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We present the applications of time-resolved spectrometer for soft X-ray (SXR) excited luminescence measurements. We use the spectrometer to monitor the delayed recombination phenomena in the scintillation response of ZnO:Ga nanoparticles, SrHfO3 microcrystalline powder, and rare-earth doped LiCaAlF6 single crystals in an extended time and dynamic range. The nanosecond soft X-ray (E\approx 0.4\ keV) pulse plasma source is used for excitation of a scintillation process. High sensitivity of our experiment is enabled by an intense nanosecond SXR pulse with a very short absorption length (<1\ \mum) in scintillation materials and sensitive fast photomultiplier-based detection. Thus, we are able to measure decay profiles with signal-to-noise ratio as high as 10^5 and with nanosecond resolution over millisecond time range. Moreover, the presented technique allows studying powder materials, due to the aforementioned extremely short absorption length of SXR. [ABSTRACT FROM PUBLISHER]

Purpose/objective(s): In the last decade, Cherenkov imaging has been demonstrated as a useful clinical technique both for real-time surface dose visualization during patient treatment and for various high-resolution QA measurements. However there remains much work to be done in the development of Cherenkov-based in vivo dosimetry. In this work, the concept of in vivo color Cherenkov imaging is introduced. It is hypothesized that Cherenkov images with sensitivity to the spectral quality of Cherenkov emission induced inside tissue can provide increased information about tissue composition as opposed to monochromatic, red-weighted images used in prior work.Materials/methods: A custom Color Cherenkov camera was created from three time-gated intensified CMOS cameras, each with varying spectral sensitivity of the photocathode, and sharing one imaging lens. A dichroic mirror assembly allowed for incoming Cherenkov light signals to be redirected according to wavelength to the appropriate camera resulting in three raw image stacks for each acquisition. These images were then reconstructed into three-channel color images via color calibration, summed, and background subtracted. In vivo color Cherenkov images of three right-sided breast patients were acquired for one treatment fraction each as part of an IRB-approved clinical trial. These images were interpreted alongside images of liquid tissue-simulating phantoms that matched tissue optical properties. Variations in oxygenation and blood volume were mimicked in this way, and the data was used to interpret the clinical images. Impacts on Cherenkov emission spectra from tissue under these various conditions were also estimated.Results: The presence of oxygenated vs deoxygenated blood in tissue has a visible impact on the color of Cherenkov emission, leading to a redder hue due to decreased attenuation of red wavelengths by oxyhemoglobin, similar to erythema or blush of tissue. This was verified in the tissue phantoms. Variations in blood concentration produce a strong blue-red trend in color space (R2 = 0.96), as verified by detailed analysis. Color Cherenkov images of right breast radiotherapy treatments displayed pink regions across the breast coincident with the treated area for all three patients, and the variations in color were interpreted relative to the phantom data.Conclusion: This first investigation of color Cherenkov imaging uncovered the natural relationship between tissue composition and the spectral quality of emitted Cherenkov light. The correlation between blood content and color will be translated in future work to in vivo sensing of variations in fat and fibroglandular content in irradiated tissues. These findings will allow for the correction of Cherenkov images to produce accurate in vivo surface dose maps during patient treatments. [ABSTRACT FROM AUTHOR]

Provides a logic-based framework for information discovery. Increase in the quantity of information available for searching due to the Internet; Systems aimed to identify potentially relevant information in the large amount of available information; Emphasis on the users' needs and beliefs; Logic-based approach to express the mechanics of information discovery.

Variations in patient positioning can profoundly influence treatment outcomes, so accurate positioning is crucial for precise radiotherapy dose delivery. This study introduces a novel application of Cherenkov imaging and hypothesizes that it allows for the precise quantification of local-regional tissue deformations to improve the accuracy of patient positioning in breast cancer radiotherapy. For the first time, local-regional deformation is quantified based on Cherenkov imaged vasculature, opening a new avenue to improve the precision of patient positioning. Optical attenuation by blood provides sufficient contrast between vasculature and surrounding tissues. After segmenting blood vessels within Cherenkov images as patient-specific biological fiducial markers, a rigid and non-rigid combined registration was deployed to quantify both inter- and intra-fraction positioning accuracy. The submillimeter accuracy was validated by imaging an anthropomorphic chest phantom with similar human vasculature during a simulated breast radiotherapy treatment, whereas the inter- and intra-fraction variations were simulated by couch shifts and respiratory motion. For 10 patients, 2D maps of local-regional tissue deformations based on non-rigid registration followed by a global shift based on a rigid registration has been quantified in the treatment region for the first time. The accuracy was validated to be within 0.83 ± 0.49 mm for the simulated inter- and intra-fraction variations. A paired t-test revealed no significant difference between the simulated and quantified variations. (P value = 0.2883 > 0.05). A retrospective Cherenkov imaging dataset including 10 breast cancer patients was analyzed for patient positioning variations within their treatment course, revealing an inter-fraction setup uncertainty of 3.71 ± 2.36 mm. Quantitative 2D deformation maps per fraction indicated local-regional deformation in addition to conventional global shifts. Much fewer deformations of 0.0487 ± 0.0385 mm quantified by the non-rigid registration performed after the rigid registration was observed compared to the rigid shift of 3.66 ± 2.35 mm in a paired t-test (P value < 0.0001), which indicates rigid registration captured the majority of global variations, with non-rigid registration addressing the residual local deformations. This study reports the first directly observed local-regional deformation and a method to precisely quantify the global and local variations in patient positioning based on rigid and non-rigid registrations using Cherenkov imaged vasculature. This novel approach demonstrates the feasibility of providing real-time quantitative imaging guidance to inform inter- and intra-fraction positioning, enhancing the precision of breast cancer radiotherapy. [ABSTRACT FROM AUTHOR]

Cherenkov imaging utilizes light emitted during radiation therapy, allowing for visualization of radiation treatments on patients. Cherenkov emissions indicate the treated region and therefore can be used for positional verification; however, there is no method to confirm that the Cherenkov image matches the prediction from the treatment planning system (TPS). In this study, the potential of incorporating a predicted surface dose overlay (PSDO) with Cherenkov image review is examined. PSDOs were generated using the TPS RTPlan and RTDose files for each beam and CT scan. A surface rendering of the patient was created using a non-zero Hounsfield unit threshold. At each point on the surface rendering, the planned dose at the surface is generated by sampling normal to and at a 5mm depth (where most of Cherenkov light is generated) into the dose volume. The PSDO is generated using a 14% isodose of the 5mm planned maximum surface dose and displayed on top of the Cherenkov images. Evaluation of the PSDO was performed on treatments delivered to phantoms at the planned position and after couch shifts to simulate inaccurate patient setups. All patient imaging review was performed on an IRB approved protocol. The patient imaging was scored as congruent if the PSDO shape, size and position visually matched the Cherenkov emissions and non-congruent if not matching. If part of the treatment area was blocked (clothes, sheets or gantry), only the visualized treatment was evaluated. In phantom studies using tangential breast plans, the predicted surface dose overlay was visually congruent at the planned position and non-congruent when the phantom was shifted from the initial position. The predicted plan overlay was less sensitive for treatment plans delivered on the abdomen of the phantom, an area that lacks distinctive anatomical features. In these areas lacking anatomy, accuracy of the technique was restored if biologic fiducials, i.e. blood vessels, were used in conjunction with the PSDO. For patient imaging, 604 treatment fractions for 40 consecutive patients receiving standard of care treatment and pre-treatment imaging were evaluated. Non-congruence of the PSDO with the Cherenkov emission image was detected in 2 treatment courses, totaling 33 of the 604 (5.4%) reviewed treatment fractions. One case was due to anatomy change that occurred during the treatment course. The second case was due to inaccuracy in patient setup and resulted in excess contralateral chest wall dose. This second case was not previously recognized by the treatment team and was not detected by pre-treatment weekly port films or daily SGRT. PSDO incorporated into Cherenkov imaging systems is a useful tool for evaluating accuracy of treatment delivery and has potential for improving treatment quality. Further work is warranted to optimize and determine the added benefit of this technique in large patient studies. [ABSTRACT FROM AUTHOR]

This study is the first direct comparison of two converted clinical linear accelerators producing ultra-high dose rate electron beams in the same way. It sought to quantify the differences in the spatial and temporal properties of the beams in relation to potential clinical impacts. FLASH beams were produced on Varian Trilogy and 21EX linear accelerators by selecting the 10MV photon mode, retracting the target and setting the carousel to an empty port to give access to the pristine electron beam. Lateral profiles of an open beam with no accessories were measured by radiographic film (depth = 2cm, SSD = 100cm) in Solid Water. Percent depth dose (PDD) was measured along the central axis with radiographic film placed at varying depths in Solid Water. The temporal pulse structure and per-pulse output was recorded with a photomultiplier tube that amplified the signal from an optical fiber placed outside the beam with film providing cumulative absolute dosimetry. Pulse-to-pulse dosimetry was further confirmed with a diode detector centered in the beam under 1cm buildup. The practical range was calculated using PDD data. Beam width was reported as the FWHM of a Gaussian fit to the profile. Dose per-pulse (DPP) was calculated using film and the number of pulses detected with the PMT. Mean dose rate was calculated using the DPP and the accelerator rep rate. As reported in the included table, spatial beam characteristics were similar between the machines with the Trilogy showing a slightly wider profile in inline and crossline directions. The DPP on the Trilogy was 19.6% higher than the 21EX at 0.90 Gy/pulse with a mean dose rate of 322 Gy/s, compared to the 270 Gy/s on the 21EX. The Trilogy accelerator exhibited more stability during the initial pulses as indicated by the higher 25% quartile dose per-pulse. The difference between the 25% and 75% quartiles was 0.25 and 0.02 Gy/pulse on the 21EX and Trilogy, respectively. The 21EX exhibited additional low-dose outliers in the initial pulses and showed significant ramp-up and variability during the first 20 pulses of a 36-pulse delivery. The Trilogy was nearly stable after the first pulse. For clinically relevant doses, the entire FLASH treatment may consist of only a few initial pulses. Stability across these initial pulses with high dose rates from the start are key to ensure the quality, repeatability, and safety of UHDR deliveries. Although significant variabilities have been observed between the two FLASH Linacs, the Trilogy demonstrated potential superiority in stability, which particularly matters for the clinical translation of FLASH-RT. [ABSTRACT FROM AUTHOR]

LiCaAlF6-based scintillators are studied under X- and soft gamma-ray excitations. Under nanosecond pulsed soft X-ray laser excitation the scintillation decay is measured with extremely high dynamical resolution and broad time scale. The undoped LiCaAlF6 shows complex temperature dependence of exciton luminescence and tunneling-driven energy transfer process in scintillation decay. In both the Ce and Eu-doped LiCaAlF6 the dominant part of measured scintillation decay is due to prompt recombination of electrons and holes at the doped emission centers. Nevertheless, the measured light yield value is considerably lower with respect to the derived upper limits. Possible origin of its deterioration is discussed. [ABSTRACT FROM AUTHOR]

In-vivo beam monitoring will be necessary for safe clinical translation of ultra-high dose rate (UHDR) proton therapy. Although there is no perfect detector for this extreme radiation environment, scintillation imaging dosimetry (SID) has shown promise for accurate dose and dose rate measurements at UHDR timescales. In this study we characterize the noise resolution of an SID system during delivery of modulated UHDR PBS proton, showcasing its utility as an online error-prevention tool. Delivery of complex, 250 MeV UHDR PBS treatment plans with PBS dose rates above 65Gy/s at treatment isocenter were designed with an in-house planning script. A set of pre-defined delivery errors were added to both simple, square-field plans, and complex plans designed for SBRT in the lungs. Spot intensity errors from 1-5% per spot and spot displacements from 1-3 mm were randomly inserted into plans. Surface dose images were collected at 4.5 kHz/0.23 mm resolution during delivery of the planned beams via an intensified CMOS camera facing a block of solid with a top scintillation layer. The average spot-to-spot intensity variations for uniform fields was 2.5+/-0.4% and spot positioning accuracy was 0.49 ± 0.15mm. In uniform fields with planned delivery errors, the SID was able to detect spot MU intensity changes of 5%, measuring 2% differences in dose, which agreed with the planned dose distribution, and spot position changes as low as 1 mm were seen on imaging. For the modulated fields, spot intensity errors as low as 2% were detected, and planned spot position errors of 0.5mm were detected. Of note, imaged dose and dose rate maps showed strong agreement between simulation and imaging, with average gamma passings rate of 98% and 99%, respectively, at 3%/2 mm. In this study, an SID was shown to be able to detect single-spot intensity errors as low as 5%, offering higher sensitivity than gamma analysis. Additionally, the proposed technique allows for monitoring dose-time profiles, potentially alerting the user if an in-delivery error has occurred in real time. [ABSTRACT FROM AUTHOR]

Cherenkov imaging has recently emerged as a tool to visualize radiation dose and detect treatment incidents in real-time. The principle relies on the proportionality between Cherenkov light emission and dose deposited within tissue, introducing an additional opportunity to use the image information as a 2D surface dose map. The Cherenkov-dose relationship is affected by tissue optical properties, and recent studies have utilized routine CT-scans to correct for optical attenuation due to fibroglandular and adipose tissues, and blood volume, in the breast. However, the bulk of the reported in vivo data is limited to light-skinned patients due to limitations of geographical demographics. It is well documented that melanin is an optical absorber of Cherenkov photons, yet no prior in vivo work has been done to characterize the effect of different skin tones on Cherenkov dosimetry. We hypothesize that skin color information can be used to correct Cherenkov images for optical attenuation relating to melanin absorption across a diverse patient population. A multi-institutional partnership was developed aiming to collect data from a more diverse patient population. A time-gated, intensified CMOS camera installed in the ceiling of a treatment room collects Cherenkov images of breast RT patients during their treatment. A standard color camera module is mounted adjacent to the Cherenkov camera to collect a color background image. Following a process developed with phantom studies, the two images are co-registered together in post-processing, RGB values are extracted from the skin over the treatment regions to calculate the relative skin luminance, L, and this value is compared to the optical emission from the corresponding Cherenkov image. A linear regression model is then used to assess the proportionality between L and Cherenkov emission intensity. The Cherenkov imaging system is being deployed in a clinic with a catchment area demographic of 67.4% Non-Hispanic White, an increase in diversity from 89.4% at the home institution. A clear relationship exists between skin color information and Cherenkov intensity, which cannot be determined like the bulk tissue properties from the CT scan alone. We found that L, derived from a wide range of melanin concentrations, is linearly proportional to Cherenkov intensity (R2 = 0.98). Each Cherenkov image can be corrected based on skin luminance to improve the Cherenkov-dose relationship across various skin types. The effect of both inter- and intra-patient skin color variations on the Cherenkov intensity can be corrected by using a linear regression model to increase the linearity between Cherenkov and deposited dose. This work will be used to improve our current CT-correction algorithm for all skin types and presents a major step towards expanding the inclusivity of Cherenkov imaging as a dosimetric tool for every patient. [ABSTRACT FROM AUTHOR]

Many modern biomedical technologies rely on detecting in vivo optical signals as a noninvasive means for diagnosis or treatment of disease. The interaction of light in superficial tissue is highly dependent on an individual's skin pigmentation (i.e. epidermal melanin) and must be considered for accurate, quantitative measurements. Cherenkov imaging, an emerging technology that detects light from patients undergoing radiation treatment, could face similar limitations. We present the first reported in vivo Cherenkov imaging study of a diverse patient population towards mitigating the impact of skin pigmentation on quantitative Cherenkov light-based dosimetry. A multi-institutional collaboration was formed to increase the opportunity for imaging a diverse population. Cherenkov imaging was completed with a time-gated, iCMOS camera, and color background images were taken simultaneously with an RGB camera module under standardized lighting. Under an IRB-approved retrospective protocol, skin pigmentation was assessed per patient by calculating the relative luminance (L = 0.2126*R + 0.7152*G + 0.0722*B) of their treated area from the color images. Additionally, 2D dose maps were generated by projecting the exponentially-weighted dose from the surface to 5mm into the body, representative of Cherenkov emission, and used for reference surface dose estimations. To date, N 6MV =23 and N 15MV =20 imaged patients, encompassing a wide variety of skin pigmentations, fit our assessment criteria: right-sided breast radiotherapy patients without reconstructive implants or temporary expanders. The initial generated intensity of Cherenkov light is proportional to the radiation dose delivered, providing a unique opportunity for non-contact, real-time surface dosimetry. However, the detected light emission is highly dependent on patients' skin pigmentation. Our results revealed that, for the same dose, the Cherenkov emission intensity was nearly four times less for dark skin patients compared to their Caucasian counterparts. Additionally, a linear relationship exists between Cherenkov intensity per unit dose and individuals' relative skin luminance, enabling a linear calibration factor based on skin pigmentation. Application of this calibration factor significantly improved Cherenkov-to-dose linearity amongst the cohort, from R2=0.79 to 0.96 for 6MV and R2=0.19 to 0.91 for 15MV (p<0.05), marking the highest reported linearity for in vivo patient data. This study is the first of its kind dedicated to assessing Cherenkov imaging amongst a diverse patient population, and developed a linear calibration technique based upon measuring the skin luminance for each patient. It demonstrates significant mitigation of the effect of skin pigmentation through the addition of color imaging, representing a critical step towards achieving quantitative Cherenkov dosimetry. [ABSTRACT FROM AUTHOR]

FLASH radiotherapy based on ultra-high dose rate (UHDR) is actively being studied by the radiotherapy community. Dedicated UHDR electron devices are currently a mainstay for FLASH studies. This work is to present the dosimetry and treatment planning tools for the UHDR capable compact electron Linac for preclinical research and FLASH-radiotherapy (RT) clinical trials. Film based dosimetry methodology has been established for the commissioning of UHDR electron Linac. Monte Carlo (MC) beam model for treatment planning was configured and validated with a simulation toolkit. The geometry and electron source characteristics, such as energy spectrum and beamline parameters, were tuned to match the central-axis depth dose (PDD) and lateral profiles for the pristine beam measured during machine commissioning. Diode-detector (UHDR capable) based beam monitoring method was implemented. To facility fast and accurate PDD measurements, MC model of the diode detector was configured, and its electron energy response was investigated. Correction method for the diode reading to facilize UHDR PDD measurements was established for routine use during preclinical research. Preclinical research acceptable treatment planning method was established. Good agreement between the MC beam model and commissioning data were demonstrated with maximal discrepancy < 3% for PDDs and profiles. 100% gamma pass rate was achieved for all PDDs and profiles with the criteria of 2mm/3%. With the criteria of 2mm/2%, maximum, minimum and mean gamma pass rates were (100.0%, 93.8%, 98.7%) for PDDs and (100.0%, 96.7%, 99.4%) for profiles, respectively. Both film and diode detector showed good agreements in PDD measurements for UHDR electron beam. A validated MC beam model for the treatment planning of UHDR capable compact Linac is presented for the first time. The beam model presented in this work should facilitate translational and clinical FLASH-RT for trials conducted on the compact UHDR electron platform. [ABSTRACT FROM AUTHOR]

Use of clinical linear accelerators in ultra-high dose rate (UHDR) mode can provide a conduit for wider access to UHDR FLASH effects, sparing normal tissue, but care needs to be taken in the use of such systems to ensure errors are avoided. A Failure Modes and Effects Analysis (FMEA) was conducted with a team involved in converting a LINAC between clinical use and UHDR experimental mode for more than one year, following the proposed methods of AAPM (The American Association of Physicists in Medicine) Task Group 100 report. A team of 9 professionals with extensive experience outlined the process map and workflow for analysis, and developed fault trees for potential errors, as well as failure modes that would results. The team scored the categories of severity magnitude (S), occurrence likelihood (O), and detectability potential (D) on a scale of 1 to 10, so that a risk priority number (RPN=S*O*D) could be assessed for each potential failure. A total of 46 potential failure modes were identified, including 5 with RPN>100, all during converting and experimental use in UHDR mode and none during conversion to clinical mode. These failure modes involved 1) patient set up, 2) gating mechanisms in delivery, and 3) detector in the beam stop mechanism. Identified methods to mitigate errors included 1) use of a checklist post conversion, 2) use of robust radiation detectors, 3) automation of QA and beam consistency checks, and 4) implementation of surface guidance during beam delivery. The FMEA process was considered critically important in this setting of a new use of a LINAC, and the expert team developed a higher level of confidence in the ability to safely move UHDR LINAC use towards expanded research access. [ABSTRACT FROM AUTHOR]

A fast-imaging technique was developed for the first in vivo Cherenkov emission imaging from an ultra-high dose rate (UHDR) electron beam source at single pulse (360 Hz) and submillimeter resolution for beam characterization and real time monitoring during delivery. A CMOS camera, gated to the UHDR LINAC, imaged the Cherenkov emission profiles pulse by pulse during the irradiation of murine limbs and intestinal region and a tissue equivalent phantom. An intensifier's effect on image quality was investigated considering signal to noise and spatial resolution. Pulse by pulse and cumulative Cherenkov emission profiles were quantified spatially and temporally. An intensifier improved the emission profile's signal to noise ratio from 15 to 280, with reduced spatial resolution (2.8 to 1.0 line pairs/mm). The profile extended beyond the treatment field edge due to the lateral scattering of the electrons and optical photons in tissue. The CMOS camera with an intensifier detected changes of ∼3mm in Cherenkov emission profiles due to expiration and inspiration during the murine respiratory cycle. The intensified camera's spatial resolution facilitated accurate detection of beam parameters as confirmed with radiochromic film (i.e., output, shift, full width half max, symmetry and flatness). The camera resolved the LINAC's ramp up in output during the first 4-6 pulses until stability was reached, agreeing with a photomultiplier tube detected Cherenkov emission during delivery. This fast-imaging technique can be utilized for in vivo intrafraction monitoring of FLASH patient treatments at single pulse resolution. It can display delivery differences during respiration, and variability in the delivered treatment's surface profile, which may be perturbed from the intended UHDR treatment especially with pencil beam scanning systems. The technique may leverage the Cherenkov emission surface profile to gate the treatment under FLASH conditions while considering beam parameters such as per pulse output or beam steering consistency during delivery. [ABSTRACT FROM AUTHOR]

Combining methods of conformal dose delivery with ultra-high dose rate (UHDR) beams is advantageous for realizing the benefits of the FLASH effect in clinical treatments. We hypothesize that deployment of intensity modulation in passive electron FLASH radiotherapy through treatment plan optimization is feasible. A beam model of an electron FLASH irradiator (delivering ∼300Gy/s at the isocenter) in the decimal ElectronRT treatment planning system (TPS) was validated with film measured lateral and percent-depth-dose (PDD) profiles. Plans were developed comparing collimated open fields and intensity modulated electron beams achieved with cylindrical passive metal compensators that vary in spacing and size. Homogeneity and conformity were quantified for plans developed in a water phantom and anonymized patient cases considering constraints in prescribed dose to the target volume and minimizing dose to organs-at-risk (OAR). The film measured profiles and TPS beam model agreed on average to within 1% and 2% for lateral profile and PDD, respectively. For a large 15 × 15 cm2 field in a water phantom the intensity modulation improved the beam flatness (∼30% to <5%) and penumbra (35 mm to 15mm) at 3 cm depth while retaining UHDR in the treatment field with a 38% reduction in central axis output while still retaining the UHDR conditions (∼180Gy/sec). The PDD exhibited <2% difference along the central axis and minimal changes to symmetry, shift, and practical range. In the rib metastasis case, the unmodulated and modulated plans treat the tumor volume with a homogeneity index (HI), improvement by 0.2. In the facial orbital plan, the conformity index improved by 8% with an improvement in HI by 0.05 and comparable dose to OARs. Intensity modulation of electrons FLASH is achievable and improves homogeneity of prescribed dose with proper treatment constraints while reducing hot spots for clinical plans. Depending on the treatment case intensity modulation can also generate superior dose distributions while retaining the UHDR conditions to best exploit the FLASH effect. Future study will focus on demonstrating dosimetric benefits quantified by tumor control probability and normal tissue complication probability models in a larger number of relevant cases. [ABSTRACT FROM AUTHOR]

Purpose/objective(s): Cherenkov imaging can uniquely record beam shapes directly on the patient, offering a brand new means of assessing patient position and treatment accuracy. We used Cherenkov imaging to assess accuracy of two patient positioning techniques, optical surfacing imaging versus traditional skin marks and room laser alignment (skin marks/lasers), during right breast irradiation.Materials/methods: All imaging data was obtained with IRB approval from patients receiving free-breathing, right breast radiation therapy with either 6X or 6X and 10X beams. Data was obtained from two separate clinics that utilize different positioning methods. Patients treated at one clinic were positioned using optical surface imaging and patients treated at a second clinic were positioned using skin marks/lasers. For each fraction imaged, DICE coefficient (% similarity) and MDC (mean distance to conformity) were measured by comparing Cherenkov imaging obtained for that fraction to the Cherenkov imaging from the initial fraction. A two-tailed t-test of unequal variance was performed to obtain P-values comparing MDC and DICE from the two positioning techniques.Results: Cherenkov images taken of 127 fractions using optical surface imaging for breast setup and 47 fractions using skin marks/lasers setup showed that MDCs were found to average 2.02 mm (std dev of 0.83mm) and 2.47mm (std dev of 0.68mm), respectively, resulting in a P value of 0.07. The mean DICE coefficients averaged 97.33% (std dev of 1.13%) and 97.19% (std dev of 1.90%) for optical surface imaging and skin marks/lasers, respectively, with a P value of 0.65. The data confirms the null hypothesis in both cases.Conclusion: Comparison of our Cherenkov image analytics from two centers, each using a separate positioning method (optical surface imaging and skin marks/lasers), revealed that there is no statistical difference in terms of MDC and DICE coefficient. This analysis confirms that both setup methods can be used confidently for patient positioning without compromising quality of care. This novel method for assessing alignment techniques is easy to use on a daily basis, adds no extra time or imaging dose to the patient, and analysis is automated, making this tool ideal for evaluating patient positioning for large numbers of treatments. Future work will examine different methods for alignment of more complex treatments such as deep-inspiration breath hold for left breast radiation. [ABSTRACT FROM AUTHOR]

Purpose/objective(s): Cherenkov imaging is a novel technique that captures light emissions during radiation therapy, allowing for visualization of radiation treatments on patients, in real-time. We hypothesized that simply viewing the Cherenkov video images, both in real-time and with post-treatment review by radiation therapists, would identify events not previously reported in the existing QA program.Materials/methods: In December 2020, Cherenkov imaging cameras were introduced into an academic medical center with an existing QA program consisting of a hospital wide incident reporting system that is anonymous, voluntary, and non-punitive. Events are reviewed monthly by a multidisciplinary group including representatives from radiation therapy, dosimetry, nursing, physics and radiation oncologists. The Cherenkov cameras were installed in each treatment bunker, positioned laterally on each side of the couch. The cameras provided continuous, real-time video images of the patients and visualization of the irradiated tissue. Live viewing of the treatments was provided via a dedicated monitor in the console room. All treatments were imaged with the exception of treatments where optical surface imaging lights were on for SGRT.Results: During this 3-month period, 12 events were reported in the hospital-based incident reporting system. Events were reviewed and categorized as 3 operational/process improvement (e.g., scheduling errors), 3 other safety events (e.g., patient falls), 3 treatment planning errors (e.g., wrong shifts calculated for setup), 1 prescription transcription error, 1 treatment delivery error (a missed treatment field), and 1 simulation error (suboptimal immobilization equipment used). Aside from a patient fall, all events were deemed to have no detectable harm to the patient. In this same time period, review of Cherenkov images identified 3 treatment delivery events, which were not identified by other means. The first was an AP-PA thoracic spine treatment and on one day, the treating therapists noted the patient's chin in the treatment field. Treatment was stopped, the patient was re-positioned for the remainder of the treatment. Second was an AP-PA lumbar spine field that on post-treatment review was noted that the patient's hands moved into the field. The third was a 3-field sacrum plan that on post-treatment review was noted that for 7 of 10 fractions, the patient's left arm was positioned over the exit RPO beam. Physics review estimated that the uninvolved arm received approximately 3 Gy.Conclusion: Viewing of Cherenkov emission imaging by the treatment team identified delivery incidents due to non-ideal patient positioning during treatment and these events were not identified in the existing QA program. Future work will focus on determining incident rates detected by Cherenkov imaging and if this imaging can identify and/or avoid treatment delivery errors from reaching the patient. Automated detection and near real time notification of such events is a work in progress. [ABSTRACT FROM AUTHOR]

Purpose/objective(s): Electron ultrahigh dose rate FLASH radiotherapy (UHDR/eFLASH-RT) is currently being extensively tested and modeled, and was studied in several rodent and large animal experiments and one clinical cancer patient. These studies suggest prospective dosimetry assessments are necessary to ensure safe delivery and widespread clinical translation of eFLASH-RT would clearly benefit from prior dose prediction and a treatment planning process that accounts for anatomical heterogeneity and complex geometries. In this study, a GAMOS Monte Carlo beam model was developed and implemented in a clinical treatment planning system for a modified UHDR electron LINAC to demonstrate eFLASH-RT planning of patients.Materials/methods: The gantry head was modelled without scattering foils or targets, representative of the LINAC modifications. Centered at the nominal energy of 10 MeV, the energy spectrum (σE) was varied to match the central axis percent depth dose (PDD) profiles of an open field measured with radiographic film. The beam's emittance cone angle (θcone) was determined by matching calculated and film measured lateral profiles, at several depths. The beam model and its configuration in the treatment planning system were validated with film measured lateral profiles and PDD's of the open field and nominal fields for clinical applicators. A GAMOS forward dose calculation was conducted for a mouse whole brain treatment and an eFLASH-RT plan was compared to a conventional electron plan for a human patient with a rib metastasis.Results: Our eFLASH beam model agrees best with measurements at σE = 0.5MeV and θcone = 3.9o ± 0.2o. The model and its treatment planning system configuration were validated 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's). The forward dose calculation showed dose was delivered to the entire mouse brain with adequate conformality (90% of the tumor volume receiving 90% of the prescribed dose). The comparison plans for the patient undergoing treatment for a rib metastasis demonstrated the capability to achieve an acceptable eFLASH-RT plan with routine accessories (90% of the tumor receiving 95% and 90% of the prescribed dose for eFLASH and conventional, respectively) in relatively complex geometry (right posterior oblique treatment with patient specific applicator cutout).Conclusion: To the best of our knowledge, this study presents the first functional beam model commissioned in a clinical TPS for eFLASH-RT, enabling treatment planning and evaluation with minimal deviation from conventional radiotherapy workflow. By producing plans with the quality comparable to conventional plans, specifically for human patients involving complex geometries and tissue heterogeneity, the clinical translation of eFLASH-RT can be expedited. The open-source methods (described in https://github.com/mr3536/eFLASHBeamModeltoTPS) can model other eFLASH irradiators with different beam characteristics. [ABSTRACT FROM AUTHOR]