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

Background And Purpose: To evaluate the benefits of adaptive radiotherapy for bladder cancer in decreasing irradiation of small bowel.

Material And Methods: 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.

Results: 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.

Conclusions: 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.