TG-51 Practice Problems
A medical physicist is performing absolute dose calibration for a 15 MeV electron beam. The depth of 50% absorbed dose, R50, was measured and a value
of 6.20 cm was obtained.
All measurements were taken with a PTW N23331 cylindrical model ion chamber. The gradient correction factor was measured and a value of 0.9855 was obtained. The ion chamber-electrometer unit
was calibrated to measure 4.846e+7 Gy/C under labratory conditions. The temperature
in the clinic at the time of measurement was 22.2oC and the pressure was 756.3 mmHg. The
average electrometer readings at bias voltages of 150 V, -150 V, and -300 V are 13.1938 nC,
-13.1756 nC, and -13.2300 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 95.16%)
**All values, unless stated within the problem, should be obtained using the TG-51 report.