The measurement of entrance and exit doses with in-vivo dosimetry in head and neck cancers and comparison with treatment planning doses

OBJECTIVES: We aimed to measure entrance-exit doses using in-vivo dosimetry for head and neck cancer patients and to compare with planning system doses, to facilitate determination of treatment accuracy. METHODS: Three diodes were calibrated using water equivalent phantom. Correction factors had been previously assessed for in-vivo diodes and applied to the readings. Dose measurements were performed on 30 treatment setups for 3 patients treated with isocentric, asymmetric left-right two lateral and supraclavicular fields using 6MV. Measured doses were compared with expected doses.RESULTS: The results indicated a small acceptable deviation from expected doses. It was found that the mean deviations for entrance and exit doses were 2.3% and 1.9%, respectively. The deviation in the delivered dose is well within the 5% International Commission on Radiation Units and Measurements (ICRU) recommendation, and thus treatment doses are determined to be in accordance with the planning system doses. CONCLUSION: It has been shown that in-vivo dosimetry performed using diodes is a reliable and high-precision method for patient dose control.