Radiation and Cancer: Understanding the Relationship

Ionizing radiation is a known carcinogen (IARC Group 1), but it is not the sole cause of cancer. Cancer is multifactorial.

Radiation-Induced Cancer

• Mechanism: DNA damage (DSBs, chromosomal rearrangements) → mutations in oncogenes/TSGs.
• Dose-response: Linear no-threshold (LNT) model for solid tumors; leukemia has linear-quadratic.
• Latency: Leukemia 2–10 yrs; solid tumors 10–40+ yrs.
• Risk factors: Young age at exposure, female sex (breast, thyroid), genetic susceptibility (ATM, BRCA), smoking synergy (lung).

Other Major Carcinogen Categories

• Genetic: Inherited mutations (BRCA, Lynch, TP53).
• Lifestyle: Tobacco (30% of cancer deaths), alcohol, diet (processed meat, low fiber), obesity, inactivity.
• Environmental: Air pollution (PM2.5), asbestos, benzene, arsenic, radon.
• Infectious: HPV (cervical, oropharyngeal), HBV/HCV (liver), H. pylori (gastric), EBV (lymphoma).
• Medical: Prior chemo/radiation, immunosuppression, hormone therapy.

Radiation in Medicine

• Diagnostic: CT (~10 mSv), X-ray (~0.1 mSv) – small individual risk; justified by benefit.
• Therapeutic: Curative intent; second malignancy risk ~0.5–2% at 10–20 yrs – outweighed by primary cancer control.

ALARA principle (As Low As Reasonably Achievable) guides medical radiation use.