Influence of bladder and rectal volume on spatial variability of a XXXX during radical radiotherapy.

@entity1 @entity150 @entity5
PURPOSE: To assess the spatial variability of a @entity150 relative to the planning target volume boundaries during radical radiotherapy, and furthermore to develop strategies to reduce spatial variability. METHODS AND MATERIALS: Seventeen @entity1 with solitary T2-T4N0M0 @entity150 were treated with a technique delivering 40 Gy/2 Gy in 20 fractions to the whole bladder with a concomitant boost to the @entity150 of 20 Gy in 1 Gy fractions in an overall time of 4 weeks. CT scans were made weekly, immediately after treatment, and matched with the planning CT scan. Spatial variability of the @entity5 , as well as bladder volume and rectal diameter, were scored for each @entity1 each week. RESULTS: In 65% of @entity1 , a part of the @entity5 appeared outside the planning target volume boundaries at least one time during the course of radiotherapy. No consistent relation of this variability with time was found. Bladder volumes and rectal diameters showed marked variability during the course of treatment. A large initial bladder volume and rectal diameter predicted a large volume variation and a large @entity5 spatial variability. CONCLUSION: In this study, a margin of 1.5 to 2 cm seemed to be inadequate in 65% of the @entity1 with respect to spatial variability. Bladder volume and rectal diameter were found to be predictive for spatial variability of a @entity150 during concomitant boost radiotherapy.
