Prostate SBRT is increasingly used in localized prostate cancer, offering a shorter treatment course while maintaining high precision. As more centers adopt prostate SBRT, practical guidance is needed to support safe implementation, consistent workflows, and appropriate patient selection.
A new ESTRO clinical practice consensus published in Radiotherapy and Oncology provides “how-to” recommendations for optimizing prostate SBRT in daily practice. The consensus was developed by a panel of experts using literature review, expert opinion, and a Delphi process to address areas of uncertainty in prostate SBRT.
Why This Guidance Matters
Prostate radiotherapy has changed substantially over the past two decades.
Moderate hypofractionation is now widely accepted, and ultra-hypofractionation has been tested in several phase III trials. Prostate SBRT delivers treatment in a small number of high-dose fractions, usually with steep dose gradients, precise image guidance, and strict motion management.
This approach can reduce the number of hospital visits and may be preferred by many patients.
However, SBRT also leaves less room for error. Accurate target delineation, organ-at-risk sparing, quality assurance, bladder and bowel preparation, and image guidance are essential for safe treatment delivery.
How the Consensus Was Developed
The ESTRO task force reviewed the available literature and developed practical recommendations to help integrate prostate SBRT into routine clinical practice.
The expert panel included radiation oncologists, medical physicists, and a radiotherapy technologist from multiple European countries. A Delphi process was used to answer 10 key questions addressing areas of controversy.
Consensus was defined as at least 75% agreement, while strong consensus required at least 90% agreement. The goal was to define minimum requirements, common practices, and optional approaches for prostate SBRT.
Patient Selection
The strongest consensus supported prostate SBRT as a standard treatment for patients with ISUP grade 2–3, cT1c–cT2c localized prostate cancer, and PSA below 20 ng/mL.
The role of prostate SBRT in high-risk disease is evolving.
Experts generally reserved SBRT for selected high-risk patients without multiple high-risk factors. The recommendations also emphasize baseline urinary function.
A maximum International Prostate Symptom Score threshold was recommended, with a median suggested cut-off of 17.
Patients with significant obstructive urinary symptoms, large post-void residuals, or recent benign prostatic hyperplasia surgery require careful selection and optimization before treatment. For patients with prior TURP, HoLEP, or prostate adenectomy, experts recommended SBRT only in selected cases, respecting a waiting period and considering the surgical cavity. The median recommended waiting time was 6 months.
Dose and Fractionation
The consensus identifies two standard prostate SBRT dose schedules. One recommended regimen is 36.25 Gy in 5 fractions of 7.25 Gy, with 40 Gy to 95% of the prostate clinical target volume.
This schedule is based on the PACE-B approach. An alternative regimen is 42.7 Gy in 7 fractions, based on the HYPO-RT-PC study.
The authors note that the optimal SBRT dose regimen has not been fully established, and ongoing trials continue to explore dose escalation, focal boosting, and dose de-escalation strategies. Treatment frequency may vary, but every-other-day or more protracted schedules appear reasonable when implementing prostate SBRT.
Target Delineation
Accurate delineation is central to prostate SBRT quality. The prostate should be contoured using planning MRI, typically T2-weighted sequences, registered to the planning CT when CT is used.
The authors emphasize careful delineation of the prostate apex and bladder base. For low-risk patients, seminal vesicles may be omitted.
For intermediate- and high-risk patients, seminal vesicle inclusion should be considered according to risk and protocol. For focal boost strategies, gross tumor volume should be defined using MRI and, where available, PSMA PET may help identify intraprostatic lesions.
Pelvic Lymph Node Radiotherapy
The consensus strongly recommends against elective pelvic lymph node irradiation together with prostate SBRT outside a clinical trial.
In the Delphi process, no experts recommended elective pelvic nodal irradiation with prostate SBRT outside a study setting.
The role of pelvic SBRT in prostate cancer remains under investigation.
Organs at Risk
The consensus stresses that prostate SBRT requires careful delineation of organs of interest and strict compliance with dose constraints.
Mandatory organs at risk include the rectum, bladder, femoral heads, and bowel when relevant. Optional structures may include the prostatic urethra, penile bulb, and crura.
Urethral dose optimization is highlighted as an important consideration, particularly to reduce urinary toxicity. The recommendations discuss both urethra steering, which aims to avoid hotspots, and urethra sparing, which reduces urethral dose below the surrounding prescription level.
Androgen Deprivation Therapy
The consensus states that androgen deprivation therapy should be used according to existing evidence-based risk-adapted guidelines, independent of the radiation fractionation schedule.
There is no evidence that SBRT removes the established role of ADT in appropriate risk groups.
For intermediate-risk and high-risk prostate cancer, ADT decisions should therefore follow standard guideline-based indications rather than being changed simply because SBRT is used.
Patient Preparation
Bladder and bowel preparation protocols are strongly recommended. The expert panel reached strong consensus in favor of using specific preparation protocols for prostate SBRT.
Controlled bladder filling and rectal emptying are important because prostate position is sensitive to organ filling and motion. A comfortably full bladder is recommended before simulation and treatment.
For shorter treatments, this may be achieved by drinking 300–500 mL of water 30–60 minutes before the session. Rectal preparation may include enemas according to institutional protocol and trial-based workflows.
Planning and Quality Assurance
Treatment plans should balance target coverage with organ-at-risk protection and should aim to reduce treatment delivery time. Typically, at least 95–98% of the planning target volume should receive 95% of the prescription dose.
The choice between homogeneous and inhomogeneous dose distribution should be guided mainly by urethral dose constraints and organ-at-risk protection. The paper also highlights the importance of strict quality assurance.
SBRT requires tighter tolerances than conventional radiotherapy because high doses are delivered in fewer fractions. Patient-specific QA should be performed according to institutional protocols and equipment capabilities.
Image Guidance and Motion Management
Image guidance is essential for safe prostate SBRT.
The consensus recommends daily pre-treatment cone-beam CT soft-tissue matching and/or fiducial marker-based systems as the minimum motion management strategy when using a planning target volume margin of at least 5 mm. For smaller margins or longer treatment times, additional intrafraction monitoring may be useful.
This can include fiducial tracking, electromagnetic transponders, ultrasound-based systems, stereoscopic imaging, or MRI-guided platforms. The paper emphasizes that daily imaging is particularly important in SBRT because there are fewer fractions, so setup errors have less opportunity to average out over time.
Adaptive Radiotherapy
MRI-guided and CBCT-based online adaptive radiotherapy may offer advantages by adjusting treatment plans to daily anatomy. Adaptive workflows can help manage changes in prostate position, rectal filling, bladder filling, and nearby organs at risk.
However, the authors note that online adaptive radiotherapy also introduces workflow and safety challenges. These include contouring review, plan adaptation, dose calculation, patient-specific QA, staff workload, and the need for rapid decision-making while the patient remains on the treatment couch.
The clinical benefit compared with non-adaptive approaches still needs further confirmation.
PSA Follow-Up
The consensus also addresses PSA kinetics after prostate SBRT.
Early PSA rises should be interpreted with caution. Transient PSA bounce is common after radiotherapy, including SBRT, and usually occurs within the first 12–18 months after treatment.
The reported incidence ranges from 10% to 40%. Because PSA bounce may resolve without intervention, early salvage therapy should generally be avoided unless biochemical failure is confirmed.
Clinical Interpretation
This ESTRO consensus provides a practical framework for centers implementing or refining prostate SBRT.
The recommendations reinforce that prostate SBRT is not simply a shorter radiotherapy schedule.
It requires careful patient selection, high-quality imaging, precise delineation, strict organ-at-risk constraints, reproducible bladder and bowel preparation, robust QA, and reliable image guidance.
The guidance is especially useful because it distinguishes minimum requirements from optional strategies, allowing departments to evaluate what is essential for safe practice and what may be added depending on equipment, expertise, and patient needs.
Clinical Takeaway
ESTRO’s clinical practice consensus supports prostate SBRT as a standard-of-care option for selected patients with localized low- and intermediate-risk prostate cancer, with expanding use in high-risk disease.
The paper provides practical recommendations for patient selection, dose and fractionation, target delineation, organs at risk, ADT, treatment preparation, QA, image guidance, motion management, adaptive radiotherapy, and PSA monitoring.
As prostate SBRT use continues to grow, these recommendations can help radiation oncology teams deliver treatment more safely, consistently, and effectively.
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