Yttrium-90 TOF-PET-Based EUD Predicts Response Post Liver Radioembolizations Using Recommended Manufacturer FDG Reconstruction Parameters

Abstract

PurposeExplaining why 90Y TOF-PET based equivalent uniform dose (EUD) using recommended manufacturer FDG reconstruction parameters has been shown to predict response.MethodsThe hot rods insert of a Jaszczak deluxe phantom was partially filled with a 2.65 GBq 90Y - 300ml DTPA water solution resulting in a 100 Gy mean absorbed dose in the 6 sectors. A two bed 20min/position acquisition was performed on a 550ps- and on a 320ps- TOF-PET/CT and reconstructed with recommended manufacturer FDG reconstruction parameters, without and with additional filtering. The whole procedure was repeated on both PET after adding 300ml of water (50Gy setup). The phantom was acquired again after decay by a factor of 10 (5Gy setup), but with 200min per bed position. For comparison, the phantom was also acquired with 18F activity corresponding to a clinical FDG whole body acquisition.ResultsThe 100Gy-setup provided a hot rod sectors image almost as good as the 18F phantom. However, despite acquisition time compensation, the 5Gy-setup provides much lower quality imaging. TOF-PET based sectors EUDs for the three large rod sectors agreed with the actual EUDs computed with a radiosensitivity of 0.021Gy-1 well in the range observed in external beam radiotherapy (EBRT), i.e. 0.01-0.04Gy-1. This agreement explains the reunification of the dose-response relationships of the glass and resin spheres in HCC using the TOF-PET based EUD. Additional filtering reduced the EUDs agreement quality.ConclusionsRecommended manufacturer FDG reconstruction parameters are suitable in TOF-PET post 90Y liver radioembolization for accurate tumour EUD computation. The present results rule out the use of low specific activity phantom studies to optimize reconstruction parameters.

TCP post-radioembolization and TCP post-EBRT in HCC are similar and can be predicted using the in vitro radiosensitivity

“…In fact, centimetric heterogeneity activity patterns are typically met in sphere radioembolization (see Fig. 1 in [ 10 ]). This explains why 90 Y TOF-PET-based EUD is able to rightly take into account the impact of the heterogeneity of the absorbed dose distribution.…”

“…3 the 100 Gy curves shapes are not similar to those of the 50 Gy setup. (reprinted from [ 10 ], true EUD computation was extended down to 3.2 mm by the present authors) …”

“…The terminology apparent radiosensitivity was introduced by Chiesa et al [ 4 ]. This value depends on the spatial resolution of the dose distribution assessment as shown in [ 10 ]. In a previous 90 Y TOF-PET-based EUD analyses, the apparent α * coefficient was estimated to be 0.038 Gy −1 [ 11 ], i.e., about tenfold lower than the intrinsic in vitro HCC 0.40 Gy −1 radiosensitivity α [ 23 ].…”

“…Centimeter scale heterogeneities in the activity distribution in RE explain these differences [ 8 ]. Such heterogeneity is sufficiently revealed by time of flight (TOF)-PET 90 Y imaging [ 8 – 10 ] to allow reunification of the efficacy threshold doses observed in RE (resin or glass spheres) and in EBRT using the EUD [ 11 ]. Previous radiobiological models developed in RE for HCC demonstrated a correlation between the tumor-absorbed dose and the clinical response assessed with conventional imaging [ 4 – 6 ].…”

Radioembolization of Hepatocellular Carcinoma with 90Y Glass Microspheres: No Advantage of Voxel Dosimetry with Respect to Mean Dose in Dose–Response Analysis with Two Radiological Methods

“…In our previous study aiming at such a demonstration [ 17 ], contrarily to our expectations, the radiobiological voxel dosimetry provided only a negligible advantage with respect to the mean dose. However, recent papers seem to confirm the validity of the voxel approach in TARE dosimetry [ 18 , 19 ]. We therefore performed a critical analysis of our previous study [ 17 ], and the following flaws were identified.…”