Small‐field output factor dependence on the field size definition in MR‐Linac.
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| Title: | Small‐field output factor dependence on the field size definition in MR‐Linac. |
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| Authors: | Das, Indra J.1 (AUTHOR) Indra.das@nm.org, Khan, Ahtesham U.1 (AUTHOR), Yadav, Poonam1 (AUTHOR) |
| Source: | Medical Physics. Jul2025, Vol. 52 Issue 7, p1-7. 7p. |
| Subjects: | Radiation, Linear accelerators, Medical dosimetry |
| Abstract: | Background: Radiation beam characteristics are primarily evaluated based on field size. However, in small fields, especially with magnetic fields used in new technology (MR‐Linac), the field size definition is altered. Typically, field size is defined by two methods: geometric and dosimetric, which are evaluated in this study. Purpose: Small field size definitions are distorted due to lateral electron disequilibrium and the presence of magnetic fields. MR‐Linac systems, which combine an MR imaging system and a linear accelerator on a single gantry, require precise evaluations of field size definitions and beam parameters, particularly for small fields. which is investigated in this study. Methods: A 0.35 T MRIdian Viewray system was evaluated using beam profiles and field output factors (FOF) with various MR‐compatible microdetectors, such as ion chamber, microDiamond, microSilicon, and plastic scintillators. Validity of geometric field size (S) and dosimetric field size (Sclin) is investigated with measurements performed with MR compatible scanning water phantom at 85 cm source‐to‐surface distance (SSD) at a depth of 5 cm. Measured FOF data was compared with treatment planning systems (TPS) and independent Monte Carlo simulations. Results: The measured Sclin data is detector and machine‐dependent, while S is machine‐dependent only. The FOF was found to be a smooth function of S within experimental uncertainties, showing higher reproducibility compared to Sclin which exhibited erratic behavior. Conclusions: It is concluded that geometric field size (S) provides accurate beam characterization data, whereas Sclin may not be a reliable parameter in MR‐Linac systems. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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