131I Induced In Vivo Proteolysis by Photoswitchable azoPROTAC Reinforces Internal Radiotherapy.

Photopharmacology, incorporating photoswitches such as azobenezes into drugs, is an emerging therapeutic method to realize spatiotemporal control of pharmacological activity by light. However, most photoswitchable molecules are triggered by UV light with limited tissue penetration, which greatly restricts the in vivo application. Here, this study proves that 131I can trigger the trans-cis photoisomerization of a reported azobenezen incorporating PROTACs (azoPROTAC). With the presence of 50 µCi mL-1 131I, the azoPROTAC can effectively down-regulate BRD4 and c-Myc levels in 4T1 cells at a similar level as it does under light irradiation (405 nm, 60 mW cm-2). What's more, the degradation of BRD4 can further benefit the 131I-based radiotherapy. The in vivo experiment proves that intratumoral co-adminstration of 131I (300 µCi) and azoPROTC (25 mg kg-1) via hydrogel not only successfully induce protein degradation in 4T1 tumor bearing-mice but also efficiently inhibit tumor growth with enhanced radiotherapeutic effect and anti-tumor immunological effect. This is the first time that a radioisotope is successfully used as a trigger in photopharmacology in a mouse model. It believes that this study will benefit photopharmacology in deep tissue.

Current clinical applications of Cerenkov luminescence for intraoperative molecular imaging.

BACKGROUND: Cerenkov luminescence imaging (CLI) is a new emerging technology that can be used for optical imaging of approved radiotracers, both in a preclinical, and even more recently, in a clinical context with rapid imaging times, low costs, and detection in real-time (Grootendorst et al. Clin Transl Imaging 4(5):353-66, 2016); Wang et al. Photonics 9(6):390, 2022). This brief review provides an overview of clinical applications of CLI with a focus on intraoperative margin assessment (IMA) to address shortcomings and provide insight for future work in this application. METHODS: A literature review was performed using PubMed using the search words Cerenkov luminescence imaging (CLI), intraoperative margin assessment (IMA), and image-guided surgery. Articles were selected based on title, abstract, content, and application. RESULTS: Original research was summarized to examine advantages and limitations of CLI compared to other modalities for IMA. The characteristics of Cerenkov luminescence (CL) are defined, and results from relevant clinical trials are discussed. Prospects of ongoing clinical trials are reviewed, along with technological advancements related to CLI. CONCLUSION: CLI is a proven method for molecular imaging and shows feasibility for determining intraoperative margins if future work involves establishing quantitative approaches for attenuation and scattering, depth analysis, and radiation safety for CLI at a larger scale.

Application of fluorocarbon nanoparticles of 131I-fulvestrant as a targeted radiation drug for endocrine therapy on human breast cancer.

BACKGROUND: Breast cancer is the most prevalent malignant tumor among women, with hormone receptor-positive cases constituting 70%. Fulvestrant, an antagonist for these receptors, is utilized for advanced metastatic hormone receptor-positive breast cancer. Yet, its inhibitory effect on tumor cells is not strong, and it lacks direct cytotoxicity. Consequently, there's a significant challenge in preventing recurrence and metastasis once cancer cells develop resistance to fulvestrant. METHOD: To address these challenges, we engineered tumor-targeting nanoparticles termed 131I-fulvestrant-ALA-PFP-FA-NPs. This involved labeling fulvestrant with 131I to create 131I-fulvestrant. Subsequently, we incorporated the 131I-fulvestrant and 5-aminolevulinic acid (ALA) into fluorocarbon nanoparticles with folate as the targeting agent. This design facilitates a tri-modal therapeutic approach-endocrine therapy, radiotherapy, and PDT for estrogen receptor-positive breast cancer. RESULTS: Our in vivo and in vitro tests showed that the drug-laden nanoparticles effectively zeroed in on tumors. This targeting efficiency was corroborated using SPECT-CT imaging, confocal microscopy, and small animal fluorescence imaging. The 131I-fulvestrant-ALA-PFP-FA-NPs maintained stability and showcased potent antitumor capabilities due to the synergism of endocrine therapy, radiotherapy, and CR-PDT. Throughout the treatment duration, we detected no notable irregularities in hematological, biochemical, or histological evaluations. CONCLUSION: We've pioneered a nanoparticle system loaded with radioactive isotope 131I, endocrine therapeutic agents, and a photosensitizer precursor. This system offers a combined modality of radiotherapy, endocrine treatment, and PDT for breast cancer.

Progressive Optimization of Lanthanide Nanoparticle Scintillators for Enhanced Triple-Activated Radioluminescence Imaging.

Lanthanide nanoparticle (LnNP) scintillators exhibit huge potential in achieving radionuclide-activated luminescence (radioluminescence, RL). However, their structure-activity relationship remains largely unexplored. Herein, progressive optimization of LnNP scintillators is presented to unveil their structure-dependent RL property and enhance their RL output efficiency. Benefiting from the favorable host matrix and the luminescence-protective effect of core-shell engineering, NaGdF4 : 15 %Eu@NaLuF4 nanoparticle scintillators with tailored structures emerged as the top candidates. Living imaging experiments based on optimal LnNP scintillators validated the feasibility of laser-free continuous RL activated by clinical radiopharmaceuticals for tumor multiplex visualization. This research provides unprecedented insights into the rational design of LnNP scintillators, which would enable efficient energy conversion from Cerenkov luminescence, γ-radiation, and ß-electrons into visible photon signals, thus establishing a robust nanotechnology-aided approach for tumor-directed radio-phototheranostics.

Amplification of Cerenkov luminescence using semiconducting polymers for cancer theranostics.

The therapeutic efficacy of photodynamic therapy is limited by the ability of light to penetrate tissues. Due to this limitation, Cerenkov luminescence (CL) from radionuclides has recently been proposed as an alternative light source in a strategy referred to as Cerenkov radiation induced therapy (CRIT). Semiconducting polymer nanoparticles (SPNs) have ideal optical properties, such as large absorption cross-sections and broad absorbance, which can be utilized to harness the relatively weak CL produced by radionuclides. SPNs can be doped with photosensitizers and have nearly 100% energy transfer efficiency by multiple energy transfer mechanisms. Herein, we investigated an optimized photosensitizer doped SPN as a nanosystem to harness and amplify CL for cancer theranostics. We found that semiconducting polymers significantly amplified CL energy transfer efficiency. Bimodal PET and optical imaging studies showed high tumor uptake and retention of the optimized SPNs when administered intravenously or intratumorally. Lastly, we found that photosensitizer doped SPNs have excellent potential as a cancer theranostics nanosystem in an in vivo tumor therapy study. Our study shows that SPNs are ideally suited to harness and amplify CL for cancer theranostics, which may provide a significant advancement for CRIT that are unabated by tissue penetration limits.

Chlorin e6-loaded goat milk-derived extracellular vesicles for Cerenkov luminescence-induced photodynamic therapy.

PURPOSE: Photodynamic therapy (PDT) is a promising cancer treatment strategy with rapid progress in preclinical and clinical settings. However, the limitations in penetration of external light and precise delivery of photosensitizers hamper its clinical translation. As such, the internal light source such as Cerenkov luminescence (CL) from decaying radioisotopes offers new opportunities. Herein, we show that goat milk-derived extracellular vesicles (GEV) can act as a carrier to deliver photosensitizer Chlorin e6 (Ce6) and tumor-avid 18F-FDG can activate CL-induced PDT for precision cancer theranostics. METHODS: GEV was isolated via differential ultracentrifugation of commercial goat milk and photosensitizer Ce6 was loaded by co-incubation to obtain Ce6@GEV. Tumor uptake of Ce6@GEV was examined using confocal microscopy and flow cytometry. To demonstrate the ability of 18F-FDG to activate photodynamic effects against cancer cells, apoptosis rates were measured using flow cytometry, and the production of 1O2 was measured by reactive oxygen species (ROS) monitoring kit. Moreover, we used the IVIS device to detect Cherenkov radiation and Cerenkov radiation energy transfer (CRET). For animal experiments, a small-animal IVIS imaging system was used to visualize the accumulation of the GEV drug delivery system in tumors. PET/CT and CL images of the tumor site were performed at 0.5, 1, and 2 h. For in vivo antitumor therapy, changes of tumor volume, survival time, and body weight in six groups of tumor-bearing mice were monitored. Furthermore, the blood sample and organs of interest (heart, liver, spleen, lungs, kidneys, and tumor) were collected for hematological analysis, immunohistochemistry, and H&E staining. RESULTS: Confocal microscopy of 4T1 cells incubated with Ce6@GEV for 4 h revealed strong red fluorescence signals in the cytoplasm, which demonstrated that Ce6 loaded in GEV could be efficiently delivered into tumor cells. When Ce6@GEV and 18F-FDG co-existed incubated with 4T1 cells, the cell viability plummeted from more than 88.02 ± 1.30% to 23.79 ± 1.59%, indicating excellent CL-induced PDT effects. In vivo fluorescence images showed a peak tumor/liver ratio of 1.36 ± 0.09 at 24 h after Ce6@GEV injection. For in vivo antitumor therapy, Ce6@GEV + 18F-FDG group had the best tumor inhibition rate (58.02%) compared with the other groups, with the longest survival rate (35 days, 40%). During the whole treatment process, neither blood biochemical analysis nor histological observation revealed vital organ damage, suggesting the biosafety of this treatment strategy. CONCLUSIONS: The simultaneous accumulation of 18F-FDG and Ce6 in tumor tissues is expected to overcome the deficiency of traditional PDT. This strategy has the potential to extend PDT to a variety of tumors, including metastases, using targeted radiotracers to provide internal excitation of light-responsive therapeutics. We expect that our method will play a critical role in precision treatment of deep solid tumors.

Minimizing adverse effects of Cerenkov radiation induced photodynamic therapy with transformable photosensitizer-loaded nanovesicles.

BACKGROUND: Photodynamic therapy (PDT) is a promising antitumor strategy with fewer adverse effects and higher selectivity than conventional therapies. Recently, a series of reports have suggested that PDT induced by Cerenkov radiation (CR) (CR-PDT) has deeper tissue penetration than traditional PDT; however, the strategy of coupling radionuclides with photosensitizers may cause severe side effects. METHODS: We designed tumor-targeting nanoparticles (131I-EM@ALA) by loading 5-aminolevulinic acid (ALA) into an 131I-labeled exosome mimetic (EM) to achieve combined antitumor therapy. In addition to playing a radiotherapeutic role, 131I served as an internal light source for the Cerenkov radiation (CR). RESULTS: The drug-loaded nanoparticles effectively targeted tumors as confirmed by confocal imaging, flow cytometry, and small animal fluorescence imaging. In vitro and in vivo experiments demonstrated that 131I-EM@ALA produced a promising antitumor effect through the synergy of radiotherapy and CR-PDT. The nanoparticles killed tumor cells by inducing DNA damage and activating the lysosome-mitochondrial pathways. No obvious abnormalities in the hematology analyses, blood biochemistry, or histological examinations were observed during the treatment. CONCLUSIONS: We successfully engineered a nanocarrier coloaded with the radionuclide 131I and a photosensitizer precursor for combined radiotherapy and PDT for the treatment of breast cancer.

Ultrasmall Downconverting Nanoparticle for Enhanced Cerenkov Imaging.

Cerenkov imaging provides an opportunity to expand the application of approved radiotracers and therapeutic agents by utilizing them for optical approaches, which opens new avenues for nuclear imaging. The dominating Cerenkov radiation is in the UV/blue region, where it is readily absorbed by human tissue, reducing its utility in vivo. To solve this problem, we propose a strategy to shift Cerenkov light to the more penetrative red-light region through the use of a fluorescent down-conversion technique, based upon europium oxide nanoparticles. We synthesized square-shape ultrasmall Eu2O3 nanoparticles, functionalized with polyethylene glycol and chelate-free radiolabeled for intravenous injection into mice to visualize the lymph node and tumor. By adding trimethylamine N-oxide during the synthesis, we significantly increased the brightness of the particle and synthesized the (to-date) smallest radiolabeled europium-based nanoparticle. These features allow for the exploration of Eu2O3 nanoparticles as a preclinical cancer diagnosis platform with multimodal imaging capability.

ImmunoPET/NIRF/Cerenkov multimodality imaging of ICAM-1 in pancreatic ductal adenocarcinoma.

PURPOSE: We dual-labeled an intercellular adhesion molecule-1 (ICAM-1) monoclonal antibody (mAb) and evaluated its effectiveness for lesion detection and surgical navigation in pancreatic ductal adenocarcinoma (PDAC) via multiple noninvasive imaging approaches, including positron emission tomography (PET), near-infrared fluorescence (NIRF), and Cerenkov luminescence imaging (CLI). METHODS: ICAM-1 expression in PDAC cell lines (BxPC-3 and AsPC-1) was assessed via flow cytometry and immunofluorescent staining. An ICAM-1 mAb labeled by IRDye 800CW and radionuclide zirconium-89 (denoted as [89Zr]Zr-DFO-ICAM-1-IR800) was synthesized. Its performance was validated via in vivo comparative PET/NIRF/CLI and biodistribution (Bio-D) studies in nude mice bearing subcutaneous BxPC-3/AsPC-1 tumors or orthotopic BxPC-3 tumor models using nonspecific IgG as an isotype control tracer. RESULTS: ICAM-1 expression was strong in the BxPC-3 and minimal in the AsPC-1 cell line. Both multimodality imaging and Bio-D data exhibited more prominent uptake of [89Zr]Zr-DFO-ICAM-1-IR800 in BxPC-3 tumors than in AsPC-1 tumors. The uptake of [89Zr]Zr-DFO-IgG-IR800 in BxPC-3 tumors was similar to that of [89Zr]Zr-DFO-ICAM-1-IR800 in AsPC-1 tumors. These results demonstrate the desirable affinity and specificity of [89Zr]Zr-DFO-ICAM-1-IR800 compared to [89Zr]Zr-DFO-IgG-IR800. Orthotopic BxPC-3 tumor foci could also be clearly delineated by [89Zr]Zr-DFO-ICAM-1-IR800. An intermodal match was achieved in the ICAM-1-targeted immunoPET/NIRF/CLI. The positive expression levels of ICAM-1 in BxPC-3 tumor tissue were further confirmed by immunohistopathology. CONCLUSION: We successfully developed a dual-labeled ICAM-1-targeted tracer for PET/NIRF/CLI of PDAC that can facilitate better diagnosis and intervention of PDAC upon clinical translation.

Bimodal Imaging of Mouse Peripheral Nerves with Chlorin Tracers.

Almost 17 million Americans have a history of cancer, a number expected to reach over 22 million by 2030. Cancer patients often undergo chemotherapy in the form of antineoplastic agents such as cis-platin and paclitaxel. Though effective, these agents can induce debilitating side effects; the most common neurotoxic effect, chemotherapy-induced peripheral neuropathy (CIPN), can endure long after treatment ends. Despite the widespread and chronic nature of the dysfunction, no tools exist to quantitatively measure chemotherapy-induced peripheral neuropathy. Such a tool would not only benefit patients but their stratification could also save significant financial and social costs associated with neuropathic pain. In our first step toward addressing this unmet clinical need, we explored a novel dual approach to localize peripheral nerves: Cerenkov luminescence imaging (CLI) and fluorescence imaging (FI). Our approach revolves around the targeting and imaging of voltage-gated sodium channel subtype NaV1.7, highly expressed in peripheral nerves from both harvested human and mouse tissues. For the first time, we show that Hsp1a, a radiolabeled NaV1.7-selective peptide isolated from Homoeomma spec. Peru, can serve as a targeted vector for delivering a radioactive sensor to the peripheral nervous system. In situ, we observe high signal-to-noise ratios in the sciatic nerves of animals injected with fluorescently labeled Hsp1a and radiolabeled Hsp1a. Moreover, confocal microscopy on fresh nerve tissue shows the same high ratios of fluorescence, corroborating our in vivo results. This study indicates that fluorescently labeled and radiolabeled Hsp1a tracers could be used to identify and demarcate nerves in a clinical setting.

Radiopharmaceutical and Eu3+ doped gadolinium oxide nanoparticles mediated triple-excited fluorescence imaging and image-guided surgery.

Cerenkov luminescence imaging (CLI) is a novel optical imaging technique that has been applied in clinic using various radionuclides and radiopharmaceuticals. However, clinical application of CLI has been limited by weak optical signal and restricted tissue penetration depth. Various fluorescent probes have been combined with radiopharmaceuticals for improved imaging performances. However, as most of these probes only interact with Cerenkov luminescence (CL), the low photon fluence of CL greatly restricted it's interaction with fluorescent probes for in vivo imaging. Therefore, it is important to develop probes that can effectively convert energy beyond CL such as ß and γ to the low energy optical signals. In this study, a Eu3+ doped gadolinium oxide (Gd2O3:Eu) was synthesized and combined with radiopharmaceuticals to achieve a red-shifted optical spectrum with less tissue scattering and enhanced optical signal intensity in this study. The interaction between Gd2O3:Eu and radiopharmaceutical were investigated using 18F-fluorodeoxyglucose (18F-FDG). The ex vivo optical signal intensity of the mixture of Gd2O3:Eu and 18F-FDG reached 369 times as high as that of CLI using 18F-FDG alone. To achieve improved biocompatibility, the Gd2O3:Eu nanoparticles were then modified with polyvinyl alcohol (PVA), and the resulted nanoprobe PVA modified Gd2O3:Eu (Gd2O3:Eu@PVA) was applied in intraoperative tumor imaging. Compared with 18F-FDG alone, intraoperative administration of Gd2O3:Eu@PVA and 18F-FDG combination achieved a much higher tumor-to-normal tissue ratio (TNR, 10.24 ± 2.24 vs. 1.87 ± 0.73, P = 0.0030). The use of Gd2O3:Eu@PVA and 18F-FDG also assisted intraoperative detection of tumors that were omitted by preoperative positron emission tomography (PET) imaging. Further experiment of image-guided surgery demonstrated feasibility of image-guided tumor resection using Gd2O3:Eu@PVA and 18F-FDG. In summary, Gd2O3:Eu can achieve significantly optimized imaging property when combined with 18F-FDG in intraoperative tumor imaging and image-guided tumor resection surgery. It is expected that the development of the Gd2O3:Eu nanoparticle will promote investigation and application of novel nanoparticles that can interact with radiopharmaceuticals for improved imaging properties. This work highlighted the impact of the nanoprobe that can be excited by radiopharmaceuticals emitting CL, ß, and γ radiation for precisely imaging of tumor and intraoperatively guide tumor resection.

Optical emission-based phantom to verify coincidence of radiotherapy and imaging isocenters on an MR-linac.

PURPOSE: Demonstrate a novel phantom design using a remote camera imaging method capable of concurrently measuring the position of the x-ray isocenter and the magnetic resonance imaging (MRI) isocenter on an MR-linac. METHODS: A conical frustum with distinct geometric features was machined out of plastic. The phantom was submerged in a small water tank, and aligned using room lasers on a MRIdian MR-linac (ViewRay Inc., Cleveland, OH). The phantom physical isocenter was visualized in the MR images and related to the DICOM coordinate isocenter. To view the x-ray isocenter, an intensified CMOS camera system (DoseOptics LLC., Hanover, NH) was placed at the foot of the treatment couch, and centered such that the optical axis of the camera was coincident with the central axis of the treatment bore. Two or four 8.3mm x 24.1cm beams irradiated the phantom from cardinal directions, producing an optical ring on the conical surface of the phantom. The diameter of the ring, measured at the peak intensity, was compared to the known diameter at the position of irradiation to determine the Z-direction offset of the beam. A star-shot method was employed on the front face of the frustum to determine X-Y alignment of the MV beam. Known shifts were applied to the phantom to establish the sensitivity of the method. RESULTS: Couch translations, demonstrative of possible isocenter misalignments, on the order of 1mm were detectable for both the radiotherapy and MRI isocenters. Data acquired on the MR-linac demonstrated an average error of 0.28mm(N=10, R2 =0.997, σ=0.37mm) in established Z displacement, and 0.10mm(N=5, σ=0.34mm) in XY directions of the radiotherapy isocenter. CONCLUSIONS: The phantom was capable of measuring both the MRI and radiotherapy treatment isocenters. This method has the potential to be of use in MR-linac commissioning, and could be streamlined to be valuable in daily constancy checks of isocenter coincidence.

Effect of Cerenkov Radiation-Induced Photodynamic Therapy with 18F-FDG in an Intraperitoneal Xenograft Mouse Model of Ovarian Cancer.

Ovarian cancer (OC) metastases frequently occur through peritoneal dissemination, and they contribute to difficulties in treatment. While photodynamic therapy (PDT) has the potential to treat OC, its use is often limited by tissue penetration depth and tumor selectivity. Herein, we combined Cerenkov radiation (CR) emitted by 18F-FDG accumulated in tumors as an internal light source and several photosensitizer (PS) candidates with matched absorption bands, including Verteporfin (VP), Chlorin e6 (Ce6) and 5'-Aminolevulinic acid (5'-ALA), to evaluate the anti-tumor efficacy. The in vitro effect of CR-induced PDT (CR-PDT) was evaluated using a cell viability assay, and the efficiency of PS was assessed by measuring the singlet oxygen production. An intraperitoneal ES2 OC mouse model was used for in vivo evaluation of CR-PDT. Positron emission tomography (PET) imaging and bioluminescence-based imaging were performed to monitor the biologic uptake of 18F-FDG and the therapeutic effect. The in vitro studies demonstrated Ce6 and VP to be more effective PSs for CR-PDT. Moreover, VP was more efficient in the generation of singlet oxygen and continued for a long time when exposed to fluoro-18 (18F). Combining CR emitted by 18F-FDG and VP treatment not only significantly suppressed tumor growth, but also prolonged median survival times compared to either monotherapy.

Intraperitoneal Glucose Transport to Micrometastasis: A Multimodal In Vivo Imaging Investigation in a Mouse Lymphoma Model.

Bc-DLFL.1 is a novel spontaneous, high-grade transplantable mouse B-cell lymphoma model for selective serosal propagation. These cells attach to the omentum and mesentery and show dissemination in mesenteric lymph nodes. We aimed to investigate its early stage spread at one day post-intraperitoneal inoculation of lymphoma cells (n = 18 mice), and its advanced stage at seven days post-inoculation with in vivo [18F]FDG-PET and [18F]PET/MRI, and ex vivo by autoradiography and Cherenkov luminescence imaging (CLI). Of the early stage group, nine animals received intraperitoneal injections, and nine received intravenous [18F]FDG injections. The advanced stage group (n = 3) received intravenous FDG injections. In the early stage, using autoradiography we observed a marked accumulation in the mesentery after intraperitoneal FDG injection. Using other imaging methods and autoradiography, following the intravenous injection of FDG no accumulations were detected. At the advanced stage, tracer accumulation was clearly detected in mesenteric lymph nodes and in the peritoneum after intravenous administration using PET. We confirmed the results with immunohistochemistry. Our results in this model highlight the importance of local FDG administration during diagnostic imaging to precisely assess early peritoneal manifestations of other malignancies (colon, stomach, ovary). These findings also support the importance of applying topical therapies, in addition to systemic treatments in peritoneal cancer spread.

Smart 131 I-Labeled Self-Illuminating Photosensitizers for Deep Tumor Therapy.

Stimulating photosensitizers (PS) by Cerenkov radiation (CR) can overcome the light penetration limitation in traditional photodynamic therapy. However, separate injection of radiopharmaceuticals and PS cannot guarantee their efficient interaction in tumor areas, while co-delivery of radionuclides and PS face the problem of nonnegligible phototoxicity in normal tissues. Here, we describe a 131 I-labeled smart photosensitizer, composed of pyropheophorbide-a (photosensitizer), a diisopropylamino group (pH-sensitive group), an 131 I-labeled tyrosine group (CR donor), and polyethylene glycol, which can self-assemble into nanoparticles (131 I-sPS NPs). The 131 I-sPS NPs showed low phototoxicity in normal tissues due to aggregation-caused quenching effect, but could self-produce reactive oxygen species in tumor sites upon disassembly. Upon intravenous injection, 131 I-sPS NPs showed great tumor inhibition capability in subcutaneous 4T1-tumor-bearing Balb/c mice and orthotopic VX2 liver tumor bearing rabbits. We believed 131 I-sPS NPs could expand the application of CR and provide an effective strategy for deep tumor theranostics.

68Ga-PSMA Cerenkov luminescence imaging in primary prostate cancer: first-in-man series.

PURPOSE: Currently, approximately 11-38% of prostate cancer (PCa) patients undergoing radical prostatectomy have a positive surgical margin (PSM) on histopathology. Cerenkov luminescence imaging (CLI) using 68Ga-prostate-specific membrane antigen (68Ga-PSMA) is a novel technique for intraoperative margin assessment. The aim of this first-in-man study was to investigate the feasibility of intraoperative 68Ga-PSMA CLI. In this study, feasibility was defined as the ability to distinguish between a positive and negative surgical margin, imaging within 45 min and low radiation exposure to staff. METHODS: Six patients were included in this ongoing study. Following perioperative i.v. injection of ~ 100 MBq 68Ga-PSMA, the prostate was excised and immediately imaged ex vivo. Different acquisition protocols were tested, and hotspots on CLI images from the intact prostate were marked for comparison with histopathology. RESULTS: By using an acquisition protocol with 150 s exposure time, 8 × 8 binning and a 550 nm shortpass filter, PSMs and negative surgical margins (NSMs) were visually correctly identified on CLI in 3 of the 5 patients. Two patients had a hotspot on CLI from cancer < 0.1 mm from the excision margin. CONCLUSION: Overall, the study showed that 68Ga-PSMA CLI is a feasible and low-risk technique for intraoperative margin assessment in PCa. The remaining patients in this ongoing study will be used to assess the diagnostic accuracy of the technique. TRIAL REGISTRATION: NL8256 registered at www.trialregister.nl on 04/11/20109.

Technical note: Generation of a Cerenkov scatter function convolution kernel for a primary proton beam.

PURPOSE: To generate a Cerenkov scatter function (CSF) for a primary proton beam and to study the dependence of the CSF on the irradiated medium. MATERIALS AND METHODS: The MCNP 6.2 code was used to generate the CSF. The CSF was calculated for light-pigmented, medium-pigmented, and dark-pigmented stratified skin, as well as for a homogeneous optical phantom, which mimics the optical properties of human tissue. CSFs were generated by binning all of the Cerenkov photons which escape the back end (end opposite beam incidence) of a 20 × 20 × 20 cm phantom. A 4 × 4 cm, 500 × 500 bin grid was used to create a histogram of the Cerenkov photon flux on the simulated medium's back surface (surface opposite beam incidence). A triple Gaussian was then used to fit the data. RESULTS: From the triple Gaussian fit, the coefficients of the CSF for the four phantom materials was generated. The individual CSF fit coefficient errors, with respect to the Gaussian representation, were found to be between 0.92% and 4.11%. The R2 value for the fit was calculated to be 0.99. The phantom material was found to have a significant effect (63% difference between materials) on the CSF amplitude and full width at half maximum (195% difference between materials). The difference in these parameters for the three skin pigments was found to be small. CONCLUSIONS: The CSF was obtained for a proton beam using the MCNP 6.2 code for a phantom constructed of light, medium, and dark stratified human skin, as well as for an optical phantom. The CSFs were then fit with a triple-Gaussian function. The coefficients can be used to generate a radially symmetric CSF, which can then be used to deconvolve a measured Cerenkov image to obtain the dose distribution.

Endoscopic Cerenkov luminescence imaging and image-guided tumor resection on hepatocellular carcinoma-bearing mouse models.

Detecting deep tumors inside living subject is still challenging for Cerenkov luminescence imaging (CLI). In this study, a high-sensitivity endoscopic CLI (ECLI) system was developed with a dual-mode deep cooling approach to improve the imaging sensitivity. System was characterized through a series of ex vivo studies. Furthermore, subcutaneous and orthotropic human hepatocellular carcinoma (HCC) mouse models were established for ECLI guided tumor resection in vivo. The results showed that the ECLI system had spatial resolution (62.5 µm) and imaging sensitivity (6.29 × 10-2 kBq/µl 18F-FDG). The in vivo experimental data from the HCC mouse models demonstrated that the system was effective to intraoperatively guide the surgery of deep tumors such as liver cancer. Overall, the developed system exhibits promising potential for the applications of tumor precise resection and novel nanoprobe based optical imaging.

Development of fluorinated naphthofluoresceins for Cerenkov imaging.

In this paper, we report the synthesis and characterization of fluorinated derivatives of naphthofluorescein (NF), a fluorescent pH-sensitive probe that can be used for functional Cerenkov imaging. The compounds were prepared using electrophilic fluorination with dilute fluorine gas under acidic conditions. The fluorination of the NF molecule occurred in the ortho positions to the hydroxyl moiety, producing mono-, di-, and tri-substituted derivatives. The properties of the fluorinated naphthofluoresceins were similar to the parent compound, retaining pH sensitivity and fluorescence capability, but showed a more acidic pKa with increasing fluorination degree and a bathochromic shift in both absorbance and fluorescence. NF and its two major fluorinated derivatives were shown to attenuate Cerenkov radiation in the basic form; the greatest attenuation was observed at wavelengths coinciding with the absorption maxima. NF also showed potential as a Cerenkov Radiation Energy Transfer (CRET) probe. Fluorinated naphthofluoresceins provide a new family of molecular imaging probes for the detection of pH in tissue and organs by using a combination of PET and Cerenkov imaging.

Radionuclide-Activated Nanomaterials and Their Biomedical Applications.

Radio-nanomedicine, or the use of radiolabeled nanoparticles in nuclear medicine, has attracted much attention in the last few decades. Since the discovery of Cerenkov radiation and its employment in Cerenkov luminescence imaging, the combination of nanomaterials and Cerenkov radiation emitters has been revolutionizing the way nanomaterials are perceived in the field: from simple inert carriers of radioactivity to activatable nanomaterials for both diagnostic and therapeutic applications. Herein, we provide a comprehensive review on the types of nanomaterials that have been used to interact with Cerenkov radiation and the gamma and beta scintillation of radionuclides, as well as on their biological applications.