Is Stereotactic Body Radiation Therapy (SBRT) alone effective for prostate cancer (PC) contained within the prostate?

SBRT Alone for Prostate-Confined Cancer

SBRT alone can be used for low-risk and select intermediate-risk prostate cancer confined to the prostate, but should NOT be used as monotherapy for high-risk disease, which requires combination with androgen deprivation therapy (ADT). 1

Risk-Stratified Approach to SBRT Monotherapy

Low-Risk Disease

• SBRT monotherapy is appropriate for low-risk prostate cancer (PSA <10 ng/mL, Gleason ≤6, clinical stage ≤T2a) confined to the prostate 1
• Single institution series report 5-year biochemical progression-free survival of 95% for low-risk patients treated with SBRT alone 1
• SBRT delivers highly conformal, high-dose radiation in 5 or fewer fractions using precise image-guided delivery 1, 2

Intermediate-Risk Disease

• For low-intermediate risk disease (Gleason 7 with PSA <10 ng/mL OR Gleason 6 with PSA 10-20 ng/mL), SBRT monotherapy may be offered 1
• Pooled analysis shows 5-year biochemical relapse-free survival of 84% for intermediate-risk patients 1
• For unfavorable intermediate-risk disease, SBRT should be combined with 6 months of ADT rather than used alone 1

High-Risk and Very High-Risk Disease

• SBRT alone is NOT appropriate for high-risk prostate cancer (PSA >20 ng/mL, Gleason 8-10, or clinical stage ≥T3) 1
• Level I evidence demonstrates that RT combined with ADT leads to significantly higher overall survival compared to RT alone in high-risk disease 1
• High-risk patients require at least 24 months of ADT in combination with radiation therapy 1
• The 5-year biochemical relapse-free survival for high-risk patients with SBRT is only 81%, which is inadequate without hormonal therapy 1

Critical Patient Selection Criteria

Absolute Contraindications to SBRT

• Prior pelvic irradiation (increased cumulative radiation toxicity risk) 2
• Active inflammatory disease of the rectum (significantly increases severe complication risk) 2
• Permanent indwelling Foley catheter (incompatible with precise targeting) 2

Relative Contraindications

• Very low bladder capacity (increased urinary toxicity) 2
• Chronic moderate or severe diarrhea (may be exacerbated) 2
• Bladder outlet obstruction requiring suprapubic catheter 2
• Inactive ulcerative colitis (risk of flare-up) 2

Facility and Technical Requirements

SBRT should only be performed at centers with appropriate technology, physics expertise, and clinical experience 1, 2. The technique requires:

• Image-guided delivery systems for precise targeting 1
• Strict quality-assurance standards 1
• Experienced radiation oncology team 1

Expected Toxicity Profile

• Up to 50% of patients experience temporary bladder or bowel symptoms during treatment 1
• Low but definite risk of protracted rectal symptoms from radiation proctitis 1, 2
• Risk of erectile dysfunction increases over time 1, 2
• Early toxicity appears similar to conventional fractionation when properly delivered 1

Common Pitfall to Avoid

The most critical error is using SBRT monotherapy for high-risk disease. The abundant Level I evidence showing survival benefit from combining RT with long-term ADT in high-risk patients cannot be ignored 1. While SBRT may be an acceptable radiation modality, it must be combined with appropriate systemic therapy based on risk stratification, not used alone 1.