Purpose: Daily kV imaging with matching on surgical clips is a standard component of the setup procedure for accelerated partial breast irradiation (APBI). Daily kV imaging contributes non-therapeutic radiation dose and may have long-term toxicity implications. Therefore, we evaluated kV imaging dose in comparison to both treatment dose and linear accelerator head leakage dose.
Methods: kV imaging doses were measured with a diagnostic ionization chamber for three Varian TrueBeam linear accelerators. The default Thorax Arms Up kV imaging protocol was used with acquisition parameters: 100kVp, 10mAs, and large body size. Three measurements were taken for each machine. To assess head leakage dose produced by a typical APBI plan, a test plan was created with X-jaw = 9.7cm, Y-jaw = 9.3cm, total MU = 443 (the mean values among 20 clinical APBI plans). Measurements were made at isocenter, 10cm, and 20cm to the right and inferior directions, respectively.
Results: Mean kV imaging doses at the isocenter were 0.1405cGy, 0.1155cGy, and 0.1198cGy for three independent machines. In comparison to the APBI treatment dose of 400cGy/fraction, these doses represent 0.02995%, 0.03513%, and 0.02888%. Mean head leakage doses were 2.738cGy at isocenter, 0.284cGy at 10cm-right, 0.173cGy at 20cm-right, 0.5468cGy at 10cm-inferior, and 0.2779cGy at 20cm-inferior.
Conclusion: Daily kV imaging contributes minutely to overall dose from a course of APBI, conferring less than one-tenth of the head leakage dose. This amount of non-therapeutic radiation exposure is not expected to have significant adverse clinical effects.
Funding Support, Disclosures, and Conflict of Interest: This research was funded in part by the NIH/NCI Cancer Center Support Grant P30 CA008748, The Lois Green Fund, and The Rose-Margulies Family Research Fund
Breast, X Rays, Radiation Risk