TG-51 Practice Problems
A medical physicist is performing absolute dose calibration for a 9 MeV electron beam. The depth of 50% absorbed dose, R50, was measured and a value
of 3.72 cm was obtained.
All measurements were taken with a PTW N30004 cylindrical model ion chamber. The gradient correction factor was measured and a value of 0.9703 was obtained. The ion chamber-electrometer unit
was calibrated to measure 4.962e+7 Gy/C under labratory conditions. The temperature
in the clinic at the time of measurement was 21.1oC and the pressure was 755.1 mmHg. The
average electrometer readings at bias voltages of 150 V, -150 V, and -300 V are 13.4670 nC,
-13.4374 nC, and -13.4959 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 PDD for this beam at clinical setup is 97.95%)
**All values, unless stated within the problem, should be obtained using the TG-51 report.