Validation of a Predictive Model After Complete Response in Rectal Cancer (Thunder)

Background of the study:

Prediction of rectal tumor response after chemoradiotherapy (CRT) might be helpful in individualizing treatment strategies, i.e., selecting patients who need less invasive surgery or another radiotherapy strategy instead of resection. For rectal cancer it is known that 10-30% of the patients will respond with a pathologic complete response (pCR) after CRT. From a retrospective study with multivariate analysis of both clinical and 2-[18F] fluoro-2-deoxy-D-glucose and positron emission tomography (FDG-PET) data, it was found that adding FDG-PET data collected before and after CRT leads to a more predictive model compared to evaluating only pretreatment clinical data. To validate this model, this registration study is proposed. Furthermore, it has been found that FDG-PET during treatment is very predictive for response and a more favorable time point to adapt treatment. Also, there are indications that adding blood biomarkers to the data, results in higher accuracy for response prediction compared to clinical and imaging data alone. Therefore, FDG-PET during treatment and blood sampling are included in the protocol to improve the accuracy of the prediction models.

Objective of the study:

The long-term research objective is to be able to select rectum cancer patients who could receive a less invasive treatment. If prediction of response is possible, surgery may be avoided when complete response after chemoradiotherapy is expected or performed with smaller incisions if stage reduction is significant. This support decision system helps to individualize patient treatment and can improve the quality of life for the patient.

Study design:

28x radiotherapy. On day 15 of radiotherapy en 8 weeks after radiotherapy: 1 PET-CT scan Before radiotherapy, on day 15 and 8 weeks after radiotherapy: blood sample taken.