Dynamical dipole gamma-ray emission in heavy-ion collisions is explored in the framework of the quan-um molecular dynamics model. The studies are focused on systems of 40Ca bombarding 48Ca and its isotopes at different incident energies and impact parameters. Yields of gamma rays are calculated and the centroid energy and dynamical dipole emission width of the gamma spectra are extracted to in-vestigate the properties of gamma emission. In addition, sensitivities of dynamical dipole -ray emission to the isospin and the symmetry energy coefficient of the equation of state are studied. The resultsshow that detailed study of dynamical dipole gamma radiation can provide information on the equation of state and the symmetry energy around the normal nuclear density.