ESTRO 2023 - Abstract Book

S647

Monday 15 May 2023

ESTRO 2023

Conclusion Vector magnitude maps derived from DIR of MRI provide an objective measure of facial asymmetry. Jacobian maps provide additional information independent of landmark measures. Using DIR, we report up to 7.8mm of mandibular asymmetry in unirradiated children. These methods will be used to derive dose-response relationships for facial bones of childhood cancer survivors. OC-0778 Quantitative 3T MRI assessment of radiation-induced damage to healthy tissues in H&N cancer patients E. Astreinidou 1 , F. Guerreiro 1 , P.J. van Houdt 2 , R. Navest 2 , B.M. Verbist 3,4 , M.A. de Jong 1,5 , N. Hoekstra 1 , S. Zijlema 2 , U.A. van der Heide 2,1 1 Leiden University Medical Center, Radiotherapy, Leiden, The Netherlands; 2 The Netherlands Cancer Institute, Radiation Oncology, Amsterdam, The Netherlands; 3 Leiden University Medical Center, Radiology, Leiden, The Netherlands; 4 HollandPTC, Radiology, Delft, The Netherlands; 5 HollandPTC, Radiotherapy, Delft, The Netherlands Purpose or Objective 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. Materials and Methods 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 √ (2wSD ² ). 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).

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