Patient-specific gamma-index analysis to evaluate 99mTc-MAA as a predictor for 90Y glass microspheres liver radioembolisation dosimetry

Abstract

ABSTRACTRadioembolisation (RE) is a minimally invasive therapy for primary/metastatic liver tumours. Yttrium-90 (90Y) microspheres (MS) are infused through the hepatic artery. Positron emission tomography (PET) allows visualisation of the 90Y-MS distribution in the liver after the RE procedure. All patients are submitted to a pretherapeutic Technetium-99m (99mTc) macroaggregated albumin (MAA) perfusion scintigraphy and single-photon emission computed tomography (SPECT) liver imaging. This work investigates the value of pre-treatment 99mTc-MAA SPECT to predict intrahepatic 90Y-MS treatment dosimetry, using the gamma-index (γ-index) analytical method. Six treatments with MAA and MS administered in the same hepatic artery branches were retrospectively selected. Multimodal images were used for semi-automatic and manual segmentation of liver and tumour volumes. Absorbed dose was calculated on SPECT and PET maps using the Imalytics Research Workstation (Philips). The γ-index calculation and analysis were performed using ‘in-house’ software with multiple distance to agreement (DTA) and dose difference (DD) tolerance criteria. γ-index passing rate values of 80% and > 90% were achieved for respectively conservative 10 mm/10% and less conservative 15 mm/15% (DTA/DD) tolerance criteria. RE treatments performed in similar conditions to planning give γ-index passing rates (several DTA/DD criteria) indicating potential predictive power of dosimetry planning for post-radioembolisation dosimetry outcome.