Abstract
AIM: This study leveraged standard-of-care CT scans of patients receiving unilateral radiotherapy (RT) for early tonsillar cancer to detect volumetric changes in the carotid arteries, and determine whether there is a dose-response relationship. METHODS: Disease-free cancer survivors (>3 months since therapy and age > 18 years) treated with intensity modulated RT for early (T1-2, N0-2b) tonsillar cancer with pre- and post-therapy contrast-enhanced CT scans available were included. Patients treated with definitive surgery, bilateral RT, or additional RT before the post-RT CT scan were excluded. Isodose lines from treatment plans were projected onto both scans, facilitating the delineation of carotid artery subvolumes in 5 Gy increments (i.e. received 50-55 Gy, 55-60 Gy, etc.). The percent-change in sub-volumes across each dose range was examined. RESULTS: Among 46 patients, 72 % received RT alone, 24 % induction chemotherapy followed by RT, and 4 % concurrent chemoradiation. The median interval from RT completion to the latest, post-RT CT scan was 43 months (IQR 32-57). A decrease in the volume of the irradiated carotid artery was observed in 78 % of patients, while there was a statistically significant difference in mean %-change (±SD) between the total irradiated and spared carotid volumes (-7.0 ± 9.0 vs. + 3.5 ± 7.2, respectively, p < 0.0001). Chemotherapy use, in addition to RT, was associated with a significant mean %-decrease in carotid artery volume compared to RT alone. No significant dose-response trend was observed in the carotid artery volume change within 5 Gy ranges. CONCLUSIONS: Our data show that standard-of-care oncologic surveillance CT scans can effectively detect reductions in carotid volume following RT for oropharyngeal cancer. Changes were equivalent between studied dose ranges, denoting no further dose-response effect beyond 50 Gy.