bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐D‐137‐01: ABR Update
Authors: Allison J , Ibbott G , Frey G
Published: July 2013

This session will present a review of the ABR requirements and policies for the initial certification of medical physicists. Changes in the program that have occurred in the last several years will be discussed. The requirements for certification for 2014 and beyond will be reviewed. Changes in the oral exam and the board eligibility policy will be presented he MOC program will also be reviewed. The changes that occurred in 2013 will be emphasized. These include the change to continuous MOC, easy public access to certification status and the new ABR My ABR website. There will be adequate time for questions and group discussion.

Learning Objectives:

1. The participant will understand the role of the ABR in the certification of medical physicists.

2. The participant will understand the ABR requirements for Medical Physics Certification.

3. he participant will understand the requirements for participation the ABR's Maintenance of Certification process.
MO‐D‐108‐03: Energy Spectrum Inference of Clinical Photon Beam by Use of PDD
Authors: Kotoku J , Haga A , Kumagai S , Saotome N , Kobayashi T
Published: July 2013

Purpose: To propose a scheme which infers an energy spectrum of X‐ray from a Linac by use of percent depth dose with an ion chamber. Methods: In this study, we assumed a linear model which relates the spectrum of clinical photon beam and percentage depth dose of the beam.The response matrix (design matrix) was calculated via our Monte Carlo simulation (EGS5). Then we estimated the photon spectrum as a solution of maximum a posteriori (MAP) estimation. The percent depth dose of 4MV X‐ray was measured with an ion chamber and 3D water phantom in Teikyo University Hospital. Results: Both estimated spectrum and modeled spectrum in the commercial treatment planning system are in good agreements. It is evident that our inference method is very effective and powerful to estimate the X‐ray energy spectrum. Although this is an only case to infer the energy spectrum of clinical photon beam, The success indicates an effectiveness of our method. Conclusion: A Bayesian method to infer an energy spectrum of clinical photon beam by use of a percentage depth dose was proposed and validated.
MO‐D‐108‐04: Validation of a Simple Portal Dose Calculation Model for Plan QA and In‐Vivo Dosimetry
Authors: Lu W , Chen M , Mo X , Parnell D , Olivera G , Galmarini D
Published: July 2013

Purpose: To validate a simple portal dose calculator for plan QA and in‐vivo dosimetry. Methods: We model portal dose as a function of the fluence map, patient attenuation, patient scatter and portal response. Fluence maps are reconstructed using control‐point sequence in RTPlan. Patient attenuation is calculated via ray‐tracing through the patient CT. The effect of patient scatter and portal response is modeled by convolution, where the convolution kernel is derived from the commissioning measurements of different beam energies, different field sizes, different phantom thickness, and different source to image distances (SIDs). For various IMRT/3D plan, phantom and patient geometry, both in‐air and in‐transit portals were calculated. The calculations were compared with portal measurements. The Gamma Index of measurements against predicted portals with various dose difference (DD) criteria (1%, 2%, 3%, 4%, 5%, etc) and distance to agreement (DTA) criteria (1 mm, 2 mm, 3 mm, 4 mm, 5 mm, etc) were calculated. The Gamma pass rates of various DD and DTA criteria were evaluated and formed a Gamma table. Results: For various IMRT beams, the head, body and lung phantoms, the in‐air and in‐transit portal calculations matched well with portal measurements. The Gamma pass rates for in‐air portal are above 97% for 2 mm, 2% criteria and above 99% for 3 mm, 3% criteria. The Gamma pass rates for in‐transit portal were above 90% for 2 mm, 2% criteria and above 95% for 3 mm, 3% criteria. Conclusion: The simple portal dose calculation model is validated via phantom measurements. The model could be used in clinic for in‐air and intransit portal prediction.
MO‐D‐108‐05: Development of An Accurate Monte Carlo Model of the Standard Clinac 6MV Beam
Authors: Egan A , Laub W
Published: July 2013

Purpose: Monte Carlo (MC) models of radiotherapy beams can be used as a comparison benchmark for other dose calculation methods. In any such comparison process, the degree to which an identified deviation represents an actual error will depend upon the accuracy of the benchmark. As part of an ongoing dosimetric study, we have sought to model the standard Varian Clinac 6MV beam as accurately as possible with the BEAMnrc MC code. Methods: In order to insure the reproducibility of our results, the accelerator head geometry was modeled exactly as specified by the manufacturer, with only the electron source parameters and jaw positions varied. Similarly, the widely available Eclipse ' tGolden Beam' t data was used for open field comparisons with a target matching criteria of 1% of local dose or 1 mm distance‐to‐agreement for all depths >= Dmax and field sizes ranging from 3×3 to 40×40 cm2. Except for target bremsstrahlung settings, all other transport parameters were left at their default values. Simulations were run for varied monoenergetic electron energy [5.6:0.05:6.2]MeV, Gaussian intensity distribution FWHM [0.0:0.05:0.25]cm, and beam divergence [0.0:0.2:1.2]°. Results: As has been previously established in the literature, matching was found to be strongly dependent on electron beam energy, intensity FWHM, and choice of bremsstrahlung settings. However, as matching approached the target criteria, results became increasingly sensitive to beam divergence as well. It was also found that when using the default bremsstrahlung settings, accuracy better than ∼2% was unobtainable. Under the specified parameter resolution, matching of all points within 1.4%/1.0mm was achieved when using the NRC bremsstrahlung cross section, the higher termed Koch and Motz bremsstrahlung angular sampling, and electron beam parameters of 5.9MeV, 0.1cm, and 0.8°. Conclusion: Under the listed constraints, significant improvements (e.g. matching ∼ 1%/1mm) in Golden Beam modeling are not likely achievable.
MO‐D‐WAB‐01: How OMICs Is Going to Impact Research Topics for Medical Physicists
Authors: Deasy JO , Gevaert O , Aerts H
Published: July 2013

The ongoing revolution in genomics provides many new research opportunities for physicists. Two crucial research areas to advance clinical oncology include the intersections between imaging and genomics, as well as the use of genomic analyses to improve patient management in radiation oncology. Confusingly, the term ‘radiogenomics’ is used for both applications. In the field of radiology, ‘radiogenomics’ refers to the underlying genomic correlates of image features, for example the correlation of tumor biopsies mRNA microarray signatures with image features. In radiation oncology and radiobiology, the term ‘radiogenomics’ refers to the impact of a patient's genotype on the relative radiosensitivity or radioresistance of normal tissues. Tumor biopsy mRNA signatures, for radiosensitivity, hypoxia, or proliferation, have been studied to predict response and to potentially individualize treatments. Blood proteomics has been applied to normal tissue responses such as radiation pneumonitis. Imaging radiogenomics can further be thought of as ‘radiomics’ + genomics, where radiomics is the extraction of quantitative image features that can be incorporated into disease classification schemes or predictive models. We will also touch on the general application of systems modeling that is so important to advancement in modern biology and response modeling. This session will emphasis new opportunities, as well as challenges and obstacles to progress. ‘Omic’ sciences will greatly impact the study and clinical use of tumor control probability and normal tissue complication probability models; the biological interpretation of image features; and the clinical implications of imaging and cancer screening.
MO‐D‐141‐01: Quantification of Tumor Hypoxia Using [18F]‐Fluoromisonidazole Positron Emission Tomography and Tracer Kinetic Modeling
Authors: Kelada O , Rockwell S , Carson RE , Decker RH , Oelfke U , Carlson DJ
Published: July 2013

Purpose: Tumor hypoxia is correlated with treatment failure in radiotherapy. The hypoxic fraction of a tumor can be difficult to define using non‐invasive imaging methods such as Positron Emission Tomography (PET). The purpose of this study is to use tracer kinetic modeling techniques to increase the accuracy and precision of hypoxic volume (HV) quantification with 18F‐fluoromisonidazole (18F‐FMISO) PET imaging. Methods: Ten male BALB/c mice with EMT‐6 tumors were selected for imaging. Anaesthetized animals were injected with 18F‐FMISO and imaged using whole‐body 120‐min dynamic PET and Computed Tomography (CT). Data from dynamic 18F‐FMISO scans for 3 mice were fit to a 2‐compartment irreversible 3‐rate constant model (K1, k2, k3) and a PATLAK model (Ki). Different thresholds were applied to the resultant Ki and k3 rate constants generated on a voxel‐by‐voxel basis to calculate the HV for each tumor. These kinetic‐derived HVs were compared to HVs generated using conventional tumor‐to‐blood (TBR) ratios. Results: Kinetically‐derived HV (using the k3 tracer binding constant and the rate of tracer influx, Ki), calculated on a voxel‐by‐voxel basis, showed an increase in HV of up to 38% over the TBR method depending on the assumed threshold. Moreover, the PATLAK kinetic model using a Ki threshold may provide better delineation and calculation of the tumor HV than a 2‐compartment pharmacokinetic model. Conclusion: For PET imaging with 18F‐FMISO, pharmacokinetic modeling can improve the accuracy and precision of tumor hypoxia quantification over that obtained with tumor‐to‐blood ratios. In particular, the PATLAK method to define a tumor HV may be superior due to a reduction in noise and to better HV localization. Ongoing studies will correlate tumor HVs with Eppendorf electrode measurements and carbonic anhydrase IX staining of histologic sections. These studies could lead to improved techniques for identifying patients likely to benefit from therapies designed to overcome hypoxic radioresistance.
MO‐D‐134‐06: A Preliminary Method Correlating Patient‐Specific Parameters with Direct Measurements to Estimate Organ Doses in CT
Authors: Sinclair L , Mench A , Griglock T , Cormack B , Bidari S , Arreola M
Published: July 2013

Purpose: In the field of Computed Tomography (CT) dosimetry, there remains a need to accurately measure organ doses. Such measurements are only meaningful if they are performed under actual clinical scanning conditions, for this purpose, a cadaver can serve as the measurement subject that most closely mimics a living patient. Organ doses were measured in 7 adult female cadaveric subjects with varying body mass indices (BMIs) and for various CT protocols. Methods: A tube placement system allowed external access to internal organs, in which optically‐stimulated luminescent dosimeters (OSLDs) were placed and used to measure dose. Dosimeter placement and location was based on organ size and distribution. In order to determine organ doses of real patients, a correlation between various patient size parameters and the measured organ doses was explored. Only measurements that could be performed on a CT image or subject‐specific parameters or data which could otherwise be obtained for an actual patient were considered for this correlation. The size parameters that were examined included: body mass index (BMI), the AP and lateral dimensions of the patient, and patient perimeter. Results: The BMIs for the 7 subjects ranged from 16.6–43.9, spanning from underweight to extreme obesity. Overall average organ doses from a CAP exam for all subjects ranged from 11.8–24.4 mGy. Generally, organ doses were shown to increase with all size parameters examined. Conclusion: For the purpose of accuracy, the estimation of patient dose in CT must be based on actual physical measurements. A complete set of direct organ dose measurements for 7 adult female cadavers has been accomplished for common CT exams with this research. It has been shown before that patient size parameters can be indicative of patient dose. This work has shown further validation of this concept.
MO‐D‐134‐07: Impact of Patient Anatomy On Patient‐Specific CT Dose: Initial Clinical Study
Authors: Liang Q , DeWerd L
Published: July 2013

Purpose: AAPM report TG‐204 suggests using size‐specific dose estimates (SSDE) as a patient CT dose reporting method. SSDEs are calculated by applying a correction factor, which is based on the patient outline size, to CTDIvol. The suggested correction factors were determined with phantom measurements or Monte Carlo simulations from four independent research groups, which utilized uniform or mostly solid phantoms. However, in some clinical CT examinations such as CT colonoscopy, considerable portions of the scanned anatomy are gas, which is quite different from the condition under which TG‐204 was established, and SSDEs may not be sufficient in these cases. The purpose of this work is to demonstrate this limitation with Monte Carlo dose calculations using patient CT images. Methods: CT images from two patient scans were used to perform Monte Carlo simulations: a normal abdomen/pelvis scan and a CT colono scopy. The patient sizes were similar according to outline dimension measurements. For Monte Carlo dose calculations, the same scanning parameters were simulated to ensure identical CTDIvol in the two cases. Bony anatomy was identified by thresholding and the mean dose to bony structures was calculated by averaging the three‐dimensional dose distribution. Left and right kidneys were contoured for organ dose calculations. Effective diameters were measured, and the correction factors were obtained from TG‐204. Results: The size‐specific conversion factors were 1.37 for both patients, thus the SSDEs of the two cases were the same in this study. The MC‐calculated mean doses from the normal abdomen/pelvis scan were higher than those from the CT colonoscopy by 7.5%, 6.5% and 12.8% for bony anatomy, left kidney and right kidney, respectively. Conclusion: The impact of patient anatomy on CT dose was demonstrated using patients of the same size. This effect should be considered for special clinical cases.
MO‐D‐134‐08: Validation of Size‐Specific Dose Estimates (SSDE) in Body CT Studies with Directly Measured Organ Doses in Adult Female Cadaveric Subjects
Authors: Sinclair L , Mench A , Griglock T , Bidari S , Cormack B , Arreola M
Published: July 2013

Purpose: To compare directly measured organ doses in cadaveric subjects with calculated size‐specific dose estimates (SSDE) for CT studies of the torso. Methods: : In 2011, the SSDE protocols were introduced by AAPM Task Group 204, which provides a library of conversion factors that can be applied directly to scanner‐generated CTDIvol for a CT exam of the torso to generate a patient‐specific dose estimate. However, the results of the SSDE formalism have not been compared to actual dose measurements. In this work, several cadaveric subjects of varying body habitus, were utilized to directly measure organ doses which Result from CT examinations. Optically‐stimulated luminescent dosimeters (OSLDs) were employed to measure dose within the following organs: thyroid, breasts, lungs, liver, stomach, small intestine, colon, ovary, uterus, and skin. Dose measurements were made for a standard Chest Abdomen Pelvis (CAP) protocol. After organ dose measurements were completed for each subject, the anterior‐posterior and lateral patient dimensions were measured on the central slice of the study to obtain the corresponding correction factor and SSDE from AAPM 204, which was then compared with the measured organ doses for each cadaver. Results: A total of four subjects were utilized for this study, with body mass indices (BMIs) ranging from 17.4–43.9. For the subject with a BMI of 17.4, the average organ dose from a CAP exam was 11.8 mGy. The corresponding SSDE for that subject was 12 mGy. Conclusion: It is observed with this data that the SSDE does accurately describe the average dose absorbed in the body. The SSDE can be effectively used as a patient dose descriptor in the clinic, while organ dose libraries and software that allow for organ dose calculation are still being developed.
MO‐F‐WAB‐01: A Comparison of 20 Free Breathing Versus AlignRT Based DIBH Breast Treatments
Authors: Sintay B , Yount C , Hawkins M , Wentworth S , Terrell J , Maurer J , Pursley J , Wiant D
Published: July 2013

Purpose: Deep inspiration breath hold (DIBH) for treatment of left breast cancer is a technique that is rapidly gaining acceptance due to the possibility of reducing heart dose, particularly dose to the left anterior descending coronary artery. We report on the treatment of twenty patients using AlignRT (VisionRT, London, UK) to monitor breath hold. Methods: Patients were simulated with a breath hold and free breathing CT scan. A treatment plan was created on each scan in the XiO treatment planning system (Elekta AB, Stockholm, Sweden). Plans consisted of two parent tangent fields and 1–2 reduced fields per side. The maximum point dose and volume receiving 30 Gy (V30) to the heart from each plan is compared. Patients were set‐up using an AlignRT reference surface generated from the breath hold scan with a 3 mm / 3 degree tolerance. Patient position was evaluated by comparing boney landmarks, breast tissue, and heart position on port images prior to the first treatment, then once per week. We examine the number of port images retaken as compared to free breathing set‐ups. Results: For DIBH plans the maximum heart dose was reduced by an average of 39% and the V30 was reduced by an average of 78%. For 16 patients that had completed treatment at this time the number of retaken port images was 9.6%, which is in line with 8.5% of retaken port images previously reported for our free breathing patients. Conclusion: Patients were generally able to complete each of the 4–6 fields in one breath hold per field. The number of port images was comparable to free breathing treatments. Treatment of left sided breast patients using DIBH is an effective way to reduce heart dose without impactful change in treatment time.
MO‐F‐WAB‐04: Does a Threshold of Tumor Motion Exist to Indicate Respiratory Gating for Proton Therapy?
Authors: Matney J , Bluett J , Li H , Court L , Liao Z , Mohan R
Published: July 2013

Purpose: To determine if a population‐based threshold of motion exists to indicate respiratory gating in proton therapy by correlating the dosimetric benefit of gating to the magnitude of tumor motion. Methods: This research estimates the benefit of respiratory gated passively scattered proton therapy for a cohort of stage III lung patients with range of tumor motion from 3 to 17 mm. Respiratory motion was defined as the tumor centroid excursion between inhale and exhale 4DCT phases. To simulate respiratory gating during free‐breathing exhale position, the exhale phase of the planning 4DCT was used for re‐planning efforts. For the respiratory gated plan, the original beam angles from non‐gated plans are maintained while new contours, beam properties, lateral blocks and compensators are redesigned. Both plans are normalized to the same target coverage. The changes in dose‐volume histogram (DVH) indices between the gated and non‐gated plans are compared against the extent of respiratory motion. Results: Gated plans for 19 patients have been completed to date. The only DVH index that correlated (Spearman rank correlation p<0.05) to respiratory motion was the mean lung dose. However, a regression line fit to this data yielded low R‐squared value of 0.19. No correlations between motion and dose reduction were found for other DVH indices in the lung, esophagus, heart or spinal cord. In addition, respiratory gating significantly reduced normal tissue dose for most of the patients. Conclusions: There is no threshold of tumor motion to predict the potential benefits of gated proton radiotherapy. Proton respiratory gating reduces normal tissue dose; however the benefit of gating is not correlated to the magnitude of tumor motion. The benefit may be due to the reduction in anatomy motion as a whole, not just the tumor motion. Other metrics should be explored to determine the need of proton respiratory gating. This project is supported by grant P01CA021239 from the National Cancer Institute.
MO‐F‐WAB‐07: A Novel 4D CT Acquisition and Analysis Technique to Account for the Effect of Cardiac Induced Lung Tissue Motion During Free Breathing
Authors: Thomas D , White B , Gaudio S , Jani S , Lee P , Lamb J , Low D
Published: July 2013

Purpose: To develop a new motion modeling technique to account for internal lung tissue displacement due to cardiac motion during free breathing CT scans. Methods: Five patients were imaged 25 successive times under free breathing conditions in alternating directions with a 64‐slice CT scanner using a low dose fast helical protocol. A pneumatic bellows around the abdomen was used to as a breathing surrogate and a 3‐lead ECG monitor simultaneously measured heart rate. The lungs were segmented from each image and deformable registration was used to register the first image to the subsequent 24 segmented images. The registered voxel locations were fitted to a linear motion model, relating the internal lung tissue deformation to the tidal volume v, airflow f and cardiac phase h. The time dependence of cardiac induced tissue displacement was characterized by a periodic function synchronized to the cardiac cycle, optimized to reduce model error, and was patient specific. The magnitude of cardiac induced motion was evaluated by comparing the discrepancies between fitted and measured motion with and without the cardiac term applied. Results: The magnitude of cardiac induced lung tissue displacement was determined to be up to 2.5mm in the lung for regions close to the myocardium. The addition of the cardiac term reduced the total number of voxels with mean errors above 1mm by 33%. Conclusion: Application of the cardiac term in the motion model reduces large errors in motion modeling in regions close to the myocardium. This work supported in part by NIH R01CA096679
MO‐F‐141‐01: X‐Ray Tubes for Medical Imaging
Authors: Behling R
Published: July 2013

Why do we find 500+ types of X‐ray tubes on the market? Why still vacuum technology to generate Bremsstrahlung, ca. 120 years after Conrad Roentgen's discovery? How do X‐ray tubes function and look like? What's next? (When?) Will we see the X‐ray LED' s, compact X‐ray Lasers or flat panel sources in medical imaging? These and more questions will be answered in this lecture. We will shortly dive into physics of X‐ray generation, study key characteristics, material boundary conditions, manufacturing technology. We will identify the quality parameters, which allow us to compare and select the proper source.In more detail we will understand design concepts of glass and metal frame, single ended and dual polar tubes, stationary anode tubes with reflection and transmission targets. We will devote a larger portion to rotating anode tubes, their bearings, anode discs, motors, cooling, heat balance. We will talk about electron emitters and beam focusing, focal spot characteristics, MTF, off‐focal radiation, focal spot deflection, stability. Side effects need to be mentioned like leakage and scattered radiation. Tube life will be discussed, ageing effects, failure pareto distributions, end‐of‐life indicators and overall cost drivers.

Employee of Philips Healthcare
MO‐F‐103‐01: Estimating Risk of Low Radiation Doses
Authors: Hendee W , O' Connor M , Calabrese E
Published: July 2013

Several articles in the medical literature over the past few years have predicted thousands of cancers and cancer deaths annually in the US population caused by radiation exposures from medical imaging. The predictions are derived from risk estimates in the National Academy of Sciences BEIR VII report. These risk estimates are highly speculative with wide confidence intervals, and the BEIR VII committee has warned against using them to estimate cancer risks to individuals or populations. They are based on risk models derived from the linear no‐threshold hypothesis of radiation risk at low doses. This hypothesis is derived from studies in the 1920s and 30s of genetic mutations in x‐irradiated Drosophila and has a history of controversy and conflict. It has been challenged by experiments at the cellular and animal levels as well as by data of cancer incidence in medically‐, occupationally‐, and environmentally‐exposed individuals. The main source of data for the BEIR VII risk estimates are the survivors of the Japanese A‐bomb explosions, a population greatly different from the US population that was exposed to radiation conditions greatly different from those of medical imaging. Even so, data from the Japanese studies frequently reveal a threshold dose for increased cancers in the irradiated populations. Collectively, the uncertainties in the derivation of the BEIR VII risk estimates, and the intrinsic speculative nature of the risk estimates themselves, cause predictions of cancers and cancer deaths to be more hypothetical than real in populations exposed to medical imaging. Several scientific organizations, including the Health Physics Society, American Association of Physicists in Medicine, the International Organization of Medical Physicists, the United Nations Scientific Committee on the Effects of Atomic Radiation, and the International Commission on Radiological Protection, have warned against making such predictions because of their speculative nature. Unfortunately, these hypothetical predictions of cancer risks are themselves a health risk, because they create anxiety in patients resulting in a reluctance to undergo medical imaging procedures prescribed for their benefit.

Learning Objective:

1. Understand the origin of cancer risk estimates in BEIR VII

2. Appreciate the limitations in applying Japanese health data to American patients

3. Be familiar with the history and limitations of the LNT model of radiation injury
MO‐F‐134‐04: Access for Minorities to Physics Education & Research Excellence (AMPERE)
Authors: Ngwa W
Published: July 2013

Purpose: The low performance and number of minorities in physics is now well documented. On interviewing minority students to find out if they could identify any obstacles, the African American Students shared that an invisible obstacle was the choice they had to often make either to go to school and lose their friends or keep them and not go to school. This presentation highlights the approach I have since employed to enhance performance/training of minorities in Physics, and how I am applying the lessons learned in enhancing Medical Physics learning at my current institution. Methods: The Access/Alliance for Minorities to Physics Education & Research Excellence (AMPERE) program was created to provide a Physics community/network for the Minority students for peer interaction where they served as friends to each other and challenged and encouraged each other to perform well in physics. I served as faculty mentor with an extra weekly tutoring session. Their performance levels before and after instituting the AMPERE program was compared. Later I applied the community model in the teaching of Radiation Therapy Physics, by creating a discussion forum online on Blackboard Learn. A survey was then conducted to compare satisfaction levels against students who took the course the previous semester without the Blackboard community. Results: A major increase in performance over 30% was observed for the AMPERE students. Initial results also provide anecdotal evidence that Medical Physics students had a better learning experience when participating on the online version of AMPERE Conclusion: Creating a community for peer interaction as with the AMPERE program or online could enhance Medical Physics learning. The results motivate a cross‐institutional study (larger population) as well as possible extension of this to the IAEA VUCCNET online program for training Medical Physicists in developing countries.
MO‐F‐116‐01: Statistics, Error Analysis, and Uncertainty Reporting in Medical Physics
Authors: Guo F , Ruan D , Cui J
Published: July 2013

Medical physics is a branch of physics so the rules with error analysis and uncertainty reporting of measurements, should be same and observed. In reality, these rules are not obeyed very well as an observation of the clinical practice shows. Partial of the causes is that physicists are from different backgrounds which have different degrees of following the requirements on applying these rules. Another reason is that clinical physicists are part of a treatment team in which other members don' t necessarily have same strict requirements as physicist should have. To communicate with other treatment members, physicists trend to use layman terms to express the physics terms which should be in a strict format. This lecture is to refresh clinical physicist's knowledge on these issues. Basic knowledge of statistics, error analysis, and uncertainty reporting will be review with examples from clinical setups, such as AAPM TG‐51 calibration, TG‐119, in‐vivo dose measurements, and treatment planning calculations. For example, how many readings should you take when a TG‐51 calibration is performed? What is the associated uncertainty with each Result? How many effective numbers should you keep there? Should it be whatever numbers since the excel spreadsheet can easily give you whatever digitals? Those sound trivia but if you take a look at your colleague's or friend's reports, they are worth of further scrutinizing. After this lecture, hopefully practicing physicists have clearer ideas about statistics, error analysis, and uncertainty reporting in their daily clinic work.

Learning Objectives:

1. To refresh clinical physicist's knowledge about statistics, error analysis, and uncertainty reporting in medical physics.

2. Clearer ideas to apply these rules in their daily clinic work.

3. Improve the clinical practice.
MO‐F‐144‐01: Ultrasound Guided Systems for RT and Treatment Planning
Authors: Hsu I , Hristov D , Salter B , Fontanarosa D
Published: July 2013

The history of radiation therapy treatment planning and delivery has been one of constant improvement in the accuracy and precision of target identification, target localization, and dose delivery. The demands on delivery have now crossed a threshold where radiation therapy is inherently dependent on image guidance as a standard of care. While much image guidance in RT is acquired with ionizing radiation modalities such as CT and fluoroscopy, ultrasound has always played a role in specialized situations. However, improving technologies for ultrasound transducers, spatial transducer localization, post‐acquisition image analysis, and automated control of acquisition parameters are creating new opportunities for ultrasound across the breadth of radiation oncology. This education session will highlight several new developments in the use of ultrasound imaging for radiation therapy treatment planning and delivery. Topics will include:* Real‐time telerobotic 3D ultrasound for soft‐tissue guidance concurrent with beam delivery* US for prostate positioning ‐ Trans‐perineal approach combined with real‐time monitoring* Challenges and opportunities of trans‐rectal ultrasound (TRUS)‐based prostate HDR brachytherapy* Speed of sound aberration evaluation and correction in ultrasound‐guided radiation therapy applications This session is intended to provide a window into how ultrasound can be used to meet the demand for a non‐ionizing, non‐invasive, real‐time image guidance solution. Attendees to the session should expect to meet the following:

Learning Objectives:

1. Understand the advantages and disadvantages of trans‐rectal and trans‐perineal approaches for ultrasound imaging during prostate HDR

2. Understand the current limitations of ultrasound for quantitatively imaging heterogeneous tissue as well as methods for detecting and correcting aberrations in soft tissue.

3. Learn how spatial tracking of ultrasound transducers and standardization of ultrasound acquisition techniques through the use of robotics can make ultrasound a viable solution for anatomical motion during radiation therapy procedures.

David Schlesinger has a research grant from Elekta, AB unrelated to the topic of this session.
MO‐F‐144‐02: Real‐Time 4D Ultrasound Prostate Gland Motion Tracking During Radiotherapy Fraction Delivery
Authors: Sandhu R , Marina O , Wloch J , Martin S , Krauss D , Yan D , Ionascu D
Published: July 2013

Purpose: The intra‐fraction variability of target position during the prostate cancer radiotherapy may cause dose discrepancy between planned and delivered dose, especially with longer hypo‐fractionated treatments. We report our clinical experience with real‐time 4D ultrasound imaging (4D‐US) to monitor intrafraction prostate motion. Methods: Three prostate patients were treated on an IRB‐approved protocol delivering 51 Gy in 10 fractions using single arc volumetric modulated arc therapy (VMAT). Each patient had three gold markers implanted and had simultaneous CT and 4D‐US simulation, followed by an MRI scan. Target and normal organs were delineated on MR images. During setup simultaneous cone‐beam CT (CBCT) and continuous 4D‐US were acquired, and during VMAT delivery (about 2 min) 4D‐US was acquired. The prostate 4D‐US position was compared to the CBCT average position, and movement during treatment was characterized. Results: The median (range) of mean intra‐fraction prostatic motion in the right‐left(RL), anterior‐posterior(AP) and superior‐inferior(SI) directions were 0.1 mm (−1.6 to 0.8 mm), 0 mm (−1.8 to 1.3 mm), and −0.1 mm (−2.2 to 1.4 mm), with respective median (range) of standard deviation were 0.2 mm (0 to 0.8 mm), 0.2 mm (0 to 1.2 mm), and 0.2 mm (0 to 0.7mm). There were 9/27 fractions with shifts >=2 mm in any direction, with an average duration of 23% of treatment time, with a single fraction having a shift greater than 3mm. The discrepancy between 4D‐US and CBCT shifts were 0.6±1.6 mm, −0.2±1.4 mm and −0.4±0.7 mm in the RL, AP and SI directions. There was one instance of flatulence during treatment setup where vertical shifts >=3 mm (up to 6.1 mm) persisted for 108 sec. Conclusion: Real‐time imaging is essential for tracking hypo‐fractionated prostate motion to reduce dosimetric uncertainty. 4D ultrasound imaging during treatment improves accuracy of dose delivery, and may allow a reduction of treatment margins.
MO‐F‐144‐03: Real‐Time Guidance and Planning in Breast High Dose Rate Brachytherapy Using 3D Ultrasound
Authors: Poulin E , Gardi L , Fenster A , Pouliot J , Beaulieu L
Published: July 2013

Purpose: In breast interstitial high dose rate (HDR) brachytherapy, the number and positions of the catheters are usually chosen manually using a preimplant CT scan. In this work, we present an innovative approach for real‐time 3D ultrasound (3DUS) planning in breast HDR brachytherapy. Methods: The end‐to‐end procedure was realized with a computer controlled robotic 3DUS system for breast brachytherapy so that both planning and guidance are possible. The scanner is mounted on the Kuske template (Nucletron, Veneendal, The Netherlands) so that the scan direction is longitudinal to the catheter axis. Software modules were developed for the acquisition and reconstruction of ultrasound images. A semi‐automatic segmentation algorithm and a needle reconstruction algorithm were integrated into the software to segment the planning target volume and reconstruct the catheter. A Centroidal Voronoi Tessellations (CVT) algorithm, in conjunction with IPSA, was used for catheter number and position optimization. The procedure was tested with 9 catheters in an agarose‐based phantom with a hypo‐echoic mass. Results: The 3DUS acquisition time is less than 7s and the catheter optimization algorithm can obtain 10 complete treatments plans, with the corresponding dosimetric indices, in 90s. The catheter optimization algorithm was shown to reduce the number of catheters to 12 without reducing the quality of the treatment. Breast PTV V100 and dose homogeneity index (DHI) calculated after the procedure were compared to the value obtained from the optimal plan calculated with the CVT algorithm. Both dosimetric indexes were still within RTOG guidelines after the procedure. However, the PTV V100 is smaller after the procedure due to the template‐based implantation. Isodoses are comparable. Conclusion: We have devised a simple, fast and efficient method for real‐time 3DUS guidance of breast HDR brachytherapy. This approach could be coupled with personalized 3D‐printed or robotic template to further optimize this brachytherapy procedure. Funding support: CIHR and NSERC
MO‐G‐137‐03: Evaluation of the Robustness of Proton Therapy Compared with IMRT Regarding Interfractional Variations for Prostate Cancer
Authors: Moteabbed M , Trofimov A , Sharp G , Lu H
Published: July 2013

Purpose: To evaluate the impact of interfractional changes on the delivered dose in proton therapy (PT) and intensity modulated radiation therapy (IMRT) for low‐intermediate risk prostate cancer. Methods: A subset of prostate patients participating in a randomized clinical trial at our institution also took part in a complementing serial imaging study. For patients randomized to receive 79.2 Gy in 44 fractions (9 weeks) of PT or IMRT, respectively, CT or Cone Beam CT scans were acquired on a weekly basis. The images were rigidly co‐registered to the planning CT to simulate the set‐up procedure. For each patient, both PT and IMRT plans were applied to each of the weekly image sets. Doses were normalized to the number of fractions to approximate the total dose received in a specific week. The weekly doses were then accumulated on the planning CT image using deformable image registration. Dose volume histograms were analyzed and compared to the original plans. The equivalent uniform doses (EUD) were calculated for targets and adjacent organs. Results: Comparison based on a representative case indicated no significant changes to the prostate dose (boost target). However, the dose to seminal vesicles was 3.7 and 5.4% lower than planned, for proton therapy and IMRT respectively. The maximum difference between the planned and accumulated EUDs for all organs at risk was below 5.5 Gy (7% of the prescribed dose), observed in the bladder. On average, the organ EUD was different from planned by 2.5 and 2.8% for protons and IMRT respectively. Conclusion: Despite the use of immobilization devices and bladder filling instruction per protocol, interfractional organ variability was observed. The data acquisition and analysis are ongoing, as patients are accrued to the trial. To date, the OAR dose changes were found to be small with no significant differences between protons and IMRT.
TU‐A‐108‐09: Reduction of Treatment Times for Breath‐Hold Patients in a Spot‐Scanning Proton Machine Through the Use of Mini‐Ridge Filters
Authors: Courneyea L , Tseung H Wan Chan , Yu J , Beltran C , Herman M
Published: July 2013

Purpose: Study the feasibility of synchrotron‐based spot‐scanning proton therapy for breath‐hold patients by reducing treatment time through the use of a Mini‐Ridge Filter (MRF) to increase the width of the Bragg peaks. Methods: Five spot‐scanning nozzles were simulated in TOPAS[1]: four with MRFs of varying maximal thicknesses (6.15mm‐24.6mm) and one without an MRF. The MRF ridges were aligned transverse to the beam, with the number of ridges (4–16) proportional to MRF thickness. The material thickness of these ridges approximately followed a Gaussian distribution. Using these simulations, Monte Carlo data was generated for Eclipse machine commissioning. For each nozzle, standard and stereotactic (SR) lung phantom treatment plans were created and assessed for delivery time and plan quality. Results: Use of an MRF resulted in a reduction of the number of energy layers needed in treatment plans, thereby decreasing the number of synchrotron spills needed and hence treatment time. For normal plans, treatment time without an MRF was 65 seconds per field, whereas all four of the MRF plans had treatment times of less than 30 seconds per field‐sufficiently low for breath‐hold. For SR plans, the shortest treatment time achieved was 47 seconds per field, compared to 94 seconds without an MRF. The time reduction had diminishing gains as the MRF thickness increased. PTV coverage and dose uniformity was comparable across all plans; however, the average dose to the surrounding lung increased from 45% of the prescription dose with no MRF up to 54% (worst case with MRF). Conclusion: An MRF can be used to reduce treatment time to aid breath‐hold treatments without compromising plan quality. To balance treatment time and normal tissue dose, the ideal choice was shown to be the thinnest MRF which achieves the timing necessary for breath‐hold.References: J. Perl et al., Med. Phys. 39, 6818
TU‐A‐108‐10: Pencil Beam Scanning Vs. Passive Scattered Proton Therapy for Pediatric Thoracic/pelvic Cancers
Authors: Moteabbed M , Yock T , Paganetti H
Published: July 2013

Purpose: To investigate if and under what conditions pencil beam scanning (PBS) will offer therapeutic benefits compared to passive scattered proton therapy for pediatric patients with tumors in the thorax/pelvis. Methods: A cohort of six pediatric patients with thorax/pelvic solid tumors treated with passive scattered protons was selected. The tumor types included prostate/bladder rhabdomyosarcoma and spinal/pelvic ewing sarcoma. Five PBS plans were created and optimized for each patient with variable beam spot sizes and utility of beam shaping devices namely apertures and range compensators. These included 12, 8 and 3 mm spot sigma at the isocenter, 12 mm spot with the use of apertures and 12 mm spot with both aperture and compensator. The conformity index for all plans was calculated to ensure sufficient tumor coverage. Dose volume histograms were analyzed and equivalent uniform dose (EUD) for each organ was computed. PBS and PSPT were compared by obtaining the % differences between the two methods for individual organs and for each patient and scanning parameter setting. Results: The results clearly indicate that PBS with 12 mm sigma spots size does not offer dosimetric or clinical advantage over PSPT. However, adding apertures or both apertures and compensators could ensure equivalent or better treatment quality. On average the EUD difference was 0.2% of the prescribed dose for the larger spot size and −3.9% when adding both beam shaping components. Decreasing the spot size further improved all plans, providing better dosimetric quality than PSPT, while alleviating the need for beam shaping devices. Conclusion: The added benefit of using PBS largely depends on the delivery configurations. We recommend the use of beam shaping components in facilities limited to larger spot size (>10mm sigma), in order to sharpen the dose penumbra and reduce the organ at risk toxicity in children with thoracic/pelvic cancers.
TU‐A‐108‐11: Nanoscaffold‐Enhanced Proton Therapy
Authors: Bronk LF , Polf JC , Driessen WHP , Gillin MT , Arap W , Pasqualini R
Published: July 2013

Purpose: To increase the biological effectiveness of proton therapy by introducing targeted gold nanoscaffolds into cancer cells. Methods: As a follow up to our previous studies in prostate cancer, lung carcinoma cells were treated with ligand‐directed nanoscaffold, non‐targeted nanoscaffold, or gold nanoparticles. Following incubation, cells were irradiated in a clinical 160MeV proton beam to doses of 1, 2, 3, 4 and 5CGE. Two irradiation geometries were tested: a depth of 2cm with spread‐out Bragg peak (SOBP) of 4cm and a depth of 9cm with a 10cm SOBP. The clonogenic assay was performed post‐irradiation to determine the effects of the various treatment paradigms on cell survival. We fit the surviving fraction (SF) data to the linear‐quadratic model for analysis. A control irradiation using Co‐60 was also performed. Results: Our analysis showed that all proton treatments resulted in lower SF than the Co‐60 treatment over the measured doses. For proton irradiations, the targeted nanoscaffold achieved the lowest SF compared to all treatments. In the range of a typical clinical fractionation (1.8–4 CGE/fraction) the nanoscaffold treatment reduced the SF by 31%–51% when compared to the untreated cells for proton irradiation at 2cm. For the 9cm depth, the reduction in cancer cell SF was 29–44% for the targeted nanoscaffold versus the untreated cells. The radiation sensitization factor calculated at 50% and 10% SF showed 42 and 20% enhancement at the 2cm depth and 40 and 14% at 9cm. Conclusion: Coupled with our previous findings in prostate cancer cells, the observed decrease in SF of lung cancer cells treated with the targeted nanoscaffold prior to irradiation indicates that the nanoscaffold enhances the effectiveness of the radiation treatment. The exact mechanism of enhancement is ambiguous and requires further study. Initial studies point to a difference in cellular response to the nanosystems as a mode of sensitization. Schissler Foundation MD Anderson Cancer Center Fellowship, Rosalie B. Hite Graduate Fellowship in Cancer Research
TU‐A‐WAB‐06: Evaluation of Articulated Registration and Application to Metastatic Bone Lesions Identification
Authors: Yip S , Morrison C , Perlman S , Liu G , Jeraj R
Published: July 2013

Purpose: Accurate skeleton registration is required to identify corresponding metastatic bone lesions over multiple scans to assess therapeutic responses of individual lesions. In articulated registration, whole‐body skeletons are registered by auto‐segmenting individual bones, then rigidly aligning them. We evaluated if articulated registration outperforms other registration algorithms in skeleton registration and lesion identification. Methods: Six prostate cancer patients with 128 total bone lesions were treated with molecular targeted therapy. Serial whole‐body [18F]NaF PET/CT images were acquired throughout treatment. Skeletons were extracted from the CT images by thresholding (HU>150). Serial skeletons were registered using rigid, deformable, and articulated registration algorithms. The registration performance was quantified as the overlapped volume (OV) of the registered skeletons. The corresponding lesions were contoured and identified on serial PET images under the guidance of a nuclear medicine physician. Each algorithm was evaluated for its ability to accurately align corresponding lesions via skeleton registration. A lesion matching score (LMS) was measured for each lesion, which quantified the percent overlap between a lesion's two corresponding contours. Results: Articulated (OV=90+/–1%) and deformable registration algorithms (OV=90+/–1%) outperformed rigid registration algorithm (OV=50+/–7%) in the skeleton registration as the rigid registration algorithm failed to capture the skeleton flexibility in the joints. The performance of articulated registration (LMS=75+/–23%) in lesion identification was also significantly better than rigid (LMS=59+/–32%, p=0.018) and deformable (LMS=46+/–39%, p=0.0003) registration algorithms. Despite superior skeleton registration performance, deformable registration algorithm failed to preserve the local rigidity of bones leading to undesirable lesion deformation and poor performance in lesion identification, leaving articulated registration as the best choice. Conclusion: Articulated registration is superior to rigid and deformable registrations by capturing global flexibility while preserving local rigidity inherent in skeleton registration. Articulated registration facilitates treatment response assessment of individual bone lesions by potentially reducing physician workload and error in lesion identification throughout treatment.