3D calculation of absorbed dose for 131I-targeted radiotherapy: a Monte Carlo study

Advances in Radionuclides and Radiolabelled Peptides for Cancer Therapeutics

Radiopharmaceutical therapy, which can detect and treat tumours simultaneously, was introduced more than 80 years ago, and it has changed medical strategies with respect to cancer. Many radioactive radionuclides have been developed, and functional, molecularly modified radiolabelled peptides have been used to produce biomolecules and therapeutics that are vastly utilised in the field of radio medicine. Since the 1990s, they have smoothly transitioned into clinical application, and as of today, a wide variety of radiolabelled radionuclide derivatives have been examined and evaluated in various studies. Advanced technologies, such as conjugation of functional peptides or incorporation of radionuclides into chelating ligands, have been developed for advanced radiopharmaceutical cancer therapy. New radiolabelled conjugates for targeted radiotherapy have been designed to deliver radiation directly to cancer cells with improved specificity and minimal damage to the surrounding normal tissue. The development of new theragnostic radionuclides, which can be used for both imaging and therapy purposes, allows for more precise targeting and monitoring of the treatment response. The increased use of peptide receptor radionuclide therapy (PRRT) is also important in the targeting of specific receptors which are overexpressed in cancer cells. In this review, we provide insights into the development of radionuclides and functional radiolabelled peptides, give a brief background, and describe their transition into clinical application.

Internal dosimetry studies of 177Lu-BBN-GABA-DOTA, as a cancer therapy agent, in human tissues based on animal data

The goal of using radiopharmaceuticals for therapeutic purposes is twofold: first, the most damage to cancer cells and, second, the most negligible dose transfers to healthy tissues. As ¹⁷⁷Lu has the potential to cure a wide range of malignancies due to its varied range of beta energies, ¹⁷⁷Lu-BBN-GABA-DOTA has been developed for therapeutic applications. In addition, ¹⁷⁷Lu-BBN-GABA-DOTA can be over-expressed on gastrin-releasing peptide (GRP) receptors of the prostate, breast, small cell lung cancer, gastric, and colon tumors. The purpose of this study was to calculate the amount of dose absorption in human body organs using medical internal radiation dose (MIRD) and GATE code methods, after animal injection. In this study, the amount of absorbed dose in different organs (spleen, kidney, Lung, Pancreas, Heart, Adrenal, Intestine, Stomach, and Liver) were calculated for 1-MBq accumulation of ¹⁷⁷Lu-BBN-GABA-DOTA in source organs (spleen, kidney, Lung, Pancreas, Heart, Adrenal, Intestine, Stomach, and Liver) using Monte Carlo Simulation (GATE code) with Zubal phantom. Moreover, compared with MIRD method, the results of the simulation showed considerable consistency. It was estimated that a 1-MBq administration of ¹⁷⁷Lu-BBN-GABA-DOTA to the human body would result in an absorbed dose of 1.07E-02 mGy and 4.97E-02 (MIRD method) and 1.26E-02 mGy and 5.19E-02 (Gate code) in the Pancreas and adrenal 120 h after injection, respectively. The highest and lowest percentage differences between MIRD and Gate results are related to the Pancreas and spleen, respectively. Finally, the results showed that there is a good agreement between MIRD method and Gate code simulation for absorbed dose estimation.

Dosimetry methods and clinical applications in peptide receptor radionuclide therapy for neuroendocrine tumours: a literature review

Background

The main challenge for systemic radiation therapy using radiopharmaceuticals (SRT) is to optimise the dose delivered to the tumour, while minimising normal tissue irradiation. Dosimetry could help to increase therapy response and decrease toxicity after SRT by individual treatment planning. Peptide receptor radionuclide therapy (PRRT) is an accepted SRT treatment option for irresectable and metastatic neuroendocrine tumours (NET). However, dosimetry in PRRT is not routinely performed, mainly due to the lack of evidence in literature and clinical implementation difficulties. The goal of this review is to provide insight in dosimetry methods and requirements and to present an overview of clinical aspects of dosimetry in PRRT for NET.

Methods

A PubMed query including the search criteria dosimetry, radiation dose, peptide receptor radionuclide therapy, and radionuclide therapy was performed. Articles were selected based on title and abstract, and description of dosimetric approach.

Results

A total of 288 original articles were included. The most important dosimetry methods, their main advantages and limitations, and implications in the clinical setting are discussed. An overview of dosimetry in clinical studies regarding PRRT treatment for NET is provided.

Conclusion

Clinical dosimetry in PRRT is feasible and can result in improved treatment outcomes. Current clinical dosimetry studies focus on safety and apply non-voxel-based dosimetry methods. Personalised treatment using sophisticated dosimetry methods to assess tumour and normal tissue uptake in clinical trials is the next step towards routine dosimetry in PRRT for NET.

Electronic supplementary material

The online version of this article (10.1186/s13550-018-0443-z) contains supplementary material, which is available to authorized users.

PATIENT-SPECIFIC DOSIMETRY FOR PEDIATRIC IMAGING OF 99mTc-DIMERCAPTOSUCCINIC ACID WITH GATE MONTE CARLO CODE

In this study, radiation absorbed dose of 99mTc-dimercaptosuccinic acid (DMSA) in critical organs was calculated using Monte Carlo simulation. Ten child patients with genitourinary abnormalities were imaged using a series of planar, SPECT and MRI, after injection with 99mTc-DMSA. Patient-specific organ segmentation was performed on MRI and used as input in GATE. Organs with substantial uptake included kidneys, bladder and liver. The mean organ absorbed dose coefficients (mGy/MBq) were 0.063, 0.058, 0.018, 0.016, 0.013 and 0.010 for the right kidney, left kidney, bones, urinary bladder wall, liver and gonads, respectively. The absorbed dose coefficients in the remainder of the body was 0.012 mGy/MBq. The authors implemented an image-based Monte Carlo method for patient-specific 3D absorbed dose calculation. This study also demonstrates the possibility to obtain patient-specific attenuation map from MRI to be used for the simulations of radiation transport and energy deposition in phantom using Monte Carlo methods.

Automated MicroSPECT/MicroCT Image Analysis of the Mouse Thyroid Gland

BACKGROUND

The ability of thyroid follicular cells to take up iodine enables the use of radioactive iodine (RAI) for imaging and targeted killing of RAI-avid thyroid cancer following thyroidectomy. To facilitate identifying novel strategies to improve 131I therapeutic efficacy for patients with RAI refractory disease, it is desired to optimize image acquisition and analysis for preclinical mouse models of thyroid cancer.

METHODS

A customized mouse cradle was designed and used for microSPECT/CT image acquisition at 1 hour (t1) and 24 hours (t24) post injection of 123I, which mainly reflect RAI influx/efflux equilibrium and RAI retention in the thyroid, respectively. FVB/N mice with normal thyroid glands and TgBRAFV600E mice with thyroid tumors were imaged. In-house CTViewer software was developed to streamline image analysis with new capabilities, along with display of 3D voxel-based 123I gamma photon intensity in MATLAB.

RESULTS

The customized mouse cradle facilitates consistent tissue configuration among image acquisitions such that rigid body registration can be applied to align serial images of the same mouse via the in-house CTViewer software. CTViewer is designed specifically to streamline SPECT/CT image analysis with functions tailored to quantify thyroid radioiodine uptake. Automatic segmentation of thyroid volumes of interest (VOI) from adjacent salivary glands in t1 images is enabled by superimposing the thyroid VOI from the t24 image onto the corresponding aligned t1 image. The extent of heterogeneity in 123I accumulation within thyroid VOIs can be visualized by 3D display of voxel-based 123I gamma photon intensity.

CONCLUSIONS

MicroSPECT/CT image acquisition and analysis for thyroidal RAI uptake is greatly improved by the cradle and the CTViewer software, respectively. Furthermore, the approach of superimposing thyroid VOIs from t24 images to select thyroid VOIs on corresponding aligned t1 images can be applied to studies in which the target tissue has differential radiotracer retention from surrounding tissues.

A review of the use and potential of the GATE Monte Carlo simulation code for radiation therapy and dosimetry applications

In this paper, the authors' review the applicability of the open-source GATE Monte Carlo simulation platform based on the GEANT4 toolkit for radiation therapy and dosimetry applications. The many applications of GATE for state-of-the-art radiotherapy simulations are described including external beam radiotherapy, brachytherapy, intraoperative radiotherapy, hadrontherapy, molecular radiotherapy, and in vivo dose monitoring. Investigations that have been performed using GEANT4 only are also mentioned to illustrate the potential of GATE. The very practical feature of GATE making it easy to model both a treatment and an imaging acquisition within the same framework is emphasized. The computational times associated with several applications are provided to illustrate the practical feasibility of the simulations using current computing facilities.

TSH and Thyrotropic Agonists: Key Actors in Thyroid Homeostasis

This paper provides the reader with an overview of our current knowledge of hypothalamic-pituitary-thyroid feedback from a cybernetic standpoint. Over the past decades we have gained a plethora of information from biochemical, clinical, and epidemiological investigation, especially on the role of TSH and other thyrotropic agonists as critical components of this complex relationship. Integrating these data into a systems perspective delivers new insights into static and dynamic behaviour of thyroid homeostasis. Explicit usage of this information with mathematical methods promises to deliver a better understanding of thyrotropic feedback control and new options for personalised diagnosis of thyroid dysfunction and targeted therapy, also by permitting a new perspective on the conundrum of the TSH reference range.