric detail and placed in a 50 cm sphere of water. The Model 200 seed geometry was previously benchmarked in a single seed configuration against published TG‐43 dosimetry parameters. Surface Crossing Tallies and Energy Deposition Tallies were used to calculate dose at specific points for comparison to dose points calculated in treatment planning software. Mesh tallies were used to create isodose lines for comparison to those calculated by the TG‐43 based treatment planning software. MCNPX flux values were converted to absolute dose based on NIST measured Air Kerma Strength and NIST measured contained activity measurements of TheraSeed® Model 200. Results: Comparison of the 75, 100, 110, 150, and 200% isodose lines for a series of planes within the treatment area yielded reasonable agreement. As expected some variation from the treatment planning software isodose lines is seen due to attenuation from surrounding seeds as well as differences in the dose distribution surrounding the seeds. Selected dose points along the urethra yielded dose values with a maximum deviation of 20% between the treatment planning software and Monte Carlo calculation. Conclusion: Full three dimensional Monte Carlo modeling of a typical treatment plan is possible in order to make dose comparisons to TG‐43 based formalism calculations for a typical treatment plan configuration. Conflict of Interest: Corresponding author is an employee of Theragenics Corporation®.
SU‐FF‐T‐42: Monte Carlo Study of Delivered Dose as a Function of Applicator Material in HDR Brachytherapy
Authors: Danford C , Gladstone D
Published: June 2005

Purpose: Intracavitary HDR brachytherapy is used to treat gynecological tumors. Our system was first delivered with acrylic cylindrical applicators but these were sensitive to heat sterilization and were replaced with Delrin. We note the density of these materials increases from 1.19 g/cm3 to 1.43 g/cm3. We investigate the effect of the higher density applicators on the delivered dose distribution using Monte Carlo calculations. Method and Materials: Doses were calculated with the EGSnrc system, using DOSRZNRC. The cylinders, tandem tubes, transfer guide tubes, and the source wire were modeled as concentric open cylinders. For full backscatter, the phantom was modeled as water outside the cylinder to a minimum distance of 22 cm from the outer surface of the applicator. Primary and secondary emitted photons were followed down to a cutoff energy of 1 keV, and Compton scattered electrons were followed down to 10 keV. Total accumulated dose was scored at the surface of each cylinder and at 5 mm and 10 mm from the surface. All clinically available cylinders from 2 cm to 4 cm diameter and for both materials were modeled. Twelve and a half billion histories were run for each study. Results: Dose to the points of interest varied from 0.5% to 1.5% between the two materials with the dose at the points of interest being higher for acrylic cylinders than for Delrin. The differences are a function of cylinder size with the largest difference seen in the 4 cm diameter cylinders. Conclusion: The change in material from acrylic to Delrin results in systematically decreased dose to the patient. This decrease in dose is a function of cylinder size but is not large enough to be clinically significant. We recommend using the Delrin cylinders as they are more easily sterilized between uses.
SU‐FF‐T‐72: Effect of Number of Beams On Dose Gradients and Quality of IMRT Plans T‐B Nguyen
Authors: Xia P
Published: June 2005

Purpose: To investigate the dose gradient as a function of number of beams and the role of beam angle selection in IMRT plans Method and Materials: A hypothetical tumor and an organ‐at‐risk (OAR) were created in a cylindrical phantom, with two different tumor‐OAR distances: 3mm and 7mm. For each tumor‐OAR arrangement, 22 plans with different beam configurations were generated using 3, 4, 6, 9 and 15 equally spaced beam angles. 6 additional plans were created for the beam number of 3, 4 and 6 using selected beam directions based on tumor‐OAR geometry. All plans were compared based on the same dose coverage to the tumor, the plan conformal index, dose gradient (defined by the minimum distance between the 90% and 20% of iso‐dose lines), maximum dose and mean dose to the OAR. Results: The dose gradient is linearly broadened as the number of beams is increased. The plan conformal index is rapidly improved from 3 to 6 beam angles. The maximum dose (defined as D1%) to the OAR is linearly decreased as the number of beams is increased while the mean dose to the OAR is decreased only from 3 to 9 beam angles. When compared to the equally spaced beam directions for a given number of beam angles, the selected beam angles can only improve the mean dose to the OAR. Conclusion: Using more beams in IMRT plans can improve plan conformality and reduce maximum dose and mean dose to the OAR, but it may broaden the dose gradient, which is defined as a minimum distance from 90% to 20% isodose lines. The tumor‐OAR geometry is not a good indicator for beam angle selection in IMRT planning. Conflict of Interest: Research is supported in part by Prowess Inc.
SU‐FF‐T‐85: Radiation Induced Cancer After Radiotherapy: The Impact of IMRT and Proton Radiotherapy
Authors: Schneider U , Lomax A , Pemler P , Besserer J , Ross D , Lombriser N , Kaser‐Hotz B
Published: June 2005

Purpose: There is concern about the increase of radiation induced malignancies with the application of modern radiotherapy treatment techniques such as IMRT and proton radiotherapy. In this work we analyze not only x‐ray scatter and neutron radiation, but also the impact of the primary dose distribution on secondary cancer incidence. Method and Materials: The organ equivalent dose (OED) concept with a linear‐exponential dose‐response curve was applied to 3D dose distributions of 30 patients who received radiotherapy treatment of prostate cancer. From the 30 patients 11 received 3D conformal radiotherapy, 11 IMRT with 6MV photons and 8 spot scanned proton radiotherapy. The IMRT treatment plans were re‐calculated with 15 MV photons. For 18 MV photons the OED was approximately calculated. From the OED of the different treatment techniques secondary cancer risk was estimated. Results: IMRT prostate treatments using low energies result in a modest increase of around 15% of radiation induced cancer compared to conventional four field planning with 15 MV photons. Using energies larger than 10 MV for IMRT could increase the probability to develop a secondary cancer by more than 20% (15MV) and 60% (18MV). The use spot scanned protons for treatment can reduce the secondary cancer incidence significantly by about 50%. Conclusion: By including the primary dose distribution into the analysis of radiation induced cancer incidence the resulting increase in risk for secondary cancer using modern treatment techniques such as IMRT is not as dramatic as expected from earlier studies. By using an energy of 6 MV only a moderate risk increase can be expected. Spot scanned protons are the treatment of choice in regard to secondary cancer incidence.
SU‐FF‐T‐107: Analytical Modeling of Pencil Beams to Include Compensator‐Related Beam Perturbations
Authors: du Plessis F , Ma C , Willemse C
Published: June 2005

Compensators can be utilized as radiation beam intensity modulators. In order to use it effectively, aspects like beam hardening and compensator‐induced scatter should be taken into account in dose calculations. The shape of the compensator for IMRT purposes can be realized through inverse planning techniques from a weight matrix. The BEAM MC code was used to generate three phase‐space files located above the jaws for generic accelerators based on Philips SL6 and SL25 machines with beam energies of 6, 8 and 15 MV. Each beam energy spectra was extracted with the BEAMDP code and were used in parallel beam source models in the DOSRZnrc MC code. Pencil beam dose distributions were scored in a cylindrical water phantom model. A series of simulations were performed where, each time, the PB was allowed to traverse a different slab thickness (0, 1, 2, 3 and 5 cm) of compensator material located at 33 cm above the water phantom model. The simulations were repeated for different materials that include wax, aluminum, copper, brass and lead. In this study it is shown how the change in the PB dose profiles at each depth can be analytically modeled so that it can be predicted as a function of material thickness. The effect of these corrections are evaluated against full Monte Carlo simulations and were found to replicate CAX depth dose curves within 1.5 percent in most cases. The inclusion of compensator effects in the PB model can then be utilized as a tool to derive the shape of a compensator from a desired dose profile in an efficient way.
SU‐FF‐T‐113: Incorporating Intra‐Fraction Motion Into IMRT Plan Optimization
Authors: Shepard D , Cao D , Earl M , Naqvi S , D'Souza W
Published: June 2005

Purpose: For treatment planning, clinicians typically compensate for respiratory motion by applying treatment margins that ensure the clinical target volume (CTV) always remains in the treatment field. We have investigated a more sophisticated approach where the pattern of organ motion is directly incorporated into both the dose calculation process and the optimization of IMRT treatment plans, and we have evaluated the degree to which plan quality can be improved by accounting for intra‐fraction organ motion during IMRT optimization. Method and Materials: In this study, we employed a convolution/superposition based dose calculation that incorporates organ motion. For each photon history, the isocenter is randomly sampled from a probability distribution defined by the respiration‐induced anatomical displacement. The resulting blurred pencil beam dose distributions have been incorporated into our IMRT plan optimizations. Comparisons were made between plans optimized using a motion‐based dose calculation and those optimized using a static dose calculation. Tests were performed for both a concave target in a phantom and a lung cancer patient. Results: For the phantom case, the mean dose to the adjacent organ‐at‐risk was reduced from 67.3% to 48.4% of the prescribed dose when motion was included in the optimization. For the lung patient, the volume of the right lung receiving greater than 80% of the prescribed dose was reduced from 14.1% to 7.2% when organ motion was included in the optimization. Conclusion: The motion‐based optimization accounts for the fact that the CTV will not be at all locations with equal probability and is thus more sophisticated than the application of patient specific margins. Consequently, significant additional sparing of critical structures can be achieved by incorporating intra‐fraction organ motion into IMRT optimization. Additionally, the agreement between the predicted and delivered doses is improved because the impact of organ motion has been accounted for in the dose calculation.
SU‐FF‐T‐122: Progressive Articulation of Radiotherapy Planning Goals Based On Soft‐Constraints
Authors: Jee K , McShan D , Fraass B
Published: June 2005

Purpose: Inverse‐planning in radiation therapy is involved with multicriteria decision‐making problems as it aims to achieve multiple planning goals that are conflicting with each other in target(s) or surrounding healthy tissues. To facilitate an intuitive and explicit way of articulating planning goals, the concept of soft‐constraints has been implemented into our in‐house IMRT planning system using a Goal Programming (GP) technique. In addition, traditional linear GP has been extended to handle nonlinear goal functions so that the nonlinear metrics highly relevant to clinical protocols (such as DVH, EUD, TCP, and NTCP) can be directly utilized in the planning process. Method and Materials: In order to achieve a high convergence speed of the optimization, a gradient‐based, nonlinear constraint search algorithm has been used in the implementation of nonlinear GP. The system is designed to handle multiple goals either by a weighted‐sum approach (Archimedean GP) or lexicographic ordering (Preemptive GP). For some planning criteria exhibiting poor numerical performance for gradient searches (e.g., min, max, DVH), surrogate models have been used in such a way that the general idea of soft‐constraint is consistently maintained. Results: For clinical IMRT cases, the nonlinear GP provides a fast and practical approach to articulate planning goals. Moreover, prioritization of planning goals based on their importance significantly simplifies the RT multicriteria problem representations. The Lagrangian Multiplier values obtained after each level of optimization facilitate informed decisions on goal tradeoffs between different priority levels. Conclusion: The soft constraint concept has been implemented for clinically relevant nonlinear criteria in RT inverse planning. Due to the fast search convergence exhibited by the present system, the planning process can be interactive with the decision maker in setting or adjusting appropriate goal levels, leading to progressive tailoring of the individual plan results. Supported in part by NIH grant R01‐CA59827.
SU‐FF‐T‐130: A Routine QA Procedure for the Varian Millennium MLC Used for Step and Shoot IMRT
Authors: Rothley D , Poteat G , Brown L , Sherfinski S
Published: June 2005

Purpose: To create a routine QA procedure that would effectively test the accuracy of a Varian Millenium MLC System that was used heavily for step and shoot IMRT. Method and Materials: We researched the literature to compare published QA procedures and extracted various tests to use at our centers. The procedure that we created consisted of 4 simple monthly tests, 5 additional quarterly tests, and 8 additional annual tests. The monthly tests were evaluated visually and took a minimal amount of time to perform. The quarterly and annual tests involved irradiating more films and analyzing most of them with the RIT113 version 4.1software. The annual tests were those provided by Varian in the “QA Tests Patterns and Procedures” manual and the RIT113 software included specific options for evaluation. Results: The machine parameters and MLC shapes were input to the Impac R&V System. Therefore the tests were simple and fairly quick to run. The analysis however was time consuming because all films must be scanned with a Vidar scanner and evaluated with the RIT113 software. The advantage of using RIT113 was that the QA documentation became organized and efficient. Conclusion: The literature contains many different MLC QA tests for a variety of equipment configurations. Furthermore we found that the AAPM Task Group ♯50 Report gives guidelines for MLC testing but does not list detailed tests. By combining several references and importing the tests in Impac, our MLC QA procedure has proven to be successful with minimal time expense. Within a very busy center performing IMRT treatments, the physicist is usually consumed with patient specific QA. This type of QA isn't usually precise enough to pick up small MLC inaccuracies and additional QA tests are necessary.
SU‐FF‐T‐134: Automated Quality Assurance Using Treatment Delivery Sinograms
Authors: Ramsey C , Mahan S
Published: June 2005

Purpose: Adaptive image‐guided radiation therapy (IGRT) is a new treatment paradigm where 1.) Patients are positioned daily using CT‐guidance and 2.) The delivery is adjusted daily to compensate for changes in the volume, position, and deformation of anatomy. Because the adaptation is performed while the patient is on the treatment table, it is impossible to perform quality assurance (QA) testing. This goal of this study was to develop new image analysis tools for the purpose of automating patient specific QA for adaptive IGRT. Method and Materials: Detector data in the form of sinograms were acquired during helical tomotherapy delivery using an arc‐shaped detector array that consists of 738 xenon‐gas filled detector cells. A software program was developed that analyzes tomotherapy sinograms by comparing one treatment delivery sinogram with a reference treatment delivery sinogram. At present, the software offers the following options: 1.) Analysis of ionization chamber entrance doses, 2.) Sinogram exit dose error detection, and 3.) Sinogram leaf error detection. Results: The first step in validating the QA system was to determine the threshold for error detection. Delivery sequences were modified by inserting MLC errors of known magnitudes. MLC errors that corresponded to 20, 10, 1, 0.1, and 0.01 percent errors in dose for 1 projection (i.e. segment) were purposely inserted into QA delivery sequences. The Automated QA tool was consistently able to detected errors of 0.01 percent or greater from the detector data at all tested data compression ratios. However, automated MLC leaf error detection would only function using uncompressed data. Conclusion: Multiple techniques have been developed for analyzing sinogram detector data during, and after tomotherapy treatment delivery. A combination of these error detection methods will be used to perform automated quality assurance for conventional and adaptive radiation therapy. Conflict of Interest: Research supported by TomoTherapy, Inc.
SU‐FF‐T‐135: Complex IMRT Plan Verification Using a Commercial MU Calculation Package
Authors: Zhang T , Norrlinger B , Heaton R , Islam M
Published: June 2005

Purpose: The general availability of IMRT treatments is constrained by the need to perform dosimetry measurements as part of the patient plan verification. While secondary IMRT MU calculators have been successfully used to validate some plans for a restricted number of sites, these calculators have suffered from unacceptably large uncertainties when applied to sites confined to the head and neck region. A strategy to reduce these calculational uncertainties has been developed which permits a greater use of IMRT MU calculators and reduces the need for dosimetric measurements, enabling a larger patient population to receive the benefits offered by IMRT treatments. Method and Materials: Segmental IMRT head and neck treatments were developed using the Pinnacle 6.2b inverse planning module. The IMRT treatment plans where then calculated on a CT image set of PMH IMRT phantom, and validation points corresponding to key target and avoidance regions where identified. The dosimetric data corresponding to these points was exported to RadCalc, a commercial IMRT MU calculator, and the calculations were compared to Pinnacle calculations and in‐phantom measurements. Results: A total of 10 clinical patient cases, each containing 7 to 9 gantry angles, were assessed. Agreement was assessed on basis of total dose delivered to the point of calculation. The measured and RadCalc calculated doses were found to agree within 3% at the high dose point and 5% at the low dose point in all cases, while the Pinnacle calculated dose was found to agree with the measured dose within 2.5% at the high dose point, with deviations as large as 13.5% observed at the low dose point. Conclusion: In‐phantom IMRT verification calculations of the total dose yields similar results as in‐phantom measurements. Consequently, a secondary MU calculator can be used to verify IMRT treatment plans and reduce the frequency of validation measurements.
SU‐FF‐T‐138: Dose Variation On the Simultaneous Irradiation of Head and Neck (H&N) Cancer and Supraclavicular Nodal Fields with Step‐And‐Shoot IMRT
Authors: Cheng C , Chopra K , Das I
Published: June 2005

Purpose: IMRT QA is just a single event in the entire treatment. The objective of an IMRT QA may be expanded to include temporal variations such as dose linearity, MLC leaf positioning, etc. Method and Materials: IMRT QA is carried out for an H&N case covering simultaneously the nodal regions in the supraclavicle. In addition, dose linearity is studied with ion chamber measurements in the MU range 1–100, and field size range from 1×1–5×5 cm2,, including elongated fields. A 2D diode array device is used to study the consistency of dose delivery by repeating the irradiation of selected fields ten times. The dose delivered and the distributions in all repeated irradiations are compared. The dynamic positioning of leaves during dose delivery is recorded. Results: The routine IMRT QA yielded acceptable agreement (4% in dose and over 2%, 3mm distance‐to‐agreement is >90%) between calculation and measurement. Dose linearity is within 2% for all fields except 5% for 1 MU. The linearity holds even for small MU segments, down to 1×1 cm2. The maximum shift in the 90% isodose line in 10 irradations > 5mm, and up to 1 cm for the 50% line. For fields with average MU/segment in the range 0.9–2, the dose variation is <1.5% in 10 repeated irradiations. While 90–95% of the dynamic leaf positioning are within 0.5 mm, about 3–6% are >10 mm. Conclusion: The standard QA acceptance criteria may not be adequate to gauge the accuracy of dose delivery, especially for sliding window techniques. The effect of the isodose shift may compromise the dose constraint to adjacent critical structures. A composite QA process incorporating leaf positioning may be warranted for comprehensive QA. Any deviations from calculation should be evaluated in the context of composite TCP and NTCP.
SU‐FF‐T‐152: Independent Dosimetric Validation of Novalis IMRT and Dynamic Conformal Plans Using PHILIPS Pinnacle3Treatment Planning System
Authors: Nehru R , Foster R , Sourivong P , Ayyangar K , Li S , Pillai S , Djajaputra D , Fung A , Thompson R , Enke C
Published: June 2005

Purpose: To study and validate the calculated dose distributions generated from Novalis inverse treatment planning system using PHILIPS Pinnacle3 treatment planning system. Method & Materials: A total of 60 clinical Novalis plans comprising of 41 Dynamic Arc and 19 IMRT plans were selected in this study. The CT images for the individual cases were exported to Pinnacle3 treatment planning system via network. A software script was developed to extract beam segments including MLC jaws, gantry, collimator and couch angles and monitor units from the RTP file generated by Novalis inverse planning system. The segmentation of MLC‐based IMRT plans from Novalis system was imported into the Pinnacle3 using the above software. The prescription and beam weights were set to reflect the treatment plan computed by the Novalis system. In all the above clinical cases, the dose distributions were computed and analyzed for homogeneous dose calculations. Results: The dosimetric results of all the above clinical cases have been analyzed. It was found that the agreement between the two systems at the isocenter dose was 1.00 ± 0.028. In addition, the shapes of isodose lines in the three principal planes(axial, coronal and sagittal) were qualitatively agreed in both the systems Conclusion: This study helps in validating the Novalis IMRT and Dynamic Conformal plans on Pinnacle3 which is well tested and documented on its convolution algorithm. These results indicate that the approach is robust and valuable for routine clinical IMRT plan validations as it takes account of entire clinical data set for the individual cases.