Caren van Roekel

43 Radioembolization a whole-liver treatment (83). This study shows that the long-term hepatotoxicity is mild. Long-term hepatotoxicity will become more and more important, since in the future, (combination) treatment with radioembolization may be applied in first- or second line settings. 6. POST-TREATMENT IMAGING AND DOSIMETRY Post-treatment imaging Currently, post-treatment imaging serves two purposes: the evaluation of technical success and the prediction of treatment efficacy. Technical success is evaluated by checking for extrahepatic deposition of microspheres and assessing the intrahepatic distribution. The heterogeneity of microsphere distribution within a lesion and the absorbed radiation dose within a lesion can be obtained. By evaluating dose-response relationships, treatment efficacy can be predicted (84). 6.1. 90 Y imaging 90 Y decays without emission of gamma photons. Bremsstrahlung x-rays are emitted along a continuous decreasing energy spectrum ranging up to 2.3 MeV. Positron emission, which produces two annihilation gamma rays, happens only in 32 out of one million decays. Thus, the quantitative imaging is limited to bremsstrahlung SPECT/CT and PET/ CT. 6.1.1. 90 Y SPECT/CT The emitted bremsstrahlung x-rays have energies that can range up to 2.3 MeV. The maximal energy usable by a gamma camera with a mechanical collimator is approximately 0.5 MeV. As a result, all acquisitions are corrupted by high energy x-rays scattering down into the acquisition window. There are five different image-degrading effects: scattering inside the patient body, penetration through collimator septa, scattering from a collimator septa, the lead fluorescence K α and K β emissions and the back-scattering from the photo multiplier tube, electronic boards and lead housing of the camera (85). 2