Room: Exhibit Hall | Forum 5
Purpose: Target localization for radiation treatment of bladder cancer is always challenging and requires improvements. This is mainly due to inter-fractional organ filling/motion. Precise image guidance is crucial. This study uses CT-on-Rails to perform IGRT for bladder cancer and compares the dosimetric benefits by evaluating daily delivered doses to the tumor and organ-at-risks (OARs).
Methods: Two non-invasive (T1, total 18Gy to entire bladder) and four T2N0M0 bladder cancer patients (total of 66Gy to partial bladder alone) were localized daily with either CTOR or CBCT. A total of 106 sets of CTOR and 35 sets of CBCT were acquired and registered with original planning CT scans by radiation therapists and approved by radiation oncologists for the daily treatment. CTOR has a resolution of 2mm slice thickness and 0.98mm axial voxel size. Non-invasive stage T1 PTVs were delineated with an overall margin of 5mm except 1.5cm superiorly and stage T2 PTVs with an overall margin of 1cm except 5mm superiorly. With daily localization CTOR images, initial plans were re-calculated and the DVHs were evaluated. Accuracy of CTOR and CBCT partial bladder alignment was also evaluated by comparing the PTV coverage.
Results: Daily shifts based on CTOR averaged to 0.75, 0.28 and 0.55cm (SI, Lat, AP directions) with maximum shifts 1.70, 0.85 and 1.22cm (SI, Lat, AP directions), respectively. Daily shifts based on CBCT averaged to 0.43, 0.09, 0.19cm (SI,Lat,AP directions), respectively. Different effects were observed for the two treatment margins on DVHs for the target and OARs. CTOR daily localization showed superior results of V100% of PTV, prostate (Dmax), rectum (Dmax, D17%, and D35%) and bowel (Dmax) coverage for the non-invasive T1 PTV setting than CBCT localization.
Conclusion: CTOR daily localization for IGRT is more dosimetrically beneficial than CBCT for bladder cancer treatment. The margin setting is crucial for inter-fractional dose evaluation.