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• There are two types of ionizing radiation: EM radiation (UV, X ray and Gamma rays) and particle radiation (alpha, beta and neutron)
• Biological effects of ionizing radiation – due to DNA damage. Either directly or indirectly.
• Radiotherapy damages cancer cell DNA by using ionizing radiation. This can affect both normal and cancer cells. Normal cells have time to heal.
• Sequence 1 - x ray photon hits target. Leads to compton scattering, pair production or photoelectric effect. Forms free radicals. Radicals damage DNA. Leads to mutation.

  Sequence 2 – x ray hits target. Leads to compton scattering, pair production or photoelectric effect. Ionizes DNA molecule. Damage DNA. Leads to mutation
• Radiotherapy – fractionation spares normal tissue and targets cancerous tissue. Gives total radiation in fractions over a period of time so healthy tissue have time to heal. Tumors are radiation sensitive. Planning increases effectiveness and decreases damage.
• Depending on the patient and treatment type, Xrays, gamma rays and electrons can be used.
• Examples are external beam radiator and brachytherapy.
• Apart from solid tumors, radiotherapy can also be used to treat blood cancers.
• In external treatments using xrays, gamma rays and electrons, multiple beams of radiation is used. Delivers minimal damage but maximum radiation dose.
• Many side effects – aching, swelling, tired, skin burn and second cancer.
• Radiotherapy treatment planning –

  Precise imaging technique used to locate tumor (MRI, ultrasound)

  Complex mathematical models used to find best appraoch to destroy tumor with minimal damage to health tissue. Leads to effective treatment.
• Treatment planning process – locate and assess tumor size and structure. Determine energy dose for tumor destruction. Plan radiation distribution within tissue (strength, no.of beams, beam direction). Minimize radiation to healthy tissue. Position patient according to plan. Measure and monitor radiation levels. Use protective masks for less exposure.
• Dosimetry simulators used for radiotherapy planning.