DRE can be useful in cases where there is discrepancy between the MRI/PET/endoscopy report, though this is a pretty rare instance. But as you can imagine, if a tumor is digitally palpable then the most inferior extent is probably lower than the "7 cm from the AV" reported by the radiologist/colonoscopist, which can change your field borders/volumes.
Not sure if we just have inconsistent radiologist/endoscopists, but I've seen MRI reports that say the tumor is 4 cm from AV but the colonoscopy report says 10 cm.