Stereotactic Radiation Therapy (SBRT/SABR) — Procedure Guide, Recovery & Risks | MyMedicPlus

Stereotactic body radiation therapy (SBRT), also called stereotactic ablative radiotherapy (SABR), delivers highly focused, high-dose radiation beams to extracranial tumours with sub-millimetre accuracy in 3-5 treatment sessions (fractions), exploiting a steep dose fall-off to ablate the tumour while sparing surrounding normal tissues. It is distinct from stereotactic radiosurgery (SRS), which targets intracranial lesions in a single fraction. SBRT is delivered using CyberKnife, dedicated LINAC systems with image guidance (VMAT, HyperArc), or helical tomotherapy. Four-dimensional CT motion management accounts for respiratory tumour movement during planning and treatment.

SBRT/SABR delivers the total radiation dose in 3–8 sessions (fractions) — called hypofractionation — compared to conventional radiotherapy which may use 25–35 daily fractions over 5–7 weeks. This hypofractionation induces additional cell death through vascular and immunological mechanisms beyond direct DNA damage. SBRT systems include the CyberKnife (robotic-mounted LINAC with image-guided delivery), the Varian TrueBeam, and the Elekta Versa HD, all providing 6 degrees of freedom positioning correction and real-time tracking of tumour motion during treatment. Stereotactic ablative radiotherapy (SABR) is the preferred UK term for extracranial stereotactic treatments. SBRT/SABR is delivered in 3–8 outpatient sessions and achieves local control rates equivalent to surgery for early-stage lung cancer in medically inoperable patients.

SBRT is indicated for medically inoperable stage I-II non-small cell lung cancer (NSCLC), oligometastatic disease (1-5 metastases to liver, adrenal gland, lung, lymph nodes, or spine), low- to intermediate-risk prostate cancer, hepatocellular carcinoma (HCC) not suitable for ablation or resection, renal cell carcinoma, and pancreatic cancer in selected cases. It is the preferred treatment for early-stage lung cancer in patients with poor pulmonary function or severe cardiopulmonary comorbidities who cannot tolerate surgical resection. Multidisciplinary tumour board review determines SBRT eligibility based on tumour size, location, and proximity to organs at risk.

Patient selection requires multidisciplinary tumour board review. For early NSCLC, patients must be medically inoperable (severe COPD with FEV1 less than 40% predicted, cardiac comorbidity, advanced age) or have refused surgery. Tumour size must be less than 5 cm (typically). PET-CT staging is mandatory to exclude nodal or distant metastatic disease. For oligometastatic disease (1–5 metastases), SBRT is used alongside systemic therapy to achieve durable local control of all metastatic sites in a growing strategy termed 'metastasis-directed therapy,' supported by the SABR-COMET and ORIOLE trials.

Treatment begins with a planning session: the patient is immobilised in a custom mould or stereotactic body frame; a 4D-CT simulation captures tumour motion through the respiratory cycle; MRI or PET-CT images are fused for target delineation. The radiation oncologist contours the tumour target volume (GTV/ITV/PTV) and critical organ constraints. Treatment planning software optimises beam arrangements for dose coverage and normal tissue sparing. Gold fiducial markers may be implanted (under ultrasound or CT guidance) for real-time tumour tracking during treatment. Each fraction is delivered over 20-60 minutes under continuous cone-beam CT image guidance verifying patient and tumour position. Total SBRT courses typically span 1-2 weeks.

Treatment is delivered in 3–8 outpatient sessions, each lasting 30–60 minutes including positioning and verification. The patient is immobilised in a custom-moulded vacuum bag or stereotactic body frame. Daily cone-beam CT (CBCT) imaging at the treatment machine verifies position before each fraction, with sub-millimetre accuracy. Fiducial gold markers implanted bronchoscopically or percutaneously allow real-time tumour tracking for lung lesions. The total biological effective dose (BED) is 100–200 Gy — 3–5× higher than conventional radiotherapy — achieving ablative tumour cell kill rates. Each SBRT fraction is delivered over 20–45 minutes with real-time image guidance (CBCT, ExacTrac, or gating) to account for respiratory and cardiac motion during beam delivery.

SBRT achieves local control rates of 85-95% at 3 years for stage I NSCLC, comparable to surgical lobectomy in matched patient populations. For hepatocellular carcinoma, 2-year local control exceeds 80% with SBRT. Prostate SBRT (5 fractions) achieves biochemical control rates equivalent to conventional fractionation at 5 years with superior patient convenience. Oligometastatic disease SBRT prolongs progression-free survival and, in selected patients, overall survival versus systemic therapy alone. As an entirely outpatient procedure with no anaesthesia, SBRT is accessible to patients with significant comorbidities who cannot tolerate surgery.

For stage I NSCLC, SBRT achieves 3-year local control of 85–95%, with cancer-specific survival of 85–90% at 3 years — oncologically equivalent to surgical lobectomy in population-matched cohort studies, though randomised trial data comparing SBRT to surgery remain limited (STARS, ROSEL trials closed early). For liver metastases from colorectal cancer, SBRT achieves 2-year local control of 70–85% when combined with systemic chemotherapy. Prostate cancer SBRT (5 fractions of 7–7.25 Gy) achieves 5-year biochemical control of 90–95% for low- and intermediate-risk disease, equivalent to 8-week conventional courses.

SBRT toxicity is site-specific. Lung SBRT: radiation pneumonitis in 5-10% of patients at 3-6 months, rib fractures adjacent to chest wall-abutting tumours (5-10%), and rarely radiation-induced brachial plexopathy. Liver SBRT: radiation-induced liver disease (RILD) in 5-10%, particularly in patients with pre-existing cirrhosis. Spine SBRT: vertebral compression fracture (10-20%), and risk of radiation myelopathy (under 1% with strict cord dose constraints). Oesophageal, bowel, and biliary toxicity are risks for abdominal SBRT. Late toxicity typically manifests at 6-24 months post-treatment and is managed with supportive care, corticosteroids, or surgical intervention for fractures.

Prostate SBRT: acute urinary and rectal symptoms (frequency, urgency, rectal discomfort) are common but typically resolve within 4–6 weeks. Late genitourinary or rectal toxicity grades ≥2 occur in 5–10%. For spine SBRT, spinal cord dose constraints are strictly observed to prevent radiation myelopathy (less than 0.1%). Vertebral body fracture at the treated level occurs in 10–40% for lesions involving the vertebral body at high doses. Patients must be counselled that not all lesions are suitable for SBRT and that assessment at a specialist centre is essential.

SBRT requires no anaesthesia and patients return home immediately after each session. Mild fatigue and, for lung treatments, a dry cough or mild dyspnoea may develop during or after the treatment course. No activity restriction is imposed between fractions or after completing treatment. Post-treatment imaging with CT or PET-CT is scheduled at 3 months and 6-monthly thereafter to assess tumour response and detect radiation-related changes. Tumour on imaging may appear unchanged or increase transiently due to radiation necrosis before shrinking (pseudo-progression), which should not be misinterpreted as treatment failure. Pulmonary function tests are repeated at 6 months for lung SBRT patients with borderline function.

Following completion of the SBRT course, imaging surveillance is performed at 3-month intervals for the first 2 years: CT for lung and liver, MRI for spine. Tumour response on CT may show initial increase in size before shrinking (pseudoprogression) — typically peaking at 6–12 months and declining thereafter. Patients must not mistake this expected radiological appearance for disease progression. Pulmonary fibrosis developing at the treatment site is a normal late finding on CT, not indicating tumour recurrence. Post-treatment fatigue resolves within 2–4 weeks in most patients. Re-staging PET-CT is performed at 6 months to assess overall treatment response.