External Beam Radiation Therapy

• Uses high-energy X-rays, electrons, or protons delivered from an external machine (linear accelerator, or LINAC) to target tumors.
• Unlike brachytherapy (where radioactive sources are placed inside the body), EBRT is non-invasive and delivered from outside.

Types of EBRT

1. 3D-CRT (Three-Dimensional Conformal RT): Uses imaging to shape beams around the tumor.
2. IMRT (Intensity-Modulated RT): Varies beam intensity for better sparing of normal tissue.
3. IGRT (Image-Guided RT): Uses imaging before/during treatment to improve precision.
4. SRS/SBRT (Stereotactic Radiosurgery/Body RT): High-dose, very precise, usually 1–5 fractions.
5. Proton Therapy: Uses protons instead of photons → less exit dose, useful in pediatrics and near critical organs.

Pharmacist’s Relevance

As an oncology pharmacist, EBRT matters because:

1. Integration with Systemic Therapy
   • EBRT is often combined with chemotherapy or immunotherapy (chemoradiation).
   • Certain drugs act as radiosensitizers (e.g., cisplatin, 5-FU, temozolomide, cetuximab).
   • Important for you to know which regimens are intended for concurrent use with EBRT.
2. Toxicity & Supportive Care
   • Acute toxicities (during/soon after treatment):
     • Skin reactions (erythema, desquamation)
     • Fatigue
     • Mucositis, esophagitis, diarrhea (site-dependent)
   • Late toxicities (months–years later):
     • Fibrosis, strictures, xerostomia, infertility, secondary malignancies.
   • Pharmacists help optimize analgesics, antiemetics, mucosal protectants, skin care, anti-diarrheals.
3. Drug–Radiation Interactions
   • Some systemic therapies increase radiation toxicity (e.g., doxorubicin, bleomycin, gemcitabine).
   • You may need to adjust timing (e.g., avoid giving certain agents concurrently with RT).
4. Radioprotectants & Adjuncts
   • Amifostine: Protects normal tissues (esp. salivary glands in head & neck RT).
   • Mesna: Not a radioprotector, but important when chemotherapy is combined.
   • Corticosteroids: Reduce edema and inflammation (esp. in brain RT).

Key Points for Oncology Pharmacist

• EBRT is local treatment, but systemic drugs can enhance or worsen its effects.
• Always check:
  • If chemo is concurrent or sequential with EBRT.
  • Patient’s ECOG PS before combined modality therapy.
  • Need for supportive meds (antiemetics, mucositis care, skin protection).
  • Potential drug-radiation toxicities.

In summary:

EBRT delivers targeted radiation externally to control tumors, often combined with systemic therapy. For pharmacists, the focus is on radiosensitizers, toxicity management, and drug–radiation interactions.