Radiation Oncology

What is radiotherapy?

The use of radiation to kill cancer cells

What is the common use of radiotherapy?

Regional therapy, but systemic is possible

It is usually combined with surgery or chemotherapy

What is the biggest benefit for radiotherapy?

Non-invasive and preserves tissue and function

High quality of life

What type of radiation is used?

Ionizing radiation (high energy)

What is Gy?

Unit of absorbed dose

What is the goal of radiotherapy?

Kill as many cancer cells as possible

• Can try to cure local cancer

• Can try to shrink local cancer

T/F radiotherapy side effects can be acute or late?

True

What is the maximum dose of radiotherapy limited by?

Normal tissues

Are animals radioactive after RT?

No, once the machine turns off it is very safe

What machine do we have at KSU?

6MB photon (x-ray) with high penetration in tissue

Multileaf collimator

6-21MeV electrons

Describe diagnostic x-ray radiation

Lower energy

Produces an image

Differential absorption-contrast

Photoelectric effect

Describe therapeutic radiation?

High energy (mega volt, not kilavolt)

Kills cancer cells

Homogenous absorption

Compton effect

What can we radiate?

All tumor types, locations, stages, all species

What are the common tumors for RT?

Soft tissue sarcoma

Mast cell tumor

Nasal tumor

Thyroid tumor

Brain tumor

Melanoma

Osteosarcoma to control pain

Only for a local lymphoma

T/F RT is always an individualized plan?

True

How do you plan where to give radiation therapy?

Use CT based 3-dimensional conformation radiation therapy planning

What are the effects of RT?

DNA damage and cell death (mitotic death and intermitotic death)

What cancer responds very quickly to RT because it divides quickly?

Lymphoma

What is most susceptible to RT?

Rapidly dividing cells 

T/F tumor response is hard to predict?

True

T/F normal tissue response is predictable?

True

What is the MOA of RT?

RT reacts with H2O creating free radicals

Free radicals interact with damaged DNA

Abnormal DNA is not able to replicate causing cell death

Where does most damage from RT come from?

Indirect effect (photon)

What type of DNA break do you want?

Double stranded because it is hard to repair

How do single strand DNA breaks repair?

Easily

Double stranded breaks that are far apart are repaired how?

Two single strand repairs

What it he problem with a single large dose of RT?

Too toxic for normal tissue

How is a course of RT described?

Tortal dose

Fractionation

Time course over it is delivered

What allows you to predict tumor control probability?

Total dose

T/F RT protocols are empirical based on clinical experience?

True

What is the most common complication of RT?

Treatment failure, not lethal dose of radation

Why do we do fractionation?

Spares normal tissue by repairing sublethal damage between doses and repopulation of cells

Increases dmage to the tumor

How does fractionation increase damage to tumor?

Reoxygenation after tx makes cells that were not susceptible susceptible to RT

Redistribute cells into radiosensitive phases

What happens if normal tissue can recover from RT quicker than tumor?

Improves therapeutic ratio

What is the susceptibility of hypoxic tumor cells to RT?

Resistant

What is the susceptibility of oxygenated tumor cells to RT?

Susceptible

Describe acute toxicity side effects?

Seen during therapy and resolves quickly

Rapidly dividing cells causeing oral mucositis, moist desquamation or something similar

Can be dose limiting

Where are acute toxicity effects located?

Wherevere the radiation therapy was

What can you do to help with acute toxicity?

Supportive care and pain control

Describe late toxicity

Slowly dividing cells occurring months to years after

Dose limiting (life limiting) can cause fibrosis or necrosis

Does NOT resolve

Cataracts are common

What are deterministic effects? (acute and late)

Dose dependent, threshold

Hard to control

Leads to cataracts

What are stochastic effects? (late only)

Dose dependent increases risk

Randomness

Hard to predict

Secondary malignancy

When is a tumor most susceptible to RT?

First time

What are some limiting factors for deciding to use RT?

Owner desire / other factors

What is definitive radiotherapy?

Curative intent to eliminate all cancer cells

Use high dose and accept acute side effects

Avoid late side effects

What is conventional fractionation?

3 Gy x 16 fractions daily sparing late responding tissue by reducing dose per fraction 

Used for definitive radiotherapy

What is sterotactic fractionation?

10Gy x 3 fractions daily sparing late responding tissue by avoiding dose to normal tissue

Used for definitive radiotherapy

Fractional has what pattern of cell killing?

Random killing the same fraction every time

T/F surgery can be added after definitive RT?

True, useful to end microscopic extensions before removal

What is the goal of palliative RT?

Alleviate C/S

Shrink mass

Can be used with any cancer even if mets is posible

What is the response rate to palliative RT?

>80% with survival 3-10 months

How do you do palliative RT?

8 Gy x 3 fractions weekly

4 Gy x 5 fractions daily