How many days do you need between extraction of a tooth and the beginning of radiation to avoid osteoradionecrosis?
Studies show that 21 days is the recommended period although the risk lessens after 14 days
What is the "golden window" when referring to post-radiation dental treatment?
It is a four month period in which you can perform invasive dental procedures after radiation and still get vascularization.
Triple H tissue has not begun to form yet
What is the invasive surgery protocol for Hyperbaric Oxygen in irradiated patients?
You get 20 pre-op sessions
1. 2.4 ATM
2. 90 minutes
3. 100% oxygen
4. 5-6 days/week
You then get 10 post op sessions
The HBO therapy protocol for patients who already have osteoradionecrosis is....
30 sessions followed by a surgical intervention, followed by 10 sessions.
Certain normal cells are more or less susceptible to radiation. Name a few and their susceptibility.
1. High Susceptibility - germinal and lymphoreticular
2. Moderate - endothelial and fibroblasts (these are important because they make up the tissues involved in healing)
3. Low - muscle and nerve
What is an ion and what role does it play in radiation therapy?
An ion is an ATOM that has gained a charge through GAIN or LOSS of a particle.
Ionization causes cell death or a change in the genetic makeup of the cell (which can lead to death by lack of ability to reproduce)
Name several types of particles used for radiation therapy...
2. Electrons - these don't penetrate deep and are used for surface lesions
3. Protons - cause little damage to surrounding tissues by killing only those cells at the end of their path. New, rare, and very expensive
Name the two broad categories of radiation used in radiation therapy..
1. Electromagnetic radiation
a. These are x-rays and gamma rays and are essentially packets of energy either from the electrons (x-ray) or the nucleus (gamma)
2. Particulate radiation
a. these are electrons, neutrons, photons, alpha particles, etc
What molecules within a cell are known to be susceptible to the free radicals/secondary particles caused by ionizing radiation?
1. nucleic acid
The amount of radiation needed to eradicate a tumor....
depends on the total number of viable CELLS
e.g. a greater dose is needed to control a 4cm tumor than a 1 cm tumor
When a cell gets hit with a sublethal dose of radiation how long does it take for it to repair itself?
Anywhere from 3 to 24 hours
What is fractionation?
It is the theory that you can divide up the amount of radiation that you need to give into multiple sessions so that less susceptible tissues won't be as affected as much.
***It should be noted, however, that the more fractions you break it up into, the more TOTAL radiation dose will be required
What is hypofractionation?
This means dividing your radiation into fewer doses and thus delivering MORE RADIATION at once in order to try to eradicate tumors that can heal themselves quickly
What role dose oxygen in the tissues play in radiation?
The more oxygenated your tissues are, the more that free radicals will occur and cause more damage.
It should be noted that tumors are often HYPOXIC due to the way they continually reproduce and outgrow their blood supply. Fractionation actually causes tumor cells to die and thus there are fewer cells hogging all of the oxygen. The tumor tissue then become more oxygenated and thus MORE SUSCEPTIBLE to the radiation. THIS IS THE PRIMARY REASON THAT FRACTIONATION IS USED IN THE FIRST PLACE!
Other than oxygen tension in the tissues, name one other reason that fractionation is used...
Fractionation ensures that cells will be irradiated during different cell phases and thus will be found to be susceptible at different times
How long after surgical resection of a tumor should you wait to begin radiation?
Not longer than four to six weeks
How long should you wait to perform a biopsy on irradiated tissue to ensure your treatment worked?
You must wait until about three months in order to evaluate the difference between morpholigically indistinguishable cells
What is the dose of radiation and time exposed that you begin to see xerostomia at?
Doses that exceed 3500cGy
How does radiation affect teeth?
It causes the death of the pulp and also odontoblasts. This causes eventual breakdown of the juction between dentin and enamel, which results in loss of the enamel and exposure of dentin
What effect does radiation have on the mucosa?
Early - acute mucositis at one to three weeks
Late - thinning, less keratinized, and fibrotic which results in easy damage and difficulty healing
How does Positron Emmision Tomography work?
You introduce a radioactive marker with a short half life (usually fluordeoxyglucose) and this goes to a metabolically active area. The highly metabolic cells take it up and use it. The molecule undergoes POSITRON EMMISION DECAY which means a positron gets emmited and collides with an ELECTRON. The positron and electron are eliminated and instead give off two GAMMA PHOTONS traveling in roughly 180 degrees away from each other. These photons are then read and interpreted by a scanner.