Aims: To determine the clinical target volume (CTV) to planning target volume (PTV) margins required for bladder coverage when using skin or bony or soft tissue matching on a daily basis.
Materials and methods: Twenty-seven patients with T2-T4 transitional cell carcinoma of the bladder were treated with daily online adaptive image-guided radiotherapy using cone beam computed tomography. All daily CTVs were contoured by a single observer. A retrospective comparison of coverage of the bladder CTV using skin, bone and soft tissue matching was conducted.
Results: With the skin set-up, bladder CTV coverage with a margin of 0.5, 1.0, 1.5, 2.0 and 2.5 cm was 0, 19, 56, 93 and 96%, respectively. For the daily set-up based on bone, the respective coverage was 0, 41, 63, 89 and 96%. For soft tissue set-up based on the geometric centre of the bladder, coverage was 52, 89, 96, 100 and 100%, respectively.
Conclusions: Based on coverage of the CTV, the required CTV to PTV margins are smaller for the daily online soft tissue set-up compared with skin or bone.
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