ESTRO 2021 Abstract Book

S1648

ESTRO 2021

Our pilot data demonstrates the feasibility of using a multiplexed assay to measure differences in baseline and Ra-223- induced changes in circulating markers in non-responders and responders. Further study is worthwhile to explore whether these circulating markers can predict response to Ra-223

PO-1934 T2w-MRI with pilocarpine administration for monitoring salivary gland function after irradiation O. Zlygosteva 1 , I. S. Juvkam 2 , H. K. Galtung 2 , T. M. Søland 2 , N. F. J. Edin 1 , E. Malinen 1,3 1 University of Oslo, Department of Physics, Oslo, Norway; 2 University of Oslo, Institute of Oral Biology, Oslo, Norway; 3 Oslo University Hospital, Department of Medical Physics, Oslo, Norway Purpose or Objective To investigate radiation-induced damages to salivary glands, reliable methods for assessing salivary gland function are necessary. State-of-the-art assessment is saliva collection, which is hampered by large uncertainties. We here report on a pre-clinical explorative T2-weighted magnetic resonance imaging (MRI) protocol with pilocarpine administration for non- invasive evaluation of salivary gland function. Materials and Methods 12-week old C57BL/6 female mice were randomised to sham treatment or low- or high-dose irradiation (30 or 43 Gy) in 10 fractions over 5 days. Two mice were included in each group. Neck irradiation was performed under anesthesia with 180 kV X-rays (0.3 Cu, dose rate 0.65 Gy min -1 at 52 cm from the target) using a Faxitron MultiRad225 system. Saliva secretion was stimulated by intraperitoneal injection of pilocarpine hydrochloride at dosage of 0.38 mg/kg. Saliva in the oral cavity was collected by cotton swab. MRI of the H&N region was performed using a 7.05 T Biospec scanner (Bruker) one week before, 3 and 52 days after irradiation. A fast T2-weighted spin-echo sequence, TurboRARE, with TE=31 ms and TR= 3100 ms was employed. At the session 52 days after irradiation, MRI was performed prior to and 30 minutes after pilocarpine administration. Mean signal intensities in volumes of interest in the submandibular gland (SMG) and in the brain (reference tissue) were extracted for all time points. The ratio of SMG signal intensity to that in the brain, S SMG /S B , was analyzed. We propose S SMG /S B as an indicator of saliva production in SMG, as high T2 signal is indicative of high fluid concentration. Results Example of a sagittal T2-weighted MR image of H&N region of a mouse in the high-dose group at day 52 is presented in Fig. 1. The ratio S SMG /S B displayed a general increase with time (Fig. 2), with a mean ratio of 2.3 and 3.2 prior to and 52 days post treatment, respectively, with no pronounced difference between treatment groups. However, S SMG /S B decreased markedly after pilocarpine injection in control and low dose groups (26 % and 29 %, respectively), but showed only a minor decrease for the high dose group (6 %). The decrease in S SMG /S B indicates lower fluid concentration due to extensive saliva secretion from undamaged SMG. The pilocarpine injection did not alter the fluid concentration in the SMG for the high-dose group, indicating loss of glandular function. Apparently, the dose delivered to the low-dose group (30 Gy) was not sufficient to cause any observable effects. The correlation between amount of collected saliva and change in S SMG /S B was 0.71.