• Progress in Medical Physics
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• v.14 no.1
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• pp.28-33
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• 2003

The aim of the study was to assess the isocenter deviation between multiple arcs and conformal beams in frameless FSRT. Forty seven patients received single isocenter radiosurgery or therapy (SRS/T) using available framelss FSRT system from Aug. 1997 to Dec. 2m. In choosing multiple arc FSRT or conformal FSRT, we had considered one of two techniques with respect to tumor size and tumor shape. In multiple arc FSRT, the average and standard deviation (SD) of the isocenter deviation was 0.2 mm (SD 0.2 mm), 0.2 mm (SD 0.2) and 0.3 mm (SD 0.2 mm)in the lateral (x), anterior-posterior (y) and cranio-caudal directions (z). In conformal FSRT, the average deviation and SD of the isocenter deviation was 0.2 mm (SD 0.2 mm), 0.3 mm(0.2 mm) and 0.4 mm (SD 0.2 mm) in the x, y and z directions. The average spacial deviation ($\Delta$r) was 0.41 mm and 0.54 mm in multiple arcs and conformal beams, respectively. The isocenter deviation using frameless FSRT system was similar value between multiple arcs and conformal beams. In practice, we believed we can select the appropriate treatment technique according to tumor shape and size.