Online Adaptation of a Head and Neck Patient with Subcutaneous Emphysema
Abstract
Purpose
Unanticipated anatomical and HU changes following CT simulation often necessitate patient resimulation, potentially delaying treatment. This case report describes the use of online CBCT-guided adaptive radiotherapy to manage post-simulation anatomical changes without significantly delaying concurrent chemoradiation.
Methods
A 55-year-old patient with biopsy-confirmed HPV-associated palatine tonsil squamous cell carcinoma (stage III) was prescribed definitive chemoradiation with Cisplatin and 70Gy in 35 fractions to the primary tumor, with a simultaneous integrated boost of 60Gy to subclinical disease and nodal region. Following CT simulation, the patient underwent tracheostomy due to progressive dyspnea-stridor, resulting in significant changes in the body habitus. Repeat CT demonstrated extensive subcutaneous emphysema. Rather than delaying treatment or acquiring a new planning CT, online Ethos CBCT-guided adaptive therapy was employed. Hypersight images and physician-modified contours from the first adaptive session were converted to a standard image-guided radiotherapy workflow for subsequent fractions.
Results
Dose coverage of the scheduled plan was suboptimal with V100% values of 88.7% compared to 95.8% for the adaptive plan. The adaptive plan demonstrated sharper dose fall-off, indicating improved target coverage and enhanced sparing of adjacent normal tissues. Subcutaneous emphysema resolved by day 9 of treatment. Dosimetric review did not necessitate additional replanning until day 27 due to significant weight loss. The complete adaptive workflow, including post-verification CBCT, required approximately 43 minutes.
Conclusion
Implementation of this adaptive workflow allowed the patient to proceed with treatment without resimulation and without delaying the initiation of planned concurrent chemotherapy. This approach also reduced workflow burden on the CT resources, the patient, and the clinical care team. Waiting for subcutaneous emphysema to resolve could require weeks to months and would not be clinically advantageous in the treatment setting.