Pilot study: The use of PET-MRI in the follow-up of RFA treated colorectal liver metastases

The main area of concern regarding radiofrequency ablation (RFA) or microwave
ablation (MWA) of colorectal liver metastases (CRLM) is the risk of developing
a local site recurrence (LSR). Imaging plays a key role in diagnosing LSR after
RFA or MWA liver treatment. When LSR is diagnosed adequately and timely,
optimal effect of repeated (minimal invasive) local treatment may be obtained.
So far a contrast enhanced (ce) CT scan is generally used for follow-up,
However, post-treatment effects in the ablation margin may complicate an
adequate diagnosis of LSR for which the addition of FDG-PET helps to
differentiate between metabolic active tumor tissue and inactive post-ablation
mass. Therefore an integrated FDG PET-CT is favourable over CT alone and the
combination of both is standard of care in our centre. Liver MRI with contrast
outperforms CT in the detection of small hepatic metastases (<1 cm), but its
role is not yet established for the follow-up after RFA or MWA. Therefore, the
combination of FDG PET to determine metabolic activity with the ability of the
MRI to detect small lesions may add to timely and correctly diagnosing a LSR.
This may lead to earlier initiation of effective treatment. With the recent
launch of PET-MRI, these two advantages can be combined.

The primary objective of this study is to evaluate the ability of PET-MRI to
detect LSR during the first year of follow-up after RFA treatment of CRLM as
compared with ceCT and PET-CT. Standard reference will be histology (when
available) or clinical follow-up.

Multi centre pilot study

All participating patients will receive follow-up according to normal standards
in our hospital (ceCT of the liver and a PET-CT 3-4 monthly in the first year).
These imaging modalities are currently leading in the evaluation of local
response to RFA and MWA treatment and to diagnose new intra- and extrahepatic
metastatic disease. Therefore in this study, the decision on treatment will not
be made based on the results of the PET-MRI, but based on PET-CT and ceCT,
sometimes in combination with CEA at the surgeons or oncologists discretion.
The PET-MRI images will be evaluated separately and results will be compared to
PET-CT and ceCT. The additional risks for participating patients with normal
renal function, when normal in- and exclusion criteria for MRI research are
being followed are limited. There is no increased exposure to radiation and the
patients only need a single dose of FDG for both PET-CT and PET-MRI. The risk
on nefrogenic systemic fibrosis after use of gadolinium is negligible in
patients with adequate renal function. Undergoing a PET-MRI of the liver will
cost the participant extra time; 45 minutes extra for scanning protocol. We
will put much effort in reducing the waiting time in between scans as much as
possible. Travel time may be longer for than usual for patients from the
Gelderse Vallei.