Contralateral Constrictor Dose Predicts Swallowing Function After Radiation for Head and Neck Cancer
Background: Radiation therapy can cause long-term dysphagia that seriously affects quality of life for survivors of head and neck cancer. This study evaluates a novel organ at risk, the contralateral pharyngeal constrictor muscles, to find out whether radiation dose to this structure predicts late swallowing function in patients with head and neck cancer.
Methods: The study included patients with head and neck cancer treated with radiation and concurrent systemic therapy at a single institution over 3 years. One-year dysphagia was defined as either the presence of a gastrostomy tube or an abnormal modified barium swallow ≥ 1 year after completion of radiation.
Results: Fifty-five patients met inclusion criteria, of which 46 were alive at 1 year. One-year dysphagia was present in 37% (n = 17) of this population. Contralateral constrictor V60 < 40% was associated with a 1-year dysphagia rate of 6%, compared with 57% in patients with V60 ≥ 40% (P < .001). An uninvolved pharynx mean dose < 45 Gy was associated with a 1-year dysphagia rate of 22%, compared with 52% in patients with an uninvolved pharynx mean dose ≥ 45 Gy (P = .03). Editing the clinical target volume off air cavities was associated with a decrease in 1-year dysphagia from 67% to 12% (P < .001), and with a reduction of contralateral constrictor V60 from 62% to 33% (P < .001). Air cavity editing was not associated with a change in locoregional recurrence or 1-year survival.
Conclusions: This is the first study to report a connection between contralateral constrictor dose and late swallowing function. The correlation between air cavity editing and contralateral constrictor V60 suggests that contralateral constrictor dose may depend partly on technique. Further studies are needed to explore whether these findings can be replicated prospectively and in other practice settings.
Pharyngoesophageal stricture is a common cause of dysphagia after IMRT for H&N cancer.16 Radiation has been shown to decrease pharyngeal function in patients with H&N cancer.17 Sparing one side of the pharynx may allow for better pharyngeal compliance throughout the length of the pharynx, possibly decreasing the rate of pharyngoesophageal stricture. Additionally, constraining the contralateral constrictor may preserve strength on this side, allowing it to compensate for weakness on the side of the primary cancer. An exercise sometimes used for dysphagia involves head rotation toward the affected side during swallowing. This technique has been shown to cause food to move to the unaffected side.18 Sparing the contralateral constrictor may help such techniques work better in patients with H&N cancer.
Few studies have commented specifically on dose to swallowing structures contralateral to the primary tumor. Two studies have proposed contralateral submandibular gland constraints for dysphagia (not xerostomia), but neither measured the dose to the contralateral constrictor muscle.9,10 Although the contralateral submandibular dose may correlate with dose to the constrictor on that side, the submandibular gland may have a less direct impact on swallowing than the constrictor muscle, and its limited dimensions may make constraints based on the gland less robust for cancers outside the oropharynx.
Another study reported improved quality of life in patients who were not treated with elective contralateral retropharyngeal radiation.19 Although it is likely that doses to the contralateral constrictor were lower in patients who did not receive elective radiation to this area, this study did not measure or constrain doses to the contralateral constrictors.
Limitations
This study is limited by its single institution, retrospective design, small sample size, and by all patients being male. The high correlation between air cavity editing and the use of SIB makes it impossible to assess the impact of each technique individually. Patients with contralateral constrictor V60 < 40% were less likely to have N2 disease, but N2 to N3 disease did not predict higher 1-year dysphagia, so the difference in N-category cannot fully explain the difference in 1-year dysphagia. It is possible that unreported factors, such as CTV, may contribute significantly to swallowing function. Nevertheless, within the study population, contralateral constrictor dose was able to identify a group with a low rate of long-term dysphagia.
Conclusions
Contralateral constrictor dose is a promising predictor of late dysphagia for patients with H&N cancer treated with radiation with concurrent systemic therapy. Contralateral constrictor V60 < 40% was able to identify a group of patients with a low rate of 1-year dysphagia in this single-center retrospective study. The correlation between air cavity editing and contralateral constrictor V60 suggests that contralateral constrictor dose may depend partly on technique. Further studies are needed to see if the contralateral constrictor dose can be used to predict long-term dysphagia prospectively and in other patient populations.
