The primary goal of this phase II study is to compare the change of EPIC HRQOL scores (1-year minus baseline) between SBRT and IMRT.

Inclusion Criteria:

• Histological confirmation of prostate adenocarcinoma
• Low or intermediate risk prostate cancer patients (i.e. T1-T2c and PSA 20 and Gleason score < 8) with the risk of pelvic node metastasis 15% as calculated by Roach's formula
• ECOG performance score 0-1
• Age ≥ 18
• History/physical examination within 2 weeks prior to registration
• Able to sign informed-consent

Exclusion Criteria:

• Patients with previous diagnosis of cancer other than prostate cancer and non-melanoma skin cancer.
• Evidence of distant metastases
• Regional lymph node involvement
• Previous radical surgery (prostatectomy), cryosurgery, or HIFU for prostate cancer
• Previous pelvic irradiation, prostate brachytherapy, or bilateral orchiectomy
• Previous hormonal therapy, such as LHRH agonists (e.g., goserelin, leuprolide) or LHRHantagonists (e.g., degarelix), anti-androgens (e.g., flutamide, bicalutamide), estrogens (e.g.DES), or surgical castration (orchiectomy)
• Unstable angina and/or congestive heart failure requiring hospitalization, transmural myocardial infarction within the last 6 months, acute bacterial or fungal infection requiring intravenous antibiotics, chronic obstructive pulmonary disease exacerbation or other respiratory illness requiringhospitalization or precluding study therapy at the time of registration
• Patients who have received prior chemotherapy.