An evaluation of radiation exposure from portal films taken during definitive course of pediatric radiotherapy

PURPOSE: Recently, considerable attention has been directed toward computed tomography radiation doses (estimated 1 to 4 cGy) received by pediatric patients, because of the potential for increasing a pediatric patient's risk for developing a secondary malignancy. However, minimal attention has been given to the radiation exposure outside the treatment field resulting from the use of portal films to visualize surrounding anatomy. The objective of this study was to quantify the radiation dose from portal imaging delivered within and outside the radiation treatment field during a course of radiation therapy. METHODS AND MATERIALS: A retrospective review was conducted of the port film dose for 56 consecutive pediatric patients who underwent definitive radiation therapy between January 2001 and January 2002. Treatment locations were classified as brain, 27 patients; abdomen, 11 patients; extremities, 9 patients; pelvis, 6 patients; and thorax, 3 patients. Using the dose per monitor unit and total number of port films taken, the total port film dose for each patient was calculated. In addition, port film dose was quantified for 5 pediatric patients undergoing intensity modulated radiation therapy. RESULTS: The mean total port dose varied from a maximum of 46 cGy for brain to a minimum of 17 cGy for thorax. The mean total port dose as a percentage of prescribed dose was less than 1.25% for all locations in this study; however, most of the port dose is a result of the open-field dose from the double-exposure technique. CONCLUSIONS: Care should be exercised while exposing port films of pediatric patients to minimize both the number of films and corresponding radiation exposure without compromising the quality of treatment delivery. Specifically, the number of monitor units used to image regions outside the treatment field should be kept to a minimum, because such exposure could lead to an increased risk of development of secondary neoplasms.