Adaptive Radiotherapy for Invasive Bladder Cancer, a Feasibility Study

Abstract

Purpose/Objective: To evaluate the feasibility of adaptive radiotherapy (ART) in combination with a partial bladder irradiation, delivering radiation to the tumor-bearing region of the bladder alone.Materials/Methods: Twenty one patients with solitary T1-T4 N0M0 bladder cancer were prospectively treated with an ART protocol. This protocol was developed to deal with treatment errors caused by organ motion and to safely reduce treatment volumes in radiotherapy for bladder cancer. In the first two weeks, patients were treated to the bladder tumor + 2 cm uniform margin (PTVCONV). During the first treatment week, daily CT scans were made immediately before or after treatment. In the second week a volume was constructed encompassing the GTV′s on the planning CT scan and the 5 CT scans acquired during the first treatment week (GTVART). The GTVART was expanded with a 1 cm uniform margin for the construction of a PTVART. Starting the third week patients were treated to this PTVART. Repeat CT scans were used to evaluate treatment accuracy.Results: On 5 out of 91 repeat CT scans (5%) the GTV was not adequately covered by the PTVART. On treatment planning of those 5 CT scans there was only one scan where the GTV was not adequately covered by the 95% iso-dose. On this particular CT scan 24% of the GTV received less than 95% of the prescribed dose. In all the other cases the GTV was adequately covered by the 95% iso-dose. The average PTVART volume was 228 cm3 (SD= 84 cm3) and average PTVCONV was 382 cm3 (SD= 129 cm3). On average the treatment volumes were reduced by 40% (range 26–57%) when comparing PTVART with PTVCONV (p<0.0001).Conclusions: The proposed adaptive strategy for bladder cancer is an effective way to deal with treatment errors caused by organ motion of the bladder. The described strategy is feasible and leads to a substantial reduction in the treatment volumes when compared with conventional strategies. Purpose/Objective: To evaluate the feasibility of adaptive radiotherapy (ART) in combination with a partial bladder irradiation, delivering radiation to the tumor-bearing region of the bladder alone. Materials/Methods: Twenty one patients with solitary T1-T4 N0M0 bladder cancer were prospectively treated with an ART protocol. This protocol was developed to deal with treatment errors caused by organ motion and to safely reduce treatment volumes in radiotherapy for bladder cancer. In the first two weeks, patients were treated to the bladder tumor + 2 cm uniform margin (PTVCONV). During the first treatment week, daily CT scans were made immediately before or after treatment. In the second week a volume was constructed encompassing the GTV′s on the planning CT scan and the 5 CT scans acquired during the first treatment week (GTVART). The GTVART was expanded with a 1 cm uniform margin for the construction of a PTVART. Starting the third week patients were treated to this PTVART. Repeat CT scans were used to evaluate treatment accuracy. Results: On 5 out of 91 repeat CT scans (5%) the GTV was not adequately covered by the PTVART. On treatment planning of those 5 CT scans there was only one scan where the GTV was not adequately covered by the 95% iso-dose. On this particular CT scan 24% of the GTV received less than 95% of the prescribed dose. In all the other cases the GTV was adequately covered by the 95% iso-dose. The average PTVART volume was 228 cm3 (SD= 84 cm3) and average PTVCONV was 382 cm3 (SD= 129 cm3). On average the treatment volumes were reduced by 40% (range 26–57%) when comparing PTVART with PTVCONV (p<0.0001). Conclusions: The proposed adaptive strategy for bladder cancer is an effective way to deal with treatment errors caused by organ motion of the bladder. The described strategy is feasible and leads to a substantial reduction in the treatment volumes when compared with conventional strategies.