ESTRO 2024 - Abstract Book

S1322

Clinical - Head & neck

ESTRO 2024

1 University Medical Center Groningen, Radiation Oncology, Groningen, Netherlands. 2 University Medical Center Groningen, Radiology, Groningen, Netherlands. 3 University Medical Center Groningen, Nuclear Medicine and Molecular Imaging, Groningen, Netherlands

Purpose/Objective:

Diffusion-weighted imaging (DWI) is a magnetic resonance imaging technique that measures the diffusion of water molecules, quantified using b-values (s/mm 2 ). Previous studies have shown that the measured diffusion of extracellular fluid in the salivary gland changes in head and neck cancer (HNC) patients after radiotherapy, which could be related to the development of xerostomia. This study aims to determine the relationship between the delta apparent diffusion coefficient (ADC) obtained from DWI scans with 7 b-values and 1) planned salivary gland radiation dose, and 2) patient-rated xerostomia scores for HNC patients. For this aim, DWI scans were acquired at 3 timepoints that matched those of the xerostomia questionnaire: before radiotherapy (PRE), 6-months (M6), and 12 months after radiotherapy (M12).

Material/Methods:

Totally 75 DWI scans, utilizing 7 b-values (0,50,100,250,500,750 and 1000 s/mm 2 ), were prospectively acquired from 25 HNC patients at PRE, M6 and M12. Patient-rated xerostomia scores (EORTC QLQ-H&N35) were collected at the same time points. The mean doses to both parotid glands and submandibular glands were determined from the radiotherapy treatment plans. Mean ADC values were derived for parotid and submandibular glands at each time point from pre-processed DWI images with 7 b-values. Delta mean ADC was calculated as the difference in the mean ADC from the salivary glands at M6 or M12 minus mean ADC at PRE. The association between the delta mean ADC of each gland and the mean doses to the corresponding glands was evaluated by Spearman correlation coefficient (rho) and the slope of a linear fit. Furthermore, the delta mean ADC from patients with no or mild xerostomia (score ≤ 2) at M6 and M12 were compared with that from patients with moderate -to-severe xerostomia (score ≥ 3) at M6 and M12 using the Mann -Whitney U test. Significant correlations (p<0.01) were observed between the mean doses to the parotid glands and the delta mean ADC at both M6 (rho=0.74) and M12 (rho=0.69) with a similar linear effect size (~1×10 -5 mm 2 /s per Gy) for both time points. For submandibular glands, only a significant correlation between delta mean ADC and the mean doses was found at M12 (rho=0.50, p=0.01) with a slope of the linear fit of 0.20 (Figure 1). These results indicate that the higher radiation dosage can lead to significantly larger water diffusion in parotid glands at both M6 and M12 and in submandibular glands at M12. The delta mean ADC for parotid and submandibular glands of patients with moderate-to-severe xerostomia at M12 was larger than that of patients with no or mild xerostomia (Figure 1). Yet, these differences were not significant in the current cohort of 25 patients (Figure 1). These results suggest that patients developing moderate-to-severe xerostomia at M12 tended to have larger water diffusion in the parotid and submandibular glands at the matched time point of M12. To illustrate this, the ADC maps of a patient who developed moderate-to-severe xerostomia at M12 are depicted in Figure 2, showing a higher mean ADC in the parotid glands at M12 (red contours) than that at PRE (green contours). Results: