Margriet Kwint

Chapter 4 78 Infiltrative changes were rarely seen as ITACs during the radiotherapy course. This appeared in 5 patients (3%) and disappeared in 2 patients (1%) during treatment. This was observed in 4 patients in week 1 (57%), 2 patients in week 2 (29%) and in 1 patient in week 3 (14%). The urgency levels of these changes were; level red in 1 patient (14%), level orange (43%) in 3 patients and level yellow in 3 patients (43%). These level red and orange changes were all associated with regression. Pleural effusion was observed in 24 patients (14%). In 20 patients, pleural effusion appeared or increased and in 4 patients pleural effusion disappeared or decreased. These changes were mainly seen in week 1 (N=9,38%), thereafter in 6 (25%), 4 (17%), 3 (13%), and 2 (8%) patients in week 2,3,4 and 5 respectively. The levels corresponding with these changes were level red in 5 patients (21%), level orange in 14 patients (58%) and level yellow in 5 patients (21%). A tumor baseline shift is a visual difference in the tumor position between the planning-CT and CBCT after a bony anatomy match[26]. In 56 patients (32%), a tumor baseline shift was observed. These baseline shifts remained within the PTV (level orange, N=46, 82%) while in 10 patients (18%) the tumor had moved outside the PTV (level red). The onset of these tumor baseline shifts were mainly observed in the first week (48%). Some of these tumor baseline shifts were combined with regression (N=24), atelectasis (N=19) and/or progression (N=8) of the tumor, which in turn, themselves may cause a tumor baseline shift. Tumor progression was observed in 22 patients (12%). This occurred in week 1 for 21 patients (95%) and in 1 patient (5%) in week 2. This was level red in 9 patients (41%), level orange in 9 patients (41%) and level green in 4 patients (18%). In the 22 patients with tumor progression, subsequent tumor regression was seen in 16 patients at a later stage during the radiotherapy course. Tumor regression was observed in 73 patients (41%). The onset of the observed regression started in week 1 in 3 patients (2%) and in week 2 for a further 10 patients (14%). All of these patients were treated with CCRT, except for one patient who only received RT. Most regression cases was first observed in week 3 (N=27, 37%) and week 4 (N=23, 32%), while in 10 patients (14%) regression started in week 5. The levels corresponding to regression were mainly level yellow (N=35, 48%), thereafter level orange (N=26, 15%) and level red (N=12, 16%). Remarkably, in the 12 patients with a level red change, 8 patients had a change in atelectasis (4x increase and 4x