Radiotherapy

Question 1

Radiotherapy principles?

Answer 1

1/3 of photons used to cause direct action (direct damage to DNA caused by free electron). Other 2/3 time free election interacts with water to make free radicals —this is indirect action (oxygen must be present bc it binds DNA/free radical combination, permanating free radical damage.

Question 2

Result of DNA damage from radiotherapy?

Answer 2

Single and double strand DNA breaks. Single little consequence and easily repaired. Double are more difficult for cell to repair and often result in death of cell.

Question 3

What is fractionation?

Answer 3

The delivery of multiple doses of radiation in intervals that allow normal tissue time to repair DNA damage. Each single dose of radiations kills the same percent of cells each time.

Question 4

What are some agents that are radiosensitizers?

Answer 4

5-flurouracil, cisplatin, carboplatin, etopiside, gemcitabine, paclitaxel.

Question 5

Side effects of radiotherapy?

Answer 5

Acute - shortly after or during RT in rapidly dividing normal tissues in treatment field. As a results of death of stem cells. Resolve 2 to 3 weeks after therapy is complete. Likelihood of experiencing acute effects is related to total dose of radiation delivered and the total time of entire treatment protocol.
Late effects - occure several months after RT in slowly proliferating normal tissues in field (endothelium or parenchymal cells). No stem cells to replace, so late effects are permenant. Likelihood of experiencing late effects is related to dose per fraction. That larger dose per fraction, the more likely to occur.