bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐264: Independent Quality Control and Quality Assurance Programs for IMRT
Authors: Minemura T , Narita Y , Tamura M , Ishikawa M , Ozawa S , Miyagishi T , Nishio T
Published: November 2011

Purpose: Recently, radiotherapy for cancer advances to the highly precise treatment by various technical progresses. The highly precise radiotherapy that seems to be intensity modulation radiation therapy (IMRT) popularizes rapidly now. Therefore high technology of radiotherapy is demanded, and the quality control / quality assurance (QC / QA) is needed. In this study, it is a purpose to make the third‐party evaluation program to perform the radiotherapy that is safe from IMRT. Methods: The measurement was executed with an anthropomorphic IMRT phantom by the on‐site visit. The IMRT phantom was divided into a phantom shell and a module. The IMRT treatment plan was drafted by each institution to satisfy the following optimization conditions. (1) The D95 prescription (PTV) was 2Gy. (2) The PTV maximum dose was considered to be less than 110 %. (3) Organ at risk (OAR) was considered to be less than 60 %. The dose inspection for a drafted IMRT treatment plan was executed with the ionization‐chamber dosimetry module and the film dosimetry module. Results: The evaluation of the absorbed dose was executed for two points in PTV. In addition, the dose distribution measured axial, coronal, and sagittal side with a film. For these measurement sides, the evaluation of the position gap was achieved in the part that the dose gradient became precipitous. For the ionization‐chamber dosimeter, the differences at two points in PTV were less than ±3 %. For the dose distribution with the films, the differences for the position gap were less than ±2 mm. Conclusions: In this study, it was developed the phantom for inspection and measurement machinery to assure of the quality for IMRT, and the third‐party evaluation program was made. In the future, it will be necessary to repeat inspection in plural institutions to raise the reliability of the inspection result.
SU‐E‐T‐265: A Simple Method for Clinical Verification of the Digital Graticule on a Per‐Patient Basis
Authors: Lambert M , Taylor M
Published: November 2011

Purpose: As clinical radiation oncology centers move away from using film, digital imagers (EPIDs) are increasingly used to verify patient setup prior to treatment. Shifts are determined via the application of a digital graticule to the MV image. In theory, the origin of the digital graticule should be perfectly aligned to the radiation isocenter, and the digital graticule displayed at the treatment console should be identical to that observed in offline software. In practice, however, discrepancies in graticule position do occur. This poster presents a simple method by which the alignment of the digital graticule to isocenter can be verified on a per‐patient basis prior to making shifts in patient setup. Methods: A metal ball bearing (BB) 2 mm in diameter was placed on the EPIDˈs imaging plate coincident with the light field crosshairs or central axis (CAX). The EPID was moved through its range of motion, 50 cm vertically, to verify that the physical BB position tracked with the CAX. Crosshair alignment was further verified by retracting and re‐extending the imager at the four cardinal gantry angles. Results: The BB appears as an opaque point in a dark field for portal images. Without obscuring patient anatomy or localization markers, it serves as a marker of the CAX to which the physician and therapists can align the digital graticule prior to making shifts in patient position for treatment. Conclusions: The BB serves as a reference point by which the accuracy of the digital graticule alignment can be verified on a per‐patient basis. As long as a patientˈs portal images include the CAX, the BB enables verification of measured shift accuracy prior to adjusting the patientˈs position for treatment.
SU‐E‐T‐266: Propagation of Human Error within a Radiation Oncology Department
Authors: Song H , Salama J
Published: November 2011

Purpose: To study propagation of human error in EBRT in a small radonc department. Methods:While reporting of medical events is mandatory, reporting of other human errors needs encouragement. A mechanism of voluntary reporting 1 was adopted. Specifically, one coordinator was assigned to collect and de‐identify all non‐medical‐event errors. Each error is categorized according to place of origin, how it was caught, and clinical impact. Each error is assigned severity score on a 5 point scale. The EBRT process is modeled into stages of a mostly serial flow: Front Desk, Nursing, MD Consultation and Rx, CT‐Sim, Treatment Planning, Pre‐Tx Physics Chart Check, Pre‐Tx RTT check, Delivery, Weekly Chart Check, and Completion Physics Chart Check. When an error propagates beyond one stage, its severity gets multiplied 2, 3… times as the missed stages increase. Error Severity SUM = Incidence × Severity Score × Propagation Multiplier. Results: On the map of error propagation are 21 recorded incidences for Jan–Feb of 2011: 17 originated in Delivery, 7 in Treatment Planning. Three errors propagated beyond one stage. The error severity map shows a different pattern of hot spots: Treatment Planning (severity score 22), Delivery (17), MD Consult (10). MD Consultˈs increased rank in severity is due to its potential to cause medical events. Pre‐Tx Physics Chart Check and Weekly Chart Check are effective error catchers as most errors end in them on the error maps. Conclusions: Map of error propagation can be used to indentify hot spots of error origination and traps for catching errors and thus be an effective tool for quality control.
SU‐E‐T‐268: The Evaluation of Dosimetric Characteristic of Radiophotoluminescent Glass Dosimeter According to Reading Methods of Reader
Authors: Son K , Shin S , Lee H , Lee S , Kim M , Ji Y , Kim K , Jung H
Published: November 2011

Purpose: Statistical checks of system parameters and follow up of readerˈs behavior will give a broader understanding into the operational characteristics of the reader and may help for proper maintenance of the system. The purpose of this study is to suggest effective use of reading methods for reducing the uncertainty in dose measurements through the investigation of characteristics of GD‐based reader system. Methods: To evaluate the characteristics of readerˈs, we performed measurement such as reproducibility of repeated reading, readout variation according to the number of GD loading on readout magazine, and deviation depending on each magazine position. To evaluate dose reproducibility we made a try to do repeated reading up to 200 times for each 15 GDs. Also, to evaluate readout variation characteristic, 80 GDs are irradiated one by one under the same irradiation conditions. Reading process was measured with 4 different cases. Lastly, to measure the deviation magazine position, we examine the readout values according to each loading position.Results: According to measurement result, reproducibility shows 1.3% lower measurement from total 200 times. Readout sensitivity of GD on magazine values is normalized to 1st position response. 1 to 5th position measured 1.015, also 1 to 10th position examined 1.022, and 1 to 20th position presented 1.035. Lastly, at all position except for 20th position of magazine, response is tend to increase gradually. It was overestimated on 2.0% of average rather than response at reference position (first position). Conclusions: According to the result, we should put each GD in consecutive order from 1st space of magazine to get accuracy value of dose and it is recommended that reading process should be performed the only first position of magazine with regard to absolute dosimetry.

This work was supported by Nuclear Research & Development Program of the National Research Foundation of Korea(NRF) grant funded by the Korean government(MEST).
SU‐E‐T‐279: Improvement of Deformable Registration Accuracy Using Modified MV CBCT Images
Authors: Kim M , Chang J , Park S , Kim T , Kang Y , Suh T
Published: November 2011

Purpose: The purpose of this study is to identify whether the change of MV CBCT intensity can improve intensity based registration accuracy using predefined modification level and filtering process. Methods: To obtain modification level, images of the cheese phantom and the deformable lung phantom which was intentionally created in the laboratory to imitate the changes of the breathing period was acquired from both kilovoltage CT (kV CT), megavoltage cone‐beam CT (MV CBCT). From the cheese phantom images, the modification level of MV CBCT was defined from the relationship between Hounsfield Units (HUs) of kV CT and MV CBCT images. ‘Gaussian smoothing filter’ was added to reduce the noise of the MV CBCT images. The intensity of MV CBCT image was changed to the intensity of the kV CT image to make the two images have the same intensity range as if they were obtained from the same modality. And then deformable registration was applied. Results: The vector differences from the result were 2.23, 1.39mm with/without modification of intensity of MV CBCT images, respectively. Conclusions: Our method has quantitatively improved the accuracy of deformable registration and could be a useful solution to improve the image registration accuracy.
SU‐E‐T‐281: Quantitative Evaluation of the MRI Image Distortion in Gamma Knife Radiosurgery
Authors: Feng W , Xu Y , Burri R , Chen H , Wuu C , Isaacson S
Published: November 2011

Purpose: To quantify the spatial distortion of the MRI images in the Elekta Leksell GammaPlan version 9 planning system using different registration methods. Methods: The RPC SRS phantom was imaged using a GE Signa HDxt 1.5Tesla MR scanner and a GE LightSpeed VCT CT scanner. Both the T1 weighted MRI images and the fast imaging employing steady state acquisition (FIESTA) MRI images were acquired, along with the axial and helical CT images. The skull shell and the target in the phantom were contoured in all the four series of images acquired. The MRI images were registered in the planning system in three different ways: 1) using the fiduciary marks in the imaging box; 2) using a global co‐registration with FOV just covering skull shell; 3) using a local co‐registration to max 8.5cm FOV at image center. The target positions in all the four series of images were compared using the software tool in the planning system. Results: The target positions as obtained from the helical and the axial CT images agree within 0.1mm. For the registration method the fiduciary marks, the T1 weighted MRI images are shifted from the CT images 0.9mm in the anterior‐posterior direction, and 0.5mm in both the superior‐inferior and the left‐right directions. The corresponding displacements for the FIESTA images are 0.6mm, 0.5mm and 0.5mm respectively. The shifts of the target positions are significantly reduced in the global co‐registration approach, and all less than 0.2mm in the local co‐registration approach. Conclusions: MRI image distortion in GammaPlan version 9 is in the sub‐millimeter range for the central region of the MRI image. The spatial distortion in the FIESTA images is smaller than that in the T1 weighted images. Co‐registration to the central region of images can reduce MRI imaging distortion effect significantly.
SU‐E‐T‐282: Magnitude and Impact of Localization Error in Stereotactic Radiosurgery(SRS) Treatments
Authors: Deng H , Li S
Published: November 2011

Purpose: Highly accurate target positioning in SRS is achieved by use of localizer. Several critical factors contributing to localization uncertainty were investigated. Methods: BrainLAB CT/X‐ray localizer and Head&Neck localizer were scanned in sequential mode with Siemens Somatom CT scanner with 2.4mm slice width (SW) and localized in BrainLAB iPlan 4.1 based on high density PVC rods. Localization quality was quantitatively evaluated. Manual correction was performed based on knowledge of the geometry and structure of the localizer. A head phantom was scanned with SW of 2.4mm and 1.2mm before and after an intentionally introduced 0.75 degree horizontal rotation to study localization uncertainty caused by localizer misalignment and choice of SW. Variation of the localized image slice thickness (ST) and image/contours distortion were checked to evaluate localization quality. Results: Image localization was affected significantly by copper wires in X‐ray inserts for CT/X‐ray localizer. Due to this localization error, ST varied by as much as 2mm and in‐plane shift by 0.15mm (2.4mm SW). Manual correction reduced ST variation from about ±84% to ±23% while mean ST remained the same; it also reduces in‐plane shift by 15% and 25% in the two orthogonal directions, respectively. Head&Neck localizer doesnˈt have X‐ray inserts, its localization uncertainty was much lower and ST varied by only ±20% without correction. The head phantom study showed that localization accuracy is affected by not only the SW but also misplacement of PVC rods due to copper wire interference. Thinner SW demonstrated higher localization quality while the 0.75 degree horizontal rotation doesnˈt have much effect. Conclusions: Copper wires in X‐ray inserts are used for angiographic localization; its higher density affects the localization of slices where PVC and copper are close. The resulting ST variation causes contouring inaccuracy and non‐negligible dosimetric impact on small target SRS planning. Manual correction significantly improves localization quality.
SU‐E‐T‐283: Deforming Planning CT Images to CBCT Images Using MIMVista
Authors: Wennerstrom E , Knill C , Bossenberger T , Snyder M
Published: November 2011

Purpose: The overarching goal of this project is to be able to use daily CBCT images to calculate the dose delivery for a single treatment. To calculate the dose, planning CT images can be deformed to match the patient anatomy at the time of delivery as shown in the daily CBCT. Our current research is looking into methods to deform the planning CT to best match the CBCT using the commercial software MIMVista. Methods: The OBI (on‐board imager) of a Varian Linac at Karmanos Cancer Institute was used to get a set of daily CBCT images for a prostate patient. The images were processed in MatLab on a voxel‐by‐voxel basis to enhance areas of low signal and to convert HU for the CBCT to HU for the planning CT. Efforts were also made to decrease signal saturation in the bone through high pixel value masking. The planning CT images were deformed to the new CBCT images using MIMVista software. Results: Converting the HUs from CBCT to planning CT values followed by applying different scaling factors gave some success in improving the deformation of the images using MIMVista. However, the resulting deformation is clearly not yet accurate enough to be applied clinically. Deformation was performed by aligning bony anatomy, therefore bony anatomy deformed significantly better than tissue. Regions of low signal, variable bladder filling, and bowel gas pockets present difficulties that still need to be resolved. Conclusions: While the CBCT image adjustments we have made have improved MIMVistaˈs ability to deform planning CT images to CBCT images, work still needs to be done to reduce the noise in the CBCT images so that the planning CT images will be able to be deformed accurately.
SU‐E‐T‐284: Quantifying Respiratory Hysteresis via an Inter‐Cluster Distance Metric
Authors: Ruan D
Published: November 2011

Purposes: Understanding the degree of respiratory hysteresis is important for motion adaptive radiotherapy, as patients with significant respiratory hysteresis may require different motion models and/or management techniques. This work aims to develop a quantitative hysteresis index, that has the right metric property and robust towards observation settings. Methods: The proposed method herein is a data‐driven, clustering‐based approach. It stems from the intuition that hysteresis manifests via the discrepancy between the inhalation and exhalation segments of the respiratory trajectory. Therefore, a semi‐supervised clustering method is first applied to partition the trajectory data into inhalation and exhalation stages, and hysteresis is characterized by an inter‐cluster distance metric that intrinsically associates the corresponding displacement at these two stages. This metric is designed to be robust to scale, dynamic range, and data size, to permit comparison of hysteretic behavior across datasets acquired under different observation protocols and/or modalities. In the absence of any existing objective characterization of hysteresis, the proposed index was computed for simulation data to corroborate with human judgment. The robustness of the proposed index is tested with cross‐validation, applied to 159 patient‐derived respiratory trajectories. Results: The proposed hysteresis index is stable, and corroborates well with human judgment. Distribution of the hysteresis index among the patient cohort shows a small subgroup of trajectories with noticeably high hysteresis. Conclusion: For the first time, a quantitative index for hysteresis has been proposed. It is a proper metric and reflects the insight as a measure of discrepancy between corresponding inhalation and exhalation segment. The presence of a small population with high hysteresis alludes to the potential to “differentiate” patients based on such index and customize the motion management strategy. We will continue to develop unsupervised clustering schemes with built‐in outlier detection, and endeavor to incorporate physiological/biomechanical insight.

Research supported in part by AACR.
SU‐E‐T‐285: Generating Lung Tumor Internal Target Volumes from 4D‐PET Maximum Intensity Projections
Authors: Lamb J , Robinson C , Bradley J , Dehdashti F , Laforest R , White B , Low D
Published: November 2011

Purpose: Positron emission tomography (PET) of lung tumors suffers from breathing‐motion induced blurring. Gated PET ameliorates motion blurring and enables visualization of lung tumor functional uptake throughout the breathing cycle but has achieved limited clinical use in radiotherapy planning. We propose a process for generating a gated PET maximum intensity projection (MIP), a 3D projection of the 4D image set comprising gated PET images, as a technique to efficiently and quantitatively incorporate respiratory‐correlated PET information into radiotherapy treatment planning. Methods: 4DCT and respiratory‐gated FDG‐PET list‐mode data were acquired of 3 patients with a total of 4 small (4–18cc), well‐encapsulated lower‐lobe lung tumors. Internal target volumes (ITVs) for the lung tumors were generated by threshold‐based segmentation of the PET‐MIP images and the un‐gated PET images, and by manual contouring of the tumor in a 4DCT‐MIP image. The normalized overlap volumes and relative volumes of ITVPET‐MIP and ITVUNGATED‐PET with respect to ITVCT‐MIP were compared. The images were also visually compared. ITVCT‐MIP was considered the gold standard for these tumors having CT‐visible morphology. Results: The mean and standard deviation normalized overlap and relative volumes between ITVPET‐MIP and ITVCT‐MIP were 0.68+−0.07 and 1.07+−0.42, respectively, averaged over all 4 tumors and 5 segmentation‐threshold values. The mean and standard deviation normalized overlap and relative volumes of ITVUNGATED‐PET and ITVCT‐MIP were 0.47+−0.12 and 0.69+−0.56 respectively. Conclusions: PET‐MIP images better match CT‐MIP images for this sample of four small CT‐visible tumors, as compared to un‐gated PET images, based on the metrics of volumetric overlap and relative volumes as well as on visual interpretation. The PET‐MIP is a way to incorporate 4DPET imaging into the process of lung tumor contouring that is time‐efficient for the radiation oncologist and involves minimal effort to implement in treatment planning software because it requires only a single PET image beyond CT‐alone contouring.
SU‐E‐T‐287: The Clinical Evaluation of a Novel Amplitude‐Based Binning Algorithm for 4D CT Reconstruction
Authors: Li H , Ramirez J Garcia , Low D , Bradley J , Robinson C , Mutic S , Parikh P
Published: November 2011

Purpose: To evaluate the performance of the first commercial amplitude‐binning algorithm for 4DCT reconstruction, to compare its reconstructed image quality to that of the phase‐binning algorithm, and to investigate possible clinical effects from changing algorithms. Methods: A department customized 4DCT motion phantom was utilized to evaluate the geometry accuracy (correct phase sequencing and motion) of the amplitude‐binning algorithm. 64 4DCT patient cases, in which 60(4) cases were acquired with 4D chest (abdomen) protocol, were collected and evaluated on the respiratory motion artifact severity. The MIP images generated from both algorithms for 10 SBRT cases were further evaluated by two radiation oncologists regarding the tumor sizes and locations. Results: The phantom experiments illustrated that, as expected, maximum inhalation occurred between 90%–10% phases, while maximum exhalation occurred between 40%–60% phases. The amplitude‐binning algorithm provides reasonable phase sequencing and motion within the 4D images. The amplitude‐binning algorithm yielded fewer respiratory motion artifacts on 24/64 cases (37.5%), comparable artifacts to the phase‐binning algorithm on 35/64 cases (54.7%), and slightly greater artifacts on 5/64 cases (7.8%). The 10 SBRT cases indicated that the reconstructed tumor sizes and locations were comparable on 9 MIP image pairs generated from amplitude‐binning and phase‐binning, respectively. However, amplitude‐binning yielded smaller tumor size on one case probably due to the very shallow respiratory amplitude occurring over several breathing cycles. Conclusions: Overall, amplitude‐binning algorithm yielded fewer or equivalent artifacts on 92.2% of cases (59/64 cases), and no dramatic difference on reconstructed tumor sizes and locations from the MIP images based on amplitude and phase binning algorithms. We suggest utilizing the amplitude‐binning 4DCT images for clinical practice, especially for SBRT cases. If very shallow respiratory waves or severe motion artifacts were found on specific cases, physicists should work with the physicians to provide the best achievable 4D images.
SU‐E‐T‐290: Dosimetry Comparison of Gating V.S. ITV Approach for Moving Targets in SBRT, Dynamic Treatments
Authors: Alezra D , Ayun M Ben , Tsvang L , Pyatigorsky V , Dubinsky S
Published: November 2011

Purpose: To measure and determined the accuracy of delivered dynamic dose IMRT or RapidArc (RA) in cases of moving targets using gating vs. internal target volumes (ITV) approach for SBRT of lung or any other moving target. Methods: A Varian breathing RPM phantom was attached to a toy wagon for simulating horizontal movements. A 2 slice Perspex phantom was placed on the wagon with option to use mini ion chamber and films for dose measurements. We investigated different setup combinations with different target moving distances 0.5, 0.7, 1.2 and 2.2cm, target sizes and shapes. All setup combinations underwent 4DCT. ITV and gated targets were delineated with ECLIPSE TPS contouring tools for all 4DCT phases. Dynamic SBRT plans ware created (RA, IMRT) with different dose rates (300, 600 MU/min) to be delivered in different number of breathing cycles, and different MLC leaves direction, parallel and perpendicular to target moving direction. Collimator position in 0, 45 and 90 deg.) Point dose and 2D dose distribution were measured and compared to the calculated dose using DVH and Gamma test. Results: The combination of dynamic SBRT and ITV approach may lead in some setup combinations to dosimetric errors of >5% in dose and >5mm in isodose distance. In general Gated SBRT is more accurate from the dosimetry point of view. Conclusions: ITV approach in SBRT dynamic treatments should be used with great caution and every dynamic SBRT protocol should take into account the dosimetry inaccuracy as a result of combination of: target moving distances; target size and shape; dose rate; number of breathing cycles; MLC leaves direction.
SU‐E‐T‐296: Dose Delivered to Gantry‐Mounted Electronics in Proton Therapy
Authors: Wroe A , Schulte R , Slater J
Published: November 2011

Purpose: To evaluate the dose equivalent from scattered and secondary radiation fields present in and around a passive proton treatment nozzle, which may pose a threat to electronic equipment.Methods: Landauer Luxel dosimeters were used to evaluate the radiation field around one of the proton passive scattering nozzles at Loma Linda University proton treatment center. These detectors use optically stimulated luminescence technology in conjunction with CR‐39 to measure doses from X, gamma, proton, beta, fast and thermal neutron radiation. The dosimeters were stationed at various positions around the gantry pit and on racks on the gantry itself to evaluate the dose to electronics. Wax shielding was also employed on some detectors to evaluate the usefulness of this material as a dose moderator. To create the scattered and secondary radiation field in the gantry enclosure, a polystyrene phantom placed at isocenter and irradiated with 250 MeV protons to a dose of 1.3 kGy over 16 hours.Results: The measured overall dose equivalent ranged from 100–6000 mrem (0.08 – 4.62 mrem/Gy primary radiation), with proton/photon, thermal neutron, and fast neutron radiation individually evaluated. The distance of the detector/electronics from isocenter and neutron producing devices, such as the collimators and first and second scatters, had a bearing on the dose received. Interestingly, the addition of 1 inch thick wax shielding decreased the fast neutron omponent by almost 50% and the overall dose equivalent by 30–40%, yet it increased the thermal neutron dose by 100% and the photon/proton dose by 50%, as there as no B‐10 component to capture thermal neutrons Conclusions: The data obtained in this study will benefit future upgrades and facility designs by identifying mounting positions for electronics that minimize radiation dose.
SU‐E‐T‐297: Neutron Fluxes at the Patient Plane and Dosages Measured at the Maze Door with Various Openings for the Jaws and MLC
Authors: Krmar M , Baucal M , Jovancevic N , Ciraj‐Bjelac O , Ganezer K
Published: November 2011

Purpose: This study was undertaken to study the effects of the jaws and MLC openings on the neutron flux and dosage. Methods: Activation detectors constructed from natural Indium (In) were exposed with and without the Cd envelope to neutrons created in the head of a 15 MV therapy linear accelerator for the purpose of estimating thermal and epithermal neutron fluences at the patient plane. All measurements were performed using openings for the jaws which defined various field sizes up to 40 cm × 40 cm. The neutron dose was measured at the maze entrance door of a therapy room. Results: Our studies determined that the epithermal neutron flux as measured using different jaws openings can differ by approximately 10%, the dose at the door is highest when the jaws are closed, and the maximal jaws opening reduces the dosage about 20%. When an MLC is inserted into a fixed geometry for the one opening of the jaws, the epithermal neutron flux can increase by up to 10%, while the neutron dose at the maze entrance door increases by approximately 6%. Conclusions: As expected, the epithermal neutron flux, as well as dosage measured at the maze door is lowest when the largest width is used for the jaw and MLC opening. The range of changes of flux and dose is determined for several different field geometries.
SU‐E‐T‐298: Re‐Evaluation of Transmissions for a Commercial Tungsten Eye Shield in Electron Beams Using Radiochromic Film
Authors: Wang Y , Wu X , MacPherson M
Published: November 2011

Purpose: To re‐evaluate the transmission factors for a commercial tungsten eye shield used in 6 and 9 MeV electron beams based on the dose to the lens edge instead of the dose at the lens center using radiochromic film Methods: The eye shields have thickness of 2 or 3 mm with a 0.5 mm or 1 mm thick aluminum cap provided to reduce backscatter. The doses to the lens edge were measured at 3 mm depth below the shields and 5 mm from the central axis using Gafchromic® film. The doses were then normalized to the dose to dmax under the same setup without eye shields in place to generate the transmission factors. In contrast, the transmission factors referred by the manufacturer were determined with the lens dose measured at 3 mm depth along the central axis Results: The transmission factors are approximately 10 to 50% higher for a 6 MeV beam and 10 to 20% higher for a 9 MeV beam than the factors referred by the manufacturer. Transmissions are in general larger for smaller eye shields. In addition, one millimeter aluminum caps can increase the transmissions significantly for a 6 MeV beam. Transmission profiles at 3 mm depth in phantom are in the same shape regardless of their sizes. Transmissions at the edge of the shielded area at 3 mm depth were determined Conclusions: For internal eye shields transmission factors determined based on doses to lens edge can be significantly larger than the ones determined based on doses to the center of the lens. Transmission profiles reported here can aid dose estimation in some other situations. Relatively larger eye shields are suggested where clinically acceptable. The 0.5 mm aluminum caps are preferable in a 6 MeV beam.
SU‐E‐T‐305: An Automated Program for Shielding Calculation of a Radiotherapy Vault
Authors: Rhodes C , Parsai E
Published: November 2011

Purpose: Shielding calculations for megavoltage radiotherapy facilities with mazes are generally straightforward but highly critical. Excel spreadsheets are often used to expedite the process; but with numerous parameters and variables setting up the spreadsheet can be more time consuming than hand calculations. In busy clinical departments the patient load may leave the physicist unable to dedicate the desirable amount of resources to pay the detailed attention due for a timely and accurate shielding calculation. The purpose of this investigation is to automate this process by streamlining workload calculations, programming lookup tables for easy access, and calculate the necessary dimensions of the primary shielding. The results of a newly written automated shielding calculator program will be compared with hand calculations performed according to NCRP Report 151. Methods: A visual basic program was written, using NCRP Report 151 as a model, to calculate the shielding needed for a linear accelerator in a simple treatment vault. In an attempt to streamline the coding of the program, a set of conditional calculations is used to accurately calculate the thickness of secondary shielding. Results: The visual basic program was able to accurately calculate the thickness of primary and secondary shielding to NCRP Report 151 calculations. Conclusion: The program can be used to calculate shielding thicknesses with accuracy for radiotherapy rooms. To make the program more pragmatic, maze shielding and neutron shielding calculations should be added. The detail of the programming steps to accommodate the NCRP 151 formulas and parameters will be presented.
SU‐E‐T‐306: Radiological Consequences of Atmospheric Releases at PET Isotope Production Facilities
Authors: Dodd A.C.
Published: November 2011

Purpose: To quantify the radiological consequences of a release of PET isotopes in gaseous form to the environment, in an urban setting. Methods: The worst case scenario is identified heuristically and an analytical treatment of the worst case scenario is made using ideas from turbulent hydrodynamics to calculate the minimum dispersion of a cloud of PET isotopes (11C, 13N, 14O, 15O & 18F) in the atmosphere emerging from a ventilation stack, either from the accelerator vault or from a hot cell. A Gaussian plume model is used to calculate the average radiological consequence. Results: It is shown that 11C production has the worst radiological consequences for an atmospheric release. Whole body and equivalent doses are calculated using Gaussian and uniform radioisotope concentration profiles in the atmosphere for skin, inhalation and external annihilation gamma fields. It is found that the worst case is when there is an atmospheric inversion present, and when the ambient temperature is higher than the stack exhaust temperature as this generates negative buoyancy. The parameters of this model are the stack exhaust velocity, temperature and diameter, the ambient temperature, the released activity, the half‐life, and the mean positron range, but not the release height. It is shown that for the Gaussian plume model the mean wind speed and release height are important as well as the release time. Conclusions: The design features of the ventilation system of a PET facility which can simply and effectively control the radiological consequences of an atmospheric release are identified. The impact of these results on current regulatory thinking on PET isotope production facility design goals and permissible releases in Canada is discussed.
SU‐E‐T‐308: Monte Carlo Assessment of the Dosimetric Characteristics of Tungsten Eye Shield on the Various Eye Structures under Oblique Incidences of Electron Beam
Authors: Lee C , Prisciandaro J , Fox C , Lee C
Published: November 2011

Purpose: To quantify the impact of the tungsten eye shield on the dose to various structures around the eye and to characterize the impact of the oblique incidence of the beam using Monte Carlo simulation. Methods: A commercially available tungsten eye shield kit (tungsten eye shield + aluminum cap) was simulated along with the NCRP human adult eye model via a Monte Carlo simulation code, MCNPX, in great detail. The thickness and diameter of the tungsten eye shield that were implemented for the study were 3 mm and 14.4 mm, respectively, whereas the accompanying aluminum cap thickness was 0.5 mm. A 9 MeV electron beam of field size 10 ×10 cm from the Varian linear accelerator was simulated and the dose distributions were tallied at different irradiation angles. The absorbed doses to lens, orbit, retina, optic nerve, macula, and eyelid were calculated and the relative dose was estimated against the dmax dose. Results: The dose to the eyelid decreased to 43 % at 60 degree oblique beam as compared to 0 degree, while the dose to the lens increased by 85 % at respective angles. At normal incident angle, the lens dose (transmission) received 0.96 % of the dose to the eyelid, while at 60 degree it increased to 4.14 %. Conclusions: This study has revealed the detailed dosimetry for the sensitive structures around the eye under the electron treatment with the tungsten eye shield. The impact of the oblique beam angle to the dose to those structures was investigated via detailed modeling of the eye shield design. The unique design and material compositions of the tungsten—aluminum eye shield can pose significant uncertainties without accurate understanding of the impact of oblique beam angle.
SU‐E‐T‐309: Significant Discrepancies Found Between the MC Simulated and Experimentally Measured Beam Shape of the Electron Beam
Authors: Krechetov S
Published: November 2011

Purpose: The treatment of tumors with intra‐operative radiotherapy is getting speed in recent years. Treatment if often complicated because of the limited field size of the available applicators. Design of new systems can be simplified by using reliable Monte Carlo models of the existing linac electron beam systems. Results can be reliable only if MC model is stable relative to the reasonably large of the original system. It was found that published model of the linac is very unstable. Methods: EGSnrc Monte Carlo simulation code BEAMnrc was used for modeling electron beams, because of its proven accuracy in modeling linear accelerator components. Monte Carlo simulation of the complex electron beam system using the previously published model of the beam source is analyzed. Then simplified model of linac without a collimator was used to simulate similarly simplified hardware. Results: While original MC model results fit experimentally measured beam shape very well, Simplified MC model and experimental measurements produce vastly different results. The MC model showed significant deviation from theory and experimental measurements. MC predicted beam width was ∼30% narrower than real one for all simulated energies. Results were compared at several different values of distance from the source. If used for actual production, results of such simulation would lead to unnecessary thick scattering plates which in turn would increase level of scattered radiation and decrease effective output dose. Conclusions: Source of the model instability found to be in wrong beam source modeling. It is concluded that use of PDD and cross‐plane profiles for validation of the full MC system is not reliable method, as it is sometimes very insensitive to the very large perturbations of the beam structure. Original beam model should be validated using most primitive model possible and only then more sophisticated simulations can be reliably performed.
SU‐E‐T‐310: Investigation of Neutron Survey Meter Response in Pulsed Fields
Authors: Niven D , Picard Y
Published: November 2011

Purpose: To determine the behavior of neutron survey meters under conditions that are not representative of calibration conditions; specifically, when performing measurements in pulsed fields consisting of both photons and neutrons as opposed to an AmBe or Cf‐252 source. It is well understood that not all types of photon survey meters are suitable for use in pulsed fields, and experience suggests that this may also be the case for measurements made using typical neutron meters. Methods: A series of measurements were performed to evaluate the response of five different neutron survey meters. The first measurements evaluated their response in monoenergetic neutron fields between 50 keV and 18 MeV produced using a Van de Graaff accelerator. Dose conversion factors were applied to the known neutron fluence and the results were in turn compared to the measured dose rates. These results were also compared to the energy response curves provided by the manufacturers. The second set of measurements focused on photon rejection. The manufacturerˈs photon rejection specifications were first verified through Cs‐137 exposures at dose rates of up to 10 Sv/h. These results were then compared to photon rejection measurements from exposures in both a 6 MV and 18MV medical accelerator field. Results: A complete analysis of the results has not been completed at the time of submission. Initial results show that some neutron survey meters commonly used in accelerator facilities may be unreliable and susceptible to spurious high readings when used in the presence of pulsed photon fields, due to the relatively high peak photon dose rates during pulses. Conclusions: The conclusions will indicate the extent of any variations in neutron survey meter response resulting from use under non‐standard conditions and discuss what impact this may have for radiation surveys performed at accelerator facilities.
SU‐E‐T‐313: Ionization Chamber Measurements in a Small, Non‐Uniform Beam ‐ Applications for Synchrotron Beam Dosimetry
Authors: Anderson D , Warkentin B , Siegbahn E A , Fallone B G
Published: November 2011

Purpose: The aim of this ongoing work is to develop a dosimetric method suitable for the biomedical beamlines at the Canadian Light Source (CLS), which offer novel imaging and therapy modalities. As a step in this process, we analyzed the response of a clinical, cylindrical ionization chamber to small, non‐uniform synchrotron beams to determine absolute dose rates in air based on clinical calibration factors obtained under broad‐beam conditions.Methods: Three detectors (Gafchromic EBT2 film, Capintec PR06C ion chamber, and PTW diamond detector) were used to determine the vertical profile of the filtered beam produced by the CLSˈs bending magnet beamline. The radial response function of the ion chamber was determined using a 100 micrometer slit beam. Matlab code incorporated this information to predict the relative ion chamber output as a function of nominal vertical beam collimation (0.1 – 8.7 mm) for both stationary and scanning ion chamber geometries. The beam‐size dependent output was also measured directly with the ion chamber.Results: The beam profile was Gaussian in shape, and measurements with all three detectors were in substantive agreement. The ion chamber response function showed the walls and inner electrode of the chamber. Predicted and measured values for the ion chamber response with varying field size were in excellent agreement for both the scanning and stationary measurements, validating the MATLAB algorithm. Based on the algorithm and using an interpolated clinical calibration factor, the dose rates for the filtered bending magnet beam ranged from 1.7 – 1.9 Gy/s at the maximum CLS storage ring current Conclusions: The excellent agreement between the predicted and measured results provides confidence that the developed model of ion chamber response to the small, non‐uniform beam is valid and suggests that absolute dose rates can be measured accurately using clinical ion chambers.
SU‐E‐T‐316: Integration of Bioluminescence Imaging with Small Animal Radiotherapy for Treatment Planning and Response Assessment
Authors: Noll J , Nelson G , Colomer M Vilalta , Ali R , Bazalova M , Graves E
Published: November 2011

Purpose: To determine the capabilities of bioluminescent imaging for planning and monitoring response for pre‐clinical radiation therapy. Method and Materials: Four experimental subjects were studied: IVIS XPM‐2 luminescent phantom (Xenogen, Alameda, CA), SCID mouse with a subcutaneous luciferase‐expressing teratoma, nude mouse with an orthotopic A549 lung tumor, and a nude mouse with an orthotopic luciferase‐expressing U87 brain tumor. BLI images were obtained both a Xenogen IVIS 3D, for multiple projection angles, and a Xenogen IVIS Spectrum BLI system for multi‐spectral imaging. CT data was collected using an RS120 microCT scanner (GE Heath Care, Milwaukee, WI). CT and BLI images were imported, registered and analyzed in the RT_Image software package. Treatment planning was conducted in RT_Image using a single beam delivery based on 2D projections from different angles. The 2D distance from the center of mass (COM) of the beamˈs eye view BLI to the center of the CT‐identified target was measured. Bioluminescence tomography and CT were compared in 3D. Results: For the XPM‐2 phantom, the distance from the treatment beam to the COM of the target was found to be 4.25 mm for 0 degree BLI projection, 1.75 mm for the 180 degree BLI projection, and 0.975 mm for 0 degree BLI projection using the surface projection. The subcutaneous teratoma model produced sub‐millimeter distance to COM in each visible projection. Conclusions: Using beamˈs eye view BLI alone does not offer a precise targeting option for every BLI case. Geometry of the subject and depth of the luminescent source affects how the signal is observed. Beam alignment based on the view alone without compensation for these factors, will likely result in mistargeting except for a few special cases. In these cases 3D BLI solutions are more robust for treatment planning. Surface sources, such as subcutaneous tumors, offer straightforward BLI targeting.
SU‐E‐T‐317: MOSFET Assessment of Radiation Dose Delivered to Mice Using the Small Animal Radiation Research Platform (SARRP)
Authors: Ngwa W , Korideck H , Chin L , Makrigiorgos M , Berbeco R
Published: November 2011

Purpose: MOSFETS were employed in this study for in situ assessment of radiation dose delivered by the Small Animal Radiation Research Platform (SARRP) to mouse anatomical target volumes: brain, left kidney, left lung, liver, pancreas and prostate. Method and Materials:MOSFET detectors were calibrated with conversion factors (CF) determined for each MOSFET as a function of depth in tissue equivalent material. Calibrated MOSFET was surgically implanted post‐euthanasia into the mouse target volume, with minimal organ disruption. Using CBCT imaging and robotic motion, the mouse was then positioned with implanted MOSFET at the isocenter of the SARRP. The depth of the MOSFET from the CBCT image and corresponding CF were used in the SARRP dose calculation program to calculate the target dose for 220 kVp and 13 mA, without heterogeneity correction. Irradiations were conducted using a 0.15 cm copper filter. Three readings per MOSFET were obtained for each organ of three euthanized male mice. The measured dose was determined by averaging the MOSFET readings for that organ. The percentage difference between the measured and calculated dose was determined. Results: The results showed differences between the calculated and measured dose of between: +1.2 to 4.6 %, −3.3 to +4.8 %, +0.9 to +5.1 %, −5.9 to +2.5 %, ‐2.3 to +1.0 %, and −4.3 to +1.4 %, for the left kidney, liver, pancreas, prostate, left lung, and brain, respectively. Conclusions: The study indicates that, for 220 kVp x‐rays, the radiation dose delivered by the SARRP to characteristic target volumes in mice is within 6% of the calculated dose. The results provide a useful assessment of the need for tissue heterogeneity corrections in SARRP dose calculations for clinically relevant tumor model sites. The work also demonstrates the feasibility of using MOSFET dosimeters for in situ assessment of SARRP radiation dose delivery.
SU‐E‐T‐320: Micro CT Assessment of Magnetic Nanoparticle Retention in Arteries for Targeting Therapeutics
Authors: Wang F , Wu S , Ma Y , Tu S
Published: November 2011

Purpose: Magnetic nanoparticles (MNP) may serve as a carrier for targeting therapeutics. In such application, it is crucial to achieve effective local retention of MNP under magnetic guidance. A micro CT imaging system of high spatial resolution was used to determine the volumetric retention of MNP subjected to magnetic guidance. Methods: Male Sprague Dawley rats were anesthetized to expose the bifurcation of abdominal aorta and iliac arteries. MNP (Chemicell) were injected intravenously while an NdFeB magnet (4.9 kG) was placed by the left iliac artery. Arteries were then ligated to preserve blood inside, removed, and fixed in paraformaldehyde solution prior to micro CT scanning. Micro CT was used to image the samples for evaluation of MNP retention in the artery. Results: Strong MNP attenuation was shown in the reconstructed images of micro CT from the experimental left‐iliac artery under magnetic influence; whereas the right arteries and aortas show little x‐ray attenuation. We further calculated the ratios of MNP volume over total sample volume to quantify the impact of external magnetic field on the MNP retention. The results show that the volume ratio of the left‐iliac artery group was much higher than that of the aorta/right artery groups. Conclusions: Our results suggest that local retention of MNP in the artery may be achieved with intravenous administration of MNP in vivo. In addition, micro CT analysis may be used for magnetic field optimization to improve local retention/distribution of MNP.