Session Item

Radiation-induced damage to the salivary glands and swallowing muscles of head-and-neck (HN) cancer patients results in long-term toxicity. Normal tissue complication probability models are based on dose-volume histograms of a few structures, without spatial information of the radiation-induced damage. This study is designed to investigate whether quantitative MRI (qMRI) techniques could potentially provide spatial assessment of such damage.

An observational, prospective, non-randomized 3 cohort study was designed. All cohorts underwent the same 3T MRI exam with qMRI measurements including T2 mapping, diffusion weighted imaging to estimate apparent diffusion coefficient (ADC), and mDixonQUANT for fat fraction (FF) quantification. Cohort 1 consists of test-retest study in healthy volunteers and provides the qMRI baseline values of healthy tissues as well as an estimate of the qMRI repeatability. Repeatability was assessed using the repeatability coefficient (RC) derived from the within-subject standard deviation (wSD), RC=1.96√(2wSD² ). Cohorts 2 and 3 consist of HN cancer patients who received the MRI exam 2 to 3 years post-RT. Patients were divided into non-toxicity and toxicity cohorts based on self-reported xerostomia and dysphagia symptoms according to EORTC QLQ H&N43, evaluated prior to the MRI exam. Patients with toxicity grade ≥2 are included in cohort 3. Parotid and submandibular glands and the pharyngeal constrictor muscle (PCM) were delineated on a T2-weighted TSE anatomical scan. Contours were propagated to the ADC, T2 and FF maps (Figure 1). The mean values (±SD) of the ADC, T2 and FF were extracted for all subjects and structures. qMRI values of the ipsilateral salivary glands were used. Significance between cohorts was evaluated using a two-independent samples t-test (p<0.05).

Twenty-six healthy volunteers had two MRI exams within a month. The RC of all qMRI values and structures is given in Table 1. Sixteen HN cancer patients have been included. Ten patients had xerostomia and 6 of these patients had also dysphagia.  The ADC values between the cohorts were similar for all structures and their differences were smaller than the RC. T2 and FF values in the patients’ salivary glands and PCM are higher than RC compared to healthy volunteers and statistically significant (p<0,05).  However, these differences are smaller between the patient cohorts, except for the T2 of the ipsilateral submandibular gland, which is higher than the RC between xerostomia and non-xerostomia cohort (Table 1).

Baseline qMRI values (ADC,T2,FF) and RC for the salivary glands and PCM were determined. Differences of the T2 and FF values in these structures between healthy volunteers, toxicity and non-toxicity cohorts suggest that T2 and FF could be potentially used for spatial assessment of the radiation-induced damage. Further investigation including more structures and dosimetric analysis should be performed.