Brost, Eric

Abstract Background The intra‐fraction motion of tumors during radiation therapy can be monitored using imaging systems based on X‐ray imaging (e.g., kV/MV radiography or CBCT) or magnetic resonance imaging (MRI). However, these techniques have limitations, including additional ionizing radiation dose and the need for complex, expensive equipment. Hence, a non‐invasive, lower‐cost motion‐tracking approach that does not add radiation would be beneficial for routine clinical applications. Purpose To study the feasibility of tracking the dynamic motion of a small gold marker in water by using Cherenkov photons produced by MV photon beams, through Monte Carlo simulations and experiments. Methods The GAMOS Monte Carlo code, which includes an optical simulation module, was used to calculate the deposited dose and Cherenkov‐light yield in a water phantom. Phase‐space files for 6, 10, 15, and 10 MV flattening filter‐free (FFF) beams served as photon sources. The simulation setup consisted of a 20 × 20 × 20 cm 3 water phantom with an 8 × 12 × 0.25 mm 3 gold planar implant at its center. Percent depth dose (PDD) and Cherenkov‐light yield were evaluated throughout the phantom and near the gold implant. For experimental validation, a 20 × 20 × 20 cm 3 glass water tank was placed on a programmable platform executing sinusoidal, sawtooth, and sharkfin motions (± 20 mm amplitude; 10‐ and 60‐s cycles). A 5 × 5 cm 2 10 MV FFF beam (2400 MU/min) irradiated the gold implant. A scientific CMOS camera (f/2.0) positioned at 80 cm from the implant captured Cherenkov images. Repeatability was quantified by the standard deviation (SD) across motion cycles. The accuracy was assessed as the absolute difference between the bright‐room reference position and the Cherenkov‐derived position. Images of the implant in sinusoidal motion were also acquired during delivery of a two‐arc brain volumetric modulated arc therapy (VMAT) plan (Arc A and Arc B). Results Monte Carlo simulations showed that Cherenkov light yield throughout the phantom closely correlated with the PDD for all beam energies. The Cherenkov light yield upstream of the gold implant increased by 6.12%, 7.16%, 9.11%, and 7.01% compared to the Cherenkov light yield without the gold implant for 6, 10 FFF, 10, and 15 MV beams, respectively. Experiments confirmed that the beam‐facing side of the gold implant appeared brighter than the opposite side, indicating enhanced backscattered electron production. Cherenkov‐based positional measurements of the periodically moving implant showed close agreement with bright‐room references. For static beams, accuracy across motion patterns was < 0.70 mm with repeatability < 0.2 mm. For the VMAT plan, the accuracies were < 0.50 mm (Arc A) and < 0.70 mm (Arc B). Conclusion The Cherenkov‐light yield was strongly correlated with the deposited dose and showed a notable enhancement around the gold implant. Cherenkov light imaging successfully tracked the dynamic motion of a gold implant in water under high‐dose rate conditions, demonstrating its potential for real‐time fiducial tracking in radiation therapy without additional radiation exposure.

AbstractBackgroundHigh dose rate brachytherapy is commonly used in the treatment of prostate cancer. Treatment planning is often performed under transrectal ultrasound (US) guidance, but brachytherapy needles can be challenging to digitize due to the presence of poor US conspicuity and imaging artifacts. The plan accuracy and quality, however, are dependent on the proper visualization of the needles with millimeter accuracy.PurposeThis work describes a technique for generating a color overlay of needle locations atop the grayscale US image. Prototype devices were developed to produce vibrations in the brachytherapy needles that generate a high contrast color Doppler (CD) signal that highlights the needle locations with superior contrast and reduced artifacts. Denoted by the acronym color VISION (Vibrationally Induced Shimmering for Identifying an Object's Nature), the technology has the potential to improve applicator conspicuity and facilitate automated applicator digitization.MethodsThree prototype vibrational devices with frequencies between 200–450 Hz were designed in‐house and evaluated with needle implants in a phantom and cadaveric male pelvis using: (1) an actuator attached to the front of a prostate needle template; (2) an actuator attached to the top of the needle template; and (3) a hand‐held actuator with a stylet, inserted directly into a needle's inner lumen. Acquired images were postprocessed in MATLAB to evaluate the potential for automated digitization.ResultsAll prototype devices produced localized shimmering in implanted brachytherapy needles in both the axial and sagittal planes. The template mounted actuators provided better vibrational coupling and ease of operation than the stylet prototype. The Michelson contrast, or visibility, of the shimmering CD signal was 100% compared with ≤40% for B‐mode imaging of a single needle. Proof‐of‐principle for automated applicator digitization using only the CD signal was demonstrated.ConclusionsThe color VISION prototype devices successfully coupled mechanical vibrations into brachytherapy needles to generate US CD shimmering and accurately highlight brachytherapy needle locations. The high contrast and natively registered signal are promising for future work to automate the needle digitization and provide a real‐time visual overlay of the applicator on the B‐mode US image.

PurposeDevelop an efficient, interactive, and instructive checklist document for the management of implanted electronic medical devices in a multimodality radiotherapy clinic.MethodsThe built‐in scripting and interactivity of a popular commercial word processor was used to develop an interactive document that changes the information presented to the user based on drop‐down selections. The interactivity and scripting were compatible with the radiation oncology information system (ROIS) which allows the document to be accessible by all team members and serve as a permanent record in a patient's electronic chart.ResultsThe final interactive document, which was clinically deployed after beta testing with a group consisting of nurses and medical physicists, presents information and action plans to the user based on multiple departmental medical device decision trees that are specific to the combination of device, treatment modality, rhythm‐pacing dependence for cardiac devices, and distance from the device to the treatment volume.ConclusionA script‐enabled interactive document was developed for a busy multimodality clinic, condensing multiple comprehensive departmental guidelines spanning multiple device types and treatment modalities into a single interactive checklist accessible within the ROIS. Given the wide accessibility of the commercial word processor, this approach could be adopted by other clinics to streamline their own respective workflows.

AbstractBackgroundApplicator conspicuity in ultrasound‐guided brachytherapy procedures is commonly impaired by imaging artifacts or non‐ideal imaging geometry, which can slow down applicator position digitization and increase the geometric uncertainty of the delivered dose distribution.PurposeThe purpose of this study was to improve the conspicuity of high‐dose rate (HDR) brachytherapy needles under B‐mode ultrasound imaging by applying an echogenic surface coating. Our hypothesis was that an echogenic coating would reduce artifacts and improve needle visualization within regions of signal degradation.MethodsIn this study, 17‐gauge, 25‐cm long titanium HDR brachytherapy needles were coated with acoustically reflective microspheres over a 2.5 cm region starting from the needle tip. Three coating thicknesses (27 μm, 40 μm, 64 μm) were compared against an uncoated control needle. The coated and uncoated needles were imaged using B‐mode ultrasound in a tissue‐equivalent prostate phantom and in a cadaverous male pelvis using a transrectal probe. Needle conspicuity was assessed under multiple conditions: a single needle implant, an implant with multiple needles between the probe and the needle of interest, and an angled needle implant. All images were assessed qualitatively for needle conspicuity and the presence of artifacts and quantitatively using grey‐scale image intensity values.ResultsThe 64 μm echogenic coating reduced the magnitude of reverberation artifacts by 31 ± 14% and comet tail artifacts by 40%–70%. The echogenic coating also improved needle contrast, measured by the relative differences in signal intensity compared with the adjacent environment, when needles were angled up to 30° with respect to the transducer probe in the cadaver. The improvements in conspicuity and artifact reduction increased with increasing coating thickness. The performance of the needles coated with the 64 μm thickness was qualitatively superior and yielded high‐contrast, well‐circumscribed signals in the cadaverous male pelvis, even under situations where a needle was acoustically shadowed by multiple other needles.ConclusionsAn echogenic surface coating reduced imaging artifacts and improved needle conspicuity under realistic clinical conditions for ultrasound‐based prostate or gynecological brachytherapy. The improved conspicuity has the potential to improve the efficiency of needle placement and the accuracy of needle position digitization during brachytherapy procedures.

AbstractBackgroundAlthough intensity‐modulated radiation therapy and volumetric arc therapy have revolutionized photon external beam therapies, the technological advances associated with electron beam therapy have fallen behind. Modern linear accelerators contain technologies that would allow for more advanced forms of electron treatments, such as beam collimation, using the conventional photon multi‐leaf collimator (MLC); however, no commercial solutions exist that calculate dose from such beam delivery modes. Additionally, for clinical adoption to occur, dose calculation times would need to be on par with that of modern dose calculation algorithms.PurposeThis work developed a graphics processing unit (GPU)‐accelerated Monte Carlo (MC) engine incorporating the Varian TrueBeam linac head geometry for a rapid calculation of electron beams collimated using the conventional photon MLC.MethodsA compute unified device architecture framework was created for the following: (1) transport of electrons and photons through the linac head geometry, considering multiple scattering, Bremsstrahlung, Møller, Compton, and pair production interactions; (2) electron and photon propagation through the CT geometry, considering all interactions plus the photoelectric effect; and (3) secondary particle cascades through the linac head and within the CT geometry. The linac head collimating geometry was modeled according to the specifications provided by the vendor, who also provided phase‐space files. The MC was benchmarked against EGSnrc/DOSXYZnrc/GEANT by simulating individual interactions with simple geometries, pencil, and square beam dose calculations in various phantoms. MC‐calculated dose distributions for MLC and jaw‐collimated electron fields were compared to measurements in a water phantom and with radiochromic film.ResultsPencil and square beam dose distributions are in good agreement with DOSXYZnrc. Angular and spatial distributions for multiple scattering and secondary particle production in thin slab geometries are in good agreement with EGSnrc and GEANT. Dose profiles for MLC and jaw‐collimated 6–20‐MeV electron beams showed an average absolute difference of 1.1 and 1.9 mm for the FWHM and 80%–20% penumbra from measured profiles. Percent depth doses showed differences of <5% for as compared to measurement. The computation time on an NVIDIA Tesla V100 card was 2.5 min to achieve a dose uncertainty of <1%, which is ∼300 times faster than published results in a similar geometry using a single‐CPU core.ConclusionsThe GPU‐based MC can quickly calculate dose for electron fields collimated using the conventional photon MLC. The fast calculation times will allow for a rapid calculation of electron fields for mixed photon and electron particle therapy.

AbstractPurposeTo evaluate the use of commercial‐grade strontium aluminate phosphorescent powder as a thermoluminescent (TL) dosimeter for clinical radiotherapy beams.Materials and MethodCommercially available Eu2+, Dy3+ co‐doped strontium aluminate powder (SrAl2O4:Eu, Dy) was annealed and then irradiated using 20 × 20 cm2 field size, with 6‐MV (PDD10 = 70.7) and 18‐MV (PDD10 = 79.4) photon beams and and 9‐MeV (R50 = 3.6), 15 MeV (R50 = 5.9) and 18‐MeV (R50 = 7.2) electron beams. To calibrate the relationship between the TL readings and the irradiated doses, TL glow curves were acquired for doses up to 600 cGy at all beam energies. For the percentage depth dose (PDD) measurement, the SrAl2O4:Eu, Dy powder was sandwiched by solid water phantoms, with varying thickness of solid water placed above to determine the depth. PDDs were measured at four representative depths and compared against the commissioning depth dose data for each beam energy.ResultsLinear dose response models of doses up to 200 cGy were created for all beam energies. Superlinearity was observed with doses greater than 200 cGy. The PDD measurement acquired experimentally agrees well with the commissioning data of the medical linear accelerator. Trapping parameters such as order of kinetics, activation energy and frequency factor have been obtained via TL glow curve analysis.ConclusionThe linear dose response demonstrates that SrAl2O4:Eu, Dy is a potential TLD dosimeter for both electron beams and photon beams at different beam energies. The PDD measurements further support its potential use in quality assurance and radiation dosimetry.