Part 11: Factors That Affect Dose (2) O2 Effect

define the following:

1. anoxic

2. hypoxic

3. aerobic

1. anoxic = no oxygen (or very low oxygen)

2. hypoxic = low oxygen

3. aerobic = higher oxygen content

__rule of oxygen sensitization

1/3

term. 1/3 Rule of Oxygen Sensitization

def. anoxic cells are only 1/3 as radiosensitive as aerobic cells.

So if you have a tumor mostly composed of anoxic cells, you’ll have to give them 3x dose of aerobic cells

OER stand for

Oxygen Enhancement Ratio

term. OER

def. the dose required in the absence of O2 to produce the SAME effect as a dose in the presence of O2

OER formula

OER = Dose Anoxic for an effect / Dose Aerobic for same effect

e.g. of an effect = cell kill

Typical OER

2.5-3.0

e.g. The dose to kill a certain anoxic cell is 300 cGy, and the dose to kill an aerobic cell of that same type is 100cGy. What is the OER?

OER = 300/100 = 3.0

_____ are an exception to the OER rule

Neutrons

and particulate radiation in general

Why are Neutrons an exception to OER?

Neutrons (and particulate radiation) act independent of O2 (we dont know why)

So what would neutrons be good for treating? Choose the best answer.

1. anoxic tumors

2. hypoxic tumors

3. aerobic tumors

1. anoxic

Reasoning: Suppose you have an anoxic tumor, you could treat it with EM radiation and give it 3x the dose = more side effects. Or treat with Neutrons and only give it 1/3 of that = less side effects

True or False: For the oxygen effect to take place, the O2 must be present at the time of irradiation

True

FYI: Scientists proved this by clamping the tails of mine and depriving them of oxygen and they found that you’d have to give them 3x the dose to produce the same kind of damage

what is this

Hyperbaric air chamber

def. an attempt to oxygenate tissues . cells in a hyperbaric air chamner

term. Hyperbaric O2 therapy

Is Hyperbaric O2 therapy typically utilized to treat tumors? Why or why not?

No. Cuz MOST cells are well oxygenated already, so this type of therapy isn’t really needed. It helps a little but it’s too extra.

Calculate the OER

OER = 450/150 = 3.0