Radiation Oncology

Kazumi Chino, M.D.Faith Hope and Love Cancer Center

Radiation Therapy

50-60% of all cancer patients will receive radiation therapy in the course of their illness

That's almost 1,000,000 people a year in the US

A Brief History of Radiation...

1895 Wilhelm Rontgen discovers x-rays

1896 Victor Despeignes uses x-rays in a

stomach cancer: the tumor shrinks and the

patient has less pain but isn't cured

1900 Francis Williams describes cure of a

breast cancer, and recommends early tx

of breast cancers to prevent metastasis

What is Radiation?

Energy from a source, traveling through material or space

So light, heat, and sound are all forms of radiation

Therapeutically, we think of photons and sub-atomic particles, moving through the body to deposit their energy in the target: cancer cells

Linear Accelerator

X-rays penetrate to a certain depth based on their energy, and then interact with tissue:

Compton Electron

The freed e- (free radical) then interacts with whatever is nearby (3-5 nm):

Ionization or ion pair formation by stripping an electron from critical molecules in the cell (DNA) = direct effect

Or ionization of water molecules, making reactive oxygen species = indirect effect

DNA Damage

Radiation Action

Local: within 3-5 nm of initiation, the free radical is spent

Normal tissues have mechanisms to halt division and repair DNA damage

Tumors have frequently lost those checks on replication, making them more easily killed by radiation damage

Other rapidly dividing cells (bone marrow, gut mucosa) are more easily killed as well

Dividing the radiation dose into fractions further exploits the difference between tumor

and normal tissue

Side Effects of Radiation

Rapidly dividing cells are more easily killed by radiation

Side effects are local: within the field of treatment or on it's edge

Early effects occur during treatment

Late effects can occur months to years after treatment

Radiation Dermatitis

Hair loss is also seen in

the treatment field

Mucositis, Esophagitis

Nausea and diarrhea

are also caused by

injury to GI mucosa

More Early Side Effects

Fatigue

Muscle aches in the treatment field, costochondritis with treatments in the chest

Radiation cystitis: increased frequency or urgency of urination, dysuria, hematuria, and an increased susceptibility to UTI

Radiation and Bone Marrow

As low as 2-4 Gy can significantly decrease bone marrow cellularity

30-40 Gy (with conventional fractionation) is enough to ablate bone marrow

LD 50 = 4.5 Gy to the whole body

Active Bone Marrow in Adults

Late Effects From Radiation

Neurocognitive deficits: 1/3 of patients receiving whole brain irradiation will have a decrease in MMSE score, peaking about 4 months after tx

Bone marrow may be replaced with fat or

fibrosis, and damage to osteogenic cells

can increase bone demineralization or

impair healing from fractures

Fibrosis

Radiation can cause fibrosis throughout tissues

In joints, this can limit range of motion

In lymph channels, this

causes lymphedema

Pulmonary Fibrosis

Radiation pneumonitis is an intermediate effect, occurring 2-12 months after treatment

Sx: SOB, low grade fever, dry cough

Inflammation is seen within the tx field

Pneuomonitis does not necessarily entail pulmonary fibrosis in the future