Fractionation And Dose Effects Flashcards
What does Protraction mean in the context of radiation therapy?
Protraction is the number of total days that the radiation is delivered over.
What is Standard Fractionation?
Standard Fractionation involves delivering 1.8-2.0 Gy per day for 5 days per week.
What is Hyperfractionation?
Hyperfractionation involves delivering 1.0 - 1.2 Gy twice per day for 5 days per week.
The hope is to provide a higher total dose with a higher probability of tumor control and less or equal side effects.
What is Accelerated Fractionation?
Accelerated Fractionation involves multiple fractions daily at 1.5 - 2 Gy per fraction.
This decreases the overall time; however, some reduction in total dose is necessary to prevent dose complications.
What is Hypofractionation?
Hypofractionation involves a larger daily dose per fraction and necessitates a reduction in total dose to avoid complications.
The objective is palliation when the patient is in bad condition.
What is Split Course in radiation therapy?
Split Course involves a larger daily fraction with a planned break in the middle of treatment to allow acute reactions to subside.
Generally not available unless the overall treatment time is decreased.
What is redistribution in the context of fractionation?
Synchronization of surviving cells into resistant mitotic phases.
Normal cells tend to remain in resistant phases, whereas tumor cells enter all phases.
What does reoxygenation refer to in fractionation?
The death of aerobic tumor cells allows hypoxic cells to become more oxygenated.
What is regeneration in relation to fractionation?
Occurs between fractions for highly mitotic cells.
What is repair in the context of fractionation?
Cellular repair of sublethal damage (SLD).
What is a Linear Relationship?
Response is directly related to dose.
What is a Non Linear Relationship?
Response is not directly proportional to dose.
What is a Nonthreshold Relationship?
Any dose, regardless of its size, is expected to produce a response.
What is a Threshold Relationship?
Has a dose at which no response would be expected.
What dose-response model do radiation protection guidelines use?
Radiation protection guidelines use the linear, nonthreshold dose-response model.
What does ‘stochastic’ mean?
‘Stochastic’ means random or probable.
What are non-threshold effects?
Non-threshold effects may occur no matter how small the dose.
What does any amount of dose carry in stochastic effects?
Any amount of dose carries a probability of inducing an effect.
How does the probability of an effect change with dose in stochastic effects?
As dose increases, probability increases.
How does the severity of the effect change with increased dose in stochastic effects?
The severity of the effect is not changed with increased dose.
What is a threshold dose?
A dose below which damage is not observed.
What happens above the threshold dose?
The severity of damage increases with an increase in dose.
What is the Doubling Dose?
Unit of measurement for determining radiation effect on mutation frequency.
What does the Doubling Dose represent?
Dose of radiation which ultimately doubles the number of spontaneous mutations.
