Feasibility of the Maastro Applicator in Rectal Cancer

The goal of this interventional pilot trial is to confirm that Maastro endoluminal HDR ( High Dose Radiation) contact brachytherapy boosting is feasible and may increase the chance of functional organ sparing of the rectum in patients with rectal cancer. Participants will be treated with chemoradiotherapy and an endoluminal boost with the Maastro applicator.

The goal of this clinical trial is to confirm that Maastro endoluminal HDR contact brachytherapy boosting is feasible and may increase the chance of functional organ sparing of the rectum in patients with rectal cancer. If at least 7 out of 10 planned Maastro applicator treatment series (3 fractions per series) can be conducted successfully from a procedural point of view the treatment will be considered feasible. The study intervention will be similar to the study treatment of arm B of the OPERA trial. Opposed to the treatment in arm B of the OPERA trial, the endoluminal boost will be given using HDR brachytherapy with the Maastro applicator instead of a CXRT (Contact X-ray Radiotherapy) device. The dose profile of the Maastro applicator is similar to the dose profile of CXRT device. As in the OPERA trial patients will be stratified based on tumor size. As the diameter of the treatment field of the largest Maastro applicator (there are two sizes) equals 2.5 cm we will stratify for tumor diameter \< 2.5 cm v ≥ 2.5 cm. In the OPERA trial patients were stratified for a tumor diameter of \< 3.0 cm v ≥ 3.0 cm as currently the largest applicator diameter for the CXRT device is 3.0 cm (currently available applicators: 2.0, 2.5 and 3.0 cm). The endoluminal boost will consist of 3 fractions with a dose equivalent to 30 Gy per fraction prescribed at the surface of the applicator. The 3 boost fractions will be delivered over a 4-week time period (week 1-2-4). Conform OPERA protocol, patients with a tumor size \< 2.5 cm will receive an upfront endoluminal HDR contact boost followed by concurrent chemoradiotherapy (25x1.8 Gy combined with capecitabine 825 mg/m2 bd on radiotherapy days). Patients with a tumor size ≥ 2.5 cm will first undergo concurrent chemoradiotherapy (25x1.8 Gy combined with capecitabine 825 mg/m2 bd on radiotherapy days) to first shrink the tumor and will receive the endoluminal HDR contact boost afterwards in order to eventually fit the tumor surface in the surface of the Maastro applicator.