Dosimetric assessment of Gadolinium-159 for hepatic radioembolization: Tomographic images and Monte Carlo simulation.

A common therapeutic radionuclide used in hepatic radioembolization is yttrium-90 (90Y). However, the absence of gamma emissions makes it difficult to verify the post-treatment distribution of 90Y microspheres. Gadolinium-159 (159Gd) has physical properties that are suitable for therapy and post-treatment imaging in hepatic radioembolization procedures. The current study is innovative for conducting a dosimetric investigation of the use of 159Gd in hepatic radioembolization by simulating tomographic images using the Geant4 application for tomographic emission (GATE) Monte Carlo (MC) simulation. For registration and segmentation, tomographic images of five patients with hepatocellular carcinoma (HCC) who had undergone transarterial radioembolization (TARE) therapy were processed using a 3D slicer. The tomographic images with 159Gd and 90Y separately were simulated using the GATE MC Package. The output of simulation (dose image) was uploaded to 3D slicer to compute the absorbed dose for each organ of interests. 159Gd were able to provide a recommended dose of 120 Gy to the tumour, with normal liver and lungs absorbed doses close to that of 90Y and less than the respective maximum permitted doses of 70 Gy and 30 Gy, respectively. Compared to 90Y, 159Gd requires higher administered activity approximately 4.92 times to achieve a tumour dose of 120 Gy. Thus; this research gives new insights into the use of 159Gd as a theranostic radioisotope, with the potential to be used as a90Y alternative for liver radioembolization.

Dosimetric Analysis of Rhizophora-based Phantom Material in Radiation Therapy Applications Using Monte Carlo GATE Simulation.

Purpose: This study aims to determine the percentage depth dose (PDD) of a phantom material made from soy-lignin bonded Rhizophora spp. particleboard coated with a gloss finish by using Monte Carlo Geant4 Application for Tomographic Emission (GATE) simulation. Materials and Methods: The particleboard was fabricated using a hot pressing technique at target density of 1.0 g·cm-3 and the elemental fraction was recorded for the simulation. The PDD was simulated in the GATE simulation using the linear accelerator Elekta Synergy model for the water phantom and Rhizophora phantom, and the results were compared with the experimental PDD performed by several studies. Beam flatness and beam symmetry were also measured in this study. Results: The simulated PDD for Rhizophora and water was in agreement with the experimental PDD of water with overall discrepancies of 0% to 8.7% at depth ranging from 1.0 to 15.0 cm. In the GATE simulation, all the points passed the clinical 3%/3 mm criterion in comparison with water, with the final percentage of 2.34% for Rhizophora phantom and 2.49% for the water phantom simulated in GATE. Both the symmetries are all within the range of an acceptable value of 2.0% according to the recommendation, with the beam symmetry of the water phantom and Rhizophora phantom at 0.58% and 0.28%, respectively. Conclusions: The findings of this study provide the necessary foundation to confidently use the phantom for radiotherapy purposes, especially in treatment planning.

Utilizing 3D Slicer to incorporate tomographic images into GATE Monte Carlo simulation for personalized dosimetry in yttrium-90 radioembolization.

PURPOSE: Monte Carlo (MC) simulation is an important technique that can help design advanced and challenging experimental setups. GATE (Geant4 application for tomographic emission) is a useful simulation toolkit for applications in nuclear medicine. Transarterial radioembolization is a treatment for liver cancer, where microspheres embedded with yttrium-90 (90 Y) are administered intra-arterially to the tumor. Personalized dosimetry for this treatment may provide higher dosimetry accuracy compared to the conventional partition model (PM) calculation. However, incorporation of three-dimensional tomographic input data into MC simulation is an intricate process. In this article, 3D Slicer, free and open-source software, was utilized for the incorporation of patient tomographic images into GATE to demonstrate the feasibility of personalized dosimetry in hepatic radioembolization with 90 Y. METHODS: In this article, the steps involved in importing, segmenting, and registering tomographic images using 3D Slicer were thoroughly described, before importing them into GATE for MC simulation. The absorbed doses estimated using GATE were then compared with that of PM. SlicerRT, a 3D Slicer extension, was then used to visualize the isodose from the MC simulation. RESULTS: A workflow diagram consisting of all the steps taken in the utilization of 3D Slicer for personalized dosimetry in 90 Y radioembolization has been presented in this article. In comparison to the MC simulation, the absorbed doses to the tumor and normal liver were overestimated by PM by 105.55% and 20.23%, respectively, whereas for lungs, the absorbed dose estimated by PM was underestimated by 25.32%. These values were supported by the isodose distribution obtained via SlicerRT, suggesting the presence of beta particles outside the volumes of interest. These findings demonstrate the importance of personalized dosimetry for a more accurate absorbed dose estimation compared to PM. CONCLUSION: The methodology provided in this study can assist users (especially students or researchers who are new to MC simulation) in navigating intricate steps required in the importation of tomographic data for MC simulation. These steps can also be utilized for other radiation therapy related applications, not necessarily limited to internal dosimetry.

Proton Therapy: Malaysian Perspective

@#Proton therapy is an advanced type of radiotherapy and the use of charged particle proton instead of high energy X-rays to treat cancer has been increasing in recent years, as it offers superior dose distribution and more effectively spares healthy tissues compared to conventional radiotherapy. Proton therapy has potential clinical advantages for some types of tumours that are difficult to treat by conventional radiotherapy, it also has the added benefits of no exit dose beyond tumour. Many countries that established cancer treatment facilities in the last decade chose proton therapy because of its lower capital cost and higher cost-effectiveness compared to carbon ions therapy. This review first describes the physical characteristics of proton beam for radiotherapy, followed by potential clinical benefits of proton beam therapy in Malaysia. The paper also discusses the challenges of implementing the first proton centre in Malaysia.