Systemic radiation therapy with unsealed radionuclides

The effect of the nucleus random location on the cellular S-values - Based on Geant4-DNA

INTRODUCTION

The nucleus is the most crucial target in cell micro-dosimetry. At cell division time, cells do not have concentric geometry synchronously. This issue will be more essential for the low-energy electron emitters. This study investigates the variety of mean absorbed dose (S-value) in the non-concentric cell-nucleus model and random nucleus location within the cell.

METHODS

The S-values were calculated by Geant4-DNA for the cell and nucleus with different radius (with the R_C/R_N ratio = 1.2, 2, 3) and the cell geometry contains nuclei with varying positions inside the cell. Two important components, cytoplasm to the nucleus (N←Cy) and the cell surface to the nucleus (N←Cs) are considered in this work for mono energetic electrons (10-100 keV). To eliminate the effect of the nucleus position (during cell division) on the S-value, the nucleus location in each run was randomly selected inside the cell to represent the cell in a floating state.

RESULTS

As the nucleus becomes closer to the cell membrane the differences are more noticeable especially for electrons with energy less than 20 keV as for R_N/R_C = 1.2, 2, and 3 about 18, 70, and 200%, respectively.

CONCLUSION

Due to the variable position of the nucleus in cell division, using a random place defined in Geant4, the calculations are getting closer to the reality while there is not such possibility for analytical method used by MIRD.

Glucose-holmium for radiotherapy: Characterization and in vitro assays

BACKGROUND

The existence of saccharide-holmium complexes, containing mono or polysaccharide molecules, is an attractive hypothesis toward a radiation therapy (RT) with beta-emitters targeting high glucose metabolic human sites. To exam such hypothesis, the aim of this study was to investigate the possible chemical interactions of Ho and glucose molecules and if glucose may be a facilitator to holmium cell internalization based on in vitro uptake assays and mass spectrometry analyses.

METHODS

The ionic-solution preparations were based on glucose-anhydrous and holmium-nitrate hydrated in aqueous solution, in non-radioactive condition. The uptakes in MDAMB231 cell lineage were evaluated, at 0 and 50 µg mL^-1 holmium solution, in incubation times of 10, 30 and 50 min. The measurements of the holmium mass into the dried cell were evaluated by Neutron Activation Analysis - NAA method. Also, the ionic solution was tested in Electrospray Ionization Mass Spectrometry (ESI-MS) in order to identify Ho and glucose interactions.

RESULTS

There were intracellular holmium-uptake in MDAMB-231 of 3.6 ± 0.1, 6.8 ± 0.2 and 9.7 ± 0.3 μg increasing linearly with incubation time. The m/z ions at 523, 586, 649, 991 and 1054 were attributed to the positively loaded species containing Ho⁺³, glucose (GLU) and NO₃^-, making up the possible molecular compound formulae, involving Ho, GLU, and anions.

CONCLUSIONS

The findings of the in vitro assay and the ESI-MS suggested a suitable holmium cell uptake, increased in function of incubation time, due to the presence of glucose and holmium chemical interactions in solution.

Peptide receptor radionuclide therapy: an overview

Peptide receptor radionuclide therapy (PRRT) is a site-directed targeted therapeutic strategy that specifically uses radiolabeled peptides as biological targeting vectors designed to deliver cytotoxic levels of radiation dose to cancer cells, which overexpress specific receptors. Interest in PRRT has steadily grown because of the advantages of targeting cellular receptors in vivo with high sensitivity as well as specificity and treatment at the molecular level. Recent advances in molecular biology have not only stimulated advances in PRRT in a sustainable manner but have also pushed the field significantly forward to several unexplored possibilities. Recent decades have witnessed unprecedented endeavors for developing radiolabeled receptor-binding somatostatin analogs for the treatment of neuroendocrine tumors, which have played an important role in the evolution of PRRT and paved the way for the development of other receptor-targeting peptides. Several peptides targeting a variety of receptors have been identified, demonstrating their potential to catalyze breakthroughs in PRRT. In this review, the authors discuss several of these peptides and their analogs with regard to their applications and potential in radionuclide therapy. The advancement in the availability of combinatorial peptide libraries for peptide designing and screening provides the capability of regulating immunogenicity and chemical manipulability. Moreover, the availability of a wide range of bifunctional chelating agents opens up the scope of convenient radiolabeling. For these reasons, it would be possible to envision a future where the scope of PRRT can be tailored for patient-specific application. While PRRT lies at the interface between many disciplines, this technology is inextricably linked to the availability of the therapeutic radionuclides of required quality and activity levels and hence their production is also reviewed.

Patient dosimetry in radionuclide therapy: the whys and the wherefores

The importance and methodology of contemporary patient dosimetry in well-established radionuclide therapies are reviewed. The different protocols used for radioiodine treatment of thyrotoxicosis are discussed. Special attention is paid to patient dosimetry in the largest safe dose approach for curative radioiodine therapy of thyroid remnants and metastases in the post-surgical treatment of differentiated thyroid cancer. Nowadays, meta-[131I]iodobenzylguanidine (131I-MIBG) therapy for neuroblastoma relies on bone marrow dose levels. Issues related to whole-body and tumour dosimetry in this type of radionuclide therapy, where, traditionally, dosimetry has played an important role, are discussed. A relatively large number of patients are treated with radiolabelled Lipiodol for hepatocellular carcinoma. Administered activities are restricted to 2.22 GBq (60 mCi) when using 131I-lipiodol because of the radioprotection measures to be taken. These radiation protection issues can be avoided by using 188Re labelled Lipiodol allowing further dose escalation. The follow-up of these patients also necessitates whole-body dosimetry. It is concluded that for treatment of malignant diseases reliable patient dosimetry is now a keystone of high quality radionuclide therapy. Where dosimetry of present medical applications focuses generally on the critical organs, in the near future accurate 3-dimensional tumour dosimetry also will become feasible by the introduction of the combined SPECT-CT and PET-CT imaging systems in the dosimetric methodology. This will allow treatment protocols based on tumour dose prescriptions as performed in external beam radiotherapy.

Accurate dosimetry: an essential step towards good clinical practice in nuclear medicine

In nuclear medicine, an increasing number of radiolabelled agents are under investigation for future use in diagnostic imaging and for applications in radionuclide therapy. All these studies require large amounts of human data to allow for statistical comparisons with existing and well established diagnostic or therapeutic methodologies. In the framework of a good clinical practice environment, clinical trials should be carried out according to international guidelines and regulations as described in the Declaration of Helsinki. Studies involving ionizing radiation, as is the case in nuclear medicine, require special consideration to comply with the ALARA (as low as reasonably achievable) principle. Special publications of the International Commission of Radiological Protection and the World Health Organization deal with this topic in medical research. From the legislation point of view, the 97/43/EURATOM Directive represents the reference to clinical research using ionizing radiation within the European Union. In order to keep the radiation dose of (healthy) volunteers as low as possible, predictive dosimetry studies based on in-vivo animal biokinetics are essential. On the other hand, patients included in dose-escalation radionuclide therapy trials should be monitored individually with respect to dosimetry of the tumour and the critical organs. In this paper the importance and methodology of contemporary patient dosimetry in diagnostic and therapeutic nuclear medicine research are reviewed. It is concluded that reliable dosimetry is essential in performing scientific clinical studies according to the principle of good clinical practice.

Options for radionuclide therapy: from fixed activity to patient-specific treatment planning

The therapeutic use of radioisotopes in medicine as unsealed sources has a long history dating back to the 1930s. The established and continuing objectives are to provide radiation dose to the target tissue at the desired cytotoxic level while avoiding or minimizing toxic effects. Selected radionuclide therapy protocols including 32P for polycythemia vera, 131I for Graves' disease, and 131I for postsurgical ablation of thyroid remnants in the management of differentiated thyroid cancer are presented for historical review with the focus on protocols for administering the radiopharmaceuticals and the role played by dosimetry. The discussion also includes consideration of complications and the assessment of outcome for these diseases. The vista for radionuclide therapy today is reviewed along with the options for determining the administered activity. Patient specific dosimetry encompasses a number of levels ranging from basic measurement of relevant biokinetic parameters and use of standard models to calculate (and extrapolate) radiation dose to sophisticated three-dimensional techniques employing fusion of physiologic and high-resolution anatomic images coupled with advanced 3-D voxel patient representation and Monte Carlo techniques for use in radiation dose calculation. The role of patient specific dosimetry in clinical trials (Phase I, II, III trials) along with its utility in treatment planning, follow-up evaluation, and elucidation of dose-response relationships is discussed. The challenge ahead for those who advocate patient specific dosimetry is to assemble the outcome data and perform the analysis to support this contention.

Clinical trial design and scoring of radionuclide therapy endpoints: normal organ toxicity and tumor response

Like other cancer therapy agents under development, radionuclide therapies are usually evaluated in a progressive series of clinical trials after basic science, human cell culture and animal model studies. Toxicities during these trials are graded using common scoring systems that are in widespread use such as the Common Toxicity Criteria from the National Cancer Institute. Information on normal tissue toxicity from radionuclides is more limited than that from external beam radiation and is more variable. Variability is likely due to many biologic factors as well as less precise dose quantitation than those used in external beam radiation practice. As expected based on known radiobiologic effects, tolerance to radionuclide therapy appears to exceed that from high dose rate external beam radiation in most organs. Although the correlation between reported dose estimates and toxicity has progressively and substantially improved over the past two decades, further progress is needed to establish optimal toxicity predictive relationships. Continued refinement of dosimetry techniques and standardization is expected to increase the accuracy and comparability of radiation dose reports between institutions as well as improve dose/response correlation.