58 - SAM

What is radiation therapy and what does it use to kill cancer cells?

Ionizing energy from photons or particles that damages cellular structures and DNA

What are the two mechanisms by which radiation causes cellular damage?

Direct action (direct DNA damage) and indirect action (radiation creates free radicals that damage DNA)

What are the three types of radiation interactions and their energy levels?

Photoelectric effect = low energy

What are the 4 R's of radiobiology?

Repair of cellular damage

What is the repair component of radiation therapy and why is fractionation beneficial?

Normal tissues repair sublethal damage within 3-24 hours while tumors repair slowly

What is reoxygenation and why are hypoxic tumors relatively radioresistant?

Oxygen stabilizes free radicals and increases cell killing

What is the most radiation-sensitive phase of the cell cycle and why is redistribution important?

G2/M phase

What is repopulation and why can it negatively affect radiation therapy?

Tumor cells regenerate between treatments

What tumor characteristics are associated with a favorable radiation response?

Small well-vascularized homogeneous tumors

What tumor characteristics are associated with an unfavorable radiation response?

Large bulky tumors with hypoxia and heterogeneous tumors with variable cell populations

What is fractionation and why is it used in radiation therapy?

Dividing the total radiation dose into multiple smaller treatments to allow normal tissue repair while improving tumor cell killing

What is the difference between conventional and palliative radiation protocols?

Conventional = 2-3 Gy 5 times/week for 4-6 weeks

What is the difference between external beam radiation and brachytherapy?

External beam delivers radiation from an external machine

How does using multiple radiation fields and collimators help protect normal tissue?

They focus radiation on the tumor from different directions, concentrating the dose at the target while reducing normal tissue exposure

What are the major treatment considerations when selecting radiation therapy?

Tumor size and location

What is the difference between acute and late radiation toxicity?

Acute toxicity occurs during or shortly after treatment and typically affects rapidly dividing tissues

What are common examples of acute radiation toxicity?

Mucositis

What are common examples of late radiation toxicity and what increases their severity?

Xerostomia

Which type of radiation toxicity typically limits the total radiation dose and what is the exception?

Late tissue toxicity typically limits total dose

Which tumors are commonly treated with radiation and what are important response characteristics?

Nasal tumors: radiation is the only modality with documented survival benefit