Dysphagia Associated Organ Sparing Radiotherapy: Defining the Limits of Tolerance for Late Toxicity

Background: Dysphagia after radiotherapy in head and neck malignancies can severely impact a patient’s physical, social and psychological quality of life. Aspiration remains the major cause of non-disease related mortality in treated patients. The purpose of this study was to analyze the dosimetric correlates in a selective Asian subset of patients who are most eligible for Dysphagia aspiration related structure (DARS) sparing. Materials and Methods :  Thirty patients with Oral or Oropharyngeal malignancies treated from March 2014 to September 2017 were analyzed for dosimetric parameters to DARS. A dosimetric and volumetric evaluation of dose parameters to the dysphagia and Aspiration associated normal structures were analyzed. The National cancer institute Common toxicity criteria for adverse events Version- 3 was used to grade late dysphagia. Subjective evaluation of dysphagia was done with University of Washington Head and Neck related quality of life Questionnaire. Dosimetric comparison between IMRT and 3DCRT technique was done and correlated to toxicity.  Results : Greater than Grade 2 dysphagia was observed in 10 patients (33%). In the 3DCRT cohort Grade 3 & 4 toxicity was higher, 50 % vs 25 %. A threshold Mean dose of 63 Gy was identified as a significant parameter above which observed Gr 3/4 toxicity was 33% (p value=0.028). The maximum dose to the base of tongue (BOT) and Superior constrictor (SC) were dosimetric parameters which achieved significance (p value=0.013 & 0.005). There was no difference in the dose delivered to DARS between 3DCRT and IMRT. However, the patient reported Dysphagia scores were higher for pain (p=0.0014) in the 3DCRT cohort and can be attributed to a higher percentage of patients exceeding Parotid tolerance (70% vs 40%). The impact of Gr 3/4 toxicity on all aspects of quality of life parameters were significantly impaired with maximum compromise on late chewing, swallowing and general perception of well-being (p value =0.001). Conclusion:  This suggests that a threshold mean dose (MD) of 63 Gy to the constrictors is statistically correlated to significant Gr 3/4 late toxicity. The high doses to the BOT and SC independently contribute to late toxicity. IMRT is more efficient in reducing severe late toxicity with a better patient reported quality of life parameters and should be the preferred treatment of choice.