TG-51 Practice Problems
A medical physicist is performing absolute dose calibration for a 12 MeV electron beam. The depth of 50% absorbed dose, R50, was measured and a value
of 4.95 cm was obtained.
All measurements were taken with a Holt plane-parallel model ion chamber. The ion chamber-electrometer unit
was calibrated to measure 4.869e+7 Gy/C under labratory conditions. The temperature
in the clinic at the time of measurement was 21.9oC and the pressure was 763.8 mmHg. The
average electrometer readings at bias voltages of 150 V, -150 V, and -300 V are 12.4514 nC,
-12.4666 nC, and -12.5183 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 96.24%)
**All values, unless stated within the problem, should be obtained using the TG-51 report.