Factors associated with acute radiation-induced nocturia in localized prostate cancer treated with proton beam therapy.

We examined factors associated with acute radiation-induced nocturia (ARIN) in patients with localized prostate cancer (LPC) treated with proton beam therapy (PBT). We included 140 patients who underwent PBT for LPC. Of these, 80 patients with implanted hydrogel spacers were treated with moderately hypo-fractionated proton therapy (MHPT) (60-66 GyRBE in 20-22 fractions) and 60 patients without hydrogel spacers were treated with normo-fractionated proton therapy (NFPT) (74-78 GyRBE in 37-39 fractions). In-room computed tomography was performed for each fraction to monitor target position. Prostate-rectum boundary matching was adopted to effectively reduce rectal dose, and position translation and pitch angle corrections were performed depending on rectal filling changes. ARIN was evaluated based on the nocturnal voiding frequencies. We first performed multivariate logistic regression (MLR) analysis to identify significant factors for ARIN. Subsequently, propensity score matching (PSM) was performed as a sensitivity analysis to address potential confounding and to assess the robustness of the findings. The analyses showed that 45/140 patients experienced ARIN during/immediately after PBT. MLR analysis showed that 'treatment regimen' (MHPT with spacer vs NFPT without spacer) was statistically significantly associated with ARIN (OR: 0.25, 95% CI: 0.09-0.67, P < 0.05). This association remained significant after PSM. In conclusion, while 'treatment regimen' was statistically associated with ARIN, this finding should be interpreted cautiously as reflecting a composite treatment strategy within the limitations of a retrospective analysis, rather than a causal relationship.