Diffusion‐weighted and dynamic contrast‐enhanced MRI to assess radiation therapy response for head and neck paragangliomas

Background and purpose The prediction of radiotherapy outcome in head and neck paragangliomas is clinically important. We investigated perfusion and diffusion markers for evaluation of response to radiotherapy of head and neck paragangliomas. Methods We retrospectively reviewed 330 consecutive patients from January 2016 to September 2019 with suspected head and neck paragangliomas, and enrolled 11 patients (2 males, 9 females; age: 55.2 ± 10.3 years) who had conventional MRI and dynamic contrast-enhanced (DCE)-MRI before and after radiation therapy. Radiation therapy, consisting of external beam radiotherapy or stereotactic radiotherapy, was conducted at the radiation oncology department in a single center. Mean apparent diffusion coefficient (ADC), normalized mean ADC, and parameters of DCE-MRI were compared between pre- and post-treatment status by paired t-test. The Pearson correlation coefficient was used for the relationship between tumor volume ratio (post-treatment status/pre-treatment status) and pre-treatment and post-treatment values. Results Mean and normalized ADC values were statistically higher in post-treatment status than pre-treatment status (p = 0.005, p = 0.005, respectively), and Ktrans (volume transfer constant between extravascular, extracellular space [EES], and blood plasma per minute) and Kep (rate transfer constant between EES and blood plasma per minute) were significantly lower in post-treatment status than pre-treatment status (p = 0.007, p = 0.027, respectively). The correlation coefficient of the relationship between tumor volume ratio and pre-treatment Ktrans (r = 0.70; p = 0.016) and between tumor volume ratio and post-treatment Ktrans and Kep (r = 0.83; p = 0.002, r = 0.8; p = 0.003, respectively) was statistically significant. Conclusions Ktrans has predictive potential to predict the response to radiation therapy of head and neck paragangliomas.