Room: Exhibit Hall
Purpose: To study the effects of bladder volume to dose volume response using Plan-of-the-day approach. This variation is due to the physiological activity of the bladder (E.g.: full/empty). To gauge clinical performance, we compared dose-volume response from Pinnacle TPS to independently measured phantom acquired dose-volume response.
Methods: Cone beam CTâ€™s that were acquired during the course of the patientâ€™s treatment were exported from MOSAIC R&V software to velocity image registration software. The images were then fused with the CT sim and bladder volumes were contoured and transferred from the CBCT to the CT sim. The contours were then exported to pinnacle TPS where a plan was then created for a small-sized (empty) bladder, an average-sized bladder, and a large-sized (full) bladder. The rectal doses were also monitored. The plans were then tested on a PTW phantom and dose-volume response was verified in the PTW Verisoft software.
Results: The D80 of the small, average, and large bladder according to the TPS were 14.82, 9.36, and 5.66 Gy respectively. The D60 of the small, average, and large bladder according to the TPS were 37.43, 20.28, and 11.7 Gy respectively. The D40 of the small, average, and large bladder according to the TPS were 68.24, 52.25, and 37.04 Gy respectively. The D20 of the small, average, and large bladder according to the TPS were 70.76, 70.23, and 70.33 Gy respectively. The rectal doses were observed to be lower than the average for the maximum bladder and the lowest for the minimum bladder.
Conclusion: There is a significant improvement in bladder dose when treating with a full bladder, as well as some rectal sparing. This is expected as the volume changes of the bladder have a greater impact on the DVH.