Margriet Kwint

Prognostic value of volumetric changes during concurrent chemoradiation 89 5 (average setup error over 3 fractions <5.2mm in each direction), then weekly CBCTs were acquired for the remainder of the treatment fractions. If a correction was executed, the shrinking action protocol restarted with three fractions including CBCT verification. This resulted in a minimum of 7 CBCT’s per patient. Between January 2013 to December 2013 an online action protocol was used; where daily CBCT’s were acquired, and a daily set-up correction was performed immediately before the start of radiation. The CBCT’s were registered to the MidP-CT based on the vertebrae, carina and\or the primary tumor. The CBCT registrations were performed by at least two trained technicians. Follow-up and endpoint definition Primary endpoints were overall survival (OS), progression free survival (PFS) and local regional control (LRC). OS was calculated from the start of treatment until the last date of follow-up or death. PFS was calculated until the date of first progression (local, regional or distant) or last date of follow-up or death. LRC was calculated until the date when a recurrence occurred within the primary tumor or in the irradiated mediastinal lymph nodes region (outfield mediastinal recurrence was considered as progressive disease but not as local recurrence). Progressive disease was scored based on available clinical data or imaging report of tumor progression. After treatment, follow-up was performed every 3 months alternating between the pulmonologist and radiation oncologist. After 2 years, follow-up was performed every 6 months. Deformable image registration and contouring Since all CBCT’s of all patients consisted of very much data, manual delineation was not possible. Therefore, the volume change of the GTV of the primary tumor was defined with deformable image registration (DIR). DIR is a process of defining a map with deformations between two images in a nonlinear way, providing a voxel to voxel mapping between 2 scans. One image is considered the fixed image (CBCT), and the other one the moving image (MidP-CT) (26-28). DIR was performed with in-house developed software (Match42). First a clip box was defined encompassing the PTV, in which the DIR of the MidP-CT to the CBCT was performed using a B-splines algorithm (29). The GTV of the MidP-CT was deformed onto the CBCT using the deformation vector field from the DIR. The GTV of the CBCT was subsequently extracted.