FINDING DOSE TO A SECOND POINT (CORD DOSE) FOR SAD SETUPS:

Using TMR's:

• TMR's are independent of Depth in the patient (since they are both initial readings are taken at the same distance)

the below equation is used when we are trying to find a dose to a second point with an SAD setup.   Below we would be given the dose to depth 2 and would need to find the dose to depth 1.

Dose to a second point (cord dose) for SAD setups ( note that the numbers are switched from the above equation because looking for dose to point 2 makes more sense than looking for dose to point 1, just did it to maintain a sense of order) :

Important:

• if the cord dose is supposed to go up the larger TMR is placed on top of the TMR2/TMR1 equation
• if the cord dose is supposed to get smaller the smallet TMR is placed on top of the TMR2/TMR1 equation
• another words the the TMR fraction in the equation is not set in stone and can be TMR2/TMR1 or TMR1/TMR2 depending on if you are looking for a smaller number (if the cord dose is deeper in the paitent that then dose to point 1) or the number you are looking for is larger (if the cord dose is not as deep as the dose to point 1)