The Effect of the Size of Radiotherapy Photon Beams on the Absorbed Dose to an Al_2O_3 Dosimeter

The effect of the size of radiotherapy photon beams on the absorbed dose to an Al2O3 dosimeter was investigated using the Monte Carlo method. The EGSnrc/DOSRZnrc program code was used to simulate the absorbed dose to the Al2O3 dosimeter, as well as the absorbed dose to water at the corresponding position in the absence of the dosimeter. The incident beams were 60Co γ and 6 MV with a different beam radius ranging from 0.1 cm to 2 cm. Results revealed that the absorbed dose ratio factor depends on the size of the incident photon beam. When the radius of the incident beam is smaller than that of the dosimeter, the absorbed dose ratio factor decreases as the incident beam size increases. The absorbed dose ratio factor reaches its minimum when the radius of the incident beam is almost the same as that of the dosimeter. When the radius of the incident beam is larger than that of the dosimeter, the absorbed dose ratio factor increases as the incident beam size increases. The maximum difference among these absorbed dose ratio factors can be up to 14% in 60Co γ beams and 23% in 6 MV beams. However, when the size of the incident beam is much larger than that of the dosimeter, the effect of the incident beam size on the absorbed dose ratio factor becomes quite small. The maximum discrepancy between the absorbed dose ratio factors and the average value is not more than 1%.

Enhancing Precision in Radiotherapy Delivery: Validating Monte Carlo Simulation Models for 6 MV Elekta Synergy Agility LINAC Photon Beam Using Two Models of the GAMOS Code

The most crucial requirement in radiation therapy treatment planning is a fast and accurate treatment planning system that minimizes damage to healthy tissues surrounding cancer cells. The use of Monte Carlo toolkits has become indispensable for research aimed at precisely determining the dose in radiotherapy. Among the numerous algorithms developed in recent years, the GAMOS code, which utilizes the Geant4 toolkit for Monte Carlo simula-tions, incorporates various electromagnetic physics models and multiple scattering models for simulating particle interactions with matter. This makes it a valuable tool for dose calculations in medical applications and throughout the patient’s volume. The aim of this present work aims to vali-date the GAMOS code for the simulation of a 6 MV photon-beam output from the Elekta Synergy Agility linear accelerator. The simulation involves mod-eling the major components of the accelerator head and the interactions of the radiation beam with a homogeneous water phantom and particle information was collected following the modeling of the phase space. This space was po-sitioned under the X and Y jaws, utilizing three electromagnetic physics mod-els of the GAMOS code: Standard, Penelope, and Low-Energy, along with three multiple scattering models: Goudsmit-Saunderson, Urban, and Wentzel-VI. The obtained phase space file was used as a particle source to simulate dose distributions (depth-dose and dose profile) for field sizes of 5 × 5 cm2 and 10 × 10 cm2 at depths of 10 cm and 20 cm in a water phantom, with a source-surface distance (SSD) of 90 cm from the target. We compared the three electromagnetic physics models and the three multiple scattering mod-els of the GAMOS code to experimental results. Validation of our results was performed using the gamma index, with an acceptability criterion of 3% for the dose difference (DD) and 3 mm for the distance-to-agreement (DTA). We achieved agreements of 94% and 96%, respectively, between simulation and experimentation for the three electromagnetic physics models and three mul-tiple scattering models, for field sizes of 5 × 5 cm2 and 10 × 10 cm2 for depth-dose curves. For dose profile curves, a good agreement of 100% was found between simulation and experimentation for the three electromagnetic physics models, as well as for the three multiple scattering models for a field size of 5 × 5 cm2 at 10 cm and 20 cm depths. For a field size of 10 × 10 cm2, the Penelope model dominated with 98% for 10 cm, along with the three multiple scattering models. The Penelope model and the Standard model, along with the three multiple scattering models, dominated with 100% for 20 cm. Our study, which compared these different GAMOS code models, can be crucial for enhancing the accuracy and quality of radiotherapy, contributing to more effective patient treatment. Our research compares various electro-magnetic physics models and multiple scattering models with experimental measurements, enabling us to choose the models that produce the most reli-able results, thereby directly impacting the quality of simulations. This en-hances confidence in using these models for treatment planning. Our re-search consistently contributes to the progress of Monte Carlo simulation techniques in radiation therapy, enriching the scientific literature.

Bessel–Gauss photon beams with fractional order vortex propagation in weak non-Kolmogorov turbulence

We model the effects of weak fluctuations on the probability densities and normalized powers of vortex models for the Bessel–Gauss photon beam with fractional topological charge in the paraxial non-Kolmogorov turbulence channel. We find that probability density of signal vortex models is a function of deviation from the center of the photon beam, and the farther away from the beam center it is, the smaller the probability density is. For fractional topological charge, the average probability densities of signal/crosstalk vortex modes oscillate along the beam radius except the half-integer order. As the beam waist of the photon source grows, the average probability density of signal and crosstalk vortex modes grow together. Moreover, the peak of the average probability density of crosstalk vortex modes shifts outward from the beam center as the beam waist gets larger. The results also show that the smaller index of non-Kolmogorov turbulence and the smaller generalized refractive-index structure parameter may lead to the higher average probability densities of signal vortex modes and lower average probability densities of crosstalk vortex modes. Lower-coherence radius or beam waist can give rise to less reduction of the normalized powers of the signal vortex modes, which is opposite to the normalized powers of crosstalk vortex modes.

Commissioning of TrueBeamTM Medical Linear Accelerator: Quantitative and Qualitative Dosimetric Analysis and Comparison of Flattening Filter (FF) and Flattening Filter Free (FFF) Beam

Motive of the study is to present quantitative and qualitative analysis and comparison of beam data measurement with FF (flattening filter) and FFF (flattening filter free) beam in a Varian TrueBeamTM Medical Linear Accelerator. Critique of beam characterization and evolution of dosimetric properties for 6 MV, 10 MV, 15 MV FF beam and 6 MVFFF, 10 MVFFF FFF beam has been carried out. We performed the comparison of photon beam data for two standard FF photon energy 6 MV, 10 MV verses 6 MVFFF, and 10 MVFFF FFF beam. Determination and comparison of parameter involved PDD (Percentage depth dose), Depth dose profile, Symmetry, Flatness, Quality index, Relative output factor, Penumbra, Transmission factor, DLG (Dosimetric leaf gap), in addition to degree of Un-flatness and off-axis ratio of FFF beam. Outcomes of presenting study had shown that change of various parameters such as Percentage depth dose curves, Shape of the depth dose profile, Transmission, Value of quality index and significant rise in surface dose for FFF in comparison with FF beam. Differences in the output factor at lower and higher field sizes for FFF beam compared to that of FF beam were found. The maximum output factor deviation between 6 MV and 6 MVFFF was found to be 4.55%, whereas in 10 MV and 10 MVFFF was 5.71%. Beam quality TPR20/10 for FFF beam was found to be lesser in magnitude, 5.42% for 6 MVFFF whereas 4.50% for 10 MVFFF compared to 6 MV and 10 MV FF beam respectively. Jaw transmission and interleaf leakage for FFF beam were found to be lesser than FF beam. Also DLG for FFF beam was found to be lesser in magnitude comparable to that of flattened beam. This study is mainly inclined towards evaluation and comparison of the FF and FFF beam. It has been observed that, the outcome of a commissioning beam data generation fully complies with vendor specification and published literature.

Self-trapping and oscillation of quadruple beams in high band gap of 2D photonic lattices

through single-site excitation. By changing the initial to the lattices, periodic oscillations of the localized quadruple state becomes a rotating doubly charged undergo charge-flipping when the rotating direction is orientation of the incident quadruple beam related quadruple mode may be obtained. The localized optical vortex （DCV） during rotation and should reversed.