Session Item

This study evaluates pharyngeal constrictors as a target for adaptive radiotherapy (ART) in head and neck cancer treatment to reduce patient reported dysphagia. Suitable ART targets exhibit anatomical changes resulting in systematic dose changes larger than 5% throughout treatment. 

A dataset of 66 oropharyngeal or nasopharyngeal patients treated with curative chemo-radiotherapy (70Gy in 33 fractions; 34 with dysphagia and 32 without) were retrospectively studied.  A summary score greater than 40 on the MD Anderson Dysphagia Inventory survey identified patients with moderate-to-severe dysphagia. Weekly cone beam CT (CBCT) and patient-reported outcomes at one-year post-RT were collected. We propagated the dose and clinical contours to weekly CBCTs using Velocity, Version 3.2.02. Dose accumulation was performed by weighting dose-volume histogram metrics by time between CBCTs. The pharyngeal constrictor mean volume and dose were calculated for each available CBCT. 

Pre-treatment factors such as alcohol intake, smoking history and P16 status were not statistically significant between asymptomatic and dysphagia groups (p>0.1775). The pharyngeal constrictor volume increased over treatment for both asymptomatic (1.60±1.54cc) and dysphagia groups (1.42±1.82cc). No changes in accumulated mean dose larger than 5% to the pharyngeal constrictors were observed (Figure 1). The maximum accumulated mean dose exhibited by the dysphagia and asymptomatic groups were 103.9% and 103.3% respectively with some inter-fraction variability amongst patients.

A 10-patient subset analysis examined pharyngeal constrictor isotropic margin expansions (±1mm, ±3mm) to evaluate nearby dose gradients. A 3mm expansion margin was chosen to replicate the largest pharyngeal constrictor thickness change observed in the literature. The expansion structure D1% metrics were not significantly different from the original plan (p>0.204). No points fell outside of the 5% error with the margin expansions (Figure 2). In the patients examined, the pharyngeal constrictors are not adjacent to the high dose region.

Figure 1. Left is the ratio of fraction-to-planned mean dose while right is the ratio of accumulated–to-planned mean dose for each patient. No patients exceeded an accumulated mean dose of 105%.

Figure 2. Expansion and original D1% dose plotted for the ±1mm and ±3mm expansions added to the pharyngeal constrictors of a 10-patient subset. There are no dosimetric changes larger than 5% and hence no large dose gradients near the original structures.

No patients in this study indicated pharyngeal constrictor mean accumulated dose changes sufficient (>5%) to suggest adaptive radiation therapy as an intervention to reduce patient reported dysphagia.