PURPOSE: Positioning of @entity1 with gynecologic @entity5 for radiotherapy has proven to be relatively inaccurate. To improve the accuracy and reduce the margins from clinical target volume (CTV) to planning target volume ( @entity343 ), on-line set-up corrections were investigated. METHODS AND MATERIALS: Anterior-posterior portal images of 14 @entity1 were acquired using the first six monitor units (MU) of each irradiation fraction. The set-up deviation was established by matching three user-defined landmarks in portal and simulator image. If the two-dimensional deviation exceeded 4 mm, the table position was corrected. A second portal image was acquired using 30 MU of the remaining dose. This image was analyzed off-line using a semiautomatic contour match to obtain the final set-up accuracy. To verify the landmark match accuracy, the contour match was retrospectively performed on the six MU images as well. RESULTS: The standard deviation (SD) of the distribution of systematic set-up deviations after correction was < 1 mm in left-right and cranio-caudal directions. The average random deviation was < 2 mm in these directions (1 SD). Before correction, all standard deviations were 2 to 3 mm. The landmark match procedure was sufficiently accurate and added on average 3 min to the treatment time. The application of on-line corrections justifies a CTV-to- @entity343 margin reduction to about 5 mm. CONCLUSIONS: On-line set-up corrections significantly improve the positioning accuracy. The procedure increases treatment time but might be used effectively in combination with off-line corrections.

On-line set-up corrections during radiotherapy of XXXX with gynecologic @entity5 .

@entity1 :: ('9606', 'Species') :: ['patients'] @entity343 :: ('187978', 'Species') :: ['PTV'] @entity5 :: ('MESH:D009369', 'Disease') :: ['tumors']
@entity1 :: (9606,Species) :: ['patients']
