Background: In three-dimensional (3-D) precision high-dose radiation therapy of lung tumors, the exact definition of the planning target volume (PTV) is indispensable. Therefore, the feasibility of a 3-D determination of respiratory lung tumor movements by the use of a multislice CT scanner was investigated.
Patients and methods: The respiratory motion of 21 lung tumors in 20 consecutively treated patients was examined. An abdominal pressure device for the reduction of respiratory movement was used in 14 patients. Two regions of the tumor were each scanned repeatedly at the same table position, showing four simultaneously acquired slices for each cycle. Stereotactic coordinates were determined for one anatomic reference point in each tumor region (Figure 1). The 3-D differences of these coordinates between the sequentially obtained cycles were assessed (Figure 2), and a correlation with the tumor localization was performed.
Results: In the craniocaudal (Z-) direction the mean tumor movement was 5.1 mm (standard deviation [SD] 2.4 mm, maximum 10 mm), in the ventrodorsal (Y-) direction 3.1 mm (SD 1.5 mm, maximum 6.7 mm), and in the lateral (X-) direction 2.6 mm (SD 1.4 mm, maximum 5.8 mm; Figures 3 to 5). Inter- and intraindividual differences were present in each direction. With an abdominal pressure device no clinically significant difference between tumors in different location was seen.
Conclusion: The 3-D assessment of lung tumor movements due to breathing is possible by the use of multislice CT. The determination, indispensable to the PTV definition, should be performed individually for several regions, because of the inter- and intraindividual deviations detected.