Purpose: To assess the clinical utility of X-ray volume imaging (XVI) for verification of bladder radiotherapy and to quantify geometric error in bladder radiotherapy delivery.
Methods and materials: Twenty subjects undergoing conformal bladder radiotherapy were recruited. X-ray volume images and electronic portal images (EPIs) were acquired for the first 5 fractions and then once weekly. X-ray volume images were co-registered with the planning computed tomography scan and clinical target volume coverage assessed in three dimensions (3D). Interfraction bladder volume change was described by quantifying changes in bladder volume with time. Bony setup errors were compared from both XVI and EPI.
Results: The bladder boundary was clearly visible on coronal XVI views in nearly all images, allowing accurate 3D treatment verification. In 93.5% of imaged fractions, the clinical target volume was within the planning target volume. Most subjects displayed consistent bladder volumes, but 25% displayed changes that could be predicted from the first three XVIs. Bony setup errors were similar whether calculated from XVI or EPI.
Conclusions: Coronal XVI can be used to verify 3D bladder radiotherapy delivery. Image-guided interventions to reduce geographic miss and normal tissue toxicity are feasible with this technology.