A double exposed portal image comparison between electronic portal imaging hard copies and port films in radiation therapy treatment setup confirmation to determine its clinical application in a radiotherapy center

Purpose: At the William Buckland Radiotherapy Center (WBRC), held-only electronic portal image (EPI) hard copies are used for radiation treatment field verification for whale brain, breast, chest, spine, and large pelvic fields, as determined by a previous study. A subsequent research project, addressing the quality of double exposed EPI hard copies for sites where field only EPI was not considered adequate to determine field placement, has been undertaken. The double exposed EPI hard copies were compared to conventional double exposed port films for small pelvic, partial brain, and head and neck fields and for a miscellaneous group. Methods and Materials: All double exposed EPIs were captured during routine clinical procedures using liquid ion chamber cassettes. EPI hard copies were generated using a Visiplex multi-format camera. In sites where port film remained the preferred verification format, the port films were generated as per department protocol. In addition EPIs were collected specifically for this project. Four radiation oncologists performed the evaluation of EPI and port film images independently with a questionnaire completed at each stage of the evaluation process to assess the following: Adequacy of information in the image to assess held placement Adequacy of information for determining field placement correction Clinician's preferred choice of imaging for field placement assessment Results: The results indicate that double exposed EPI hard copies generally do contain sufficient information to permit evaluation of field placement and can replace conventional double exposed port films in a significant number of sites. These include the following: pelvis fields < 12 x 12 cm, partial brain fields, and a miscellaneous group. However for radical head and neck fields, the preferred verification image format remained port him due to the image hard copy size and improved contrast for this media. Thus in this department hard copy EPI is the preferred modality of field verification for all sites except radical head and neck treatments. This should result in an increase in efficiency of workload management and patient care. (C) 2001 Elsevier Science Inc.