radiation oncology
DESCRIPTION
Kazumi Chino, M.D. Faith Hope and Love Cancer Center. Radiation Oncology. 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. - PowerPoint PPT PresentationTRANSCRIPT
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Radiation Oncology
Kazumi Chino, M.D.Faith Hope and Love Cancer Center
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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
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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 thepatient has less pain but isn't cured
1900 Francis Williams describes cure of a breast cancer, and recommends early txof breast cancers to prevent metastasis
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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
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Linear Accelerator
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X-rays penetrate to a certain depth based on their energy, and then interact with tissue:
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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
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DNA Damage
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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
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Dividing the radiation dose into fractions further exploits the difference between tumor
and normal tissue
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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
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Radiation Dermatitis
Hair loss is also seen inthe treatment field
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Mucositis, Esophagitis
Nausea and diarrheaare also caused byinjury to GI mucosa
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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
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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
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Active Bone Marrow in Adults
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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
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Fibrosis
Radiation can cause fibrosis throughout tissues
In joints, this can limit range of motion
In lymph channels, this causes lymphedema
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Pulmonary Fibrosis
Radiation pneumonitis is an intermediate effect, occurring 2-12 months after treatment
Sx: SOB, low grade fever, dry coughInflammation is seen within the tx field
Pneuomonitis does not necessarily entail pulmonary fibrosis in the future