Margriet Kwint

Intra anatomical changes during radiotherapy 79 4 decrease) and in 5 of these 8 patients, a baseline tumor shift was also seen. In total 7 tumor baseline shifts were scored in patients with a level red regression. Therefore, regression was not always the sole cause of level red. Level red was scored due to changes in atelectasis and tumor baseline shifts in 10 patients, which was a result of regression. The median time interval between planning-CT and start of the treatment (first CBCT) was 10 days (range 2-20 days). No significant correlation was found between this time interval and tumor progression (p=.270), level red change (p=.783) and new radiotherapy treatment plans (p=.744). Patients with stage III lung cancer (N=134) had a significantly higher chance of receiving a repeat treatment plan if the time interval between the planning-CT and start of treatment was more than one week (p=.040; correlation coefficient=.178). Tumor progression had a higher chance of a level red change (p=.001; correlation coefficient=.286) and development of this change in the first week (p=<.001; correlation coefficient=.431). There was also a higher chance of developing atelectasis (p=.028; correlation coefficient=.165) and tumor regression (p=.001; correlation coefficient=.241) observed in patients with tumor progression. The decision for a new treatment plan correlated significantly with tumor progression (p=.001), atelectasis (p=.006), tumor baseline shift (p=.005), an ITAC in the first week (p=.012) and level red change (p=<.001). There was no significant correlation found with patient characteristics (mentioned in Table 1), and ITACs. Table 2: Intra thoracic anatomical changes (N=210) in 128 patients ITACs N Atelectasis developing/increasing 28 (13%) Atelectasis resolving/decreasing 12 (6%) Tumor baseline shift 56 (27%) Infiltrative changes 6 (3%) Tumor regression 73 (35%) Tumor progression 22 (10%) Pleural effusion 13 (6%) Total 210 (100%)