bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐B‐105‐01: Successes and Challenges Associated with Monte Carlo Treatment Planning in the Clinic
Authors: Chetty IJ , Cygler J
Published: July 2013

The availability of Monte Carlo (MC)‐based codes optimized for photon and electron beams in patient‐specific geometries has enabled the use of MC‐based dose calculations for radiotherapy treatment planning in the routine clinical setting. These codes have made it possible to perform MC‐based photon and electron beam dose calculations within minutes on typical treatment planning computational platforms. As efficient and accurate MC codes become more widely utilized in the clinic, it is important that strategies and paradigms for clinical commissioning and implementation of these systems be formulated and discussed. This lecture will focus on such strategies, challenges and successes associated with the use of MC‐based dose calculations for external photon and electron beam therapy in the clinic.

Learning Objectives:

1. To provide an educational review of the physics of the MC method including discussion of the approaches used for coupled photon and electron transport.

2. To discuss currently available MC‐based photon and electron algorithms fast enough for clinical implementation.

3. To describe the development of beam models for photon and electron beam treatment planning.

4. To discuss the factors associated with MC dose calculation within the patient‐specific geometry, such as statistical uncertainties, CT‐number to material density assignments, and reporting of dose‐to‐medium versus dose‐to‐water.

5. To review paradigms and approaches for commissioning and experimental verification of MC‐based photon and electron beam dose calculation algorithms.

6. To summarize the approaches being used in evaluating the clinical impact of MC‐based photon dose calculations and the associated issues.

NIH/NCI R01 CA106770; Varian Medical Systems, Palo Alto, CA
MO‐D‐105‐01: Safety Profile Assessment: A Tool for Improving Safety and Quality in Radiotherapy
Authors: Dunscombe P , Brown D , Greener A , O' Neill M , Sutlief S , Woodward M , Yorke E , Ford E
Published: July 2013

Purpose: To develop an on‐line questionnaire‐based tool for documenting, benchmarking and improving quality and safety in radiotherapy clinics. Methods: The Safety Profile Assessment (SPA) Tool, a project of the AAPM Work Group on Prevention of Errors, was built principally on four foundations: validated survey tools from the Agency for Healthcare Research and Quality; a published review of safety recommendations in seven recent authoritative documents; an AAPM white paper on incident learning; and the requirements for accreditation of radiation oncology practices within the ACR/ASTRO system as of 2011. The authors performed several iterations of the SPA prototype before further refinement at a workshop with detailed input from representatives of ASTRO, AAMD, ASRT and SROA for content validity. SPA was subsequently released to 32 centers for pilot testing. Results: SPA consists of 92 statements divided into four major sections: 1) Institutional Culture, 2) Quality Management, 3) Managing Change and Innovation and 4) Clinical Performance. The assessor identifies compliance with each statement on a five‐point Likert scale and can also add free text. Output options are pie charts giving an overall visual impression of the safety profile of a radiotherapy department and bar graphs allowing benchmarking against all radiotherapy contributors to the SPA database. Additionally SPA supports a Quality/Safety Improvement Tracking Log and links to relevant literature. In pilot testing, SPA required on average 1.3 hours to complete. Pilot test participants ranked SPA highly for ease of use and utility for improving safety. Pilot participants further noted that completing the SPA as a group improves efficiency and completion and also facilitates interaction of clinical staff. Conclusion: SPA distills advice and experience from a variety of authoritative sources into a convenient, logically configured, on‐line resource, which has received overwhelmingly positive reviews during pilot testing. SPA is now being configured for on‐line distribution through the AAPM website. The project was funded by the AAPM through the budget allocated to the Working Group on the Prevention of Errors.
MO‐D‐105‐03: The Medical Physicist's Role in the Oversight of Lead Shielding Installation in Nuclear Medicine: What to Look For
Authors: Pasciak A , Handley S
Published: July 2013

Purpose: All diagnostic medical physicists are familiar with postinstallation lead shielding surveys in radiographic and CT imaging rooms. Survey techniques ranging from visual inspection to transmission measurements are detailed for these types of procedure rooms in NCRP‐147. However, shielding requirements in PET/CT are vastly different, with little published guidance on post installation physics survey techniques. Methods: A complex PET/CT shielding installation is used as a pictorial example of the issues faced by a medical physicist performing a survey of newly installed shielding in nuclear medicine. In this example, every common thickness of lead shielding is used, from 1/32″ lead laminated sheetrock to 3/8″ lead laminated plywood. Even the use of 3/4″ interlocking lead bricks is discussed along with the necessary supporting structure for a lead wall of this thickness . Particular attention will be paid to penetrations and ductwork with specific regard to the increased difficulty associated with shielding these items in PET/CT suites. Results: The PET/CT shielding installation in question has been completed. At different stages through the installation, many issues were identified by physicists and were subsequently addressed by shielding contractors. An example of such an issue was the need to install overlapping lead astragals at the abutment between adjacent sheets of lead laminated plywood‐‐a practice which is not necessary for lead laminated sheetrock. Similar examples where installation requirements of lead shielding in PET/CT differ significantly from the requirements in X‐ray are presented. Conclusion: As technology improves, modern PET/CT systems are able to perform full body imaging in far less time than was previously required. As a Result, higher patient workloads are possible, thereby increasing facility shielding requirements. Medical physicists will need to familiarize themselves with the differences in the post‐installation lead shielding survey techniques required for PET with those traditionally used for X‐ray imaging rooms.
MO‐D‐108‐01: Cloud‐Based Monte Carlo Patient‐Specific Quality Assurance (QA) Method for Volumetric‐Modulated Arc Therapy (VMAT): Clinical and Educational Impacts
Authors: Chen X , Xing L , Mok E , Luxton G , Bush K
Published: July 2013

Purpose: Patient‐specific QA for VMAT is labor‐intensive,especially in cases which tend to be associated with severe heterogeneities or small aperture beams. We developed a robust cloud‐based Monte Carlo method as an independent QA tool or backup for commercial dosimeters. It is also educationally innovative because it helps physicists to comprehend the underlying physics of complex VMAT procedures. Methods: The workflow of the cloud‐based voxel Monte Carlo method(cVMC++) developed here is the following: (1) After a VMAT plan is approved by the physician, a dose verification plan is created and delivered to the phantom using the Varian Trilogy™ or TrueBeam™ system. (2) Actual delivery parameters (i.e., dose fraction, gantry angle, and MLC leaf position) are extracted from dynamic log or trajectory files. (3) Based on the delivery parameters, a new phase space is constructed for each control point. The 3D dose distribution in the phantom containing the detector array (e.g., Delta 4 from ScandiDos) are then recomputed using cVMC++. (4) Comparison and Gamma index analyses are then conducted to evaluate the agreement between measured, recomputed, and planned dose distributions. To enhance the educational function, we are developing visualization and animation modules to display the intermediate processes such as leaf movement, dose distribution and DVH accumulation with each control point. The software has been wrapped as a web‐based service so that it can readily be used by physicists via a browser. To test the robustness of this system, we examined several representative VMAT treatments. Results: For all cases, agreement between measured, recomputed and planned doses was examined with the gamma criterion of >90% of the points satisfying <3% of relative dose difference and <3 mm of distance to agreement. Conclusion: The proposed method offers a robust patient specific QA tool for VMAT treatments and provides a valuable educational tool for physicists. NIH (1R01 CA133474) and Department of Radiation Oncology of Stanford University Seed Grant
MO‐D‐108‐06: Off‐Axis Ratio Based Correction for the Determination of TMR for Flattening‐Filter Free (FFF) Mode Beams
Authors: Chung H , Prado K , Kinsey E , Yi B
Published: July 2013

Purpose: Due to the nature of the beam fluence of the flattening‐filter free (FFF) mode from Varian TrueBeam linear accelerator, the tissue‐maximum ratio (TMR) conversion formalism from percent‐depth dose (PDD) may not be appropriate at large field sizes and large depths. The purpose of this work was to establish an analytical correction formalism which accounts for the differences in FFF‐mode beam profiles that corrects for small differences in TMR between the calculations and measurements. Methods: Two FFF‐mode beams (6‐MV and 10‐MV) were investigated using Varian TrueBeam linear accelerator. Initially, the analytical correction formalism starts out with the TMR conversion equation which is the product of the PDD, inverse square, and phantom scatter ratio. A ratio of two off‐axis ratios (OARs) at the surface and depth of interest is determined for a given field size. This OAR ratio is multiplied with the phantom scatter term in the TMR conversion equation to account for small differences in TMR values at large field sizes (>= 15 × 15 cm2) and depths (>= 15 cm). Results: For 10‐MV FFF‐mode, the difference between the measured and the standard TMR formalism ranged from ‐ 3.2% to ‐ 0.9% (mean = ‐ 1.8% and 1‐standard deviation = 0.7%) for field sizes >= 15 × 15 cm2 and >= 15 cm depth. When the proposed correction formalism was applied to the TMR conversion formalism, the difference between the measured and the corrected TMRs for field sizes >= 15 × 15 cm2 and >= 15 cm depth ranged from −0.7% to −0.2% (mean = −0.4% and 1‐standard deviation = 0.1%). Similar relationships were observed for 6‐MV FFF‐mode. Conclusion: The analytical correction formalism which accounts for the differences in the FFF‐mode beam profiles has been shown to correct for the small differences in TMR that were observed without the correction.
MO‐D‐108‐07: Comparison of Electron Monte Carlo and Pencil‐Beam Algorithms in Clinical Electron Beam Radiation Dosimetry
Authors: Liu Z , Hargrove I , Tazi A , Barrett J
Published: July 2013

Purpose: Electron Monte Carlo (eMC) and Pencil‐Beam (PB) algorithms are both used clinically for electron beam radiation dosimetry. The purpose of this study is to evaluate the two calculation algorithms with reference to the standard electron beam dosimetry parameters and isodose distributions in practical clinical applications. Methods: eMC and PB algorithms were both commissioned in Eclipse treatment planning system. Standard radiation dosimetry parameters ‐ ‐including percent depth dose, beam profile width, and output factors‐‐were calculated in homogeneous water phantom for various combinations of electron energy and cone applicators. The calculation results were compared with the measured data. The two algorithms were also compared in clinical situation. A phantom simulating chest wall and lung was created and used for dose calculation. A 9 MeV electron beam with a customized cutout on the 20−20 cone was used at fixed SSD of 100cm. The calculation setting for eMC was 1% precision, 1.5‐mm grid, and strong Gaussian smoothing. For PB, 2.5mm grid was used for dose calculation. Results: The difference between measured and calculated depths of R100, R90, R80, and R50 for both algorithms is less than 1mm for all combinations of energies and cone applicators. For the field width and output factors, eMC affords slightly better agreement with measurement than PB does. For practical phantom calculations with both surface irregularity and heterogeneity, eMC shows a more reasonable isodose distribution. Comparing to eMC, PB algorithm tends to overestimate the dose neighboring the air cavity and underestimate the dose past the air cavity in a water phantom. For surface irregularity, eMC and PB show similar results though. Conclusion: eMC and PB algorithms are accurate in the calculation of standard electron dosimetry parameters. Both eMC and PB can handle the surface irregularity very well. eMC is superior to PB in terms of heterogeneity.
MO‐D‐108‐08: Fast Monte Carlo Electron‐Photon Transport Code Using Hardware Accelerators: Preliminary Results for Brachytherapy and Radionuclide Therapy Cases
Authors: Su L , Du X , Liu T , Xu X
Published: July 2013

Purpose: Although Monte Carlo methods provide the most accurate radiation dose calculation for medical physics applications, long simulation time remains an impediment for its routine utilization. An electron‐photon coupled Monte Carlo code ARCHER ‐ Accelerated Radiation‐transport Computations in Heterogeneous EnviRonments ‐ is being developed at Rensselaer Polytechnic Institute as a software testbed for emerging heterogeneous high performance computers that utilize accelerators such as GPUs. This paper describes the development of ARCHER and demonstrates its preliminary applications involving brachytherapy and radionuclide therapy. Methods: In ARCHER code electron transport was modeled by mixed condensed history method. Photon transport was simulated in analog. The energy range handled was from 10 keV to 30 MeV. The hardware platform involved a desktop with Intel Xeon X5660 CPU and six NVIDIA Tesla™ M2090 GPUs. ARCHER was benchmarked against MCNPX and EGSnrc on slab geometry. In addition, we used ARCHER to calculate Ir‐192 brachytherapy dose distribution and to evaluate Y‐90 beta SAF in radionuclide therapy. Results: The depth dose and lateral dose at different depth were tallied and compared with results from MCNPX and EGSnrc. For 99.1% of all tested voxels, the dose difference between ARCHER and EGSnrc was within 2% of the dose maximum. In the brachytherapy calculation, all the major organ doses from ARCHER matched those from MCNPX within statistical error. In the Y‐90 internal source case, ARCHER gave similar SAF value with MCNPX. Meanwhile the simulation speed was 2∼3 orders faster than MCNPX and EGS using single GPU. With multiple GPUs, the simulation time can be decreased almost linearly. Conclusion: We developed an electron photon coupled Monte Carlo code ARCHER. Preliminary testing showed good agreement with prevailing general purpose codes, while its speed was hundreds even thousands times faster. We are working on applying ARCHER to Brachytherapy and radionuclide therapy and have encouraging preparatory Result.
MO‐D‐141‐02: Evaluation of Optimal Gating Respiratory Motion Management Technique On PET Quantification
Authors: Lee K , Hristov D , Casey M , Rajaram R
Published: July 2013

Purpose: To evaluate the uncertainty of PET quantification resulting from irregular breathing patterns when optimal gating (HD‐Chest) acquisition is performed on a Siemens Biograph PET‐CT scanner. Methods: A NEMA phantom containing spherical VOIs (Volumes‐of‐Interest) with diameters of 28, 22, 17, 13, and 10 mm was scanned on a moving platform. Seven breathing traces that were previously recorded optically from lung PET patients and one synthetic regular trace were used to drive the platform. Motion amplitudes for individual traces were 5∼20 mm peak‐to‐peak with intra‐traces amplitude variances ranging between 1.6 mm to 10.3 mm. For each trace, the average (SUVavg) and maximum (SUVmax) standard uptake values within the VOIs were calculated. VOIs volumes were also evaluated at a threshold equal to 10% of SUVmax. Relative percent deviations of these parameters from ground truth values derived from a static acquisition were calculated. Results: The average deviations for all patient breathing patterns were 10.5% (SD=5.9%), 11% (SD=7.9%), and 9% (SD=9.3%) for volume, SUVavg, and SUVmax, respectively. The average deviations for the regular breathing pattern were 3.8%, 5.2%, and 6.6% for volume, SUVavg, and SUVmax, respectively. VOI size significantly affected the uncertainty. For the 28 mm VOI the average deviations were 6.9%, 6.6%, and 2.7% for volume, SUVavg, and SUVmax, respectively while for the 10 mm VOI these were 11.8%, 15.1%, and 19.3% for volume, SUVavg, and SUVmax, respectively. Without any breathing motion management technique in place, the average deviations for the regular breathing pattern were 16.6%, 42.8%, and 42.4% for volume, SUVavg, and SUVmax, respectively. Conclusion: The optimal gating (HD‐Chest) technique improved the PET quantification. However, one needs to take the residual deviations for regular and for all irregular breathing patterns into account for PET quantification. M. Casey and R. Rajaram are the employees of Siemens Medical Solutions
MO‐D‐141‐05: Dictionary Learning in Compressed Sensing Using Undersampled Data in PET Imaging
Authors: Valiollahzadeh S , Clark J , Mawlawi O
Published: July 2013

Purpose: Compressed sensing in PET imaging usually leverages the sparse representation of the acquired data in a predefined domain to help recover potential undersampling in the sinogram space. The majority of CS methods use analytical predefined sparsifying transforms such as wavelets, curvelets, and finite transforms. In this work, we evaluate the dictionary learning (DL) transform to reconstruct PET images from partially sampled data and compare the results with a fully sampled image. Methods: Let X=Dα represent an overlapping 4×4 pixel patches obtained from the partially sampled image, D is a matrix containing coefficients of the dictionary transform and a is a sparse vector. Our objective is to optimize X=Dα subject to the constraints that the a coefficients be sparse and more importantly that Dα be bounded by a Poisson likelihood penalization. This optimization is performed iteratively (n=500) in two steps for all patches concurrently: once we update the columns of D and once we update the α coefficients. This algorithm was tested using an IEC phantom containing 6 spheres with a sphere to background ratio of 10:1. The phantom was imaged on a D‐RX PET/CT scanner twice; once with all detectors operational (baseline) and once with 4 detector blocks at each of 0, 90, 180 and 270° turned off ‐ partially sampled (PS). The PS and DL‐recovered images were compared to baseline by calculating the percent error in mean activity concentrataion (AC) in the 6 spheres and background. Results: The percent error in AC in the 6 spheres (largest ‐ smallest) and background for PS (DL‐recovered) images were –22.5(6.3), –15.6(13.7), –19.6(7.8), –22.2(9.8), – 14.2(25), –11.9(21.4), and –33.3(22.2) respectively. Conclusion: Poisson compressed sensing with DL seems to be a good approach to recover partially sampled PET data. This approach has implications towards reducing scanner cost while maintaining PET accurate image quantification.
MO‐D‐134‐04: Calculating Size Specific Dose Estimates (SSDE): The Effect of Using Water Equivalent Diameter (WED) Vs. Effective Diameter (ED) On Organ Dose Estimates When Applying the Conversion Coefficients of TG204
Authors: Khatonabadi M , Oria D , Mok K , Cagnon C , DeMarco J , McNitt‐Gray M
Published: July 2013

Purpose: AAPM Task Group (TG) 204 described the Size‐Specific Dose Estimate (SSDE) using effective diameter (ED) as the size parameter in the conversion tables. The purpose of this investigation was to assess the effect on SSDE when a different size metric, water equivalent diameter (WED), was used with the conversion tables; and to compare these values to results from detailed Monte Carlo (MC) simulations. Methods: For a set of 101 thoracic and 82 abdomen/pelvis scans, including adult and pediatric patients, both ED and WED were calculated at the middle of the scan length. Each size metric was used as the input value to the SSDE conversion tables in TG204 to obtain two sets of SSDE values (SSDEED and SSDEWED). Additionally, voxelized patient models were generated from original scans and used in MC simulations to estimate dose to liver, spleen, and kidneys in the abdomen/pelvis, as well as lung and glandular breast tissue in the thoracic examinations under fixed tube current mode. SSDEED, SSDEWED were compared to organ doses by calculating percent differences and Root Mean Square errors. Results: For the abdomen, SSDEED and SSDEWED resulted in different RMSE from organ dose (for kidneys 8.8% and 6.4%, respectively) while SSDEWED demonstrated higher correlation with kidney dose than SSDEED (0.89 and 0.78, respectively). Similarly, for thorax, SSDEED and SSDEWED showed different RMSE (for lung 17.0% and 13.1%, respectively), with higher correlation for SSDEWED than SSDEED (0.92 and 0.78, respectively). Conclusion: Generated conversion factors based on ED appear to be applicable to WED and as originally assumed using WED not only improves dose estimates in the thorax but it also improves estimates in the abdomen. It is worth mentioning that these conclusions only apply to fixed tube current examinations while for tube current modulated (TCM) exams new set of conversion factors are recommended. Dr. Michael McNitt‐Gray Institutional research agreement, Siemens AG Recipient research support Siemens AG Consultant, Flaherty Sensabaugh Bonasso PLLC Consultant, Fulbright and Jaworski, LLC Maryam Khatonabadi: ipient research support Siemens AG
MO‐D‐134‐10: Using HVL and KVp to Portray An X‐Ray Source for Dose Calculations in CT
Authors: Sommerville M , Poirier Y , Kouznetsov A , Tambasco M
Published: July 2013

Purpose: To show that the nominal peak tube voltage potential (kVp) and measured half‐value layer (HVL) are sufficient to generate energy spectra and fluence profiles for fast and accurate machine‐specific dose computations in Computed Tomography (CT). Methods: Spatial variation of the x‐ray source spectrum was found by measuring HVL across the internal bowtie filter axis and using the nominal kVp settings and third‐party software Spektr to generate the spectra. The beam fluence was calculated by multiplying in‐air dose measurements along the filter axis with the integral product of the spectra and the in‐air NIST mass‐energy attenuation coefficients. Dose calculations were performed using a previously validated in‐house hybrid deterministic and stochastic kV x‐ray dose computation algorithm (kVDoseCalc). To ensure dose convergence while minimizing calculation time, we examined the sensitivity of kVDoseCalc to the number of photons seeded. We modeled the source of a Philips Brilliance Big Bore CT scanner for 90, 120, and 140 kVp settings. Doses measured using a Farmer‐type Capintec ion chamber (0.6 cc) placed in a cylindrical poly methyl methacrylate (PMMA) phantom were compared to those computed with kVDoseCalc. Results: The number of photons seeded required to keep the average statistical uncertainty in dose less than .1% was found to be 1.25 million. The average percent difference between calculation and measurement pooled over all 12 positions in the phantom was found to be 1.68%, 1.60%, and 1.25% for 90, 120, and 140 kVp, respectively. The maximum percent difference between calculation and measurement was less than 3.64% pooled over all energies and measurement positions. Thirty‐one out of a total of 36 simulation conditions were within the experimental uncertainties associated with measurement reproducibility and chamber volume effects. Conclusion: Our source characterization technique, which derives incident fluence and spectra from measurements of HVL across the bowtie profile, is sufficient for accurate machine‐specific CT dose computations.
MO‐D‐144‐02: Ultrasound Transducer Localization Using the CyberKnife's X‐Ray System
Authors: Bruder R , Ipsen S , Jauer P , Ernst F , Blanck O , Schweikard A
Published: July 2013

Purpose: 4D ultrasound has become an alternative for image guidance and motion compensation in radiosurgery. Nevertheless, a two‐step localization has to be performed when using ultrasound. In addition to target localization inside the ultrasound volume, the transducer itself has to be localized and the target position has to be transformed into treatment coordinates. Methods: The CyberKnife (Accuray Inc.) features a stereo X‐ray system which is used for patient and fiducial marker localization. Accessing only the raw X‐ray images, we designed a software package for additional marker detection. To measure the physical camera parameters, X‐ray phantoms were designed and a non‐orthogonal stereo camera calibration was performed on 50 calibration X‐ray pairs. Algorithms were developed for three‐dimensional single marker localization and six‐dimensional localization of marker geometries. Different X‐ray marker geometries were designed and attached to the ultrasound transducer. The final system was evaluated and compared to the on‐board localization system using a 6‐axis industrial robot to position different marker geometries at 150 randomly distributed positions over the acquisition volume. Results: Two marker geometries with 20 and 50mm base lengths were localized using the on‐board and newly developed software. The mean translational error for the on‐board localization is 0.202mm, for the new system 0.218mm. The rotational error of the on‐board system could be reduced from 0.212 to 0.053 degrees for the 50mm marker and from 0.272 to 0.076 degrees for the 20mm marker geometry. Conclusion: We have shown that ultrasound transducers can be localized using the CyberKnife x‐ray system. The rotational accuracy of the localization could be increased by a factor of four, which is important for high marker‐to‐ultrasound‐target distances. Furthermore, using the full area of the flat‐panel detectors without pre‐processing steps the tracking volume was increased by 70 percent, which helps detecting patient/fiducials and transducer at the same time.
MO‐E‐500‐01: Point and Counter Point Debate: The More Important Heavy Charged Particle Radiotherapy of the Future Is More Likely to Be with Heavy Ions Rather Than Protons
Authors: Smith A , Jaekel O
Published: July 2013

Over the past decade there has been considerable interest and progress in the use of heavy ions such as protons and carbon in an attempt to improve the effectiveness of radiotherapy. Both have a physical advantage over photons because of their Bragg peaks, but only heavier ions such as carbon have a potential biological advantage. This has led to the claim that the most important heavy charged particle radiotherapy of the future is more likely to be with heavy ions rather than protons, and this is the premise argued in this debate.Arguments FOR the Proposition include:• relative to protons, heavier ions exhibit reduced lateral scattering, reduced range straggling, and increased dose to the tumor compared to the entrance dose• accurate positioning of the Bragg peak can be verified by in vivo measurements with heavier ions but not with protons• with heavier ions there is increased RBE in the tumor compared to normal tissues• with heavier ions there is increased effectiveness in hypoxic tumorsArguments AGAINST the Proposition include:• proton facilities cost 2–3 times less than those for heavier ions• cost and size of isocentric gantries for protons are much less• there are large uncertainties in the RBE in the heavier ion Bragg peak• with protons, there is the potential for reoxygenation during a course of therapy• due to fragmentation, heavier ion beams exhibit a tail of high‐LET radiation beyond the Bragg peakArguing for the Proposition is Oliver Jakel, Ph.D. Dr. Jakel completed his Ph.D. in Theoretical Physics at the University Erlangen, Germany in 1994. He then moved to the Department for Medical Physics, German Cancer Research Center (DKFZ), Heidelberg, where he is currently Full Professor and Director of the Heidelberg Ion Beam Therapy Facility of the University Hospital. Arguing against the Proposition is Alfred R. Smith, Ph.D. Dr. Smith obtained his Ph.D. in Physics from Texas Tech University, Lubbock, TX, in 1970. After completing a Postdoctoral Fellowship in Medical Physics at The University of Texas, M. D. Anderson Hospital and Tumor Institute, he held faculty positions at several institutions until he moved back to M. D. Anderson in 2002 as a Full Professor and Director of Proton Therapy Development, a position he held until 2010.

Learning Objectives:

1. To understand why heavy ions might be more suitable than photons for the treatment of some cancers

2. To understand the relative benefits of therapy with heavier ions compared with protons

3. To understand the relative benefits of therapy with protons compared with heavier ions
MO‐F‐105‐01: Challenges of Increased Controls of Radioactive Materials
Authors: Fairobent L , Blankenship B
Published: July 2013

Shortly after the terrorist attacks of September 11, 2001, heightened concerns were expressed about the use of risk‐significant radioactive materials in a malevolent act. In the changed threat environment after the attacks of September 11, 2001, the Commission determined that certain licensed material should be subject to enhanced security requirements and safeguarded during transport, and that individuals with unescorted access to risk‐significant quantities of radioactive material should be subject to background investigations. The NRC initially regulated these changes by Order. Since then, the NRC has developed a final regulation which when complied with will replace existing orders. The first part of this session will address the NRC's final rule and guidance document. This final rule is effective on May 20, 2013 with compliance required by March 19, 2014.The second part of this session will address the experience and practicalities of implementing the Orders and the process required for compliance with the final rule.

Learning Objectives:

1. Individuals will understand the content and complexity of the final 10 CFR 37 and its corresponding guidance document.

2. Individuals will understand if the 10 CFR 37 requirements are applicable to their Radioactive Materials Program.

3. Individuals will understand the complexity and challenge in implementing 10 CFR 37 requirements in practice.
MO‐F‐108‐01: Deformable Dose Reconstruction to Evaluate Image‐Guidance Strategies in Free‐Breathing Liver SBRT
Authors: Velec M , Dawson L , Brock K
Published: July 2013

Purpose: To evaluate the delivered dose following image‐guidance strategies for liver SBRT. Methods: The delivered dose was reconstructed using deformable image‐registration (DIR) on the retrospectively sorted (4D) cone‐beam CT (CBCT) for 30 SBRT patients (15 with multiple tumors). Plans created on exhale 4D‐CT, for 27–60 Gy/6 fractions, were delivered in free‐breathing after 3D‐CBCT rigid liver alignment. Dose was also reconstructed after simulating two rigid alignment strategies on the exhale 4D‐CBCT: the liver or the tumor directly (using DIR to predict tumor position). Delivered doses were compared to the planned 4D breathing dose, modeled with DIR of 4D‐CT. Results: Residual mean tumor errors >3 mm occurred in nine patients (30%) following free‐breathing 3D‐CBCT (max: 10 mm), and two patients (6.6%) following liver or tumor 4D‐CBCT alignment (maximum: 3.3 mm). With free‐breathing 3D‐CBCT, the delivered minimum tumor doses decreased by more than 1 Gy compared to planned dose for 4 (13%) patients. For 2 of these 4 patients, aligning the liver or tumor on 4D‐CBCT reduced the dose decreases from −1.4 Gy, to within −0.5 Gy. The other 2 patients had multiple tumors and substantial liver deformation, resulting in minimum tumor doses decreases (max: −4.3 Gy) following free‐breathing 3D‐CBCT, that were reduced with either liver (max: −2.7 Gy) or tumor (max: −2.2 Gy) 4D‐CBCT alignment. For normal gastrointestinal tissues receiving >30 Gy, the delivered maximum doses deviated by −11.5 to 2.6 Gy, with one exceeding the planning constraint by 0.7 Gy following free‐breathing 3D‐CBCT. Aligning the liver or tumor on 4D CBCT reduced normal tissue deviations (range: −6.3, 2.7 Gy) without exceeding planning constraints. Conclusion: 4D‐CBCT guidance for liver SBRT has been clinically implemented. The improved correlation between the 4D planning dose and delivered dose can be largely accomplished with 4D alignment of the liver, and should allow for planning margin reduction. This research is supported by the NIH, 5RO1CA124714‐02, and a Canadian Institutes for Health Research Fellowship. Patient data was acquired during clinical trials supported by the National Cancer Institute of Canada, #18207, and CIHR, #202477. K.K. Brock has financial interest in the deformable registration technology through a licensing agreement with RaySearch Laboratories.
MO‐F‐108‐03: Encouraging the Dose Homogeneity in Lung SBRT by Reweighted Total‐Variation (TV) Minimization
Authors: Kim H , Li R , Lee R , Xing L
Published: July 2013

Purpose: To meet stronger dose constraints required in lung SBRT, the high dose inhomogeneity inside the PTV has been considered potentially beneficial; yet it may cause clinically unwanted damage. This work, therefore, proposes to lower the dose inhomogeneity by using reweighted total‐variation(TV) minimization(min.) in lung SBRT, while achieving the safe plan quality that the inhomogeneous plan can do. Methods: RTOG 0915 protocol regulating lung SBRT planning prescribes far stronger dose constraints around and outside PTV by high/intermediate dose spillage (HDS/IDS), where the tissue around the target is protected from high dose (lower HDS) and steep dose fall‐off gradient outside the PTV is required by IDS constraint. Inside the PTV, however, the high dose inhomogeneity has been encouraged to lower the HDS when dose fall‐off gradient is sufficiently steep. It could, however, irradiate too high dose to the marginal side of PTV or healthy tissues in actual treatment. Thus, this study employed reweighted TV min. to lower dose inhomogeneity in lung SBRT by simplifying the fluence‐map complexity, while preserving HDS/IDS constraints that inhomogeneous plan can perform. To validate it, the pre‐treated lung SBRT data was applied with three cases: homogeneous/inhomogeneous plans by TV min. and homogeneous plan by reweighted TV min (proposed). Results: Reweighted TV min. with homogeneous plan successfully yields as low HDS around the PTV as the inhomogeneous plan can do, while maintaining the same steep fall‐off gradient outside the target. Even compared with the homogeneous plan with TV min., the proposed method can further enhance the dose homogeneity inside the PTV mainly due to the decrease in the fluence‐map complexity by reweighting process. Conclusion: Reweighted TV min. can improve such plan safety as protecting healthy tissue with steep fall‐off gradient required in lung SBRT without the necessity of increasing the dose inhomogeneity inside the PTV.
MO‐F‐108‐07: Impact of Additional Intensity Modulation On Arc‐Based Stereotactic Body Radiotherapy (SBRT) for Lung Cancer
Authors: Liu H , Ye J , Kim J , Deng J , Chen Z
Published: July 2013

Purpose: A single‐isocenter multi‐segment dynamic conformal arc technique (SiMs‐arc) has been used in our department in the past three years for efficient planning and delivery of over 200 lung SBRT treatments. The purpose of this study is to investigate the impact of additional intensity‐modulation made available by Varian RapidArc on the dosimetric quality and delivery efficiency of arc‐based lung SBRT. Methods: Four patients previously treated with lung SBRT using SiMs‐arc were selected. SiMs‐arc plans were generated with the isocenter located in the geometric center of patient axial plane (to allow for collision‐free gantry rotation around the patient) and six 60°‐arc segments spanning from 1° to 359°. Two RapidArc plans, one using the same arc geometry as SiMs‐arc and the other using typical partial arcs (210°) with the isocenter inside PTV, were generated for each patient. All plans, generated using Eclipse V10.0, were normalized with PTV V100 to 95%. PTV coverage, dose to organs‐at‐risk and total MUs were compared to assess the impact of additional intensity‐modulation provided in RapidArc. Results: RapidArc plans produced higher PTV D99 (by 1.0%–3.1%) and minimum dose (by 2.4% to 9.8%); better PTV conformality index (by 1%–8%); and less volume of 50% dose outside 2cm from PTV (by 0–20.8cc) than the corresponding SiMs‐arc plans. No significant dose differences were observed for lungs, trachea, chest wall and heart. RapidArc using partial‐arcs had lowest maximum dose to spinal cord. RapidArc plans required 1.5 to 1.91 times more MUs than SiMs‐arc plans to deliver the same dose. Conclusion: Additional intensity‐modulation enlisted by RapidArc produces modest dosimetric improvements over conformal arcs for lung SBRT, but requires more MUs (by a factor > 1.5) to deliver. The dosimetric improvements, most notably in PTV minimum dose and in dose conformality for irregularly shaped PTVs, may outweigh the increased MUs in using RapidArc.
MO‐F‐108‐10: Implementation of 4Pi Non‐Coplanar Converging (4PiNC) Beams Using a Conical Delivery Geometry
Authors: Chang J , Wang S , Cho D , Sabbas A , Chao K
Published: July 2013

Purpose: To study the feasibility of a proposed conical delivery system for implementing 4PiNC beams. Methods: In the proposed novel 4PiNC beam delivery system, the x‐ray source aims at the isocenter but rotates around a point on the superior‐inferior axis in a conical fashion. Mathematically, each rotation forms a cone where the vertex is the isocenter and the base is the area bounded by the circular trajectory of the x‐ray source. By changing the cone angle (90 ‐ vertex angle), the proposed 4PiNC system allows hundreds of non‐coplanar beams to be delivered without couch rotation. We developed a simple treatment planning system to investigate the dosimetry for an elliptic cylinder phantom. The planning target volume was a sphere inside the phantom. The three‐dimensional dose calculation was calculated using the TMR table, off‐axis ratios and output factors of a 6 x‐ray beam commissioned for radiosurgery cones. Planning parameters (depth, off‐axis distance…) were calculated analytically. The dose grid contained 100×100×100 voxels with a voxel size of 2×2×2 mm^3. Results: Dose distributions were calculated for (A) 263 beams using cone angles 0, ±20, ±40, ±60, ±80 degree, (B) 153 beam using cone angles 0, 20, 40, 60, 80 degree and (C) 179 beams using cone angles 0, ±20, ±40 degree. Highly conformed dose distributions were achieved with conformity indexes 1.12, 1.11 and 1.19 for case (A), (B) and (C), respectively. The dose falloff (80%–20% of the central dose profile) was 8 mm, 8 mm and 11 mm, respectively. Conclusion: We proved in principle that the proposed 4PiNC beam delivery system can provide excellent dose distribution (low conformity index and fast dose falloff) without couch rotation. The proposed system can significantly improve the treatment plan quality and avoid couch‐gantry collisions, a common patient safety concern of c‐arm linear accelerators, when delivering non‐coplanar beams. This work was partially supported by a DOD grant DOD W81XWH1010862.
MO‐F‐WAB‐06: Validation Framework and Benchmarking for Markerless Tumor Trajectory Estimation
Authors: Chen S , Weiss E , Roman N , Hugo G
Published: July 2013

Purpose: To develop a validation framework for markerless tumor trajectory estimation algorithms and use this framework to optimize markerless tumor trajectory estimation in cone beam CT (CBCT) projections. Methods: Fiducial markers implanted in and near the tumor in six lung cancer patients were segmented in CBCT projections and the 3D marker trajectories were reconstructed. A correction based on the tumor position in the reconstructed CBCT, the tumor‐to‐marker displacement (T‐M) was added to the marker trajectory to generate the reference tumor trajectory. Four combinations of T‐M based on two marker segmentation methods and two tumor position measurement methods were evaluated. Since T‐M is expected to be fairly stable from day to day, optimal T‐M was evaluated based on day‐to‐day variability. For markerless tracking, three means of generating templates for 2D registration (a cylindrical template, expanded gross tumor volume (Ex‐GTV), and Ex‐GTV with padding to override non‐target edges (padded template)) were compared using the validation framework. A constraint method was also implemented to regularize the 2D registration. Results: The optimal T‐M was generated by planning CT to CBCT registration of the target volume along with marker segmentation from the projections. The mean (standard deviation) absolute registration error in five patients using the three different template methods were 5.3 (6.5) mm for the Ex‐GTV template, 6.1 (6.4) mm for the cylinder template, and 3.5 (5.0) for the padded template. The 90% error level was 12.4, 13.3, and 7.9 mm for the three methods, respectively. The mean registration error was reduced further to 2.1 (2.5) mm (90% error of 4.3 mm) with the constraint method. Conclusion: A validation framework for markerless trajectory measurement was optimized. The padded template method with constraints agreed best with the implanted marker trajectories. E Weiss receives research support from Varian Medical Systems.
MO‐F‐WAB‐08: Are Planning Target Volumes Derived From 4DCT Scans Adequate When Treating Lung SBRT with Static Tracking Methods?
Authors: McGuinness C , Descovich M
Published: July 2013

Purpose: A unique capability of the CyberKnife system is dynamic target tracking. However, at our institution 68% of lung cancer patients are determined ineligible for this approach. Rather, their tumors are tracked statically using the vertebral column for alignment. The internal target volume (ITV) is delineated on the 4DCT scan and an additional margin is added to account for setup uncertainty. We seek appropriate ITV to PTV expansion needed for patients treated in this manner. Methods: Data from 12 patients (37 fractions) were included in this study. Each patient was treated with dynamic tracking and underwent 4DCT scanning at the time of simulation. The GTV and ITV were contoured and additional margins were added to the ITV to create the PTV. 3D target positions over the course of treatment (1–1.5 hours) were extracted from the log files. Based on these positions, a set of adjusted GTV contours was created and used to calculate the fraction of GTV extending outside of the PTV over the course of treatment (data were integrated over time for each sampling position). Results: Of the 37 fractions included, 35 (95%) show less than 5% of the GTV outside the PTV for a margin of 3.6 mm, and less than 2% of the GTV outside the PTV for a margin of 5 mm. Conclusion: The results of this study provide guidelines for selecting appropriate ITV‐PTV margins when treating lung patients on CyberKnife using spine alignment. We found that a 5 mm ITV to PTV margin is adequate to assure >98% of tumor coverage for 95% of the patients. However, this margin represents a worse case scenario. It does not reflect the fact that target motion due to patient drift is corrected for by spinal alignment. A method for separating the two sources of motion will be investigated. Separate research contract from Accuray Inc.
MO‐F‐134‐01: The Desktop Magnet: Simulation/tutoral Software for MRI Education
Authors: Gauntt D
Published: July 2013

Purpose: To effectively teach radiology residents the fundamental physics behind magnetic resonance imaging based on a semi‐classical model of the photon. Method: The Desktop Magnet is a Java application that comprises both a set of tutorials and a programming environment to simulate the running of custom written pulse protocols. The tutorials can mostly be presented in a single hour‐long lecture that covers from the semi‐classical model of the electron to spin‐warp imaging. Alternately, the interested student may study them at leisure. The tutorials are interactive, allowing the student to adjust the parameters of the simulations. Each year our first year residents take an introductory MR physics class; for the past two years, one lecture of this class is a presentation of the tutorials in lecture format. As a test of the validity of the simulation kernel used, the program can display a prediction of the reconstructed MRI image using established analytic formulae for spin echo images, gradient echo images, and RF spoiled images. Results: The reconstructed images from the simulated MR sequences qualitatively match the analytic predictions very well. Feedback from the residents on the utility of the lecture has been limited but positive. Conclusion: By avoiding the use of a quantum mechanical formalism, and using accurate animated images to illustrate concepts, the Desktop Magnet is a potentially useful aid to teaching MRI at a level suitable for radiology.
MO‐F‐134‐06: Innovative Approach Towards a Paperless Physics Residency Management System
Authors: Schubert L , Miften M
Published: July 2013

Purpose: Documentation of a resident's progress can be difficult to collect and disseminate, resulting in minimal utilization by current residents and faculty. The goal of this work is to use an electronic management system to enhance communication by providing centralized program information and real‐time tracking of resident progress. Methods: A web‐based residency management database (Medhub, Inc.) was adapted for use in a physics residency program. To distribute program information, announcements, policies, rotation objectives, and required readings were uploaded. The rotation schedule, machine assignments, and educational conference calendar with associated files and attendance records were added. To document resident progress, requirements for over 30 different clinical procedures were added, for which the resident logged the total number of procedures performed. Resident demographics and files documenting activities and achievements were added. An extensive evaluation system was created with over ten different electronic evaluation and report forms produced. Results: Results are shown for the initial eight months of program existence consisting of one resident and eight physics faculty. 130 documents were uploaded, and 100% of required documents were downloaded by the resident. 135 educational conferences and meetings were offered, of which the resident attended 121. The resident logged a total of 299 clinical procedures. A total of 11 evaluations were submitted. The resident reviewed 100% of respective evaluations within an average of 2.1 days. The resident submitted 19 status reports detailing weekly activities, 100% of which were reviewed by faculty within an average of 4.2 days. Conclusion: We have successfully incorporated a paperless, web‐based management system in a physics residency program. This system has played a central role in optimizing the training experience of the resident by providing a vehicle for easy documentation of resident activities, frequent monitoring and feedback of training progress, and widespread communication of program developments.