ACO/ARO/AIO-22 - External Beam Radiotherapy Combined With Endorectal High-dose-ratebrachytherapy in Elderly and Frail Patients With Rectal Cancer. A Prospective Multicentre Trial of the German Rectal Cancer Study Group

Epidemiological data indicate that more than 50% of patients with newly-diagnosed rectal cancer are older than 70 years, with rising numbers expected over the next decades. Albeit total mesorectal excision (TME) is considered part of the standard multimodal therapy in rectal cancer, elderly and frail rectal cancer patients are often unable to undergo radical surgery as the risk of surgical complications and postoperative mortality rises with increasing age and comorbidity. In an analysis of the Colorectal Cooperative Group UK (1988-200) in 34.194 patients with colorectal cancer, 21% of those aged over 85 years did not undergo operation, while the rates of no surgical intervention were 11% in the 75-84 years age group. Furthermore, these patients often receive no treatment at all due to frailty and concurrent diseases, resulting in local and/or systemic disease progression with associated symptoms and impaired quality of life (QoL).

Significant advances have been made in modern radiotherapy (RT), which can provide a valuable alternative non-operative treatment strategy for elderly and frail patients. Notably, to achieve clinical complete response (cCR) with RT alone, high doses are needed. Recent data from randomized trials (OPERA, MORPEUS) in young and fit patients with rectal cancer indicate that increased RT doses can be safely delivered following external beam (chemo)radiotherapy (EBRT) followed by endoluminal radiotherapeutic modalities, such as contact X-ray brachytherapy (CXB) or high-dose rate endorectal brachytherapy (HDR-BT). However, prospective studies testing this therapeutic concept in elderly and frail patients with rectal cancer remain limited. Also, despite the wide availability of brachytherapy, applicability of this concept remains largely unexplored in this challenging age subgroup in Germany.

The ACO/ARO/AIO-22 prospective trial will aim to evaluate the efficacy of EBRT in combination with endorectal HDR-BT to achieve local control (cCR) and maintain QoL in elderly and frail patients with rectal cancer that are considered unfit for radical surgery, but amenable to EBRT in combination with endorectal HDR-BT or CXB.

The ACO/ARO/AIO-22 incorporates several aspects that make this prospective study important:

1. treatment decision making is challenging in elderly/frail patients with rectal cancer, whereas standardized treatment guidelines for this patient cohort are lacking, thus necessitating new clinical trials to establish the best possible treatment in this clinical setting;
2. the combination of EBRT and HDR-BT has been shown to result in high rates of tumor response with almost 90% overall response and cCR rates of approximately 50-80%, especially in young and fit patients with early stage tumors, whereas prospective trials in elderly/frail patients remain limited;
3. due to its very steep dose gradient, endorectal HDR-BT enables the delivery of a very high radiation dose to the tumor with a very steep decrease in the volume of normal tissue, thus increasing treatment efficacy while keeping toxicity low;
4. albeit already tested in different countries such as France, the Netherlands and the UK, the concept of combining EBRT with endorectal HDR-BT has not been widely tested in Germany yet and, thus, a prospective study is needed to evaluate its efficacy and safety in elderly/frail patients with rectal cancer, to develop expertise and to make this modality widely available for this challenging patient cohort.