Changes in the respiratory pattern during radiotherapy for cancer in the lung

Background and purpose: To quantify changes in patients' diaphragm motion pattern over the course of radiotherapy and to evaluate the implications of these changes for 4D radiotherapy. Patients and methods: From January 2004 to October 2004, 10 patients with lung malignancies treated at our department underwent weekly respiratory motion verification during the course of external beam radiation. An onboard kilovoltage imaging system was used to acquire fluoroscopy weekly for patients with lung neoplasms. The diaphragm position as a function of time was extracted automatically from the fluoroscopy and used to calculate the daily mean and daily SD of motion. The diaphragm position was related to both a bony reference point and machine isocenter. Changes in the daily mean and daily SD in relation to the reference (first day) daily mean and reference daily SD were measured. Results: The mean change in the daily mean was 0.32 mm±6.11 mm in relation to the bony reference point and 0.38 mm±6.28 mm in relation to isocenter. The mean change in the daily SD was 0.91 mm±1.81 mm. The mean systematic change in the daily mean was 4.97 mm, and the mean random change in the daily mean was 3.61 mm. Conclusions: Daily verification of 4D radiotherapy techniques to assess the necessity of online set-up correction may be required due to the large change in the mean diaphragm position observed for these patients. However, the variation of the daily SD was small for most patients. Adaptive adjustment of the margin may be necessary for those patients with larger variation of the daily SD.