RESUMEN
PURPOSE: To investigate the effect of the probiotic Lactobacillus acidophilus on the percentage volume change of the rectum (PVCR), a crucial factor of prostate movement. METHODS AND MATERIALS: Prostate cancer patients managed with tomotherapy as a radical treatment were enrolled in the study to take a probiotic capsule containing 1.0×10(8) colony-forming units of L acidophilus or a placebo capsule twice daily. Radiation therapy was performed at a dose of 78 Gy in 39 fractions. The PVCR, defined as the difference in rectal volume between the planning computed tomographic (CT) and daily megavoltage CT images, was analyzed. RESULTS: Forty patients were randomized into 2 groups. The L acidophilus group showed significantly lower median rectal volume and median PVCR values than the placebo group. L acidophilus showed a significant reduction effect on the PVCR (P<.001). However, the radiation therapy fraction number did not significantly influence the PVCR. CONCLUSIONS: L acidophilus was useful in reducing the PVCR, which is the most important determining factor of prostate position, during radiation therapy for prostate cancer.