Papers by Dimitris Mihailidis
SU-F-T-305: Clinical Effects of Dosimetric Leaf Gap (DLG) Values Between Matched Varian Truebeam (TB) Linacs
Medical Physics, Jun 1, 2016
PURPOSE The dosimetric leaf gap (DLG) is an important parameter to be measured for dynamic beam d... more PURPOSE The dosimetric leaf gap (DLG) is an important parameter to be measured for dynamic beam delivery of modern linacs, like the Varian Truebeam (TB). The clinical effects of DLG-values on IMRT and/or VMAT commissioning of two "matched" TB linacs will be presented. METHODS AND MATERIALS The DLG values on two TB linacs were measured for all energy modalities (filtered and FFF-modes) as part of the dynamic delivery mode commissioning (IMRT and/or VMAT. After the standard beam data was modeled in eclipse treatment planning system (TPS) and validated, IMRT validation was performed based on TG1191 benchmark, IROC Head-Neck (H&N) phantom and sample of clinical cases, all measured on both linacs. Although there was a single-set of data entered in the TPS, a noticeable difference was observed for the DLG-values between the linacs. The TG119, IROC phantom and selected patient plans were furnished with DLG-values of TB1 for both linacs and the delivery was performed on both TB linacs for comparison. RESULTS The DLG values of TB1 was first used for both linacs to perform the testing comparisons. The QA comparison of TG119 plans revealed a great dependence of the results to the DLG-values used for the linac for all energy modalities studied, especially when moving from 3%/3mm to 2%/2mm γ-analysis. CONCLUSION The DLG-values have a definite influence on the dynamic dose, delivery that increases with the plan complexity. We recommend that the measured DLG-values are assigned to each of the "matched" linacs, even if a single set of beam data describes multiple linacs. The user should perform a detail test of the dynamic delivery of each linac based on end-to-end benchmark suites like TG119 and IROC phantoms.1Ezzel G., et al., "IMRT commissioning: Multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119." Med. Phys. 36:5359-5373 (2009). partly supported by CAMC Cancer Center and Alliance Oncology.
SU-E-I-42: Size-Specific Dose Estimates (SSDE) Modified for Lung Inhomogeneities: A Practical Approach
Medical Physics, Jun 1, 2013
PURPOSE his work recommends a method of estimating the patient effective diameter (ED) parameter ... more PURPOSE his work recommends a method of estimating the patient effective diameter (ED) parameter in the thoracic area in order to compute the Size-Specific Dose Estimates (SSDE) for both adult and pediatric patients, taking into account the lung inhomogeneities. METHODS A well-established method of estimating effective distance/depth (sometimes called radiological depth) in radiotherapy treatment planning for lung inhomogeneities, is recommended here. The method requires the use of an average relative electron density for the lung tissue of rho(Lung)=0.3 to be used so a corrected lateral (LAT) patient thickness and ED is determined. Based on the new ED the dose correction factor, as per TG-204, can be selected. This method was compared with the current recommendation by TG-204 and another correction method for lung inhomogeneities from the literature. RESULTS Improved estimation of patient ED that incorporates lung inhomogeneities was compared to that computed by a radiotherapy treatment planning system. The two methods agreed to within 5% for the cases studied. This difference is smaller than the 12-20% between the recommended method by TG-204 and another published correction method. In addition, the results showed that the effective AP thickness is not necessary to be accounted for by this approach. CONCLUSIONS A fast and easy method of computing patient effective LAT thickness and ED in order to estimate SSDE is based on the use of a relative electron density for the lung tissue. The more accurate LAT thickness and patient ED allow the selection of a dose correction factor out of the TG-204 tables that would take into account in some way the tissue heterogeneities in the thoracic area. This method may potentially be used in cone-beam CT image guided radiotherapy where estimation of patient imaging doses is required.
WE-A-BRE-01: Debate: To Measure or Not to Measure
Medical Physics, May 29, 2014
Recent studies have highlighted some of the limitations of patient-specific pre-treatment IMRT QA... more Recent studies have highlighted some of the limitations of patient-specific pre-treatment IMRT QA measurements with respect to assessing plan deliverability. Pre-treatment QA measurements are frequently performed with detectors in phantoms that do not involve any patient heterogeneities or with an EPID without a phantom. Other techniques have been developed where measurement results are used to recalculate the patient-specific dose volume histograms. Measurements continue to play a fundamental role in understanding the initial and continued performance of treatment planning and delivery systems. Less attention has been focused on the role of computational techniques in a QA program such as calculation with independent dose calculation algorithms or recalculation of the delivery with machine log files or EPID measurements. This session will explore the role of pre-treatment measurements compared to other methods such as computational and transit dosimetry techniques. Efficiency and practicality of the two approaches will also be presented and debated. The speakers will present a history of IMRT quality assurance and debate each other regarding which types of techniques are needed today and for future quality assurance. Examples will be shared of situations where overall quality needed to be assessed with calculation techniques in addition to measurements. Elements where measurements continue to be crucial such as for a thorough end-to-end test involving measurement will be discussed. Operational details that can reduce the gamma tool effectiveness and accuracy for patient-specific pre-treatment IMRT/VMAT QA will be described. Finally, a vision for the future of IMRT and VMAT plan QA will be discussed from a safety perspective. LEARNING OBJECTIVES 1. Understand the advantages and limitations of measurement and calculation approaches for pre-treatment measurements for IMRT and VMAT planning 2. Learn about the elements of a balanced quality assurance program involving modulated techniques 3. Learn how to use tools and techniques such as an end-to-end test to enhance your IMRT and VMAT QA program.
Journal of Applied Clinical Medical Physics, Aug 10, 2022
The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society who... more The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized. The following terms are used in the AAPM practice guidelines: Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. While must is the term to be used in the guidelines, if an entity that adopts the guideline has shall as the preferred term, the AAPM considers that must and shall have the same meaning.Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.
SU-E-T-201: Issues Encountered in Film-Based IMRT QA
Medical Physics, Jun 1, 2011
Purpose: To investigate characteristics of EDR2 film‐based IMRT QA with an eye towards moving fro... more Purpose: To investigate characteristics of EDR2 film‐based IMRT QA with an eye towards moving from isodose line comparisons to more objective gamma statistical analysis. Methods: IMRT QA was performed on Siemens Linacs using a traditional ion‐chamber‐and‐film phantom setup for step‐and‐shoot IMRT plans. All beams were delivered at their actual gantry angles and to the same film. Fiducial beams were used to fix film location for comparison with calculated dose. Dose was calculated on the Pinnacle planning system (8.0m). The EDR2 films were developed using a Kodak PP‐XOMAT film processor that has been remanufactured by Picker. Films were scanned with a VIDAR VXR‐16 Dosimetry Pro film digitizer using RIT 113 v5.2 software. Calibration films were created using crossed step wedges with doses calculated by Pinnacle. Gamma was calculated using the standard software settings of 3% / 4 mm. Results: For each QA film, the normalization doses (target to measured), mean gamma, and percentage of points failing the gamma limit (gamma < 1) were recorded. These percentages were found to be considerably higher in many cases than the often‐used limit of 5%. This problem was reduced when a new calibration film was used every week and developed together with the QA films; however, the mean fraction of points failing the gamma criterion was still 7%, with 45% of films failing. The mean gamma was 0.4. The product of (target dose) * (mean gamma) * (3%/100%) was relatively constant and averaged 2.3 cGy. Conclusions: Various factors were found to be relevant to the deviations observed, especially film calibration and the target dose (which sets the dose scale for gamma). In many cases, the problem was due to a poorly functioning film processor, resulting in films with streaks and artifacts; this problem was solved by service but recurs on occasion.
Springer eBooks, 2008
, except for brief excerpts in connection with reviews or scholarly analysis. Use in connection w... more , except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. While the advice and information in this book are believed to be true and accurate at the date of going to press, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein.
A Joint International Effort: Report on TG359
Physica Medica, Dec 1, 2022
40Ca (p, 2p) and medium modifications
Bulletin of the American Physical Society, Apr 1, 1993
The authors are investigating nuclear medium effects using exclusive (p, 2p) scattering data on 4... more The authors are investigating nuclear medium effects using exclusive (p, 2p) scattering data on 40Ca at 200 MeV and 300 MeV. These medium effects arise due to density dependent reduction in nucleon and meson masses in the nucleus. They have performed density dependent DWIA calculations based on a modified THREEDEE code, to get an estimate of medium modified observables such
Inelastic proton scattering from Pt isotopes and the interacting boson model
Physical review, Aug 1, 1991
... AM Mack, and M. Gazzaly School of Physics, University of Minnesota, Minneapolis, Minnesota 55... more ... AM Mack, and M. Gazzaly School of Physics, University of Minnesota, Minneapolis, Minnesota 55455 KW Jones Los Alamos National Laboratory, Los Alamos, New Mexico 87545 G. Pauletta and L. Santi University of ... [25] F. Todd Baker, A. Sethi, V. Penumetcha, GT Emery, WP ...
Polarized-proton elastic scattering from polarized ^{13}C
Physical Review Letters, 1990
The p--&amp;amp;amp;amp;amp;amp;amp;gt;+13C--&amp;amp;amp;amp;amp;amp;amp;gt; (polarized ... more The p--&amp;amp;amp;amp;amp;amp;amp;gt;+13C--&amp;amp;amp;amp;amp;amp;amp;gt; (polarized target) elastic-scattering spin observables A000n (target analyzing power) and A00nn (spin-correlation parameter) were determined at 497.5 MeV over the laboratory angular range 12°-30° with statistical uncertainties typically +/-(0.02-0.06). Results of distorted-wave Born approximation calculations, based on either the relativistic or the nonrelativistic impulse approximation, are in reasonable agreement with these new data.
Physical Review C, 2000
Double differential cross sections d 2 /dd⍀ and spin-flip probabilities S nn have been measured f... more Double differential cross sections d 2 /dd⍀ and spin-flip probabilities S nn have been measured for the 40 Ca(p ជ ,p ជ Ј) reaction at E p ϭ319 MeV. The angular range of the experiment was 10.5°р lab р23°and the range of excitation energies was 6рр47 MeV. These data and earlier data at smaller angles are compared to calculations employing random phase approximation nuclear structure and a distorted wave impulse approximation reaction model.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1993
Tr + and Tr-production cross sections for 800-MeV protons on C and Cu have been measured at labor... more Tr + and Tr-production cross sections for 800-MeV protons on C and Cu have been measured at laboratory angles of 0°, 3°, 5°, 7°, 10°, 15°, and 20°. Pions were analyzed using the High Resolution Proton Spectrometer (HRS) facility for momenta from 364 to 675 MeV/c. Particle identification was made utilizing a time-of-flight method. We estimate the total systematic and statistical error to be ± 15% for measurements at 0°and 3°and ± 10% at other angles. These data have been used to determine the optimum energy and pion production angle for injection into a proposed superconducting accelerator for pions. Protons are the main source of contamination for a Tr + beam. Proton-to-pion ratios are given for laboratory angles of 5°and larger .
Combining natural and artificial intelligence for robust automatic anatomy segmentation: Application in neck and thorax auto‐contouring
Medical Physics, Jul 27, 2022
BackgroundAutomatic segmentation of 3D objects in computed tomography (CT) is challenging. Curren... more BackgroundAutomatic segmentation of 3D objects in computed tomography (CT) is challenging. Current methods, based mainly on artificial intelligence (AI) and end‐to‐end deep learning (DL) networks, are weak in garnering high‐level anatomic information, which leads to compromised efficiency and robustness. This can be overcome by incorporating natural intelligence (NI) into AI methods via computational models of human anatomic knowledge.PurposeWe formulate a hybrid intelligence (HI) approach that integrates the complementary strengths of NI and AI for organ segmentation in CT images and illustrate performance in the application of radiation therapy (RT) planning via multisite clinical evaluation.MethodsThe system employs five modules: (i) body region recognition, which automatically trims a given image to a precisely defined target body region; (ii) NI‐based automatic anatomy recognition object recognition (AAR‐R), which performs object recognition in the trimmed image without DL and outputs a localized fuzzy model for each object; (iii) DL‐based recognition (DL‐R), which refines the coarse recognition results of AAR‐R and outputs a stack of 2D bounding boxes (BBs) for each object; (iv) model morphing (MM), which deforms the AAR‐R fuzzy model of each object guided by the BBs output by DL‐R; and (v) DL‐based delineation (DL‐D), which employs the object containment information provided by MM to delineate each object. NI from (ii), AI from (i), (iii), and (v), and their combination from (iv) facilitate the HI system.ResultsThe HI system was tested on 26 organs in neck and thorax body regions on CT images obtained prospectively from 464 patients in a study involving four RT centers. Data sets from one separate independent institution involving 125 patients were employed in training/model building for each of the two body regions, whereas 104 and 110 data sets from the 4 RT centers were utilized for testing on neck and thorax, respectively. In the testing data sets, 83% of the images had limitations such as streak artifacts, poor contrast, shape distortion, pathology, or implants. The contours output by the HI system were compared to contours drawn in clinical practice at the four RT centers by utilizing an independently established ground‐truth set of contours as reference. Three sets of measures were employed: accuracy via Dice coefficient (DC) and Hausdorff boundary distance (HD), subjective clinical acceptability via a blinded reader study, and efficiency by measuring human time saved in contouring by the HI system. Overall, the HI system achieved a mean DC of 0.78 and 0.87 and a mean HD of 2.22 and 4.53 mm for neck and thorax, respectively. It significantly outperformed clinical contouring in accuracy and saved overall 70% of human time over clinical contouring time, whereas acceptability scores varied significantly from site to site for both auto‐contours and clinically drawn contours.ConclusionsThe HI system is observed to behave like an expert human in robustness in the contouring task but vastly more efficiently. It seems to use NI help where image information alone will not suffice to decide, first for the correct localization of the object and then for the precise delineation of the boundary.
TH-C-218-01: How to Implement an IGRT and SBRT with Siemens Linacs and the Brainlab ExacTrac System
Medical Physics, Jun 1, 2012
Image guided stereotactic radiotherapy is a treatment modality that combines a variety of new tec... more Image guided stereotactic radiotherapy is a treatment modality that combines a variety of new technologies from imaging, to treatment planning and treatment delivery. It has been the primary method of treatment for several cranial and extra cranial tumors, where accurate patient immobilization and setup, tumor delineation, complex treatment planning and pre‐treatment imaging, are necessary for accurate treatment delivery. Typically, the coverage of the topic has been for a single‐technology, single‐vendor system, for example, MVCBCT by Siemens was presented, against kVCBCT by Elekta and Varian or MVCT by Tomotherapy, all for IG and/or SBRT purposes. The clinical reality many times is far from single‐vendor technology. Many medium and small size clinics upgrade their delivery systems (linacs) for IG and SBRT by add‐ons coming from multiple vendors. As an example, a Siemens linac with Brainlab Exactrac IG system and third party treatment planning system, all put together to provide IG and SBRT programs within the clinical environment. Users find themselves up against issues that are not necessarily addressed by a course that describes a closed single‐vendor IG/SBRT systems, like a Novalis TX with i‐plan or Tomotherapy or Cyberknife or others. This presentation will outline the main issues and give a step‐by‐step method for clinical implementation of all the components in order to achieve the final goal. Points of caution for the user, limitations and financial considerations will be part of the presentation. Learning objectives: 1. To gain insight into the issues that come up when technologies from various vendors are combined towards an integrated IG and/or SBRT program. 2. To understand the step‐by‐step method of integration of the involved technologies towards their clinical implementation. 3. To develop the understanding of the importance of benchmarking of IG and SBRT programs and usefulness of end‐to‐end testing. 4. To develop the ability to deal with the technical limitations of the technologies chosen to be implemented in the clinic.
EP-1734: AAPM TG-119 benchmarking of a novel jawless dual level MLC collimation system
Radiotherapy and Oncology, May 1, 2017
EP-1738: Performance of a new EPID panel and opportunities for a fast MV-CBCT acquisition
Radiotherapy and Oncology, May 1, 2017
Medical Physics, Jul 28, 2009
British Journal of Radiology, 1999
WE-C-BRB-07: Influence of MLC Width on Intensity Modulated Plans
Medical Physics, Jun 1, 2011
ABSTRACT
WE-G-218-01: Management of RT Patients with Implanted Cardiac Devices: Updated Recommendations?
Medical Physics, Jun 1, 2012
It has been long time since AAPM published TG-34 on cardiac pacemakers of older technology, which... more It has been long time since AAPM published TG-34 on cardiac pacemakers of older technology, which has been the standard document for clinical use, even today, for pacemakers (ICPs) and for defibrillators (ICDs), alike. Management of RT patients with recent technology cardiac devices has been widely published in literature without the provision of a new comprehensive and concise set of recommendations. The various effects of interaction of non-ionizing and ionizing radiations with those devices are crucial to be studied and accounted for during RT treatment deliveries. Thus, AAPM has formed the new TG-203 to work on this issue and provide recommendations to the clinical user for management of patients with cardiac devices when receiving RT. It has been numerous postings that we see in medical physics list server groups inquiring advices on dealing with these devices during patient imaging and radiation treatments. As treatment delivery technologies (IMRT, SBRT, dose escalations, proton beams, etc) and ICP/ICD technology advance, the need to address the management of patients with such devices receiving radiation treatment becomes increasingly important. ICDs offer the same functionality as ICPs, but they are also able to deliver a high-voltage shock to the heart, if needed. Finally, major discrepancies exist among manufacturer recommendations and wide variations exist among radiation therapy facilities regarding patient management precautions. LEARNING OBJECTIVES 1. Provide a review on sources of potential malfunctions of modern ICPs and ICDs, including malfunction mechanisms from high-LET radiations and transient effects attributed to medical imaging procedures for radiotherapy. 2. Provide a review on management of radiotherapy patients with cardiac implanted devices. 3. Utilize recently available data and computation methods of out-of-field/peripheral dose by scattered photons and secondary neutrons in order to assess cumulative doses on the ICPs and ICDs, during current treatment deliveries (IMRT, SBRT, proton beam therapy, etc). Risk of failure associated with these doses will be discussed. 4. Provide recommendations for management of radiotherapy patients with implanted cardiac devices including the initial patient evaluation stage, dosimetric evaluation to the ICP/ICD during treatment simulation, treatment planning and treatment delivery. Recommendations for the final evaluation of the integrity and functionality of the device after treatment completion will be assessed.
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Papers by Dimitris Mihailidis