Synchronous monitoring of external/internal respiratory motion: validity of respiration-gated radiotherapy for liver tumors.

<bold>Purpose: </bold>Four-dimensional (4D) radiotherapy, in particular respiration gating for the treatment of lung tumors, is gaining popularity. Its utility for other sites, however, has not been investigated fully. The purpose of this study was to see whether 4D therapy is feasible for liver tumors.<bold>Material and Methods: </bold>Six patients (five with hepatomas and one with metastatic liver tumor) had a fiducial, gold marker 1.5 mm in diameter implanted in the vicinity of their liver tumors. The inner and external (i.e., upper abdominal wall) respiratory movements were simultaneously recorded using a real-time tumor-tracking radiotherapy system and respiration monitor equipment applied to the mid to upper abdomen.<bold>Results: </bold>The fluctuations from the baseline position of liver tumors were small; the mean absolute value was 3.92 +/- 1.94 mm. The mean right-left, anteroposterior, and craniocaudal total movements were 4.19 +/- 2.46, 7.23 +/- 2.96, and 15.98 +/- 6.02 mm, respectively. The phase shift was negligible.<bold>Conclusion: </bold>Liver tumors may be suitable for respiration-gated radiotherapy, and they may become curable with 4D radiotherapy. [ABSTRACT FROM AUTHOR]