ESTRO 2024 - Abstract Book

S3928

Physics - Image acquisition and processing

ESTRO 2024

Material/Methods:

A calibration phantom was developed, including 10 inserts filled with AGuIX® with a NPs concentration range from 0 to 1 mmol/L. MRI sequences with variable flip angles (VFA) of 2, 3, 5, 7, 15, 20, 35° were acquired to correlate the change in absolute T1 signal to NPs concentrations. For 8 patients, first NP injection was preceded with an MRI (MR0) to determine the baseline T1 in the Gross Tumor Volume (GTV) and MR1 and MR2 were acquired 4h after injection at the fractions F1 and F11 of the radiotherapy. Two physicians delineated the GTV on the T2 weighted sequence of each patient’s MRI series, as well as the bladder and a VOI located in healthy fatty tissues close to the tumor. The two sequences were acquired in the same spatial frame during the same examination. After rigid registration, contours were reported on the generated T1 maps (Olea Sphere®). The T1 distribution of each VOI was established and modelled by normalized Gaussian functions. Using the calibration curve, the T1 distributions in the GTV obtained after NPs injection were converted into NPs concentration distributions and corrected of the non-water equivalence of the tissues. Follow-up of patients enabled quantification to be correlated with clinical results. For the first time, the location of the NPs was also observed in patient biopsies using microscopy based on the detection of Secondary Ion Mass Spectrometry. Harvested tissue of 8 patients collected before the brachytherapy (4– 6h after the third injection) were analyzed by Inductively Coupled Plasma – Mass Spectrometry (ICP-MS). Two additional biopsies collected 165 and 202 days after brachytherapy (P3 and P9) were dosed.

NPs concentrations obtained in the tumor were compared with those determined by the MRI-based method.

NPs concentrations were then reproduced by incubating 3D in vitro cell models composed of HeLa cells embedded in collagen matrix (0.5 mmol/L for 4h and 24h). Based on clonogenic assays, the radio-enhancement effects were quantified for radio- and brachy- therapies, with irradiation conditions similar to those used in clinic (6 MV VMAT, Novalis Tx).