1. The problem statement, all variables and given/known data
Doing some past papers but I got stuck to this question! Any medical physicists can give me a hand please?
A patient is treated with a 6MVphoton beam, 12.5 x 12.5cm at 110cm (Source to Axis Distance: SAD) to a 9cm depth. The machine is calibrated to deliver 1.0cGy per MU at 100cm for a 10 x 10cm field. The number of monitor units required to deliver 150cGy at the isocentre is?
Given the information below:
Tissue Maximum Ratio (TMR) for 6Mv Photons
Depth (cm) | 10 x 10cm | 12 x12cm | 14 x 14cm |
1.5 | 1.0000 | 1.0000 | 1.0000 |
9.0 | 0.810 | 0.818 | 0.824 |
A. 183
B. 210
C. 247
D. 221
2. Relevant equations
MU = DOSE / ( OUTPUT FACTOR X SAD FACTOR)
SAD FACTOR = (SAD/ SAD + D)2
3. The attempt at a solution
Tried using the equations to solve but still not getting the correct answer which is supposed to be 221.
I got 183 but without using the SAD factor.