Rectal cancer typically necessitates a combination of radiotherapy (RT), chemotherapy, and surgery. The associated functional disorders and reduction in quality of life have led to an increasing interest in organ preservation strategies. Response strongly correlates with RT dose, but dose escalation with external beam remains limited even with modern external beam RT techniques because of toxicity of the surrounding tissues. This study reports on the use of Papillon, an endocavitary Radiotherapy device, in the treatment of rectal cancer. The device delivers low energy X-rays, allowing for safe dose escalation and better complete response rate. Between January 2015 and February 2024, 24 rectal cancer patients were treated with the addition of a boost delivered by Papillon to standard RT, with or without chemotherapy, in an upfront organ preservation strategy. After a median follow-up (FU) of 43 months, the organ preservation rate was 96% (23/24), and the local relapse rate was 8% (2/24). None of our patients developed grade 3 or more toxicities. Our results demonstrate that the addition of Papillon contact RT provides a high rate of local remission with sustained long-term organ preservation, offering a promising alternative to traditional surgical approaches in patients with rectal cancer.