Calculate MUs for a 3-field pancreas. The
gantry angles are as follows: AP(0), Right Lateral(270), Left Lateral(90). The
lateral fields have 15 degree wedges(WF=.912). The AP field is weighted 60%,The Llat is weighted 20%. The Rlat is weighted 20%. Each fraction receives 200
cGy. The AP field has an SSD of 95 and
has a field size of 10x10, The right lat has an SSD=85 and a field size of 5x5,
The left lat SSD=92 and field size of 7x9. The tray factor is .934.
- AP field
- D=5
- f.s.=10x10
- dose= 200x .60=120
- tray factor= .934
- NO WEDGE
- TMR(depth = 5,f.s.=10x10)= .928
- OF(f.s.=10x10)=1.032
120/(.928)(1.032)(.934)=134 MU (AP FIELD)
- RT LAT field
- D=15
- f.s.=5x5
- dose=200 x .20=40
- wedge factor=.912
- tray factor=.934
- TMR(d=15, f.s.=5x5)=.602
- OF(f.s.-5x5)=.980
40/(.602)(.980)(.912)(.934)=79.6= 80 MU (Right Lat Field)
- Left Lat Field
- D=8
- f.s.=7x9 2(2x9)/7+9=7.9= 8x8(E sq)
- dose= 200 x .20= 40
- wedge factor= .912
- tray factor= .934
- TMR(fs=8x8, d=8) = .829
- OF=(fs=8x8)= 1.01
40/(.829)(1.01)(.912)(.934)=56.08= 56 MU (Left Lat Field)
- interpolation:
- TMR OF
- Depth of
- 8:
- Field
- sizes:
- 5x5=.809 .980
- 6x6=.816 .990
- 7x7=.822 1.00
- 8x8=.829 1.01
- 9x9=.835 1.02
- 10x10= .842 1.032
.842-.809=.033/5=
.0066 (each step of TMR)
1.032-.980=.052/5=
.0104 (each step of OF)