bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐J‐64: Daily Localization of Moving Targets with Non‐Gated Cone‐Beam CT Imaging
Authors: Lin T , Paskalev K , Chen Y , Hossain M , Xu Q , Ma C
Published: July 2008

Purpose: This work quantifies the organ motion artifact magnitudes on Cone Beam Computed Tomography (CBCT) images by comparing to 4DCT with Maximum Intensity Projection (MIP) and Average Intensity Projection (AIP) phase‐combination methods and thus to recommend a target oriented alignment procedure. Method and Materials: Varian Trilogy on‐board ExactArms kV CBCT system and GE LightSpeed 4‐slice CT integrated with Respiratory Position Management (RPM) 4DCT scanner are used in this study. An in‐house made motor driven lung‐shaped phantom with a 4 cm diameter golf ball, which simulates the same sinusoidal movement with a changeable motion amplitude, is scanned by both CBCT and 4DCT. The motion of phantom was set along patient superior‐inferior direction with a 1‐cm peak‐to‐peak amplitude and a 5‐second cycle. The signal gradients, target elongations and shapes in both organ motion direction and the orthogonal motion‐free direction are compared between MIP, AIP based phase combinations of 4DCT, as well as helical CT and CBCT images. The Contrast‐to‐Noise Ratio (CNR) is also studied in CBCT for identifying the streaking artifacts from motion artifacts. Results: We observed a blurred CBCT image with organ motion artifacts. The CBCT images have less steep signal gradient at the edge, so FWHM is used to judge the motion artifact magnitude. To compare to full‐phase‐combined MIP images, which reflects a full range of 1 cm motion for 5 cm total length at motion direction (S‐I) and 4 cm width at motion‐free direction (L‐R), CBCT shows a up to 2mm pure streaking artifact at L‐R direction and an up to 2 mm combined blurred and streaking artifacts at S‐I direction. Streaking artifacts at the target image is not pronounced from CNR calculations. Conclusion: CBCT images show good presentation (within 2 mm) to perform the daily localization procedure based on the soft tissue target alignment to full‐phase 4DCT plans.
SU‐GG‐J‐71: Development of Carbon Nanotube Field Emission Micro‐Radiotherapy System for Cancer Research
Authors: Wang S , Liu Z , Schreiber E , Sultana S , Zhou O , Chang S
Published: July 2008

Purpose: To demonstrate the feasibility of a carbon nanotube (CNT) field emission FE) technology based novel multi‐pixel array x‐ray micro‐radiotherapy (micro‐RT) system for fast conformal and intensity‐modulated radiotherapy (IMRT) irradiation for small animals. When it is developed, the CNT FE micro‐RT system will be integrated with the already developed CNT FE micro‐CT for real time imaged‐guided IMRT and treatment response observation in small animals. Method and Materials: The micro‐RT system comprises a CNT pixel cathode array for individual pixel beam generation and control, a transimission anode for x‐ray production, and a pixel beam collimation array to converts the Bremstrahlung x‐rays to x‐ray pixel beams. Each x‐ray beam is 2 mm × 2 mm at the irradiation object and the beam energy should be 100 kV or higher. Micro‐RT dosimetry is computed using Monte Carlo simulation techniques. A CNT cathode array for the prototype of micro‐RT consists of 50 (5 × 10) individual addressable pixel cathode. The single array offers a maximum radiation field size of 10 mm × 20 mm at the irradiation object. The eventual micro‐RT system is consisted of several x‐ray pixel beam arrays within a donut‐shape structure. Results: We have designed and fabricated a 50‐pixel beam cathode array for the prototype micro‐RT. The FE current of the 50 pixel beams is uniform. Each cathode pixel is individually addressable and can produce emission current of 4 mA/pixel. Conclusion: We have demonstrated the feasibility to fabricate the CNT FE cathode array. A micro‐RT system consisted of 5 × 10 pixel beam array. The next step is to fabricate the anode and pixel beam collimation system, and assemble the entire prototype micro‐RT system for feasibility demonstration. The proposed multi‐pixel array x‐ray micro‐RT system is capable of electronically defining radiation field shape and intensity modulation pattern for small animal irradiation.
SU‐GG‐J‐75: Dosimetric and Image Quality Analysis of a New Ultrafine Imaging Mode in TomoTherapy
Authors: Bichay T , Chen C , Meadows J , Schippers D , Lucas D , Ruchala K , Chao E
Published: July 2008

Purpose: TomoTherapy MVCT can be carried out using three distinct imaging modes: Fine, Normal and Coarse. These correspond to a CT slice thickness of 2 mm, 4 mm and 6 mm. In this study we evaluate a new Ultrafine mode allowing slice thickness of 1 mm. Measurements in a phantom are carried out to estimate typical patient dose for all 4 modes. Image quality for the various modes is compared. Method and Materials: A standard TomoTherapy solid water “cheese” phantom was used for all dosimetric analyses. Measurements were made at superficial (0.5 cm) and deep (15.0 cm) regions using ionization chambers. Image quality was evaluated using a megavoltage CT phantom containing 0.067–1.0 Lp/mm. In addition, clinical images of a cranium containing 2 mm gold markers were also evaluated for quality. The collimator width was maintained at standard settings for Fine, Normal and Coarse modes, and reduced to finer settings for the new Ultrafine mode. Results: The collimator opening on our unit was measured at isocenter and was found to be 0.69 cm in the three standard modes, and 0.39 cm in the new Ultrafine mode. The measured imaging dose was: Ultrafine 2.07 cGy, Fine 2.44 cGy, Normal 1.30 cGy and Coarse 0.90 cGy. Dose at superficial and deep regions was similar. The axial views for all four modes show similar resolution as expected since a 512×512 matrix is used regardless of mode. However, the sagittal images show considerable improvement, in both phantom and clinical studies, when imaged in Ultrafine mode. Conclusion: A new Ultrafine collimator setting for TomoTherapy, allowing a resolution of 1 mm in the sagittal plane, is characterized. This improvement is gained without increased patient exposure compared to the standard 2 mm Fine mode. This new imaging mode is expected to be particularly useful in radiosurgery.
SU‐GG‐J‐79: Effect of Body Weight On Patient Setup for Prostate Helical Tomotherapy Treatments
Authors: Schubert L , Rasmussen K , Westerly D , Adkison J , Mackie T , Ritter M , Tome W , Paliwal B
Published: July 2008

Purpose: To determine the effect of body weight and anatomical fat on initial setup for prostate patients receiving daily image guidance on helical tomotherapy. Method and Materials: Initial setup corrections from MVCT imaging were retrospectively analyzed for 25 prostate patients. All patients were set up in the head‐first supine position to skin tattoos, and immobilization consisted solely of foam knee pillows and foot rings. Patients were stratified into two groups based on body weight being above and below the median weight of all analyzed patients. Distributions of setup corrections in the lateral, longitudinal, and vertical directions were assessed. Additional preliminary analysis of anatomical fat comparing measurements of transverse areas of the body at the L4‐L5 vertebral inter‐space and setup tattoo levels was performed on planning CT images of 13 out of the 25 patients. Results: The mean setup corrections in the positive vertical direction were significantly greater for Group A (patients weighing > 213 lbs) than for Group B (⩽ 213 lbs), which were 11.5 mm and 4.3 mm, respectively. This may be attributable to increased couch sag occurring with increased weight and with placing the patient head‐first instead of feet‐first. Variances for Group A were larger than for Group B, which show an increased variation in initial setup for the heavier patient group. The anatomical fat measures corresponded well with each other, indicating that the location of the body used for initial patient setup seems to correlate with methods used to characterize abdominal fat. Conclusion: Our measurements of setup corrections suggest that daily imaging is of greater benefit for heavier patients. Analysis of anatomical fat measures suggests that characteristics of the location of the setup tattoos are affected by abdominal fat. Conflict of Interest: Some authors have a financial interest in TomoTherapy, Inc.
SU‐GG‐J‐83: Evaluation of Bayesian Methods for Estimation of Organ Motion and Patient Setup Variation
Authors: Jansson H , Rehbinder H , Keller H , Moseley D
Published: July 2008

Purpose: In adaptive radiation therapy, organ motion and patient setup can be measured and parameterized during treatment to refine the therapy. Bayesian statistics has previously been suggested to decrease the parameter estimate uncertainty by combining knowledge about population statistics with patient measurements. Our objective is to quantify the gain in using Bayesian statistics. Method and Materials: Analytical expressions were derived for two estimators of patient specific systematic and random error: SE, sample estimators based on only patient measurements and BE, Bayesian estimators based on patient measurements combined with population statistics. Analytical expressions were derived for the mean‐squared‐errors (MSE) for these estimators. These theoretical results were compared to results obtained from a data set of actual prostate positions for 15 patients, acquired in 42 fractions. Results: BE are in a mean square sense always better compared to SE. For the systematic error, the MSE ratio between SE and BE is where n is the number of fractions, Σ the standard deviation (SD) of the systematic error and σ the SD of the random error. This means that for a typical prostate case with σ/Σ=1 and n=5, the RMS (root mean square) reduction using BE is 9%. The improvement in estimating the random error is in generally much larger. The MSE ratio between SE and BE is where Λ is the SD of σ2, which means that for a case with σ2/Λ=1 and n=5 the RMS reduction is 33%. Experimental data confirms the qualitative content of the theoretical analysis. Conclusion: By combining measurements of geometrical changes in patient anatomy with population data more robust estimates of organ motion can be obtained. These estimates constitute a more reliable basis for adaptive replanning, for example through individualized PTV design. Conflict of Interest: Research sponsored by RaySearch Laboratories AB.
SU‐GG‐J‐87: Evaluation of Organ Motion for Prostate IMRT Treatment Using 4D CT
Authors: Li J , Burman C , Chan M , Sim S
Published: July 2008

Purpose: To investigate organ motion during IMRT prostate cancer treatment using 4D CT and evaluate its dosimetric impact. Method and Materials: Twenty‐five prostate patients (9 prone and 16 supine) were evaluated. All patients underwent 4D CT simulation using Philips Brilliance AcQSim. The Bellows System was utilized to track respiratory organ motion. Patients' organ movements were measured using the “cine” mode developed by Philips Medical. MIP images were composed from 4D scan for each patient. Volumes of prostate, bladder and rectum were contoured using the conventional CT (CCT) and 4D CT, and their volumetric differences were compared. IMRT plans generated for each patient based on CCT were applied to the organ volumes contoured on the MIP images. Dosimetric impact of respiratory motion on the IMRT treatment of prostate cancer was evaluated. Results: All nine prone patients demonstrated significant organ movements in comparison with patients in supine position. Due to the motions of prostate, bladder and rectum the MIP based volumes were larger compared with those from CCT. From MIP images, volumes of prostate, rectum and bladder on average were 19%, 11% and 9%, respectively, larger than corresponding volumes from CCT. Applying IMRT plan to the enlarged volumes defined with MIP images, we found that the dose coverage for prostate (D95) were reduced by a median value of 3.3% (1.6% – 4.2%), and doses of rectum and bladder changed by median values of 4.3% (0.2% – 7.6%) and 0.4% (−13.2% – +12.9%), respectively, when compared with those obtained for the standard IMRT plans using CCT. Conclusion: Prostate patients treated prone experienced larger organ movements than those in a supine position. Overall dosimetric variations are significant. 4D CT is useful in defining the range of organ motion and its dosimetric impact on IMRT prostate treatment.
SU‐GG‐J‐97: From a Phase‐Based to Displacement‐Based Gate Using a Custom Designed Software Application
Authors: Santoro J , Mageras G , Yorke E
Published: July 2008

Purpose: The Varian Real‐Time Position Management (RPM) system allows respiratory gating based on either phase or amplitude of the breathing waveform. RPM‐based phase gating during treatment is not robust in some patients because of unusual or mildly irregular breathing. We developed a robust method to convert a phase‐based breathing gate determined from physician's inspection of target motion imaged during 4D‐CT simulation to an equivalent displacement‐based gate for gated external beam treatment using the RPM respiratory system. Method and Materials: The application parses respiratory data from the simulation RPM breathing trace, extracts displacement, time and phase information and calculates a suggested displacement gate based on the physician‐specified phase gate. The displacement versus phase information is fitted; values of this function at the lower and upper bounds of the phase thresholds, and the average of these two values are extracted. We also calculate the mean and standard deviation of the displacements, and the duty cycles for each of the three displacement values and the original phase gate. The similarity of the average value displacement gate to the phase gate is evaluated by comparing their respective duty cycles and the mean displacement and standard deviation within each gate, which are measures of baseline drift and residual in‐gate motion. Results: An equivalent displacement gate can be derived from a physician‐specified phase gate. The mean of the mean of displacements for 5 patients is 0.160 cm for the phase gate and 0.108 cm for the displacement gate, the mean of residuals is 0.094 cm and 0.177 cm, and 39.1% and 37.6% for the mean duty cycles respectively. Conclusion: Displacement gates can be consistently derived from phase based gates, thus facilitating migration from a phase‐based simulation session to displacement‐based treatment sessions.
SU‐GG‐J‐112: Integration and Verification of 3T Magnetic Resonance Spectroscopic Imaging in Radiation Therapy Treatment Planning
Authors: Muruganandham M , Bayouth J , Kearney W , Smith M , Buatti J
Published: July 2008

Purpose: The purpose of this work is to test the feasibility of MRSI integration into brain tumor RT planning using a custom‐built MRSI head phantom as well as a case study. Method and Materials: A special MRSI head phantom was constructed with spatially well‐defined tube inserts. Each tube contains different pre‐determined concentrations of metabolite solutions that mimic different degrees of brain tumor burden and were immersed in a background solution that emulate normal brain metabolite levels. The 3D MRSI data were acquired on a Siemens 3T TRIO TIM scanner using PRESS (point resolved spectroscopy) sequence with TE/TR: 135/1510 ms, 16×16×8 matrix, FOV: 16×16×8 resulting in MRSI voxel size of 10×10×10 mm3. Registration of MRSI (gray scale DICOM) data with planning CT and creation of metabolite‐derived target contours were performed on Pinnacle treatment planning system. Target contours created using MRSI‐derived tumor metabolic abnormalities were compared with those created based on morphological (T2 and T1 contrast weighted) MRI scans. Results: The CT‐MR (T1) registration accuracy was found to be within 1 mm, with no spatial distortion during MRSI. Registration errors were found in the TPS due to field‐of‐view size and origin difference between studies. These were corrected using a simple algorithm to determine the translation. Re‐scaled MRSI pixel values allowed automated segmentation of metabolic ratios and were consistent with those identified on the control console of the MRI scanner. When applied to a clinical case, a 42 cc (or 58%) reduction in the treated volume of the PTV was possible, assuming the CNI ratio of 2.5 included all microscopic extension of disease requiring the boost dose. Conclusion: MRSI derived functional information can be incorporated into RT planning for brain tumors well within the registration tolerance limits of current planning process.
SU‐GG‐J‐117: Investigational Low Dose MV CBCT for Daily Pediatric Localization
Authors: Beltran C , Faddegon B , Bani‐Hashemi A , Merchant T
Published: July 2008

Purpose: Extraneous irradiation is a major concern in pediatric radiation oncology. A modified version of the Siemens MV CBCT has been developed that allows for low dose and high contrast imaging. We will determine the required setup margin stratified by age, tumor site, sedation, and treatment position in an IRB approved pediatric localization protocol of where low‐dose megavoltage cone‐beam CT (LD‐MV CBCT) is a central component. Method and Materials: Research participants are assigned a non‐ionizing localization technique based on disease site, treatment position, age, and use of anesthesia. Along with the protocol localization technique, each research participant will receive a LD‐MV CBCT at the start of each fraction and the end of every other fraction. Per protocol, the LD‐MV CBCT delivers only 1.0cGy per scan at isocenter for each research participant. The proper CBCT settings are determined with aid of a treatment planning system. The pre‐treatment LD‐MV CBCT will be used to assess the accuracy of the localization technique and the post‐treatment LD‐MV CBCT will quantify the rigidity of the immobilization schema. The resultant data will provide quantitative information about the inter‐ and intra‐fractional motion of the target, which comprises the SM portion of the PTV. Results: In one week, the dose to the research participant due to the daily pre and post‐treatment LD‐MV CBCT will be approximately 7.5cGy. The CBCT will supplant routine verification ports films, which, if obtained twice a week, would deliver approximately 5.0cGy at isocenter. The research participant will receive only 2.5cGy a week in additional dose when daily LD‐MV CBCT is used compared to twice a week port films. Conclusion: We will have motion and imaging data on 40 research participants by August 2008, with a planned 200 research participants for the protocol. Conflict of Interest: Supported in part by Siemens Medical USA.
SU‐GG‐J‐124: Management of Image‐Guidance Dose in Radiotherapy Treatment Planning
Authors: Ding G , Deeley M , Coffey C
Published: July 2008

Purpose: Recent studies demonstrate that imaging procedures in radiotherapy for patient setup may add significantly to the doses to the normal tissues of the radiotherapy patient, especially using MV and kV cone‐beam CT (CBCT). These imaging procedures add the dose to an already high level of therapeutic radiation to organs. Accounting for image‐guidance dose is becoming increasingly important for radiation oncologists with regards to the total dose limit for normal tissues. This study is to accurately model and quantitate the additional dose from image‐guidance procedures, especially kV CBCT, as part of radiotherapy dose in the patient treatment planning. Method and Materials: Unlike megavoltage photon beam in which the dose calculations mainly depend on the electron density of the media, the dose calculations of kilovoltage x‐ray depend on atomic number of the medium due to the photo‐electric effect. Therefore, kV x‐ray dose calculation is not available in current radiotherapy treatment planning systems. The Monte Carlo code BEAMnrc was used to generate kV CBCT beams and DOSXYZnrc was used to calculate dose to the patient using volumetric CBCT images. The dose‐volume‐histograms (DVHs) for organs were evaluated. Results: For a representative head‐and‐neck cancer patient treated with 33 fractions of IMRT, if the kV‐CBCT procedure was used in each treatment fraction, the accumulative imaging dose can total 230 cGy to 95% of the eye volume, a minimum of 132 cGy to 90% of the soft tissues within the imaged volume, and 528 cGy to 90% of the cervical vertebral volume. Conclusion: The DVH analyses show significant doses to radiosensitive organs from repeated CBCT procedures. Hence, the management of imaging dose during radiotherapy is important to reduce the risk of complications. Total therapeutic dose limits in the treatment planning process may need to include the additional x‐ray dose to radiosensitive organs from image‐guidance procedures.
SU‐GG‐J‐125: Marker‐Based Strategies for Predictive, On‐Line Monitoring of Dynamic Treatments with MV Projection Images
Authors: Tryggestad E , Ford E , McNutt T , Susil R , DeWeese T , Wong J
Published: July 2008

Purpose: Given the need to dose escalate under high precision, hypo‐fractionated RT for certain anatomic targets, especially those where respiratory motion is important, requires better capabilities for real‐time treatment monitoring. At present, CBCT‐based systems, such as Synergy (Elekta) and Trilogy (Varian) tend to rely on a single daily, pre‐treatment volumetric snapshot. Here, we describe a general system of real‐time treatment verification using radiographic markers and kV and MV cine/flouro that can be applied to both static and dynamic (IMRT; arc‐based) therapies on CBCT IGRT systems. Method and Materials: A set of mock‐treatment datasets were recorded from simultaneous MV and kV cine/flouro imaging under varied treatment scenarios using an experimental Synergy system (Elekta Inc., Crawley, UK). We employ a commercially available programmable motion phantom (Modus Medical Devices, Inc.) modified to accommodate an arbitrary arrangement of metallic markers and to simulate patient respiration. The radiographic markers are identified on a baseline CT dataset (simulation or pre‐treatment CBCT) and a 3D tolerance ROI is constructed for each marker. This ROI is then projected onto the MV imaging plane and is superimposed on the current MV image. This mask is also used to refine the automated marker tracking algorithm. Results: Development work is ongoing, supported by the aforementioned phantom measurements. Patient treatment data will be used to refine the software tools and demonstrate the clinical feasibility of this method. Dynamic‐MLC fields pose an interesting challenge. A “predictive” technique is employed whereby the tracking algorithm has a priori knowledge of field shapes and “expected” marker positions at given segments or gantry angles. Conclusion: This marker‐tracking technique can be applied to any static beam or arc‐based intensity‐modulated delivery and can be employed with the standard equipment available on most modern linear accelerators.
SU‐GG‐J‐139: On the Clinical Implementation of Gold Nanoparticle‐Aided Radiation Therapy (GNRT)
Authors: Cho S , Krishnan S , Vassiliev O
Published: July 2008

Purpose: To present possible strategies for the clinical implementation of gold nanoparticle‐aided radiation therapy (GNRT). Method and Materials: GNRT is an emerging treatment modality currently under development. GNRT would provide a way to substantially escalate the tumor dose far beyond the current limit while maintaining the normal tissue dose at the levels comparable to conventional radiation therapy. The current study investigated possible strategies for clinical implementation of GNRT by surveying existing in‐vivo data and performing Monte Carlo (MC) calculations for the cases mimicking typical clinical situations. The cases included in this study were a brachytherapy case using Yb‐169 source and an external beam radiation therapy (EBRT) case using low energy‐enhanced megavoltage photon beams (e.g., 4 MV and 2 MV) that can be generated by a slight modification of a conventional design of linear accelerators. Results: The MC calculations suggest the macroscopic dose enhancement factor (MDEF) within the tumor region could be 42 and 200%, for the gold concentration levels of 7 and 18 mg Au/ g tumor, respectively, with Yb‐169 source. The current results also suggest the macroscopic dose enhancement ranging 10 to 40% could be achievable across the tumor volume with low energy‐enhanced megavoltage photon beams at a realistic tumor gold concentration (e.g., between 7 and 30 mg Au/g tumor). Besides, the current investigation indicates the dose distributions due to low energy‐enhanced megavoltage photon beams could be created comparable to those due to conventional megavoltage beams, while producing the suggested level of tumor dose enhancement. Conclusion: According to the current study, GNRT appears to be very feasible via a brachytherapy apparoch using Yb‐169 source. GNRT also appears to be feasible for EBRT with low energy‐enhanced megavoltage photon beams. The tumor dose under these implementation scenarios may be enhanced further with an active targeting of tumor cells with gold nanoparticles.
SU‐GG‐J‐141: Optimization of Translational Corrections to Compensate For Rotational and Deformable Target Deviations in Image Guided Radiotherapy
Authors: Yue N , Kim S , Lewis B , Jabbour S , Narra V , Goyal S , Haffty B
Published: July 2008

Purpose: To develop a strategy to optimize the translational corrective shifts to compensate for rotational and deformable deviations in IGRT. Method and Materials: The proposed optimization strategy involves two steps: a volume‐based optimization followed by a dose‐based optimization. The planned PTV is first exported in DICOMRT format to an in‐house software package and made readily available. After patient is positioned on the treatment table following initial setup reference, CBCT images are acquired. The treatment CTV is determined based on these CBCT images, and is imported into the in‐house software package. The volume‐based optimization process is started to optimize the translational corrections so that maximum amount of the treatment CTV is located within the planned PTV. These translational corrections are applied and dose calculation is then performed based on the acquired CBCT images without any alteration of planed beam parameters. Since any change of patient external contours is imaged on the CBCT, this dose calculation yields the initial dose distribution in which the change of patient external contour is taken into account. Thereafter, the translational corrections are further optimized by maximizing a dose‐based objective function. During this optimization process and as the translation corrections are adjusted, dose is constantly recomputed to take into account the changes of depth and distance relative to beams, because the translation movements may cause changes of depth and distance of the treatment CTV. The Hill‐Climbing optimization algorithm is used in the optimization processes. Results and Conclusion: The proposed optimization strategy and the corresponding software package have been developed and validated. This strategy was applied to three fractions of treatment of a prostate patient. It was found that the developed optimization strategy might potentially compensate for certain rotational and deformable deviations with translational correction. Further evaluation is needed for cases in which more dramatic deviations are observed.
SU‐GG‐J‐142: Patient Scatter Analysis for A New Generation of Portal Imaging Sensors Based On Thin‐Film Cadmium Telluride
Authors: Shvydka D , Parsai E , Kang J , Pearson D , Feldmeier J
Published: July 2008

Purpose: An X‐ray detector using a layer of polycrystalline Cadmium Telluride (CdTe) in combination with metal plate, serving as a converter of incoming x‐rays into electrons, is investigated for therapeutic radiation oncology imaging. Using Monte Carlo simulation, we performed a theoretical analysis of the spatial frequency dependent detective quantum efficiency (DQE) for this detector system. A range of optimal parameters were obtained for this new generation of megavoltage detectors using thin film one of which is the consideration of the influence of patient scatter, a significant component of the realistic detector input on the image quality. Method and Materials: We examined several choices of metal plate for the thin‐film CdTe detector under 6 MV x‐ray beam of Elekta Precise Linac by Monte Carlo simulations, using MCNP5 software package. Introduction of scatter degrades the image quality by adding noise to both the signal and its variance. We evaluated the effect of patient scatter in terms of loss in the image contrast (C), corresponding to signal reduction component, and loss in differential signal‐to‐noise ratio (DSNR), reflecting increase in signal variance. Results: The contrast and differential signal‐to‐noise ratio losses have been modeled for a range of thin film CdTe thicknesses, as well as several combinations of metal plate materials of varying thickness. We found that the thicker metal plate of denser material, such as tungsten, helps reducing the effect of patient scatter, decreasing losses in both parameters. Additionally, increase in CdTe sensor thickness also improves the image quality. Conclusion: Relatively small targeted thickness of polycrystalline CdTe sensor layer, in the range of 10 to 600 microns, makes it more susceptible to the influence of patient scatter. Addition of metal plate to the detector not only enhances its DQE due to energy absorption, but also facilitates reduction of noise due to patient scatter.
SU‐GG‐J‐145: Physics Support for Intraprostatic Treatment of Patients with Locally Recurrent Prostate Cancer with the PSA‐Activated Protoxin PRX302
Authors: Boyer A , Coffield S , Culp L , Frankel A , Merchant N , Abi‐Habib R
Published: July 2008

Purpose: PRX302 is a protoxin in which the native furin‐cleaved pro‐domain has been modified to be proteolytically cleaved by PSA. PSA releases a C‐terminal inhibitory peptide to generate the active toxin, that inserts into the cell membrane to form 1.5 nm pores inducing ion leakage, loss of membrane integrity and cell death. We report on the physics support of a Phase I clinical trial of administration of PRX302 in patients with locally recurrent prostate cancer after radiation therapy. Method and Materials: 24 patients were enrolled. Dose‐escalation consisted of seven cohorts of 3 to 6 patients, each receiving a dose between 0.03 and 3 μg of PRX302/g of prostate. PRX302 was delivered as a multi‐deposit, transrectal ultrasound‐guided, transperineal injection using a modified brachytherapy technique. Images were acquired with a Hawk Type 2102 EXL (B&K Medical, Herlev, Denmark) ultrasonic unit using a rectal probe. The ultrasound display was calibrated against the needle template before each procedure. Commercial treatment planning software (Variseed. Varian Medical Systems) was adopted to select the location and concentration of the injections. Results: The maximal tolerated dose was not reached despite a 100‐fold dose increase. No drug‐related SAEs were observed. Preliminary data suggested biological activity of PRX302. PSA levels decreased in 63% of patients. The percentage of positive prostate biopsy cores post‐therapy decreased in 75% of patients with 3 patients having no positive cores at 30 days following PRX302 therapy. Conclusion: Active medical physics participation in these clinical trials contributed to the preliminary findings that transperineal administration of PRX302 is safe and well tolerated in patients with localized recurrent prostate cancer. MTD was not reached and PRX302 showed convincing signs of biological activity that will be further evaluated in future efficacy studies planned with medical physics input.

Conflict of Interest: This Trial was sponsored by Protox Therapeutics, Inc.
SU‐GG‐J‐149: Position Verification of Breast Treatment with Breath‐Hold Technique Using 3D‐Surface and Fluoroscopic Imaging
Authors: Flampouri S , Snead F , Huh S , Symonds‐Tayler R , Louis D , Li Z , Palta J
Published: July 2008

Purpose: To evaluate the reproducibility and stability of target position for left breast radiotherapy treatment on deep inhalation breath‐hold and to determine their dosimetric impact. Method and Materials: Six patients were treated using Active Breathing Coordinator (ABC). A 4D‐CT was acquired along with an ABC scan during simulation to establish geometric advantages of breath‐hold treatments. Through patient's treatment course, 3D‐surface movies were acquired with VisionRT periodically during breath‐hold (30 breath‐holds/patient). Comparison of the frames was performed to evaluate intra‐breath‐hold drifts and inter‐breath‐hold position reproducibility. For evaluation of the 3D‐surface images and correlation with internal structures, fluoroscopic images of the chest wall were also acquired 4 times (6–8 breath‐holds/patient). Additionally the images were correlated with inhaled air volumes as calculated from the breathing signal. A dosimetric study was performed to determine the effect of breath‐hold drifts and position differences. Results: Intra‐breath‐hold drifts were determined by comparison of the first with the subsequent 3D‐surface frames. Each patient presented consistent behavior throughout her treatment, with the most stable having sub‐millimeter surface motion in 20s and the least 2.5mm in 13s hold. Measurements of the rib motion from the fluoroscopic images correlated within 1 mm with the surface motion. However for some of the patients, slow diaphragmatic motion up to 8mm was observed. Patient variability was also observed on inter‐breath‐hold reproducibility. On average for all patients, 2 mm body surface position difference was observed between breath‐holds. This variation correlated with the air volumes inhaled as calculated from the breathing signal. It was proven dosimetrically that even for the least stable patients, ABC holds advantage over free breathing. Conclusion: Although, there are limits on position reproducibility and stability with deep inhalation breath‐holds, treating left breast patients with this method is beneficial. 3D‐surface imaging is an important tool for monitoring motion for near the surface treatments.
SU‐GG‐J‐178: The Development of Eye Fixation Software for the Proton Therapy of Eye Tumors
Authors: Shin D , Yoon M , Lim Y , Kim D , Kwak J , Park S , Lee S , Park S , Cho K
Published: July 2008

Purpose: Proton therapy is suggested as a next generation radiation therapy with their great dose localization performance compared with linear accelerator. Although proton therapy is recommended for eye melanoma treatment due to its excellence in dose localization, the patient positioning system (PPS) is essential since small error in PPS may cause significant damage to the patient. In this study, we developed an automatic real time eyeball tracking system for the treatment of eye melanoma. Method and Materials: A new automatic eye tracking system was developed using Labview 8.2 software with GUI based development tool (National Instrument), Vision development tool and image acquisition board(National Instrument). The real time image for eye movement was taken using CCD camera, which was transferred to the homemade image analysis program. Using computer outside the treatment room, a real time eye ball tracking based on image pattern matching method was realized by comparing a treatment template image used in the treatment planning with a real time image acquired from CCD camera. Results: Based on the real time image analysis system, we achieved the real time eye ball tracking system with a resolution less than 0.01mm for the eye ball movement which will be used for the treatment of ocular tumor in proton therapy. Conclusion: New automatic eye tracking system has been developed for ocular tumor treatment which is going to be used in the clinical trial with the gating system.

Key words: Eye tracking system, Proton therapy, Ocular, Eye treatment.
SU‐GG‐J‐189: Use of a Clinically Relevant Digital PET Chest Phantom to Investigate the Threshold Required to Define a PET‐Based Target Volume
Authors: Aristophanous M , Pelizzari C
Published: July 2008

Purpose: To examine the relationship between the threshold required to segment PET‐based target volumes placed in inhomogeneous background provided by a digital PET chest phantom. Method and Materials: We placed four spheres of uniform activity and sizes ranging from 2–13ml in the lung, mediastinum and lung/mediastinum boundary in the chest of a digital PET phantom. The intensity of the spheres was adjusted to obtain different target to background (T/B) ratios and the threshold as a percent of the maximum image intensity required to get the true tumor volume was estimated. We also constructed a spherical target of non‐uniform activity by placing a spatial Gaussian activity distribution in the larger (13ml) sphere and adjusting its intensity to obtain various T/B ratios. Results: The results suggest that a threshold varying from 37–55% may be required to segment the true target volume depending on the location and size of the target. Smaller targets and ones placed in higher background activities (such as the mediastinum) require higher thresholds than larger targets or the ones placed in lower intensity background (such as the lung). Adding inhomogeneity in the intensity of the target results in lower thresholds required and smaller difference between the threshold required to segment targets in higher and lower image intensity backgrounds. Conclusion: For the first time to our knowledge we present a study investigating PET‐based threshold segmentation in a realistic situation, where the target's background activity is similar to what is seen in clinical cases. The most important finding of this study is the indication that lesions in the mediastinum require higher thresholds than the ones in normal lung or at the boundary between lung and mediastinum.
SU‐GG‐J‐193: Using Small‐Deformation Linear‐Elastic Registration to Quantifying Ventilation‐Competent Lung Imaging From Clinical 4DCT Datasets: Toward Selective Avoidance IMRT for Locally Advanced Non‐Small‐Cell Lung Cancer
Authors: Monroe W , Kim Y , Christensen G , Wu X , Bayouth J , Bhatia S , McGuire S , Siochi R , Waldron T
Published: July 2008

Purpose: To verify the feasibility of a small‐deformation inverse‐consistent linear‐elastic (SICLE) registration algorithm in quantifying ventilation‐competent sublung images from 4D CT datasets. Materials/Method: SICLE, a deformable image registration algorithm developed at the University of Iowa, was utilized to register the 100% inhalation and 100% exhalation phases of the lung which were extracted from clinical 4D CT datasets. The SICLE method performs inverse consistent image registration in which the forward and reverse transformations are estimated jointly while minimizing the inverse consistency error. After deformable registration, ventilation was calculated using the equation on voxels of the inhalation and exhalation images, where HU is in Hounsfield Units and ΔV/Vex is the change in regional volume divided by the local volume. Results: SICLE was found to be efficient and consistent in deformable image registering lung CT image datasets with different phases. 3D ventilation images were quantified and given in coronal, transverse, and sagittal view. Quantitative ventilation in a given region of interest was also determined. Ventilation‐competent sublung regions were constructed with different functionality levels of 90, 70, 50, and 30%. Conclusion: Utilizing a small‐deformation inverse‐consistent linear‐elastic registration algorithm, it was feasible to quantify ventilation competent subregions from clinical 4D CT datasets. Given the availability of 4D CT technology, this study opens a pathway to integrate functional lung information into radiotherapy for locally advanced non‐small‐cell lung cancer.
SU‐GG‐J‐194: Use of Synchronized Beam Switching for Real‐Time 3D KV‐MV Internal Marker Tracking with Step‐And‐Shoot IMRT
Authors: Wiersma R , Riaz N , Mao W , Xing L
Published: July 2008

Purpose: Combined kV‐MV imagining can provide real‐time 3D tumor position information during the actual radiotherapy delivery. Since the treatment delivery beam is used for tracking, only one kV x‐ray source is required for full 3D localization, offering total diagnostic dose reduction and cost savings in comparison to other stereoscopic based methods. Currently, kV‐MV tracking requires simultaneous imagining by both kV and MV imaging systems for real‐time 3D marker positioning. However, with step‐and‐shoot IMRT, treatment beam interruption can result in loss of geometric information, preventing accurate 3D localization. This work uses controlled kV beam switching, together with a correlation algorithm, to maintain continuous real‐time 3D internal marker tracking with step‐and‐shoot IMRT. Method and Materials: A Varian Trilogy, equipped with both kV and MV imaging systems, was used to deliver step‐and‐shoot IMRT prostate plans to a pelvic phantom containing embedded gold cylindrical markers. A correlation algorithm, designed to interconnect detected fiducial locations between the kV and MV imagers, was used for spatial estimation. Actual 3D prostate motion data artificially segmented with kV and MV beam interruptions typical to a step‐and‐shoot IMRT plan was tested with the technique. Results: Application of the correlation function to prostate motion data containing artificially placed beam interruptions results in a tracking accuracy of less than < 2 mm RMS in comparison to the actual motion. For kV source‐to‐detector distances < 70 cm MV scatter interference on kV images is significantly reduced with synchronized kV/MV beam switching. Conclusions: In the presence of beam interruption, correlation can be used to compensate for missing spatial information allowing for full real‐time 3D kV‐MV tracking with step‐and‐shoot IMRT. Additionally, controlled kV beam switching is effective in increasing kV image quality by reducing MV scatter interference.
SU‐GG‐J‐195: Utility of a Calibrated Deformation Map to Aid Treatment Position and Monitoring Guidance in Deforming Anatomy with Electromagnetic Transponders
Authors: Kashani R , Hadley SW , Kessler ML , Litzenberg DW , Balter JM
Published: July 2008

Purpose: To investigate the utility of tracking motion and deformation in various regions of a deforming geometry given a predetermined “calibrated” deformation map and relative position of a small number of embedded electromagnetic transponders. Method and Materials: Three electromagnetic transponders were inserted into a reproducibly deformable phantom and localized with CT. Tumor‐simulating spheres were embedded at different positions relative to the transponders. The phantom was imaged at 7 compression (“breathing”) states, and the transponders and tumors were localized on each image volume. Deformation maps relating a reference (end inhalation) to all other states were estimated using a B‐spline based registration technique. Principal component analysis was applied to the deformation maps to find the most significant modes of deformation in the phantom. This created a calibration state for the deformation which can be used along with the measured transponder positions to estimate the deformation at arbitrary time point during a breathing cycle. Results: Tests performed based on information from one transponder showed variable uncertainty (8 mm) in predicting arbitrary target positions at different states during a breathing cycle. Application of all three transponders to the first component of deformation showed very high accuracy with a mean error of less than 1mm for deformation maps calibrated on 5 breathing states. Using only the 2 extremes of the breathing cycle, the mean error increased to 2mm, showing some dependence on the number of states used in calibration of the deformation map. Extrapolation of the breathing state past the calibration data by an additional 1cm of compression showed reasonable accuracy (3.5 mm). Conclusion: A calibrated deformation map can potentially be used as an aid to dynamic tracking of deforming anatomy during treatment. Experiments are ongoing to evaluate the dynamic behavior of the calibrated maps to real‐time data from the tracking system. Supported by NIHP01CA59827.
SU‐GG‐T‐02: Inverse Optimization for Cervix Cancer Brachytherapy Including Automatic Loading, DVH Optimization and Modification Restriction Adapted From Manual Planning
Authors: Kirisits C , Trnkova P , Baltas D , Dimopoulos J , Pötter R
Published: July 2008

Purpose: This study tests the difference in dosimetric values and performance between a new Hybrid Inverse Planning Optimization (HIPO) tool for cervix cancer brachytherapy and conventional manual optimization. Method and Materials: The clinically used treatment plans of ten tandem/ring (T/R) and ten cases with additional needles (T/R+N) planed with PLATO (v14.3, Nucletron) were included. Standard loading patterns were manually optimized to reach an optimal coverage with 7 Gy per fraction to the High Risk‐CTV and dose constraints for organs at risk. A second plan was retrospectively created with OncentraGYN (v0.9.14, Nucletron). Anatomy based automatic dwell position loading was used to produce loading patterns similar to standard Fletcher loadings, but adapted to the topography of bladder, rectum, and sigmoid. The optimization algorithm included individual dwell time gradient restrictions and modification restriction for the T/R and needle optimization to preserve the spatial high dose and dwell time distribution as accepted for manual plans. Results: HIPO could achieve a better target coverage (V100) for all T/R and 7 T/R+N patients. The D2cc per fraction for bladder, rectum and sigmoid was on average lower by 0.2 Gy, 0.4 Gy, 0.2 Gy respectively for T/R patients and 0.6 Gy, 0.3 Gy, 0.3 Gy for T/R+N patients (e.g.: a decrease from 4.5 to 4 Gy per fraction means a total dose reduction of 5 Gy EQD2 for a 4 fraction schedule). In 7/10 cases the dwell time in the additional needles was lower as with manual planning. The optimization procedure including handling, evaluation and calculation time (<3s per run) was lower compared to manual treatment planning. Conclusion: HIPO is a feasible and quick method for treatment planning in cervix cancer brachytherapy. Essential is anatomy based loading, anatomy based optimization and a dedicated concept to control spatial dwell time distribution. Conflict of Interest: Research sponsored by Nucletron.
SU‐GG‐T‐03: Dosimetric Study of HDR 192Ir and LDR 125I Brachytherapy Sources Using the Penelope Monte Carlo Code
Authors: Benhabib SM , Zhu D , Austerlitz C , Mota H , Sempau J , Allison R , Sibata C
Published: July 2008

Purpose: To determine the dosimetric parameters of two HDR models 192Ir (microSelectron, and M‐19), and LDR 125I brachytherapy sources. Method and Materials: In this study we used the microSelectron and M‐19 models, and also source (Amersham OncoSeed model 6711). Penelope Monte Carlo transport code was used. All the photonic interactions were taking into account. AAPM TG‐43 was followed to determine the dosimetric properties1. 2D dose distribution, dose rate constant, anisotropy and radial dose functions were determined. Results: For both Iridium models, the 2D‐dose distribution agrees very well with published data for radius 1 ⩽ r ⩽ 5 cm, the difference was less than 3 %. The dose rate constant is 1.11654 cGy h−1 U−1 for microSelectron and 1.12456 cGy h−1 U−1 M‐19 model. Less than 3 % difference was observed for the radial dose function for radius 1 < r < 5 cm for both Iridium models. The DRC for was found to be 0.984 cGy h−1 U−1, and less than 3 % difference for the radial dose function in comparison with published data in TG‐43. Conclusion: Extensive work had been done on and brachytherapy sources. Daskalov et al2, Medich et al3, and Granero et al4, used different source models and different Monte Carlo transport codes, but the difference for the dosimetric parameters between all these studies was less than 5 %. In this study we used Penelope Monte Carlo code to determine the dosimetric parameters. The results showed 3 % difference for 2D dose distribution, DRC, and radial dose function for Iridium sources and 3 % difference for Iodine source.