Background and purpose: Changes in lung density due to atelectasis, pleural effusion and pneumonia/pneumonitis are observed in lung cancer patients. These changes may be an indication for adaptive radiotherapy in order to maintain target coverage and avoid increased risk of normal tissue complications.
Material and methods: CBCT scans of 163 patients were reviewed to score lung changes and find the incidence, the impact of geometric and dosimetric changes and the timing of appearance and disappearance of changes.
Results: 23% of the patients had changes in the lung related to pleural effusion, atelectasis or pneumonia/pneumonitis. In 9% of all patients, the appearance or disappearance of a change introduced a shift of the tumor or lymph nodes relative to the spine >5mm. Only major density changes affected the dose distribution, and 9% of all patients needed adaptive treatment planning due to density changes. In total, 12% of all patients did benefit from an adaptive treatment plan and in 85% of these patients, an atelectasis did change.
Conclusions: An adaptive strategy was indicated for 12% of the patients due to atelectasis, pleural effusion or pneumonia/pneumonitis. The predominant cause for adaptation was atelectasis. No systematic pattern in the appearance and disappearance of the changes were observed and hence weekly evaluation is preferable.
Keywords: Adaptive RT; Atelectasis; IGRT; NSCLC; SCLC.
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