Background Irradiation of the carotid artery during radiotherapy (RT) for head/neck cancer (HNC) increases intima-media thickness, plaque formation and risk of stroke. However, the effects of RT on plaque composition are unknown. Intraplaque neovascularization (IPN) is a precursor to intraplaque haemorrhage and thus considered to be a marker of plaque instability. Contrast-enhanced ultrasound (CEUS) is a novel method of indirectlyassessing plaque vulnerability by detection of IPN.
Methods B-mode and CEUS carotid ultrasonography were performed in survivors of HNC who had received RT >2 yrs previously and had received >50Gy dose to the ipsilateral neck. Patients with bilateral RT were excluded. Baseline patient demographics were noted. Long and short axis views of the ipsilateral (RT side) and contralateral (non-RT side) carotid arteries were recorded, first in B-mode and then CEUS, using a continuous IV infusion of Sonovue contrast. IPN was graded semi-quantitatively as absent (Grade 0), limited to the adventitia/plaque base (Grade 1) or extensive and/or extending into the plaque body (Grade 2) by a doctor blinded to the laterality of RT.
Results A total of 49 patients were enrolled. Mean age was 57 ± 8yrs, 69% were male and mean BMI was 26 ± 4 kg/m2. The mean interval from RT to carotid imaging was 5.3 ± 2.6 years. Plaques were found in 38 (78%) patients, of whom 36 had plaques on the RT vs. 17 on the non-RT side (73 vs. 35%, p < 0.001). IPN was seen in 29/36 patients with RT-side vs. 7/17 patients with non-RT side plaques (81 vs. 41%, p = 0.004). Grade 2 IPN was seen in 14/36 patients with RT-side vs. 2/17 patients with non-RT side plaques (39 vs. 12%, p = 0.04).
Conclusions This is the first study to assess carotid plaque composition in HNC patients treated with RT. IPN, detected non-invasively by CEUS, is more prevalent in plaques from irradiated arteries. These results indicate that the increased risk of stroke in such patients may be due to RT-mediated proliferation of IPN.
- Carotid Artery
- Contrast Ultrasound
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