Time-dose effects in the matching of adjacent radiotherapy fields

When adjacent radiotherapy fields are treated in different times, the dose fraction at the junction of the fields is different from that within the portals. When the width of the gab between the fields is adjusted to produce equality of dose at the junction, it will not give equality with respect to radiobiological effect. The authors have used Ellis's NSD equation to take into account time-dose relationships in the matching of adjacent fields. Distribution of physical dose and biologically effective dose in the region near the junction of opposed pairs of parallel 60Co fields are given.