ESTRO 2022 - Abstract Book

S132

Abstract book

ESTRO 2022

should concentrate on improving the implementation of 4DCT ventilation in the RT planning workflow and investigating functional planning at a larger scale. This opens the way for prospective functional lung avoidance studies.

PD-0157 Change in FDG-PET uptake of bone marrow: Radiation dose-response and possible compensatory effect

A.B. Olin 1 , I.R. Vogelius 2 , L. Højgaard 3 , F.L. Andersen 3 , B.M. Fischer 3

1 Rigshospitalet, Dept. of Oncology & Dept. of Clinical Physiology and Nuclear Medicine, Copenhagen, Denmark; 2 Rigshospitalet, Dept. of Oncology, Copenhagen, Denmark; 3 Rigshospitalet, Dept. of Clinical Physiology and Nuclear Medicine, Copenhagen, Denmark Purpose or Objective Hematological toxicity after chemoradiotherapy is partially caused by direct radiation to the highly radiosensitive bone marrow, but the dose-response and the potential compensatory effect in non-irradiated bone marrow remain to be better understood. For this purpose, FDG-PET allows assessment of the metabolic activity within the bone marrow and is correlated with higher cellularity and proliferative activity. This study explored how bone marrow within individual vertebrae responds to radiotherapy for NSCLC patients, by measuring changes in FDG-PET uptake from baseline to end of radiotherapy and correlating with the dose to the individual vertebrae. Materials and Methods We identified and analyzed 15 NSCLC patients referred for radiotherapy with curative intent (66 Gy in 33 fractions) between Jan 2019-Dec 2019, all having an FDG-PET/CT before treatment and a follow-up PET/CT within 12 months. Each vertebra was segmented and labeled (cervical (C1-7); thoracic (T1-12); and lumbar (L1-L5) vertebrae) using CT as input to the deep learning model winning MICCAI’s VerSe challenge 2019. The FDG-PET mean standardized uptake values (SUV mean ) within each vertebra at baseline and follow-up were assessed and their relative differences were calculated with baseline as reference ( Δ SUV mean ). The delivered mean dose (D mean ) to each vertebra was obtained from the dose plan. We used Spearman's correlation ( ρ ) to measure the association between the D mean and Δ SUV mean using data from all vertebrae across all patients. Results The SUV mean for each vertebra at baseline and follow-up and the corresponding D mean are shown for an illustrative patient in Fig 1. A drop in SUV mean for vertebrae receiving high doses is seen together with a potentially compensating increased uptake for the vertebrae receiving only scatter dose.

Figure 1: SUV mean of each vertebra at baseline and follow-up (left y-axis) and the corresponding D mean (right y-axis). Across all vertebrae, there was a strong correlation between D mean and Δ SUV mean ( ρ =-0.43, p-val<0.0001), with uptake decreasing with increasing dose. This can also be seen from Fig 2, showing a scatterplot of the D mean and Δ SUV mean and a rolling mean line to indicate the trend. There is a slightly increased SUV mean at low D mean , supporting the hypothesis of a compensatory response to radiation injury in the irradiated vertebrae. However, the individual out-of-field responses are mixed so a greater understanding is needed.