In vivo measurements during radiation treatment of head and neck cancer patients

Abstract

Purpose

The evaluation of quality of head and neck patient irradiation by analysis of entrance and exit doses measurements, calculation of midline doses, dosimetric errors calculation and analysis, and defining their sources.

Material and Methods

The study included 262 patients (300 fields). 1015 entrance and 863 exit doses were measured. 863 midline doses were calculated. 50 measurements wre performed using TLD and the remaining by semiconductor diodes.

Results

The mean dosimetric errors of midline, entrance and exit doses were respectively 0.42%, −1.04% and −0.27%. Numerous sources of errors were found and some of them were corrected during the treatment. There were the following most important factors influencing the value of dosimetric error: kind of wedge filters and fixating masks, SSD, tumour and detector localization, irradiation technique, time of radiotherapy and discrepancies between real and measured thickness of irradiated volume.

Conclusion

The value of dosimetric error is not constant and it may change during long time of fractionated radiation treatment. Some anatomical (tumour localisation, density of surrounding tissues) and techical (irradiatin technique, immobilization masks, wedge filters and the discrepancy between planned and real SSD) parameters of irradiation have to be precisely defined and checked out during the treatment because they can be the main sources of dosimetric errors.