SpaceOAR System Pivotal Study

Inclusion Criteria: * Subjects greater than 18 years old * Subjects must have pathologically confirmed invasive adenocarcinoma of the prostate and must be planning to undergo IMRT * Subjects must have clinical stage T1 or T2 as determined from a biopsy taken within 6 months of the baseline/screening visit with Gleason Score less than or equal to 7 * Subjects Screening/Baseline laboratory testing must meet the following laboratory value criteria: PSA less than or equal to 20 ng/mL,hematocrit greater than 30%,serum creatinine less than 2.0 mg/dl, serum AST and ALT less than 2.5 times upper limit of institution normal, and serum bilirubin less than 2.0 mg/dl * Subject or authorized representative, has been informed of the nature of the study and has provided written informed consent, approved by the appropriate Institutional Review Board (IRB) of the respective clinical site Exclusion Criteria: * Prostate greater than 80cc documented within 3 months preceding the Screening/Baseline visit * Subjects with extracapsular extension of the prostate cancer, with greater than 50% of the number of biopsy cores positive for cancer, metastatic disease, other ongoing cancers which will be treated during the study, or subjects for whom pelvic lymph node radiotherapy is planned * Subjects with any prior invasive malignancy (except non-melanomatous skin cancer) unless the subject has been disease free for a minimum of 5 years. * Subjects who are indicated for androgen deprivation therapy or who have been treated with androgen therapy within the prior 3 months.