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The complete Primus LINAC detailing the position of each component of the treatment head together with the 10 cm  10 cm applicator and phase-space file position.
Source publication
In Intra-Operative Radiation Therapy (IORT) the tumour site is surgically exposed and normal tissue located around the tumour may be avoided. Electron applicators would require large surgical incisions; therefore, the preferred mechanism for beam collimation is the IORT cone system. FLASH radiotherapy (FLASH-RT) involves the treatment of tumours at...
Contexts in source publication
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... were repeated for the 15 cm  15 cm applicator. A schematic of the Siemens Primus Linac can be seen in Figure 1 below. ...
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... 3 below shows the absolute differences of pertinent characteristic MC-calculated points relative to measurements for PDD curves for {E} for the 15 cm  15 cm applicator. Figure 10. Comparison of measured and MC profiles for 18 MeV at 2.5 cm depth, and 4.5 cm depth for the 19 mm IORT Open Cone, and 2.5 cm depth, and at 4.5 cm depth for the 45 mm cone. ...
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... are shown in Table 4. Very good agreement is shown between measured and simulated data (MC) with differences within one percent. Figure 11. PDD data for IORT cones with cutouts for the 19 mm cone and for 6 and 18 MeV, and for the 45 mm cone for 12 MeV. ...
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... the cross-plane results are reported below in Figure 8 for 6 MeV electron beams. Similar data are also shown for the 12 and 18 MeV beam cases in Figures 9 and 10. ...
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... in the MC data is within 1%. Figure 11 shows PDD data for IORT cones with cutouts inserted, as depicted in Figure 3. Data are shown for the 19 mm cone with cutout (top left) and (top right) for the 6 and 18 MeV cases. The 45 mm cone data is shown in the bottom left and right panels for the 12 and 18 MeV cases. ...
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... differences were within 3% of the local values. In Figure 12, beam profile data are shown for the 19 mm cone for 6 (left) and 18 MeV (right) beam energy. All simulation data has an uncertainty within 1%. ...
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... ensure the MC modelling process is accurate, great care should be taken to ensure that the CMs and input parameters used in the MC build of the accelerator are correct. The incident electron energy Figure 12. Profile data for the 6 and 18 MeV electron beams for the 19 mm cone. ...
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... step could only be reached after stage I and stage II of this study to commission the MC results with measurement. Since we continue with verification in stage III, we limit the benchmark data to field PDD and profile data, as shown in Figures 11 and 12 Here we see good agreement with the MC and water tank measured data. This is reflected in the dosimetric data in Tables 9, 10, and 11 for the three cone sizes in {C} at the beam energies {E} studied. ...
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... were repeated for the 15 cm  15 cm applicator. A schematic of the Siemens Primus Linac can be seen in Figure 1 below. ...
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... 3 below shows the absolute differences of pertinent characteristic MC-calculated points relative to measurements for PDD curves for {E} for the 15 cm  15 cm applicator. Figure 10. Comparison of measured and MC profiles for 18 MeV at 2.5 cm depth, and 4.5 cm depth for the 19 mm IORT Open Cone, and 2.5 cm depth, and at 4.5 cm depth for the 45 mm cone. ...
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... are shown in Table 4. Very good agreement is shown between measured and simulated data (MC) with differences within one percent. Figure 11. PDD data for IORT cones with cutouts for the 19 mm cone and for 6 and 18 MeV, and for the 45 mm cone for 12 MeV. ...
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... the cross-plane results are reported below in Figure 8 for 6 MeV electron beams. Similar data are also shown for the 12 and 18 MeV beam cases in Figures 9 and 10. ...
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... in the MC data is within 1%. Figure 11 shows PDD data for IORT cones with cutouts inserted, as depicted in Figure 3. Data are shown for the 19 mm cone with cutout (top left) and (top right) for the 6 and 18 MeV cases. The 45 mm cone data is shown in the bottom left and right panels for the 12 and 18 MeV cases. ...
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... differences were within 3% of the local values. In Figure 12, beam profile data are shown for the 19 mm cone for 6 (left) and 18 MeV (right) beam energy. All simulation data has an uncertainty within 1%. ...
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... ensure the MC modelling process is accurate, great care should be taken to ensure that the CMs and input parameters used in the MC build of the accelerator are correct. The incident electron energy Figure 12. Profile data for the 6 and 18 MeV electron beams for the 19 mm cone. ...
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... step could only be reached after stage I and stage II of this study to commission the MC results with measurement. Since we continue with verification in stage III, we limit the benchmark data to field PDD and profile data, as shown in Figures 11 and 12 Here we see good agreement with the MC and water tank measured data. This is reflected in the dosimetric data in Tables 9, 10, and 11 for the three cone sizes in {C} at the beam energies {E} studied. ...
Citations
... Comparison between the simulated and experimentally measured results showed good agreement for different maximum dose ranges (R max , R 90 , R 80 , and R 50 ). The deviation between the MC-calculated percent depth dose (PDD) curves and the measurements was 5.2% [25]. EGSnrc (release v2023) MC software modules, namely BEAMnrc and DOSXYZnrc, were employed to create a treatment plan for whole-brain RT. ...
Simple Summary
FLASH radiotherapy (RT) delivering ultra-high dose rate radiation can reduce normal tissue toxicity while effectively treating tumors. However, implementing FLASH RT in clinical settings faces challenges like limited depth penetration and complex treatment planning. Monte Carlo simulation is a valuable tool to optimize FLASH RT. Radiation detectors, including diamond detectors like microDiamond and ionization chambers, play a crucial role in accurately measuring dose delivery. Moreover, optically stimulated luminescence dosimeters and radiochromic films are used for validation. Advancements are being made to improve detector accuracy in FLASH RT. Further research is needed to refine treatment planning and detector performance for widespread FLASH RT implementation, which can potentially revolutionize cancer treatment.
Abstract
Radiotherapy (RT) using ultra-high dose rate (UHDR) radiation, known as FLASH RT, has shown promising results in reducing normal tissue toxicity while maintaining tumor control. However, implementing FLASH RT in clinical settings presents technical challenges, including limited depth penetration and complex treatment planning. Monte Carlo (MC) simulation is a valuable tool for dose calculation in RT and has been investigated for optimizing FLASH RT. Various MC codes, such as EGSnrc, DOSXYZnrc, and Geant4, have been used to simulate dose distributions and optimize treatment plans. Accurate dosimetry is essential for FLASH RT, and radiation detectors play a crucial role in measuring dose delivery. Solid-state detectors, including diamond detectors such as microDiamond, have demonstrated linear responses and good agreement with reference detectors in UHDR and ultra-high dose per pulse (UHDPP) ranges. Ionization chambers are commonly used for dose measurement, and advancements have been made to address their response nonlinearities at UHDPP. Studies have proposed new calculation methods and empirical models for ion recombination in ionization chambers to improve their accuracy in FLASH RT. Additionally, strip-segmented ionization chamber arrays have shown potential for the experimental measurement of dose rate distribution in proton pencil beam scanning. Radiochromic films, such as GafchromicTM EBT3, have been used for absolute dose measurement and to validate MC simulation results in high-energy X-rays, triggering the FLASH effect. These films have been utilized to characterize ionization chambers and measure off-axis and depth dose distributions in FLASH RT. In conclusion, MC simulation provides accurate dose calculation and optimization for FLASH RT, while radiation detectors, including diamond detectors, ionization chambers, and radiochromic films, offer valuable tools for dosimetry in UHDR environments. Further research is needed to refine treatment planning techniques and improve detector performance to facilitate the widespread implementation of FLASH RT, potentially revolutionizing cancer treatment.
Background
In preparation of future clinical trials employing the Mobetron electron linear accelerator to deliver FLASH Intraoperative Radiation Therapy (IORT), the development of a Monte Carlo (MC)‐based framework for dose calculation was required.
Purpose
To extend and validate the in‐house developed fast MC dose engine MonteRay (MR) for future clinical applications in IORT.
Methods
MR is a CPU MC dose calculation engine written in C++ that is capable of simulating therapeutic proton, helium, and carbon ion beams. In this work, development steps are taken to include electrons and photons in MR are presented. To assess MRs accuracy, MR generated simulation results were compared against FLUKA predictions in water, in presence of heterogeneities as well as in an anthropomorphic phantom. Additionally, dosimetric data has been acquired to evaluate MRs accuracy in predicting dose‐distributions generated by the Mobetron accelerator. Runtimes of MR were evaluated against those of the general‐purpose MC code FLUKA on standard benchmark problems.
Results
MR generated dose distributions for electron beams incident on a water phantom match corresponding FLUKA calculated distributions within 2.3% with range values matching within 0.01 mm. In terms of dosimetric validation, differences between MR calculated and measured dose values were below 3% for almost all investigated positions within the water phantom. Gamma passing rate (1%/1 mm) for the scenarios with inhomogeneities and gamma passing rate (3%/2 mm) with the anthropomorphic phantom, were > 99.8% and 99.4%, respectively. The average dose differences between MR (FLUKA) and the measurements was 1.26% (1.09%). Deviations between MR and FLUKA were well within 1.5% for all investigated depths and 0.6% on average. In terms of runtime, MR achieved a speedup against reference FLUKA simulations of about 13 for 10 MeV electrons.
Conclusions
Validations against general purpose MC code FLUKA predictions and experimental dosimetric data have proven the validity of the physical models implemented in MR for IORT applications. Extending the work presented here, MR will be interfaced with external biophysical models to allow accurate FLASH biological dose predictions in IORT.
