bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐FF‐A2‐04: An Accurate Mechanical Quality Assurance Procedure for a New High Performance Linac
Authors: Lovelock DM , Wang P , Kirov A , Lim S , LoSasso T
Published: August 2010

Purpose T o establish QA procedures for the mechanical systems of a new linac that has been developed to deliver radiation, using image‐guidance, to the target with improved spatial accuracy. The procedures are required to be able to detect mechanical errors of much less than 1 mm, be independent of the linac's own readouts and calibration procedures, and be fast enough for the physicist to perform on a monthly or more frequent schedule. Method and Materials In image guided delivery, mechanical properties that will affect the spatial accuracy with which dose is delivered include:

• radiation isocenter ‐imaging origin displacement,

• position errors of the jaws and MLC leaves,

• accuracy with which the patient support couch can respond to a change in position request.

To measure these quantities, we use the machine's kV, MV, and infra‐red imaging systems. We report on the techniques used, and the estimates of their accuracy. Results The preliminary estimate of the measurement uncertainty of the radiation isocenter — imaging origin offset is ± 0.3 mm. The observed offset is within the measurement error. The accuracy of the field size seen in the MV images is ± 0.2mm. Couch accuracy for shifts of up to 2 cm, the magnitudes expected using image guidance, was found to be within the measurement error. The ability to control the machine using scripts allows gantry and collimator positioning, couch positioning, beam delivery and imaging in all modes, to be sequenced and performed automatically. Thus the time required for a complete mechanical QA procedure is greatly shortened. Conclusion The imaging components of a new linac can be positioned with sufficient reproducibility and accuracy to allow their use in a mechanical QA program that can achieve the sub‐mm accuracy needed for this machine. Research supported by Varian Medical Systems
MO‐FF‐A2‐05: Dosimetry of Low Energy Electronic Brachytherapy X‐Ray Source
Authors: Kriminski S , Dorgu A , Gong J , Pavord D
Published: August 2010

Purpose: To determine dose delivered by electronic brachytherapy source of ∼50kVp. Current protocol developed by AAPM task group 61 requires in air measurements to “would be the surface.” This approach is not possible for the geometry used for brachytherapy treatment. The brachytherapy protocol by AAPM task group 43 requires knowledge of the dose rate constant not available for our source. Method and Materials: The X‐ray beam was generated by Intrabeam (Carl Zeiss Meditec, Jena, Germany) using 4 cm in diameter applicator. To minimize the effects of perturbation of photon fluence by the ion chamber and decrease the uncertainty in the position of point of measurement, small volume, 6.25 mm, thimble ion chamber was used (A1SL, Standard Imaging, Middletown, WI). The effect of fluence perturbation and stem were assumed to be negligible. Al Half value layer (HVL) of the beam was determined. Dose to air calibration factor Nk was measured in calibration laboratory (K&S Associates, Nashville, TN) for two HVL values and then interpolated for HVL value of the beam. Water measurements were performed. Effective point of measurement was determined analytically. Beam hardening, changing Nk and water to air ratio of mass energy absorption coefficient were neglected. Results: Al HVL was 0.91+−0.10 mm. In the clinically significant range our measurements and vendor's data agreed within expected error (1.5 mm or 4%). Main error contributors are position of the effective measurement point and uncertainty in Nk; the latter has two components: from calibration laboratory and from beam quality determination. For larger distances measured dose is 7–15% higher, than vendor's data. This is likely caused by the increase in Nk due to beam hardening.Conclusion: While measurement of dose was possible and our results agree with the data provided by vendor, further refinement of the method and use of alternative approach are necessary.
TU‐A‐BRA‐01: Non‐Coplanar Treatment of Hypofractionated Intracranial SRT with Tomotherapy
Authors: Murphy S , Yang C , Sheth N , Chen Y
Published: August 2010

Purpose: To report on a newly developed positional device and dosimetric results in Tomotherapy intracranial hypofractionated

Stereotactic Radiosurgery Treatment (SRT) with non‐coplanar beam characteristics. Methods: An in‐house developed positional device has been adapted to generate the non‐coplanar dosimetric effects in selected hypofractionated intracranial SRT patients. Three different head positions and CT data sets of same patients were scanned to provide the basic panning information. Contrast is also provided to delineate CTV. Dose constraints for PTV and OARs were scaled down according to the total composite dose (30Gy is split into 12Gy, 12Gy and 6Gy with 5 treatment fractions). The ability to change the rotational angles of the head for each treatment fraction would reduce the volume of normal brain tissue irradiated to lower clinically significant doses and increase the dose gradient surrounding the treatment area. Due to the TomoTherapy nature of helical co‐planar treatment, this methodology will generate a composite non‐coplanar delivery in order to reduce the low dose spread inside the PTV slices. Planning was performed with the three CT data sets and the composite dosimetry was evaluated to prove the clinical efficacy. Results and Discussion: Clinical dosimetry results indicate improved dosimetry coverage while minimizing the scattered dose to the volume slices of PTV. Composite dosimetry indicated the 50% isodose volume minus target volume was reduced by 9.4% for a small tumor (0.7cm3). For a medium tumor (2.5cm3), the volume was reduced by 8.9% and for a large tumor (4.2cm3), the volume was reduced by 13.0%. All those reduction ha shown by manipulating the various head treatment positions, we can achieve lower dose sparing inside the volume of PTV slices. Conclusions: Our developed device and composite dosimetric results have shown the clinical benefits to improve the dose gradient and minimize the low dose region inside the PTV CT slices.
TU‐A‐BRA‐02: Flattening Filter Free RapidArc Treatment with Trilogy MX Linear Accelerator
Authors: Hrbacek J , Lang S , Dossenbach T , Bocanek J , Klöck S
Published: August 2010

Objective: To evaluate optimization of flattening filter free (FFF) IMRT/RapidArc in Eclipse treatment planning system (Varian Medical Systems) and to verify performance of Trilogy MX linear accelerator (Varian Medical Systems) delivering these plans. Materials and Methods: A diversified group of clinical IMRT/RapidArc plans was optimized using two flattened beams (X6, X10) and two FFF beams (X6FFF, X10FFF) of Trilogy MX accelerator. In order to investigate the influence of high doserates available for FFF beams (up to 1400 MU/min for X6FFF and 2400 MU/min for X10FFF) RapidArc plans for FFF beams were optimized at different maximum doserates. Plans were mutually compared and verified using gafchromic dosimetry. Results: A comparable outcome in terms of achieved target coverage and organ sparing is observed for FFF and flattened beams. For RapidArc plans with standard fraction dose, the use of FFF beams can lead to better organ sparing as the optimizer benefits from larger doserate range. For hypofractionated RapidArc treatments, significant treatment time reduction (more than factor 4) can be achieved. For sliding window IMRT, doserate needs to be selected in proportion to fraction dose. Gafchromic film verification of the plans delivered by Trilogy MX shows an excellent agreement with the calculated dose distribution for all four energies. Large reduction of scattered radiation has been measured for FFF beam based plans. Conclusion: While IMRT and RapidArc plans based on flattened and FFF beams lead in general to comparable dose distributions, there is a significant reduction of scatter radiation and more time‐efficient delivery achieved for FFF beams.
TU‐A‐BRA‐04: Choreographing Couch and Collimator in Volumetric Modulated Arc Therapy
Authors: Yang Y , Zhang P , Happersett L , Xiong J , Yang J , Chan M , Mageras G
Published: August 2010

Purpose: The Trilogy® MX (Varian Medical Systems) supports simultaneous motion of the couch, gantry and collimator during volumetric modulated arc therapy (VMAT). This study investigates the feasibility and potential advantages of treating CNS tumors using VMAT with such capabilities. Method and Materials: To guide the selection of couch, gantry and collimator trajectories, a score function estimates the geometric overlap between tumor and organs at risk (OAR) for each couch/gantry combination. An initial set of beam trajectory candidates includes couch and gantry combinations, that correspond to minima found in a search of the overlap score map excluding zones of collision and long beam paths through the patient. This set is clustered into multiple continuous arcs subject to mechanical limitations. Following determination of couch/gantry trajectories, a principal component analysis finds the collimator angle at each beam orientation that minimizes residual tumor‐OAR overlap. A purpose‐developed VMAT optimization algorithm determines the optimal MLC position and MU for control points within each arc. A planning study of seven CNS patients compared trajectory VMAT with dynamic gantry, leaf, couch and collimator motion (Tra‐VMAT), standard non‐coplanar VMAT (Std‐VMAT, no couch/collimator motion within subarcs), and non‐coplanar IMRT plans. Results: Tra‐VMAT yields improved tumor dose conformality, lowered maximum dose to optic nerve, brainstem and chiasm, by 6%, 1.8%, 0.9%, 1.3%, respectively, relative to Std‐VMAT. Tra‐VMAT also yields higher PTV minimum dose, reduced maximum dose to chiasm, optic nerve, and cochlea, and reduced cochlea mean dose, by 4.4%, 1.5%, 6.4%, 10.2%, 8.9%, respectively, relative to IMRT. Tra‐VMAT average beam‐on time is comparable to Std‐VMAT, but significantly (42%) less compared to IMRT. Conclusion: Optimized couch/collimator trajectories can be integrated with VMAT. Trajectory VMAT, with improved mechanical flexibility, results in better dosimetric properties and improved treatment efficiency in the treatment of CNS tumors. Conflict of Interest: Sponsered by Varian Medical System
TU‐A‐204C‐01: New Technologies for Image Quality Improvement and Dose Reduction in CT
Authors: Mahesh M
Published: August 2010

From 1998 onwards there has been evolutionary advances in multiple‐row detector computed tomography (MDCT) technologies with demand for improved spatial and temporal resolution and three‐dimensional imaging. This has led to rapid race to develop MDCT scanners that yield the highest number of slices per CT gantry rotation (4‐16‐64‐128‐320). At the same time, the number of CT examinations performed in the United States has been growing at an annual rate of approximately 10% with nearly 68 million procedures performed in 2007 alone. The apparent increase in the number of CT procedures, protocols and the associated radiation dose and risks has drawn considerable attention. It appears that the so‐called ‘slice wars’ with regard to the number of slices provided per CT gantry rotation may be reaching a plateau and increasing concerns about radiation dose due to CT examinations are fueling the efforts to reduce radiation dose and leading to the beginning of the so‐called ‘dose wars’.

A number of radiation dose reduction strategies are been developed. At the same time, an effort to provide further improvement in image quality and image quantification at lower radiation dose is gaining ground. Dual energy CT (DECT) methods are slowly emerging from research and becoming a clinical reality. The dual x‐ray source (Dual‐source CT), fast tube voltage (kVp) switching, single x‐ray source dual detection (sandwich detector), photon counting detection and dual‐scanning approaches are few of the different approaches currently developed for performing DECT. In addition, new technologies are been developed to further improve image quality, enhance diagnostic information and at the same time yield low radiation dose.

There is an increasing demand for the medical physicists to assist clinicians in developing, reviewing and recommending changes to the clinical protocols. Therefore, it is critical for the medical physicists to become familiar with the new technologies such as dual‐energy CT and to understand strategies to reduce radiation doses in CT, image quantification methods and many other aspects.

In this lecture, new technologies that are currently developed, such as dual energy CT, image quantification method, radiation dose reducing strategies and others will be discussed.

Learning Objectives:

1. To become familiar with radiation dose reduction strategies in CT.

2. To understand various image quality improvements in CT.

3. To describe various technological approaches to perform dual‐energy CT (DECT).
TU‐A‐202‐01: Peak Skin Dose Reconstruction and TJC Sentinel Event
Authors: Anderson J , Arbique G , Guild J
Published: August 2010

In 2005, the Joint Commission established a new reviewable Sentinel Event tied to radiation exposure. Proper identification and investigation of Sentinel Events are critical issues for maintaining Joint Commission accreditation of a hospital, mandating that the physicist correctly approach this problem. The newly defined sentinel event treats both radiotherapy and fluoroscopy, but we consider only the issues arising from the specific inclusion of prolonged fluoroscopy procedures that result in high (> 1500 rads) cumulative skin doses. The specific details of what constitutes the fluoroscopic Sentinel Event, mechanisms for detecting potential events, how to investigate an event, and what happens in the course of reviewing a Sentinel Event are addressed.

The air kerma monitors required by the FDA on fluoroscopic equipment manufactured since 2006 are very useful tools for dose determination in these cases, but they do not provide a direct or complete answer. Case studies are reviewed that illustrate how to estimate doses both with and without cumulative air kerma readings.

Learning Objectives:

1. Review the definitions of the new Joint Commission Sentinel Event for fluoroscopic radiation exposure.

2. Identify monitoring policies and procedures to detect potential fluoroscopic Sentinel Events.

3. Discuss practical aspects and pitfalls of using air kerma monitors and technique values to calculate maximum skin doses.
TU‐B‐BRA‐02: X‐Ray Plus Electron Radiotherapy with an Extendable MLC
Authors: Ge Y , O'Shea T , Faddegon B
Published: August 2010

Purpose: To demonstrate precision treatments with mixed electron and x‐rays beam without moving the patient or room re‐entry, focusing on concomitant electron boost and Intensity Modulated Photon and Electron Radiotherapy (IMPERT), the latter to reduce integrated dose to reduce secondary malignancies Method and Materials: X‐ray Plus Electron Radiotherapy (XPERT) utilizes an extendable multi‐leaf collimator (MLC) and accurate dose calculation. A commercial add‐on x‐ray MLC was used for shaping 6–21 MeV electron fields at source‐to‐collimator distances of 71.6 cm and 81.6 cm, projecting a maximum field size, with 8.6 cm air gap, of 19×17 cm2. The electron part of the treatment was forward planned using Monte Carlo simulation, validated with measurement. The x‐ray part was planned on a commercial planning system. IMPERT treatment of stylized phantoms were planned to give insight into choice of electron energy and dose, and IMRT optimization parameters for different sizes, shapes and positions of targets and organs‐at‐risk (OAR). IMPERT plans of patients were compared to the IMRT plan used to treat the patient. Results: 20–80% penumbra with 8.6 cm gap increased from 1–2.3 cm with decreasing energy. MLC scatter was 4–9% of the dose with decreasing energy and had a modest effect on the penumbra. A plan consisting of strip fields of increasing energy showed depth modulation of 2.0–6.5 cm at 80% of the maximum dose. In the stylized cases and the pediatric patient, IMPERT achieved comparable target coverage to IMRT with x‐rays alone, with reduced energy deposition in OAR and in normal tissue. Conclusions: XPERT treatment with a commercial add‐on x‐ray MLC and Monte Carlo dose calculation is clinically feasible. The thick leaves added manageable scatter while essentially eliminating leakage. IMPERT can be used to reduce integrated dose without compromising OAR avoidance and target coverage. Sponsored in part by Nucletron and LinaTech.
TU‐B‐BRA‐05: Evaluation of the New Varian Trilogy MX Flattening Filter Free 6 MV and 10 MV Photon Beams
Authors: Poffenbarger B
Published: August 2010

Purpose: The Trilogy MX is a new linear accelerator designed by Varian Medical Systems to provide enhanced treatment delivery options. Among these is a flattening filter free (FFF) photon beam mode that can achieve unprecedented high dose rates of up to 3000MU/min. A preliminary investigation of the high intensity beam properties and treatment capabilities has been performed. Method and Materials: PDD, profile and Total Scatter Factor data were measured for the 6MV FFF and 10MV FFF beams and compared to non‐FFF data. The modeling of the FFF beam by the Eclipse planning system AAA algorithm was investigated for IMRT and RapidArc treatment modalities. Results: The FFF PDDs had a shallower dmax and steeper falloff beyond dmax. The FFF profiles appearing almost triangular in shape and exhibit an advantageous lower profile tail dose. The Total Scatter Factors varied less with field size for the FFF beams then for the filtered beams. Calculated and measured dose distributions agreed to within 2%/2mm for IMRT fields and 4%/2mm for RapidArc fields on average (10% dose threshold, 95%+ pass rate). Measured and calculate dose distribution profiles agreed well. Conclusion: A preliminary investigation shows that the Eclipse planning system (AAA algorithm) can accurately model the FFF beam. It is expected that the high dose rate beams will be particularly useful for radiosurgical treatments where large doses are delivered in a given session; for RapidArc treatments where the increased dose rate allows for faster gantry travel and more dose per gantry angle; and also for respiratory gated treatments because the high dose rate will reduce the treatment time and minimize the delivery interruptions. Conflict of Interest: Research sponsored by Varian.
TU‐B‐204B‐01: A Novel Off‐Axis Scanning Method for Improved CBCT FOV and Reconstruction Using Compressed Sensing
Authors: Li T , Li X , Yang Y , Heron D , Huq M.S.
Published: August 2010

Purpose: Current on‐board imaging systems commonly used by modern linear accelerators have a limited field of view (FOV) for a cone‐beam CT (CBCT) scan, which is typically less than 50 cm. Consequently, truncation artifacts often occur for large patients. The goal of this work is to investigate a novel method to increase the FOV for current on‐board CBCT systems. Method: When a large patient is scanned with CBCT, any region outside the FOV is only partially sampled within a short range of projection angles, and at any other angles no x‐ray beams may pass through that region. To increase the sampling rate for the region outside the FOV, we have designed a new source trajectory by shifting the center of rotation during a CBCT scan. This resulted in a reduced sampling rate at the central area and increased sampling rate at the edges. The tradeoff led to a more balanced sampling for an increased FOV. An iterative algorithm was also developed in order to reconstruct the CT image under the new sampling scheme using a compressed sensing technique. The method was validated by computer simulations for a Varian Trilogy CBCT system. A phantom created from CT images of a lung patient was used in the simulations. The isocenter movement followed a near‐ellipse trajectory while the x‐ray source/detector rotated around the object. Results: Under the clinical half‐fan settings with FOV of 45 cm, the truncation artifacts were tremendous for the simulated CBCT scanS. With the new scanning method, artifact‐free imageS can be obtained with the FOV as large as 75 cm. Conclusions: A novel CT scanning geometry was designed and tested, which can dramatically increase the FOV without significant compromise of the CBCT image quality.
TU‐B‐204B‐02: A Study of the Effect of Inline and Perpendicular Magnetic Fields on Beam Characteristics of Medical Linear Accelerator Electron Guns
Authors: Constantin D , Fahrig R , Keall P
Published: August 2010

Purpose: Integrated MRI‐linacs have the potential for real‐time volumetric imaging and targeting. Both inline (main MRI field parallel to linac beam) and perpendicular (main field orthogonal to linac beam) configurations are considered. The MRI fringe fields affect beam generation and transport, particularly the electron gun, where the electron energy is the lowest and thus magnetic fields have the largest effect. This work characterizes the electron gun behavior in external magnetic fields for inline and perpendicular configurations. Methods: Two electron guns were studied, the Litton L2087 and Varian VTC6364. Based on fringe field measurements of a 0.5T open bore MRI scanner (GE Signa SP), field strengths of 0–0.16T were computed with the finite elements method. Space charge beam simulations were performed for both inline and perpendicular configurations. Emitted current and beam deflection were determined. Results: For the inline configuration, the electron beam remains aligned with the gun axis. As the field strength increases, the emitted current has an initial plateau of constant value after which its value decreases to a minimum near 0.06T. The minimum of the emitted current is 26% and 21% from the zero field value for Litton and Varian guns respectively. Above 0.06T, the emitted current increases monotonically. For the perpendicular configuration, the electron beam is deflected from the gun axis even at small field strengths. The beam deflection increases with the magnetic field value, leading to a sharp decrease of the emitted current which completely vanishes at about 0.007T for Litton and 0.006T for Varian. Conclusion: For the inline configuration, there is always emitted current along the gun axis thus leading to the possibility to adapt the gun geometry for optimal beam generation compatible with the inline configuration. For the perpendicular configuration, magnetic shielding of the electron gun is required to avoid beam bending. Support: NIH T32‐CA09695
TU‐B‐204B‐03: Volumetric Ultrasound Guided Online Adaptive Partial Breast Irradiation
Authors: Gu X , Nelson T , Men C , Jia X , Liang Y , Jiang S
Published: August 2010

Purpose: To develop and innovative Volumetric Ultrasound guided Online Adaptive Partial Breast Irradiation system (VUSABI) for the improvement of the precision of the delivery of prescribed radiation dose to the target volume while sparing the adjunct normal breast tissues. Method and Materials: The VUSABI system consists of a volumetric breast ultrasound (VBUS) scanning system and an online adaptive replanning system. The VBUS system developed for early breast cancer detection is a non‐ionizing radiation, non‐compression, and operator‐free imaging system. It can provide real‐time, high quality volumetric breast images in pendulant position with low cost. A GPU‐based innovative supercomputing online adaptive replanning environment (SCORE) was developed for general‐purpose online adaptive radiotherapy (ART). The major components of SCORE system are: image registration, dose calculation, plan re‐optimization, and treatment plan user interface. We are integrating VBUS and SCORE into the whole VUSABI system by hardware integration and software adaptation. In this paper, we report on our progress of the VUSABI system development. Results: The performance of VBUS system was evaluated with both breast phantoms and patients. With the VBUS scanner, a 3D ultrasound breast image can be acquired in ∼18 sec and reconstructed in ∼ 5 sec. the overall performance are satisfactory. The initial PBI treatment plan was generated with Eclipse planning system. The major components of SCORE system were developed and evaluated with digital phantom data and clinical patient data. The whole replanning process can be accomplished in ∼10 second using a NVIDIA Tesla C1060 GPU platform. Conclusion: We are in the progress of developing VUSABI system. According to the initial results, the VUSABI system will be able to produce an optimized treatment plan based on a VBUS scan within 2 minutes when considering human intervention such as contour modification.
TU‐B‐204B‐05: Quantitative Evaluation and Optimization of an Algorithm for Non‐Rigidly Registering Serial CT Images to the Planning CT during Prostate‐Cancer Radiation Therapy
Authors: Wang Y , Sleeman W , Zhang C , Christensen G , Weiss E , Williamson J
Published: August 2010

Purpose: To identify the optimal parameters for a non‐rigid registration algorithm and to assess its accuracy for deformably registering serial prostate cancer CT images acquired during radiation therapy. Such registrations are needed to map organ segmentations from the planning CT onto daily replanning CTs and for cumulative dose reconstruction. Method and Material: Data sets were provided by the Netherlands Cancer Institute and consisted of multislice CT images of 17 prostate cancer patients each scanned 10–12 times during radiation therapy. One physician contoured bladder, rectum, and prostate on all images. The small‐deformation, inverse‐consistent linear‐elastic (SICLE) registration algorithm (TMI 20: 568, 2001) was used to estimate the deformation vector field (DVF) that simultaneously matched CT intensity (intensity matching, IM) and the three segmented regions (contour matching, or CM). IM was used to find DVFs mapping the first image (source) to each of the other subsequent images (target images) for all patients. IM + CM and CM was assessed for a pair of images for each of 10 patients. Endpoints included comparing deformed source contours to manually drawn target contours via the Dice similarity Index (DSI) and Pearson Correlation Coefficient (CC). CC and difference images (deformed source‐target) were used to quantify IM accuracy. Results: IM+CM vs. IM increased mean DSI from 0.78 to 0.95, 0.84 to 0.92, and 0.77 to 0.90 for rectum, prostate, and bladder, respectively, with CC improvements of 14%, 9%, 12%. Compared to CM, IM+CM produced better soft‐tissue registration outside contoured regions, with minimal IM loss relative to IM alone. Conclusion: IM registrations failed to produce acceptable registrations in about 1/3 of the cases, with accurate rectal deformation proving to be especially challenging. Simultaneously contour and intensity matching gave the best overall registration accuracy. Supported by Grant P01 CA 116602.
TU‐B‐202‐01: Revision of NRC's Safety Culture Policy Statement and Proposed 10 CFR Part 37, “Physical Security of Byproduct Material.”
Authors: Carpenter C
Published: August 2010

NRC is in the process of updating and expanding its 1989 policy statement on safety culture to include the full range of NRC regulated activities and to better address security issues. NRC published its draft safety culture policy statement in the Federal Register (74 FR 57525) November 6, 2009, and held a public work shop February 2010. One NRC objective is to develop a common definition of safety culture, and safety‐culture‐related language that can be used by the NRC, the Agreement States, licensees, and others involved with nuclear materials in the United States. NRC believes safety culture is important in ensuring safety, security, and the protection of the environment in the use of regulated materials and is a leading indicator of a licensee's performance. NRC has a responsibility to consider safety culture as part of its oversight responsibilities. Under the Medical Policy Statement, it is clear that for medical use licensees NRC has regulatory responsibility over not only the radiation safety of the public and radiation workers but also patients, when appropriate. NRC expects its licensees to have and maintain a safety‐conscious work environment in which employees and contractors are encouraged to raise safety concerns (including patient radiation safety concerns) and feel free to raise these concerns both to their own management and to the NRC without fear of retaliation. These concerns should be promptly reviewed, properly prioritized, appropriately resolved, and timely feedback provided to those raising the concerns. In NRC's inspection report for the Department of Veteran's Affairs multiple medical events involving prostate brachytherapy, one of the underling root causes and concerns was the lack of a positive safety culture environment to encourage medical physicists and others to raise concerns to the licensee.

NRC is developing a proposed rule, to among other things, add a new Title 10 Code of Federal Regulations Part 37, “Physical Security of Byproduct Material.” The proposed rule would include in the regulations the security requirements NRC implemented by Orders to certain licensees for the use of category 1 and category 2 quantities of radioactive material. These include provisions for the background investigation and access authorization program, provisions for physical protection during use of category 1 and category 2 quantities of radioactive material, and security provisions for the transport of category 1 and category 2 quantities of radioactive material. Medical physicists are affected by the Orders and proposed rule only if they use category 1 and category 2 quantities of radioactive material.

Learning Objectives:

1. Understand NRC's proposed expansion of its Safety Culture Policy.

2. Understand basic physical security provisions of NRC's proposed 10 CFR Part 37.
TU‐C‐BRA‐01: Memorial to Lester Skaggs
Authors: Oldham M.
Published: August 2010

Memorial to Lester Skaggs
TU‐C‐BRA‐04: A New Approach to Model‐Based Dose Calculations for Kilovoltage Beams
Authors: Pawlowski J , Coffey C , Ding G
Published: August 2010

Purpose: The additional radiation dose delivered to radiotherapy patients from repeated image guidance procedures is a growing concern. This study presents a new approach to model‐based dose calculation that overcomes the deficiencies of currently available model‐based algorithms in the kilovoltage regime. Method and Materials: Monte Carlo techniques were used to calculate the dose to patients resulting from kV‐CBCT scans for multiple scan sites including the head‐and‐neck, chest, and pelvis. Both dose‐to‐medium and dose‐to‐water were calculated using realistic simulated kV‐CBCT beams to find a correlation between the effective thickness of bone (dEB) traversed by an x‐ray beam to reach a voxel and the correction factor needed to correct the model‐based dose calculation. A program was written to facilitate the calculation of dEB in which the incident beam profiles and isocenter relative to a scanned patient were taken into account. Results: A strong correlation between dose correction factor and dEB was observed. A unique correction factor calibration curve as a function of dEB was derived and used to predict patient dose. Compared to gold standard Monte Carlo calculated dose distributions, the resulting mean dose error for each patient was less than 3% for bone and 2% for soft‐tissue. This was in contrast to model‐based calculations, which resulted in mean errors of up to −103% for bone and 8% for soft‐tissue. Conclusion: The derived correction factor as a function of effective bone thickness is capable of accurately calculating the dose to bone and soft‐tissue by making use of patient CT data and the incident kV‐CBCT beam information. The accuracy of this new approach is patient and scan site independent because it takes into account the spectral changes of the x‐ray beam. With the addition of a commissioned kV‐CBCT beam this new approach can facilitate inclusion of imaging dose in radiotherapy treatment planning.
TU‐C‐BRA‐05: Dose‐Volume Histogram Comparison between Deformable and Rigid Motion Registration in Four‐Dimensional Planning for Moving Targets
Authors: Zhang G , Feygelman V , Huang T , Stevens C , Li W , Dilling T
Published: August 2010

Purpose: Four‐dimensional (4D) dosimetry is necessary for accurate treatment planning of moving tumors. Full 4D dosimetry involves deformable image registration for 4D dose accumulation.. However, these algorithms are computationally intensive and may fail if significant artifacts are present in 4D CT images. An alternative 4D dose accumulation method is introduced as an approximation of full 4D dose calculations. Method and Materials: In our method, the deformable motion is approximated by the rigid motion. Deformable image registration is avoided in 4D dose calculation, reducing the computational time significantly. The motion magnitude and direction of each region of interest (ROI) is determined by the center‐of‐mass (COM) displacement. Dose matrices are registered using the COM motion vectors between respiratory phases. The dose‐volume histograms (DVH) generated based on the rigid motion 4D dose calculations, DVHrig, are compared with the ones generated by the full 4D dosimetry method, DVH4D, and the original 3D plans, DVH3D. A total of 6 lung cancer patients with various tumor sizes and motion ranges were randomly selected and studied retrospectively. Results: For target volumes and normal structures, DVHrig is always closer to DVH4D, the gold standard in this study, than DVH3D is. The differences depend on the volume, motion range and dose homogeneity of the original plans. For the target volumes, DVHrig often shows a better approximation to DVH4D than it does for the normal structures. Conclusion: Using rigid motion in 4D dose calculation eliminates the deformable image registration process. The DVH comparison shows that it is a good approximation to the full 4D dose calculations. This approximation not only makes an alternative 4D planning method possible when artifacts are significant in 4D CT images, but also reduces computation time significantly. This could potentially simplify practical clinical implementation of 4D treatment planning.
TU‐C‐BRA‐06: Analysis of Influential Factors of Dose Delivery to a Moving Tumor in Proton Radiotherapy Using Uniform Scanning Beam
Authors: Zhao Q , Wu H , Das I , Cheng C
Published: August 2010

Introduction: Tumor motion changes the dose to the tumor and organs‐at‐risk (OAR) from the treatment plan, which may be more serious in proton therapy, especially with a uniform scanning beam because of the energy stacking technique. This project aims to analyze the major factors on a uniform scanning beam. A 4D adaptive treatment planning strategy optimized with real‐time motion pattern is proposed. Materials and Methods: The CT images of a lung patient are used. The temporal beam delivery information for each energy layer is retrieved from the log file. Tumor motion tracked using fiducial markers at 30Hz is used in the simulation. The GTV to PTV margin and the smearing margin are 7 and 7.5mm. The prescribed dose is 4250 cGy. The 4D dose distribution is calculated based on dose volumes, contours, tumor respiratory motion and temporal beam delivery information under different starting respiratory phases, irregular breathing pattern and different dose rate. Results: Starting respiratory phase, dose rate and breathing pattern all have noticeable effects on the actual dose distribution delivered in uniform scanning proton beam. 95% of the GTV received only 3807 cGy for irregular motion vs 4032 cGy for regular motion. The dose are 4032, 3944, 4088 and 4107 cGy respectively for beam starting phase in the middle of end‐of‐exhale, inhale, at the beginning of exhale, and in the middle of exhale. The dose is 4032 and 3942 cGy respectively for dose rate of 348 and 284 MU/min. Conclusion: A 4D treatment planning system and real time external or internal tumor position monitor system are needed for treatment of moving target using uniform scanning proton beam. After each treatment fraction, the actual delivered dose should be calculated and the initial treatment plan may be adjusted to account for the motion so as to satisfy the predefined dose constraints.
TU‐C‐BRA‐07: Combined Use of Megavoltage Cone‐Beam CT and Monte Carlo for Accurate Dose Calculation in Presence of High‐Z Material
Authors: Hu W , Morin O , Pouliot J
Published: August 2010

Purpose: High atomic number (Z) materials complicate the use of kilo‐voltage CT in dose calculation. This work investigates the use of Megavoltage Cone‐Beam CT (MVCBCT) and a Monte Carlo (MC) dosecalculation engine to obtain a more realistic dose distribution for these clinical cases. Method and Materials: MVCBCT images of phantoms of different sizes (head and pelvis) were acquired. The phantoms were implanted with a combination of high‐Z materials (aluminum, titanium, lead, gold). A cone‐beam reconstruction software developed in‐house was used to obtain the voxel intensities represented as “float data” on 32 bits. Matlab programs were used to convert float values to integers (CT#) and to obtain CT#‐to‐electron density calibrations. The theoretical attenuation coefficient for each material was calculated using the published data in National Institute of Standards and Technology. MC simulations with EGSnrc/BEAMnrc code were compared to measurements and calculation in a commercial treatment planning system. Phantom and patient images were simulated with MCRTP. Results: A good linear fit (R‐squared value = 0.97) is found between the “float data” and theoretical attenuation coefficients for available high‐Z materials. With this fit function, the “float data” can be converted to the attenuation coefficient maps for generating the CT numbers. Obtained CT numbers show no intensity truncation. For a clinical hip prosthesis case, the maximal CBCT CT# is 10857 instead of 3071 in the commercial CT. Simulations on phantom demonstrated a better dosimetric accuracy using MVCBCT and MC (2–5%) than CT and a commercial TPS (∼14%). Conclusion: A more accurate method was developed to obtain dose distributions in presence of high Z materials. MVCBCT was able to accurately represent the material electron densities. Monte Carlo clearly outperformed a conventional planning system at simulating the dose distributions in presence of metallic objects. Conflict of Interest: Research supported by Siemens.
TU‐C‐204B‐06: Performance Evaluation of a Dual Cone‐Beam CT (Dual CBCT) System
Authors: Li H , Giles W , Roper J , Bowsher J , Yin F
Published: August 2010

Purpose: Very little information is available for clinical CBCT imaging using a dual‐detector system. This study assesses the performance of a recently developed bench‐top dual large‐flat‐panel detectors cone beam computed tomography (CBCT) system and to characterize the imaging quality of the system for image‐guided radiation therapy (IGRT). Method and Materials: A dual‐detector CBCT system with two large flat panels has been developed in our laboratory. Two systems were arranged orthogonally to each other on one optical bench. The designed source‐to‐detector distances and source‐to‐isocenter distances are 150 cm and 100 cm, respectively. The detectors are 40 × 30cm2 in size with 194μm‐pixels (Varian Paxscan 4030CB flat panels). A custom bow‐tie filter was designed for each subsystem. A tungsten wire phantom was scanned in order to evaluate the spatial resolution of the system. The Catphan phantom was also scanned to characterize noise, and Hounsfield unit (HU) linearity. The noise is evaluated by the homogenous slice and HU measurement is characterized by the sensitometric slice inside the Catphan. The performance of dual‐detector CBCT system is compared to that of single‐detector subsystem. Results: The spatial resolution of the dual‐detector CBCT system was almost the same as a single‐detector system and is mainly confined by the more inferior subsystem. No degradation in the noise performance of the dual CBCT system in comparison to a single CBCT system was observed. The measured signal‐to‐noise ratio was approximately 27.2 across one uniform slice. The reconstructed pixel values have demonstrated good linearity against known HU numbers. Linear fitting has shown an r2 value of 0.9985 for the sensitometric inserts. Conclusion: The dual‐detector CBCT system has comparable physical characteristics compared to a single‐detector CBCT system and therefore warrants further advanced application of the whole system. Conflict of Interest: This work is supported in part by Varian Medical Systems.
TU‐C‐204B‐09: A Novel Approach to Tracking Intrafraction Prostate Motion during Volumetric Modulated Arc Therapy with Tomosynthesis
Authors: Zhou J , Turian J , Lee E , Templeton A , Liao Y , Chu J
Published: August 2010

Purpose: To investigate a novel approach that uses independent kV onboard imager and tomosynthesis acquisition to detect intrafraction prostate movement/deformation during volumetric modulated arc therapy (VMAT). Method and Materials: Intrafraction motion poses a significant problem in VMAT treatment due to a substantially high dose rate during the treatment. To rapidly detect intrafraction motion, a tomosynthesis acquisition scheme accompanied by an onboard kV imager that can rotate independent of treatment gantry has been simulated and the performance in detecting motion has been investigated. The mutual information (MI) between the reference and the reconstructed tomosynthesis images in a ROI was used to assess intrafraction motion. Twenty two CBCT data acquired before each fraction for one prostate patient have been used to simulate intrafraction motion. The prostate motion was characterized by the displacement of the prostate mid‐posterior (MP) points in CBCT data and in the Sim CT. The correlation between the MI and MP displacement was calculated and a paired t‐test for the MI between group 1 (MP displacement ≤ 3 mm) and group 2 (MP displacement > 3 mm) was conducted. Results: The MI is sensitive to small shift/deformation and the correlation between the MI and MP displacement is 0.81, which suggests that MI can successfully predict motion. The MI of Group 2 is significantly lower than that of group 1 (P < 0.05), which suggests this method can reduce the margin by 3 mm and theoretically increase the dose to the prostate by 10 Gy. Conclusion: The proposed technique is a novel extension to the fixed kV system. It can detect intrafraction motion > 3mm and respond to the motion in less than 5s. It has a substantial potential in dealing with intrafraction motion for other sites and adaptive radiation therapy as well.
TU‐C‐204B‐10: Beam's‐Eye‐View MV Fluoroscopy during SBRT for Tumor Tracking and Treatment Verification
Authors: Christensen J , Kirichenko A , Colonias A , Gayou O
Published: August 2010

Purpose The radiotherapy treatment beam captured in megavoltage fluoroscopy (MVF) mode contains a record of tumor motion during treatment. This study's objectives were to use MVF to: 1) verify whether a tumor remains fully within the treatment beam; and 2) assess the reduction of tumor motion during the beam‐on period by respiratory gating. Method and Materials Electronic portal imaging was used to capture beam's‐eye ‐view fluoroscopic movies of target movement within the treatment beam during SBRT. Dose rate was 300 MU/min; no imaging dose beyond the treatment dose was required. Images were captured at 7–13 frames/sec. Three lung cancer and 2 liver cancer patients were studied over 5 fractions each; 2 were respiratory gated. For liver tumors, implanted gold fiducial markers and surgical clips provided surrogates of tumor motion. Custom image analysis and tracking software was written using MeVisLab/VTK/ITK. Deformable registration between image frames was used to warp tumor contours and compute the tumor center of mass and tumor borders relative to the ITV/PTV as a function of time. Results MVF tumor tracking yielded tumor range‐of‐motion measurements of 4–10 mm in the lung cancer patients, and liver fiducial tracking yielded motion measurements of 14mm and 11mm in the liver cancer patients. Large tumor motions due to infrequent large inspirations were reduced by respiratory gating with 75% inspiration threshold. Ungated motion was measured from pre‐treatment cone‐beam projection data. Gating reduced the tumor range of motion from 14mm to 9mm for the lung patient and from 17mm to 14mm for liver patient. Conclusions Motion measured via MV fluoroscopy during SBRT can be used to verify whether planned margins are adequate and evaluate the effectiveness of respiratory gating. Future work towards real ‐time processing could provide control signals for gating or dynamic multi ‐leaf collimators. Research sponsored by Siemens Corporation.
TU‐C‐201C‐01: NCI Initiatives on Translational Research: An Overview of Opportunities
Authors: Clarke L
Published: August 2010

NCI has initiated a number of new initiatives that are focused on the development of methods to develop and robustly validate current and next generation of imaging platforms. Over the last decade while there has been significant development of a range of imaging platforms and methods that are designed to address the cancer problem, such as screening of early cancer; cancer diagnosis, characterization, prediction and measurement of response to therapy, and image guided therapy including drug delivery systems. However as imaging methodologies move towards multi‐modality and molecular imaging platforms, coupled with recent advances in nano‐carriers and molecular probes, the ability to robustly validate these technologies, and perform multi‐parametric and quantitative measurements, is becoming increasingly complex. In addition the next generation of imaging technologies often involves imaging at resolution scales from the cellular to the organ level, where traditional pathological validation strategies are often limited. Thus the development and in particular the robust validation of these technologies, including clinical decision making, as required in the new era of personalized medicine, poses significant barriers for FDA approval, CMS reimbursement and ultimately their commercial dissemination as enabling tools for pre clinical and clinical research in cancer.

NCI therefore has initiated several new initiatives that specifically address support for translational research that includes a means to broadly engage the research and industry community to develop both public resources and consensus methods to validate these emerging imaging platforms. The new initiatives will be of interest to medical physicists and computer scientists involved in imaging research and clinical practice.

Learning Objective:

1. Understand the opportunity for research support for translational research at NCI

2. Understand the importance of development a consensus on how to validate emerging imaging technologies.