SU‐E‐J‐35: Imaging Dose in Radiotherapy: An Institution‐Based Study

Abstract

Purpose: Image‐guided radiotherapy (IGRT) has become an essential component in comprehensive radiation therapy. However, this method of localization also carries with it increased radiation dose to the patient. As a center with multiple imaging modalities for IGRT, the goal of this research was to quantify the imaging dose received by patients in different treatment and IGRT setups throughout the course of treatment. Methods: At our institution, the IGRT modalities used are MV port films, kV port films, ExacTrac, and kV cone‐beam CT (CBCT). There are currently two different IGRT‐equipped linear accelerators in use at our facilities. Each type of machine was tested for the imaging modalities it utilized. The exposure values for a single image were compared to the AAPM TG‐75 values to see whether the values fell within the previously published data. The exposure values were then converted to dose and multiplied by the conventional fractionation scheme for the associated area of treatment in order to compare the imaging dose to the total treatment dose for that site. Results: The majority of exposures fell within the guidelines of the AAPM TG‐75 report. Imaging doses, as a percentage of treatment dose, were all less than 1%. Conclusion: This study helped to establish baseline values for periodic imaging quality assurance and provided support that imaging doses in our facilities are reasonable in terms of previously published data and the ALARA principle. The exposure values for our institution align well with those listed in TG‐75, and as long as repeat imaging is kept to a minimum, imaging doses will remain only a small percentage of total treatment dose.