Dosimetric evaluation of matching Co-60 and electron fields for treatment of head and neck cancers

Abstract

The management of head and neck tumours frequently requires matching photon and electron fields. Enface electron fields are employed to boost the dose to the tissues overlying the spinal cord. The objective of this study is to measure the dose distribution in the matched region between the opposing Co-60 and the enface electron fields. In this study film dosimetry technique was applied to measure dose profiles at depths of 1, 2, and 3 cm in the junction of the matching Co-60 and electron (9MeV) fields. To investigate the changes in the dose distributions due to set-up uncertainties, dose profiles were measured at these depths using 2-10 mm in 2 mm steps overlaps and gaps between the photon and electron fields. The results showed that +20% and - 9% dose inhomogeneities occurred at the junction region at 1, 2, and 3 cm depth with 8 mm gap on the skin between the fields. It was concluded that these hot and cold spots might be clinically acceptable for the junction region between Co-60 and electron fields.