Empty Versus Full Bladder Protocols in Radiotherapy Planning for Localised Prostate Cancer: A Dosimetric Study

When planning prostate radiotherapy, full bladder preparation is widely used to displace bowel and bladder from high-dose regions but is difficult to reproduce and can prolong workflows.

Twenty men with localised prostate cancer ± seminal vesicles underwent CT simulation with full and empty bladders. VMAT plans prescribing 60Gy in 20 fractions, with simultaneous integrated boost to 66Gy for Dominant intraprostatic lesions where indicated, were created on both datasets. Bladder, rectum, CTV and PTV were compared; dose-volume histogram (DVH) endpoints included V30 and V60. Paired t-tests (two-sided α = 0.05) were used to assess differences.

Bladder volumes were significantly lower with the empty-bladder preparation (median 126.4 cm³; range 49.0-246.3; p < 0.001) versus full bladder (median 276.0 cm³; range 159.3-625.7). CTV volumes were comparable (empty 65.9 cm³ vs. full 62.8 cm³; p = 0.100). CTV dose was slightly reduced with empty bladder (60.0 Gy vs. 60.1 Gy; p < 0.001), a statistically significant but clinically negligible difference, while PTV coverage (D50%) remained similar (60.5 vs. 60.3 Gy; p = 0.365). Bladder V30 was higher with an empty bladder (26.9% vs. 20.7%; p < 0.001), while V60 was comparable (0.8% vs. 1.0%; p = 0.368). In contrast, rectal V30 was lower with an empty bladder (15.6% vs. 19.9%; p = 0.002), and V60 was low in both groups (0.1% vs. 0.4%; p = 0.077).

Empty bladder planning maintained target coverage, increased bladder V30, and reduced rectal V30, with all other dose constraints satisfied. This approach may enhance comfort and efficiency without compromising dosimetry.