Radiological and clinical findings following rectal contact X-ray brachytherapy (Papillon technique) - how to assess response

Purpose
Rectal contact X-ray brachytherapy (Papillon radiotherapy) has recently received approval from the National Institute for Health and Care Excellence. In particular, it is suitable for elderly patients who are high-risk for a major operation, but it may also be undertaken for patients who wish to avoid a stoma. It is imperative to be able to identify clinical response or tumor regrowth on surveillance magnetic resonance imaging (MRI) and sigmoidoscopy. This article aims to help clinicians to interpret MRIs and endoscopic appearances following Papillon radiotherapy.

Material and methods
MRI and sigmoidoscopy images are presented from a case series of seven non-consecutive, heterogeneously treated patients with T2 to 3C N0 rectal adenocarcinoma. Treatments included transanal excision, adjuvant or neoadjuvant chemo/chemoradiotherapy, and Papillon radiotherapy. These patients wished to avoid a stoma or were high-risk for a major operation. These cases have been chosen to demonstrate response assessment alone.

Results
The “black spider” sign of maturing, low signal fibrosis on MRI was found to be reassuring, as was the presence of a flat scar on endoscopy. Residual tumor mass or intermediate signal suggest equivocal response, which may necessitate transanal excision. Loss of low signal fibrosis, or the development of soft tissue nodularity or mass should prompt biopsy.

Conclusions
MR scans should be used in combination with endoluminal mucosal assessment (and digital rectal examination) to determine response following Papillon radiotherapy. This is the first paper to describe both the endoscopic and imaging findings following Papillon radiotherapy.