Spontaneous remission of rectal ulcer associated with SpaceOAR(®) hydrogel insertion in radiotherapy for prostate cancer

INTRODUCTION: The SpaceOAR(®) hydrogel system separates the prostate and rectum to reduce rectal irradiation during prostate radiotherapy. However, it could induce rectal toxicity. CASE PRESENTATION: A 75‐year‐old man with localized prostate cancer underwent external beam radiotherapy with the use of SpaceOAR(®) System. However, postimplant magnetic resonance imaging showed hydrogel infiltration to the rectum. Three months after implantation, he complained of bowel symptoms, including bloody stool. Colonofiberscopy and computed tomography revealed a rectal ulcer associated with SpaceOAR(®) hydrogel insertion. He was treated with fasting, fluid replacement, and blood transfusion. One year after implantation, complete healing was confirmed during outpatient follow‐up. CONCLUSION: To our knowledge, this is the first report of a rectal ulcer associated with SpaceOAR(®) hydrogel insertion assessed by magnetic resonance imaging beforehand. Postimplant magnetic resonance imaging evaluation might be a useful follow‐up tool in such cases.