Fractionation in Radiotherapy: Principles and Effects

Dose Fractionation

Dividing radiation dose into multiple smaller doses.

Single Radiation Dose

One large dose causing extensive skin damage.

Multifraction

Daily radiation doses over several weeks.

Tumour Control

Better achieved with fractionated doses than single doses.

4 Rs of Radiobiology

Repair, Reassortment, Repopulation, Reoxygenation principles.

Repair of Sublethal Damage

Cells recover from non-lethal radiation injury.

Reassortment

Cells move into radiosensitive phases during treatment.

Repopulation

Surviving cells proliferate between radiation doses.

Reoxygenation

Increased oxygen levels enhance tumour sensitivity.

Therapeutic Ratio

Tumour control percentage versus normal tissue damage.

Dose-Response Curve

Sigmoid shape showing response to radiation doses.

Tolerance Dose

Dose producing acceptable treatment complication probability.

Serially Arranged Tissues

Tissues where failure of one cell affects function.

Non-Serially Arranged Tissues

Tissues where partial failure does not affect function.

Nominal Standard Dose (NSD)

Total dose related to number of fractions and time.

Strandquist Plot

Graph showing total dose versus treatment time.

Early-Responding Tissues

Tissues like skin that respond quickly to radiation.

Late-Responding Tissues

Tissues like spinal cord that respond slowly.

Sigmoidal Curve

Shape of dose-response relationship for normal tissues.

α/β Ratio

Dose at which linear and quadratic cell killing equal.

Higher α/β Ratio

Indicates sensitivity to larger doses of radiation.

Lower α/β Ratio

Indicates better response to fractionated radiation therapy.

G1 Phase

Cell cycle phase before DNA synthesis.

G0 Phase

Resting phase in the cell cycle.

Radiosensitivity

Cellular response to radiation exposure.

Proliferation

Cell division and growth rate affecting radiation response.

Functional Reserve Capacity

Percentage of organ needed for adequate function.

Hyperfractionation

Multiple small doses given in a day.

Excessive Prolongation

Too long treatment time allows tumor cell proliferation.

Dose-Response Relationship

Correlation between radiation dose and biological response.

Fraction Size

Amount of radiation given in one treatment session.

Overall Treatment Time

Total duration of the radiation therapy regimen.

Tumour Cell Survival

Ability of cancer cells to survive radiation exposure.

Clonogens

Surviving cells in a tumor that can proliferate.

Accelerated Repopulation

Increased division rate of surviving tumor cells post-treatment.

Treatment Completion

Finishing therapy as soon as possible for effectiveness.

Tumor Growth Curve

Graph showing tumor size changes over time.

Local Control

Ability to control tumor growth in the treated area.

Tpot

Potential tumor doubling time, indicating growth rate.

Sublethal Damage Repair

Cellular repair of non-lethal radiation-induced damage.

CHART

Continuous hyperfractionated accelerated radiation therapy protocol.

Acute Reactions

Immediate side effects occurring during or shortly after treatment.

Late Effects

Delayed side effects occurring long after treatment.

Clinical Trials

Research studies testing new treatment protocols.

Oropharyngeal Cancer

Cancer located in the oropharynx region of the throat.

Radiotherapy

Treatment using high-energy radiation to kill cancer cells.

Fractionation Studies

Research analyzing effects of dose division on treatment outcomes.

Tumor Control Rate

Percentage of patients with controlled tumor growth post-treatment.

Treatment Regimen

Planned schedule of radiation doses for patients.

Lethal Complications

Severe side effects that can lead to patient death.

Radiation Dose

Amount of radiation delivered to tissues during treatment.

Hypofractionation

Delivering larger dose fractions in fewer sessions.

Stereotactic Radiosurgery (SRS)

Single fraction treatment for brain tumors.

Stereotactic Body Radiotherapy (SBRT)

Few fractions for body tumors, like lung cancer.

High Dose Rate (HDR) Brachytherapy

Localized high radiation dose in limited fractions.

Tumor Control Probability (TCP)

Likelihood of controlling tumor based on dose.

Biologically Effective Dose (BED)

Dose adjusted for biological effectiveness in tissues.

Linear-Quadratic Model

Describes cell killing by radiation dose.

Effective Dose-Response Relationship

Straight line correlating dose and survival fraction.

Endothelial Cell Damage

Causes tumor hypoxia leading to cell death.

Redistribution in Cell Cycle

Cells move to radiation-sensitive phases post-treatment.

Radioresistance

Tissue's ability to withstand radiation damage.

Hypoxic Cells

Cells with low oxygen, resistant to radiation.

Dose Gradient

Variation of radiation dose around the target.

Local Control Rates

Success rate of controlling tumor growth locally.

Conventional Treatment

Standard regimen of multiple small fractions.

Concomitant Boost

Simultaneous higher dose to a smaller tumor area.

Radiotherapy Advances

Technological improvements enhancing treatment precision.

Tissue Response

How tissues react to radiation exposure.

Fractionation Regimen

Schedule for delivering radiation doses.