PROSTATE SBRT (5 FRACTIONS):
THE PACE TRIAL EXPLAINED
Radical prostate radiotherapy completed in 5 sessions — the PACE-B trial confirmed SBRT is non-inferior to 39-fraction IMRT, with 5-year outcomes now published.
analyticsAt a Glance
- check_circlePACE-B: non-inferior to IMRT at 5 years (BCF-free survival)
- check_circle36.25 Gy in 5 fractions — treatment in under 2 weeks
- check_circleEndorsed by AUA, ASTRO, and EAU guidelines
- check_circleAvailable at specialist centres in India and China
Why 5 Fractions? The Radiobiology of Prostate SBRT
Prostate cancer has an unusually low α/β ratio (~1.5–2 Gy), making it exceptionally sensitive to larger doses per fraction. This radiobiological property is the foundation for ultra-hypofractionation.
“The prostate's low α/β ratio means larger doses per fraction are biologically more damaging to tumour cells — and the basis for SBRT's efficacy in fewer treatments.”
High BED with Fewer Fractions
5 × 7.25 Gy (36.25 Gy total) delivers a biologically effective dose of ~170 Gy₁.₅ — substantially higher than the BED of 39-fraction IMRT regimens, explaining equivalent or superior tumour control.
Patient Convenience
5 sessions vs 39 sessions (conventional IMRT) or 28 sessions (moderate hypofractionation) — reducing total treatment burden for patients without compromising outcomes.
The PACE Trials: What the Evidence Shows
The PACE programme (Prostate Advances in Comparative Evidence) included two randomised trials addressing SBRT in different clinical settings.
PACE-B (Localised Prostate Cancer)
Randomised 874 patients (low and intermediate risk) to SBRT (36.25 Gy / 5 fx) vs conventional/moderate hypofractionation. 5-year BCF-free survival: 95.8% (SBRT) vs 94.6% (control). Grade ≥2 GI/GU toxicity: no significant difference.
PACE-A (SBRT vs Surgery)
Compared SBRT to robotic prostatectomy for localised prostate cancer. Primary endpoint was urinary and bowel function quality of life. Results demonstrated SBRT patients maintained better bowel and sexual function scores at 2 years.
PACE-B 5-Year Results at a Glance
- 95.8%SBRT BCF-Free Survival (5-yr)Biochemical/clinical failure-free survival, PACE-B
- 94.6%Control Arm BCF-Free (5-yr)Conventional/moderate hypofractionation arm
- 10.4%Grade ≥2 GU Toxicity (SBRT)At 5-year follow-up, no significant difference vs control
- 2.5%Grade ≥3 GU Toxicity (SBRT)Severe urinary toxicity remained low
Prostate SBRT vs Conventional IMRT: Head-to-Head
Key differences between 5-fraction SBRT and conventional 39-fraction IMRT for localised prostate cancer.
| Parameter | SBRT (5 fx) | Conventional IMRT (39 fx) |
|---|---|---|
| Total dose | 36.25 Gy | 78 Gy |
| BED₁.₅ (prostate) | ~170 Gy | ~140 Gy |
| Treatment duration | 1–2 weeks | 8 weeks |
| 5-yr BCF-free survival | 95.8% (PACE-B) | 94.6% (PACE-B control) |
| Grade ≥2 GU toxicity | 10.4% at 5 yr | Comparable (no sig. difference) |
| Grade ≥2 GI toxicity | 3.2% at 5 yr | Comparable |
| Guideline endorsement | AUA, ASTRO, EAU (2022+) | Long-established standard |
SBRT Advantages and Considerations
Understanding the strengths and practical considerations of prostate SBRT for shared decision-making.
Advantages of SBRT
- Ultra-short treatment course5 sessions vs 39 for IMRT — major quality-of-life advantage
- Non-inferior oncologic controlPACE-B 5-year data confirms equivalent BCF-free survival
- No anaesthesia or recoveryOutpatient treatment with same-day discharge
- High biological dose to prostateBED advantage over moderate hypofractionation for low-α/β tumours
Practical Considerations
- High-risk patients require additional ADTSBRT monotherapy is not standard for high-risk or locally advanced disease without ADT
- Fiducial markers often requiredGold seed implantation needed for real-time tumour tracking at most centres
- Rectal spacer recommendedSpaceOAR gel placement reduces rectal dose — requires procedure before SBRT
Related SBRT Resources
Further reading on SBRT across different cancer sites and clinical scenarios.
Frequently Asked Questions
Prostate SBRT and the PACE Trial
Is prostate SBRT the same as CyberKnife?
CyberKnife is one platform used to deliver prostate SBRT, but SBRT can also be delivered using standard linear accelerators equipped with image guidance and stereotactic capabilities (e.g., TrueBeam, Varian Edge, Elekta Versa HD). The PACE-B trial used linac-based SBRT at most centres, demonstrating that the treatment is platform-agnostic when delivered to the same dose and fractionation specifications.
Is prostate SBRT appropriate for high-risk prostate cancer?
Prostate SBRT monotherapy is primarily validated for low and intermediate-risk localised disease (PACE-B eligibility criteria). For high-risk localised prostate cancer, SBRT may be combined with androgen deprivation therapy (ADT) and pelvic nodal irradiation, though this combination has less mature randomised evidence than SBRT alone. Discuss with a radiation oncologist whether SBRT alone or combined with ADT is appropriate for your risk category.
What are the main side effects of prostate SBRT?
Urinary irritative symptoms (frequency, urgency, dysuria) are the most common acute side effects, peaking in the first 2–4 weeks after treatment and typically resolving within 3 months. Late Grade ≥2 GU toxicity was reported in 10.4% of patients at 5 years in PACE-B. Bowel toxicity is low (<3% Grade ≥2) with modern rectal dose constraints. Erectile function decline mirrors that seen with IMRT.
Do I need hormone therapy (ADT) alongside prostate SBRT?
For low-risk disease: no ADT is required. For favourable intermediate-risk: ADT is optional based on shared decision-making. For unfavourable intermediate-risk: short-course ADT (4–6 months) may improve outcomes. For high-risk disease: long-course ADT (2–3 years) is recommended alongside radiation. The PACE-B trial treated low and favourable intermediate-risk patients without mandatory ADT.
Where is prostate SBRT available in India and China?
Prostate SBRT with fiducial tracking is available at multiple centres in India (Tata Memorial Hospital, Apollo Hospitals, HCG, Rajiv Gandhi Cancer Institute) and China (PUMCH, Zhongshan, Fudan Shanghai Cancer Centre). Treatment costs in India are significantly lower than in Western countries, making India a practical option for international patients seeking this treatment. CancerFax can coordinate a direct consultation and eligibility review.
How CancerFax Helps
CancerFax is a specialist cancer access and patient-navigation platform. We help patients and families understand their options, organise medical records, coordinate hospital communication, and support cross-border treatment planning where appropriate.
We help collect and organise reports, scans, pathology, biomarker results, and treatment history for structured case review.
We communicate with hospitals or trial teams to assess whether a case may be suitable for further screening.
We support appointment coordination, document submission, translation, and direct communication with international departments.
For international patients, we help with practical coordination — travel planning, hospital admission guidance, and local support.
If this option is not suitable, we help explore other relevant treatments, clinical trials, or advanced care pathways.
From inquiry through to follow-up, our coordinators provide a single point of contact for the family.
CancerFax does not guarantee treatment access, eligibility, or clinical outcome. Our role is to help patients access accurate information, structured review, and appropriate specialist pathways.
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This content is for informational purposes only and does not constitute medical advice. Always consult a qualified oncologist before making treatment decisions.