TG-51 Practice Problems
A medical physicist is performing absolute dose calibration for a 6 MV photon beam. The percent depth dose at 10 cm depth, %dd(10)Pb, for a 10 x 10 cm2
field size at 100 cm SSD was measured and a value of 68.03% was obtained.
All measurements were taken with a PTW N30002 model ion chamber. The ion chamber-electrometer unit
was calibrated to measure 4.891e+7 Gy/C under labratory conditions. The temperature
in the clinic at the time of measurement was 20.5oC and the pressure was 763.8 mmHg. The
average electrometer readings at bias voltages of 150 V, -150 V, and -300 V are 13.9374 nC,
-13.9369 nC, and -13.9396 nC, respectively. Each measurement was taken after 100 machine monitor
units (MU) had been delivered. What is the value of the absorbed dose to water at dmax for an SSD
setup, in cGy/MU? (The SSD for this beam at clinical setup is 100 cm)
**All values, unless stated within the problem, should be obtained using the TG-51 report.