Purpose: Our purpose was to evaluate the utility of time-fixed bladder volume control and adaptive bladder volume control with ultrasonography (US).
Materials and methods: Seventy-five patients with prostate cancer treated with proton-beam therapy were enrolled. Treatment plans were created using computed tomography (CT) images obtained 60 min after urination with usual water intake. Just before each irradiation, bladder volume was measured with US at the directed urine collection time. Bladder volume was calculated according to orthogonal diameters. A bladder volume of <50 ml was considered to reflect a collapsed bladder. The percentage of collapsed bladders was examined in total and from the first to fifth irradiations.
Results: In total, 1,439 US confirmations (51 %) in 2,821 fractions were obtained and analyzed. A collapsed bladder was observed 152 of 1,439 times (11 %) in total, and the percentages of collapsed bladders from the first to fifth irradiations were 32 %, 18 %, 16 %, 12 %, and 7 %, respectively.
Conclusion: Time-fixed bladder control is associated with a risk of bladder volume insufficiency. Adaptive bladder volume control with initial US feedback could decrease the risk of bladder volume insufficiency.