The aims of this work were to measure the entrance and exit dose for patient
treated for head and neck tumors. The target absorbed dose was determined
from the exit and entrance dose measurement.
Twenty patients were evaluated. The results were compared to the calculated
values and the midline dose was determinate and compared with the prescribed
dose.
80 entrance doses and 80 exit doses measurements were performed. The average
difference from expected values was 1.93% for entrance dose (SD
1.92%) and –0.34% for exit dose (SD 4.1%). The target absorbed
dose differed from prescribed dose values by 2.94% (1.97%) for the
results using the Noël method and 3.34% (SD: 2.29%) with the
Rizzotti method.
The total uncertainty budget in the measurement of the absorbed entrance and
exit dose with diode, including diode reading, correction factors and diode
calibration coefficient, is determined as 3.02% (1 s).
Simple in vivo dose measurements are an additional safeguard against major setup
errors and calculation or transcription errors that were missed during
pre-treatment chart check.