Intrafractional prostate motion during online image guided intensity-modulated radiotherapy for XXXX .

@entity1 @entity263 @entity343 @entity41
INTRODUCTION: Intrafractional motion consists of two components: (1) the movement between the on-line repositioning procedure and the treatment start and (2) the movement during the treatment delivery. The goal of this study is to estimate this intrafractional movement of the prostate during @entity263 radiotherapy. MATERIAL AND METHODS: Twenty-seven @entity1 with @entity263 and implanted fiducials underwent a marker match procedure before a five-field IMRT treatment. For all fields, in-treatment images were obtained and then processed to enable automatic marker detection. Combining the subsequent projection images, five positions of each marker were determined using the shortest path approach. The @entity41 ( @entity41 ) after kV-MV based prostate localization, the prostate position as a function of time during a radiotherapy session and the required margins to account for intrafractional motion were determined. RESULTS: The mean @entity41 and standard deviation in the antero-posterior, cranio-caudal and left-right direction were 2.3  1.5 mm, 0.2  1.1 mm and -0.1  1.1 mm, respectively. Almost all motions occurred in the posterior direction before the first treatment beam as the percentage of excursions>5 mm was reduced significantly when the @entity41 was not accounted for. The required margins for intrafractional motion increased with prolongation of the treatment. Application of a repositioning protocol after every beam could decrease the 1cm margin from CTV to @entity343 by 2 mm. CONCLUSIONS: The @entity41 is the main contributor to intrafractional motion. This @entity41 after on-line prostate localization and @entity1 repositioning in the posterior direction emphasizes the need to speed up the marker match procedure. Also, a prostate IMRT treatment should be administered as fast as possible, to ensure that the pre-treatment repositioning efforts are not erased by intrafractional prostate motion. This warrants an optimized workflow with the use of faster treatment techniques.
