Why combine them

Conventional radiotherapy plans on a CT taken days earlier and verifies position with X-ray/cone-beam CT, which shows bone well but soft tissue poorly. An MR-LINAC gives continuous soft-tissue imaging during treatment, so the team can see the actual tumour and nearby organs on the day, and while the beam is on.

What it enables

• Daily online adaptation: re-plan to the anatomy of the day (bladder/rectal filling, tumour shrinkage) rather than a weeks-old plan.
• Real-time gating & tracking: deliver the beam only when the tumour is in position, following breathing motion.
• Mobile targets: particularly valuable for pancreas, liver, prostate, kidney and other sites that move or sit near sensitive organs.

Practical notes

Adaptive sessions take longer and need a specialised on-couch workflow with physics and radiographers present. MR-only planning (synthetic CT from MRI) is developing to streamline it. It is a leading example of MRI moving from diagnosis into the treatment itself.

Reference: Hall WA et al. The transformation of radiation oncology using real-time MRI guidance. Nat Rev Clin Oncol reviews; Winkel D et al. MR-guided adaptive radiotherapy overview. Clin Transl Radiat Oncol 2019;18:54–59.