In a 76‑year‑old man with T3b (seminal‑vesicle invasion) prostate cancer, Gleason 4+3 (grade 7), PSA 40 ng/mL, pathologic N1 pelvic nodes and M1a infrarenal para‑aortic nodal metastases, can stereotactic body radiotherapy (SBRT) to the prostate alone at 36 Gy in 6 fractions be used as definitive treatment?

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Last updated: February 27, 2026 • View editorial policy

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SBRT Monotherapy is Inappropriate for This Patient

This 76-year-old man with T3bN1M1a metastatic prostate cancer requires combined-modality therapy with external beam radiotherapy (EBRT) to the prostate at ≥74 Gy, pelvic nodal irradiation, and long-term androgen deprivation therapy (ADT) for 2-3 years—not SBRT monotherapy at 36 Gy in 6 fractions. 1

Why SBRT Monotherapy Fails This Patient

Disease Extent Precludes Focal Treatment

  • This is metastatic disease (M1a para-aortic nodes) with regional nodal involvement (N1), not localized prostate cancer. The presence of infrarenal para-aortic nodal metastases and pelvic nodal disease (N1) categorically excludes this patient from any prostate-only treatment approach. 1

  • T3b disease (seminal vesicle invasion) alone represents locally advanced cancer requiring treatment beyond the prostate capsule. Studies demonstrate that T3b disease has 5-year biochemical recurrence-free survival of only 32% with surgery alone, improving to 68-78% with high-dose radiotherapy (≥74 Gy) plus ADT. 2

  • The Gleason 4+3 pattern (not "low risk" as stated) carries intermediate-high risk biology. This is a critical mischaracterization—Gleason 4+3 with PSA 40 ng/mL represents high-risk disease, not low-risk. 3

Evidence-Based Treatment Requirements

For metastatic disease (M1), guidelines mandate:

  • Androgen suppression using bilateral orchidectomy or LHRH agonist as first-line treatment. 1

  • For locally advanced T3b disease specifically, external beam radiotherapy with ADT improves survival. Patients with T3b disease require dose-escalated EBRT (≥74 Gy) to the prostate and involved seminal vesicles, combined with 2-3 years of adjuvant hormonal therapy. 1

  • High-dose radiotherapy (≥74 Gy) achieves 78% 5-year biochemical control in T3b disease versus 56% with lower doses (<74 Gy). 2

SBRT Dose is Grossly Inadequate

  • The proposed 36 Gy in 6 fractions is biologically equivalent to approximately 60 Gy in conventional fractionation—far below the minimum 70 Gy standard for localized disease, let alone the ≥74 Gy required for T3b. 1, 2

  • No guideline or high-quality study supports SBRT monotherapy for T3b disease with nodal metastases. All evidence for SBRT pertains to low-risk, organ-confined disease (T1-T2a, Gleason ≤6, PSA <10), which this patient categorically does not have. 4

Correct Treatment Algorithm for This Patient

Step 1: Systemic Control

  • Initiate long-term ADT (LHRH agonist) immediately, planned for 2-3 years total duration. 1
  • Use short-course antiandrogen to prevent disease flare when starting LHRH agonist. 1

Step 2: Definitive Radiotherapy

  • Deliver dose-escalated EBRT to the prostate at 76-80 Gy using intensity-modulated radiotherapy (IMRT) or 3D conformal technique. 2, 5
  • Include the involved seminal vesicles in the high-dose volume (76-80 Gy). 5
  • Irradiate pelvic lymph nodes given N1 disease. 5
  • Consider treating para-aortic nodes given M1a involvement, though this extends beyond standard fields. 5

Step 3: Enhanced Local Control Options

  • For selected patients, consider adding brachytherapy boost (HDR or LDR) to the prostate after 40-50 Gy EBRT, which achieves 83% 5-year biochemical control in high-risk disease. 2, 6
  • One study specifically in T3b patients using 103-Pd implant (100 Gy) to prostate and proximal seminal vesicles followed by 45 Gy EBRT achieved 60.6% 15-year biochemical freedom from failure. 6

Critical Pitfalls to Avoid

  • Do not misclassify this as "low-risk" disease. Gleason 4+3, PSA 40, T3b, N1, M1a represents high-risk/metastatic disease requiring aggressive multimodal therapy. 1, 3

  • Do not treat the prostate in isolation when nodal disease is present. Failure to address pelvic and para-aortic nodes will result in rapid progression. 5

  • Do not use short-course ADT (6 months). Metastatic disease requires 2-3 years of ADT, and some patients may require indefinite therapy. 1

  • Do not underestimate the importance of radiation dose. Each 10 Gy increment above 70 Gy significantly improves biochemical control in high-risk disease. 2

Prognosis with Appropriate Treatment

  • With high-dose EBRT (≥74 Gy) plus long-term ADT, 5-year biochemical control rates of 68-78% are achievable even in T3b disease. 2
  • Adding brachytherapy boost may improve this to 83%. 2
  • However, the presence of M1a disease significantly worsens prognosis, and this patient should be counseled that cure is unlikely, with treatment goals focused on prolonging survival and maintaining quality of life. 1

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

3
Guideline

Treatment Recommendations for Intermediate-High Risk Prostate Cancer

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

4
Guideline

Management of Low-Risk Prostate Cancer in a 66-Year-Old Male

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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