ESTRO 2024 - Abstract Book

S5284 2353

Radiobiology - Normal tissue radiobiology

ESTRO 2024

Proffered Paper

X-irradiation, but not proton irradiation, induces an inflammatory cytokine response in saliva

Olga Zlygosteva 1 , Inga S Juvkam 2 , Hans Christian Aas 3 , Hilde Galtung 2 , Tine M Søland 2 , Brita S Sørensen 4 , Nina J Edin 1 , Eirik Malinen 5 1 University of Oslo, Department of Physics, Oslo, Norway. 2 University of Oslo, Institute of Oral Biology, Oslo, Norway. 3 University of Oslo, Department of Medical Biochemistry, Oslo, Norway. 4 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark. 5 Oslo University Hospital, Department of Radiation Biology, Oslo, Norway

Purpose/Objective:

Radiotherapy of the head and neck may cause late toxicities such as hyposalivation. Proton therapy may reduce the dose to healthy tissues and subsequent organ damage compared to conventional X-ray therapy, but differences between the two types of radiation in underlying biological responses need to be elucidated. Radiotherapy may result in the release of cytokines that is involved in an inflammatory response causing cell death and fibrosis, among others. The purpose of this work was to monitor cytokine expression in saliva after irradiation of the head and neck in mice with X-rays or protons and link the expression levels to late cellular responses in terms of acinar atrophy in salivary glands.

Material/Methods:

Thirty-five female C57BL/6J mice were used. Anesthetized mice were irradiated with a treatment field covering the oral cavity, pharynx, and major salivary glands. X-irradiation to a total dose of 65 Gy was delivered in 10 fractions over 10 days (6.5 Gy x 10). Proton irradiation was done with a pencil beam scanning system delivering two different treatment plans. The transmission plan (TP) used 60 MeV protons shooting through the animals, giving virtually the same physical dose distribution as the X-rays. The Bragg plan (BP) employed 25 MeV protons giving the Bragg peak approximately at the midline of the mice. Animals were given 6.5 Gy x 7 and 6.5 Gy x 6 for TP and BP, respectively, to reach the same acute response as for X-rays. Saliva was collected 3 days before and 10, 35, 70 and 105 days after onset of irradiation. Analysis of salivary cytokines (corrected for total protein concentration) involved in inflammation was performed using an 11-Plex Luminex Assay kit including MIP-1α, KC, G-CSF, IFN-γ, IL-1α, IL-1b, IL-6, IL-12 p70, IP-10, TIMP-1, and TNF. Principal component analysis (PCA) was used for unsupervised evaluation and exploration of the predictive role of the cytokine expression profiles. Animals were euthanized at day 105 and acinar cell density (ACD) in sections of the submandibular glands was assessed by MIST1/DAPI immunohistochemistry. One-way ANOVA and linear regression with estimates of significance (P-value) and Pearson’s correlation coefficient squared (r2) was used for statistical analysis.

Results:

In histological sections, ACD was significantly reduced in all three irradiated groups (X-ray, TP, BP) compared to controls (P<0.001). However, the reduction was most pronounced for the proton irradiated groups, where both TP and BP resulted in significantly lower ACD compared to X-rays. Saliva production and ACD was overall significantly correlated (r2=0.59). Of the included cytokines, MIP-1α, KC, G-CSF, IL-1α, TIMP-1 and TNF had expression levels above the detection limit. Figure 1 shows standard scores averaged over these six cytokines with time after irradiation. X-rays resulted in significantly increased expression levels of all measurable cytokines