Rad Bio 1 Exam 2 Review

Radioprotectors

Sulhydryl compounds

• Cysteine

• Cyysteamine

Structural features

• Free SH group

• Carbon link

• Protein ends

Dose reduction factor (DRF)

Dose of radiation in the presence of the drug/ Dose of radiation in the absence if the drug

Mechanism of action for radioprotectors

• Free radical scavenging

• Hydrogen atom donation

Fractionation

Produces better tumor control for a given normal tissue toxicity than a single large dose

4 R’s

• Repair

• Reassortment

• Repopulation

• Reoxygenation

Alpha/Beta Ratio

Dose at which cell killing by linear and quadratic components is similar

Malformations

Seen during major organ development

• relevant structures that are rapidly dividing

Growth disturbances

Can be induced at any time of fetal development

• Mostly in late pregnancy though

Seen with or without malformations

Factors affecting fetal effect

• Total dose

• Stage of gestation

• Dose rate

Microcephaly

• No threshold

• Increases with dose

• Not seen if irradiated post 16 weeks

Mental retardation

• 8-25 weeks post conception

  • Greatest from 8-15 weeks

Alpha LQ Formulism

• Represents the log_e of the cells killed per Gy

• Linear portion of the curve

Beta LQ Formulism

• Represents the log_e of the cells killed per Gy squared

• Portion of the curve that bends

Alpha/Beta Ratio (unit of Dose)

Dose at which the linear and quadratic component of cell killing are equal

Biological Effect Formula

BED= (nd) * (1+d/(alpha/beta)

Early effects

10

Late effects

3

Kick off time

Starts off time for rapid proliferation in tumors appears to be 3-4 weeks (21-28 days)

Nominal Standard Dose (NSD)

The dose given in a single exposure that would take connective tissue to the tolerance level

Use of TDF tables

Compare fractionation regimens