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Forty two patients with high energy open fractures were involved into the study to investigate whether an indocyanine green (ICG)-based dynamic contrast-enhanced fluorescence imaging (DCE-FI) can be used to objectively assess bone perfusion and guide surgical debridement. For each patient, fluorescence images were recorded after 0.1 mg/kg of ICG was administered intravenously. By utilizing a bone-specific kinetic model to the video sequences, the perfusion-related metrics were calculated. The results of this study shown that the quantitative ICG-based DEC-FI can accurately assess the human bone perfusion during the orthopedic surgery.

Daylight photodynamic therapy is an effective treatment for actinic keratoses and relies on a minimum PpIX-effective light exposure dose being delivered during treatment. As such, daylight dosimetry is an important aspect of this treatment. Relatively simple measurements of illuminance may be converted to PpIX-effective irradiance, and subsequently exposure dose, via a conversion model (the O'Mahoney model). This model has been verified against spectral irradiance data from the UK, however the accuracy of the model has not been determined outside the UK. In this work, we test the O'Mahoney model against spectral irradiance measurements from several global locations to within bounds of a median deviation of ±10 %. The median percentage deviations are shown to be independent of location latitude and longitude. The model can be used confidently to determine PpIX-effective irradiance from illuminance measurements irrespective of location and can be widely implemented as an effective and low-cost means of accurately measuring effective light exposure for this important treatment.

The field of medical physics has struggled with the role of research in recent years, as professional interests have dominated its growth toward clinical service. This article focuses on the subset of medical physics programs within academic medical centers and how a refocused academic mission within these centers should drive and support Discovery and Invention with Ventures and Engineering for Research Translation (DIVERT). A roadmap to a DIVERT-based scholarly research program is discussed here around the core building blocks of: (a) creativity in research and team building, (b) improved quality metrics to assess activity, (c) strategic partnerships and spinoff directions that extend capabilities, and (d) future directions driven by faculty-led initiatives. Within academia, it is the unique discoveries and inventions of faculty that lead to their recognition as scholars, and leads to financial support for their research programs and reconition of their intellectual contributions. Innovation must also be coupled to translation to demonstrate outcome successes. These ingredients are critical for research funding, and the two-decade growth in biomedical engineering research funding is an illustration of this, where technology invention has been the goal. This record can be contrasted with flat funding within radiation oncology and radiology, where a growing fraction of research is more procedure-based. However, some centers are leading the change of the definition of medical physics, by the inclusion or assimilation of researchers in fields such as biomedical engineering, machine learning, or data science, thereby widening the scope for new discoveries and inventions. New approaches to the assessment of research quality can help realize this model, revisiting the measures of success and impact. While research partnerships with large industry are productive, newer efforts that foster enterprise startups are changing how institutions see the benefits of the connection between academic innovation and affiliated startup company formation. This innovation-to-enterprise focus can help to cultivate a broader bandwidth of donor-to-investor networks. There are many predictions on future directions in medical physics, yet the actual inventive and discovery steps come from individual research faculty creativity. All success through a DIVERT model requires that faculty-led initiatives span the gap from invention to translation, with support from institutional leadership at all steps in the process. Institutional investment in faculty through endowments or clinical revenues will likely need to increase in the coming years due to the relative decreasing size of grants. Yet, radiology and radiation oncology are both high-revenue, translational fields, with the capacity to synergistically support clinical and research operations through large infrastructures that are mutually beneficial. These roadmap principles can provide a pathway for committed academic medical physics programs in scholarly leadership that will preserve medical physics as an active part of university academics.

Breast-conserving surgery requires that resection margins be cancer-free, but re-excision rates due to positive margins have remained near 20% for much of the last decade with high variability between surgical centers. Recent studies have demonstrated that volumetric X-ray imaging improves margin assessment over standard techniques, given the speed of image reconstruction and full three-dimensional sensing of all margins. Deep learning approaches for automated analysis of volumetric medical image data are gaining traction and could play an important role streamlining the clinical workflow for intra-surgical specimen imaging. X-ray imaging systems currently deployed in clinical studies suffer from poor tumor-to-fibroglandular tissue contrast, motivating the development of adjuvant tools that could potentially complement volumetric X-ray scanning and further improve the future of intra-surgical margin assessment by real-time augmented guidance for the surgeon.

Significance: The study has confirmed the feasibility of using ultraviolet (UV) excitation to visualize and quantify desmoplasia in fresh tumor tissue of pancreatic adenocarcinoma (PDAC) in an orthotopic xenograft mouse model, which provides a useful imaging platform to evaluate acute therapeutic responses. Aim: Stromal network of collagen prominent in PDAC tumors is examined by imaging fresh tissue samples stained with histological dyes. Fluorescence signals are color-transferred to mimic Masson’s trichrome staining. Approach: Murine tumor samples were stained with Hoechst, eosin, and rhodamine B and excited at 275-nm. Fluorescence signals in the visible spectrum were captured by a CMOS color camera with high contrast and resolution at whole-tumor slice field of view. Results: Fluorescence imaging using UV excitation is capable of visualizing collagen deposition in PDAC tumors. Both fluorescence and histology data showed collagen content of up to 30%. The collagen modulation effect due to photodynamic priming treatment was observed showing 13% of collagen reduction. Necrosis area is visible and perfusion imaging using Texas Red dextran is feasible. Conclusions: The study demonstrates collagen visualization in fresh PDAC tumor samples using UV excitation. This imaging platform also provides quantitative stromal information from fiber analysis and visibility of necrosis and perfusion, suitable for therapeutic response assessment of photodynamic therapy.

Ultra-high dose rate electron sources require dose rate independent dosimeters and a calibrated dose control system for accurate delivery. In this study, we developed a single-pulse dose monitoring and a real-time dose-based control system for a converted clinical linear accelerator (LINAC). A point scintillator detector was coupled to a gated amplifier and a real-time controller for dose monitoring and feedback control loop. The controller was programmed to integrate dose and measure pulse width of each radiation pulse and gate the LINAC beam when the prescribed dose was delivered. The scintillator was mounted in solid water phantom and placed underneath mice skin for in vivo dose monitoring. Additionally, the scintillator was characterized in terms of its radiation stability, mean dose-rate, and dose per pulse dependence. Dose integration was performed for each radiation pulse and displayed in real-time. The scintillator was shown to be linear with mean dose-rate (40-380 Gy/s) and dose per pulse (0.3-1.3 Gy/Pulse) to within +/- 3%. However, the plastic scintillator was subject to significant radiation damage (16%/kGy) and would need to be calibrated frequently. Pulse-counting control was accurately implemented with direct correspondence between the intended and the actual delivered pulses. The dose-based control was sufficient to gate on any pulse of the LINAC. In-vivo dosimetry monitoring with a 1 cm circular cut-out revealed that a ramp-up of 4-5 pulses was present during which the average dose per pulse was ~0.045 +/- 0.004 Gy/Pulse, whereas after the ramp-up it stabilized at 0.65 +/- 0.01 Gy/Pulse. The tools presented in this study can be used to determine the beam parameter space pertinent to the FLASH effect. Additionally, this study is the first instance of real-time dose-based control for a modified LINAC at ultra-high dose rates., Comment: 30 Pages, 7 Figures

Clinical measurements of O2 in tissues will inevitably provide data that are at best aggregated and will not reflect the inherent heterogeneity of O2 in tissues over space and time. Additionally, the nature of all existing techniques to measure O2 results in complex sampling of the volume that is sensed by the technique. By recognizing these potential limitations of the measures, one can focus on the very important and useful information that can be obtained from these techniques, especially data about factors that can change levels of O2 and then exploit these changes diagnostically and therapeutically. The clinical utility of such data ultimately needs to be verified by careful studies of outcomes related to the measured changes in levels of O2.

Purpose: A Monte Carlo (MC) beam model and its implementation in a clinical treatment planning system (TPS, Varian Eclipse) are presented for a modified ultra-high dose-rate electron FLASH radiotherapy (eFLASH-RT) LINAC. Methods: The gantry head without scattering foils or targets, representative of the LINAC modifications, was modelled in Geant4. The energy spectrum ({\sigma}E) and beam source emittance cone angle ({\theta}cone) were varied to match the calculated and Gafchromic film measured central-axis percent depth dose (PDD) and lateral profiles. Its Eclipse configuration was validated with measured profiles of the open field and nominal fields for clinical applicators. eFLASH-RT plans were MC forward calculated in Geant4 for a mouse brain treatment and compared to a conventional (Conv-RT) plan in Eclipse for a human patient with metastatic renal cell carcinoma. Results: The beam model and its Eclipse configuration agreed best with measurements at {\sigma}E=0.5 MeV and {\theta}cone=3.9+/-0.2 degrees to clinically acceptable accuracy (the absolute average error was within 1.5% for in-water lateral, 3% for in-air lateral, and 2% for PDD). The forward dose calculation showed dose was delivered to the entire mouse brain with adequate conformality. The human patient case demonstrated the planning capability with routine accessories in relatively complex geometry to achieve an acceptable plan (90% of the tumor volume receiving 95% and 90% of the prescribed dose for eFLASH and Conv-RT, respectively). Conclusion: To the best of our knowledge, this is the first functional beam model commissioned in a clinical TPS for eFLASH-RT, enabling planning and evaluation with minimal deviation from Conv-RT workflow. It facilitates the clinical translation as eFLASH-RT and Conv-RT plan quality were comparable for a human patient. The methods can be expanded to model other eFLASH irradiators., Comment: 14 Pages, 6 Figures, 1 Supplementary Material

Significance: Deep-tissue penetration by x-rays to induce optical responses of specific molecular reporters is a new way to sense and image features of tissue function in vivo. Advances in this field are emerging, as biocompatible probes are invented along with innovations in how to optimally utilize x-ray sources. Aim: A comprehensive review is provided of the many tools and techniques developed for x-ray-induced optical molecular sensing, covering topics ranging from foundations of x-ray fluorescence imaging and x-ray tomography to the adaptation of these methods for sensing and imaging in vivo. Approach: The ways in which x-rays can interact with molecules and lead to their optical luminescence are reviewed, including temporal methods based on gated acquisition and multipoint scanning for improved lateral or axial resolution. Results: While some known probes can generate light upon x-ray scintillation, there has been an emergent recognition that excitation of molecular probes by x-ray-induced Cherenkov light is also possible. Emission of Cherenkov radiation requires a threshold energy of x-rays in the high kV or MV range, but has the advantage of being able to excite a broad range of optical molecular probes. In comparison, most scintillating agents are more readily activated by lower keV x-ray energies but are composed of crystalline inorganic constituents, although some organic biocompatible agents have been designed as well. Methods to create high-resolution structured x-ray-optical images are now available, based upon unique scanning approaches and/or a priori knowledge of the scanned x-ray beam geometry. Further improvements in spatial resolution can be achieved by careful system design and algorithm optimization. Current applications of these hybrid x-ray-optical approaches include imaging of tissue oxygenation and pH as well as of certain fluorescent proteins. Conclusions: Discovery of x-ray-excited reporters combined with optimized x-ray scan sequences can improve imaging resolution and sensitivity.

We examine the value of an active line scan with spatial gating for imaging sub-diffuse, wide-field reflectance microtexture. Line scanning combined with spatial gating and linear translation can be used for localized detection of features in the surface layer of a turbid target. The line scan provides broadband spatial frequency modulation, and the spatial gating effectively high-pass filters the reflectance. The major benefit of this approach is that of high dynamic range (70%–90%) signal preservation and high contrast to noise when imaging at high spatial frequencies. Alternative approaches, such as spatial frequency domain imaging, are degraded by low dynamic range in demodulated images, making it nearly impossible to image over a wide field of view at frequencies over 1.5 m m − 1 using commercial technology. As such, active line scanning with spatial gating presents as an inherently high sensitivity and high dynamic range method of imaging microscopic scattering features in only the surface layer of a turbid medium.

Significance: The necessity to use exogenous probes for optical oxygen measurements in radiotherapy poses challenges for clinical applications. Options for implantable probe biotechnology need to be improved to alleviate toxicity concerns in human use and facilitate translation to clinical trial use. Aim: To develop an implantable oxygen sensor containing a phosphorescent oxygen probe such that the overall administered dose of the probe would be below the Federal Drug Administration (FDA)-prescribed microdose level, and the sensor would provide local high-intensity signal for longitudinal measurements of tissue pO2. Approach: PtG4, an oxygen quenched dendritic molecule, was mixed into an agarose matrix at 100 μM concentration, allowing for local injection into tumors at the total dose of 10 nmol per animal, forming a gel at the site of injection. Cherenkov-excited luminescence imaging (CELI) was used to acquire the phosphorescence and provide intratumoral pO2. Results: Although PtG4 does not form covalent bonds with agarose and gradually leaches out into the surrounding tissue, its retention time within the gel was sufficiently long to demonstrate the capability to measure intratumoral pO2 with the implantable gel sensors. The sensor’s performance was first evaluated in vitro in tissue simulation phantoms, and then the sensor was used to measure changes in oxygen in MDA-MB-231 tumors during hypofractionated radiotherapy. Conclusions: Our study demonstrates that implantable oxygen sensors in combination with CELI present a promising approach for quantifying oxygen changes during the course of radiation therapy and thus for evaluating the tumor response to radiation. By improving the design of the gel–probe composition in order to prevent leaching of the probe into the tissue, biosensors can be created that should allow longitudinal oxygen measurements in tumors by means of CELI while using FDA-compliant microdose levels of the probe and thus lowering toxicity concerns.

Cherenkov-excited luminescence has previously been demonstrated as a method to improve the depth sensitivity of in vivo optical imaging1–4 and could be an alternative to optical imaging with fluorescence in deeper penetrance. An example application of Cherenkov-excited luminescence is to excite an oxygen-sensitive luminescent compound during radiation therapy utilizing only the radiation as an excitation source and a sensitive camera for detection, as shown in Fig. 1(a). In conventional in vivo fluorescence imaging, utilizing an excitation laser or LED light, there is an exponential decay of the source as it propagates into tissue dictated approximately by the effective attenuation coefficient, μeff, defined by diffusion theory as μeff=3μa(μa+μs′) where the latter coefficients are for absorption and transport reduced scattering, respectively.6 In Cherenkov excitation, the excitation light is produced throughout the volume directly proportional to the dose of the radiation beam for electrons above the 220 keV threshold, following the same build up and fall off with depth, as shown in Fig. 1(c). While in both cases, laser or Cherenkov excitation, the light still has to escape the tissue and is therefore attenuated exponentially by μeff on the way out at the emission wavelength bands, there is still a major benefit from having the exciting light within the volume of tissue. Yet, in comparing optical excitation to radiation beam excitation, it is hard to clearly quantify the benefits for Cherenkov, and so in this study, the (i) spatial resolution, (ii) depth sensitivity, and (iii) optimal fluorophores for Cherenkov excitation, are each examined computationally with Monte Carlo simulations. Open in a separate window Fig. 1 Schematic illustration (a) of an in vivo application of Cherenkov-excited luminescence where Cherenkov light is generated at depths into tissue. In this illustration, a mouse with a hypoxic flank tumor and normal muscle tissue are injected with an oxygen-sensitive phosphorescent compound. As the x-ray beam passes through the tissue, Cherenkov emissions occur and excite the luminescent compound. In vivo imaging can resolve the depth-integrated voxels, and the resulting estimates can be tabulated into a histogram to describe the heterogeneous extracellular oxygen concentration.5 The photon energy distribution used in subsequent Monte Carlo simulations is shown in (b) which determine the characteristics of the Cherenkov intensity and depth within the tissue. The percentage depth-dose (PDD) curves for 10 cm×10 cm photon (6 and 18 MV) and electron (6 and 18 MeV) beams in water are shown in (c) where electrons have a higher chance of interaction and deposit dose more superficially, whereas photon beams must first generate a high-energy electron through Compton scattering before Cherenkov emissions can occur. Cherenkov emissions are correlated with dose, so the PDD can be used as an estimate of the depth distribution of the optical emissions.

In this study, an indocyanine green (ICG)-based dynamic contrast- enhanced fluorescence imaging (DCE-FI) technique was evaluated as a method to provide objective real-time data on bone perfusion using a porcine osteotomy model. DCE-FI with sequentially increasing injury to osseous blood supply was performed in 12 porcine tibias. There were measurable, reproducible and predictable changes to DCE-FI data across each condition have been observed on simple kinetic curve-derived variables as well variables derived from a novel bone-specific kinetic model. The best accuracy, sensitivity and specificity of 89%, 88% and 90%, have been achieved to effectively differentiate injured from normal/healthy bone.

Purpose The extreme microscopic heterogeneity of tumors makes it difficult to characterize tumor hypoxia. We evaluated how changes in the spatial resolution of oxygen imaging could alter measures of tumor hypoxia and their correlation to radiation therapy response. Methods and Materials Cherenkov-Excited Luminescence Imaging in combination with an oxygen probe, Oxyphor PtG4 was used to directly image tumor pO2 distributions with 0.2 mm spatial resolution at the time of radiation delivery. These pO2 images were analyzed with variations of reduced spatial resolution from 0.2 mm to 5 mm, to investigate the influence of how reduced imaging spatial resolution would affect the observed tumor hypoxia. As an in vivo validation test, mice bearing tumor xenografts were imaged for hypoxic fraction and median pO2 to examine the predictive link with tumor response to radiation therapy, while accounting for spatial resolution. Results In transitioning from voxel sizes of 200 μm to 3 mm, the median pO2 values increased by a few mm Hg, and the hypoxic fraction decreased by more than 50%. When looking at radiation-responsive tumors, the median pO2 values changed just a few mm Hg as a result of treatment, and the hypoxic fractions changed by as much as 50%. This latter change, however, could only be seen when sampling was performed with high spatial resolution. Median pO2 or similar quantities obtained from low resolution measurements are commonly used in clinical practice, however these parameters are much less sensitive to changes in the tumor microenvironment than the tumor hypoxic fraction obtained from high-resolution oxygen images. Conclusions This study supports the hypothesis that for adequate measurements of the tumor response to radiation therapy, oxygen imaging with high spatial resolution is required to accurately characterize the hypoxic fraction.

Concurrent chemoradiotherapy is used for advanced cancers, but the chemotherapy is dose limited by normal tissue toxicity. Localized X-ray activation of chemotherapy could overcome this, as studied here, with release from self-assembled nanomicelles (NMs) created from copolymers loaded with doxorubicin (DOX) having a photocleavable o-nitrobenzyl ester (o-Ne) group. The micelles demonstrated release of DOX from X-ray-induced Cherenkov light and conversion from a caged hydrophobic form to hydrophilic DOX, which achieves nuclear localization. Folate on the exterior of the NMs directed them for effective intracellular uptake prior to irradiation. Irradiation with 8 Gy released the DOX, which then entered the cell nucleus, providing near-complete in vivo tumor eradication and negligible off-target organ damage. Micelles were assembled from molecular component materials that are commonly in human use. This study realizes triple targeting in chemoradiation with potential for cell-receptor-mediated uptake, localized radiotherapy activation, and nuclear relocalization, all leading to limited off-target toxicity.

Purpose: In this study, procedures were developed to achieve efficient reversible conversion of a clinical linear accelerator (LINAC) and deliver electron FLASH (eFLASH) or conventional beams to the treatment room isocenter. Material & Methods: The LINAC was converted to deliver eFLASH beam within 20 minutes by retracting the x-ray target from the beam's path, positioning the carousel on an empty port, and selecting 10 MV photon beam energy in the treatment console. Dose per pulse and average dose rate were measured in a solid water phantom at different depths with Gafchromic film and OSLD. A pulse controller counted the pulses via scattered radiation signal and gated the delivery for preset pulse count. A fast photomultiplier tube-based Cherenkov detector measured per pulse beam output at 2 ns sampling rate. After conversion back to clinical mode, conventional beam output, flatness, symmetry, field size and energy were measured for all clinically commissioned energies. Results: Dose per pulse of 0.86 +/- 0.01 Gy (310 +/- 7 Gy/s average dose rate) were achieved at isocenter. The dose from simultaneous irradiation of film and OSLD were within 1%. The PMT showed the LINAC required about 5 pulses before the output stabilized and its long-term stability was within 3% for measurements performed at 3 minutes intervals. The dose, flatness, symmetry, and photon energy were unchanged from baseline and within tolerance (1%, 3%, 2%, and 0.1% respectively) after reverting to conventional beams. Conclusion: 10 MeV FLASH beams were achieved at the isocenter of the treatment room. The beam output was reproducible but requires further investigation of the ramp up time in the first 5 pulses, equivalent to, Manuscript: 21 Pages, 1 Table, 8 Figures; Supplementary Material A: 2 Pages, 2 Figures; Appendix: Film Dosimetry: 2 Pages, 2 Tables

Significance: Extremity injury represents the leading cause of trauma hospitalizations among adults under the age of 65 years, and long-term impairments are often substantial. Restoring function depends, in large part, on bone and soft tissue healing. Thus, decisions around treatment strategy are based on assessment of the healing potential of injured bone and/or soft tissue. However, at the present, this assessment is based on subjective clinical clues and/or cadaveric studies without any objective measure. Optical imaging is an ideal method to solve several of these issues. Aim: The aim is to highlight the current challenges in assessing bone and tissue perfusion/viability and the potentially high impact applications for optical imaging in orthopaedic surgery. Approach: The prospective will review the current challenges faced by the orthopaedic surgeon and briefly discuss optical imaging tools that have been published. With this in mind, it will suggest key research areas that could be evolved to help make surgical assessments more objective and quantitative. Results: Orthopaedic surgical procedures should benefit from incorporation of methods to measure functional blood perfusion or tissue metabolism. The types of measurements though can vary in the depth of tissue sampled, with some being quite superficial and others sensing several millimeters into the tissue. Most of these intrasurgical imaging tools represent an ideal way to improve surgical treatment of orthopaedic injuries due to their inherent point-of-care use and their compatibility with real-time management. Conclusion: While there are several optical measurements to directly measure bone function, the choice of tools can determine also the signal strength and depth of sampling. For orthopaedic surgery, real-time data regarding bone and tissue perfusion should lead to more effective patient-specific management of common orthopaedic conditions, requiring deeper penetrance commonly seen with indocyanine green imaging. This will lower morbidity and result in decreased variability associated with how these conditions are managed.

Receptor heterogeneity in cancer is a major limitation of molecular targeting for cancer therapeutics. Single-receptor-targeted treatment exerts selection pressures that result in treatment escape for low-receptor-expressing tumor subpopulations. To overcome this potential for heterogeneity-driven resistance to molecular targeted photodynamic therapy (PDT), we present for the first time a triple-receptor-targeted photoimmuno-nanoconjugate (TR-PIN) platform. TR-PIN functionalization with cetuximab, holo-transferrin, and trastuzumab conferred specificity for epidermal growth factor receptor (EGFR), transferrin receptor (TfR), and human epidermal growth factor receptor 2 (HER-2), respectively. The TR-PINs exhibited up to a 24-fold improvement in cancer cell binding compared with EGFR-specific cetuximab-targeted PINs (Cet-PINs) in low-EGFR-expressing cell lines. Photodestruction using TR-PINs was significantly higher than the monotargeted Cet-PINs in heterocellular 3D in vitro models of heterogeneous pancreatic ductal adenocarcinoma (PDAC, MIA PaCa-2 cells) and heterogeneous head and neck squamous cell carcinoma (HNSCC, SCC9 cells) containing low-EGFR-expressing T47D (high TfR) or SKOV-3 (high HER-2) cells. Through their capacity for multiple tumor target recognition, TR-PINs can serve as a unique and amenable platform for the effective photodynamic eradication of diverse tumor subpopulations in heterogeneous cancers to mitigate escape for more complete and durable treatment responses.

Fluorescence imaging is severely limited by the background and autofluorescence of tissues for in vivo detection of circulating tumor cells (CTCs). Time-gated luminescence (TGL) imaging, in combination with luminescent probes that possess hundreds of microsecond emission lifetimes, can be used to effectively suppress this background, which has predominantly nanosecond lifetimes. This Letter demonstrates the feasibility of TGL imaging using luminescent probes for the in vivo real time imaging and tracking of single CTCs circulating freely in the blood vessels with higher accuracy given by substantially higher signal-to-noise ratio. The luminescent probe used in this Letter was a commercial E u 3 + chelate (EuC) nanosphere with a super-long lifetime of near 800 µs, which enabled TGL imaging to achieve background-free detection with ∼ 5 times higher SNR versus steady state. Phantom and in vivo mouse studies indicated that EuC labeled tumor cells moving in medium or bloodstream at the speed of 1–2 mm/s could be captured in real time.

Purpose A Geant4-based TOPAS Monte Carlo toolkit was utilized to model a Varian ProBeam proton therapy system, with the aim of providing an independent computational platform for validating advanced dosimetric methods. Materials and methods The model was tested for accuracy of dose and linear energy transfer (LET) prediction relative to the commissioning data, which included integral depth dose (IDD) in water and spot profiles in air measured at varying depths (for energies of 70 to 240 MeV in increments of 10 MeV, and 242 MeV), and absolute dose calibration. Emittance was defined based on depth-dependent spot profiles and Courant-Snyder's particle transport theory, which provided spot size and angular divergence along the inline and crossline plane. Energy spectra were defined as Gaussian distributions that best matched the range and maximum dose of the IDD. The validity of the model was assessed based on measurements of range, dose to peak difference, mean point to point difference, spot sizes at different depths, and spread-out Bragg peak (SOBP) IDD and was compared to the current treatment planning software (TPS). Results Simulated and commissioned spot sizes agreed within 2.5%. The single spot IDD range, maximum dose, and mean point to point difference of each commissioned energy agreed with the simulated profiles generally within 0.07 mm, 0.4%, and 0.6%, respectively. A simulated SOBP plan agreed with the measured dose within 2% for the plateau region. The protons/MU and absolute dose agreed with the current TPS to within 1.6% and exhibited the greatest discrepancy at higher energies. Conclusions The TOPAS model agreed well with the commissioning data and included inline and crossline asymmetry of the beam profiles. The discrepancy between the measured and TOPAS-simulated SOBP plan may be due to beam modeling simplifications of the current TPS and the nuclear halo effect. The model can compute LET, and motivates future studies in understanding equivalent dose prediction in treatment planning, and investigating scintillation quenching.

Purpose: The goal of this work was to create a technique that could measure all possible spatial and temporal delivery rates used in pencil-beam scanning (PBS) proton therapy. The proposed system used a fast scintillation screen for full-field imaging to resolve temporal and spatial patterns as it was delivered. Methods and Materials: A fast intensified CMOS camera imaged used continuous mode 10 ms temporal frame rate and 1x1 mm^2 spatial resolution, imaging a scintillation screen during clinical proton PBS delivery. PBS plans with varying dose, dose rate, energy, field size, and spot-spacing were generated, delivered and imaged. The captured images were post processed to provide dose and dose rate values after background subtraction, perspective transformation, uniformity correction for the camera and the scintillation screen, and calibration into dose. Results: The linearity in scintillation response with respect to varying dose rate, dose, and field size was within 2%. The quenching corrected response with varying energy was also within 2%. Large spatio-temporal variations in dose rate were observed, even for plans delivered with similar dose distributions. Dose and dose rate histograms and maximum dose rate maps were generated for quantitative evaluations. With the fastest PBS delivery on a clinical system, dose rates up to 26.0 Gy/s were resolved. Conclusions: The scintillation imaging technique was able to quantify proton PBS dose rate profiles with spot weight as low as 2 MU, with spot-spacing of 2.5 mm, having an ultimate 1x1 mm^2 spatial resolution. These dose rate temporal profiles, spatial maps, and cumulative dose rate histograms provide useful metrics for the potential evaluation and optimization of dose rate in treatment plans.

BACKGROUND Current practices for fluorescence-guided cancer surgery utilize a single fluorescent agent, but homogeneous distribution throughout the tumor is difficult to achieve. We hypothesize that administering a perfusion and a molecular-targeted agent at their optimal administration-to-imaging time will improve whole-tumor contrast. EXPERIMENTAL DESIGN Mice bearing subcutaneous xenograft human synovial sarcomas were administered indocyanine green (ICG) (3 mg/kg) or ABY-029 (48.7 μg/kg)-an epidermal growth factor receptor-targeted Affibody molecule-alone or in combination. Fluorescence contrast and signal distribution were compared between treatment groups. Two commercial fluorescence imaging systems were tested for simultaneous imaging of ICG and ABY-029. RESULTS ABY-029 has a moderate positive correlation with viable tumor (ρ = 0.2 ± 0.4), while ICG demonstrated a strong negative correlation (ρ = -0.6 ± 0.1). The contrast-to-variance ratio was highest in the ABY-029 +ICG (2.5 ± 0.8), compared to animals that received ABY-029 (2.3 ± 0.8) or ICG (2.0 ± 0.5) alone. Moreover, the combination of ABY-029 + ICG minimizes the correlation between viable tumor and fluorescence intensity (ρ = -0.1 ± 0.2) indicating the fluorescence signal distribution is more homogeneous throughout the tumor milieu. CONCLUSION Dual-agent imaging utilizing a single channel in a commercial fluorescence-guided imaging system tailored for IRDye 800CW is a promising method to increase tumor contrast in a clinical setting.

Many tumors for which fluorescence guided surgery (FGS) has been developed are surface tumors, where direct visualization by the surgeon is straightforward. On the other hand, cancers such as soft-tissue sarcomas, are present at a subsurface level. Resection of these sub-surface tumors is performed using 'wide local excision' where a single, complete mass is removed with an intact zone of normal tissue (~ 1 cm 'margin'). We used a phantom model for sarcoma with near infrared fluorophore IRDye800 CW that defined different tissue properties. We compare the detection sensitivity of two commercially available near infrared (NIR) surgical imaging systems, Solaris (Perkin Elmer) and SPY PHI (Novadaq) using the phantom models of sarcoma. We also determine targeted fluorescence signal on both systems for blinded surgical phantom dissection by a surgeon. The fluorescence intensities are higher for Solaris than for SPY-PHI. On average, the fluorescence increased with an increase in intralipid concentration and decreased with an increase in blood concentration. The depth of imaging was higher for Solaris than for SPY PHI. Using the target values, the surgeon successfully dissected all phantoms using Solaris. Using fat phantoms for SPY PHI, the surgeon cut through four out of the total. Further improvement in FGS will improve cancer recurrence and morbidity.

With an adequate tissue dataset, supervised classification of tissue optical properties can be achieved in SFDI images of breast cancer lumpectomies with deep convolutional networks. Nevertheless, the use of a black-box classifier in current ex vivo setups provides output diagnostic images that are inevitably bound to show misclassified areas due to inter- and intra-patient variability that could potentially be misinterpreted in a real clinical setting. This work proposes the use of a novel architecture, the self-introspective classifier, where part of the model is dedicated to estimating its own expected classification error. The model can be used to generate metrics of self-confidence for a given classification problem, which can then be employed to show how much the network is familiar with the new incoming data. A heterogenous ensemble of four deep convolutional models with self-confidence, each sensitive to a different spatial scale of features, is tested on a cohort of 70 specimens, achieving a global leave-one-out cross-validation accuracy of up to 81%, while being able to explain where in the output classification image the system is most confident. Spanish Ministry of Science, Innovation and Universities (FIS2010-19860, TEC2016-76021-C2-2-R), Spanish Ministry of Economy, Industry and Competitiveness and Instituto de Salud Carlos III (DTS17-00055, DTS15- 00238), Instituto de Investigación Valdecilla (INNVAL16/02, INNVAL18/23), Spanish Ministry of Education, Culture, and Sports (FPU16/05705).

PURPOSE To demonstrate the potential benefits of remote camera-based scintillation imaging for routine quality assurance (QA) measurements for magnetic resonance guided radiotherapy (MRgRT) linear accelerators. METHODS A wall-mounted CMOS camera with a time-synchronized intensifier was used to image photons produced from a scintillation screen in response to dose deposition from a 6 MV FFF x-ray beam produced by a 0.35 T MR-linac. The oblique angle of the field of view was corrected using a projective transform from a checkerboard calibration target. Output sensitivity and constancy was measured using the scintillator and benchmarked against an A28 ion chamber. Field cross-plane and in-plane profiles were measured for field sizes ranging from 1.68 × 1.66 cm2 to 20.02 × 19.92 cm2 with both scintillation imaging and using an IC profiler. Multileaf collimator (MLC) shifts were introduced to test sensitivity of the scintillation imaging system to small spatial deviations. A picket fence test and star-shot were delivered to both the scintillator and EBT3 film to compare accuracy in measuring MLC positions and isocenter size. RESULTS The scintillation imaging system showed comparable sensitivity and linearity to the ion chamber in response to changes in machine output down to 0.5 MU (R2 = 0.99). Cross-plane profiles show strong agreement with defined field sizes using full width half maximum (FWHM) measurement of

Biological tissue characterization using optical imaging techniques often focus on optical property quantification, a process that relies on a diffuse or sub-diffuse light transport model. Assumptions associated with each light transport model reduce the applicability and increase the computational and/or experimental complexity of the techniques. Scattering orientation index and texture metrics quantified for human breast tissues are free of light transport assumptions and were quantified using the demodulated reflectance from wide-field structured light imaging. This work suggests that wide-field tissue diagnostics might be possible without model-based optical property quantification and instead using assumption-free scatter orientation and textural information.

Fluorescence imaging for surgical guidance is a proven modality that allows for visualization of fluorescent markers in numerous biological imaging applications. As the field continues to develop there is an urgent need for fluorescence-imaging standards that enable system characterization and performance monitoring. Here, we present a long-term stable standard that mimics indocynine green (ICG) spectral behavior and is capable of probing the sensitivity of commercially available imaging systems. The standard is composed of three different tests: a varying concentration sensitivity test (0.1nM-3000nM), a tissue-equivalent-depth sensitivity test (0.2mm-7mm), and a 1951 USFA fluorescence resolution test. The fluorescence standard platform developed can incorporate 3-D printing with tissue-equivalent layers, enabling a wide variety of anatomical-specific designs. The manufacturing capabilities developed allow for incorporation of different fluorophores for applications beyond ICG and NIR.

The AAPM sanctioned a task group to study performance metrics for fluorescence guided surgery systems, with the goal of establishing professional guidance documentation which would initiate future efforts in standardization and ultimately a more standardized approach to this field. While tissue phantoms and test targets are widely used in radiology, the field of surgical guidance has not had any clear consensus around the idea of quantifying performance goals. The field is largely driven by manufacturers stating performance goals and training surgical users. There has been little interchangeability between systems, yet the field is now quite crowded with possible systems to use for indocyanine green imaging. The task group studied the problem and has converged towards a set of ideal goals and recommendations.

The most common treatment for early-stage breast cancer involves breast-conserving surgery (BCS), which is a local resection of malignant tissue. BCS success relies on the presence of healthy tissue margins surrounding each resection. However, approximately 20% of BCS patients require follow-up surgery to remove residual tumor. Micro-computed tomography and optical structured light imaging were investigated for intraoperative margin assessment. Specimens were imaged immediately after resection and before surgical inking, and image data were compared to postoperative histopathology. The study demonstrated the feasibility of imaging during BCS and generated a baseline multimodal dataset of whole BCS resections, including positive margin signatures.

Significance: Expanded use of fluorescence-guided surgery with devices approved for use with indocyanine green (ICG) has led to a range of commercial systems available. There is a compelling need to be able to independently characterize system performance and allow for cross-system comparisons. Aim: The goal of this work is to expand on previous proposed fluorescence imaging standard designs to develop a long-term stable phantom that spectrally matches ICG characteristics and utilizes 3D printing technology for incorporating tissue-equivalent materials. Approach: A batch of test targets was created to assess ICG concentration sensitivity in the 0.3- to 1000-nM range, tissue-equivalent depth sensitivity down to 6 mm, and spatial resolution with a USAF test chart. Comparisons were completed with a range of systems that have significantly different imaging capabilities and applications, including the Li-Cor® Odyssey, Li-Cor® Pearl, PerkinElmer® Solaris, and Stryker® Spy Elite. Results: Imaging of the ICG-matching phantoms with all four commercially available systems showed the ability to benchmark system performance and allow for cross-system comparisons. The fluorescence tests were able to assess differences in the detectable concentrations of ICG with sensitivity differences >10× for preclinical and clinical systems. Furthermore, the tests successfully assessed system differences in the depth-signal decay rate, as well as resolution performance and image artifacts. The manufacturing variations, photostability, and mechanical design of the tests showed promise in providing long-term stable standards for fluorescence imaging. Conclusions: The presented ICG-matching phantom provides a major step toward standardizing performance characterization and cross-system comparisons for devices approved for use with ICG. The developed hybrid manufacturing platform can incorporate long-term stable fluorescing agents with 3D printed tissue-equivalent material. Further, long-term testing of the phantom and refinements to the manufacturing process are necessary for future implementation as a widely adopted fluorescence imaging standard.

Purpose Tattoo fiducials are commonly used in radiotherapy patient alignment, and recent studies have examined the use of UV-excited luminescent tattoo ink as a cosmetic substitute to make these visible under UV illumination. The goal of this study was to show how luminescent tattoo inks could be excited with MV radiation and imaged during beam delivery for direct visualization of field position. Methods A survey of nine UV-sensitive tattoo inks with various emission spectra were investigated using both UV and MV excitation. Images of liquid solutions were collected under MV excitation using an intensified-CMOS imager. Solid skin-simulating phantoms were imaged with both surface-painted ink and in situ tattooing during dose delivery by both a clinical linear accelerator and cobalt-60 source. Results The UV inks have peak fluorescence emission ranging from approximately 440 to 600 nm with lifetimes near 11-16 μs. The luminescence intensity is approximately 6x higher during the x-ray pulse than after the pulse, however, the signal-to-noise is only approximately twice as large. Spatial resolution for imaging was achieved at 1.6 mm accuracy in a skin test phantom. Optical filtering allows for continuous imaging using a cobalt source and provides a mechanism to discriminate ink colors using a monochromatic image sensor. Conclusions This study demonstrates how low-cost inks can be used as fiducial markers and imaged both using time-gated and continuous modes during MV dose delivery. Phantom studies demonstrate the potential application of real-time field verification. Further studies are required to understand if this technique could be used as a tool for radiation dosimetry.

Significance: Photodynamic therapy (PDT) involves complex light-drug-pathophysiology interactions that can be affected by multiple parameters and often leads to large variations in treatment outcome from patient to patient. Direct PDT dosimetry technologies have been sought to optimize the control variables (e.g., light dose, drug administration, tissue oxygenation, and patient conditioning) for best patient outcomes. In comparison, singlet oxygen (O21) dosimetry has been tested in various forms to provide an accurate and perhaps comprehensive prediction of the treatment efficacy. Aim: We discuss an advanced version of this approach provided by a noninvasive, continuous wave dosimeter that can measure near-infrared spectrally resolved luminescence of both photosensitizer (PS) and O21 generated during PDT cancer treatment. Approach: This dosimetry technology uses an amplified, high quantum efficiency InGaAs detector with spectroscopic decomposition during the light treatment to continuously extract the maximum signal of O21 phosphorescence while suppressing the strong PS luminescence background by spectrally fitting the data points across nine narrow band wavelengths. O21 and PS luminescence signals were measured in vivo in FaDu xenograft tumors grown in mice during PDT treatment using Verteporfin as the PS and a continuous laser treatment at 690 nm wavelength. Results: A cohort of 19 mice was used and observations indicate that the tumor growth rate inhibition showed a stronger correlation with O21 than with just the PS signal. Conclusions: These results suggest that O21 measurement may be a more direct dosimeter of PDT damage, and it has potential value as a definitive diagnostic for PDT treatment, especially with spectral separation of the background luminescence and online estimation of the PS concentration.

Cherenkov light emission from tissue undergoing radiation therapy is a complex function of the dose deposition and is reduced by the optical attenuation of the tissue. A diffusion theory based integral of the remitted light is presented, using the assumption that only Cherenkov photons from the first 8 mm of tissue are able to appreciably escape from the surface. This depth restriction falls within the linear build-up region for both electron and photon beams used in radiotherapy. The resulting expression for Cherenkov light fluence formulated here indicates that the outgoing intensity is dependent upon the quasi-linear dose build up gradient (k2) in the first 8 mm of tissue, is inversely proportional to the optical absorption (μa), and is relatively independent of the scattering coefficient (μs / ). Numerical evaluation suggests that the diffuse component of Cherenkov light emission dominates over any unscattered photons, suggesting that the radiation build-up factor dominates what is imaged off the surface. This observation could allow for linear corrections to Cherenkov images with knowledge of tissue optical properties and for better interpretation of the origin of Cherenkov from tissue.

Biomedical imaging techniques are often limited by the loss of resolution with depth due to light scattering in biological tissue. Beyond a few millimeters in depth, diffuse transport dominates and makes high resolution imaging impossible using conventional techniques. In this work, light sheet imaging using x-ray photons was developed with a keV x-ray source. This partially overcomes this scattering by generating light within tissue at depth. The light excites fluorescent probes that can be used for tumor tracking based upon molecular targeting. Most of the fluorescent probes have a lifetime in the nanosecond range. In this study, the use of a portable linear accelerator delivering 30-ns x-ray pulses was explored. Using x-ray excitable fluorophores, light was generated within a tissue phantom. Image stacks were acquired using an intensified camera (PiMAX4 – Princeton Instrument – USA) placed perpendicularly to the slicing direction of the sample. A solid-state silicon photomultiplier was used to gate acquisition. Although this delayed acquisition slightly, it improved the fluorescence signal-to-noise ratio (SNR). A deconvolution algorithm counteracted the blurring effects of tissue, and image stacks were converted to 3D reconstructions. In summary, nanosecond x-ray pulses can be used to excite fluorophores through radioluminescence phenomenon. Combined with slice imaging, this approach shows promise for time-resolved x-ray luminescence.

Background Hypoxic lesions often respond poorly to cancer therapies. Particularly, photodynamic therapy (PDT) consumes oxygen in treated tissues, which in turn lowers its efficacy. Tools for online monitoring of intracellular pO2 are desirable. Methods The pO2 changes were tracked during photodynamic therapy (PDT) with δ-aminolevulinic acid (ALA) in mouse skin, xenograft tumors, and human skin. ALA was applied either topically as Ameluz cream or systemically by injection. Mitochondrial pO2 was quantified by time-gated lifetime-based imaging of delayed fluorescence (DF) of protoporphyrin IX (PpIX). Results pO2-weighted images were obtained with capture-times of several seconds, radiant exposures near 10 mJ/cm2, spatial resolution of 0.3 mm, and a broad dynamic range 1−50 mmHg, corresponding to DF lifetimes ≈20−2000 μs. The dose-rate effect on oxygen consumption was investigated in mouse skin. A fluence rate of 1.2 mW/cm2 did not cause any appreciable oxygen depletion, whereas 6 mW/cm2 and 12 mW/cm2 caused severe oxygen depletion after radiant exposures of only 0.4−0.8 J/cm2 and Conclusions Time-gated imaging of PpIX DF seems to be a unique tool for direct online monitoring of pO2 changes during PDT with a promising potential for research purposes as well as for comparatively easy clinical translation to improve efficacy in PDT treatment.

Due to the lack of objectively measurable or quantifiable methods to assess the bone perfusion, the success of removing devitalized bone is based almost entirely on surgeon's experience and varies widely across surgeons and centers. In this study, an indocyanine green (ICG)-based dynamic contrast-enhanced fluorescence imaging (DCE-FI) has been developed to objectively assess bone perfusion and guide surgical debridement. A porcine trauma model (n = 6 pigs × 2 legs) with up to 5 conditions of severity in loss of flow in each, was imaged by a commercial fluorescence imaging system. By applying the bone-specific hybrid plug-compartment (HyPC) kinetic model to four-minute video sequences, the perfusion-related metrics, such as peak intensity, total bone blood flow (TBBF) and endosteal bone blood flow to TBBF fraction (EFF) were calculated. The results shown that the combination of TBBF and EFF can effectively differentiate injured from normal bone with the accuracy, sensitivity and specificity of 89%, 88% and 90%, respectively. Our subsequent first in human bone blood flow imaging study confirmed DCE-FI can be successfully translated into human orthopaedic trauma patients.

ABY-029, an anti-epidermal growth factor receptor (EGFR) Affibody molecule labeled with IRDye 800CW, has been used in three Phase 0 microdosing clinical trials for fluorescence guided surgery. In May of 2019, the clinical trials were put on hold because the ABY-029 produced under Good Manufacturing Practices (GMP) for human administration had come to the end of term in which the drug product was known to be stable. Stability testing was halted due to limitations in supply of a suitable reference standard and a required test product being discontinued from commercial sale. In order to complete the remaining patients in the three clinical trials, new stability tests were developed and the GMP batch of ABY-029 drug product tested under the new protocols. The GMP batch of ABY-029 passed all stability tests under the new protocols and the Federal Drug Administration (FDA) has given permission to complete the remaining patients with stability testing of ABY-029 performed for each patient. The tests developed and used to test ABY-029 drug product stability are described here.

Purpose A remote imaging system tracking Cherenkov emission was analyzed to verify that the linear accelerator (linac) beam shape could be quantitatively measured at the irradiation surface for Quality Audit (QA). Methods The Cherenkov camera recorded 2D dose images delivered on a solid acrylonitrile butadiene styrene (ABS) plastic phantom surface for a range of square beam sizes, and 6 MV photons. Imaging was done at source to surface distance (SSD) of 100 cm and compared to GaF film images and linac light fields of the same beam sizes, ranging over 5 × 5 cm2 up to 20 × 20 cm2 . Line profiles of each field were compared in both X and Y jaw directions. Each measurement was repeated on two different Clinac2100 machines. An interreader comparison of the beam width interpretation was completed using procedures commonly employed for beam to light field coincidence verification. Cherenkov measurements are also done for beams of complex treatment plan and isocenter QA. Results The Cherenkov image widths matched with the measured GaF images and light field images, with accuracy in the range of ±1 mm standard deviation. The differences between the measurements were minor and within tolerance of geometrical requirement of standard linac QA procedures conducted by human setup verification, which had a similar error range. The measurement made by the remote imaging system allowed for beam shape extraction of radiation fields at the SSD location of the beam. Conclusions The proposed Cherenkov image acquisition system provides a valid way to remotely confirm radiation field sizes and provides similar information to that obtained from the linac light field or GaF film estimates of the beam size. The major benefit of this approach is that with a fixed installation of the camera, testing could be done completely under software control with automated image analysis, potentially simplifying conventional QA procedures with appropriate calibration of boundary definitions, and the natural extension to capturing dynamic treatment beamlets at SSD could have future value, such as verification of beam plans with complex beam shapes, like IMRT or "star-shot" QA for the isocenter.

PURPOSE: CCD cameras are employed to image scintillation and Cherenkov radiation in external beam radiotherapy. This is achieved by gating the camera to the linear accelerator (Linac) output. While a direct output signal line from the target current can be used, this approach can induce delay in the trigger signal, and potentially alter Linac performance through electrical feedback. A scintillating detector for stray radiation inside the Linac room was developed to act as an untethered trigger for camera-based dosimetry, thereby overcoming the issues of time delay and altered Linac performance. METHODS: A scintillator coupled silicon photomultiplier detector was optimized and systematically tested for location sensitivity and for use with both X-rays and electron beams, at different energies and field sizes. Two different scintillator sizes were used for the study. Images captured using the physical trigger were compared to the stray radiation trigger. The issue of false positive event detection, due to additional neutron activated products with high energy beams, was addressed. RESULTS: For X-ray beams, the detector module triggered 130–80 ns before the Linac target current signal output line. The designed circuit provided ample output voltage for the camera to trigger for distances up to 3m from the isocenter with a 6MV, 5×5cm beam, using a Ø3×20 mm(3) crystal. With a larger scintillator size, the detector could be placed even beyond 3m distance. False positive triggering was reduced by a coincidence detection scheme. Negligible fluctuations were seen in time-gated imaging of Cherenkov intensity on a body phantom, when comparing directly connected vs this remote triggering approach. CONCLUSION: This scintillator-diode trigger can be used for remote Cherenkov imaging or remote scintillator dosimetry imaging during radiotherapeutic procedures. Moreover, the module overcomes the delay caused by wire-based triggering and solves the issue of false triggering from stray radiation.

Since many types of cancers overexpress EGFR, this surface receptor has been used as a target for therapy or diagnosis of malignant disease. Uptake kinetics of EGFR-targeted fluorescent Affibody (ABY-029) were studied with a view toward optimizing efficacy of tumor detection in a glioma as a function of both delivered dose and concurrent administration of unlabeled cetuximab (an EGFR antagonist). U251 glioma cells were inoculated in brain of nude rats, and the fluorescence from each brain was analyzed after the administration of ABY-029. Although cetuximab was able to systematically block ABY-029 binding to EGFR in a dose-dependent manner in cell culture, no influence on the tumor-to-normal brain contrast was seen when unlabeled cetuximab was administered prior to ABY-029. Ex vivo imaging of ABY-029 fluorescence showed increasing values of the tumor-to-normal brain ratio with an increasing injected dose. A saturation value was obtained at a dose of 245 μg kg-1 which represents a 10-fold increase over a "microdose" value. According to FDA, the microdose of protein products is considered ≤30 nanomoles due to its difference in molecular weight as compared to synthetic drugs. This observation indicates that glioma detection will be optimal if the ABY-029 dose exceeds the "microdose" value.

Background Roughly 23% of breast conserving surgery (BCS) patients undergo a second re-excision procedure due to pathologically positive surgical margins. We investigated the feasibility and potential value of micro-Computed Tomography (micro-CT) as a surgical margin guidance tool during BCS. Methods A cohort of 32 BCS specimens was prospectively imaged with a pre-clinical micro-CT system upon arrival in the surgical pathology laboratory. Reconstructed micro-CT scans were evaluated retrospectively by an experienced breast radiologist, who provided binary determinations whether lesions extended to the specimen margin. These readings were then compared to the final pathological diagnosis and to 2D specimen radiography readings. Results Of the 32 specimens imaged, 28 had malignant and four had benign pathological diagnoses. Overall five (four malignant, one benign) of the 32 specimens had lesion tissue extending to the margin. For all 32 specimens, micro-CT reconstructions were calculated (

Daylight-mediated photodynamic therapy (d-PDT) as a treatment for actinic keratosis (AK) is an increasingly common technique due to a significant reduction in pain, leading to better patient tolerability. While past studies have looked at different light sources and delivery methods, this study strives to provide equivalent PpIX-weighted light doses with the hypothesis that artificial light sources could be equally as effective as natural sunlight if their PpIX-weighted fluences were equalized. Normal mouse skin was used as the model to compare blue LED light, metal halide white light, and natural sunlight, with minimal incubation time between topical ALA application and the onset of light delivery. A total PpIX-weighted fluence of 20 J(eff)/cm(2) was delivered over 2 hours, and the efficacy of response was quantified using three acute bioassays for PDT damage: PpIX photobleaching, Stat3 crosslinking, and quantitative histopathology. These bioassays indicated blue light was slightly inferior to both sunlight and white light, but that the latter two were not significantly different. The results suggest that metal halide white light could be a reasonable alternative to daylight PDT, which should allow a more controlled treatment that is independent of weather and yet should have similar response rates with limited pain during treatment.

PURPOSE The purpose of this study was to identify the optimal treatment geometry for total skin electron therapy (TSET) using a new optimization metric from Cherenkov image analysis, and to investigate the sensitivity of the Cherenkov imaging method to floor scatter effects in this unique treatment setup. METHODS Cherenkov imaging using an intensified charge coupled device (ICCD) was employed to measure the relative surface dose distribution as a 2D image in the total skin electron treatment plane. A 1.2 m × 2.2 m × 1 cm white polyethylene sheet was placed vertically at a source to surface distance (SSD) of 300 cm, and irradiated with 6 MeV high dose rate TSET beams. The linear accelerator coordinate system used stipulates 0° is the bottom of the gantry arc, and progresses counterclockwise so that gantry angle 270° produces a horizontal beam orthogonal to the treatment plane. First, all unique pairs of treatment beams were analyzed to determine the performance of the currently recommended symmetric treatment angles (±20° from the horizontal), compared to treatment geometries unconstrained to upholding gantry angle symmetry. This was performed on two medical linear accelerators (linacs). Second, the extent of the floor scatter contributions to measured surface dose at the extended SSD required for TSET were imaged using three gantry angles of incidence: 270° (horizontal), 253° (-17°), and 240° (-30°). Images of the surface dose profile at each angle were compared to the standard concrete floor when steel plates, polyvinyl chloride (PVC), and solid water were placed on the ground at the base of the treatment plane. Postprocessing of these images allowed for comparison of floor material-based scatter profiles with previously published simulation results. RESULTS Analysis of the symmetric treatment geometry (270 ± 20°) and the identified optimal treatment geometry (270 + 23° and 270 - 17°) showed a 16% increase in the 90% isodose area for the latter field pair on the first linac. The optimal asymmetric pair for the second linac (270 + 25° and 270 - 17°) provided a 52% increase in the 90% isodose area when compared to the symmetric geometry. Difference images between Cherenkov images captured with test materials (steel, PVC, and solid water) and the control (concrete floor) demonstrated relative changes in the two-dimensional (2D) dose profile over a 1 × 1.9 m region of interest (ROI) that were consistent with published simulation data. Qualitative observation of the residual images demonstrates localized increases and decreases with respect to the change in floor material and gantry angle. The most significant changes occurred when the beam was most directly impinging the floor (gantry angle 240°, horizontal -30°), where the PVC floor material decreased scatter dose by 1-3% in 7.2% of the total ROI area, and the steel plate increased scatter dose by 1-3% in 7.0% of the total ROI area. CONCLUSIONS An updated Cherenkov imaging method identified asymmetric, machine-dependent TSET field angle pairs that provided much larger 90% isodose areas than the commonly adopted symmetric geometry suggested by Task Group 30 Report 23. A novel demonstration of scatter dose Cherenkov imaging in the TSET field was established.

Low signal-to-noise ratios and limited imaging depths restrict the ability of optical-imaging modalities to detect and accurately quantify molecular emissions from tissue. Here, by using a scanning external X-ray beam from a clinical linear accelerator to induce Cherenkov excitation of luminescence in tissue, we demonstrate in vivo mapping of the oxygenation of tumours at depths of several millimetres, with submillimetre resolution and nanomolar sensitivity. This was achieved by scanning thin sheets of the X-ray beam orthogonally to the emission-detection plane, and by detecting the signal via a time-gated CCD camera synchronized to the radiation pulse. We also show with experiments using phantoms and with simulations that the performance of Cherenkov-excited luminescence scanned imaging (CELSI) is limited by beam size, scan geometry, probe concentration, radiation dose and tissue depth. CELSI might provide the highest sensitivity and resolution in the optical imaging of molecular tracers in vivo.

In this work, Cherenkov-excited molecular sensing was used to assess the potential for simultaneous quantitative sensing of two NIR fluorophores within tissue-simulating phantoms through spectral separation of signals. Cherenkov emissions induced by external beam gamma photon radiation treatment to tissues/tissue-simulating phantoms were detectable over the 500-900-nm wavelength range. The presence of blood was demonstrated to reduce the integrated intensity of detected Cherenkov emissions by nearly 50%, predominantly at wavelengths below 620 nm. The molecular dyes, IRDye 680RD and IRDye 800CW, have excitation and emission spectra at longer wavelengths than the strongest blood absorption peaks, and also where the intensity of Cherenkov light is at its lowest, so that the emission signal relative to background signal is maximized. Tissue phantoms composed of 1% intralipid and 1% blood were used to simulate human breast tissue, and vials containing fluorophore were embedded in the media, and irradiated with gamma photons for Cherenkov excitation. We observed that fluorescence emissions excited by the Cherenkov signal produced within the phantom could be detected at 5-mm depth into the media within a 0.1-25 μ M fluorophore concentration range. The detected fluorescence signals from these dyes showed linear relationships with radiation doses down to the cGy level. In vivo tests were successful only within the range near a μ M, suggesting that these could be used for metabolic probes in vivo where the local concentrations are near this range.