**Radiation Therapy for Cancer: Comprehensive Guidelines**

**1. Introduction**
Radiation therapy (radiotherapy) is a crucial modality in the treatment of cancer, utilizing high-energy radiation to destroy cancer cells. These guidelines provide an evidence-based approach to radiation therapy from patient evaluation to post-treatment follow-up.

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**2. Patient Evaluation and Selection**
- **Diagnosis Confirmation**: Histopathological confirmation of cancer.
- **Staging**: Clinical staging using imaging (CT, MRI, PET-CT) and biopsy.
- **Indications for Radiation**:
  - Primary treatment
  - Adjuvant therapy post-surgery
  - Palliative treatment for symptom relief
  - Prophylactic treatment in high-risk patients
- **Contraindications**:
  - Pregnancy (relative contraindication, except in life-threatening cases)
  - Certain connective tissue disorders (e.g., scleroderma)
  - Previous excessive radiation exposure

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**3. Radiation Treatment Planning**
- **Multidisciplinary Team Approach**:
  - Radiation oncologist, medical physicist, dosimetrist, radiation therapist, and oncology nurse.
- **Simulation and Imaging**:
  - CT simulation for treatment planning.
  - MRI/PET for improved tumor localization if needed.
- **Immobilization**:
  - Use of masks, molds, or body frames for patient stability.
- **Treatment Planning Systems (TPS)**:
  - 3D conformal radiation therapy (3D-CRT)
  - Intensity-modulated radiation therapy (IMRT)
  - Image-guided radiation therapy (IGRT)
  - Stereotactic body radiotherapy (SBRT) for small tumors
  - Proton beam therapy in specific cases

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**4. Radiation Delivery Techniques**
- **External Beam Radiation Therapy (EBRT)**:
  - Linear accelerators deliver photons or electrons.
  - Fractionation schedules vary based on cancer type.
- **Brachytherapy (Internal Radiation)**:
  - Used for prostate, cervical, and breast cancer.
  - High-dose-rate (HDR) vs. low-dose-rate (LDR) implants.
- **Radiosurgery**:
  - Stereotactic radiosurgery (SRS) for brain tumors.
  - Stereotactic body radiation therapy (SBRT) for lung, liver, or spine tumors.

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**5. Dose Prescription and Fractionation**
- **Curative Intent**:
  - Standard fractionation: 1.8-2 Gy per fraction, 5 days per week.
  - Hypofractionation: Higher doses per fraction for specific cases.
  - Hyperfractionation: Smaller doses given more than once daily.
- **Palliative Intent**:
  - Lower total doses with fewer fractions.
  - Example: 30 Gy in 10 fractions for pain relief.

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**6. Side Effects and Management**
- **Acute Toxicities** (during or shortly after treatment):
  - Skin reactions (erythema, desquamation) – Managed with topical agents.
  - Fatigue – Encouraging rest and proper nutrition.
  - Mucositis and esophagitis – Symptomatic relief with analgesics and dietary modifications.
  - Diarrhea (pelvic radiation) – Antidiarrheals and dietary adjustments.
- **Late Toxicities** (months to years post-treatment):
  - Fibrosis, secondary malignancies, chronic pain.
  - Endocrine dysfunction (thyroid, pituitary) – Managed by endocrinologists.
  - Cognitive decline (brain radiation) – Cognitive therapy and medications.

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**7. Follow-up and Surveillance**
- **Regular Assessments**:
  - First follow-up: 4-6 weeks post-treatment.
  - Subsequent visits: Every 3-6 months for 2-3 years, then annually.
- **Imaging and Biomarkers**:
  - Periodic imaging to assess treatment response.
  - Tumor markers (PSA for prostate cancer, CEA for colorectal cancer, etc.).
- **Psychosocial Support**:
  - Mental health counseling, rehabilitation services, and support groups.
- **Survivorship Care**:
  - Lifestyle modifications, screening for secondary cancers, and ongoing symptom management.

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**8. Special Considerations**
- **Pediatric Radiation Therapy**:
  - Lower doses and specialized techniques to minimize long-term effects.
- **Geriatric Patients**:
  - Treatment tailored to comorbidities and functional status.
- **Radiation in Pregnancy**:
  - Highly individualized; shielding and alternative therapies considered.

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**9. Conclusion**
Radiation therapy remains a cornerstone of cancer treatment, with advancements improving efficacy and reducing toxicity. A patient-centered, multidisciplinary approach ensures the best outcomes while minimizing adverse effects.

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**10. References and Further Reading**
- National Comprehensive Cancer Network (NCCN) Guidelines
- American Society for Radiation Oncology (ASTRO) Guidelines
- European Society for Radiotherapy & Oncology (ESTRO) Recommendations