Impact of beam quality on megavoltage radiotherapy treatment techniques utilizing gold nanoparticles for dose enhancement

The Effect of Dose Enhancement in Tumor With Silver Nanoparticles on Surrounding Healthy Tissues: A Monte Carlo Study

Objectives: Cancer-related death rates account for approximately one-third of all deaths, and this rate is increasing remarkably every year. In this study, we examined the dose enhancement factor (DEF) in the tumor and surrounding tissues by adding different concentrations of silver nanoparticles (AgNPs) to the brain tumor using the Monte Carlo (MC) technique. Methods: This study used MCNP6.2 simulation software. A Planning Target Volume (PTV) of 1 × 1 × 1 cm3 was placed in the center of a cubic cranial model with dimensions of 5 × 5 × 5 cm3. Five different simulations were initially generated using the simple method. These simulations included pure PTV and PTV consisting of 4 different silver concentrations (5, 10, 20, and 30 mg/g). Additionally, a model was created using the nanolattice method, considering the size, position, and distribution of the AgNPs. Irradiation was performed using a source with a 6 MV linac photon spectrum. Measurements were performed using the *f8 tally, and DEF values were calculated. Results: In the simulation study using the simple method, the DEF value of PTV increased linearly with concentration, whereas the DEF values were lower than the simulation results with the nanolattice model (1.9 vs 1.4 for 30 mg/g NP concentration). Performing the simple method, we observed no remarkable dose increase in lateral OARs surrounding PTV. While a remarkable dose decrease was observed in distal OARs, a dose increase in the proximal OAR was observed, which was consistent with that of PTV. However, according to the results obtained by performing the nanolattice method, the dose increase was observed in both the proximal OAR and the distal OAR and was similar to that of PTV. Conclusion: While enhancing the dose in the tumor by adding NPs into the tumor, it is essential to consider whether it also increases the OAR dose. In addition, simulation studies on NPs showed that the dose increase varied significantly with particle size, position, and distribution. Hence, these factors should be considered carefully.

Nanoparticle-Mediated Radiotherapy: Unraveling Dose Enhancement and Apoptotic Responses in Cancer and Normal Cell Lines

Cervical cancer remains a pressing global health concern, necessitating advanced therapeutic strategies. Radiotherapy, a fundamental treatment modality, has faced challenges such as targeted dose deposition and radiation exposure to healthy tissues, limiting optimal outcomes. To address these hurdles, nanomaterials, specifically gold nanoparticles (AuNPs), have emerged as a promising avenue. This study delves into the realm of cervical cancer radiotherapy through the meticulous exploration of AuNPs' impact. Utilizing ex vivo experiments involving cell lines, this research dissected intricate radiobiological interactions. Detailed scrutiny of cell survival curves, dose enhancement factors (DEFs), and apoptosis in both cancer and normal cervical cells revealed profound insights. The outcomes showcased the substantial enhancement of radiation responses in cancer cells following AuNP treatment, resulting in heightened cell death and apoptotic levels. Significantly, the most pronounced effects were observed 24 h post-irradiation, emphasizing the pivotal role of timing in AuNPs' efficacy. Importantly, AuNPs exhibited targeted precision, selectively impacting cancer cells while preserving normal cells. This study illuminates the potential of AuNPs as potent radiosensitizers in cervical cancer therapy, offering a tailored and efficient approach. Through meticulous ex vivo experimentation, this research expands our comprehension of the complex dynamics between AuNPs and cells, laying the foundation for their optimized clinical utilization.

Gold-Nanoparticles-Enhanced Production of Reactive Oxygen Species in Cells at Spread-Out Bragg Peak under Proton Beam Radiation

This study investigates the radiobiological effects of gold nanoparticles (GNPs) as radiosensitizers for proton beam therapy (PBT). Specifically, we explore the enhanced production of reactive oxygen species (ROS) in GNP-loaded tumor cells irradiated by a 230 MeV proton beam in a spread-out Bragg peak (SOBP) zone obtained by a passive scattering system. Our findings indicate that the radiosensitization enhancement factor is 1.24 at 30% cell survival fraction, 8 days after 6 Gy proton beam irradiation. Since protons deposit the majority of their energy at the SOBP region and interact with GNPs to induce more ejected electrons from the high-Z GNPs, these ejected electrons then react with water molecules to produce excessive ROS that can damage cellular organelles. Laser scanning confocal microscopy reveals the excessive ROS induced inside the GNP-loaded cells immediately after proton irradiation. Furthermore, the damage to cytoskeletons and mitochondrial dysfunction in GNP-loaded cells caused by the induced ROS becomes significantly severe, 48 h after proton irradiation. Our biological evidence suggests that the cytotoxicity of GNP-enhanced ROS production has the potential to increase the tumoricidal efficacy of PBT.

Mechanisms of Nanoscale Radiation Enhancement by Metal Nanoparticles: Role of Low Energy Electrons

Metal nanoparticles are considered as highly promising radiosensitizers in cancer radiotherapy. Understanding their radiosensitization mechanisms is critical for future clinical applications. This review is focused on the initial energy deposition by short-range Auger electrons; when high energy radiation is absorbed by gold nanoparticles (GNPs) located near vital biomolecules; such as DNA. Auger electrons and the subsequent production of secondary low energy electrons (LEEs) are responsible for most the ensuing chemical damage near such molecules. We highlight recent progress on DNA damage induced by the LEEs produced abundantly within about 100 nanometers from irradiated GNPs; and by those emitted by high energy electrons and X-rays incident on metal surfaces under differing atmospheric environments. LEEs strongly react within cells; mainly via bound breaking processes due to transient anion formation and dissociative electron attachment. The enhancement of damages induced in plasmid DNA by LEEs; with or without the binding of chemotherapeutic drugs; are explained by the fundamental mechanisms of LEE interactions with simple molecules and specific sites on nucleotides. We address the major challenge of metal nanoparticle and GNP radiosensitization; i.e., to deliver the maximum local dose of radiation to the most sensitive target of cancer cells (i.e., DNA). To achieve this goal the emitted electrons from the absorbed high energy radiation must be short range, and produce a large local density of LEEs, and the initial radiation must have the highest possible absorption coefficient compared to that of soft tissue (e.g., 20-80 keV X-rays).

Gold Nanoparticles in Triple-Negative Breast Cancer Therapeutics

BACKGROUND

Triple-negative breast cancer (TNBC) is the most aggressive type of breast cancer with enhanced metastasis and poor survival. Though chemotherapy, radiotherapy, photothermal therapy (PTT), photodynamic therapy (PDT), and gene delivery are used to treat TNBC, various side effects limit these therapeutics against TNBC. In this review article, we have focused on the mechanism of action of gold nanoparticles (AuNPs) to enhance the efficacy of therapeutics with targeted delivery on TNBC cells.

METHODS

Research data were accumulated from PubMed, Scopus, Web of Science, and Google Scholar using searching criteria "gold nanoparticles and triple-negative breast cancer" and "gold nanoparticles and cancer". Though we reviewed many old papers, the most cited papers were from the last ten years.

RESULTS

Various studies indicate that AuNPs can enhance bioavailability, site-specific drug delivery, and efficacy of chemotherapy, radiotherapy, PTT, and PDT as well as modulate gene expression. The role of AuNPs in the modulation of TNBC therapeutics through the inhibition of cell proliferation, progression, and metastasis has been proved in vitro and in vivo studies. As these mechanistic actions of AuNPs are most desirable to develop drugs with enhanced therapeutic efficacy against TNBC, it might be a promising approach to apply AuNPs for TNBC therapeutics.

CONCLUSION

This article reviewed the mechanism of action of AuNPs and their application in the enhancement of therapeutics against TNBC. Much more attention is required for studying the role of AuNPs in developing them either as a single or synergistic anticancer agent against TNBC.

Dosimetry Effects Due to the Presence of Fe Nanoparticles for Potential Combination of Hyperthermic Cancer Treatment with MRI-Based Image-Guided Radiotherapy

Nanoparticles have proven to be biocompatible and suitable for many biomedical applications. Currently, hyperthermia cancer treatments based on Fe nanoparticle infusion excited by alternating magnetic fields are commonly used. In addition to this, MRI-based image-guided radiotherapy represents, nowadays, one of the most promising accurate radiotherapy modalities. Hence, assessing the feasibility of combining both techniques requires preliminary characterization of the corresponding dosimetry effects. The present work reports on a theoretical and numerical simulation feasibility study aimed at pointing out preliminary dosimetry issues. Spatial dose distributions incorporating magnetic nanoparticles in MRI-based image-guided radiotherapy have been obtained by Monte Carlo simulation approaches accounting for all relevant radiation interaction properties as well as charged particles coupling with strong external magnetic fields, which are representative of typical MRI-LINAC devices. Two main effects have been evidenced: local dose enhancement (up to 60% at local level) within the infused volume, and non-negligible changes in the dose distribution at the interfaces between different tissues, developing to over 70% for low-density anatomical cavities. Moreover, cellular uptakes up to 10% have been modeled by means of considering different Fe nanoparticle concentrations. A theoretical temperature-dependent model for the thermal enhancement ratio (TER) has been used to account for radiosensitization due to hyperthermia. The outcomes demonstrated the reliability of the Monte Carlo approach in accounting for strong magnetic fields and mass distributions from patient-specific anatomy CT scans to assess dose distributions in MRI-based image-guided radiotherapy combined with magnetic nanoparticles, while the hyperthermic radiosensitization provides further and synergic contributions.

Gold Nanoparticles Enhancing Generation of ROS for Cs-137 Radiotherapy

Radiotherapy is an important modality for the treatment of cancer, e.g., X-ray, Cs-137 γ-ray (peak energy: 662 keV). An important therapy pathway of radiation is to generate the double strand breaks of DNA to prohibit the proliferation of cancer cells. In addition, the excessive amount of reactive oxygen species (ROS) is induced to damage the organelles, which can cause cellular apoptosis or necrosis. Gold nanoparticles (GNPs) have been proven potential as a radiosensitizer due to the high biocompatibility, the low cytotoxicity and the high-Z property (Z = 79) of gold. The latter property may allow GNPs to induce more secondary electrons for generating ROS in cells as irradiated by high-energy photons. In this paper, the radiobiological effects on A431 cells with uptake of 55-nm GNPs were studied to investigate the GNPs-enhanced production of ROS on these cells as irradiated by Cs-137 γ-ray. The fluorescence-labeling image of laser scanning confocal microscopy (LSCM) shows the excessive expression of ROS in these GNPs-uptake cells after irradiation. And then, the follow-up disruption of cytoskeletons and dysfunction of mitochondria caused by the induced ROS are observed. From the curves of cell survival fraction versus the radiation dose, the radiosensitization enhancement factor of GNPs is 1.29 at a survival fraction of 30%. This demonstrates that the tumoricidal efficacy of Cs-137 radiation can be significantly raised by GNPs. Because of facilitating the production of excessive ROS to damage tumor cells, GNPs are proven to be a prospective radiosensitizer for radiotherapy, particularly for the treatment of certain radioresistant tumor cells. Through this pathway, the tumoricidal efficacy of radiotherapy can be raised.

A Nanomedicine Structure-Activity Framework for Research, Development, and Regulation of Future Cancer Therapies

Despite their clinical success in drug delivery applications, the potential of theranostic nanomedicines is hampered by mechanistic uncertainty and a lack of science-informed regulatory guidance. Both the therapeutic efficacy and the toxicity of nanoformulations are tightly controlled by the complex interplay of the nanoparticle's physicochemical properties and the individual patient/tumor biology; however, it can be difficult to correlate such information with observed outcomes. Additionally, as nanomedicine research attempts to gradually move away from large-scale animal testing, the need for computer-assisted solutions for evaluation will increase. Such models will depend on a clear understanding of structure-activity relationships. This review provides a comprehensive overview of the field of cancer nanomedicine and provides a knowledge framework and foundational interaction maps that can facilitate future research, assessments, and regulation. By forming three complementary maps profiling nanobio interactions and pathways at different levels of biological complexity, a clear picture of a nanoparticle's journey through the body and the therapeutic and adverse consequences of each potential interaction are presented.

Quantifying Radiosensitization of PSMA-Targeted Gold Nanoparticles on Prostate Cancer Cells at Megavoltage Radiation Energies by Monte Carlo Simulation and Local Effect Model

Active targeting gold nanoparticles (AuNPs) are a very promising avenue for cancer treatment with many publications on AuNP mediated radiosensitization at kilovoltage (kV) photon energies. However, uncertainty on the effectiveness of AuNPs under clinically relevant megavoltage (MV) radiation energies hinders the clinical translation of AuNP-assisted radiation therapy (RT) paradigm. The aim of this study was to investigate radiosensitization mediated by PSMA-targeted AuNPs irradiated by a 6 MV radiation beam at different depths to explore feasibility of AuNP-assisted prostate cancer RT under clinically relevant conditions. PSMA-targeted AuNPs (PSMA-AuNPs) were synthesized by conjugating PSMA antibodies onto PEGylated AuNPs through EDC/NHS chemistry. Confocal fluorescence microscopy was used to verify the active targeting of the developed PSMA-AuNPs. Transmission electron microscopy (TEM) was used to demonstrate the intracellular biodistribution of PSMA-AuNPs. LNCaP prostate cancer cells treated with PSMA-AuNPs were irradiated on a Varian 6 MV LINAC under varying depths (2.5 cm, 10 cm, 20 cm, 30 cm) of solid water. Clonogenic assays were carried out to determine the in vitro cell survival fractions. A Monte Carlo (MC) model developed on TOPAS platform was then employed to determine the nano-scale radial dose distribution around AuNPs, which was subsequently used to predict the radiation dose response of LNCaP cells treated with AuNPs. Two different cell models, with AuNPs located within the whole cell or only in the cytoplasm, were used to assess how the intracellular PSMA-AuNP biodistribution impacts the prostate cancer radiosensitization. Then, MC-based microdosimetry was combined with the local effect model (LEM) to calculate cell survival fraction, which was benchmarked against the in vitro clonogenic assays at different depths. In vitro clonogenic assay of LNCaP cells demonstrated the depth dependence of AuNP radiosensitization under clinical megavoltage beams, with sensitization enhancement ratio (SER) of 1.14 ± 0.03 and 1.55 ± 0.05 at 2.5 cm depth and 30 cm depth, respectively. The MC microdosimetry model showed the elevated percent of low-energy photons in the MV beams at greater depth, consequently resulting in increased dose enhancement ratio (DER) of AuNPs with depth. The AuNP-induced DER reached ~5.7 and ~8.1 at depths of 2.5 cm and 30 cm, respectively. Microdosimetry based LEM accurately predicted the cell survival under 6 MV beams at different depths, for the cell model with AuNPs placed only in the cell cytoplasm. TEM results demonstrated the distribution of PSMA-AuNPs in the cytoplasm, confirming the accuracy of MC microdosimetry based LEM with modelled AuNPs distributed within the cytoplasm. We conclude that AuNP radiosensitization can be achieved under megavoltage clinical radiotherapy energies with a dependence on tumor depth. Furthermore, the combination of Monte Carlo microdosimetry and LEM will be a valuable tool to assist with developing AuNP-aided radiotherapy paradigm and drive clinical translation.

Quantification of Nanoscale Dose Enhancement in Gold Nanoparticle-Aided External Photon Beam Radiotherapy

The recent progress in Nanotechnology has introduced Gold Nanoparticles (AuNPs) as promising radiosensitizing agents in radiation oncology. This work aims to estimate dose enhancement due to the presence of AuNPs inside an irradiated water region through Monte Carlo calculations. The GATE platform was used to simulate 6 MV photon histories generated from a TrueBeam^® linear accelerator with and without a Flattening Filter (FF) and model AuNPs clusters. The AuNPs size, concentration and distribution pattern were examined. To investigate different clinical irradiation conditions, the effect of field size, presence of FF and placement of AuNPs in water were evaluated. The range of Dose Enhancement Factors (DEF = Dose_Au/Dose_Water) calculated in this study is 0.99 ± 0.01-1.26 ± 0.02 depending on photon beam quality, distance from AuNPs surface, AuNPs size and concentration and pattern of distribution. The highest DEF is reported for irradiation using un-flattened photon beams and at close distances from AuNPs. The obtained findings suggest that dose deposition could be increased in regions that represent whole cells or subcellular targets (mitochondria, cell nucleus, etc.). Nevertheless, further and consistent research is needed in order to make a step toward AuNP-aided radiotherapy in clinical practice.

Remote sensing array (RSA) for linac beam monitoring

The purpose of the present work is to evaluate the feasibility of a novel real-time beam monitoring device for medical linacs which remotely senses charge carriers produced in air by the beam without intersecting and attenuating the beamline. The primary goal is to elaborate a theoretical concept of a possible detector geometry and underlying physical model that allows for determination of clinically relevant beam data in real time, namely MLC leaf positions and dose rate. The detector consists of two opposing electrode arrays arranged in two possible orientations around the beamline. Detection of charge carriers is governed by electromagnetic principles described by Shockley–Ramo theorem. Ions produced by ionization of the air column upstream of patient move laterally in an external electric field. According to the method of images, mirror charges and mirror currents are formed in the strip electrodes. Determination of MU rate and MLC positions using the measured signal requires solution of an inverse problem. In the present work we adopted a Least-Square approach and characterized detector response and sensitivity to detection of beam properties for different electrode geometries and MLC shapes. Results were dependent on MLC field shape and the leaf position within the active volume. The accuracy of determination of leaf positions were in the sub-mm range (up to 0.25–1 mm). Additionally, detector sensitivity was quantified by simulating ions/pulse delivered with a radiation transport deterministic computation in 1D in CEPXS/ONEDANT. For a 6 MV linac pulse, signal amplitude per pulse was estimated to be in the lower pA to fA range. We computationally demonstrated feasibility of the remote sensing detector capable of measuring beam parameters such as MLC leaf positions and dose range for each pulse. Future work should focus on optimizing the electrode geometry to increase sensitivity and better reconstruction algorithms to provide more accurate solutions of the inverse problem.

Incorporation of Low Concentrations of Gold Nanoparticles: Complex Effects on Radiation Response and Fate of Cancer Cells

(1) Background: In oncology research, a long-standing discussion exists about pros and cons of metal nanoparticle-enhanced radiotherapy and real mechanisms behind the tumor cell response to irradiation (IR) in presence of gold nanoparticles (GNPs). A better understanding of this response is, however, necessary to develop more efficient and safety nanoparticle (NP) types designed to disturb specific processes in tumor cells. (2) Aims and Methods: We combined 3D confocal microscopy and super-resolution single molecule localization microscopy (SMLM) to analyze, at the multiscale, the early and late effects of 10 nm-GNPs on DNA double strand break (DSB) induction and repair in tumor cells exposed to different doses of photonic low-LET (linear energy transfer) radiation. The results were correlated to different aspects of short and long-term cell viability. SkBr3 breast cancer cells (selected for the highest incidence of this cancer type among all cancers in women, and because most breast tumors are treated with IR) were incubated with low concentrations of GNPs and irradiated with ⁶⁰Co γ-rays or 6 MV X-rays. In numerous post-irradiation (PI) times, ranging from 0.5 to 24 h PI, the cells were spatially (3D) fixed and labeled with specific antibodies against γH2AX, 53BP1 and H3K9me3. The extent of DSB induction, multi-parametric micro- and nano-morphology of γH2AX and 53BP1 repair foci, DSB repair kinetics, persistence of unrepaired DSBs, nanoscale clustering of γH2AX and nanoscale (hetero)chromatin re-organization were measured by means of the mentioned microscopy techniques in dependence of radiation dose and GNP concentration. (3) Results: The number of γH2AX/53BP1 signals increased after IR and an additional increase was observed in GNP-treated (GNP(+)) cells compared to untreated controls. However, this phenomenon reflected slight expansion of the G2-phase cell subpopulation in irradiated GNP(+) specimens instead of enhanced DNA damage induction by GNPs. This statement is further supported by some micro- and nano-morphological parameters of γH2AX/53BP1 foci, which slightly differed for cells irradiated in absence or presence of GNPs. At the nanoscale, Ripley’s distance frequency analysis of SMLM signal coordinate matrices also revealed relaxation of heterochromatin (H3K9me3) clusters upon IR. These changes were more prominent in presence of GNPs. The slight expansion of radiosensitive G2 cells correlated with mostly insignificant but systematic decrease in post-irradiation survival of GNP(+) cells. Interestingly, low GNP concentrations accelerated DSB repair kinetics; however, the numbers of persistent γH2AX/53BP1 repair foci were slightly increased in GNP(+) cells. (4) Conclusions: Low concentrations of 10-nm GNPs enhanced the G2/M cell cycle arrest and the proportion of radiosensitive G2 cells, but not the extent of DNA damage induction. GNPs also accelerated DSB repair kinetics and slightly increased presence of unrepaired γH2AX/53BP1 foci at 24 h PI. GNP-mediated cell effects correlated with slight radiosensitization of GNP(+) specimens, significant only for the highest radiation dose tested (4 Gy).

Requirements for Designing an Effective Metallic Nanoparticle (NP)-Boosted Radiation Therapy (RT)

Simple Summary

Recent advances in nanotechnology gave rise to trials with various types of metallic nanoparticles (NPs) to enhance the radiosensitization of cancer cells while reducing or maintaining the normal tissue complication probability during radiation therapy. This work reviews the physical and chemical mechanisms leading to the enhancement of ionizing radiation’s detrimental effects on cells and tissues, as well as the plethora of experimental procedures to study these effects of the so-called “NPs’ radiosensitization”. The paper presents the need to a better understanding of all the phases of actions before applying metallic-based NPs in clinical practice to improve the effect of IR therapy. More physical and biological experiments especially in vivo must be performed and simulation Monte Carlo or mathematical codes based on more accurate models for all phases must be developed.

Abstract

Many different tumor-targeted strategies are under development worldwide to limit the side effects and improve the effectiveness of cancer therapies. One promising method is to enhance the radiosensitization of the cancer cells while reducing or maintaining the normal tissue complication probability during radiation therapy using metallic nanoparticles (NPs). Radiotherapy with MV photons is more commonly available and applied in cancer clinics than high LET particle radiotherapy, so the addition of high-Z NPs has the potential to further increase the efficacy of photon radiotherapy in terms of NP radiosensitization. Generally, when using X-rays, mainly the inner electron shells are ionized, which creates cascades of both low and high energy Auger electrons. When using high LET particles, mainly the outer shells are ionized, which give electrons with lower energies than when using X-rays. The amount of the produced low energy electrons is higher when exposing NPs to heavy charged particles than when exposing them to X-rays. Since ions traverse the material along tracks, and therefore give rise to a much more inhomogeneous dose distributions than X-rays, there might be a need to introduce a higher number of NPs when using ions compared to when using X-rays to create enough primary and secondary electrons to get the desired dose escalations. This raises the questions of toxicity. This paper provides a review of the fundamental processes controlling the outcome of metallic NP-boosted photon beam and ion beam radiation therapy and presents some experimental procedures to study the biological effects of NPs’ radiosensitization. The overview shows the need for more systematic studies of the behavior of NPs when exposed to different kinds of ionizing radiation before applying metallic-based NPs in clinical practice to improve the effect of IR therapy.

On the Equivalence of the Biological Effect Induced by Irradiation of Clusters of Heavy Atom Nanoparticles and Homogeneous Heavy Atom-Water Mixtures

A multiscale local effect model (LEM)-based framework was implemented to study the cell damage caused by the irradiation of clusters of gold nanoparticles (GNPs) under clinically relevant conditions. The results were compared with those obtained by a homogeneous mixture of water and gold (MixNP) irradiated under similar conditions. To that end, Monte Carlo simulations were performed for the irradiation of GNP clusters of different sizes and MixNPs with a 6 MV Linac spectrum to calculate the dose enhancement factor in water. The capabilities of our framework for the prediction of cell damage trends are examined and discussed. We found that the difference of the main parameter driving the cell damage between a cluster of GNPs and the MixNP was less than 1.6% for all cluster sizes. Our results demonstrate for the first time a simple route to intuit the radiobiological effects of clusters of nanoparticles through the consideration of an equivalent homogenous gold/water mixture. Furthermore, the negligible difference on cell damage between a cluster of GNPs and MixNP simplifies the modelling for the complex geometries of nanoparticle aggregations and saves computational resources.

Gold nanoparticle detection and quantification in therapeutic MV beams via pair production

PURPOSE

We propose a new detection method of gold nanoparticles (AuNP) in therapeutic megavoltage (MV) x-ray beams by means of coincidence counting of annihilation photons following pair production in gold.

METHODS

The proposed MV x-ray induced positron emission (MVIPE) imaging technique is studied by radiation transport computations using MCNP6 (3D) and CEPXS/ONEDANT (1D) codes for two water phantoms: a 35 cm slab and a similarly sized cylinder, both having a 5 cm AuNP filled region in the center. MVIPE is compared to the standard x-ray fluorescence computed tomography (XFCT). MVIPE adopts MV x-ray sources (Co-60, 2 MV, 6 MV, 6 MV with closed MLC and 15 MV) and relies on the detection of 511 keV photon-pairs. XFCT uses kilovoltage sources (100 kVp, 120 kVp and 150 kVp) and imaging is characterized by analysis of k _α1,2 Au characteristic lines. Three levels of AuNP concentration were studied: 0.1%, 1% and 10% by weight.

RESULTS

Annihilation photons in the MVIPE technique originate both in the AuNP and in water along the x-ray beam path with significantly larger production in the AuNP-loaded region. MVIPE signal from AuNP is linearly increasing with AuNP concentration up to 10%wt, while XFCT signal reaches saturation due to self-absorption within AuNP. The production of annihilation photons is proportional to the MV source energy. MVIPE technique using a 15 MV pencil beam and 10 wt% AuNP detects about 4.5 × 10³ 511 keV-photons cm^-2 at 90° w/r to the incident beam per 10⁹ source photons cm^-2; 500 of these come from AuNP. In contrast, the XFCT technique using 150 kVp detects only about 100 k _α1-photons cm^-2 per 10⁹ source photons cm^-2.

CONCLUSIONS

In MVIPE, the number of annihilation photons produced for different MV-beam energies and AuNP concentrations is significantly greater than the k _α1 photons generated in XFCT. Coincidence counting in MVIPE allows to avoid collimation, which is a major limiting factor in XFCT. MVIPE challenges include the filtering of Compton scatter and annihilation photons originating in water.

A detailed experimental and Monte Carlo analysis of gold nanoparticle dose enhancement using 6 MV and 18 MV external beam energies in a macroscopic scale

Dose enhancement due to gold nanoparticles (GNPs) has been quantified experimentally and through Monte Carlo simulations for external beam radiation therapy energies of 6 and 18 MV. The highest enhancement was observed for the 18 MV beam at the highest GNP concentration tested, amounting to a DEF of 1.02. DEF is shown to increase with increasing concentration of gold and increasing energy in the megavoltage energy range. The largest difference in measured vs. simulated DEF across all data sets was 0.3%, showing good agreement.

Nanoscale dosimetric consequences around bismuth, gold, gadolinium, hafnium, and iridium nanoparticles irradiated by low energy photons

In the current study, nanoscale physical dose distributions around five potential nanoparticles were compared. Five potential nanoparticles including bismuth, gold, gadolinium, hafnium, and iridium nanoparticles in the form of a sphere with a diameter of 50 nm were simulated in a water medium. The MCNPX (2.7.0) Monte Carlo code with updated libraries was used for calculations of electron dose deposition and electron flux in water from 25 nm up to 4000 nm with a step of 25 nm. Also, secondary electron spectra after irradiation of nanoparticles with mono-energetic photons with energies of 30, 60, 100 keV were derived. The nano-scale distance-dose curves showed a very steep gradient with distance from nanoparticle surface up to 60 nm and after this point, a gradual decrease was seen. The dose deposition characteristics in the nano-scale were dependent on the type of nanoparticle as well as photon energy. Our results concluded that for each photon energy in the energy range of 30-100 keV, a suitable nanoparticle can be selected to boost the effect of energy deposition by low energy photon beams used in brachytherapy.

Increased carcinoembryonic antigen expression on the surface of lung cancer cells using gold nanoparticles during radiotherapy

PURPOSE

Tumor-associated antigens are a promising target of immunotherapy approaches for cancer treatments but rely on sufficient expression of the target antigen. This study investigates the expression of the carcinoembryonic antigen (CEA) on the surface of irradiated lung cancer cells in vitro using gold nanoparticles as radio-enhancer.

METHODS

Human lung carcinoma cells A549 were irradiated and expression of CEA on the cell surface measured by flow cytometry 3 h, 24 h, and 72 h after irradiation to doses of 2 Gy, 6 Gy, 10 Gy, and 20 Gy in the presence or absence of 0.1 mg/ml or 0.5 mg/ml gold nanoparticles. CEA expression was measured as median fluorescent intensity and percentage of CEA-positive cells.

RESULTS

An increase in CEA expression was observed with both increasing radiation dose and time. There was doubling in median fluorescent intensity 24 h after 20 Gy irradiation and 72 h after 6 Gy irradiation. Use of gold nanoparticles resulted in additional significant increase in CEA expression. Change in cell morphology included swelling of cells and increased internal complexity in accordance with change in CEA expression.

CONCLUSIONS

This study showed an increase in CEA expression on human lung carcinoma cells following irradiation. Increase in expression was observed with increasing radiation dose and in a time dependent manner up to 72 h post irradiation. The results further showed that gold nanoparticles can significantly increase CEA expression following radiotherapy.

Radiosensitization by Gold Nanoparticles: Impact of the Size, Dose Rate, and Photon Energy

Gold nanoparticles (GNPs) emerged as promising antitumor radiosensitizers. However, the complex dependence of GNPs radiosensitization on the irradiation conditions remains unclear. In the present study, we investigated the impacts of the dose rate and photon energy on damage of the pBR322 plasmid DNA exposed to X-rays in the presence of 12 nm, 15 nm, 21 nm, and 26 nm GNPs. The greatest radiosensitization was observed for 26 nm GNPs. The sensitizer enhancement ratio (SER) 2.74 ± 0.61 was observed at 200 kVp with 2.4 mg/mL GNPs. Reduction of X-ray tube voltage to 150 and 100 kVp led to a smaller effect. We demonstrate for the first time that the change of the dose rate differentially influences on radiosensitization by GNPs of various sizes. For 12 nm, an increase in the dose rate from 0.2 to 2.1 Gy/min led to a ~1.13-fold increase in radiosensitization. No differences in the effect of 15 nm GNPs was found within the 0.85–2.1 Gy/min range. For 21 nm and 26 nm GNPs, an enhanced radiosensitization was observed along with the decreased dose rate from 2.1 to 0.2 Gy/min. Thus, GNPs are an effective tool for increasing the efficacy of orthovoltage X-ray exposure. However, careful selection of irradiation conditions is a key prerequisite for optimal radiosensitization efficacy.

Impact of secondary particles on microdistribution of deposited dose in biological tissue in the presence of gold and gadolinium nanoparticles under photon beam irradiation

It is experimentally proven that nanoparticles of high-Z materials can be used as radiosensitizers for photon beam therapy. In the authors’ opinion, data available as of today on the impact of secondary particles (electrons, photons and positrons generated in biological tissue by penetrating beam of primary photons) on the distribution of deposited dose during photon beam therapy in the presence of nanoparticles, are insufficient. Investigation of this impact constituted the main goal of this work.

Two-stage simulation was performed using Geant4 platform. During the first stage a layer of biological tissue (water) was irradiated by monoenergetic photon sources with energies ranging from 10 keV to 6 MeV. As the result of this modeling spectra of electrons, photons and positrons were obtained at the depth of 5 cm. During the second stage the obtained photon spectra were used to irradiate gold, gadolinium and water nanoparticles. Radial distributions of energy deposited around nanoparticles were obtained as the result of this modeling.

Radial DEF (Dose Enhancement Factor) values around nanoparticles of gold and gadolinium positioned in water at the depth of 5 cm were obtained after processing the collected data. Contributions from primary photons and secondary particles (electrons, photons and positrons generated in the layer of water with 5-cm thickness by the penetrating beam of primary photons) in the additional dose deposited around the nanoparticles were calculated as well.

It was demonstrated that layer of biological tissue placed between the source of photons and nanoparticles considerably changes the initial spectrum of photons and this change is significant in the analysis of mechanism of radiosensitization of biological tissues by nanoparticles for all energies of photon sources (up to 6 MeV).

It was established that interaction of electrons and positrons with nanoparticles does not lead to significant increase of additional dose in the vicinity of their surfaces and can be most likely excluded from consideration in the analysis of radiosensitization mechanism of nanoparticles.

Monte Carlo dosimetry modeling of focused kV x-ray radiotherapy of eye diseases with potential nanoparticle dose enhancement

PURPOSE

Eye plaque brachytherapy is the most common approach for intraocular cancer treatment. It is, however, invasive and subject to large setup uncertainty due to the surgical operation. We propose a novel-focused kV x-ray technique with potential nanoparticle (NP) enhancement and evaluate its application in treating choroidal melanoma and iris melanoma by Monte Carlo (MC) dosimetry modeling.

METHODS

A polycapillary x-ray lens was used to focus 45 kVp x rays to achieve pinpoint accuracy of dose delivery to small tumors near critical structures. In addition to allowing for beam focusing, the use of kV x rays takes advantage of the strong photoelectric absorption of metallic NPs in that energy regime and hence strong radiosensitization. We constructed an MC simulation program that takes into account the x-ray optic modeling and used GEANT4 for dosimetric calculation. Extensive phantom measurements using a prototype-focused x-ray system were carried out. The MC simulation of simple geometry phantom irradiation was first compared to measurements to verify the x-ray optic lens modeling in conjunction with the Geant4 dosimetric calculation. To simulate tumor treatment, a geometric eye model and two tumor models were constructed. Dose distributions of the simulated treatments were then calculated. NP radiosensitization was also simulated for two concentrations of 2 nm gold NP (AuNP) uniformly distributed in the tumor.

RESULTS

The MC-simulated full width at half maximum (FWHM) and central-axis depth dose of the focused kV x-ray beam match those measured on EBT3 films within ~10% around the depth of focus of the beam. Dose distributions of the simulated ocular tumor treatments show that focused x-ray beams can concentrate the high-dose region in or close to the tumor plus margin. For the simulated posterior choroidal tumor treatment, with sufficient tumor coverage, the doses to the optic disc and fovea are substantially reduced with focused x-ray therapy compared to eye plaque treatment (3.8 vs 39.8 Gy and 11.1 vs 53.8 Gy, respectively). The eye plaque treatment was calculated using an Eye Physics plaque with I-125 seeds under TG43 assumption. For the energy spectrum used in this study, the average simulated dose enhancement ratios (DERs) are roughly 2.1 and 1.1 for 1.0% and 0.1% AuNP mass concentration in the tumor, respectively.

CONCLUSION

Compared to eye plaque brachytherapy, the proposed focused kV x-ray technique is noninvasive and shows great advantage in sparing healthy critical organs without sacrificing the tumor control. The NP radiation dose enhancement is considerable at our proposed kV range even with a low NP concentration in the tumor, providing better critical structure protection and more flexibility for treatment planning.

Relative biological effectiveness study of Lipiodol based on microdosimetric-kinetic model

OBJECTIVES

We examine the contrast agent Lipiodol effect on the relative biological effectiveness (RBE) values for flattening filter free (FFF) and flattening filter (FF) beams of 6 MV-Xray (6 MVX) and 10 MVX.

METHODS

Lipiodol was placed at 5 cm depth in water. According to the microdosimetric kinetic model, the RBE values for killing the human liver hepatocellular cells were calculated from dose and lineal energy (yd(y)) from Monte Carlo simulations. RBE_200kVX and RBE_Co were defined as the ratios of dose using reference radiation (200 kVX, Co-ɤ) to the dose of test radiation (FFF and FF beams for 6 MV and 10 MV) to produce the same biological effects. The dose enhancement RBE (RBE_DE) was defined as the ratios of a dose without Lipiodol to with Lipiodol using to produce the same biological effects. The dose needed to achieve 10% (D_10%) and 1% cell survival (D_1%) was evaluated by cell surviving fraction (SF) formula.

RESULTS

The deviation of mean y‾_D values with and without Lipiodol were 3.9-4.8% for 6 MVX and 3.5-3.6% for 10 MVX. The RBE_200kVX and RBE_Co with Lipiodol were larger than that without Lipiodol. The RBE_DE was larger for FFF beam than for FF beam. The deviation of RBE_DE for FFF and FF beams of 6 MVX was larger than that of 10 MVX.

CONCLUSION

The presence of Lipiodol seemed to locally increase the absorbed dose and to also cause an enhancement of the relative biological effectiveness.

Theranostic gold-magnetite hybrid nanoparticles for MRI-guided radiosensitization

The main limitation of drug-enhanced radiotherapy concerns the difficulty to evaluate the effectiveness of cancer targeting after drug administration hindering the standardization of therapies based on current radiosensitizing compounds. The challenge regards the development of systems able to combine imaging and radiotherapy enhancement in order to perform highly reliable cancer theragnosis. For these reasons, gold-magnetite hybrid nanoparticles (H-NPs) are proposed as innovative theranostic nanotools for imaging-guided radiosensitization in cancer treatment. In this work we propose a novel method for the synthesis of hydrophilic and superparamagnetic Tween20-stabilized gold-magnetite H-NPs. Morphology and chemical composition of nanoparticles were assessed by transmission electron microscopy, x-ray diffraction analysis and ion-coupled plasma optical emission spectroscopy. Colloidal stability and magnetic properties of nanoparticles were determined by dynamic light scattering and magnetometry. The potentialities of H-NPs for magnetic resonance imaging were studied using a human 4T-MRI scanner. Nanoparticles were proven to induce concentration-dependent contrast enhancement in T2*-weighted MR-images. The cytotoxicity, the cellular uptake and the radiosensitization activity of H-NPs were investigated in human osteosarcoma MG63 cell cultures and murine 3T3 fibroblasts, using specific bioassays and laser scanning confocal microscopy. H-NPs did not exhibit significant toxicity and were demonstrated to be internalized by cells. A significant x-ray enhancement at specific H-NPs exposure concentrations was evidenced on MG63 cell line.

The dichotomous nature of dose enhancement by gold nanoparticle aggregates in radiotherapy

AIM

In nanoparticle-aided radiotherapy, the computational paradigm has been that inside the cell, nanoparticles are distributed sparsely and solitarily. However, experiments reveal significant cluster formation, which affects radiosensitization and must be considered in clinical treatment planning. We characterize the impact of gold nanoparticle agglomeration on the predicted radiation dose enhancement as function of size, geometry, morphology and incident beam energy.

MATERIALS & METHODS

Next-generation coupled electron-photon deterministic computations were performed using subnanometric unstructured spatial mesh.

RESULTS

Unlike single nanoparticles, agglomerates develop two types of dose enhancement, smooth peripheral distributions and isolated hotspots, which depend on the cluster size and geometry in opposite ways.

CONCLUSION

The peripheral dose enhancement may have less importance than the hotspots, which can have greater contribution to cell kill via radical creation. Hence, aggregate formation may be beneficial in nanoparticle-aided radiotherapy.

Dual-Energy CT Imaging of Tumor Liposome Delivery After Gold Nanoparticle-Augmented Radiation Therapy

Gold nanoparticles (AuNPs) are emerging as promising agents for both cancer therapy and computed tomography (CT) imaging. AuNPs absorb x-rays and subsequently release low-energy, short-range photoelectrons during external beam radiation therapy (RT), increasing the local radiation dose. When AuNPs are near tumor vasculature, the additional radiation dose can lead to increased vascular permeability. This work focuses on understanding how tumor vascular permeability is influenced by AuNP-augmented RT, and how this effect can be used to improve the delivery of nanoparticle chemotherapeutics. Methods: Dual-energy CT was used to quantify the accumulation of both liposomal iodine and AuNPs in tumors following AuNP-augmented RT in a mouse model of primary soft tissue sarcoma. Mice were injected with non-targeted AuNPs, RGD-functionalized AuNPs (vascular targeting), or no AuNPs, after which they were treated with varying doses of RT. The mice were injected with either liposomal iodine (for the imaging study) or liposomal doxorubicin (for the treatment study) 24 hours after RT. Increased tumor liposome accumulation was assessed by dual-energy CT (iodine) or by tracking tumor treatment response (doxorubicin). Results: A significant increase in vascular permeability was observed for all groups after 20 Gy RT, for the targeted and non-targeted AuNP groups after 10 Gy RT, and for the vascular-targeted AuNP group after 5 Gy RT. Combining targeted AuNPs with 5 Gy RT and liposomal doxorubicin led to a significant tumor growth delay (tumor doubling time ~ 8 days) compared to AuNP-augmented RT or chemotherapy alone (tumor doubling time ~3-4 days). Conclusions: The addition of vascular-targeted AuNPs significantly improved the treatment effect of liposomal doxorubicin after RT, consistent with the increased liposome accumulation observed in tumors in the imaging study. Using this approach with a liposomal drug delivery system can increase specific tumor delivery of chemotherapeutics, which has the potential to significantly improve tumor response and reduce the side effects of both RT and chemotherapy.

Monte Carlo evaluation of the potential benefits of flattening filter free beams from the Oncor® clinical linear accelerator

OBJECTIVES

To evaluate the potential privileges of flattening filter-free (FFF) photon beams from Oncor® linac for 6 MV and 18 MV energies.

METHODS

A Monte Carlo (MC) model of Oncor® linac was built using BEAMnrc MCCode and verified by the measured data using 6 MV and 18 MV energies. A comprehensive set of data was also characterized for MC model of Oncor® machine running with and without flattening filter (FF) for 6 MV and 18 MV beams in six field sizes. The investigated characteristics included mean energy, energy spectrum, photon spatial fluence, superficial dose, percent depth dose (PDD), dose output, and out-of-field dose with two indexes of lateral dose profile and isodose curve at three depths.

RESULTS

Using FFF enhanced the energy uniformity 3.4±0.11% (6 MV) and 2.05±0.09% (18 MV) times and improved dose output by factor of 2.91 (6 MV) and 4.2 (18 MV) on the central axis, respectively. Using FFF also reduced the PDD dependencies by 9.1% (6 MV) and 5.57% (18 MV). In addition, using FFF had a lower out-of-field dose due to the reduced head scatter and softer spectra.

CONCLUSIONS

The findings in this study suggested that using FFF, Oncor® machine could achieve better treatment results with lower dose toxicity and a shorter beam-on time.

Recent Advances in Cancer Therapy Based on Dual Mode Gold Nanoparticles

Many tumor-targeted strategies have been used worldwide to limit the side effects and improve the effectiveness of therapies, such as chemotherapy, radiotherapy (RT), etc. Biophotonic therapy modalities comprise very promising alternative techniques for cancer treatment with minimal invasiveness and side-effects. These modalities use light e.g., laser irradiation in an extracorporeal or intravenous mode to activate photosensitizer agents with selectivity in the target tissue. Photothermal therapy (PTT) is a minimally invasive technique for cancer treatment which uses laser-activated photoabsorbers to convert photon energy into heat sufficient to induce cells destruction via apoptosis, necroptosis and/or necrosis. During the last decade, PTT has attracted an increased interest since the therapy can be combined with customized functionalized nanoparticles (NPs). Recent advances in nanotechnology have given rise to generation of various types of NPs, like gold NPs (AuNPs), designed to act both as radiosensitizers and photothermal sensitizing agents due to their unique optical and electrical properties i.e., functioning in dual mode. Functionalized AuNPS can be employed in combination with non-ionizing and ionizing radiation to significantly improve the efficacy of cancer treatment while at the same time sparing normal tissues. Here, we first provide an overview of the use of NPs for cancer therapy. Then we review many recent advances on the use of gold NPs in PTT, RT and PTT/RT based on different types of AuNPs, irradiation conditions and protocols. We refer to the interaction mechanisms of AuNPs with cancer cells via the effects of non-ionizing and ionizing radiations and we provide recent existing experimental data as a baseline for the design of optimized protocols in PTT, RT and PTT/RT combined treatment.

Comparison of gadolinium nanoparticles and molecular contrast agents for radiation therapy-enhancement

PURPOSE

Nanoparticles appear as a novel tool to enhance the effectiveness of radiotherapy in cancer treatments. Many parameters influence their efficacy, such as their size, concentration, composition, their cellular localization, as well as the photon source energy. The current Monte Carlo study aims at comparing the dose-enhancement in presence of gadolinium (Gd), either as isolated atoms or atoms clustered in nanoparticles (NPs), by investigating the role played by these physical parameters at the cellular and the nanometer scale. In parallel, in vitro assays were performed in presence of either the gadolinium contrast agent (GdCA) Magnevist^® or ultrasmall gadolinium NPs (GdNPs, 3 nm) for comparison with the simulations.

METHODS

PENELOPE Monte Carlo Code was used for in silico dose calculations. Monochromatic photon beams were used to calculate dose enhancements in different cell compartments and low-energy secondary electron spectra dependence with energy. Particular attention has been placed on the interplay between the X-ray beam energy, the Gd localization and its distance from cellular targets. Clonogenic assays were used to quantify F98 rat glioma cell survival after irradiation in the presence of GdNPs or GdCA, using monochromatic X-rays with energies in the 30 keV-80 keV range from a synchrotron and 1.25 MeV gamma photons from a cobalt-60 source. The simulations that correspond to the experimental conditions were compared with the experimental results.

RESULTS

In silico, a highly heterogeneous and clustered Gd-atom distribution, a massive production of low energy electrons around GdNPs and an optimal X-ray beam energy, above the Gd K-edge, were key factors found to increase microscopic doses, which could potentially induce cell death. The different Gd localizations studied all resulted in a lower dose enhancement for the nucleus component than for cytoplasm or membrane compartments, with a maximum dose-enhancement factor (DEF) found at 65 keV and 58 keV, respectively. In vitro, radiosensitization was observed with GdNPs incubated 5 h with the cells (2.1 mg Gd/mL) at all energies. Experimental DEFs were found to be greater than computational DEFs but follow a similar trend with irradiation energy. However, an important radiosensitivity was observed experimentally with GdNPs at high energy (1.25 MeV), whereas no effect was expected from modeling. This effect was correlated with GdNPs incubation time. In vitro, GdCA provided no dose enhancement at 1.25 MeV energies, in agreement with computed data.

CONCLUSIONS

These results provide a foundation on which to base optimizations of the physical parameters in Gd radiation-enhanced therapy. Strong evidence was provided that GdCA or GdNPs could both be used for radiation dose-enhancement therapy. There in vivo biological distribution, in the tumor volume and at the cellular scale, will be the key factor for providing large dose enhancements and determine their therapeutic efficacy.

Targeted dose enhancement in radiotherapy for breast cancer using gold nanoparticles, part 2: A treatment planning study

PURPOSE

In recent years, there has been growing interest in the use of gold nanoparticles (GNPs) combined with radiotherapy to improve tumor control. However, the complex interplay between GNP uptake and dose distribution in realistic clinical treatment are still somewhat unknown.

METHODS

The effects of different concentrations of 2 nm diameter GNP, ranging from 0 to 5×105 nanoparticles per tumoral cell, were theoretically investigated. A parametrization of the GNP distribution outside the target was carried out using a Gaussian standard deviation σ, from a zero value, relative to a selective concentration of GNPs inside the tumor volume alone, to 50mm, when GNPs are spatially distributed also in the healthy tissues surrounding the tumor. Treatment simulations of five patients with breast cancer were performed with 6 and 15 MV photons assuming a partial breast irradiation. A closed analytical reformulation of the Local Effect Model coupled with the estimation of local dose deposited around a GNP was validated using an in vitro study for MDA-MB-231 tumoral cells. The expected treatment outcome was quantified in terms of tumor control probability (TCP) and normal tissue complication probability (NTCP) as a function of the spatially varying gold uptake.

RESULTS

Breast cancer treatment planning simulations show improved treatment outcomes when GNPs are selectively concentrated in the tumor volume (i.e., σ = 0 mm). In particular, the TCP increases up to 18% for 5×105 nanoparticles per cell in the tumor region depending on the treatment schedules, whereas an improvement of the therapeutic index is observed only for concentrations of about 105 GNPs per tumoral cell and limited spatial distribution in the normal tissue.

CONCLUSIONS

The model provides a useful framework to estimate the nanoparticle-driven radiosensitivity in breast cancer treatment irradiation, accounting for the complex interplay between dose and GNP uptake distributions.

A Monte Carlo study of I-125 prostate brachytherapy with gold nanoparticles: dose enhancement with simultaneous rectal dose sparing via radiation shielding

We investigate via Monte Carlo simulations a new ¹²⁵I brachytherapy treatment technique for high-risk prostate cancer patients via injection of Au nanoparticle (AuNP) directly into the prostate. The purpose of using the nanoparticles is to increase the therapeutic index via two synergistic effects: enhanced energy deposition within the prostate and simultaneous shielding of organs at risk from radiation escaping from the prostate. Both uniform and non-uniform concentrations of AuNP are studied. The latter are modeled considering the possibility of AuNP diffusion after the injection using brachy needles. We study two extreme cases of coaxial AuNP concentrations: centered on brachy needles and centered half-way between them. Assuming uniform distribution of 30 mg g^-1 of AuNP within the prostate, we obtain a dose enhancement larger than a factor of 2 to the prostate. Non-uniform concentration of AuNP ranging from 10 mg g^-1 and 66 mg g^-1 were studied. The higher the concentration in a given region of the prostate the greater is the enhancement therein. We obtain the highest dose enhancement when the brachytherapy needles are coincident with AuNP injection needles but, at the same time, the regions in the tail are colder (average dose ratio of 0.7). The best enhancement uniformity is obtained with the seeds in the tail of the AuNP distribution. In both uniform and non-uniform cases the urethra and rectum receive less than 1/3 dose compared to an analog treatment without AuNP. Remarkably, employing AuNP not only significantly increases dose to the target but also decreases dose to the neighboring rectum and even urethra, which is embedded within the prostate. These are mutually interdependent effects as more enhancement leads to more shielding and vice-versa. Caution must be paid since cold spot or hot spots may be created if the AuNP concentration versus seed position is not properly distributed respect to the seed locations.

Optimization of photon beam energies in gold nanoparticle enhanced arc radiation therapy using Monte Carlo methods

As a recent area of development in radiation therapy, gold nanoparticle (GNP) enhanced radiation therapy has shown potential to increase tumour dose while maintaining acceptable levels of healthy tissue toxicity. In this study, the effect of varying photon beam energy in GNP enhanced arc radiation therapy (GEART) is quantified through the introduction of a dose scoring metric, and GEART is compared to a conventional radiotherapy treatment. The PENELOPE Monte Carlo code was used to model several simple phantoms consisting of a spherical tumour containing GNPs (concentration: 15 mg Au g^-1 tumour, 0.8 mg Au g^-1 normal tissue) in a cylinder of tissue. Several monoenergetic photon beams, with energies ranging from 20 keV to 6 MeV, as well as 100, 200, and 300 kVp spectral beams, were used to irradiate the tumour in a 360° arc treatment. A dose metric was then used to compare tumour and tissue doses from GEART treatments to a similar treatment from a 6 MV spectrum. This was also performed on a simulated brain tumour using patient computed tomography data. GEART treatments showed potential over the 6 MV treatment for many of the simulated geometries, delivering up to 88% higher mean dose to the tumour for a constant tissue dose, with the effect greatest near a source energy of 50 keV. This effect is also seen with the inclusion of bone in a brain treatment, with a 14% increase in mean tumour dose over 6 MV, while still maintaining acceptable levels of dose to the bone and brain.

Targeted nanoparticles for tumour radiotherapy enhancement-the long dawn of a golden era?

Despite considerable progress in (I) our understanding of the aetiopathology of head and neck cancer and (II) the precise delivery of radiotherapy, long-term survival rates for many patients with head and neck cancer remain disappointingly low. Over the past years, gold nanoparticles (NP) have emerged as promising radiation dose enhancers. In a recent study published in Nanoscale, Popovtzer et al. have used gold NP coated with an antibody against the epidermal growth factor receptor (EGFR) in an attempt to enhance radiation-induced tumour cell killing in a head and neck cancer xenograft model. They report a significant impact of the combined treatment with radiation and gold NP on tumour growth and suggest an involvement of apoptosis, inhibition of angiogenesis and diminished tissue repair. In this perspective, we illustrate the underlying radiobiophysical concepts and discuss some of the challenges associated with this and related nanoparticle-radiotherapy studies from a physics, chemistry, biology and therapy angle. We conclude that strong interdisciplinary collaborations spanning all these areas are crucially important to proceed towards effective cancer treatment with gold NP "from bench to bedside".

Monte Carlo simulations guided by imaging to predict the in vitro ranking of radiosensitizing nanoparticles

This article addresses the in silico-in vitro prediction issue of organometallic nanoparticles (NPs)-based radiosensitization enhancement. The goal was to carry out computational experiments to quickly identify efficient nanostructures and then to preferentially select the most promising ones for the subsequent in vivo studies. To this aim, this interdisciplinary article introduces a new theoretical Monte Carlo computational ranking method and tests it using 3 different organometallic NPs in terms of size and composition. While the ranking predicted in a classical theoretical scenario did not fit the reference results at all, in contrast, we showed for the first time how our accelerated in silico virtual screening method, based on basic in vitro experimental data (which takes into account the NPs cell biodistribution), was able to predict a relevant ranking in accordance with in vitro clonogenic efficiency. This corroborates the pertinence of such a prior ranking method that could speed up the preclinical development of NPs in radiation therapy.

Low Z target switching to increase tumor endothelial cell dose enhancement during gold nanoparticle-aided radiation therapy

PURPOSE

Previous studies have introduced gold nanoparticles as vascular-disrupting agents during radiation therapy. Crucial to this concept is the low energy photon content of the therapy radiation beam. The authors introduce a new mode of delivery including a linear accelerator target that can toggle between low Z and high Z targets during beam delivery. In this study, the authors examine the potential increase in tumor blood vessel endothelial cell radiation dose enhancement with the low Z target.

METHODS

The authors use Monte Carlo methods to simulate delivery of three different clinical photon beams: (1) a 6 MV standard (Cu/W) beam, (2) a 6 MV flattening filter free (Cu/W), and (3) a 6 MV (carbon) beam. The photon energy spectra for each scenario are generated for depths in tissue-equivalent material: 2, 10, and 20 cm. The endothelial dose enhancement for each target and depth is calculated using a previously published analytic method.

RESULTS

It is found that the carbon target increases the proportion of low energy (<150 keV) photons at 10 cm depth to 28% from 8% for the 6 MV standard (Cu/W) beam. This nearly quadrupling of the low energy photon content incident on a gold nanoparticle results in 7.7 times the endothelial dose enhancement as a 6 MV standard (Cu/W) beam at this depth. Increased surface dose from the low Z target can be mitigated by well-spaced beam arrangements.

CONCLUSIONS

By using the fast-switching target, one can modulate the photon beam during delivery, producing a customized photon energy spectrum for each specific situation.

Monte Carlo simulation of proton therapy using bio-nanomaterials

Introduction

In recent years, there has been a spectacular development in nanomedicine field with new nanoparticles for diagnosis and cancer therapy. Although most researchers have been always interested in gold nanoparticles (GNPs)

Materials and methods

In the present work we present a comparison between the use of bio-nanomaterials in proton therapy.

Conclusion

Consequently, our results show that platinum nanoparticles (PtNPs) present an interesting advantages comparing with GNPs and silver nanoparticles. On the other hand, the use of PtNPs facilitates in a considerable way the proton therapy.

Nanomedicine in the application of uveal melanoma

Rapid advances in nanomedicine have significantly changed many aspects of nanoparticle application to the eye including areas of diagnosis, imaging and more importantly drug delivery. The nanoparticle-based drug delivery systems has provided a solution to various drug solubility-related problems in ophthalmology treatment. Nanostructured compounds could be used to achieve local ocular delivery with minimal unwanted systematic side effects produced by taking advantage of the phagocyte system. In addition, the in vivo control release by nanomaterials encapsulated drugs provides prolong exposure of the compound in the body. Furthermore, certain nanoparticles can overcome important body barriers including the blood-retinal barrier as well as the corneal-retinal barrier of the eye for effective delivery of the drug. In summary, the nanotechnology based drug delivery system may serve as an important tool for uveal melanoma treatment.

Standards and Methodologies for Characterizing Radiobiological Impact of High-Z Nanoparticles

Research on the application of high-Z nanoparticles (NPs) in cancer treatment and diagnosis has recently been the subject of growing interest, with much promise being shown with regards to a potential transition into clinical practice. In spite of numerous publications related to the development and application of nanoparticles for use with ionizing radiation, the literature is lacking coherent and systematic experimental approaches to fully evaluate the radiobiological effectiveness of NPs, validate mechanistic models and allow direct comparison of the studies undertaken by various research groups. The lack of standards and established methodology is commonly recognised as a major obstacle for the transition of innovative research ideas into clinical practice. This review provides a comprehensive overview of radiobiological techniques and quantification methods used in in vitro studies on high-Z nanoparticles and aims to provide recommendations for future standardization for NP-mediated radiation research.

Nanoscale radiation transport and clinical beam modeling for gold nanoparticle dose enhanced radiotherapy (GNPT) using X-rays

We review radiation transport and clinical beam modelling for gold nanoparticle dose-enhanced radiotherapy using X-rays. We focus on the nanoscale radiation transport and its relation to macroscopic dosimetry for monoenergetic and clinical beams. Among other aspects, we discuss Monte Carlo and deterministic methods and their applications to predicting dose enhancement using various metrics.