Intrafraction variation of mean XXXX position during image-guided hypofractionated stereotactic body radiotherapy for lung cancer.

@entity1 @entity5 @entity24926
PURPOSE: Prolonged delivery times during daily cone-beam computed tomography (CBCT)-guided lung stereotactic body radiotherapy (SBRT) introduce concerns regarding intrafraction variation ( @entity24926 ) of the mean target position (MTP). The purpose of this study was to evaluate the magnitude of the @entity24926 -MTP and to assess target margins required to compensate for @entity24926 and postonline CBCT correction residuals. @entity1 , treatment, and @entity5 characteristics were analyzed with respect to their impact on @entity24926 -MTP. METHODS AND MATERIALS: A total of 126 @entity1 with 140 @entity5 underwent 659 fractions of lung SBRT. Dose prescribed was 48 or 60 Gy in 12 Gy fractions. Translational target position correction of the MTP was performed via onboard CBCT. @entity24926 -MTP was measured as the difference in MTP between the postcorrection CBCT and the posttreatment CBCT excluding residual error. RESULTS: @entity24926 -MTP was 0.2    1.8 mm, 0.1    1.9 mm, and 0.01    1.5 mm in the craniocaudal, anteroposterior, and mediolateral dimensions and the @entity24926 -MTP vector was 2.3    2.1 mm. Treatment time and excursion were found to be significant predictors of @entity24926 -MTP. An @entity24926 -MTP vector greater than 2 and 5 mm was seen in 40.8% and 7.2% of fractions, respectively. @entity24926 -MTP greater than 2 mm was seen in heavier @entity1 with larger excursions and longer treatment times. Significant differences in @entity24926 -MTP were seen between immobilization devices. The stereotactic frame immobilization device was found to be significantly less likely to have an @entity24926 -MTP vector greater than 2 mm compared with the alpha cradle, BodyFIX, and hybrid immobilization devices. CONCLUSIONS: Treatment time and respiratory excursion are significantly associated with @entity24926 -MTP. Significant differences in @entity24926 -MTP were found between immobilization devices. Target margins for @entity24926 -MTP plus post-correction residuals are dependent on immobilization device with 5-mm uniform margins being acceptable for the frame immobilization device.
