Film Portal Imaging Research Articles

SU-E-T-155: RapidArc Delivery Performance Using EDR2 Film and EPID Measurement

Purpose: The Varian RapidArc is a system for volumetric modulated arc therapy (VMAT) technique. To obtain the accuracy,efficiency and reliability of the optimal conformal dose during treatment, RapidArc delivery depends on the controlling capabilities and synchronicity such as variable dose rate, variable gantry speed and dynamic multileaf collimator(DMLC). This study describes the development and implementation EDR2 film and electronic portal imaging device(EPID) during commissioning and quality assurance procedures for RapidArc radiotherapy delivery system. Methods: The tests were designed to evaluate RapidArc performance using EDR2 film and EPID tools. The accuracy of DMLC position during gantry rotation, the ability to vary and control the dose‐rate and gantry speed, the synchronization of variable DMLC speed and dose‐rate were examined. Results: The picket fence test of MLC in stationary gantry and RapidArc modes were implemented. EDR2 film and EPID showed good consistency for obtaining the patterns, and the minimal analysis of leaf accuracy test measured with film was better than 0.4mm with EPID. The synchronicity test, a fully dynamic field, was designed to uniformly irradiate seven parts of a square field using different combinations of gantry speed and dose rate. Comparing with a corresponding open field for the influence of beam flatness and asymmetry, both EDR2 film and EPID were found to yield good results, with a mean deviation of 0.24% vs 0.19%. During evaluating accurate correlated motion of DMLC speed, gantry speed and dose‐rates, the dose of four parts in a field showed good agreement, with a mean deviation of 0% vs 0.01%. The analysis of dose patterns was less than 2%. Conclusion: This study demonstrated that EDR2 film and EPID system can be used as reliable and efficient quality assurance tools for RapidArc delivery performance. Of course, the use of VMAT QA measurement with EPID increases the efficiency of routine QA.

Rotation of the Sacrum During Bellyboard Pelvic Radiotherapy

Patients with cervical, uterine, and rectal carcinomas are usually treated in the prone position using the bellyboard positioning device. Specific and uncomfortable prone position gives rise to uncertainties in the daily set-up of patients during the treatment. During investigation of translational movements, rotational movements of the pelvis are observed and investigated. The film portal imaging is used to discover patient positioning errors during treatment. We defined the rotational set-up errors by angle deviations of the sacrum. Thirty-six patients were included in the study; 15 patients were followed during the whole treatment and 21 during the first 5 consecutive treatment days. The image acquisitions were completed in 84%. Systematic and random positioning errors were analyzed in 725 images. Approximately half of the patients had adjusted to the bellyboard in the first few fractions, with sacrum angles remaining the same for the rest of the treatment. The other half had drifts of the sacrum angle during the whole treatment. The rotation of the sacrum during treatment ranged up to 14°, causing the usual set-up verification and correction procedure to result in errors up to 15 mm. Rotational movements of the patient pelvis during bellyboard pelvis radiotherapy can introduce considerable patient position error.

Implementing of the offline setup correction protocol in pelvic radiotherapy: safety margins and number of images

Background. Patient positioning errors in pelvic radiotherapy at Department of Oncology and Radiotherapy in Osijek are explored in order to establish the offline setup correction protocol and determine the safety margins. Material and methods. Film portal imaging is used during the whole treatment in order to find patient positioning errors. Eleven patients are included in the study and 420 images are analyzed. Setup errors are found by measuring distances between the center of the field and bony landmarks. Systematic and random errors are analyzed. Results. Safety margins that should be employed at our department are 11 mm, 13 mm and 14 mm in mediolateral, craniocaudal and anteroposterior direction, respectively. Time trend is found only in an aged, obese patient with a hip problem. No action level offline setup protocol was employed by taking and averaging first four images in mediolateral and craniocaudal and 5 images in anteroposterior direction. Conclusions. Since time trend is found only in a patient who was hard to position because of his age, obesity and the hip problem, we decided that such patients are to be positioned without a bellyboard and in supine position. Time trends are not found in all of the other patients so we employed the offline setup error protocol by averaging setup errors from the first few consecutive images. Safety margins that will ensure 90 % probability of depositing at least 95 % of the prescribed dose in the target are calculated. Safety margins and number of images that should be taken showed that the most inaccurate positioning was in the anteroposterior direction.

An observer study: comparison of computed radiography to electronic and film portal imaging

Introduction: Computed radiography (CR) is an imaging facility that does not require the use of hard copy film, digital images are obtained with a photostimulable phosphor plate, which replaces film, in a cassette. As the first UK radiotherapy site to trial CR, we are collecting data to assess the feasibility of using CR in radiotherapy treatment verification.Method: From 30 patients undergoing radical radiotherapy, 10 were consecutively accrued to three sites: pelvis, thorax and head and neck. Treatment verification images were taken using current protocols, but substituting standard imaging for CR images on one fraction. Four independent observers were used: two clinical oncologists and two therapy radiographers. Observers rated CR, electronic portal imaging (EPI) and enhanced contrast (EC) films of the three sites for both landmark visibility and ease of verification decision, using a numerical scoring system.Results: Ratings for visibility of landmarks and for verification decision were similar for CR and film/EPI images for most landmarks. However, CR images rated poorly compared to EC film in the head and neck region with landmarks such as thyroid cartilage and cricoid cartilage rating as ‘not clear’. CR images rated better than EPI images for both visibility and verification decision on the majority of landmarks in the pelvis region.Conclusion: Results gathered from a relatively small sample size have provided the following conclusion. The visibility of landmarks in CR images is comparable to that in film and EPI. Verification of treatment images based on CR is comparable to that of the current imaging media in the department.

Design of a graticule indicating central axis position for use with portal imaging

This technical note describes a port film graticule that can be used to determine the central axis of a portal image when used with megavoltage film or on-line electronic portal imaging. The construction and quality control of the portal film graticule are highlighted.

Electronic and film portal images: a comparison of landmark visibility and review accuracy

Purpose: To quantitatively compare a scanning liquid ion chamber electronic portal imaging device (SLIC-EPID) and an amorphous silicon flat panel (aSi) EPID with portal film in clinical applications using measures of landmark visibility and treatment review accuracy.Methods and Materials: Six radiation oncologists viewed 39 electronic portal images (EPIs) from the SLIC-EPID, 36 EPIs from the aSi-EPID, and portal films of each of these treatment fields. The physicians rated the clarity of anatomic landmarks in the portal images, and the scores were compared between EPID and film. Nine hundred portal image reviews were performed. EPID and film portal images were acquired with known setup errors in either phantom or cadaver treatments. Physicians identified the errors visually in portal films and with computerized analysis for EPID.Results: There were no statistically significant (p < 0.05) differences between film and SLIC-EPID in ratings of landmark clarity. Eleven of 12 landmarks were more visible in aSi-EPID than in film. Translational setup errors were identified with an average accuracy of 2.5 mm in film, compared to 1.5 mm with SLIC-EPID and 1.3 mm with aSi-EPID.Conclusions: Both EPIDs are clinically viable replacements for film, but aSi-EPID represents a significant advancement in image quality over film.

Apport de l’imagerie de haute énergie dans un service de radiothérapie et incorporation de celle-ci dans un système en réseau

To directly compare the clinical efficacy of electronic to film portal images and the advantages of comparing directly on the monitor the simulation image and the portal image. Material and methods. – This study was designed to compare clinical efficacy of electronic to film portal images acquired using a liquid matrix ion-chamber electronic portal imaging device (EPID) and a conventional film system. Two radiation oncologists served as observers and evaluated a total of 30 sets of images for three different treatment sites: lung, pelvis, and head/neck. Each set of images included a simulation image, a portal film, a video paper print of electronic portal images, and a video prints of electronic portal images. Four to six anatomical landmarks were selected from each treatment site. Each observer was asked to rate each landmark in terms of its clinical visibility and to rate the ease of making the pertinent verification decision in the corresponding electronic and film portal images with the aid of the simulation image. The time needed to obtain and analyse a conventional portal image and an EPID would be analysed for the radiotherapist and the medical technicians. Results. – Ratings for the visibility of landmarks and for the verification decision of treatment ports were similar for electronic and film images for most landmarks. However, vertebral bodies and several landmarks in the pelvis such as the acetabulum and pubic symphysis were more visible in the electronic portal images than in the portal film images. For the medical technicians, the EPID is more comfortable, and they do not need to develop any images. Conclusion. – The visibility of landmarks in electronic portal images is comparable to that in film portal images. Verification of treatment ports based only on electronic portal images acquired using an electronic portal imaging device is generally achievable. Thus the integration of the EPID and simulation image in a network provides more flexibility in the daily work of a medical radiotherapy team.

An observer study for direct comparison of clinical efficacy of electronic to film portal images

Purpose : To directly compare clinical efficacy of electronic to film portal images. Methods and Materials : An observer study was designed to compare clinical efficacy of electronic to film portal images acquired using a liquid matrix ion-chamber electronic portal imaging device and a conventional metal screen-film system. Both images were acquired simultaneously for each treatment port and the electronic portal images were printed on gray-level thermal paper. Four radiation oncologists served as observers and evaluated a total ot 44 sets of images for four different treatment sites: lung, pelvis, brain, and head/neck. Each set of images included a simulation image, a double-exposure portal film, and video paper prints of electronic portal images. Eight to nine anatomical landmarks were selected from each treatment site. Each observer was asked to rate each landmark in terms of its clinical visibility and to rate the ease of making the pertinent verification decision in the corresponding electronic and film portal images with the aid of the simulation image. Results: Resultings for the vesibility of landmarks and for the verification decision of treatment ports were similar for electronic and film images for most landmarks. However, vertebral bodies and several landmarks in the pelvis suchs as the acetabulum and pubic symphsis were more visible in the portal film images than in the electronic portal images. Conclusion: The visibility of landmarks in electronic portal images is comparable to that in film portal images. Verification of treatment ports based only on electronic portal images acquired using an electronic portal imaging device is generally achievable.

Clinical use of on-line portal imaging for daily patient treatment verification

Purpose : To determine the ease of use by clinical staff and reliability of an electronic portal imaging system and evaluate the potential to utilize on-line imaging to assess accuracy of daily patient treatment positioning in radiation therapy. Methods and Materials : A computer controlled fluorescent screen-mirror imaging system was used to acquire online portal images. A physician panel assessed on-line image quality relative to standard portal film. Clinical use of the imager was implemented through a protocol where images were obtained during the first six monitor units of external beam. The images were visually compared to a reference portal and patient setup was adjusted for errors exceeding 5 mm. Subsequent off-line analysis was utilized to give insight into the magnitude of clinical setup error in the visually accepted images. Results : Physician evaluation of on-line image quality with an initial 211 images found that 70% were comparable or superior to standard film portal images. Eighty percent of treatment fields fit completely within the on-line imaging area. Eight percent of on-line images were rejected due to poor image quality. Twelve percent of the daily treatment setups imaged required adjustment overall, but specific field types predictably required more frequent adjustment (pelvic and mantle fields). Off-line analysis of accepted images demonstrates that 18% of the final images had setup errors exceeding 5 mm. Conclusion : On-line imaging facilitated daily portal alignment and verification. Ease of use, almost instantaneous viewing and consistent ability to identify and locate anatomical landmarks imply the potential for on-line imaging to replace film based approaches. Retrospective analysis of daily images reveals that visual assessment of setup is not sufficient for eliminating localization errors. Further improvement is required with respect to detecting localization error and fully encompassing larger field sizes.