Adaptive radiotherapy in muscle invasive urinary bladder cancer--an effective method to reduce the irradiated bowel volume.

Abstract

To evaluate the benefits of adaptive radiotherapy for bladder cancer in decreasing irradiation of small bowel. Five patients with muscle invasive bladder cancer received adaptive radiotherapy to a total dose of 55.8-65 Gy with daily cone-beam computed tomography scanning. The whole bladder was treated to 45-50.4 Gy, followed by a partial bladder boost. The plan of the day was chosen from 3 to 4 pre-planned treatment plans according to the visible extent of bladder wall in cone-beam computed tomography images. Dose volume histograms for intestinal cavity volumes were constructed and compared with corresponding histograms calculated for conventional non-adaptive radiotherapy with single treatment plan of 2 cm CTV-PTV margins. CTV dose coverage in adaptive treatment technique was compared with CTV dose coverage in conventional radiotherapy. The average volume of intestinal cavity receiving ≥ 45 Gy was reduced from 335 ± 106 cm(3) to 180 ± 113 cm(3) (1SD). The maximum volume of intestinal cavity spared at 45 Gy on a single patient was 240 cm(3), while the minimum volume was 65 cm(3). The corresponding reduction in average intestinal cavity volume receiving ≥ 45 Gy calculated for the whole bladder treatment only was 66 ± 36 cm(3). CTV dose coverage was improved on two out of five patients and decreased on three patients. Adaptive radiotherapy considerably reduces dose to the small bowel, while maintaining the dose coverage of CTV at similar level when compared to the conventional treatment technique.