SU‐E‐J‐08: Assessing and Minimizing the Dose From KV Cone Beam CT to Pediatric Patients Undergoing Radiation Therapy

Abstract

Purpose: To assess the dose from kilovoltage cone beam CT to pediatric patients undergoing image‐guided radiation therapy and to compare the dose between standard and low dose protocols. Methods: Imaging dose to several pediatric patients undergoing image‐guided radiation therapy, and methods to reduce it, have been assessed using a treatment planning system (TPS) and Monte Carlo (MC). The imaging dose from an Elekta XVI kV CBCT system has been added to the treatment plans to calculate total dose to patients. The maximum dose and its location, dose to isocenter and various organs, and its correlation with patient size and body mass index (BMI), have been analyzed. The calculations have been performed using standard imaging protocols and low dose and/or modified ones. The TPS calculations have been supplemented with MC to assess the dose to bone and skin which cannot be accurately calculated using the TPS. Results: Employing a lower dose imaging technique for pediatric patients by: 1) Choosing a pre‐set imaging protocol using a lower technique that may be designated for a different anatomic region, i.e. using the Head and Neck protocol on a pelvic scan, or 2) Modifying a standard imaging protocol by reducing the mAs or number of frames, could substantially reduce the imaging dose. The image quality of the lower dose techniques has been found to be acceptable for patient position verification. Using a low dose or modified protocol could Result in an 18 fold decrease in the imaging dose. Conclusion: In order to most accurately track exposure, dose from daily kilovoltage CBCT can be added to pediatric patient treatment plans using previously commissioned kV CBCT beams in a treatment planning system and supplemented with Monte Carlo calculations. A technique for delivering lower dose is suggested and differences between standard and low dose protocols have been quantified.