Cone Beam CT Imaging Analysis of Interfractional Variations in Bladder Volume and Position During Radiotherapy for Bladder Cancer
Portions of the data from this work were presented at the 50th Annual Meeting of the American Society of Therapeutic Radiology and Oncology, Boston, MA, September 21–25, 2008, the 27th Meeting of the European Society of Therapeutic Radiology and Oncology, Göteborg, Sweden, September 14–18, 2008, and the 22nd Annual Meeting of the Canadian Association of Radiation Oncology, Montreal, Canada, September 10–13, 2008.
Received 28 October 2008; received in revised form 16 February 2009; accepted 9 March 2009. published online 19 June 2009.
Purpose
To quantify daily bladder size and position variations during bladder cancer radiotherapy.
Methods and Materials
Ten bladder cancer patients underwent daily cone beam CT (CBCT) imaging of the bladder during radiotherapy. Bladder and planning target volumes (bladder/PTV) from CBCT and planning CT scans were compared with respect to bladder center-of-mass shifts in the x (lateral), y (anterior-posterior), and z (superior-inferior) coordinates, bladder/PTV size, bladder/PTV margin positions, overlapping areas, and mutually exclusive regions.
Results
A total of 262 CBCT images were obtained from 10 bladder cancer patients. Bladder center of mass shifted most in the y coordinate (mean, −0.32 cm). The anterior bladder wall shifted the most (mean, −0.58 cm). Mean ratios of CBCT-derived bladder and PTV volumes to planning CT-derived counterparts were 0.83 and 0.88. The mean CBCT-derived bladder volume (± standard deviation [SD]) outside the planning CT counterpart was 29.24 cm3 (SD, 29.71 cm3). The mean planning CT-derived bladder volume outside the CBCT counterpart was 47.74 cm3 (SD, 21.64 cm3). The mean CBCT PTV outside the planning CT-derived PTV was 47.35 cm3 (SD, 36.51 cm3). The mean planning CT-derived PTV outside the CBCT-derived PTV was 93.16 cm3 (SD, 50.21). The mean CBCT-derived bladder volume outside the planning PTV was 2.41 cm3 (SD, 3.97 cm3). CBCT bladder/ PTV volumes significantly differed from planning CT counterparts (p = 0.047).
Conclusions
Significant variations in bladder and PTV volume and position occurred in patients in this trial.
∗Department of Radiation Oncology, Cross Cancer Institute, Edmonton, Alberta, Canada
†Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada
‡Department of Experimental Oncology, Cross Cancer Institute, Edmonton, Alberta, Canada
Reprint requests to: Don Yee, M.D., Department of Radiation Oncology, Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta, Canada T6G 1Z2. Tel: (+1) 780 432 8783; Fax: (+1) 780 432 8380
This work was funded by a grant from Varian Medical Systems.
Conflict of interest: DY holds a research grant from Varian Medical Systems.
ABSTRACT