Introduction The aim of this study was to analyze the differences between 99 m Tc-MAA SPECT and 90 Y-microsphere PET dosimetry investigating imaging (spatial resolution, partial volume effect, noise) and clinical factors (catheter positioning, modified vascularization, MAA/microsphere distribution). Methods Nineteen 90 Y-glass microsphere radioembolizations of hepatocellular carcinoma patients were analyzed in this study. For each treatment, predictive and post-treatment doses to tumor and normal liver (NL) were calculated with a dedicated software (PLANET® Dose, DOSIsoft, Cachan, France) applying a convolution method based on voxel-S factors. The mean ( ± standard deviation) administered activity was 3.5 GBq ( ± 1.2) for a mean tumor volume of 546 mL ( ± 408mL). In addition to the tumor average dose ( D avg ) , dose metrics extracted from dose volume histograms were analyzed: minimum dose to 70% and 50% of the tumor volume ( D 70 and D 50 ) and percentage of the tumor volume receiving at least 205 Gy ( V 205 ) , as recommended in the literature for glass-microsphere treatments [ [1] Garin E, Lenoir L, Rolland Y, et al. 99mTc-MAA SPECT/CT based dosimetry accurately predicts tumour response and survival in hepatocellular carcinoma patients treated with 90Y-loaded glass microspheres: preliminary results. J Nucl Med. 2012;53:255–263. Google Scholar ]. Difference and correlation between predictive and post-treatment doses were assessed using a paired Student's t test and Pearson's correlation coefficient. Spatial concordance analysis at the voxel level between MAA and microsphere distributions is ongoing. This should provide additional information to better understand the part of dose differences related to clinical factors. Results Conclusions The overall good correlation observed between predictive and post-treatment dosimetry confirm the MAA predictive value. A tendency of 90 Y-microsphere PET to underestimate 99 m Tc-MAA SPECT doses was observed.

Introduction Today, dose computation for Selective internal radiation therapy (SIRT) is based on methods easy to apply clinically. Several studies highlight dose-effect relationship for SIRT. As a result, interest enhances for advanced calculations and dose analysis tools as the ones used in external beam radiation therapy (EBRT). The Nuclear Medicine department of Montpellier University Hospital (MUH) implemented a new system to meet this need. This study describes the methodology applied, its interest and the questions raised illustrated by some clinical cases. Methods For every patient treated by SIRT, the dosimetry referred as “standard” applied at MUH follows the method described by Garin et al. [ [1] Garin E. Lenoir L. Rolland Y. Edeline J. Mesbah H. Laffont S. et al. Dosimetry based on 99mTcMacroaggregated albumin SPECT/CT accurately predicts tumor response and survival in hepatocellular carcinoma patients treated with 90Y-loaded glass microspheres: preliminary results. J Nucl Med. 2012; 53: 255-263 Crossref PubMed Scopus (197) Google Scholar ]. This is based on the partition model for which the volumes of interest are defined using Syngo® software (Siemens, Erlangen, Germany) on SPECT images acquired after the injection of macro-aggregates of albumin (MAA) labelled with 99Tcm. Recently, the implementation of a treatment planning system (TPS), PLANET® Dose (DOSIsoft, Cachan, France), allows to perform dosimetry at the voxel level. This is done through two major steps: predictive dosimetry based on MAA-SPECT images and in vivo control dosimetry using PET images acquired after the injection of yttrium-90 (90Y) microspheres (Fig. 1). Dose distribution is especially evaluated for tumoral and non-tumoral liver delineated on the injected CT or MR images by the radiology team. Dose computation rests on a convolution method based on voxel S factors. Pre and post treatment dosimetries are analyzed by the mean dose to the volume, the dose-volume histograms (DVH) and the isodose curves. Results The comparison between both dosimetric approaches (standard and at the voxel level) pointed out some differences. This particularly allowed to highlight the TPS contribution according to various aspects that were observed through clinical cases. A first aspect is related to the volume definition (functional only vs. anatomical and/or functional) for which the TPS contribution is especially interesting for complex clinical cases (multiple tumor sites, heterogeneous or partially targeted lesions, liver failure). This kind of system then allows dose evaluation in any compartment (volume at risk, portal vein thrombosis, multiple lesions, viable tumor, etc.). Moreover, voxelized dosimetry allows to analyze dose distribution uniformity with advanced tools (isodoses, DVH, etc.) in order to better assess areas of over/under dosing. Finally, being able to perform post-treatment dosimetry in order to know the real delivered dose and to sum several treatment sessions can play an important role in the patient therapeutic care. Conclusion Integrating a TPS like the ones used in EBRT in the SIRT process allowed to increase the medical team confidence and accuracy in the prescription of the activity to administer and to better control the dose delivered during the treatment. Setting up these new tools open the way to a more advanced personalization of this therapy.

Objectifs Realisation d’une radioembolisation en vue d’une lobectomie radique droite utilisant des microspheres en resine chargees en Y90 en vue d’une eventuelle resection chirurgicale chez une patiente suivie pour un hepatocarcinome avec thrombose portale droite tumorale. Materiels et methodes Suite a des douleurs de l’hypochondre droit, un volumineux hepatocarcinome du foie droit avec thrombose portale droite tumorale sur cirrhose virale C non traitee, Child A, a ete decouvert chez une patiente de 53 ans. Un traitement par radioembolisation ayant comme objectif une lobectomie radique droite fut decide en reunion de concertation pluridisciplinaire d’oncologie digestive. La scintigraphie aux macroagregats d’albumine techneties, realisee apres l’arteriographie pretherapeutique objectivait une distribution des macroagregats au niveau du foie droit et de la lesion tumorale ainsi qu’un bon ciblage de la thrombose portale droite. Le shunt hepato-pulmonaire etait estime a 2,62 %. La patiente a beneficie d’un traitement par radioembolisation avec microspheres de resine chargees en Y90. Resultats Sur l’examen TDM de suivi, realise a 3 mois apres traitement, on objective une tres bonne reponse tumorale estimee a 80 % et une nette regression de la thrombose portale droite. Une hepatectomie chirurgicale droite devient possible et elle est realisee 4 mois apres le traitement par radioembolisation. Conclusions La lobectomie radique par radioembolisation pourrait constituer une nouvelle strategie therapeutique. Une dosimetrie previsionnelle realisable sur les acquisitions SPECT-CT aux macroagregats d’albumine techneties et une dose personnalisee semble indispensable pour un traitement efficace. Des etudes dosimetriques, afin d’evaluer la dose seuil pour une lobectomie radique et une bonne reponse tumorale pour les microspheres en resine chargees en Y90, sont necessaires compte tenu de leur action irradiante et emboligene et des effets probablement conjugues.