Reducing the Risk of Post-RT Aspiration by Sparing Specific Aspiration Related Organs at Risk.

PURPOSE/OBJECTIVE(S): Radiotherapy (RT)-induced aspiration is a serious and potentially life-threatening side effect. We identified functional swallowing units (FSUs), musculature involved in larynx elevation and tongue base retraction (R&O 2019; 130:62). FSUs were strongly related to aspiration. We developed a prediction model with baseline aspiration status and dose in FSUs as factors which performed well in predicting videofluoroscopy assessed RT-induced aspiration, at 6 months. FSUs are not yet recognized as Swallowing Organs at Risk (SWOARs) in daily practice and in treatment plan optimization. In the current study, we aimed to apply the aspiration prediction model in RT treatment plan optimization to actively spare the FSUs and establish the potential to reduce the risk of late RT-induced aspiration.

MATERIALS/METHODS: The planning study included 30 HNC patients treated with definitive radiotherapy. We optimized VMAT plans directly on logistic regression models (R&O 2021; 162:85), including normal tissue complication probability (NTCP) models for xerostomia, dysphagia and aspiration, and logistic models for target volume coverage and overall plan quality. Automated plans were created with and without using the NTCP-model for aspiration, i.e., with and without specific sparing of the previously identified FSU, including musculature associated with aspiration. The FSU sparing plans were created with and without assuming baseline aspiration. All NTCP models were weighted equally during optimization. The NTCP of toxicities including salivary, swallowing and speech problems, pain and general symptoms were evaluated for each plan.

RESULTS: All plans complied with all treatment planning quality criteria and were successful in limiting the risk of xerostomia and dysphagia. Plans optimized using the NTCP model for aspiration significantly reduced the risk of late aspiration (p < 0.001) and in all 30 patients. The optimizer of the planning system increased its efforts to spare the FSUs even more when baseline aspiration was assumed. Therefore, the aspiration risk reduction was greatest in these plans (average risk was reduced from 73.9 to 60.6%, versus from 37.8 to 29.5% in plans assuming no aspiration at baseline). Aspiration risk reduction by sparing FSUs did not reduce overall plan quality. A slight redistribution of dose was seen as a result of FSU sparing. The largest observed NTCP increase was 0.6% for moderate-to-severe xerostomia. FSU sparing unintentionally reduced the average NTCP of moderate-to-severe hoarseness and speech problems with 2.1% and 1.2%, respectively.

CONCLUSION: Sparing all specific aspiration related organs at risk, including FSUs, during RT has the potential to significantly reduce the risk of RT-induced aspiration, especially in patients with pre-existing baseline aspiration. With automatic planning, FSUs sparing does not increase complexity of the treatment planning process and does not compromise treatment plan quality.