[Oral Communication] Dosimetría 3D en Radioembolización Hepática Con Microesferas Cargadas Con Ytrio-90: Reporte de Caso

*3D Dosimetry for Selective Internal Radiation Therapy of unresectable liver cancers using Yttrium-90 loaded Microspheres: Case Report

M. Kafrouni1,2, M. Fourcade1, S. Vauclin2, A.D. Ilonca1, D. Mariano-Goulart1
1 Nuclear Medicine Department, Montpellier University Hospital, Montpellier, FRANCE
2 Dosisoft SA, Cachan, FRANCE

Presented at ALFIM 2016

Introduction: Today, the 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). New systems are available to meet these needs. The Nuclear Medicine department of Montpellier University Hospital implemented one of them for treatment planning and in vivo dose control purposes. This study reports a clinical case to describe the potential of 3D voxel-based personalized dosimetry compared to standard approach.

Materials and Methods: Report of a 68-year-old male patient with liver metastasis from colorectal carcinoma. The patient had been recently treated by intensified hepatic intra-arterial chemotherapy with risk of hepatic function damage. Besides, SIRT target volume was the whole liver. For these reasons, a narrow dose constraint of 30Gy to non tumoral liver (NTL) was set to preserve enough hepatic integrity. The treatment was made of 2 steps: 99Tcm-macroaggregated albumin (MAA) hepatic perfusion to assess lung shunt/90Y activity to inject using SPECT exam, and 90Y-microspheres (MS) treatment controlled by PET exam.

The MIRD-based partition model was considered as standard approach. Using isocontour method in Syngo software (Siemens, Erlangen, Germany), tumoral liver (TL) and NTL were defined on the MAA uptake to estimate activity to administer and related doses (DTL-uptake/DNTL-uptake).

In addition, predictive dosimetry was performed using a SIRT treatment planning system (TPS) (PLANET Dose, DOSIsoft, Cachan, France). Four lesions were identified and anatomically contoured on MRI exam. One of them, referred as “central” was SIRT main target. Doses to anatomical total TL, central lesion and NTL volumes (respectively DTL-anat/Dcentral-anat/DNTL-anat) were calculated by Voxel S-Values dose kernel convolution.

Then, the patient underwent SIRT with resin MS (SIR-Spheres, SIRTeX, Sydney, Australia). PET-based post-treatment dosimetry was performed as in vivo control. For both pre/post treatments, dosimetry was studied as for EBRT using dose volume histogram (DVH)/isodose display and was compared to standard approach.

Results: Both the standard and TPS calculations estimated respectively DNTL-uptake and DNTL-anat close to 30Gy threshold. TPS-based DVH provided additional information of 12Gy to 80% of the anatomical NTL. Standard and TPS approach evaluated respectively DTL-uptake=118Gy and DTL–anat=71Gy/Dcentral-anat=115Gy. Using 3D dose map, dose to the gallbladder could also be assessed.

Additional information provided by the TPS allowed to slightly adjust the activity to be injected delivering sufficient dose to TL while saving NTL as much as possible.
TPS-based post-treatment dosimetry was performed and enabled to confirm the operating differences during injection (right hepatic artery vasospasm and temporary micro-catheter setup to avoid gallbladder irradiation).

Conclusion: SIRT TPS turned out to be a clinical decision-making tool thanks to the possible risk/benefit balance optimization. This can be especially interesting for patients with limited liver integrity. It can also help assessing dose to anatomical tumors which are sometimes partially targeted. The study will be carried out with further patients to open the way to more personalized SIRT dosimetry.