Adaptive radiotherapy for gastrointestinal malignancies

Adaptive radiotherapy (ART) is an advanced form of image-guided radiotherapy that involves the re-contouring and re-planning of a patient's treatment plan, either while the patient is on the table (online) or in between fractions (offline). ART allows for the adjustment of a treatment plan to respect a patient's changes in internal anatomy, something that is critical in the treatment of gastrointestinal (GI) malignancies in which the mobile and radiosensitive GI tract plays a key role in driving toxicity. Herein we review the indications for both online and offline ART in GI cancers.

Online ART plays a critical role in the treatment of pancreatic cancer when using stereotactic body radiotherapy (SBRT). A variety of ART workflows have demonstrated that ART allows for the safe dose-escalated treatment of locally advanced pancreatic cancer. In addition to pancreatic cancer, there are now a bevy of data demonstrating that ART plays a key role in the treatment of liver cancers and abdominal oligometastases when using SBRT and allows for the safe delivery of single-fraction abdominal SBRT. While lower GI cancers are generally not treated with SBRT-like doses, both online and offline ART workflows have been shown to potentially reduce toxicity in patients with anal and rectal cancers. Improved integration of artificial intelligence and direct-to-unit workflows in ART hold promise that the overall process can become more efficient, allowing for more widespread adoption in GI radiation oncology.

ART is an expanding radiotherapy paradigm in which a patient's treatment plan is adjusted to match observed changes in patient anatomy and has been successfully incorporated into the treatment of a variety of GI cancers. The successful implementation of workflows in pancreatic cancer, liver cancers, and lower GI cancers, amongst others, as well as incorporation into multi-center clinical trials, suggest that ART will continue to play a critical role of GI radiation oncology for years to come. As improvements in efficiency and access allow for increasing use of ART world-wide, we predict that ART will continue to play a critical part in the management of patients with GI malignancies.