External Beam Radiotherapy — How It Works, Benefits & Recovery — Procedure Guide, Recovery & Risks | MyMedicPlus

External beam radiotherapy (EBRT) is a cancer treatment modality that delivers focused high-energy ionising radiation beams — generated by a linear accelerator (LINAC) — from outside the body to precisely defined tumour targets, causing lethal double-strand DNA breaks in rapidly dividing cancer cells while sparing as much surrounding normal tissue as possible. Modern EBRT has undergone a technological revolution driven by advanced treatment planning software, image guidance, and beam delivery techniques. Intensity-modulated radiotherapy (IMRT) uses computer-optimised multi-leaf collimator shaping to modulate the beam intensity across each field, sculpting a high-dose region tightly around the tumour with steep dose gradients protecting critical organs. Volumetric modulated arc therapy (VMAT) delivers IMRT in a continuous arc rotation around the patient in 1.5–3 minutes per fraction, compared with 10–15 minutes for step-and-shoot IMRT. Image-guided radiotherapy (IGRT) uses daily kilovoltage X-ray or cone-beam CT imaging acquired on the treatment couch to verify patient positioning before each fraction, reducing setup uncertainty and allowing tighter planning margins. Stereotactic ablative body radiotherapy (SABR/SBRT) delivers ultra-high doses per fraction (10–20 Gy) in 3–5 fractions using multiple non-coplanar beam arrangements and breath-hold or respiratory gating, achieving dose distributions that rival surgical outcomes for early-stage lung cancer, liver, prostate, and spinal metastases. Proton therapy uses proton beams rather than photons to deliver the Bragg peak — a physical dose peak at a precise depth — reducing exit dose and offering theoretical normal tissue advantages for selected paediatric and adult tumours.

EBRT is a primary or adjuvant treatment across a wide spectrum of cancers and some benign conditions. Curative-intent indications include: prostate cancer (low, intermediate, and high risk — definitive EBRT achieves equivalent survival to surgery), head and neck squamous cell carcinoma (concurrent chemoradiotherapy is standard of care), non-small cell lung cancer (stereotactic SABR for Stage I, concurrent CRT for Stage III), cervical cancer (external pelvic radiotherapy plus concurrent cisplatin followed by brachytherapy), and brain tumours (glioblastoma, medulloblastoma, ependymoma, primary CNS lymphoma). Adjuvant post-surgical EBRT reduces local recurrence in breast cancer (whole-breast irradiation after lumpectomy reduces 10-year recurrence from 30% to 10%), rectal cancer (short-course 5×5 Gy preoperatively or long-course 50.4 Gy with concurrent 5-FU), endometrial cancer, and soft-tissue sarcoma with close surgical margins. Palliative EBRT provides effective pain relief for bone metastases in 60–80% of patients, treats spinal cord compression, controls haemoptysis or haematuria from tumour bleeding, and manages obstruction from locally advanced tumours. Benign indications include keloid scars (post-excision radiotherapy reduces recurrence from 60% to 10%), acoustic neuroma, and trigeminal neuralgia (stereotactic radiosurgery).

The radiotherapy process begins at the CT simulation appointment, typically 1–2 weeks before treatment starts. The patient is immobilised in the reproducible treatment position using custom-made thermoplastic masks (for head and neck/brain), a vacuum-formed body bag (for lung/liver), or a knee cushion and foot support (for prostate/pelvis). A CT scan from the simulation is acquired with or without intravenous contrast and transmitted to the radiotherapy planning workstation. The radiation oncologist contours the gross tumour volume (GTV), clinical target volume (CTV), planning target volume (PTV — adding setup margins), and all organs at risk (OAR: spinal cord, heart, lungs, kidneys, bowel, optic structures). A medical physicist generates a VMAT or IMRT treatment plan optimising dose coverage of the PTV while respecting dose constraints for each OAR. Plan quality is reviewed and approved at a departmental plan review meeting. Before the first treatment, a cone-beam CT is acquired on the LINAC to match the patient's anatomy to the planning CT and verify position. Each fraction (individual treatment session) takes 10–30 minutes on the LINAC table, of which beam-on time is typically 2–10 minutes. Most patients receive 15–35 fractions delivered Monday–Friday over 3–7 weeks, though hypofractionated schedules (higher dose per fraction, fewer fractions) are now standard for prostate, breast, and lung SABR.

EBRT offers curative treatment without surgical incision for many cancers, preserving organs and function that surgery would remove. Breast-conserving surgery followed by EBRT achieves equivalent 20-year survival to mastectomy (Early Breast Cancer Trialists' Collaborative Group meta-analysis) while preserving the breast. Definitive chemoradiotherapy for oropharyngeal, laryngeal, and anal cancers avoids permanent tracheostomy, total laryngectomy, or colostomy — life-altering surgical outcomes — while achieving equivalent or superior survival rates. Modern SBRT for early-stage non-small cell lung cancer achieves 3-year local control rates exceeding 90% in patients who are medically inoperable, making SBRT the preferred treatment for this population. For prostate cancer, modern EBRT with IGRT delivers 10-year biochemical control rates of 85–93% for low-risk, 75–85% for intermediate-risk, and 60–70% for high-risk disease, comparable to radical prostatectomy with superior urinary continence preservation in most series. Palliative EBRT rapidly resolves bone pain from metastases in over 70% of patients — a 20 Gy in 5 fractions or 8 Gy single fraction — and achieves paraplegia reversal in 70–80% of patients treated within 24 hours of cord compression onset. EBRT can be repeated at progression for reirradiation of selected recurrences using modern proton or photon techniques.

Acute radiation toxicity develops during treatment and peaks 1–2 weeks after completion before resolving over 4–8 weeks. Site-specific acute effects include: dermatitis (skin erythema, moist desquamation for breast/chest wall and head and neck irradiation), mucositis and xerostomia (head and neck cancers — requires aggressive supportive care, feeding tube in 20–30% of high-dose head and neck CRT patients), dysuria and haematuria (prostate), bowel frequency and urgency (pelvis), fatigue (universal, especially with concurrent chemotherapy), nausea (upper abdominal), and hair loss (within the radiation field only). Late radiation toxicity occurs months to years after treatment and reflects permanent normal tissue injury. Important late effects include: radiation fibrosis (lung, causing dyspnoea — limited by modern IMRT with strict V20 and mean lung dose constraints), xerostomia from parotid gland irradiation (reduced but not eliminated with IMRT parotid sparing), bowel stricture or fistula (less than 2% with modern pelvic IMRT dose constraints), bladder contracture (less than 5% with modern prostate EBRT), secondary malignancy risk (approximately 0.5–1% absolute excess risk at 10 years — lower than equivalent chemotherapy regimens), and lymphoedema. Radiation necrosis of bone (osteoradionecrosis — particularly mandible in head and neck) requires aggressive dental prophylaxis and in severe cases surgery.

During treatment, patients are assessed weekly by the radiation oncologist and oncology nurse for toxicity review, weight, and supportive care needs. Fatigue increases progressively through the treatment course and continues for 4–6 weeks after the last fraction before gradually improving. Head and neck cancer patients require aggressive mucositis management including chlorhexidine mouthwash, benzydamine rinses, analgesics, and nutritional support — enteral feeding via nasogastric tube or percutaneous gastrostomy is initiated in 20–30% of patients receiving radical chemoradiotherapy. Skin care with non-perfumed moisturising cream reduces acute dermatitis in breast and head and neck patients. Pelvic EBRT patients are advised on bowel management with loperamide and low-residue diet during treatment. After treatment completion, acute toxicities resolve over 4–8 weeks. Most patients return to light activities within 1–2 weeks and full activities within 6–8 weeks of treatment end. First post-treatment response assessment (CT, MRI, or PET-CT) is typically at 8–12 weeks after completion. Cancer markers (PSA for prostate, CEA for rectal) are monitored 3-monthly for 2 years, then 6-monthly. Late effects are monitored at annual follow-up and managed by relevant specialists (dietitian, physiotherapist, continence advisor, dentist).