Inclusion Criteria:

          -  Age ≥ 18

          -  Histologically confirmed adenocarcinoma of the prostate gland by needle core samples
             with assigned Gleason score

          -  Subjects ADT naive or subjects who are already on ADT treatment and scheduled to
             receive radiation therapy for their adenocarcinoma of prostate are eligible. An 8-week
             course of ADT is required to be completed prior to NBTXR3 administration and
             initiation of radiation therapy.

          -  Pelvic and para-aortic lymph nodes must be negative on CT-scan or MRI of the abdomen
             and pelvis performed within 12 weeks prior to enrollment into the study

          -  Prostate adenocarcinoma with High Risk (HR) and Unfavorable Intermediate Risk (UIR)
             for recurrence classification as determined by one of the following combinations:

               -  High risk (HR): subjects with one or more of the following risk factors:

                    -  Clinical stage: T3/T4

                    -  Gleason score (GS): 8-10

                    -  PSA > 20

                    -  N0

               -  Unfavorable Intermediate Risk (UIR): subjects with no HR features but with one or
                  more of the following adverse risk factors:

                    -  At least 2 of the following 3 factors: Gleason score(GS) 3+4=7 and/or PSA
                       10-20 and/or T2b/c

                    -  Gleason score (GS) 4+3=7

                    -  Greater than 50% of biopsy cores positive and at least one other risk
                       factor:

        Gleason score (GS) 7 and/or PSA 10-20 and/or T2b/c

          -  No evidence of bone metastases (M0) on bone scan within 120 days prior to registration
             (PET/CT is an acceptable substitute). Equivocal bone scan findings are allowed if bone
             CT or MRI of hot spots are negative for metastasis

          -  Baseline serum PSA value performed with an FDA-approved assay within 120 days prior to
             registration. Study entry PSA should not be obtained within 10-day period following
             prostate biopsy or following initiation of hormonal therapy

          -  ECOG performance status must be 0 or 1

          -  Adequate function of bone marrow:

               -  Hemoglobin > 100 g/L

               -  Absolute Neutrophils > 1.5 x 109/L

               -  Platelets > 100 x 109/L,

          -  Adequate function of kidney:

               -  Serum creatinine < 1.5 x ULN

          -  Adequate function of liver:

               -  AST ≤ 3.0 x ULN

               -  ALT ≤ 3.0 x ULN

               -  Total bilirubin ≤ 1.5 x ULN

          -  Non-Childbearing Potential: Male subjects and their partners must meet one of the
             following criteria to be considered of non-childbearing potential:

               -  Males have undergone sterilization with appropriately confirmed absence of sperm
                  in the post-vasectomy ejaculate, or

               -  Heterosexually active males and their partners of childbearing potential must
                  agree or use at least 2 forms of highly effective methods of contraception,
                  including at least 1 barrier method. Highly effective methods of contraception
                  are those that, alone or in combination, result in a failure rate of <1% per year
                  when used consistently and correctly (i.e., perfect use). Contraception must
                  include male condom or female condom used with a spermicide (i.e., foam, gel,
                  film, cream, suppository) as well as established use of oral, injected or
                  implanted hormonal methods of contraception, correctly placed intrauterine device
                  or intrauterine system.

        Exclusion Criteria:

          -  Written Informed Consent not obtained, signed and dated

          -  History of colorectal surgery, or repeated endoscopic examinations/interventions
             related to anorectal diseases or proximal urethral stricture requiring dilatation

          -  Prostate size volume ≥90 cc

          -  Brachytherapy with EBRT in subjects whose prostate volume is >60cc

          -  Severe, active co-morbidity, defined as follows:

               -  Inflammatory bowel disease, active rectal diverticulitis, Crohn's disease
                  affecting the rectum, anal stenosis or ulcerative colitis. (Nonactive
                  diverticulitis and Crohn's disease not affecting the rectum are allowed)

               -  Unstable angina and/or congestive heart failure requiring hospitalization within
                  the last 6 months

               -  Myocardial infarction within the last 6 months

               -  Acute bacterial or fungal infection requiring intravenous antibiotics at the time
                  of randomization

               -  Acquired Immune Deficiency Syndrome (AIDS) based upon current CDC (Centers for
                  Disease Control) definition

          -  Prior invasive malignancy, except non-melanoma skin cancer, carcinoma in-situ of the
             bladder or head and neck region, unless disease free for a minimum of 2 years

          -  Subjects with congenital long QT syndrome or subjects taking Class IA, Class III or
             Class IC anti-arrhythmic medications will require a cardiologist's evaluation prior to
             eligibility assessment. subjects with cardiovascular diseases can be included as long
             as the benefits of androgen deprivation therapy outweigh the potential risk of
             cardiovascular events

          -  Uncontrolled lung disease

          -  Subjects with any evidence of distant metastases

          -  subjects with any contraindication to pelvic radiotherapy including, but not limited
             to, previous pelvic radiotherapy or brachytherapy

          -  Presence of bilateral hip replacement prostheses

          -  Hormonal therapy (luteinizing hormone-releasing hormone [LHRH] agonist or oral
             anti-androgen) exceeding 4 months prior to registration

          -  Declared high-risk for anesthesia by attending anesthesiologist, cardiologist, or
             other physician

          -  Complete initial work up earlier than 12 weeks prior to subject registration

          -  Subjects unable to comply with scheduled visits, treatment plans, laboratory tests,
             and other study procedures

          -  Subjects participating in another clinical investigation at the time of signature of
             the informed consent.