bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐302: Response of OneDoseTM and TLD100 Dosimeters Over 6MV to Pd‐103 Equivalent Energies
Authors: Yu Z , Tailor R , Ibbott G , Wells N , Prado K
Published: April 2010

Purpose: Two widely available in vivo dosimeters are TLD and MOSFET detectors. Both detectors are significantly energy dependent, especially in the keV energy region. The purpose of this work is to measure the energy dependence of LiF:Mg,Ti TLD‐100 and OneDose™ (Sicel) MOSFET detectors with particular emphasis on low energy x‐rays and gamma‐rays. Methods: Eleven beams, covering an energy range 6MV down to equivalent of 103Pd x‐rays have been employed for this work. All detectors were irradiated in air to ∼50 cGy water‐equivalent dose. Other than the 60Co, beams were calibrated with Farmer ionization chambers just prior to detector irradiations. Dose rate for 60Co was based on clinical calibration data. For the 60Co and 137Cs beams, detectors were “sandwiched” between 5mm and 1.2mm buildups respectively. Thicknesses of the detectors were adequate to establish electronic equilibrium for the lower energy beams. To reduce uncertainty in the mean response, twelve samples were irradiated with each beam. The OneDose™ detectors have dimensions 6×33×1mm. TLD samples in the form of flat packs (10×10×0.3mm) were made by sealing ∼22mg powder in thin (0.06mm) poyethylene. Results: Since OneDose™ detectors were factory‐calibrated with 60Co, both OneDose™ and TLD responses were normalized to 60Co. For OneDose™, over‐response relative to 60Co is observed to be largest (3.50±0.04) at 100 kVp beam (HVL 4.14 mmAl), and negligible at high energies (137Cs to 6MV). For TLD, over‐ response at 75kVp beam (HVL 2.09 mmAl) is observed to be 1.53. More data at lower energies and at 192Ir energy are in progress. Conclusion: Response of TLD and OneDose™ relative to 60Co has been measured over a wide energy range (6MV down to equivalent of 103Pd x‐rays). For TLD, our measured results agree with the recently published values fairly closely. OneDose™ results appear reasonable when compared with other type of MOSFET detectors.
SU‐FF‐T‐303: How Accurate Are Treatment Planning System Isodose Values Outside the Treatment Field?
Authors: Howell R , Scarboro S , Kry S , Smith S , Yaldo D , Stovall M
Published: April 2010

Purpose: The purpose of this work was to quantify the discrepancy between the out‐of‐field doses as reported by a treatment planning system (TPS) to the actual measured doses. Method and Materials: Out‐of‐field doses were determined at the same location in phantom for a range of distances from the field edge using the treatment planning system (TPS) and thermoluminescent dosimeters (TLD). A typical radiation plan for Hodgkin lymphoma was created using Eclipse TPS (Varian Medical Systems, Palo Alto, CA) for an anthropomorphic male dosimetry phantom. TLD capsules were placed in the phantom at distances ranging from 1.25 cm to 18.75 cm inferior to the field edge. The phantom was irradiated with the full treatment plan dose. TLDs were read using an established laboratory protocol with an error of ⩽3%. For comparison, the out‐of‐field doses at the same positions were determined in the TPS using the point dose measurement tool. Results: As expected, the doses from both the TLD and TPS decrease exponentially as a function of distance from the field edge. Close to the field edge (within 1.25 cm), the TPS overestimated the actual dose by approximately 13%. At larger distances from the field edge the TPS underestimated dose with the magnitude of the underestimation increasing with increasing distance from the field edge. At a distance of 11.25 cm from the field edge, the TPS underestimated the dose by 53%. The TPS reported no dose at distances greater than 12 cm from the field edge. Conclusion: Studies requiring doses to organs out of the treatment field should not rely on the treatment planning system. Measurements using anthropomorphic phantoms or mathematical calculation models that are benchmarked for out‐of‐field doses should be used to determine doses to peripheral organs and tissues.
SU‐FF‐T‐307: A Multileaf Collimator Quality Assurance Tool for Modulated Electron Radiation Therapy
Authors: Emam I , Fan J , Jin L , DIB A El , Ma C
Published: April 2010

Purpose: Modulated electron radiation therapy (MERT) is an efficient treatment modality for shallow tumors. MERT provides superior target dose uniformity and conformity and spares distal critical structures. We have acquired a portable, motorized eMLC for MERT delivery at our institution. This work aims to investigate a quality assurance (QA) tool to check the leaf position accuracy for the eMLC using aSi‐EPID images. Materials and methods: The motorized eMLC consists of 27 pairs of 6mm width, 2cm thick tungsten leaves. Standard eMLC patterns were designed to test actual leaf positions using EPID images (pixel size:0.392mm) taken with 6MV photon beams. Compared to electron beams, photon beams provide sharper EPID images and therefore more precise leaf location determination. The leaf‐end positions were detected using an edge function, calibrated using film data to derive the optimal window‐level and contrast. A computer program was developed to check the leaf‐end position automatically using the EPID images. The position tolerance was set to 1mm. Results: Optimal image parameters have been obtained to detect eMLC leaf‐end position accurately. Extensive analysis of standard (reference) eMLC fields showed that EPID detected leaf‐end positions agreed their actual positions to ±2 pixels. After the eMLC leaves were moved back and forward 50 times the maximum leaf position error was 3 pixels. Online MERT eMLC segmented fields showed higher quality; leaf positions were within 0.5mm of their actual positions. We are using this eMLC QA tool to study the eMLC long‐term accuracy. Conclusion: An eMLC QA tool has been developed to check the leaf‐end position accuracy for MERT beam delivery using EPID images. This can be used as a routine QA procedure to ensure the accuracy of the eMLC so as to use a Monte Carlo based dose verification tool with the MUs and leaf sequences from the record and verify system.
SU‐FF‐T‐310: Evaluation of Angular Response of 2D Diode Array Detectors with Buildup Phantom
Authors: Chan M , Li J , Wang P , Burman C
Published: April 2010

Purpose: To evaluate the angular response of a 2D diode array with a buildup phantom using simulated volumetric modulated arc therapy (VMAT) beams. Method and Materials: A 2D diode array (MapCHECK™) with a 5‐cm thick buildup phantom (MapPHAN™) was scanned in horizontal and vertical orientations on a Philips Brilliance Big Bore CT scanner. Four treatment plans were generated for the phantom in 4 settings at 2 orientations with 10×10 cm2 open fields or different MLC‐shaped fields. All plans consist of eighteen equally spaced 6MV photon beams. Inhomogeneity corrections were applied to all four treatment plans. Dose deliveries were carried out on a Varian Cl‐iX machine while MapCHECK™ with MapPHAN™ combination was used for measuring the delivered doses with reproduced scanning parameters. The measured doses were compared with the plans using an in‐house evaluation software. A measured arc calibration factor from the setup was determined and applied to the final measurements. Results: The measured isodoses of all four plans show agreement with the plans. A gamma index with a 3% (dose difference, DD) and 3mm (distance‐to‐agreement, DTA) criteria was also used to evaluate comparisons of measured and TP data. Among the four plans in this study, the plan of horizontal position with different MLC‐shaped fields had the highest passing rate and the plan of vertical position with open fields was the worst. This is probably because the calibration is at horizontal position and different MLC shapes could even out some uncertainties due to the limited number of detectors. Conclusions: In this independent study, the angular response of MapCHECK™ with MapPHAN™ for rotational dosimetry has been evaluated in both coronal and sagittal directions. Results from our unique setting demonstrate that with the use of a properly calibrated 2D diode array and a buildup phantom VMAT patient QA is feasible and accurate.
SU‐FF‐T‐313: Dosimetry Quality Assrance in Japan
Authors: Minemura T , Ishikura S , Miyagishi T
Published: April 2010

Purpose: The Outreach Radiation Oncology and Physics (ORP) section has provided quality assurance support programs for designated regional cancer centers (300 institutions), prefecture regional cancer centers (50 institutions), and institutions participating in clinical trials since Nov. 2007 Japan. Our mission is to contribute to the construction of a system whereby patients with cancer can receive the appropriate treatment based on scientific findings regardless of the region in which they reside. As independent quality assurance and quality control services, we monitor the output for radiotherapy beams, the dosimetry data utilized by institutions, the calculational algorithms used during treatment planning, and each institution's quality control procedures. The methods of monitoring include mailed and on‐site dosimetry. Method: Mailed dosimetry (Radio‐Photo‐Luminescence) is used as a screening method. Our section is a reception office which monitors dose output data. For measurement, we use another institution's services (Association for nuclear Technology in Medicine). Our on‐site dosimetry is performed based on RPC programs. During the on‐site visit, each institution's person in charge of quality assurance is interviewed, physical measurements are made of the radiotherapy machines, and dosimetry and quality assurance data are reviewed. An institution becomes a priority for an “on‐site dosimetry visit” if a mailed dosimetry discrepancy exceeding 5% is suspected. The remainder of the prioritization scheme is based on regional cancer centers. Dosimetry measurements are intended to verify the validity of important mechanical and radiation parameters (output, field size dependence, tissue‐maximum dose ratio, wedge factor). Conclusion: For criteria, the TG‐40 guidelines are used for the review of QA procedures. Mechanical and ion chamber measurements are made in air and water. The beam calibration and radiation parameter are ±3 and ±2%, respectively. We have provided on‐site dosimetry visit programs for 17 linear accelerators since Nov. 2007. All of the institutions were within the permissible limit.
SU‐FF‐T‐316: 3 Years of Data Collection and Analysis of Film Flatness and Symmetry Using Vidar/ RIT Software From Different Centers Nation Wide
Authors: Movahed A
Published: April 2010

Purpose: To analyze accuracy and dependability of RIT software / Vidar Scanner in film flatness and symmetry measurement nationwide. Method and Materials: EDR and V films were exposed to 200 MU 6X & 15X radiations at depth of 10cm in solid water phantom, 100cmSSD with filed size of 20×20cm. Measurements were repeated with different phantom orientation, phantom of different vendors, and different packs of films, different processor, and different linac machines. Water beam scanning was done with PTW water tank at the lowest speed, central axis and at steps of 3cm off axis. Profiles were analyzed using Memphysto software. Exposed films were scanned at different 90' intervals and flipped in each orientation for comparison. Measurements were repeated at different centers with different linac and different RIT software and Vidar Scanner Results: RIT's film flatness scanning shows an area of increased intensity on the left hand side of the scan regardless of using different Linac machine, Vidar scanner or the orientation of the phantom being used. No mirror images were obtained in RIT when the flatness film was scanned flipped or if rotated at different angles. Results of ‘Scan info’ test performed weekly on Vidar scanner for three months showed no failure and passed the overall performance and water beam scanning profile collected by PTW showed persistent uniform symmetry and flatness using TG‐45 guidelines. Conclusions: None of the mentioned effects were seen while scanning a patient's QA film. Only in scanning of flatness film, one would notice the above effects. RIT believes that a systemic scanner bias (within Vidar production specifications) may be causing this effect and is working on methods to compensate for any systemic scanner bias.
SU‐FF‐T‐317: Physics Quality Assurance in the Evolving Industry
Authors: Blodgett K , Readshaw A , Coopey B , Gayou O
Published: April 2010

Purpose: To present the changes we made in our department of 8 radiation oncology centers to keep pace with the industry. The changing field has been the topic of task groups, seminars and symposiums with the expectation that groups like ASTRO, AAPM and NCI would help re‐write new specifications and guidelines. As with all members of the medical physics community, we await the new guidelines but continuously adopt our own quality assurance (QA) procedures to meet the demands of our changing fields. This paper addresses how we have approached these issues and how we have changed our QA processes. Method and Materials: The ever evolving industry in Radiation Oncology has forced medical physicists to develop new quality assurance (QA) procedures. Additional QA procedures are required for electronic portal imager devices (EPID), multileaf collimators (MLC), film processors, mega‐voltage cone beam CT (MVCB‐CT) tests, and QA on functional imaging devices such as PET/CT, SPECT and MRI. Results: A listing of added quality assurance procedures and specifications is shown. It demonstrates a higher level of testing that goes beyond TG40 to assure safe, accurate and reliable beam delivery. We have identified the need to address the addition of hardware, the growing use of computers, higher levels of imaging, and the move to adaptive treatments. Conclusion: We added procedures to all of our daily, weekly and monthly QA processes. This included linear accelerators, imaging and planning devices. These procedures have assured that we maintain reasonable and effective QA assessments in line with the changing industry. We expect that these or similar standards will be organized and adapted by medical physics organizations to assure uniform standards throughout all radiation oncology operations.
SU‐FF‐T‐319: Dosimetrical Properties and Applications of the StarCheck
Authors: Poppe B , Chofor N , Foschepoth S , Looe H , Ruehmann A , Willborn K
Published: April 2010

Purpose: The characteristics of the StarCheck system are evaluated. Method and Materials: The StarCheck (T10032, PTW‐Freiburg, Germany) consists of 512 ionisation chambers arranged in both main axes, as well as in both diagonal directions (chamber entrance window 2mm × 8 mm, height 5 mm, center‐to‐center distance 3mm). To allow a high spatial resolution, the narrow side is oriented perpendicular to the axes. Additional detectors are arranged within a 10 cm × 10 cm, 20 cm × 20 cm and 26 cm × 26 cm square. The center‐to‐center distance for the latter one is 5 mm, thus enabling a MLC position verification for MLCs down to 5 mm projection width. For all chambers within these square arrangements the chamber size is 4 mm × 4 mm with a height of 5 mm. Results: The effective point of measurement was found to be 7.5 mm under the surface of the array. Within an uncertainty of +/−0.1 mm no difference could be found between 6 and 15 MV. Output factor measurements utilizing the central chamber of the array showed no significant deviation from diode measurements for field sizes larger than 2 cm × 2 cm. Checks such as daily stability of accelerator output, field flatness and symmetry, light‐radiation field coincidence and MLC calibration or energy checks have been performed. The measurements agreed well with our standard systems 2D‐ARRAY 729 and QC6‐Plus (both PTW‐Freiburg, Germany). Furthermore the system allows on‐line adjustments e.g. during maintenance of the accelerator. Conclusion: The StarCheck proofed itself as a reliable and easy to handle measurement device which can be used for daily routine quality assurance as well as for maintenance adjustments of the accelerator. Due to the small detector cross section on the main axes, penumbra measurements can be performed with sufficient accuracy.
SU‐FF‐T‐320: The Radiological Physics Center's Annual TLD Machine Calibration Audit and Its Impact On Clinical Trials
Authors: Followill D , Lowenstein J , Palmer L , Ibbott G
Published: April 2010

Purpose: Demonstrate the importance of the annual TLD machine calibration audit for clinical trial patient dosimetry. Material and Methods: The RPC TLD postal audit program, begun in 1977, currently monitors ∼14,000 megavoltage beams at ∼1700 institutions that participate in NCI sponsored cooperative group clinical trials. This TLD audit uses capsules containing LiF powder and mini‐phantoms that are shipped to institutions annually. The TLD are irradiated, returned to and read by the RPC. The TLD dose is compared to the institution's stated dose. The RPC's acceptance criterion is ±5% and results falling outside the ±5% criterion are investigated to resolve potential dosimetry errors. Results: At the 770 institutions that contribute the majority of the clinical trial patients, ∼5% of the beams audited fall outside the 5% criterion. Correspondingly, 15–20% of the institutions have one or more beams with a potential calibration error. The standard deviation of the RPC/Inst. TLD results is 2.1% about a mean of 0.999. Most institutions rarely have dosimetry errors in two consecutive years. If the frequency of the audit were to occur biennially then the number of potential errors detected would nearly double during that time period (700 vs. 1200 beams) to include ∼33% of the institutions. As the number of uncorrected calibration errors increases, the uncertainty in dose delivered to trial patients also increases. An increase in clinical trial patient dose uncertainty, even at the 2–3% level, can reduce a trial's ability to show differences between experimental arms. Conclusions: Megavoltage beam calibration is the one dosimetry parameter that is unique to each machine and highly dependent on personnel. An independent TLD annual audit serves to detect potential calibration errors. These errors can be resolved, reducing the uncertainty in the doses delivered to clinical trial patients.

Work supported by CA010953, CA081647 awarded by NCI, DHHS
SU‐FF‐T‐324: Comparison of RTPS and Monte Carlo Dose Distributions in Heterogeneous Phantoms for Clinical Photon Beams
Authors: Nakaguchi Y , Araki F , Fukuda S
Published: April 2010

Purpose: To compare dose distributions from three different radiotherapy treatment planning systems (RTPS) with those from Monte Carlo (MC) calculations and measurements, in heterogeneous phantoms for photon beams. Methods and Materials: This study used four algorithms for RTPS: AAA (analytical anisotropic algorithm) implemented in the Eclipse (Varian Medical Systems) treatment planning system, CC (collapsed cone) superposition from the Pinnacle (Philips), and MGS (multigrid superposition) and FFT (fast Fourier transform) convolution from XiO (CMS). The dose distributions from these algorithms were compared with those from MC and measurements in a set of heterogeneous phantoms. The phantom inhomogeneities mimic relevant clinical treatment sites, which include lung slab, lung‐bone slab, bone‐lung slab, mediastinum, and tumor geometries. The benchmark comparisons were performed in lung densities of 0.30 g/cm3 and a bone density 1.819 g/cm3 for 3×3, 5×5, and 10×10 cm2 field sizes, 4, 6, 10, and 15 MV photon beams. Results: MC dose distributions agreed much better with measured data than the superposition algorithm in a set of heterogeneous phantoms. The difference in dose distributions between Eclipse‐AAA and MC were up to 15%. Eclipse‐AAA underestimated the dose inside the lung region for low energies of 4 and 6 MV, and in constant, overestimated in the tissue region. The dose distributions from Pinnacle‐CC and XiO‐MGS almost agree with those of MC and measurements but increase errors at15 MV, especially for a small field of 3×3 cm2. The FFT convolution extremely overestimated the dose inside the lung slab compared to MC. Conclusions: The dose distributions from the superposition algorithms almost agree with those from MC as well as measured values at 4 and 6 MV. The dose errors for Eclipse‐AAA are lager in lung model phantoms for 4 and 6 MV. The FFT convolution should not use for dose calculations in heterogeneous regions.
SU‐FF‐T‐344: Backscatter Correction Factor for Megavoltage Photon Beam
Authors: Hu Y , Zhu T
Published: April 2010

Purpose: For routine clinical dosimetry of photon beams, it is often necessary to add backscatter phantom material to ensure full backscatter. Available data, however, only exists for Co‐60 and 9cm thickness is required to achieve full backscatter condition. This study is to establish the minimum backscatter thickness required for 6 and 15MV photon beams and to determine the correction factor for backscatter material in case of insufficient thickness. Material and method: Backscatter correction factor, BCF(s,d,t), is defined as the ratio of absorbed dose measured on phantom central‐axis with square field size s and thickness d of full backscatter to that with backscatter thickness t. Measurements were performed in SAD geometry with a 0.125cc thimble chamber. The field sizes are 5×5, 10×10, 20×20 and 30×30cm at depth of dmax (1.5 cm for 6MV and 3 cm for 15MV), 5 and 20cm for backscatter thicknesses of 2, 4, 5, 8 and 10cm. To verify 10cm thickness provides full backscattering, we also measured at 11cm and 20cm. 7.5cm Styrofoam is placed behind the solid‐water pieces to avoid backscattering from the table. A convolution method is used to calculate BCF using Monte‐Carlo (MC) generated point‐spread kernels for clinical photon beams between Co‐60 and 24MV. Result and discussion: MC simulation agrees with the measurements within 0.8% in the same physical trend. We've attributed the difference between the measurement and calculation to difference in beam quality. BCF increases for decreasing energies and increasing field sizes. The largest correction occurs at depth of maximum dose, 0.978 for 6MV and 0.988 for 15MV.Conclusion: We concluded that backscatter thickness is 6.5cm for 6MV and 5.5cm for 15MV. If 4cm backscatter thickness is used, BCF is 0.995 and 0.988 for 10×10 and 30×30cm under 6MV and is 0.996 and 0.993 for 10×10 and 30×30cm under 15MV at dmax respectively.
SU‐FF‐T‐353: Influence of a Novel Transmission Detector On 6 MV X‐Ray Beam Characteristics
Authors: Venkataraman S , Malkoske K , Jensen M , Nakonechny K , Asuni G , McCurdy B
Published: April 2010

Purpose: A new 2‐D ionisation chamber array from IBA Dosimetry has been investigated at our center for its use as a dosimetric verification tool. This study evaluates the influence of this detector on 6MV X‐ray beam properties. Materials & Methods: COMPASS is a 2‐D transmission array of 1600 plane parallel ionisation chambers with an active area of 40 × 40 cm2. The transmission characteristics of the chamber and the influence of the detector on the 6MV X‐ray beam parameters in the build‐up and beyond were studied. PTW Markus Model 329 chamber was used for measurements in the build‐up region and diode was used for relative dosimetry beyond dmax. The following relative dose parameters were compared with and without the transmission detector in the path of the beam: central axis PDD; profiles at 1.4 and 10 cm depths; transmission factor at 10 cm. Results: For moderately narrow beam geometric conditions (smaller fields, larger SSDs) the increase in surface dose with COMPASS was small. The surface dose profiles also showed expected behavior within the field i.e., increased doses for COMPASS compared to open fields. Beyond dmax, the differences between open and COMPASS profiles were negligible. The transmission factors were very consistent throughout the range of field sizes and SSDs investigated. The mean value was 0.967 with a standard deviation of 0.002. Comparison to measurements with an acrylic block tray has shown that the insertion of the transmission detector has a similar effect on the radiation beam as a standard block tray. Conclusions: With the exception of the transmission factor, the only other influence of the transmission detector on a 6MV beam is an increase in dose in the buildup region. Our measurements show that the differences between open and COMPASS fields were found to be insignificant beyond dmax. Research partially sponsored by IBA Dosimetry.
SU‐FF‐T‐359: MapPhan with MapCHECK and Im'RT MatriXX for Real Gantry Angle IMRT QA
Authors: He R , Yang C
Published: April 2010

Purpose: A study was performed using two commercially available 2D detector array systems for IMRT patient specific QA by resetting all beam angels to gantry angle at zero degree and leaving all beam angles as planned to investigate and verify the dose delivery accuracy, limitation of the devices in the QA procedures. Method and Materials: Calibration was established at 0 degree beam angle, with the beam normal to the array plane. This study utilized one complicated head and neck IMRT plan with 9 fields (18 spitted fields). The Varian Eclipse treatment planning system (TPS) with Anisotropic Analytical Algorithm and Varian 21Ex LINAC were used for this study. The 2D array systems tested were MapCHECK with MapPhan from Sun Nuclear Corporation, and Im'RT MatriXX from IBA. Two QA phantoms were constructed by (1) MapPhan with MapCHECK and (2) solid water with MatriXX. The summed dose measured was compared to calculated one using two phantoms. Results: At gantry zero degree, 99.7% pass rate for MapPhan with MapCHECK was achieved using 3% and 3 mm DTA criteria in absolute mode and 99.2% for MatriXX. At true planned angle, 93.4% pass rate for MapPhan with MapCHECK and 93.0% for MatriXX. Conclusions: Although all arrays performed reasonably well in the composite dose for real gantry angles, it may indicate the loss of QA information in the composite. Since with the beam normal to the detector plane of 2D array, all measurement points carry the same information weight. Whereas delivery angles between normal and parallel, measurement carries varying amounts of weight for each point samples or not sampled depending on field size and beam angles. The application of a 2D array to real gantry angle IMRT QA requires careful considerations.
SU‐FF‐T‐371: 3D Dose Distribution Around Two Low‐Energy X‐Ray Brachytherapy Seeds
Authors: Massillon‐JL G , Minniti R , Mitch M , Soares C
Published: April 2010

Purpose: We present an investigation of the 3D absorbed dose distribution around two low‐energy photon ( and ) brachytherapy seeds. Method: A new version of BANG gel coupled with a small format laser computer tomography scanner has been used. The measurements were performed with a spatial resolution of 100 μm in all dimensions. The radial dose function, g(r), as well as the absorbed dose rate in the plane (2D) parallel to the longitudinal axis of the sources has been obtained at various radial distances. Results: At large distances from the source, the absorbed dose delivered is similar to that predicted from published Monte Carlo calculations for both seeds. However for distances close to the source, the differences are quite significant for the seed. The largest difference is observed for the absorbed dose delivered by the seed. A significant enhancement of the absorbed dose is observed in the radial dose function for distances below 4 mm. This difference between the calculations and the measurement is not only in magnitude but also in the shape of g(r). The shape of the absorbed dose function predicted by published Monte Carlo calculations assumes essentially that the emission outside the seed encapsulation is that of a pure photon emitter. However the observed enhancement suggests the contribution of other radionuclide in the seed with radiation emission types resembling that of a short range interaction such as high energy beta particles or electrons. Conclusion: Based on these results, high‐energy gamma spectrometry measurements have to be performed in order to determine the possible presence of impurity radionuclides in this seed and their relative contribution to the emergent spectrum of photons and electrons. The observations presented in this work at close distances from the source can only be revealed with a high‐spatial resolution dosimetry system.
SU‐FF‐T‐372: Novel Neutron Dosimetry Using Radiochromic Films for 10 MeV Neutrons
Authors: Brady S , Gunasingha R , Howell C , Crowell A , Fallin B , Yoshizumi T
Published: April 2010

The purpose of this paper is to estimate neutron doses using radiochromic XRQA films. Five radiochromic films, placed at varying distances from the neutron source and a water bottle, were exposed to a flux of 10 MeV neutrons produced via the d(d, n)He reaction using the Tandem accelerator at Triangle Universities Nuclear Laboratory at Duke University. An estimation of the neutron flux was obtained by neutron activations of two sets of aluminum and gold activation foils. One foil of each type was placed at the front and back sides of the water target. The flux calculation was based on gamma spectroscopy of the irradiated foils using HPGe detectors. A Monte Carlo (MC) simulation based on FLUKA2008 code was also used to estimate the 10 MeV neutron dose for the same geometry. The accuracy of the results from MC was verified by the comparison of dose on water target from MC with the dose calculated on the same target using flux and the ICRU data tables. Based on these results, a calibration curve was obtained for optical density of the film vs. absorbed neutron dose in the range of 0–20 Gy. We have demonstrated the potential application of radiochromic films for neutron dosimetry. This research was, in part, supported by National Institute of Allergy and Infectious Diseases Grant 5U19 AI067798‐03
SU‐FF‐T‐374: Dynamic Anthropomorphic Eye Phantoms for Targeting and Dose Verification of a Novel Ophthalmic Radiosurgical Device
Authors: Firpo M , Chell E , Herron M
Published: April 2010

Purpose: Age‐related Macular Degeneration (AMD) is the leading cause of blindness in people over 65 in the U.S. It is a neovascular disease that can result in profound and rapid loss of central vision and has been shown to be susceptible to radiotherapy. A 100kVp tabletop stereotactic radiosurgical (SRS) device has recently been developed to treat AMD. Here we evaluate a new set of anthropomorphic eye phantoms for verifying the targeting and dosimetric accuracy of the device. Method and Materials: A series of eye phantoms were developed to match human eyes in size and shape. The phantoms are made of Solid Water, have a post at the cornea to attach to the clinical fixation assembly, and at the retina have a cutout with fiducial posts that support the precise mounting of laser‐cut pieces of radiochromic film. After irradiation of the phantom, a flatbed scanner and image analysis software are used to assess the accuracy of beam targeting using the fiducial holes in the film. Multiple “treatments” were repeated on stationary phantoms to assess system precision and accuracy. A dynamic eye was also created by attaching set of stepper motors to a phantom. While irradiating the phantom, the motors were driven with clinically‐measured human eye motions to simulate actual treatment and test the automatic beam shut‐off of the system when motion exceeded an established threshold. Results: Phantom measurement precision of 0.1mm was achieved. Static repeated delivery of the therapy showed a system precision of 0.2mm and an accuracy of 0.4mm. Analysis of films irradiated while the eye phantom was being driven with clinically‐measured human motion verified the gating algorithm was capable of protecting radiosensitive structures. Conclusion: The eye phantoms demonstrate that a specialized ophthalmic SRS device can accurately target the back of the eye.

Research Supported by Oraya Therapeutics
SU‐FF‐T‐377: Liquid Scintillation Detector System for Real‐Time IMRT Quality Assurance
Authors: Poenisch F , Archambault L , Briere T , Gillin M , Beddar S
Published: April 2010

Purpose: A liquid scintillation (LS) detector system has been developed to verify dose delivered to a 3D volume. The feasibility of such a system as an IMRT quality assurance device is demonstrated. Method and Materials: The LS detector system consists of an opaque tank (20cm × 20cm × 23cm), a light‐tight conduit and an air‐cooled CCD type camera (Luca, Andor Technology, South Windsor, CT) placed 80 cm away from the center of the tank to minimize stray radiation. The Liquid Scintillator used in this system is BC‐531 (Saint‐Gobain, Newbury, OH). The detector system was irradiated with a 6‐MV photon beam in step‐and‐shoot IMRT delivery mode from a Varian Clinac 21EX. A series of light images were acquired during beam‐on time over all segments of one treatment field. The measured light was compared with the predicted light signal, which was calculated from forward projection of the convolved 3D dose volume obtained from the treatment planning system. Results: An integration time of 150 ms was adequate to provide a resolution of 1 cGy at a dose rate of 400 cGy/min. Frame‐by‐frame acquisition demonstrated the advantage of reduced noise over a single long‐time acquisition. Images acquired during irradiation could easily be distinguished from dark images, since their standard deviation was higher by at least a factor of three. The measured light signal showed good agreement with the predicted light image. Differences occurred due to the light scattering and light reflection. Conclusion: We have validated the LS detector system during step‐and‐shoot IMRT delivery. Further improvements are required to optimize the blurring filter kernel, improve the efficiency of the workflow and add a quantitative analysis of the light output.

Supported by the NCI (1R01CA120198‐01A2)
SU‐FF‐T‐384: A Proto‐Type Design of a Real Tissue Phantom for the Validation of Deformation Algorithm and 4D Dose Calculations
Authors: Szegedi M , Rassiah‐Szegedi P , Hinkle J , Salter B
Published: April 2010

Purpose: The purpose of this work is to design a biologically realistic, real‐tissue phantom for use in validation of non‐compressible deformation algorithms and 4D dose calculations. Method and Materials: A phantom motion‐controller capable of driving both sinusoidal and non‐periodic patient‐based breathing patterns via a piston drive mechanism was applied to porcine liver tissue. It was programmed to generate diaphragmatic‐like motion that would result in internal motion/deformation that would be similar to 4D CT recorded motion of implanted liver markers in patients. The similarity of marker motion pattern in the liver phantom compared to implanted markers in real patient was evaluated by 4D CT. The consistency of phantom motion over time was assessed. Results: Reproducibility of markers motion was consistent over a period of 90 minutes. Internal fiducial motion/deformation was seen to be similar to that of patient internal fiducial motion, and was reproducible up to elongations of 3 cm. Conclusion: The phantom motion is biologically realistic, and faithfully simulates real patient liver motion and deformation. The induced liver tissue motion is reproducible up to elongations of 3 cm and over time periods of up to 90 minutes.
SU‐FF‐T‐386: Validation of the Delta4 Dosimetry Phantom Against Ionometric Measurements
Authors: Calvo O , Gutiérrez A , Stathakis S , Mavroidis P , Moral S , Esquivel C , Shi C , Papanikolaou N
Published: April 2010

Purpose: To validate a 3D dose calculation methodology used by the 3D Delta4™ phantom. Method and materials: Measurements were performed using a TomoTherapy™ HiArt™ and a Varian 2300C/D™. A pinpoint PTW N31006 chamber with a sensitive volume of 0.016cc was use for point dose measurements. The Delta4™ phantom (ScandiDos AB, Uppsala, Sweden) was modified to accept the ion chamber. Eight (n=8) quality assurance plans were created in both planning systems. Plans covered a range of doses from 20% to 160% (20% steps) of the prescribed dose using Pinnacle3 TPS. Tomotherapy plans covered doses from 20% to 100% (20% steps) and a DQA plan with 200% of the prescribed dose. Treatment plan, DQA plan, DQA dose and structures were exported via DICOM RT to the Delta4™ software. At each delivery, a point dose measurement was recorded. Point dose measurements and calculated doses by the Delta4™ were compared against the calculated dose of the treatment planning systems. Furthermore, point dose measurements were compared against the Delta4™ calculated dose. Results: The preliminary results showed that chamber measurements agree with Pinnacle3 within 0.3% to 2%. The Delta4™ system have an excellent response at higher doses while at lower doses the percent differences are compared to the ones obtained by the pinpoint chamber. Tomotherapy delivery results showed good agreement between the pinpoint chamber and Delta4™ with percent differences ranging from 0.03% to 5% with better response at high doses Conclusion: Delta4™ showed good agreement with the pinpoint chamber in the dose calculation, which shows that the system 3D dose calculation methodology is able to predict the same or better doses compared to the pinpoint chamber measurements.
SU‐FF‐T‐387: Performance of a Portable MOSFET Dosimetry System for In‐Vivo Dose Measurements in Orthovoltage Treatments and Kilovoltage Cone Beam CT
Authors: Amin M , Kohli K , Norrlinger B , Lindsay P , Heaton R , Ramaseshan R , Hallil A , Islam M
Published: April 2010

Purpose: The purpose of this work is to characterize the portable MOSFET dosimetry system for kilovoltage radiation beams, and investigate its use for in‐vivo dose measurements in orthovoltage treatments and kilovoltage (kV) cone beam computed tomography (CBCT) imaging. Materials and methods: A newly developed MOSFET portable dosimetry system (Best Medical Canada) was characterized and compared against the mobileMOSFET system (Best Medical Canada) for reproducibility, linearity, angular dependency for kilovoltage energies, ranging from 40kVp to 225kVp. Calibration factors were derived for 15 photon energies at 2cm depth of solid water with references to the doses measured according to TG‐61 guidelines. Surface dose measurements were performed on solid water phantom, simulating treatment conditions of patients under treatment. The kV CBCT doses were measured on a Varian linear accelerator (Varian Onboard Advanced Imaging 1.4) for patients undergoing CBCT. Results: The responses of the portable dosimetry system were found to be similar to those of the MobileMOSFET system in terms of sensitivity, reproducibility, linearity, and angular dependency. MOSFET sensitivity for standard sensitivity MOSFETs with standard bias was found to be from 4.63±0.1mV/cGy to 2.63±0.1mV/cGy in the energy range investigated. The average of the dose difference between the MOSFET measurements and the expected skin doses for orthovoltage treatment was (−0.1±2.25)%. The CBCT doses for patients undergoing prostate treatment, shows good agreement with the expected published values. Conclusion: The results of the investigation suggest that the charcateristics of MOSFET portable dosimetry system is very similar to those of the mobileMOSFET system. The dosimetry system was found be suitable for surface dose measurements in orthovoltage treatment, as well as in kV CBCT imaging and therefore, can be used as an in‐vivo dosimeter for routine clinical use.
SU‐FF‐T‐399: Characterizing Secondary Gamma Fluence From a Scanned Beam Proton Therapy Nozzle
Authors: Peterson S , Polf J
Published: April 2010

Purpose: Recently, several studies have investigated the use of secondary prompt gamma‐ray emission as a method for dose verification. The purpose of this study was to characterize the secondary prompt gammas produced within a scanned beam proton therapy nozzle. Characterizing the scattered gammas will help determine the prompt gamma fluence created within the treatment nozzle and its proportion to that created within the patient. Method and Materials: Monte Carlo simulations were performed using a model of a clinical scanned‐beam treatment nozzle to investigate the gamma fluence at the end of the nozzle. Energy spectrums were calculated for low, medium and high proton beam energies at the isocenter and several points off‐axis. The energy peaks from the spectrum were used to identify specific nozzle elements responsible for the scattered photons. The simulations were also performed with a tissue phantom placed at the isocenter to estimate the ratio of scattered gammas radiation from the nozzle to scattered radiation from the patient. Results: Calculated results show that the gamma fluence created in the nozzle is 1% of the gamma fluence created by the patient at isocenter. The gamma fluence from the tissue phantom falls off more quickly than the nozzle gamma fluence as you move laterally away from isocenter, resulting in up to 7% of the total gamma fluence coming from the nozzle. Conclusion: Based on the proportion of gamma production by the nozzle and the significant oxygen and carbon emission lines from the nozzle, we think that in order to isolate the spectrum emitted from the patient from that emitted from the nozzle, it would be necessary to shield the detector from the prompt gamma produced in the nozzle.
SU‐FF‐T‐422: Dependency of Proton Dose On Tissue Composition Investigated Using Monte Carlo Models of Hounsfield Number Conversion and Cadaver‐Based Anatomical Data
Authors: Liu Y , Shi C , Xu X , Chen W , Jette D , Papanikolaou N
Published: April 2010

Purpose: In this study, we performed dependency study of proton dose on tissue composition using Monte Carlo models of Hounsfield number conversion and cadaver‐based anatomical data Method and Materials: Monte Carlo methods provide the most accurate radiation dose calculation technology as it take into account detailed materials properties, such as materials composition, mass density and interaction cross section. Monte Carlo simulation calculates the energy deposit per mass of each small volume (voxel) after a patient is presented by a large number of voxels. Two methods of building patient‐specified Monte Carlo models have been used in this study: one is to convert patient's CT Hounsfield numbers to materials; the other way is assign anatomical detailed materials using cadavers' segments. Dose distribution and dose volume histogram were compared based on the Monte Carlo models. Results: The dose distribution at the iso‐center slice, the 95% did not cover conformally to the ROI for Hounsfield MC model with shifting 2∼3 mm superior to the ROI. Dose volume history for planning tumor volume (PTV), Brain, Pituitary and Chiasm were used for evaluating the effect of tissue composition. The mean doses difference for PTV was 2.1% for the cadaver‐based MC and Hounsfield conversion MC model. The mean dose difference for Brain, Pituitary and Chiasm was less than 1.0%. Conclusion: Proton radiation dose was calculated and closely compared using two Monte Carlo models: one from CT Hounsfield number conversion and the other from human anatomically detailed Cadaver segments. It is found that the effect of different tissue composition on proton radiation dose calculation is complex involving organs at risk. Our method using cadaver‐based Monte Carlo model for proton dose calculation was shown to be suitable for benchmarking other Monte Carlo dose calculation methods and for providing tissue heterogeneity correction due to the effect of tissue composition.
SU‐FF‐T‐423: Time‐Dependent Monte Carlo Dose Calculation Method for Dynamic Movement of All Linac Components in Presence of Patient Motion
Authors: Naqvi S , Lasio G , D'Souza W
Published: April 2010

Purpose: Radiation therapy has become increasingly complex over the past several years, with simultaneous moving parts, such as the gantry/MLC (IMAT), or gantry/MLC/couch (Tomotherapy). With multiple moving components, deterministic dose calculation methods will prove ineffective as the computational cost of discretization in n‐dimensions increases exponentially with n. Monte Carlo methods, which are immune to the effects of increased dimensionality, can be exploited for this purpose. In this work, a dynamic Monte Carlo dose calculation engine is developed to account for arbitrary rotational and translational movements of the jaws, MLC, gantry and couch in the presence of patient's breathing motion within the approximation of rigid body motion. Methods and Results: In each history of the dynamic Monte Carlo run, a point in the delivery control point sequence of a dynamic delivery is randomly sampled. The values of 130 variables (angles or positions) are determined by linear interpolation between adjacent control points. A photon is sampled from a source and raytraced through the detailed collimator structure and the patient simulation phantom. Dose is deposited via randomly sampled monoenergetic kernel rays issued from photon interaction poins. The method also enables temporal correlation with breathing motion waveforms, and can be used to evaluate time‐dependent interplay effects of patient motion with respect to all moving parts of the linac. A typical plan using a 4 mm voxel grid requires approximately 5‐10 minutes to compute on a single 2.4 GHz Pentium microprocessor to achieve 2% statistics in the peak dose region. Conclusion: The method allows simultaneous simulation of gantry, collimator, MLC, couch and patient motion, and, therefore, provides an efficient and accurate means to calculate dose for arbitrarily complex dynamic treatments. It opens the computational door for exploring more degrees of freedom in treatment planning to achieve better dose distributions for radiation therapy patients.
SU‐FF‐T‐426: Fast 4D Monte Carlo Dose Calculations in Deforming Anatomies
Authors: Heath E , Kawrakow I
Published: April 2010

Purpose: The voxel warping approach to 4D dose calculation calculates the dose deposition on a deformed dose grid in order to determine the contribution of dose deposited at one anatomical state to a reference state. The current implementation of this method in the defDOSXYZnrc Monte Carlo code resulted in a significant increase in computation times. The purpose of this work was an efficient implementation of the voxel warping method in the VMC++ Monte Carlo. Three alternative deformed voxel geometry definitions were investigated to see how they influence the remapped dose calculation efficiency and accuracy. Method and Materials: A set of new deformable geometry classes was created for VMC++ which were compiled as dynamic shared libraries that could be loaded at run time. We implemented three different deformable geometries: a deformed dodecahedron geometry and two geometries based on tetrahedral elements with alternate divisions of the voxel faces. Dose calculations using the new deformable VMC++ geometry were validated by comparison with defDOSXYZnrc by calculating remapped dose in a deforming water phantom and a lung patient deformed from Inhale to Exhale. Dose distributions were compared using the gamma index as well as the Kawrakow‐Fippel test to distinguish systematic discrepancies from dose differences due to random statistical uncertainties. Results: Efficiency gains of the order of 100 were obtained relative to defDOSXYZnrc. A further factor of 1.2 gain in efficiency was realized with the tetrahedral geometries. VMC++ and defDOSXYZnrc calculations were found to agree within 1% in the deforming phantom. Although it could be demonstrated that different folding of the voxel faces influences the dose calculation no differences were found in the patient dose distributions calculated using the different geometries.

Conclusion: We have implemented a new deformed geometry class in the VMC++ Monte Carlo code which makes possible efficient and accurate 4D dose calculations.