What are the usual guidelines for External Beam Radiation Therapy (EBRT)?

Guidelines for External Beam Radiation Therapy (EBRT)

External Beam Radiation Therapy (EBRT) should utilize CT-based treatment planning and conformal blocking as the standard of care, with treatment volumes and doses tailored to the specific cancer type and stage.

General EBRT Planning Principles

Imaging for Treatment Planning

• CT-based treatment planning is considered standard of care 1
• MRI is preferred for determining soft tissue and parametrial involvement in advanced tumors 1
• PET imaging helps define nodal volumes in patients who are not surgically staged 1

Dose and Fractionation

• Standard fractionation: 1.8-2.0 Gy per daily fraction 1
• Total dose for microscopic disease: 45-50 Gy 1
• Boost doses of 10-15 Gy may be considered for gross unresected adenopathy 1

Treatment Techniques

• 3D conformal radiation therapy is the baseline approach
• Advanced techniques include:
  • Intensity Modulated Radiation Therapy (IMRT)
  • Volumetric Modulated Arc Therapy (VMAT)
  • Stereotactic Body Radiation Therapy (SBRT)/Stereotactic Ablative Radiotherapy (SABR) 1

Disease-Specific Guidelines

Lung Cancer

• Early-stage NSCLC: SBRT (6-18 Gy per fraction, 2-8 fractions) for medically inoperable patients 1
• Locally advanced NSCLC: Concurrent or sequential chemoradiotherapy (45 Gy total) 1
• Palliative EBRT: Higher dose regimens (30 Gy/10 fractions or greater) for good performance status patients 1
• Poor performance status patients: Shorter fractionation schedules (20 Gy/5 fractions, 17 Gy/2 fractions, 10 Gy/1 fraction) 1

Cervical Cancer

• Target volumes should include:
  • Gross disease (if present)
  • Parametria and uterosacral ligaments
  • Vaginal margin (at least 3 cm from gross disease)
  • Presacral nodes and other nodal volumes at risk 1
• For negative nodes: Include external iliac, internal iliac, and obturator nodal basins 1
• For higher risk of nodal involvement: Add common iliacs 1
• For documented common iliac/para-aortic involvement: Extend field to renal vessels 1
• Definitive treatment: 45 Gy EBRT followed by brachytherapy boost to total 80-85 Gy to point A 1
• Post-hysterectomy: 45-50 Gy to vaginal cuff, parametria, and adjacent nodal basins 1

Uterine Cancer

• Pelvic RT should target:
  • Gross disease (if present)
  • Lower common, external, and internal iliacs
  • Parametrium
  • Upper vagina
  • Presacral lymph nodes (in patients with cervical involvement) 1
• Extended field: Include entire common iliac chain and para-aortic region 1
• Post-hysterectomy: Vaginal brachytherapy boost options:
  • HDR boost after EBRT: 5-6 Gy × 2 fractions to vaginal mucosa
  • HDR vaginal brachytherapy alone: 7 Gy × 3 fractions at 0.5 cm depth or 6 Gy × 5 fractions to vaginal surface 1

Technical Considerations

IMRT and Advanced Techniques

• Benefits: Minimizing dose to bowel and critical structures 1
• Appropriate for: Post-hysterectomy setting, para-aortic nodes, and treating gross disease in regional lymph nodes 1
• Caution: IMRT should not replace brachytherapy for central disease in patients with intact cervix 1
• Requirements: Careful attention to target/normal tissue definitions, patient/organ motion, soft tissue deformation, and rigorous quality assurance 1

SBRT/SABR

• Primarily used for early-stage lung cancer and oligometastatic disease 1
• Uses high-dose radiation (6-18 Gy) in fewer sessions (2-8) 1
• Achieves high biological effectiveness while sparing surrounding tissues 1

Integration with Other Treatment Modalities

Combination with Chemotherapy

• Concurrent cisplatin-based chemotherapy is standard during EBRT for cervical cancer 1
• Options include cisplatin alone or cisplatin + 5-fluorouracil 1

Combination with Brachytherapy

• Brachytherapy is critical for definitive therapy in cervical cancer 1
• Usually performed using intracavitary approach with intrauterine tandem and vaginal colpostats 1
• Typically initiated toward latter part of EBRT when tumor regression permits satisfactory brachytherapy apparatus geometry 1

Common Pitfalls and Caveats

1. Inadequate target volume definition leading to geographic miss
2. Excessive normal tissue inclusion in high-dose regions
3. Inappropriate substitution of IMRT for brachytherapy in central disease
4. Failure to account for organ motion and setup uncertainties
5. Inadequate image guidance for precise treatment delivery

By following these guidelines, EBRT can be delivered with precision and accuracy to maximize tumor control while minimizing toxicity to surrounding normal tissues.