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preRADAR: towards Response ADAptive Radiotherapy for non-operative management of intermediate-risk rectal cancer

Short description

Clinical trial on a new treatment for patients with rectal cancer. The highest, safe irradiation dose for rectal cancer on the magnetic resonance-guided linear accelerator (MR-Linac; a new, more precise radiation device) is being investigated. Additionally, this trial evaluates whether this higher irradiation dose increases the probability of non-operative management.

Aim of the research

This trial investigates whether it is safe to give two, three, four or five additional irradiation fractions on the MR-Linac in patients with rectal cancer who are standardly treated with five irradiation fractions and rectal surgery. In this study, 'safe' means that a maximum of 1 in 9 patients will experience significant side effects from the irradiation treatment. The aim of the higher irradiation dose is to increase the probability of non-operative management in patients with rectal cancer.

After the standard treatment of five irradiation fractions for rectal cancer, no visible tumor is left in 1 in 10 patients. In that case, rectal surgery (and the formation of an ostomy) can be safely avoided. Instead of surgery, patients are regularly followed up using MRI scans and/or endoscopy (non-operative management). The chance that the tumor will completely disappear has been associated with the irradiation dose administered on the tumor. After administration of the highest irradiation dose of this trial, we expect that in 4 in 10 patients, instead of in 1 in 10, the tumor will completely disappear.

In this trial, the irradiation treatment is administered on the MR-Linac. This is a new irradiation device that can irradiate more precisely than conventional irradiation equipment by using MR images. Therefore, the higher irradiation dose is not expected to cause a lot of additional side effects compared to the standard treatment. This trial will look for the highest irradiation dose without compromising side effects. A second, subsequent trial will evaluate whether the higher irradiation dose increases the probability of non-operative management of rectal cancer.

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