Skin Dose Modeling and Measurement in a High Field In-Line MRI-Linac System

The Australian MRI-Linac prototype radiotherapy system has been shown to generate significant entry skin or surface dose increases. This arises from electron contamination focusing toward the isocenter caused by 1 T MRI field being in-line with x-ray beam. aim of this study is present accurate Monte Carlo modeling these changes and compare them previous experimental measurements. Accurate will improve confidence in pathway forward treatment planning for clinical trials. A COMSOL Multiphysics model was used a 3D magnetic map be corresponding Geant4 simulations. simulations included source (6 MV Linac), multileaf collimators (MLCs), 30 cm × water phantom located its front at beam isocenter. Simulations were performed distance (SSD) 1,819 mm nominal sizes 2 cm, 6 10 cm. Central axis percentage depth (PDD) (or skin) doses 70 ?m calculated using high-resolution scoring voxels thickness. results compared data collected MO Skin ™ on system. provides great detail into how heavily confined focused central due presence field. concentration significantly increases up 320% size For 128% 217%, respectively, as absence simulation are generally good agreement, ±10%, previously same sizes. first time, detailed have confirmed sufficiently accurate. These provide solid framework estimating more clinically relevant plan scenarios that envisaged near future.