bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐GG‐J‐165: Reconstruction of Missing Data On Kilovoltage and Megavoltage Cone‐Beam CT Images for Adaptive Radiation Therapy
Authors: Cheong K , Kang S , Hwang T , Bae H , Kim K , Kim S , Lee M , Oh D , Suh T 
Published: July 2008

Purpose: Kilovoltage (kV) or megavoltage (MV) cone‐beam CT (CBCT) technique become popular nowadays for patient setup verification and dose recalculation aiming image‐guided radiation therapy. In case of kV CBCT, field‐of‐view (FOV) is large enough to cover whole thoracic or pelvic region at detector off‐set mode while length of image set is limited and MV CBCT, vice versa. In this study, we dealt with missing data issue; compensation of missing part with kV CT images used for treatment planning. Method and Materials: First, obtained kV or MV CBCT images were registered with the planning kV CT images respectively. For kV CBCT, CT slices beyond the obtained volume were filled with planning CT data. For MV CBCT, overlapped regions in the kV CT images with the MV CBCT images after registration were substituted with the MV CBCT data. To reduce statistical discrepancies of pixel numbers between CBCT images and kV CT images and to minimize dose recalculation error, pixel number mapping and spatial filtering were employed. Varian Clinac iX and Siemens Primus linacs were used for CBCT image acquisition. Image registration and dose recalculation were implemented using Pinnacle3 ver 8.0d. Proposed algorithm were tested for chest and pelvic regions of a humanoid phantom and patients. Isodose comparison and gamma index were adopted as evaluation criteria. Results: Dose calculation result with the reconstructed CT image set agreed with calculation done with kV CT meaningfully within 2% on a phantom but error was up to 5% for clinical cases. Discrepancies were mainly due to anatomic changes and incomplete match of boundaries at the interface of two image set. Conclusion: The reconstruction algorithm showed a possibility of adaptive radiation therapy using CBCT images but image quality of CBCT data needs to be improved more.Research sponsored by MOST (Korean government).
SU‐GG‐P‐02: The Role of Medical Physicists in the Revised International Radiation Safety Standards
Authors: Borras C 
Published: July 2008

Purpose: The 1996 version of the International Basic Safety Standards for the Protection against Ionizing Radiation and for the Safety of Radiation Sources (BSS) [IAEA Safety series 115], used world‐wide as the basis for radiation protection legislation/regulations, is being revised by several cosponsoring international organizations to be consistent with the new ICRP Recommendations. This paper will focus on major changes regarding medical exposures and the role of medical physicists. Method and Materials: The current BSS draft is including, for the first time, the term “medical physicist”, replacing the expressions in the previous version: “expert” in “radiotherapy physics”, “radiodiagnostic physics” and/or “nuclear medicine physics”. This step is crucial towards the recognition by the International Labor Organization of medical physicists as health professionals, a pre‐requisite in many countries for hiring medical physicists in hospitals. The draft is also expanding the medical physicist's role in medical exposures, now a “principal party” together with the “radiological medical practitioner” and the “employer, owner and/or administrator”. Results: Medical physicists are responsible for imaging, calibration, dosimetry and quality assurance requirements. “For therapeutic uses of radiation”, these activities shall “be conducted by or under the supervision of a medical physicist with competence in the relevant field (radiation oncology or nuclear medicine)”. “For diagnostic and image‐guided interventional uses of radiation”, they shall be “fulfilled by, or under the oversight of or with the advice of, a medical physicist with competence in the relevant field”; the degree of involvement “determined by the omplexity of the particular use of radiation and the ensuing radiation risks”.Conclusion: The AAPM should play a prominent role in the BSS revision process through two mechanisms: the IOMP, the international organization representing medical physics globally, and the official delegation of the US, which, as any member state of the cosponsoring organizations, has to approve the standards.
SU‐GG‐T‐259: Dose Discrepancies in the Buildup Region and Their Impact On IMRT Field Dosimetry
Authors: Hsu S , Moran J , Chen Y , Kulasekere R , Roberson P 
Published: July 2008

Purpose: The accuracy of the buildup dose for radiotherapy treatment planning suffers from challenges in both measurement and calculation. This study was designed to improve the parameter fit in the contamination term of the convolution/superposition calculation algorithm based on more accurate measurements and to evaluate the impact of residual discrepancies on IMRT fields for normal and oblique incidences. Method and Materials: The percent depth and profile doses were measured in the buildup region in Solid Water using an Attix parallel plate chamber with over‐response correction factors and using Kodak XV film with dynamic calibration curves. The doses were measured at superficial depths ranging from 0.2 to 1.5 cm for 5×5, and 10×10 cm2 fields and 0°, 45°, and 70° incidences. Contamination term parameter fit preference was given to normal incidence. Two segmental head‐and‐neck IMRT fields were recalculated with the new fit parameters as a function of incident angle. Comparison indices (γ and dose‐gradient compensation) were used to quantify the agreement between measurements and calculations for the IMRT fields. Results: After parameter refit, the agreement between measurements and calculations were improved. Differences were still present for some dose profiles. The profile measurements showed larger field widths and sharper penumbras. The local deviations of percent depth dose (PDD) comparisons were within 2% and 5% for normal and oblique incidences, respectively. For IMRT fields, the incident angle did not greatly influence the agreement between calculation and measurement. Comparison indices were lower for shallower depths. Conclusion: Refitting the parameters in the contamination term using more accurate measured buildup doses improved the accuracy of calculations in the buildup region. Contamination term modifications may be required to better account for the influence of incident angle.Supported by NIHP01CA59827.
SU‐GG‐T‐279: Evaluation of a Novel 4D In‐Vivo Dosimeter
Authors: Cherpak A , Hallil A , Ding W , Cygler J 
Published: July 2008

Purpose: To present the latest quality assurance and characterization tests of the RADPOS 4‐D in vivo dosimetry system. Method and Materials: The dosimetric evaluation of this system included the measurement of in‐air dose profiles in , 6 MV, and 18 MV beams, and the investigation of the dependence of detector response on beam angle and field size. The stability and accuracy of the positioning component of the RADPOS detector was studied as well as the effect of metals and other commonly used materials on the RADPOS signal. Results: The dose profiles measured with the RADPOS detector and the diode agreed in within 0.41%, 0.53%, and 2.69% for the , 6 MV, and 18 MV beams, respectively. The angular response of the RADPOS probe over 360° was isotropic within 1.6% (1SD). Over a period of seventy minutes, the position of the RADPOS was read every 30 s and found stable within 0.37 mm. The system can also measure the displacement of a RADPOS detector with an accuracy of (0.45 ± 0.07) mm and (0.75 ± 0.07) mm for step sizes up to 50 mm and 200 mm respectively. The only materials that caused significant interference with the RADPOS signal were aluminum, brass, steel and lead. However, once the separation between the detector and the sample was >100 mm, the interference was minimal (the average deviation was less than 1.00 mm for all samples and sizes). Conclusion: Results of the preliminary tests indicate that the device can be used for in‐vivo dosimetry in and high‐energy beams from linear accelerators. Future work will involve technical improvements to the device, experiments in a 4D phantom and finally patient in‐vivo dosimetry.Acknowledgement: This project has been supported by a grant from HTX‐OCE‐IRAP and Best Medical.
SU‐GG‐T‐322: Determination of the Optimum Statistical Uncertainty and Voxel Size to Perform Monte Carlo Based Dose Calculation in the Context of Radiotherapy
Authors: Isambert A , Morrow S , Husson F , Salvat F , Lefkopoulos D 
Published: July 2008

Purpose: To evaluate the influence of statistical uncertainty and voxel size on target dose volume histograms (DVH) calculated with a Monte Carlo based treatment planning system (TPS). To determine the maximum uncertainty level and voxel size acceptable in the context of external beam radiotherapy. Method and Materials: First, the effect of increasing voxel sizes was investigated by studying the display of material and mass density matrices related to patient CT images. Then, the dose calculations were performed using the TPS ISOgray™ (Dosisoft) based on a fast Monte Carlo simulation code called PENFAST. The dose deposition due to electron beams was calculated for one breast plan. Intramammary node DVH were calculated first for increasing statistical uncertainty (1σ) levels of 0.7%, 1%, 1.3%, 2%, 3% and 6%, and secondly by increasing voxel sizes from 2×4×2 mm3 to 8×8×8 mm3. The same study was conducted for one medulloblastoma radiotherapy plan. Spinal cord DVH were calculated for uncertainty levels (1σ) of 1.3%, 1.7%, 2%, 3%, 5%, 12% and voxel sizes from 2.1×3×2.1 mm3 to 5.7×6×5.7 mm3. Results: The consequence of increasing voxel sizes is the blurring of material and mass density matrices by averaging values contained in neighbouring voxels which must be avoided at the interface between heterogeneities. The study of the DVH for both breast and medulloblastoma plans showed that they were not modified for statistical uncertainty levels (1σ) below 2% and voxel sizes below 4×4×4 mm3. Conclusion: This work indicates that, in clinical context, to save computation time while keeping the reliability of the target DVH for clinical use, Monte Carlo based dose calculation can be performed with uncertainty level (1σ) below 2% and voxel size which must not be greater than 4×4×4 mm3.This work was performed in the framework of the Project MAESTRO (IP CE503564) granted by the European Commission.
SU‐GG‐T‐350: X‐Ray Beam Model Benchmarks
Authors: Sawkey D , Schreiber E , Faddegon B 
Published: July 2008

Purpose: Determine fluence, differential in energy and angle, of Siemens Oncor 6/18 MV x‐ray beams, a necessary step towards an accurate, easily‐commissionable beam model for Monte Carlo treatment planning. Method and Materials: Dose to water is measured under various conditions, including: various field sizes including the largest; flattening filter present and removed; energy, steering tuned from nominal values to outside manufacturer acceptance criteria; target position moved along beam axis; filters. Energy is determined from depth dose curve measured with no target, flattening filter, or primary scattering foil (in electron mode, using x‐ray beam parameters). Spot size is determined using an alternating layer spot size camera. Spot position, beam angle, primary collimator and flattening filter positions are determined geometrically from profile scans vs. distance. Positions of treatment head elements, density of flattener, verified by direct measurement. Monte Carlo simulations with EGSnrc, taking asymmetry into account with beam angle and position, modified BEAMnrc code allowing lateral shifts of component modules, and modified ‘flatfilt’ component module allowing shift of flattening filter relative to primary collimator. Results: Comparison of electron PDD to Monte Carlo yields the beam energy to within positional accuracy and systematic uncertainty of Roos detector. Precision of geometrical measurements is sufficiently high to constrain inputs. Simulations agree to measurement within 1%/1 mm. Fluence is determined accurately over range of clinically acceptable beams. Conclusion: We determine, with reliable uncertainty estimates, input parameters for Monte Carlo simulation of Siemens 6/18 MV x‐ray beams. Close agreement is obtained to measured data over range of beam tuning. The method is applicable to other types of linacs and provides fluence benchmarks of clinical x‐ray beams for development of an accurate, easily‐commissioned beam model.Support from NIH R01 CA104777‐01A2.
SU‐GG‐T‐471: Potential Dosimetric Benefits of Four‐Dimensional Radiation Treatment Planning
Authors: Starkschall G , Britton K , McAleer M , Jeter M , Kaus M , Bzdusek K , Mohan R , Cox J 
Published: July 2008

Purpose: Four‐dimensional (4D) dose calculations involve computing radiation doses on each phase of a 4D computed tomography (CT) image data set, deforming the dose matrices based on the deformations needed to register each phase with a reference phase, and accumulating the doses on the reference phase based on these deformations. The purpose of the present work is to determine the extent of dosimetric differences between conventional three‐dimensional (3D) dose calculations and 4D dose calculations based on deformation of organ models. Method and Materials: 4D dose calculations were performed on a set of 15 patients with Stage III non‐small‐cell lung cancer using a model‐based deformable registration algorithm on a research version of a commercial radiation treatment planning system. Patients were planned using internal target volumes based on explicit motion of the clinical target volume in the 4D data set and setup margins based on clinical practice. Target volume coverage as well as doses to critical structures calculated using the 4D methodology were compared to those calculated using conventional 3D methodology. Results: For 11 of 15 patients, CTV coverage was comparable in the 3D and 4D calculations, whereas for 7 of 15 patients, PTV coverage was comparable. For the other patients, the 4D calculation indicated a sufficient difference in target volume coverage so that replanning should have been done. No correlations could be established between 3D and 4D differences and GTV size or extent of GTV motion. Negligible differences were observed between 3D and 4D dose‐volume relationships for normal anatomic structures. Conclusion: To ensure that target volumes are not underirradiated when respiratory motion may affect the dose distribution, 4D dose calculations should be performed.This work has been supported in part by a Sponsored Research Agreement with Philips Healthcare.
MO‐A‐350‐01: Out‐Of‐Field Dosimetry for Secondary Cancer Studies: Past Experience and Future Needs
Authors: Xu X George , Followill David 
Published: July 2008

Patients treated with ionizing radiation carry a risk of developing second cancers in their life times. Factors contributing to the recently renewed concern about this risk include improved cancer survival rates, younger patient pool, as well as emerging treatment modalities such as IMRT and proton therapy that can potentially prolong secondary exposures to healthy tissues or expose patients to neutrons. In the past 20 years, external beam treatment technologies have evolved significantly, and there is an overwhelming amount of data on both dosimetry and epidemiological studies. This lecture reviews historical studies related to the assessment of scatter and leakage radiation from classical radiation therapy, 3D‐Conformal x‐ray therapy, intensity‐modulated x‐ray therapy (IMRT and tomotherapy), and proton therapy. The concept of high‐, intermediate‐ and low‐dose regions outside the primary treatment field is introduced. Terms such as “secondary cancers,” “organ‐average equivalent dose,” “out‐of‐field,” and “peripheral dose” are reviewed. Comparison of secondary doses from different treatment modalities, make/energy of accelerator and for adult and pediatric treatments is also made. Concomitant dose from IGRT localization and verification procedures involving cone‐beam CT is briefly discussed. This is followed by a detailed review on methods of performing measurements in physical phantoms using different types of radiation detectors, as well as Monte Carlo simulations using gender‐ and age‐specific “virtual patient” computational models. Finally future needs on dosimetry and epidemiological studies are discussed.Educational Objectives:1. Understand the importance of secondary cancer risk in radiation treatment.2. Understand basic concepts in radiation dosimetry associated with secondary cancer studies.3. Understand practical methods of measurement and Monte Carlo simulation for the assessment of organ‐average equivalent doses for various treatment modalities.
MO‐A‐AUD A‐01: Review of AAPM Task Group Report No. 105
Authors: Chetty IJ , Rogers DWO 
Published: July 2008

A special class of Monte Carlo (MC)‐based dose calculation codes optimized for photon and electron beams in patient‐specific geometries has invigorated interest in the use of MC‐based dose calculations for radiotherapy treatment planning. In general, this class of “second generation” codes, including VMC++, XVMC, and DPM, among others, employ electron‐step algorithms that converge faster, i.e. fewer condensed‐history steps are required for the same precision versus “first‐generation” codes (such as EGS and MCNP). These advances, coupled with the use of sophisticated variance reduction techniques (e.g. directional bremsstrahlung splitting), have made it possible to perform MC‐based photon beam dose calculations, in some instances, of the entire linear accelerator treatment head and patient‐geometry, within minutes on a single processor. Consequently, several commercial vendors have released or are currently in the process of releasing MC algorithms for photon and/or electron beam treatment planning. With the impending availability of MC‐based dose calculation algorithms for routine clinical treatment planning, it is important that strategies and paradigms for clinical commissioning and implementation of these systems be formulated and discussed. We provide a review of AAPM Task Group Report No. 105 (Med. Phys. 34 (2007) 4818–4853), a document which outlines the important aspects of a MC‐based dose calculation algorithm, from the basic aspects of the use of the MC method for radiation transport to the application of this approach in routine clinical photon and electron beam treatment planning.Educational 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 review the methods used to improve the MC simulation efficiency.3. To briefly review the vendor transport codes currently used for clinical treatment planning.4. To describe the development of beam models for clinical treatment planning.5. 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.6. To discuss the issues associated with experimental verification of MC algorithms.7. To briefly review the potential clinical implications of MC calculated dose distributions.8. To provide example timing comparisons of the major vendor MC codes in the clinical setting.
MO‐A‐AUD C‐02: Clinical Implementation of Respiration Motion Correlated Imaging, Treatment Planning and Delivery
Authors: Vedam S 
Published: July 2008

Respiratory motion is a significant factor in determining a suitable planning target volume (PTV) that surrounds the demonstrable gross tumor volume (GTV) in the radiotherapy of mobile lesions. The advent of respiratory phase correlation (4D) and multi‐slice CT technology has enabled patient‐specific determination of both demonstrable tumor volume and its motion from a single acquisition. Management of such additional information during treatment planning and delivery however presents several challenges. Furthermore, guidelines for establishing clinical treatment planning and delivery protocols based on respiratory correlated imaging data differ from one institution to the other. The purpose of this presentation is to educate the community on the different respiratory correlated radiotherapy approaches currently available and compare the benefits and pitfalls in each case. Special focus will be on treatment planning, dose calculation and treatment delivery related issues.Educational Objectives:1. Understand the different respiratory correlated treatment planning and delivery approaches.2. Compare the benefits and pitfalls of each of the above approaches.3. Develop and establish respiratory correlated imaging, treatment planning and delivery appropriate to the available equipment.
MO‐A‐351‐01: Digital Mammography Update: Design and Characteristics of Current Systems
Authors: Kanal K 
Published: July 2008

Full Field Digital Mammography (FFDM) systems are fast becoming popular and replacing conventional film‐screen mammography systems. FFDM systems use a digital detector instead of screen‐film to capture the image of the breast. Several FFDM systems based on different digital detector design and materials are currently available. Some systems are characterized as direct conversion detectors and some are based on indirect conversion process. The digital detectors can be characterized by image quality metrics such as detector quantum efficiency (DQE) and modulation transfer function (MTF).In this lecture, the physics and technology of the digital detectors used in FFDM will be discussed as well as the advantages and applications arising due to the availability of these systems will be presented. The most recent commercially available systems will also be discussed.Educational Objectives:1. Understand the physics of digital detector technology.2. Understand the image quality metrics such as DQE and MTFRecognize that vendors use varying detector technology in FFDM systems.3. Appreciate the advantages and disadvantages of digital mammography systems.