Evaluation of the dosimetric characteristics of 10 MV flattened and unflattened photon beams in a heterogeneous phantom

Abstract

Background:The free flattening filter (FFF) beam can affect the characteristics of the linac output such as the maximum dose depth, surface dose, dose in the fall-off area, and doses outside the field because the beam hardening effect does not occur in the FFF linac head. Therefore, the present study aimed to investigate the influence of the FFF beam on the dose distribution in an inhomogeneous phantom using the EGSnrc/DOSXYZnrc Monte Carlo package. Materials and Methods: In the present study, an Elekta Infinity 10 MV photon beam equipped with a multileaf collimator Agility linear accelerator was used. Two types of virtual inhomogeneous phantoms were built for percent depth doses (PDDs) and dose profiles measurement. The first phantom comprised four layers: water (4 cm thickness), bone (2 cm thickness), lung tissue (5 cm thickness), and water (19 cm thickness). The second phantom had a half-lung tissue slab and a half-bone slab (10 cm thickness) on the left side of the water. Results: The PDD curves in the inhomogeneous phantom considerably decreased in the lung area for small exposure fields because the charged particle equilibrium was not achieved. The dose in the lung was higher than the dose in the water when the charged particle equilibrium was reached. Meanwhile, the dose in the bone is always lower than the dose in the water. Conclusions: The dose distribution of flattening filter (FF) and FFF beams in the inhomogeneous phantom was the same in the small field of exposure. However, differences in dose distribution are increasingly apparent for larger field sizes.

Monte Carlo Simulation-Based BEAMnrc Code of a 6 MV Photon Beam Produced by a Linear Accelerator (LINAC)

“…Based on previous findings, simulating 6 MV photon beam as the MC methods indicates that contribution of electrons is less than 3 % of maximum total dose for 10×10 cm 2 field sizes [12]. Other previous study running on 12 MV states that the electron contamination giving contribution in surface dose is less than 1 % for field size 10×10 cm 2 [13].…”

“…The depth of maximum doses between the modeling and the experimental results has relatively no differences at a range of correction factor of 0.04 to 0.15. A study of high-energy linear accelerator (10 MV) performed by Yani [13] shows that the differences are less than 2 %. The measurement performed by S. Didi for the Tomographic Emission Monte Carlo software shows that the dose differences is about 0.02 % [8].…”

Normal tissue objective (NTO) tool in Eclipse treatment planning system for dose distribution optimization

“…4 Intensity-modulated radiation therapy (IMRT) is a radiotherapy technique that provides good dose-totarget conformity and homogeneity compared to conventional 3D-conformal radiation therapy (3D-CRT) technique. [5][6][7][8] The IMRT technique is carried by modulating the radiation intensity using a multi-leaf collimator (MLC) to form several segments of the radiation field. This process is performed under computer control using the inverse planning optimization technique.…”