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Ben Mijnheer - One of the best experts on this subject based on the ideXlab platform.

  • a literature review of Electronic Portal Imaging for radiotherapy dosimetry
    Radiotherapy and Oncology, 2008
    Co-Authors: Wouter Van Elmpt, Sebastiaan Nijsten, M Wendling, Philippe Lambin, L N Mcdermott, Ben Mijnheer
    Abstract:

    Electronic Portal Imaging devices (EPIDs) have been the preferred tools for verification of patient positioning for radiotherapy in recent decades. Since EPID images contain dose information, many groups have investigated their use for radiotherapy dose measurement. With the introduction of the amorphous-silicon EPIDs, the interest in EPID dosimetry has been accelerated because of the favourable characteristics such as fast image acquisition, high resolution, digital format, and potential for in vivo measurements and 3D dose verification. As a result, the number of publications dealing with EPID dosimetry has increased considerably over the past 15 years. The purpose of this paper was to review the information provided in these publications. Information available in the literature included dosimetric characteristics and calibration procedures of various types of EPIDs, strategies to use EPIDs for dose verification, clinical approaches to EPID dosimetry, ranging from point dose to full 3D dose distribution verification, and current clinical experience. Quality control of a linear accelerator, pre-treatment dose verification and in vivo dosimetry using EPIDs are now routinely used in a growing number of clinics. The use of EPIDs for dosimetry purposes has matured and is now a reliable and accurate dose verification method that can be used in a large number of situations. Methods to integrate 3D in vivo dosimetry and image-guided radiotherapy (IGRT) procedures, such as the use of kV or MV cone-beam CT, are under development. It has been shown that EPID dosimetry can play an integral role in the total chain of verification procedures that are implemented in a radiotherapy department. It provides a safety net for simple to advanced treatments, as well as a full account of the dose delivered. Despite these favourable characteristics and the vast range of publications on the subject, there is still a lack of commercially available solutions for EPID dosimetry. As strategies evolve and commercial products become available, EPID dosimetry has the potential to become an accurate and efficient means of large-scale patientspecific IMRT dose verification for any radiotherapy department. c 2008 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 88 (2008) 289–309.

  • A literature review of Electronic Portal Imaging for radiotherapy dosimetry
    Radiotherapy and Oncology, 2008
    Co-Authors: Wouter Van Elmpt, Leah Mcdermott, Sebastiaan Nijsten, M Wendling, Philippe Lambin, Ben Mijnheer
    Abstract:

    Electronic Portal Imaging devices (EPIDs) have been the preferred tools for verification of patient positioning for radiotherapy in recent decades. Since EPID images contain dose information, many groups have investigated their use for radiotherapy dose measurement. With the introduction of the amorphous-silicon EPIDs, the interest in EPID dosimetry has been accelerated because of the favourable characteristics such as fast image acquisition, high resolution, digital format, and potential for in vivo measurements and 3D dose verification. As a result, the number of publications dealing with EPID dosimetry has increased considerably over the past ∼15 years. The purpose of this paper was to review the information provided in these publications. Information available in the literature included dosimetric characteristics and calibration procedures of various types of EPIDs, strategies to use EPIDs for dose verification, clinical approaches to EPID dosimetry, ranging from point dose to full 3D dose distribution verification, and current clinical experience. Quality control of a linear accelerator, pre-treatment dose verification and in vivo dosimetry using EPIDs are now routinely used in a growing number of clinics. The use of EPIDs for dosimetry purposes has matured and is now a reliable and accurate dose verification method that can be used in a large number of situations. Methods to integrate 3D in vivo dosimetry and image-guided radiotherapy (IGRT) procedures, such as the use of kV or MV cone-beam CT, are under development. It has been shown that EPID dosimetry can play an integral role in the total chain of verification procedures that are implemented in a radiotherapy department. It provides a safety net for simple to advanced treatments, as well as a full account of the dose delivered. Despite these favourable characteristics and the vast range of publications on the subject, there is still a lack of commercially available solutions for EPID dosimetry. As strategies evolve and commercial products become available, EPID dosimetry has the potential to become an accurate and efficient means of large-scale patient-specific IMRT dose verification for any radiotherapy department. © 2008 Elsevier Ireland Ltd. All rights reserved.

  • dose response and ghosting effects of an amorphous silicon Electronic Portal Imaging device
    Medical Physics, 2003
    Co-Authors: L N Mcdermott, R J W Louwe, Janjakob Sonke, M Van Herk, Ben Mijnheer
    Abstract:

    The purpose of this study was to investigate the dose-response characteristics, including ghosting effects, of an amorphous silicon-based Electronic Portal Imaging device (a-Si EPID) under clinical conditions. EPID measurements were performed using one prototype and two commercial a-Si detectors on two linear accelerators: one with 4 and 6 MV and the other with 8 and 18 MV x-ray beams. First, the EPID signal and ionization chamber measurements in a mini-phantom were compared to determine the amount of buildup required for EPID dosimetry. Subsequently, EPID signal characteristics were studied as a function of dose per pulse, pulse repetition frequency (PRF) and total dose, as well as the effects of ghosting. There was an over-response of the EPID signal compared to the ionization chamber of up to 18%, with no additional buildup layer over an air gap range of 10 to 60 cm. The addition of a 2.5 mm thick copper plate sufficiently reduced this over-response to within 1% at clinically relevant patient-detector air gaps (> 40 cm). The response of the EPIDs varied by up to 8% over a large range of dose per pulse values, PRF values and number of monitor units. The EPID response showed an under-response at shorter beam times due to ghosting effects, which depended on the number of exposure frames for a fixed frame acquisition rate. With an appropriate build-up layer and corrections for dose per pulse, PRF and ghosting, the variation in the a-Si EPID response can be reduced to well within +/- 1%.

  • first clinical tests using a liquid filled Electronic Portal Imaging device and a convolution model for the verification of the midplane dose
    Radiotherapy and Oncology, 1998
    Co-Authors: Ronald Boellaard, M. Van Herk, Hans Uiterwaal, Ben Mijnheer
    Abstract:

    BACKGROUND AND PURPOSE: Recently, algorithms have been developed to derive the patient dose from Portal dose measurements using a liquid-filled Electronic Portal Imaging device. These algorithms have already been validated for several phantom geometries irradiated under clinical conditions. It is the aim of the present study to investigate the applicability of a liquid-filled Electronic Portal Imaging device in combination with these algorithms for two-dimensional midplane dose verification in clinical practice. MEASUREMENTS AND METHODS: Portal dose images were obtained during several patient treatments under routine clinical conditions. Measurements were performed to verify the midplane dose during radiotherapy of larynx cancer with 4 MV beams, breast and lung cancer with 8 MV beams and prostate cancer with both 8 and 18 MV beams. Midplane doses, determined from Portal dose measurements and analyzed with our algorithms, were compared with midplane doses calculated with our three-dimensional (3D) treatment planning system (TPS). RESULTS: For the larynx treatment the measured 2D midplane dose agreed within 2.0% with TPS calculations in most parts of the field. Larger differences were found in a small region below the skin due to the absence of electron equilibrium, which is not taken into account in our Portal dose analysis. For breast irradiations the measured midplane dose showed a homogeneous distribution in the AP direction in the axial plane, while high dose regions were observed in the cranial and caudal part of the breast. Portal dose measurements and TPS calculations agreed within 2.5% for most of the prostate and lung irradiations. For a few of the prostate and lung treatments larger local differences were found due to differences between the actual patient anatomy and the planning CT data, e.g. as a result of variable gas filling in the rectum and anatomical changes in the lung. CONCLUSIONS: Portal dose measurements with a liquid-filled Electronic Portal Imaging device can be used to determine the 2D midplane dose for various treatment sites in clinical practice. Portal in vivo dosimetry has proven to be important in detecting changes in the patient's anatomy and its influence on the dose delivery. It is concluded that Portal dosimetry is an excellent tool for accurate and independent verification of the dose in the entire (2D) midplane during patient treatment. However, a limited number of patients were involved in this study and the results are therefore preliminary. More research is needed to fully assess the clinical value of Portal dose measurements.

  • transmission dosimetry with a liquid filled Electronic Portal Imaging device
    International Journal of Radiation Oncology Biology Physics, 1996
    Co-Authors: Marion Essers, M. Van Herk, Hugo Lanson, Ronald Boellaard, Ben Mijnheer
    Abstract:

    PURPOSE: To assess the accuracy of transmission dose rate measurements for various phantom-detector geometries, performed with an Electronic Portal Imaging device (EPID) and to compare these transmission dose rate values with exit dose rate data. METHODS AND MATERIALS: Transmission dose rate values on the central beam axis and beam profiles were measured with an EPID consisting of a matrix of liquid-filled ionization chambers. These data were compared with transmission and exit dose rate values, obtained using air-filled ionization chambers for a number of field sizes, phantom thickness, and phantom-detector distances. Various homogeneous and inhomogeneous phantoms were applied. RESULTS: The increase in dose rate with field size is larger for the EPID than in air, due to the larger amount of side scatter in the EPID. The difference has been taken into account by a deconvolution of the EPID images. An additional build-up layer on top of the commercial device is needed to reach dose maximum at the liquid ionization chambers for photon beam energies higher than about 4 MV. The transmission off-axis ratios (OAR) determined with the EPID and in air agreed within 2% for all tested cases, after deconvolution of the EPID signal. The agreement between the EPID-and exit-OAR decreased with increasing phantom-detector distance and the presence of inhomogeneities. For a phantom-detector distance of about 10 cm, the EPID- and exit-OARs agree within 2.5%. The difference could be up to 8% for an air inhomogeneity and a phantom-detector distance of 30 cm. CONCLUSIONS: The difference between EPID measurements and measurements in air can be explained by side scatter effects in the EPID and lack of adequate buildup, and can easily be taken into account. The loss of scatter compared with the situation at the exit side of the phantom explains the difference between transmission and exit dose values. At short phantom-detector distances, good agreement exists between transmission and exit dose rate. This implies that at this distance, the EPID can be used for simple comparison with exit dose calculations during patient treatments. At larger distances, more sophisticated conversion methods are required.

M. Van Herk - One of the best experts on this subject based on the ideXlab platform.

  • a method for geometrical verification of dynamic intensity modulated radiotherapy using a scanning Electronic Portal Imaging device
    Medical Physics, 2002
    Co-Authors: Lennert S Ploeger, Kenneth G. A. Gilhuijs, Monique H P Smitsmans, M. Van Herk
    Abstract:

    In order to guarantee the safe delivery of dynamic intensity modulated radiotherapy (IMRT), verification of the leaf trajectories during the treatment is necessary. Our aim in this study is to develop a method for on-line verification of leaf trajectories using an Electronic Portal Imaging device with scanning read-out, independent of the multileaf collimator. Examples of such scanning imagers are Electronic Portal Imaging devices (EPIDs) based on liquid-filled ionization chambers and those based on amorphous silicon. Portal images were acquired continuously with a liquid-filled ionization chamber EPID during the delivery, together with the signal of treatment progress that is generated by the accelerator. For each Portal image, the prescribed leaf and diaphragm positions were computed from the dynamic prescription and the progress information. Motion distortion effects of the leaves are corrected based on the treatment progress that is recorded for each image row. The aperture formed by the prescribed leaves and diaphragms is used as the reference field edge, while the actual field edge is found using a maximum-gradient edge detector. The errors in leaf and diaphragm position are found from the deviations between the reference field edge and the detected field edge. Earlier measurements of the dynamic EPID response show that the accuracy of the detected field edge is better than 1 mm. To ensure that the verification is independent of inaccuracies in the acquired progress signal, the signal was checked with diode measurements beforehand. The method was tested on three different dynamic prescriptions. Using the described method, we correctly reproduced the distorted field edges. Verifying a single Portal image took 0.1 s on an 866 MHz personal computer. Two flaws in the control system of our experimental dynamic multileaf collimator were correctly revealed with our method. First, the errors in leaf position increase with leaf speed, indicating a delay of approximately 0.8 s in the control system. Second, the accuracy of the leaves and diaphragms depends on the direction of motion. In conclusion, the described verification method is suitable for detailed verification of leaf trajectories during dynamic IMRT.

  • clinical use of Electronic Portal Imaging report of aapm radiation therapy committee task group 58
    Medical Physics, 2001
    Co-Authors: Michael G Herman, M. Van Herk, Peter R T Munro, Shlomo Shalev, James M Balter, David A Jaffray, Kiarin P Mcgee, John W. Wong
    Abstract:

    AAPM Task Group 58 was created to provide materials to help the medical physicist and colleagues succeed in the clinical implementation of Electronic Portal Imaging devices (EPIDs) in radiation oncology. This complex technology has matured over the past decade and is capable of being integrated into routine practice. However, the difficulties encountered during the specification, installation, and implementation process can be overwhelming. TG58 was charged with providing sufficient information to allow the users to overcome these difficulties and put EPIDs into routine clinical practice. In answering the charge, this report provides; comprehensive information about the physics and technology of currently available EPID systems; a detailed discussion of the steps required for successful clinical implementation, based on accumulated experience; a review of software tools available and clinical use protocols to enhance EPID utilization; and specific quality assurance requirements for initial and continuing clinical use of the systems. Specific recommendations are summarized to assist the reader with successful implementation and continuing use of an EPID.

  • leaf position verification during dynamic beam delivery a comparison of three applications using Electronic Portal Imaging
    Medical Physics, 2000
    Co-Authors: M Partridge, M. Van Herk, P M Evans, Lennert S Ploeger, Geoffrey J Budgell, Hayley V James
    Abstract:

    The use of a dynamic multileaf collimator(MLC) to deliver intensity-modulated beams presents a problem for conventional verification techniques. The use of Electronic Portal Imaging to track MLC leaves during beam delivery has been shown to provide a solution to this problem. An experimental comparison of three different verification systems, each using a different Electronic Portal Imaging technology, is presented. Two of the systems presented are commercially available imagers with in-house modifications, with the third system being an in-house built experimental system. The random and systematic errors present in each of the verifications systems are measured and presented, together with the study of the effects of varying dose rate and leaf speed on verification system performance. The performance of the three systems is demonstrated to be very similar, with an overall accuracy in comparing measured and prescribed collimator trajectories of approximately ±1.0 mm . Systematic errors in the percentage delivered dose signal provided by the accelerator are significant and must be corrected for good performance of the current systems. It is demonstrated that, with suitable modifications, commercially available Portal Imaging systems can be used to verify dynamic MLC beam delivery.

  • first clinical tests using a liquid filled Electronic Portal Imaging device and a convolution model for the verification of the midplane dose
    Radiotherapy and Oncology, 1998
    Co-Authors: Ronald Boellaard, M. Van Herk, Hans Uiterwaal, Ben Mijnheer
    Abstract:

    BACKGROUND AND PURPOSE: Recently, algorithms have been developed to derive the patient dose from Portal dose measurements using a liquid-filled Electronic Portal Imaging device. These algorithms have already been validated for several phantom geometries irradiated under clinical conditions. It is the aim of the present study to investigate the applicability of a liquid-filled Electronic Portal Imaging device in combination with these algorithms for two-dimensional midplane dose verification in clinical practice. MEASUREMENTS AND METHODS: Portal dose images were obtained during several patient treatments under routine clinical conditions. Measurements were performed to verify the midplane dose during radiotherapy of larynx cancer with 4 MV beams, breast and lung cancer with 8 MV beams and prostate cancer with both 8 and 18 MV beams. Midplane doses, determined from Portal dose measurements and analyzed with our algorithms, were compared with midplane doses calculated with our three-dimensional (3D) treatment planning system (TPS). RESULTS: For the larynx treatment the measured 2D midplane dose agreed within 2.0% with TPS calculations in most parts of the field. Larger differences were found in a small region below the skin due to the absence of electron equilibrium, which is not taken into account in our Portal dose analysis. For breast irradiations the measured midplane dose showed a homogeneous distribution in the AP direction in the axial plane, while high dose regions were observed in the cranial and caudal part of the breast. Portal dose measurements and TPS calculations agreed within 2.5% for most of the prostate and lung irradiations. For a few of the prostate and lung treatments larger local differences were found due to differences between the actual patient anatomy and the planning CT data, e.g. as a result of variable gas filling in the rectum and anatomical changes in the lung. CONCLUSIONS: Portal dose measurements with a liquid-filled Electronic Portal Imaging device can be used to determine the 2D midplane dose for various treatment sites in clinical practice. Portal in vivo dosimetry has proven to be important in detecting changes in the patient's anatomy and its influence on the dose delivery. It is concluded that Portal dosimetry is an excellent tool for accurate and independent verification of the dose in the entire (2D) midplane during patient treatment. However, a limited number of patients were involved in this study and the results are therefore preliminary. More research is needed to fully assess the clinical value of Portal dose measurements.

  • transmission dosimetry with a liquid filled Electronic Portal Imaging device
    International Journal of Radiation Oncology Biology Physics, 1996
    Co-Authors: Marion Essers, M. Van Herk, Hugo Lanson, Ronald Boellaard, Ben Mijnheer
    Abstract:

    PURPOSE: To assess the accuracy of transmission dose rate measurements for various phantom-detector geometries, performed with an Electronic Portal Imaging device (EPID) and to compare these transmission dose rate values with exit dose rate data. METHODS AND MATERIALS: Transmission dose rate values on the central beam axis and beam profiles were measured with an EPID consisting of a matrix of liquid-filled ionization chambers. These data were compared with transmission and exit dose rate values, obtained using air-filled ionization chambers for a number of field sizes, phantom thickness, and phantom-detector distances. Various homogeneous and inhomogeneous phantoms were applied. RESULTS: The increase in dose rate with field size is larger for the EPID than in air, due to the larger amount of side scatter in the EPID. The difference has been taken into account by a deconvolution of the EPID images. An additional build-up layer on top of the commercial device is needed to reach dose maximum at the liquid ionization chambers for photon beam energies higher than about 4 MV. The transmission off-axis ratios (OAR) determined with the EPID and in air agreed within 2% for all tested cases, after deconvolution of the EPID signal. The agreement between the EPID-and exit-OAR decreased with increasing phantom-detector distance and the presence of inhomogeneities. For a phantom-detector distance of about 10 cm, the EPID- and exit-OARs agree within 2.5%. The difference could be up to 8% for an air inhomogeneity and a phantom-detector distance of 30 cm. CONCLUSIONS: The difference between EPID measurements and measurements in air can be explained by side scatter effects in the EPID and lack of adequate buildup, and can easily be taken into account. The loss of scatter compared with the situation at the exit side of the phantom explains the difference between transmission and exit dose values. At short phantom-detector distances, good agreement exists between transmission and exit dose rate. This implies that at this distance, the EPID can be used for simple comparison with exit dose calculations during patient treatments. At larger distances, more sophisticated conversion methods are required.

J Pouliot - One of the best experts on this subject based on the ideXlab platform.

  • daily Electronic Portal Imaging of implanted gold seed fiducials in patients undergoing radiotherapy after radical prostatectomy
    International Journal of Radiation Oncology Biology Physics, 2005
    Co-Authors: Daniel C Schiffner, Michele Aubin, J Pouliot, Katsuto Shinohara, Alexander Gottschalk, M Lometti, Joycelyn L Speight, Mack Roach
    Abstract:

    Purpose: The aim of this study was to measure interfraction prostate bed motion, setup error, and total positioning error in 10 consecutive patients undergoing postprostatectomy radiotherapy. Methods and Materials: Daily image-guided target localization and alignment using Electronic Portal Imaging of gold seed fiducials implanted into the prostate bed under transrectal ultrasound guidance was used in 10 patients undergoing adjuvant or salvage radiotherapy after prostatectomy. Prostate bed motion, setup error, and total positioning error were measured by analysis of gold seed fiducial location on the daily Electronic Portal images compared with the digitally reconstructed radiographs from the treatment-planning CT. Results: Mean (± standard deviation) prostate bed motion was 0.3 ± 0.9 mm, 0.4 ± 2.4 mm, and −1.1 ± 2.1 mm in the left–right (LR), superior–inferior (SI), and anterior–posterior (AP) axes, respectively. Mean set-up error was 0.1 ± 4.5 mm, 1.1 ± 3.9 mm, and −0.2 ± 5.1 mm in the LR, SI, and AP axes, respectively. Mean total positioning error was 0.2 ± 4.5 mm, 1.2 ± 5.1 mm, and −0.3 ± 4.5 mm in the LR, SI, and AP axes, respectively. Total positioning errors >5 mm occurred in 14.1%, 38.7%, and 28.2% of all fractions in the LR, SI, and AP axes, respectively. There was no significant migration of the gold marker seeds. Conclusions: This study validates the use of daily image-guided target localization and alignment using Electronic Portal Imaging of implanted gold seed fiducials as a valuable method to correct for interfraction target motion and to improve precision in the delivery of postprostatectomy radiotherapy.

  • daily Electronic Portal Imaging for morbidly obese men undergoing radiotherapy for localized prostate cancer
    International Journal of Radiation Oncology Biology Physics, 2004
    Co-Authors: L E Millender, Michele Aubin, J Pouliot, Katsuto Shinohara, Mack Roach
    Abstract:

    Abstract Purpose We summarize our experience with a series of morbidly obese men treated using daily online Portal Imaging and implanted gold markers to guide external beam radiation therapy (EBRT). Methods and materials Three consecutive morbidly obese men were treated with EBRT for localized prostate cancer. Daily Electronic Portal Imaging was used to verify patient position. The magnitude and direction of patient positioning error were documented for each fraction. Results The absolute magnitude of positioning error was greatest in the left-right direction with a mean of 11.4 mm/fraction (median, 8 mm; range, 0–42 mm). Mean error in the superior-inferior direction was also substantial at 7.2 mm/fraction (median, 5 mm; range, 0–47 mm). Anteroposterior error was the least problematic with a mean value of 2.6 mm/fraction (median, 2.5 mm; range, 0–8 mm). Conclusions Daily Electronic Portal Imaging combined with gold fiducial markers dramatically improves the precision of EBRT in the treatment of morbidly obese men with prostate cancer. Setup error rather than organ motion appears to be the dominant force in positioning error in obese men.

  • Electronic Portal Imaging device detection of radioopaque markers for the evaluation of prostate position during megavoltage irradiation a clinical study
    International Journal of Radiation Oncology Biology Physics, 1997
    Co-Authors: E Vigneault, J Pouliot, Jacques Laverdiere, Marc Dorion
    Abstract:

    PURPOSE: This study was designed to assess daily prostatic apex motion relative to pelvic bone structures during megavoltage irradiation. METHODS AND MATERIALS: Radioopaque markers were implanted under ultrasound guidance near the prostatic apex of 11 patients with localized prostatic carcinoma. Patients were subsequently treated with a four field-box technique at a beam energy of 23 MV. During treatment, on-line images were obtained with an Electronic Portal Imaging device (EPID). The marker was easily identified, even on unprocessed images, and the distance between the marker and a bony landmark was measured. Timelapse movies were also reviewed. After the completion of treatment, a transrectal ultrasound examination was performed in 8 of 11 patients, to verify the position of the marker. RESULTS: We acquired over 900 digital Portal images and analyzed posterioanterior and right lateral views. The quality of Portal images obtained with megavoltage irradiation was good. It was possible to evaluate pelvic bone structures even without image histogram equalization. Moreover, the radioopaque marker was easily visible on every online Portal image. The review of timelapse movies showed important interfraction motion of the marker while bone structures remained stable. We measured the position of the marker for each fraction. Marker displacements up to 1.6 cm were measured between 2 consecutive days of treatment. Important marker motions were predominantly in the posteroanterior and cephalocaudal directions. In eight patients, we verified the position of the marker relative to the prostatic apex with ultrasound at the end of the treatments. The marker remained in the trapezoid zone. Intratreatment images reviewed in two cases showed no-change in marker position. Our results, obtained during the treatment courses, indicate similar or larger prostate motions than previously observed in studies that used intertreatment x-ray films and CT images. Marker implantation under transrectal ultrasound was well tolerated. CONCLUSIONS: Radioopaque marker and the use of Electronic Portal Imaging give a direct evaluation of prostatic motion during radiation treatment. As suggested in previous studies the motions observed are predominantly in the posteroanterior and cephalocaudal directions. Therefore, prostate motion during treatment is important and must be considered especially when using conformal therapy.

  • the role of Electronic Portal Imaging in tangential breast irradiation a prospective study
    Radiotherapy and Oncology, 1995
    Co-Authors: A Lirette, J Pouliot, M Aubin, M Larochelle
    Abstract:

    Side effects due to irradiation of normal tissues and local failure can be associated with deviations in the patient positioning in radiation therapy. In particular, tangential breast irradiation may include normal lung tissue or even a small portion of the heart in the field. A prospective study was performed to assess the precision and the reproducibility of the tangential breast irradiation technique with the help of on-line Electronic Portal Imaging devices (EPID). The influence of respiration on the treatment set-up was evaluated. Also, a comparison was made with simulation films to study the degree of concordance with the intended treatment. Twenty patients with early breast cancer receiving post-operative radiotherapy were entered in the study. Geometrical parameters were measured from daily on-line Portal images taken for approximately 17 fractions of each tangential fields. Multiple images were also acquired (six per field) for six fractions for all patients, yielding a total of 2120 images including the simulator films. Random and systematic errors were obtained. Variations of the parameters between various fractions and within the same fraction were about 3 mm (1 SD) or less. Variation between simulation and treatment set-up was 4.3 mm or less. Large maximum deviations, reaching 22.9 mm, were observed in rare cases. This confirms the need to implement daily verification procedures and to correct deviations in the treatment set-up. The study has shown that EPID can help reaching a high accuracy in patient treatment.

M Islam - One of the best experts on this subject based on the ideXlab platform.

  • quality assurance of electron beams using a varian Electronic Portal Imaging device
    Physics in Medicine and Biology, 2013
    Co-Authors: Y Wang, Robert K Heaton, B Norrlinger, M Islam
    Abstract:

    The feasibility of utilizing an Electronic Portal Imaging device (EPID) for the quality assurance of electron beams was investigated. This work was conducted on a Varian 2100iX machine equipped with an amorphous silicon (aS1000) Portal imager. The linearity of the imager pixel response as a function of exposed dose was first confirmed. The short-term reproducibility of the EPID response to electron beams was verified. Low (6 MeV), medium (12 MeV) and high (20 MeV) energies were tested, each along with small (6???6?cm2), medium (10???10?cm2) and large (20???20?cm2) applicators. Acquired EPID images were analyzed using an in-house MATLAB code for radiation field size, penumbra, symmetry and flatness. Field sizes and penumbra values agreed with those from film dosimetry to within 1?mm. Field symmetry and flatness constancies were measured over a period of three weeks. The results indicate that EPID can be used for routine quality assurance of electron beams.

Shlomo Shalev - One of the best experts on this subject based on the ideXlab platform.

  • clinical use of Electronic Portal Imaging report of aapm radiation therapy committee task group 58
    Medical Physics, 2001
    Co-Authors: Michael G Herman, M. Van Herk, Peter R T Munro, Shlomo Shalev, James M Balter, David A Jaffray, Kiarin P Mcgee, John W. Wong
    Abstract:

    AAPM Task Group 58 was created to provide materials to help the medical physicist and colleagues succeed in the clinical implementation of Electronic Portal Imaging devices (EPIDs) in radiation oncology. This complex technology has matured over the past decade and is capable of being integrated into routine practice. However, the difficulties encountered during the specification, installation, and implementation process can be overwhelming. TG58 was charged with providing sufficient information to allow the users to overcome these difficulties and put EPIDs into routine clinical practice. In answering the charge, this report provides; comprehensive information about the physics and technology of currently available EPID systems; a detailed discussion of the steps required for successful clinical implementation, based on accumulated experience; a review of software tools available and clinical use protocols to enhance EPID utilization; and specific quality assurance requirements for initial and continuing clinical use of the systems. Specific recommendations are summarized to assist the reader with successful implementation and continuing use of an EPID.

  • a quality control test for Electronic Portal Imaging devices
    Medical Physics, 1996
    Co-Authors: R Rajapakshe, K Luchka, Shlomo Shalev
    Abstract:

    A quality control (QC) test suitable for routine daily use has been developed for video based Electronic Portal Imaging devices. It provides an objective and quantitative test for acceptable image quality on the basis of the high contrastspatial resolution and the contrast‐to‐noise ratio (CNR). The test uses a phantom consisting of five sets of high‐contrast rectangular bar patterns with spatial frequencies of 0.1, 0.2, 0.25, 0.4, and 0.75 lp/mm. Data obtained during a one month calibration period were used to determine a critical frequency f c for the relative square wave modulation transfer function and a critical contrast‐to‐noise ratio (CNR c ). Subsequent measurements indicating significant deviations from these critical values result in warning messages to the operator indicating potential problems in system performance. Measurements over a period of two years show that the QC test provides a sensitive indication of Imaging performance.

  • Assessing radiation and light field congruence with a video based Electronic Portal Imaging device
    Medical Physics, 1996
    Co-Authors: K. Luchka, Shlomo Shalev, D. Chen, Georgi Gluhchev, R Rajapakshe
    Abstract:

    Projected light fields are used on treatment simulators and teletherapy treatment units to delineate the size and position of the radiation beam. Any discrepancy between these fields will lead to a systematic field placement error, with possibly serious implications with regard to the accuracy of the delivered dose distribution in the patient. Conventionally, film has been used for regular quality control tests of light and radiation field congruence, but this is a time consuming method and is not suitable for daily checks. A new method is described that uses a specially designed test phantom, a video-based Electronic Portal Imaging device, and a personal computer to test for radiation and light field congruence on treatment accelerators. This method consists of aligning the test phantom in the light field of a treatment linac and acquiring an Electronic Portal image. A computer program then automatically analyzes the image and determines the degree of congruence between the two fields. The final result of the test is a go, warning, or no go decision depending on the extent of misalignment between the light and radiation fields. Two algorithms were tested for reproducibility (