Functional Swallowing Units (FSUs) as organs-at-risk for radiotherapy. PART 2: Advanced delineation guidelines for FSUs

Highlights

• Delineation of Functional Swallowing Units is feasible on CT and supported by MRI.

• Dysphagia NTCP models may be improved using new DVH data as potential predictors.

• Swallowing sparing strategies can be better targeted with new structures definition.

Abstract

Background and purpose

In a separate article (PART 1), a rationale and explanation of the physiology-and-anatomy-based concept of Functional Swallowing Units (FSUs) was presented. FSUs are swallowing muscles not included in the set of commonly defined swallowing organs at risk (SWOARs). They are involved in three crucial swallowing components: hyolaryngeal elevation (HLE), tongue base retraction (TBR) and tongue motion. This paper is a continuation of PART 1 and it provides detailed computed tomography (CT)-based delineation guidelines for FSUs, which presumably are also at risk of radiation-induced dysphagia.

Material and methods

Following analysis of swallowing physiology and human anatomy, presented in PART 1, CT-based delineation guidelines for defined FSUs were created. Delineation was performed by the first author and revised by a panel of experts.

Results and conclusions

Detailed delineation guidelines are presented for seven FSUs involved in HLE, TBR and tongue motion. The guidelines are supplemented by CT and MRI-based exemplary illustrations and complete CT/MRI-based delineation atlases (available online). This paper provides information essential to the implementation of the FSU concept in radiation practice, and supports uniform contouring, data collection and further improvement of swallowing sparing radiation-based strategies.