Marco Di Francesco

Medical image registration is the process of transforming different sets of image data into one coordinate system. Deformable image registration (DIR), as opposed to rigid image registration, allows for non-linear transformations such as stretching and shrinking.
DIR can be especially useful in assessing cumulative dose to healthy organs at risk between fractions and treatment courses.

The MUHC recently obtained the license to Varian’s deformable image registration algorithm, Velocity DIR. The goal of this project is to commission the use of Velocity DIR in the context of lung re-irradiation patients (patients who received at least two courses of treatment to the lung with significant time elapsed between courses). Currently, assessing cumulative dose to re-irradiation patients is challenging due to patient anatomical changes between treatment courses, like weight gain/loss. DIR can prove to be an effective method of doing so.

The commission protocol is closely following the procedure suggested by AAPM’s TG-132. Registration metrics such as the DICE coefficient and the determinant of the Jacobian matrix will be measured for digital 4DCT phantoms. Then, a retrospective analysis with the same metrics will be performed on 20 lung re-irradiation cancer patients treated at the MUHC to validate and assess the reliability of Velocity.