Use Of Electronic Portal Imaging Research Articles

Clinical use of electronic portal imaging to analyse tumor motion variation during a 3D-conformal prostate cancer radiotherapy using online target verification and implanted markers

Purpose: To evaluate the daily treatment setup variation and the interfraction and intrafraction prostate motion with portal imaging and implanted fiducial markers during irradiation with a 3D conformal radiotherapy for localized prostate cancer patients. Methods : By remote verification, shifts from isocenteric positioning and inter/intra-fraction prostate motion were investigated for 34 patients treated supine with escalated dose conformal radiotherapy. To limit the effect of inter-fraction prostate motion, patients were planned and treated with an empty rectum and a comfortably full bladder. Daily pre-therapy and treatment electronic portal images were obtained for anterior and lateral treatment fields according to an on-line target localization protocol using three gold markers. From these images, random and systematic set-up errors were measured by matching corresponding patients’ gold markers on reference digitally reconstructed radiographs (DRR). Superior-inferior, anterior-posterior and lateral motions were measured from the displacement of the gold markers implanted into the prostate before planning. A planning target volume (PTV) was derived to account for the measured prostate motion and field placement deviations. Results: Analysis of 1,278 portal images to determine changes in the radiation field during the course of treatment. From the data, random isocenter positioning deviations were 2.66 mm, 2.78 mm and 2.59 mm for vertical, lateral and longitudinal movements respectively. The systematic deviations were 3.15 mm, 3.09 mm and 2.52 mm for vertical, lateral and longitudinal movements respectively. From the verification process, it was realized that 44.7%, 42.8% and 31.4% of the vertical, lateral and longitudinal prostate migrations respectively needed correction/shift. Conclusion : Random set-up errors were small using real-time isocenter placement corrections. Inter-fraction prostate motion remained the largest source of treatment error, and observed motion was greatest at the laterals. In the absence of real-time pre-treatment imaging of the prostate position, using sequential portal films of implanted gold markers, portions of the PTV is missed and surrounding tissues not spared. This research improves quality assurance by confirming the prostate position within the treatment field over the course of therapy. ----------------------------- Cite this article as : Acquah GF, Gustavsson M, Doudoo CO, Agbeve RK, Schiestl B. Clinical use of electronic portal imaging to analyze tumor motion variation during a 3D-conformal prostate cancer radiotherapy using online target verification and implanted markers. Int J Cancer Ther Oncol 2014; 2 (4):02044. DOI : 10.14319/ijcto.0204.4

The use of Electronic Portal Imaging in Continuous Mode to Correlate External Marker Motion with Internal Tumor Motion during Respiratory-monitored Treatment

The use of Electronic Portal Imaging in Continuous Mode to Correlate External Marker Motion with Internal Tumor Motion during Respiratory-monitored Treatment

Accuracy and Reproducibility of Conformal Radiotherapy using Data from a Randomised Controlled Trial of Conformal Radiotherapy in Prostate Cancer (MRC RT01, ISRCTN47772397)

AimsThe MRC RT01 trial used conformal radiotherapy to the prostate, a method that reduces the volume of normal tissue treated by 40–50%. Because of the risk of geographical miss, the trial used portal imaging to examine whether treatment delivery was within the required accuracy. Material and methodsIn total, 843 patients were randomly assigned to receive 64Gy in 32 fractions over 6.5 weeks or 74Gy in 37 fractions over 7.5 weeks. Field displacements and corrections were recorded for all imaged fractions. Displacement trends and their association with time, disease and treatment set-up characteristics were examined using univariate and multivariate analyses. A Radiographer Trial Implementation Group (RTIG) was set up to inform the quality assurance process and to promote the development of best practice. ResultsTreatment isocentre positioning was within 5mm in every direction on 6238 (83%) of the 7535 fractions imaged. In total, 532 (81%) of 695 included patients had at least one ≥3mm displacement and 415 (63%) had at least one ≥5mm displacement. Univariate, multivariate and stepwise models of ≥5mm displacements showed an increased likelihood of displacement in weeks 1 and 2 with low melting point alloy (LMPA) blocks compared with multileaf collimators, film verification compared with electronic portal imaging (EPI) and increased number of fractions imaged. Except for LMPA, this was also seen for ≥5mm displacements in weeks 3–6. ConclusionsAccurate conformal treatment was delivered. The use of EPI was associated with increased reported accuracy. The RTIG was a crucial part of the quality assurance process.

Clinical Use of Electronic Portal Imaging

Accurate and routine target localization is necessary for successful outcome in radiation therapy treatments. Electronic portal imaging devices (EPIDs) provide an advanced tool with digital technology to improve target localization and maintain clinical efficiency. EPIDs are ubiquitous in the radiation therapy clinic, and they provide a powerful and flexible tool to collect and process data in a quantitative manner to improve treatment accuracy for virtually any treatment site. This manuscript provides an overview of the clinical implementation process for effective use of EPIDs. It continues with a review of correction strategies and finally highlights numerous examples of effective clinical application of EPID.

The use of electronic portal imaging to verify patient position during intensity-modulated radiotherapy delivered by the dynamic MLC technique

Purpose : The precise shape of the three-dimensional dose distributions created by intensity-modulated radiotherapy means that the verification of patient position and setup is crucial to the outcome of the treatment. In this paper, we investigate and compare the use of two different image calibration procedures that allow extraction of patient anatomy from measured electronic portal images of intensity-modulated treatment beams. Methods and Materials : Electronic portal images of the intensity-modulated treatment beam delivered using the dynamic multileaf collimator technique were acquired. The images were formed by measuring a series of frames or segments throughout the delivery of the beams. The frames were then summed to produce an integrated portal image of the delivered beam. Two different methods for calibrating the integrated image were investigated with the aim of removing the intensity modulations of the beam. The first involved a simple point-by-point division of the integrated image by a single calibration image of the intensity-modulated beam delivered to a homogeneous polymethyl methacrylate (PMMA) phantom. The second calibration method is known as the quadratic calibration method and required a series of calibration images of the intensity-modulated beam delivered to different thicknesses of homogeneous PMMA blocks. Measurements were made using two different detector systems: a Varian amorphous silicon flat-panel imager and a Theraview camera-based system. The methods were tested first using a contrast phantom before images were acquired of intensity-modulated radiotherapy treatment delivered to the prostate and pelvic nodes of cancer patients at the Royal Marsden Hospital. Results : The results indicate that the calibration methods can be used to remove the intensity modulations of the beam, making it possible to see the outlines of bony anatomy that could be used for patient position verification. This was shown for both posterior and lateral delivered fields. Conclusions : Very little difference between the two calibration methods was observed, so the simpler division method, requiring only the single extra calibration measurement and much simpler computation, was the favored method. This new method could provide a complementary tool to existing position verification methods, and it has the advantage that it is completely passive, requiring no further dose to the patient and using only the treatment fields.

39 Oral The use of electronic portal imaging to verify the patient set-up and delivery of intensity modulated radiotherapy

39 Oral The use of electronic portal imaging to verify the patient set-up and delivery of intensity modulated radiotherapy

Clinical use of electronic portal imaging: report of AAPM Radiation Therapy Committee Task Group 58.

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.

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.

Guide to clinical use of electronic portal imaging

Guide to clinical use of electronic portal imaging

Guide to clinical use of electronic portal imaging.

The Electronic Portal Imaging Device (EPID) provides localization quality images and computer‐aided analysis, which should in principal, replace portal film imaging. Modern EPIDs deliver superior image quality and an array of analysis tools that improve clinical decision making. It has been demonstrated that the EPID can be a powerful tool in the reduction of treatment setup errors and the quality assurance and verification of complex treatments. However, in many radiation therapy clinics EPID technology is not in routine clinical use. This low utilization suggests that the capability and potential of the technology alone do not guarantee its full adoption. This paper addresses basic considerations required to facilitate clinical implementation of the EPID technology and gives specific examples of successful implementations. © 2000 American College of Medical Physics. PACS number(s): 87.53.–j, 87.57.–s

186 ポータルイメージング(EPI)システムを用いた不整形照射野の照射野係数の推定

186 ポータルイメージング(EPI)システムを用いた不整形照射野の照射野係数の推定

Electronic portal imaging device detection of radioopaque markers for the evaluation of prostate position during megavoltage irradiation: A clinical study

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 protal 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. Conclusion : 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.

Use of electronic portal imaging to assess cardiac irradiation in breast radiotherapy

An audit was performed to assess the frequency of cardiac irradiation in patients receiving radiotherapy for left-sided breast cancer. Images from an ‘online’ electronic portal imaging device were reviewed in patients who were treated with a tangential pair of megavoltage fields. In 169 consecutive patients treated on a Philips SL25 6 MV linear accelerator equipped with an SRI 100 imaging device, the cardiac apex was included in the radiotherapy field in 15 patients (9%). The long term sequelae of such cardiac irradiation is uncertain. The results of this audit suggest that careful treatment technique and quality control with portal imaging can minimize unnecessary cardiac irradiation in the majority of patients.

Pictorial review: comparison of portal imaging and megavoltage verification films for conformal pelvic irradiation.

This study has evaluated the use of electronic portal imaging (EPI) as a replacement for megavoltage verification films in the treatment of conformal pelvic patients. The two methods of imaging have been compared in 40 patients. Several advantages of EPI were identified, including case of image acquisition. regular assessment of reproducibility of set-up and the possibility of on-line intervention when necessary. The findings suggest that EPI is a suitable replacement for films.