Liver and pancreas cancers are intrinsically radioresistant, and thus require large radiation doses for tumor control. However, several radiosensitive gastrointestinal (GI) organs at risk (OARs) are located near tumors in these locations, including the duodenum, stomach, and bowel. This complicates hypofractionated and stereotactic ablative radiation treatment (SBRT) of the liver and pancreas, because the tolerance doses for these OARs must be maintained to avoid life-threatening toxicities. Maintaining GI tolerances can greatly reduce the amount of ablative dose to the tumor, and hence may limit the SBRT effectiveness in terms of local control and overall survival. Moreover, respiratory motion and daily anatomic variations from intra- and inter-fractional motion impose additional therapeutic challenges. This is especially true for pancreatic cancer, as tumors often lie next to the duodenum, requiring sharp dosimetric gradients between the target and this OAR. Obtaining sharp dosimetric gradients is also complicated by daily anatomic variations from transient GI gas filling and peristalsis; these variations can affect daily dose distributions and warrant dynamic changes in the dosimetric gradient position to maintain GI OAR tolerances. Thus, consideration of these variations in the treatment planning and delivery workflow is essential. Image guidance using cone-beam CT may not provide adequate soft-tissue visualization of OARs adjacent to the tumor in the abdomen. Even advanced image guidance methods involving CT-on-rails or MR-guided radiotherapy (MRgRT) may not provide optimal treatments if an online adaptation approach is not used. Therefore, selecting patients for SBRT based on optimal tumor position with respect to OARs is essential to ensure safe delivery of SBRT and avoid exceeding GI tolerances, but this limits the population that can be treated with this ablative approach. Implementing a daily online adaptive workflow may allow additional pancreatic and liver patients to receive SBRT and provide the optimal therapeutic intervention. In this session, we will highlight the challenges with using SBRT for liver and pancreas cancers and present potential alternatives using online adaptation with both CT-on-rails and MRgRT approaches that may allow safe dose escalation beyond what can be achieved with current methods.
1. Highlight the importance of daily volumetric imaging with soft-tissue contrast in the treatment of liver and pancreas tumors.
2. Highlight the effect of sharp dose gradients and daily variations in dose distributions to OARs
3. Present strategies using online adaptation to minimize the compounded dosimetric effects from high-dose gradients and daily variations in gastrointestinal anatomy.
Funding Support, Disclosures, and Conflict of Interest: Dr. Sawakuchi's research was supported in part by RP170040, 1R21CA252411-01, Emerson Collective, MD Anderson Cancer Center. Dr. Sawakuchi has research agreements with Alpha Tau Medical and Artios Pharma.