Does intensity-modulated radiation therapy (IMRT) alter prostate size? Magnetic resonance imaging evaluation of patients undergoing IMRT alone

Aim To assess the changes in prostate size in patients with prostate cancer undergoing intensity-modulated radiation therapy (IMRT). Background The effect of size change produced by IMRT is not well known. Materials and methods We enrolled 72 patients who received IMRT alone without androgen-deprivation therapy and underwent magnetic resonance imaging (MRI) examination before and after IMRT. The diameter of the entire prostate in the anterior–posterior (P-AP) and left–right (P-LR) directions was measured. The transitional zone diameter in the anterior–posterior (T-AP) and left–right (T-LR) directions was also measured. Results The average relative P-AP values at 3, 6, 12, 24, and 36 months after IMRT compared to the pre-IMRT value were 0.94, 0.90, 0.89, 0.89, and 0.90, respectively; the average relative P-LR values were 0.93, 0.92, 0.91, 0.91, and 0.90, respectively. The average P-AP and P-LR decreased by approximately 10% during the 12 months post-IMRT, and remained unchanged thereafter. The average relative T-AP values at 3, 6, 12, 24, and 36 months after IMRT compared to the pre-IMRT value were 0.93, 0.88, 0.91, 0.87, and 0.89, respectively; the average relative T-LR values were 0.96, 0.90, 0.91, 0.87, and 0.88, respectively. The average T-AP and T-LR also decreased by approximately 10% during the 12 months post-IMRT, and remained unchanged thereafter. At 12 months after IMRT, the average relative T-AP was significantly lower in patients with recurrence than in those without recurrence. Conclusions The average prostate diameter decreased by approximately 10% during the 12 months after IMRT; thereafter remained unchanged.