Can Dysphagia Aspiration Related Structures (DARS) Be Spared In Patients With Oropharyngeal Cancers? Dosimetric Evaluation In A Prospective Study Of DARS Optimized Intensity Modulated Radiation Therapy

Background: The dysphagia-aspiration related structures (DARS) play an integral role in the normal swallowing mechanism. This study was done with the purpose of evaluating the feasibility of sparing DARS in various head and neck cancer sites treated with definitive DARS optimized intensity modulated radiation therapy (IMRT) and concurrent chemotherapy. Methods: : Target volumes, organs at risk and in addition individual DARS were delineated including the superior, middle, and inferior pharyngeal constrictor muscles, supraglottic and glottic larynx, base of tongue, esophageal inlet muscles and cervical esophagus in 35 patients with head and neck squamous cell carcinoma. Volume based dose constraints were applied to the DARS outside the planning target volume (PTV). IMRT plan was then generated to limit doses to DARS without compromising PTV dose coverage. Results: : Twelve (34.3%) patients had an oropharyngeal primary (OPX),18 (51.4%) had a laryngeal and 5 (14.3%) patients had hypophyaryngeal primary. The mean dose to the DARS was 47.93Gy for the entire group while it was 54.6Gy in oropharyngeal primaries and 44.4Gy in laryngopharyngeal primaries. DARS mean dose of ≤45Gy could be achieved in a significantly lesser number of patients with oropharyngeal primaries (p<0.02). Similarly, DARS mean dose was 42.25Gy in patients with N0 disease, 49.6Gy with ipsilateral involved nodes, and 55Gy with bilateral disease. Sparing of DARS was feasible when the volume of PTV was ≤150cc (p<0.025). Conclusion: Sparing of DARS structures appears to be challenging in patients with oropharyngeal cancers without compromising the dose to the PTVs while it is feasible in laryngeal and hypopharyngeal cancers. DARS sparing is feasible when the PTV volume is ≤150cc and in patients with negative or unilateral nodal disease. Trial Registration: This study was registered retrospectively with the Clinical Trials Registry of India on 9 th November 2017. The registration number is CTRI/2017/11/010442.