ESTRO 2022 - Abstract Book

S456

Abstract book

ESTRO 2022

30 H&N cancer patients were included in a prospective study. They received RT with 70 Gy in 35 fractions over 7 weeks. PSMA PET/CT was acquired in treatment position at baseline and at 6-months post-RT. The PET scans were deformably registered to the planning CT and the associated dose distribution. Dose, pre-RT SUV and post-RT SUV were extracted for every voxel inside each delineated parotid salivary gland. The data was analysed using a generalised linear mixed effects model using a log link. Results Fig. 1 shows the dose distribution, and baseline and post-RT PSMA PET images of one patient. The baseline SUV was observed to moderate the effect of dose on the post-RT SUV. The population and patient-specific dose-response curves for the parotid glands, can be seen in Fig. 2. The model fit the data well with an R 2 of 0.79. The D 50 of the population-curve is 34 Gy. The population curve indicates that for a 1 Gy increase in dose, the post-treatment SUV decreases by 1.8%, for a baseline SUV of 10.

Conclusion The PSMA PET response in salivary glands after RT demonstrates a strong relationship between dose and loss of secretory cells. Differences in patient sensitivity can also be observed, which the model can account for. The population curve could potentially be used in dose planning, using a planning objective to maximize the predicted post-treatment SUV. This could be improved upon further by using a pre-treatment PSMA scan to get patient-specific curves.

OC-0507 Differential effect of PBS Proton FLASH on tumor control and skin toxicity in a mouse leg model

B.S. Sørensen 1 , M.K. Sitarz 1 , C. Ankjærgaard 2 , J. Johansen 1 , C.E. Andersen 3 , E. Kanouta 1 , C. Grau 1 , P. Poulsen 1

1 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark; 2 DTU , Health Tech, Roskilde, Denmark; 3 DTU , Health Tech, Roskilde, Denmark

Purpose or Objective