Fig. 2.

Center of mass (COM) approach for correlation of the site of local recurrence (LR) to the original treated volumes: CT scans with a LR (red colour). After co-registration, the original CTVb (orange) and original PTVb (green) were projected onto the recurrence CT scan. As the co-registration inaccuracy was 3 mm, a circle (blue) was created around the COM (blue dot) with a radius of 3 mm. The COM might be anywhere within the blue circle. Left panel A: the recurrence in this patient was considered as marginal CTVb and in-field PTVb. Right panel B: the recurrence in this patients was considered in-field for both CTVb and PTVb.