Intro to Radiation Oncology

What is ionizing radiation? Goals in CA?

Contrallable energy that can be directed at tumors or regions at risk. Goal is to kill cancer without irreparably damaging normal tissues

Mechanism of radiation

DNA damage leading to cell death via direct(damage to structure) and indirect(making ROS)

Direct effect of radiation

DNA is directly ionized → ~30% of damage

Indirect effect of radiation

Water radiolysis → free radicals → DNA damage (~70% of damage)

Define brachytherapy

Placement of radioactive sources inside or adjacent to tumor

Why precise dose delivery matters?

Tumor control dose is close to normal tissue toxicity dose → steep dose‑response curves

Why whole‑body irradiation is impossible?

Dose required to kill tumor (~70 Gy) is fatal to normal tissues

Conventional fractionation (Bruce Lee)

1.8–2 Gy per fraction, daily M–F

SBRT/SABR (the Rock)

Few fractions with very high dose per fraction (ablative)

Proton therapy advantage + disadvantage

Bragg peak → no exit dose → less normal tissue toxicity. VERY $$ + not always necessary

Parallel organ radiation injury

Organ composed of many units damage to one unit compensated by others (e.g., liver, lung)

Serial organ radiation injury

Continuous structure damage to one segment causes total organ dysfunction (e.g., spinal cord, bowel)