Rectal toxicity of 3-dimensional conformal radiation therapy following hydrogel spacer (Space OAR) injection for men with prostate cancer

Purpose: To evaluate whether hydrogel spacer injection, which increases the distance between the prostate and rectum, prior to local radiation therapy for prostate cancer reduces rectal and bladder toxicity.Patients and methods: With institutional review board approval (05-004), we retrospectively reviewed rectal and bladder toxicity after local radiation therapy in patients with prostate cancer who were followed up for more than 1 year.Results: We included 156 patients who had received local radiation therapy. Their ages ranged from 63 to 86 years, with an average of 75 years. Most patients were treated only on the prostate and seminal vesicles. All prostate sites were irradiated as follows: whole pelvis with prostate in 10 patients, whole pelvis with prostate and metastatic sites in six, and prostate and metastatic sites in eight. Radiation therapy (70-74 Gy) was performed for the prostate. Irradiation of 45-46.8 Gy was applied to whole pelvic and para-aortic lymph nodes, with 54-60 Gy applied to bone metastatic sites. In one case, stereotactic body radiation therapy (36 Gy) was performed for a sacral bone metastatic site. The hydrogel spacer was injected in 39 patients. Rectal toxicity was reported in 21 patients without (17.9%) and 3 patients with (7.7%) the hydrogel spacer. Bladder toxicity was reported in five patients without and only one patient with the hydrogel spacer.Conclusion: Hydrogel spacer injection prior to local radiation therapy for prostate cancer reduces rectal radiation exposure, lowers the risk of rectal complications, and may be a promising method for boosting the irradiation dose in the future.