Search

Monte Carlo (MC) based treatment planning solutions for FLASH have typically been confined within proprietary treatment planning systems (TPS), lacking a true open-source implementation. This study aims to establish an open-source treatment planning workflow by integrating the Tool for Particle Simulation (TOPAS) MC code with a Python graphical user interface (GUI) to accurately calculate 3D dose across various electron cut-out apertures and geometries. The treatment head of the FLASH-enabled Linac was modeled using CAD files. Depth dose and beam profiles were acquired using radiographic film with different circular collimators. A beam model was created through inverse Bayesian optimization, minimizing the difference between measured and simulated profiles. The total particle count for each radiation pulse passing through the beam current transformer (BCT) on the mobile electron linear accelerator was estimated from measurements and then the BCT was integrated into the MC simulation, establishing a calibration relationship between MC output, absolute dose and number of histories. The whole workflow was then used for end-to-end testing incorporating an anatomically correct 3D printed mouse phantom. Inverse optimization yielded a beam energy of 8.4 MeV with a spread of 1 MeV and a source spot size of 2 mm with an angular spread of 4 degrees. The simulated and measured depth dose for the 10 cm collimator agreed to within <1% of each other. Simulated beam profiles for various insert sizes exhibited good agreement (<3%) with the measured profiles, although variations were noted in the low dose region for all profiles. A Python GUI was developed enabling the importation of CT scans and beam apertures to calculate 3D dose distributions by invoking the TOPAS MC code for simulation. A recent multi-institutional dosimetric audit uncovered discrepancies of up to 10%, particularly in areas with tissue inhomogeneities. Given the tissue-protective benefits of FLASH radiation are on the order of 10-20%, it is imperative to employ precise planning and delivery tools. Our open-source MC beam model and Python GUI will be invaluable resources for ensuring accuracy in FLASH research, with the potential for seamless adaptation into clinical trials. [ABSTRACT FROM AUTHOR]

Longitudinal monitoring of tumor volume is a fundamental component of preclinical biomedical research. We explored the use of inexpensive portable ultrasound (US) probes as a viable, cost-and time-efficient alternative to the standard caliper-based volume measurements in laboratory settings, aiming to compare these methods and establish a more precise measurement technique. 5 BALB/c and 5 C57Bl6/J mice were shaved and injected subcutaneously with 105 colon (CT26) or lung (LLC1) carcinoma cells on the flank. At day 14, tumor length and width (LxW) were measured with either calipers or a portable handheld US probe (frequency: 8-20MHz, maximum depth: 4cm), which provided 2D images across the LxW. Tumors were subsequently excised and imaged with cone-beam computed tomography (CBCT) to obtain a gold-standard volume measurement. The widely-used ellipsoid volume formula was applied to US- and caliper-derived LxW as well as to LxW and the US-derived tumor depth (D) measured from the orthogonal cross-section. In addition to these methods, we developed a novel algorithm designed to estimate tumor volumes from regions of interest (ROIs) defined on two orthogonal US cross sections. The CBCT volumes ranged from 30-170mm3, with an average volume of 82.8 ± 49.6mm3. The average of the caliper-derived volume was 206% ± 76% of the reference volume, the average US-derived volume estimated from the caliper formula was 106% ± 41%, and the average volume from the US-derived LxWxD applied to the traditional ellipsoid formula was 90% ± 34%. The average from the ROI-derived volumes from the 2 orthogonal US views was 94% ± 12%. Our study demonstrates the feasibility of rapid US-based measurement of tumor volumes that offers improved accuracy relative to standard caliper-based approaches. The adoption of a portable handheld US probe for acquiring width, length, and depth measurements enhances the precision of the average tumor volume estimations by ∼100% when applied to the ellipsoid formula. The calculated volumes from the ROIs using two orthogonal US views closely align with this improved performance and exhibit the least variability across tumors, suggesting that this approach is better suited for tumors with irregular shapes. Although image collection with US was initially two times lengthier than caliper measurements, we anticipate that with increased user proficiency, the time required could decrease further. [ABSTRACT FROM AUTHOR]

Commercial devices capable of delivering FLASH radiotherapy are being introduced into radiobiology research. There is a critical necessity for a unified dosimetric protocol to ensure dosimetric consistency across institutes. This work introduces a collaborative, multi-institutional dosimetry protocol designed to validate and standardize dosimetry across two research facilities using FLASH intraoperative systems. Two independent institutes used the same collimator design (4x4 cm2) and same beam parameters to deliver 12 or 14 Gy with FLASH or conventional (CONV) dose rates. For dosimetry, replicates of a realistic anatomy 3D-printed mouse phantom with coronal or sagittal division allowing insertions of radiochromic films, and a set of films (sourced from a singular source) were sent from Institute 1 to Institute 2. The institutes independently calibrated the target doses for FLASH using films from the phantom against the associated measurements from the embedded toroid of the system, and for CONV against the total number of MU. Ultimately, 80 experimental toroid measurements for FLASH (40 per target dose) were acquired in 4 days, with 5 set of films per modality per day of measurement. The films were returned to Institute 1 for analysis and the experimental values for FLASH and CONV were calculated. For 12 Gy target dose, the toroid-derived FLASH doses combined for Institute 1 vs Institute 2 were 11.85 ± 0.11 Gy vs 12.32 ± 0.16 Gy, for 14 Gy were 14.12 ± 0.07 Gy vs 14.09 ± 0.01 Gy. for CONV 11.74 ± 0.23 Gy vs 12.19 ± 0.20 Gy and for 14 Gy were 13.86 ± 0.21 Gy vs 14.47 ± 0.31 Gy. The differences between measured and target doses, as well as between FLASH and CONV doses, were within 3%, and the inter-institutional dose differences were under 5%. Enhancing the protocol could entail incorporating an extra calibration step before the experimental dates to fine tune dose alignment between institutions. The success of the collaborative, multi-institutional dosimetry protocol, using realistic anatomy 3D-printed mouse phantom, is evidenced by the demonstrated consistency in preclinical radiobiological experiments across distinct research facilities. [ABSTRACT FROM AUTHOR]