Adaptive radiotherapy for invasive bladder cancer: A feasibility study

Purpose: To evaluate the feasibility of adaptive radiotherapy (ART) in combination with a partial bladder irradiation. Methods and Materials: Twenty-one patients with solitary T1-T4 N0M0 bladder cancer were treated to the bladder tumor + 2 cm margin planning target volume (PTVCONV). During the first treatment week, five daily computed tomography (CT) scans were made immediately before or after treatment. In the second week, a volume was constructed encompassing the gross tumor volumes (GTVs) on the planning scan and the five CT scans (GTVART). The GTVART was expanded with a 1 cm margin for the construction of a PTVART. Starting in the third week, patients were treated to PTVART. Repeat CT scans were used to evaluate treatment accuracy. Results: On 5 of 91 repeat CT scans (5%), the GTV was not adequately covered by the PTVART. On treatment planning, there was only one scan in which the GTV was not adequately covered by the 95% isodose. On average, the treatment volumes were reduced by 40% when comparing PTVART with PTVCONV (p < 0.0001). Conclusion: The adaptive strategy for bladder cancer is an effective way to deal with treatment errors caused by variations in bladder tumor position and leads to a substantial reduction in treatment volumes.