bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐D‐214‐01: 4D‐MRI for Radiation Therapy of Moving Tumors
Authors: Yin F , Biederer J , Cai J , Parikh P
Published: November 2011

Four‐dimensional computed tomography (4D‐CT) has been widely used in radiation therapy for imaging moving tumors, especially in the thoracic regions. In other body sites such as the abdominal, 4D‐CT is limited due to its intrinsic low soft‐tissue contrast. Additional concern for 4D‐CT includes increased radiation dose to the patient since a 4D‐CT scan typically generates 10 times more data than a regular CT scan.

On the other hand, magnetic resonance imaging (MRI) has excellent soft‐ tissue contrast and implies no known radiation hazard. 4D‐MRI can be used to improve the determination of patient specific tumor motion margin for radiation therapy, especially for the tumors in the abdominal regions where non‐contrast enhanced 4D‐CT has limitations. It can be applied for repeated or prolonged measurements covering multiple respiratory cycles to monitor individual changes in respiration frequency and depth. It is therefore desirable to develop 4D‐MRI techniques to address the problems associated with 4D‐CT.

There are different approaches to develop the 4D‐MRI technique. The more frequently applied approach is based on repeated fast 3D MR pulse sequences and requires sophisticated hardware. Another approach is to retrospectively sort slice MR images acquired continuously throughout the volume based on respiratory phases. While both approaches have the promise of becoming useful imaging tools for tumor motion management in radiation therapy, they have their own pros and cons. For the first approach, its temporal resolution (∼0.7 frame/s) and spatial resolution (3–4 mm) are limited resulting in an overestimation of tumor size as the mass is volume averaged into many voxels during motion and an underestimation of lesion displacement. The second approach will require some type of respiratory surrogate (either external or internal) and is therefore subject to similar limitations as 4D‐CT.

However, a simple but most robust approach for the delineation of tumor positions and trajectories during respiration is the averaging of multiple single slice MR acquisitions over time within a MIP‐display. This largely reduces the complexity of the technique and still provides sufficient information for the definition of motion adapted target volume definition which enhances the probability of its clinical application.

Learning Objectives:

1. To discuss the need of 4D‐MRI technique for improving patient care in radiation therapy

2. To present the latest development of 4D‐MRI imaging techniques and their differences.

3. To discuss the application of 4D‐MRI in tumor motion management and treatment planning in radiation therapy
MO‐D‐110‐01: Benefit Risk Assessment: Identifying the at Risk Patient; SYMPOSIUM‐Estimating Patient‐Specific Radiation Dose from Fluorosocpy
Authors: Chambers C
Published: November 2011

Radiation dose management for fluoroscopically‐ guided interventional medical procedures requires a combined effort from physicians, physicists and government regulators. Paramount to this process is an understanding of the benefits and risk for these procedures. For cardiovascular disease, despite the increasing prevalence in a setting of escalating risk factors, mortality has steadily decreased. Diagnostic and therapeutic fluoroscopic imaging has undoubtedly attributed to this as seen specifically in the areas of acute myocardial infarction, sudden cardiac arrest, and heart failure therapy. All facilities should have a radiation safety program as part of the institutional quality assurance umbrella with specific focuses on dose management as it applies to the equipment, physician, and patient. The regular interactions between the physicist and physician/staff assure proper equipment purchase and maintenance, initial and annual training, and patient dose assessment. The current challenges of the high risk patient require specific attention. As techniques and equipment advance, application of procedures expands and previously “untreatable” patients are approached. Patient factors such as morbid obesity, diabetes and repeat procedures are seen more as the norm rather than the exception. Complex anatomy in elderly, critically ill patients dictate challenging clinical decisions before, during, and after the procedure. This presentation will present a best practice approach to the challenges of benefit risk assessment in patients undergoing fluoroscopically‐guided interventional procedures.
MO‐D‐110‐03: Calculating Organ Dose from Fluoroscopy
Authors: Alaei P
Published: November 2011

Calculating organ dose from fluoroscopy procedures has been of interest to radiology and cardiology communities for many years. Published work in this area includes those that employed Monte Carlo methods to calculate organ doses from fluoroscopy procedures in phantom and those that extrapolated the organ doses from skin dose or exposure measurements.

Another tool which could potentially be used to compute organ doses from fluoroscopy is a treatment planning system routinely used for creating radiation therapy treatment plans. Although a treatment planning system is designed to compute dose distribution in the megavoltage energy range, its use in the diagnostic energy range is a possibility, at least for one commercial system. This requires knowledge of certain fluoroscopic beam data which can be obtained by measurements or by relying on available published data, and a CT scan of the patient. This tool, once validated, can provide detailed dose distribution within any organ exposed to radiation.

This lecture provides details of the use of a radiation therapy treatment planning system for dose calculation in diagnostic energies with examples of dose distribution from fluoroscopic procedures in adults and children.

Learning Objectives:

1. Learn about the methods of organ dose computation from fluoroscopy

2. Learn the details of using a treatment planning system for fluoroscopic dose calculation

3. Learn the magnitude of typical organ doses encountered in fluoroscopy
MO‐D‐110‐04: Imaging Symposium
Authors: Huda W
Published: November 2011

Patients who undergo medical imaging procedures such as fluoroscopy are exposed to ionizing radiations. The quantification of the amount of radiation used to perform a given examination is achieved by the Kerma Area Product (KAP) that is incident on the patient, together with appropriate information on the beam quality (i.e., Half Value Layer). A formal methodology will be presented to show how Kerma Area Product (KAP) in fluoroscopy, as well as the corresponding patient effective dose, can be converted into individual patient radiation risk provided appropriate account is taken of the irradiation geometry, patient size and demographics. It is concluded that patient specific risks in medical imaging are essential for identifying indicated examinations, where the patient benefit exceeds any radiation risk. Of equal importance is the fact that current scientific knowledge may be employed to enable practitioners to compute patient risks for any type of fluoroscopy based examination.
MO‐D‐211‐01: Low Dose Molecular Breast Imaging
Authors: OˈConnor M
Published: November 2011

Background: Several new nuclear medicine‐based breast imaging techniques have emerged over the last few years. These include Positron Emission Mammography (PEM), Breast Specific Gamma Imaging (BSGI) and Molecular Breast Imaging (MBI). These techniques usually employ doses of ∼ 10 mCi F‐18 FDG in the case of PEM, or 20–30 mCi Tc‐99m sestamibi in the cases of BSGI or MBI. In addition to their potential value as adjunct diagnostic tools, these techniques hold promise as potential adjuncts to screening mammography particularly for women with dense breast tissue where the sensitivity of mammography is known to be reduced. A previous study has shown MBI to have 2–3 times the sensitivity and equivalent specificity to screening mammography in women with dense breasts. However, the current administered doses employed in these techniques deliver effective radiation doses that are ∼10 times higher than mammography.

From the BEIR VII tables, the lifetime associated risks from PEM, BSGI and MBI can be calculated and compared to that of screening mammography. These estimates indicate that in order to achieve a comparable radiation burden to mammography, the administered doses of F‐ 18 FDG and Tc‐99m sestamibi need to be reduced to less than 2 mCi F‐18 FDG and 4 mCi Tc‐99m sestamibi.

This presentation will briefly review the clinical literature demonstrating the value of these new techniques in both diagnostic and screening applications, and will review the dosimetry and estimated lifetime associated risks from these technologies. It will then focus on one of these technologies — MBI, and will illustrate how we can optimize the physics of the collimation and detector to achieve a 5‐fold reduction in the required dose of Tc‐99m sestamibi for clinical studies. We will also review possible post‐acquisition processing techniques that may enable further reduction in dose, along with alternative radiopharmaceuticals that deliver low doses due to their biodistribution.

A total of 4 dose reduction schemes will be discussed — a) development of optimized collimation for single‐photon imaging, b) improved utilization of the energy spectral characteristics of the gamma cameras, c) implementation of noise reduction and resolution recovery algorithms, and d) use of adaptive geometric mean algorithms for combination of images from opposing detectors. In addition we will consider alternative radiopharmaceuticals, such as Tc‐99m MDP that deliver a lower radiation burden than Tc‐99m sestamibi.

We will demonstrate that image quality obtained with low‐dose MBI performed with 4 mCi Tc‐99m sestamibi matches that of standard MBI performed with 20 mCi dose. Low‐dose MBI presents radiation risks to the patient comparable to that of digital screening mammography, allowing its safe implementation as a screening technique.
MO‐D‐220‐01: In Vivo Quantitative Vascular Imaging of Tumors Using 3D Photoacoustic Imaging
Authors: Thornton M , Stantz K , Kruger R
Published: November 2011

Purpose: Employ volumetric photoacoustic computed tomography (PA‐CT) imaging to monitor key indices of tumor biology in tumor bearing mice without the use of exogenous contrast. In this study we describe the scanning system and its use in tracking in vivo tumor vasculature and tumor volume, through tumor growth and following treatment by anti‐angiogenic therapy, in both control and treated animals. Methods: A PA‐CT scanner, specifically designed for mouse imaging, employs a sparse array of 128 discrete transducer elements (3mm in diameter, 5MHz center frequency) arranged on a hemispherical surface, a tunable NIR pulsed laser (680– 950nm), and a digital acquisition system with 128 channels. The tissue being imaged is illuminated directly by pulses of laser light and the resulting photoacoustic signals are recorded. The photoacoustic data is reconstructed using a modified 3‐D Radon transform to produce a spherical volume 25mm in diameter. EGFR+ MCF‐7 breast cancer cells were injected into two groups (control and treatment) of mice (n=6). The tumors were allowed to grow to approx. 10mm in size at which point the treatment group was injected with a single dose of Avastin (40mg/kg). The mice were scanned at 17, 27, and 34 days post‐implantation. Results: The tumor vascularity was quantified by measurement of hemoglobin (Hb) content in the tumor. The Avastin treated mice showed an average decrease of 65% in hemoglobin content following treatment while the control group had an average increase in tumor Hb content of 33%. Conclusions: The strong absorption of NIR light by oxy‐hemoglobin and deoxy‐hemoglobin provides a useful contrast mechanism for photoacoustic imaging without the use of exogenous contrast agents. Photoacoustic imaging is well suited to in vivo studies of cancer therapies where the tumor vasculature is a marker of the efficacy of the therapy or intervention.

Funding Support, Disclosures, and Conflict of Interest: M. Thornton is an employee of Endra Inc.
MO‐D‐220‐03: Thermoacoustic Imaging of Porcine Kidneys
Authors: Catenacci J , Roggenbuck M , Patch S
Published: November 2011

Purpose: To demonstrate the feasibility of thermoacoustic (TA) imaging to detect microvasculature surrounding tumors embedded 6+ centimeters deep. Methods: Ex vivo imaging of porcine kidneys in a custom TA testbed demonstrates 6cm depth penetration. Chilled glycine solution serves as acoustic couplant. Submicrosecond radiofrequency pulses with carrier frequency 108 MHz and peak power of 40kW generate TA pressures. Step‐ and‐shoot volumetric scanning is performed by rotating and translating the kidney while the transducer remains stationary. Translation increment is 3.6mm between slices. Focused single‐element videoscan transducers with center frequencies of 1 MHz and 2.25 MHz collect signals, which are amplified by a 54dB preamp. Lightly filtered single‐slice sinograms are backprojected in‐plane to reconstruct images. TA signal generated by vials of blood product and pure anticoagulant are compared with TA signal from pure water. Vials are manually positioned, diminishing repeatability of these experiments, so multiple realizations of each are presented. Results: Reconstructions of the kidneys clearly track progression of calyces from one slice to the next. In vivo, calyces are filled with urine, which can have widely varying electrical conductivity. TA signal strength is directly proportional to electrical conductivity but is also a function of other tissue parameters: bulk modulus, thermal expansion coefficient, and specific heat capacity. In our testbed, the calyces fill with glycine, which has low conductivity, causing signal dropout in the calyces. TA pressures generated by both blood product and pure anticoagulant generate orders of magnitude stronger signal than pure water. Conclusions: We demonstrate whole organ TA imaging is possible with 108 MHz RF irradiation. Furthermore, at 108 MHz, blood is highly conductive and generates strong signal, supporting the hypothesis that TA may be able to detect microvasculature surrounding aggressive tumors.

This work was supported by NIH grant 5 R21 CA137364‐02.
MO‐D‐220‐04: Imaging of Arthritis with Both Light and Ultrasound
Authors: Wang X , Chamberland D , Jiang Y
Published: November 2011

Purpose: To explore the potential of photoacoustic tomography (PAT), as an emerging optical imaging technology, for early diagnosis of inflammatory joint disorders and accurate monitoring of disease progression and response to therapy. Methods: Pulsed laser light in the near‐infrared (NIR) region was directed toward a joint with resultant ultrasonic signals recorded and used to reconstruct images that present the optical properties in subsurface joint tissues. The feasibility of this bench‐top joint imaging system in delineating soft articular tissue structures in a noninvasive manner was validated first on rat models and then on human peripheral joints harvested from fresh cadavers. Based on the study on a commonly used adjuvant induced arthritis rat model, the capability of PAT to differentiate arthritic joints from the normal was also examined. Results: With sufficient imaging depth in the NIR region, PAT can realize tomographic imaging of a human or a small‐animal joint as a whole organ noninvasively. Based on the optical contrast, various intra‐ and extra‐articular tissues, including skin, fat, muscle, blood vessels, periosteum and bone, were presented successfully in images with satisfactory spatial resolution that was primarily limited by the bandwidth of detected photoacoustic signals rather than by optical diffusion as occurs in traditional optical imaging. In comparison with the images from the normal joints, significant differences were found in the images from the inflammatory joints, including enlarged periosteum diameter and enhanced intra‐articular optical absorption. Conclusions: By presenting additional optical contrast and tissue functional information such as blood volume and blood oxygen saturation, PAI is a natural and promising complement to conventional ultrasound technologies for musculoskeletal imaging. PAT, with its intrinsic advantages, may provide a unique opportunity to enable early diagnosis of inflammatory joint disorders, e.g. rheumatoid arthritis, and to monitor therapeutic outcomes with improved sensitivity and accuracy.
MO‐D‐220‐05: Optoacoustic Thermometry for Noninvasively Monitoring Thermal‐ Ablation Therapy in Real‐Time
Authors: Chitnis P , Mamou J , Gross D
Published: November 2011

Purpose: to demonstrate the feasibility of optoacoustic imaging (OAI) and a signal processing scheme based on singular‐value decomposition (SVD) for noninvasively monitoring localized temperature changes during thermal‐ ablation therapy. Methods and Materials: A bolus of Indocyanine Green (ICG), which strongly absorbs 800‐nm light, was injected in excised chicken and bovine samples using a 26‐gauge needle in order to mimic optical absorption in a blood‐rich tumor. A wire thermocouple was inserted at the injection site to provide “ground truth” measurement of local temperature. A custom‐designed, 1.5‐MHz high‐intensity focused transducer (HIFU) transducer delivered therapeutic energy in two modes: continuous wave (CW) mode and pulsed mode (80% duty cycle, thermometry performed intermittently during the off periods); and two focal intenstities: 1 kW/cm2 (cavitation absent) or 4 kW/cm2 (cavitation present). The HIFU transducer had a central opening to accommodate a linear, diagnostic imaging probe. The light from a pulsed, 800‐nm laser was delivered at the injection site using a bifurcated fiber bundle oriented normal to the imaging plane. The optoacoustic signals emanating from the target site were simultaneously acquired and digitized across the 64 central elements of the imaging array using a fully‐programmable research ultrasound engine at a pulse‐repetition rate of 10 Hz. SVD analysis of the time‐varying OA signals was performed to extract the contributions of temperature change. Results: The OA amplitude exhibited a direct correlation with change in temperature during heating induced by HIFU and subsequent cooling; this provided adequate means of monitoring temperature changes during pulsed HIFU exposures. Despite the presence of broadband noise associated with inertial cavitation for CW HIFU exposures at high intensity, the SVD analysis was able to extract the local temperature‐time profile accurately with root‐mean‐squared error less than 5C. Conclusion: OAI provides a viable, noninvasive method for monitoring local temperature changes in tissue during thermal‐ablation therapies.

This research was support by the Bioengineering Research Fund provided by Riverside Research
MO‐D‐220‐06: Progress on an Ultrasonic Imaging System for Radiation Dosimetry
Authors: Tosh R , Chen‐Mayer H
Published: November 2011

Purpose: To assess the temperature sensitivity and spatial resolution of an ultrasonic imaging array to be used for radiation dosimetry. Methods: A circular array of ultrasonic transducers is used to image radiation heating of water in a phantom. The array is constructed of 128 PVDF sensors arranged in a circle of 177.8 mm radius that are multiplexed to analog input and output digitizers that are synchronized via high‐precision timing and triggering circuits used for measuring time‐of‐flight of ultrasonic tonebursts with central frequency of 1 MHz. The time‐of‐flight data are inverted to obtain average water temperature along the flight path between each transmitter/receiver pair, and the ensemble of such data is passed to a filtered backprojection algorithm for tomographic reconstruction of 2D temperature profiles at a refresh rate of about 10s per scan. The expected linear spatial resolution of the array is ∼ 5mm, and the system is designed to resolve temperature changes below 1 mK. Initial testing of the system has been done with thermal stimuli provided by an incandescent spotlight which is focused in the imaging plane. Results: With the ∼7 mm spotlight filament dissipating ∼60W focused in the imaging plane of the array, thermal disturbances of 2‐cm fwhm in size are recorded, measuring ∼10 mK near the peak and temperature resolution approaching sub‐mK levels. A crude validation of the temperature sensitivity has been done by incorporating a calibrated thermistor probe near the beam hot‐spot for comparison with the image data. Conclusions: Initial testing of an imaging system based on ultrasonic thermometry indicates that the instrument may be suitable for testing in ionizing radiation beams, where it would be used for imaging 2D dose distributions in real time.
MO‐D‐220‐08: Quantitative Embryonic Central Nervous System Imaging Using High‐ Frequency Annular Arrays
Authors: Ketterling JA , Aristizabal O , Mamou J , Filoux E
Published: November 2011

Purpose: The central nervous system (CNS) is the first organ to develop during mammalian embryogenesis and the CNS dynamically evolves well into the postnatal stages. Abnormal CNS phenotypes are normally visualized in vivo or with fixed samples using magnetic resonance imaging (MRI). Current MRI coil technology does not permit early‐stage in vivo imaging of the mouse embryo CNS. Here, a custom‐made, high‐frequency‐ultrasound annular‐array system operating at 38 MHz was utilized to perform in vivo imaging of early‐stage mouse embryo CNS. Methods: A custom‐made ultrasound scanning system using a piezopolymer‐based annular array was utilized for the imaging studies. The array had five equal‐area elements, a 6 mm total aperture, and a 12 mm geometric focus. The scanning system was designed to perform five scans across an object in order to acquire all transmit‐to‐receive data (25 data sets). This data was then synthetically focused to achieve enhanced depth of field and lateral resolution. In addition, the system utilized a coded‐excitation scheme to enhance SNR and penetration depth, and a respiratory gate to reduce motion artifacts. A full 3D volumetric data set could be acquired in approximately 2 minutes. Results: In vivo, in utero volumetric data were acquired from 78 mouse embryos spanning embryonic days 10 to 13. The data sets were processed with a semi‐automated image segmentation algorithm and brain volumes were calculated. The results indicated that during these mid‐gestational stages, there was an increase in CNS volume of 38% while volumetric renderings revealed the complex remodeling of the neuroarchitecture showing more cell proliferation than increase in brain mass. Conclusions: High‐frequency annular arrays with coded excitation offer an effective means of acquiring in vivo, in utero ultrasound data of the embryonic mouse and can be used to rapidly analyze the normal or abnormal development of the CNS during longitudinal studies.

This research was supported by the National Institutes of Health (EB008606).
MO‐D‐220‐09: Detection Methods of Ultrasound Transducer Artifacts: Dynamic Clips, Static Median, and Subtracted Median Images
Authors: King D , Hangiandreou N , Tradup D , Stekel S
Published: November 2011

Purpose: The detection of ultrasound artifacts due to transducer failure is important for maintaining image quality. The aim of this study is to evaluate 3 methods for detecting ultrasound artifacts, involving direct evaluation of dynamic B‐mode clips and 2 types of single frame statistical images. Methods: A range of artifacts of varying severity were artificially created for 28 transducers of varying models. The appearance of these artifacts was substantially similar to actual artifacts detected during ultrasound scanner acceptance testing and routine quality assurance. A second set of 28 matching transducers contained no artifacts. A 10 second clip was recorded of a dynamic speckle pattern from a custom liquid phantom (“dynamic clip”). A single‐frame image was obtained by computing the median values at each pixel location over all frames of the clip (“median image”). This single frame median image was then subtracted from a baseline median image previously obtained with no induced artifact (“subtracted median”). All images were evaluated by 6 observers and the mean sensitivity and specificity for the three artifact detection methods estimated. Results: In all cases the dynamic clip had the lowest sensitivity (61%) of the three detection methods. The subtracted median images had the highest sensitivity of 97% and while maintaining a high specificity of 92%. Conclusions: For routine quality control, the use of subtracted median images allows detection of artifacts with very good sensitivity and specificity. For acceptance testing, where there are no previous baseline images available for subtraction, the use of median images is useful, although comparison with median images from different transducers of the same model and/or multiple observers should be made to decrease the incidence of false‐positive findings. If statistical images are not available, direct inspection of the dynamic B‐mode clips is useful for acceptance testing and quality control, but with lower sensitivity.
MO‐F‐BRA‐02: Measurements of Neutron Dose Equivalent for Uniform Scanning Proton Beams
Authors: Zheng Y , Liu Y , Zeidan O , Schreuder A , Keole S
Published: November 2011

Purpose: Neutron exposure is of concern in proton therapy, and varies with beam delivery technique and treatment conditions. The purpose of this study is to investigate the neutron dose equivalent per therapeutic dose, H/D, under various treatment conditions for uniform scanning beams employed at our proton therapy center. Methods: Using a wide energy neutron dose equivalent detector (SWENDI‐ II, ThermoScientific, MA), we measured the neutron dose equivalent as a function of proton range, modulation width, beam scanning area, collimation aperture size and snout position. The influence of other factors on neutron dose equivalent, such as aperture material and the presence of a compensator were also evaluated. Neutron dose equivalents for various treatment sites were estimated. Comparison among different proton facilities and modalities (passive scattering, uniform scanning and pencil beam scanning) was performed. Results: The H/D values for uniform scanning beams varied from about 0.2 mSv/Gy for a 5 cm range and 2 cm SOBP width beam to 2.3 mSv/Gy for 30 cm range and 30 cm modulation width beam. H/D increased rapidly with proton range and modulation width, and decreased slowly with aperture size and snout retraction. H/D increased almost proportionally to the beam scanning area. The presence of a compensator actually reduced the H/D compared to that without a compensator present. Aperture material and compensator material also has an influence on neutron dose equivalent, but the influence is relatively small. Conclusions: This study presents H/D as a function of treatment parameters for uniform scanning proton beams. For similar treatment conditions, the H/D value was slightly lower than that from the passive scattering beam but higher than that from a spot scanning beam. Minimizing the beam scanning area could effectively reduce neutron dose equivalent for uniform scanning beams, down to the level of that generated in spot scanning.
MO‐F‐BRB‐02: Dosimetric Comparison of Acuros XB Deterministic Radiation Transport Method with Monte Carlo and Model‐Based Convolution Methods in Heterogeneous Media
Authors: Han T , Mikell J , Salehpour M , Mourtada F
Published: November 2011

Purpose: To compare the dosimetric performance of a novel deterministic radiation transport method, Acuros XB (AXB), to Monte Carlo (MC) and two standard clinical convolution Methods: the anisotropic analytical algorithm (AAA) and the collapsed‐cone convolution (CCC) Methods: A multi‐layer slab virtual phantom with three different materials (soft tissue, bone, and lung) was used for this study. 2.5, 5, and 10 cm fields for both 6 and 18MV were investigated. Depth dose and lateral dose profiles from AXB in Eclipse were compared to EGSnrc MC simulations, AAA in Eclipse, and CCC in Pinnacle3.. To quantify dose distribution differences between AXB and AAA or CCC, 3D gamma index analyses were conducted for regions defined by AAPM TG‐53. Results: The AXB calculations were found to be closer to MC than both AAA and CCC for all the investigated fields. The average differences of depth dose profiles between MC and AXB, AAA or CCC was within 1.1%, 4.4%, and 2.2%, respectively for all fields and energies. More specifically, differences in bone were up to 1.1 %, 6.4%, and 1.6%; differences in lung were up to 0.9%, 11.6%, and 4.5% for AXB, AAA and CCC respectively. AXB was also found to have better dose predictions than AAA and CCC at the tissue interfaces where back‐scatter occurs. 3D gamma index analyses (percent of voxels passing 2%/2mm) showed that the dose differences between AAA and AXB are significant (under 60% passed) in bone for 6 MV, and in lung for both energies. The differences between AXB and CCC were smaller with over 90% passing except in lung for the 18 MV 10cm field. Conclusions: For the fields studied in heterogeneous media, AXB dose prediction ability appears to be comparable to MC and superior to current clinical convolution methods.
MO‐F‐BRB‐05: Dose Calculation of KV Cone‐Beam CT by Use of Pinnacle
Authors: Kotoku J , Haga A , Saegusa S , Arai N , Kobayashi T , Waga K , Sakumi A , Itoh S , Kida S , Saotome N , Nakagawa K , Kanemitsu H , Ishioka K
Published: November 2011

Purpose: For dose calculation of kV Cone Beam CT (CBCT), Monte‐Carlo simulation method is the best for accuracy. However, Monte‐Carlo method is very time‐consuming. Therefore it is not practical to be used in daily clinical work. The CTDI has been a useful tool to estimate dose for human bodies, however, this index is not intended to calculate the dose distribution in our bodies. Clearly, we need a reasonably fast and accurate calculation method. We propose a new calculation method by use of super position algorithm in Pinnacle. We calculated low‐energy kernels in the range of 10– 100 keV and implemented them in Pinnacle3 and estimated the dose from CBCT. Methods: We used a user code of EGSnrc to make low energy kernels. To implement a cross section of low energy photons in the kernels, a cross section table on NIST XCOM was used. Then we implemented these kernels for 10–100 keV in Pinnacle3 and the modeling of the kV cone beam was performed. In order to validate the accuracy of them, we calculated a PDD and beam profiles in a water phantom and compared them to the measured values. To simulate the dose distribution in a human body, we used a RANDO phantom and measured the dose with glass dosimeters. Results: The comparison of the results shows good agreement of the calculated beam profiles and measured values. Estimated maximum dose in the body from the RANDO phantom measurement was about 2 cGy that is about 1 % of the clinical dose. The discrepancy between glass dose and calculated dose by Pinnacle is within 20–30 %. Conclusions: A fast and reasonably accurate dose calculation method by use of Pinnacle3 was proposed and validated. This is the first step toward a total treatment planning involving CBCT dose in clinical use.
MO‐F‐BRC‐05: Minimization of the Total Inter‐Segment Time for the Real‐Time Tumor Tracking with Step & Shoot IMRT
Authors: Han‐Oh S , Yang X , Lerma F , Miller R , Yi B
Published: November 2011

Purpose: We developed an algorithm to minimize total inter‐segment time (TIST) for the MLC‐based real‐time tumor tracking with step‐and‐shoot IMRT. This algorithm optimizes a starting phase of tumor motion for each segment to minimize TIST. Methods: The optimizing algorithm consists of four steps: (1) implementation of feathering motion for the closed leaves that will be opened at the next segment, (2) calculation of inter‐segment time for all segments, (3) reordering segments to minimize TIST, and (4) optimization of the starting phase of tumor motion for each segment to minimize TIST. Thirty step‐and‐shoot IMRT fields from five patients with lung and abdominal cancer were used to test the algorithm. Tumor motion was varied with a period (2.0 to 4.0 s) and a peak‐to‐peak distance (0.5 to 4.0 cm). TIST and duty cycle for each field were compared to those from the strategy of starting each segment at end‐of‐exhale. Results: The TIST was reduced by 54.0% on average (from 30.2 ± 16.9 to 13.9 ± 10.6 s) and, the effective duty cycle was increased from 32 ± 10% to 52 ± 15% for a tumor motion with 4 s and 1.0 cm peak‐to‐peak. More reduction in the TIST was observed from 45.1 to 72.1% with an increase of the period from 2 to 8 s; effect of reduction was degraded by 54.5 to 46.2% when the peak‐to‐peak increased from 0.5 to 4.0 cm. The TIST increased when a field size formed by x‐jaws increased (correlation coefficient: 0.7). Conclusions: : Total treatment time was reduced noticeably with the algorithm presented in this study so that real‐time tumor tracking can be delivered with step‐and‐shoot IMRT with an increased duty cycle.

This research was supported in part by a NIH grant 1R01CA133539‐01A2 and in part by the Intramural Research Program of the NIH, NCI.
MO‐F‐214‐05: The Impact of 6MV Non‐Reference Photon Energy Spectra on OSLD Response
Authors: Scarboro S , Followill D , Kerns J , Kry S
Published: November 2011

Purpose: Optically stimulated luminescent dosimeters (OSLD) are becoming more popular for dose measurement in a clinical setting. The OSLD response is dependent on photon energy and that energy response is typically determined only for the photon spectrum at the reference dose calibration point (dmax on CAX for a 10cm×10cm field). Previous work has shown that variations exist in photon energy spectra as a result of measurement conditions and treatment parameters; however the effects of these energy variations on OSLD response have not been characterized. Method and Materials:Theoretical energy correction factors were calculated for a range of clinical conditions, including 6MV static and modulated (IMRT) fields, in‐field and out‐of‐field measurement positions, and in the presence of heterogeneous materials. These factors were calculated using previously determined photon energy spectra and Burlin cavity theory. Measured energy correction factors using OSLD nanoDots™ from Landauer, Inc. have also been determined under matching conditions, and the measured and calculated responses were compared. Results: When OSLD are used to measure dose for in‐field locations, the dosimeter response was as much as 5% different from the reference location due to perturbations in the spectra. The presence of heterogeneities at in‐field measurement locations did not significantly impact the OSLD response; however a substantial energy response occurred for the soft spectra that exist outside of the treatment field. At these measurement locations, OSLD may over‐respond by 20% or more, relative to the response at the dose calibration location. Conclusion: OSLD exhibit a non‐trivial energy response due to the increased effective atomic number. Variations in the photon energy spectra may impact the response of OSLD by as much as 20% and additional non‐reference energy correction factors may be necessary when measuring dose away from the dose calibration position.

Work supported by PHS grant CA 10953 awarded by NCI, DHHS
MO‐F‐214‐08: A New Method for Linear Accelerator Characterization for VMAT Using Cine‐EPID
Authors: Rowshanfarzad P , Sabet M , McCowan P , McCurdy B , OˈˈConnor D , Greer PB
Published: November 2011

Purpose: A cine‐EPID based method to separately measure the mechanical motion characteristics of gantry, jaws and multi‐leaf collimator as a function of gantry angle during VMAT has been developed. Methods: Irradiations were performed using 6 MV beams of a Varian Trilogy linear accelerator with an aS1000 EPID. Images were acquired using 360 MU irradiations at 600 MU/min in cine acquisition mode at 2 Hz frame‐rate. To establish the gantry isocentre, a Winston‐Lutz technique was used with a circular collimator rigidly attached to the gantry head. The displacement of the centre of a fixed tungsten ball at isocentre from the field centre was determined on each image with a sub‐pixel thresholding technique. EPID coordinates were transformed to room coordinates. Jaw and MLC sag relative to the gantry head were determined from the displacement of a gantry‐mounted tungsten ball relative to static jaw and MLC positions. MLC speed constancy was determined by segmenting MLC positions on each image for a constant leaf‐speed test pattern. Gantry speed constancy was assessed with an independent liquid‐based inclinometer and the linac gantry angle potentiometer. Results: The gantry isocentre was ∼ 1 mm amplitude with changes in isocentre occuring over time suggesting frequent measurement is required. Jaw sag was found to be very small ∼ 0.2 mm amplitude, with MLC sag ∼ 0.6 mm. Average leaf speed was found to be consistent for the MLC leaves however the variation in speed varied systematically across the leaf bank which requires further investigation. Gantry speed was consistent although the inclinometer was found to lag ∼ 2 degrees in reading from the potentiometer. Conclusions: The cine‐EPID based method quantifies the mechanical motion characteristics of the linac as a function of gantry angle during arc‐therapy with improved precision and efficiency of quality assurance over previous methods.

This work supported by NHMRC Grant 569211
MO‐F‐214‐09: Ion Radiography: Measuring High Soft Tissue Contrast and WEPL with An Amorphous Silicon Detector
Authors: Telsemeyer J , Huber L , Jäkel O , Martišíková M
Published: November 2011

Purpose: Ion beam therapy is a highly precise form of radiotherapy, which offers the potential for higher dose to the tumor, while better sparing of healthy tissue as compared to photons. Currently, dose calculations, patient positioning verification and diagnostics are based on X‐ray radiography or computed tomography. However, there are several predicted advantages for ion radiography in comparison to X‐ray imaging. Ideally, the stopping power of the particles traversing through the patient can be measured directly, which would improve the treatment planning accuracy (Med. Phys. 32(1), 2005). Furthermore, ion radiographies may be used for on‐board patient positioning verification with very low dose to the patient (Med. Phys. 22(4), 1995) and for cancer diagnostics due to the high soft tissue contrast (Investigative Radiology 13(2), 1978). To exploit these possibilities, we are currently investigating an amorphous silicon flat‐panel detector (RID256L by Perkin Elmer, Inc. Wiesbaden, Germany) for radiographic imaging with ions. Methods: In this contribution we investigate detailed studies on soft tissue contrast and direct measurement of water‐equivalent path length (WEPL). 10 mm thick soft tissue‐equivalent rods (Gammex 467‐ Phantom), embedded in PMMA, have been irradiated with protons and carbon ions at the Heidelberger Ion‐Beam Therapy Center (HIT), Germany. Additional slabs of PMMA were placed between the phantom and the detector to measure the contrast in different depths. Results: The high tissue contrast reached in the ion radiographies enables to differentiate between all six soft tissue equivalent inserts, ranging from adipose to liver, even in high penetration depths. By comparing the measured signal with reference measurements in depth of PMMA, the water‐equivalent thickness of the inserts could be determined with an accuracy better than 0.5% of the known thickness. Conclusions: Our measurements show that the investigated flat‐panel is promising for patient diagnostic ion imaging and direct WEPL measurements.

This work is funded by the Virtual Institute “Heavy Ion Therapy” of the HGF under the contract no. 15185.
MO‐F‐110‐01: Analysis of Distribution of Procedure Time and Dose in Interventional Radiography (IR): Setting Thresholds for Case Review
Authors: Dickinson R , Kanal K , Zamora D , Stewart B
Published: November 2011

Purpose: It is traditional to review clinical cases when the time or entrance skin dose (ESD) reach or surpass certain thresholds (e.g. 60 minutes or 2Gy). We believe that the relevant threshold should be more closely tied to the clinical procedure performed. We aim to provide relevant time and dose thresholds for flagging IR procedures for quality assurance (QA) review by statistically characterizing the distribution of cases for each procedure type. Methods: Fluoroscopic time and cumulative air kerma (AK) were manually recorded for all IR procedures. We generated a report that separated data by procedure type, and estimated the ESD. For each procedure type, outliers were removed and we calculated the mean (x) and standard deviation (SD) for time and ESD distributions. We set the flagging threshold for time and ESD as x+2SD for each procedure. Results: For Neuro (NIR) and Vascular (VIR) whereby cases are interventional or therapeutic (e.g. TIPS, embolization), the distribution yielded an average dose at or greater than 2Gy. Over a three month period, the percent of total procedures flagged using 2Gy and x+2SD thresholds were 24.1% and 7.1% for NIR and 17.2% and 6.9% for VIR, respectively. Conversely, for lower‐dose procedures (e.g. PICC/port/drain placements, GI, GU), the average dose is less than 2Gy, and the flagged cases were 2.8% and 7.1% for the respective thresholds. Conclusions: In addition to thresholds based on radiation injury, thresholds based on population statistics for given procedures should be used for QA review. Doing so provides a relevant threshold for identifying cases that deliver higher dose with respect to other identical procedure types. For high‐dose procedures where the mean ESD is often over 2Gy, the number of review cases will be limited. For lower‐dose procedures where the mean ESD is less than 2Gy, case review includes atypically high dose administration.
MO‐F‐110‐04: Experimental Validation of a Novel Approach to Fast and Accurate Kilovoltage Dose Computation
Authors: Poirier Y , Tambasco M , Kouznetsov A
Published: November 2011

Purpose:To validate a novel hybrid method for the calculation of kilovoltage (kV) x‐ray dose. Methods: We performed experimental validation of a novel hybrid approach for calculating dose deposited by imaging beams (<150 kVp). The approach involves computing the primary photon component deterministically and scattered component stochastically, accounting for the real micro cross sections of the materials involved. Depth dose and profile measurements for the Varian® On‐Board Imaging® unit in the radiographic mode using a 125 kVp x‐ray beam (4.6 mm Al half‐value layer) were performed. The measurements were made using a Farmer‐type Capintec ion chamber (0.06cc) in homogeneous and heterogeneous phantoms. A phantom consisting of Certified Therapy‐Grade Solid Water® (Gammex 457) was used to measure the dose under homogeneous conditions. The heterogeneous phantom was constructed using lung‐ equivalent material (Gammex 455) and bone‐equivalent material (Gammex 450). Results: Measurements in the homogeneous phantom agreed with theoretical calculations within 2% for depth doses and within 2% of the central axis dose for profiles. Local agreement in highly attenuated regions such as depths >10 cm or outside the beam edge were about 10%. However, the dose differences in these regions were less than 2% of the maximum dose. Conclusions: This work provides experimental validation of our hybrid calculation method. The next step will be to test the algorithm using more complex phantoms, such as the anthropomorphic Rando® phantom, which mimics patient geometry as well as inhomogeneities. This is a crucial step in the validation of an independent tool to calculate patient dose from kV beams such as cone‐beam CT and brings us closer to our goal of calculating patient‐specific dose from imaging procedures.
MO‐F‐110‐08: Yields and Dosimetry Estimates for Radioisotopes Produced in Proton‐Induced Reactions on Enriched Molybdenum Targets
Authors: Hou X , Grimes J , Benard F , Ruth TJ , Celler A
Published: November 2011

Purpose: To investigate radiation dosimetry for 99mTc produced by medical cyclotrons, based on theoretical reaction cross‐sections and yields. Several other technetium isotopes produced in a cyclotron are chemically inseparable from 99mTc. This could increase patient absorbed dose. We compared the resulting doses to those from 99mTc produced by conventional 99Mo/99mTc generators. Methods: We simulated natural and enriched molybdenum thick targets irradiated by 10–30MeV protons. All reaction channels leading to any given reaction product were considered in final yields. The cross‐section calculations were performed using the EMPIRE code. A computer graphical user interface for automatic calculation of isotope yields and activities was created. The pertechnetate, phosphonate as well as MIBI radiation absorbed doses were calculated by OLINDA/EXM 1.1 using the adult male reference. Generator produced 99mTc was assumed to have 100% radionuclide purity. Results: The thick target yields for 99mTc, 99gTc and other isotopes were determined for 16‐ 10MeV, 19‐10MeV and 24‐10MeV energy protons. The difference of radiation doses between pure‐Tc (reactor produced) and mixture‐Tc (cyclotron produced) in main organs were estimated. In highly enriched targets (99.5% 100Mo), the mixture‐Tc doses are about 0.5% larger than the pure‐Tc doses. These differences decreased in the first few hours from the end of beam (EOB) and then increased to 1 % after 24 hours from EOB. In targets with lower enrichment (97.4% 100Mo), the 0–8 hours after EOB doses from the mixture‐Tc isotopes exceeded the pure‐99mTc dose by ∼1% or less. For radiopharmaceuticals injected in patients 24 hours after EOB, this difference increased to 2–5%. Conclusion: Other radioisotopes, which will be produced in the cyclotron together with 99mTc must be considered for their potential to increase patient dose exposure. The differences between the radiation absorbed doses from technetium produced by cyclotrons and nuclear reactors are minimal at EOB, and increase slightly after 24 hours.
MO‐F‐110‐09: Development of Computational Lymph Node Models for Pediatric Hybrid Phantoms for Nuclear Medicine Dosimetry
Authors: Lee C , Bolch W
Published: November 2011

Purpose: To develop computational lymph node models implemented within a series of pediatric hybrid phantoms which can be utilized for nuclear medicine dosimetry Methods: The algorithm for generating lymphatic nodes within adult hybrid phantom which we previously reported was improved to use for International Commission on Radiological Protection (ICRP)‐compliant pediatric hybrid phantoms which include newborn, 1‐ year, 5‐year, 10‐year, and 15‐year male and female phantoms. First, a total of 16 lymphatic node anatomical sites were defined within the pediatric hybrid phantoms: extrathoracic, cervical, thoracic (upper and lower), breast (left and right), mesentery (left and right), axillary (left and right), cubital (left and right), inguinal (left and right), and popliteal (left and right) nodal regions. Second, individual lymphatic node positions are randomly sampled in spherical tissue volume centered at each of the previously selected lymphatic node regions. Third, tissue spheres representing individual lymphatic nodes are then created to populate each nodal region of the phantom, with the normal standard nodal diameter until a total lymphatic node mass is achieved to match age‐dependent total reference masses derived from ICRP Publication 66 and 89 reference data. The lymphatic nodes were generated within a total of 10 pediatric hybrid phantoms and coupled with a Monte Carlo code, MCNPX2.6 to estimate radionuclide S values for I‐131 distributed within different lymphatic node sites. Results: Lymphatic node models of which masses were matched to ICRP reference values were implemented into the pediatric hybrid phantom series. An illustrative set of radionuclide S values for I‐131 were calculated where regional lymphatic nodes are considered to be independent source and target regions of patient. Conclusion: The new lymphatic node model suggested in this study can be utilized to obtain anatomically realistic dosimetry in lymphoma patients treated by radionuclide therapy.