MRI and PET in patients with locally advanced rectal cancer treated with preoperative radiochemotherapy.

For locally advanced rectal cancer the standard therapy is 5 weeks
radiochemotherapy (RCT) followed by surgery 4-8 weeks afterwards. Surgery is
performed independent of the response on RCT and is attended with substantial
morbidity. In distal rectal tumours most patients need a colostomy. When a low
anterior resection is performed faecal continence can be a serious problem. And
other postoperative complications include urinary incontinence, pain in the
anoperineal region and impaired bowel function or sexuality.
As shown in different studies there is an occurrence of a pathological complete
respons (pCR) ranging from 12-24 % after standard preoperative RCT with
capecitabine for locally advanced rectal cancer. A retrospective study
Habr-Gama et al. reported that tumour resection could be omitted in patients
with persisting clinical complete response (cCR) after 12 months. Surgical and
non-surgical treatment groups had comparable overall and disease free survival
and local recurrence rates. These findings indicate the possibility to perform
RCT as sole treatment in patients with a good response. To discriminate
patients with a good response from patients with a poor response, a tool is
needed to monitor the treatment response. FDG-PET and MRI alone both have been
used to assess treatment response, but the accuracy of these methods alone is
not sufficient to safely defer surgical treatment.

To evaluate the feasibility to assess treatment response on radiochemotherapy
for locally advanced rectal cancer by repeated anatomical and functional MRI
and FDG-PET.

Explorative prospective diagnostic pilot study investigating the feasibility to
use MRI and FDG-PET in the imaging before, during and after radiochemotherapy
for response assessment on radiochemotherapy for locally advanced rectal
cancer. Imaging response measurements will be compared with the pathological
specimen as gold standard.

For study purposes the patients will undergo two extra MRI scans and two
FDG-PET scans. The MRI scans will be performed with an intravenous contrast
agent. These scans will be scheduled in combination with standard diagnostic
scans, radiation treatment or standard follow-up appointments. The additional
MRI scans will be performed during the third week of the radiochemotherapy and
4 weeks after the end of the pre-operative treatment. The additional FDG-PET
scans will be performed before and in the third week of the treatment. The
FDG-PET scans will be planned on the same day as and preceding the MRI scans.
For the patients included in the study, there is no individual benefit, besides
close clinical follow up. For each FDG-PET there is an irradiation load of 5-10
mSv, this is comparable with two CT scans and this involves moderate risk for
the patient. However this irradiation load is negligible comapring to the
irradiation treatment this irradiation load is delivered to the total body.
Ttherefore we exclude patients from later studies involving irradiation except
studies which patients directly benefit from.