A comparison study of profile measurements of unflatten photon beams utilizing various detector arrays.

Abstract

Author(s): Mr. Kanakavel Kandasamy, E. James Jebaseelan Samuel

Introduction: For routine beam profile analysis of a linear accelerator, two-dimensional array detectors are used to characterize the beam's flatness, symmetry, radiation field size, and penumbra of a given photon-flattening filter beam. However, the objective of this research was to assess the suitability of various array detectors by comparing the dosimetric parameters of an FFF beam profile.

Materials and Methods: Profiles were measured utilizing the 729, 1500, 1600, Starcheck arrays, Pinpoint 3D with Beamscan system, and EPID Panel. A 100 MU radiation dose was applied to 6FFF and 10FFF beams with square fields of 10 cm² x 10 cm², 15 cm² x 15 cm², and 20 cm² x 20 cm², respectively, using a Varian True Beam Linear Accelerator. All detectors kept at the isocenter of the Linac to be unique. Dosimetric parameters, including FWHM, off-axis ratio, degree of unflatness, penumbra, and symmetry, were extracted from measured FFF beam profiles utilizing PTW Beamscan software.

Results: In terms of field size, the 729 array exhibited the greatest deviation from nominal field size at 10 cm² x 10 cm² for both FFF beams in FWHMs. 1.05 mm represented the greatest possible deviation for the 729 array. In comparison to the even field diameters of 10x10 cm² and 20 cm² x 20 cm², the 729 array exhibited the greatest FWHM deviation. With the 1500 array, however, the effect was the exact opposite. A maximum difference of 1.49 mm was recorded in the 15 cm² x 15 cm² field, while the remaining two fields exhibited differences of less than 1 mm. It was determined that the maximal degree of unflatness for the 1600SRS and 729 arrays was 10.8 mm and 9.72 mm, respectively, in comparison to the Pinpoint 3D chamber. A declining trend was identified in the Penumbra analysis, commencing with the 729, followed by the 1500, 1600SRS, Starcheck, Pinpoint 3D, and EPID detectors. An elevation of approximately 13 mm was recorded for the 729 array, while the EPID recorded 3 mm. Conversely, it was demonstrated that the beam symmetry and OAR of every detector array were below 1%.

Conclusion: It is evident from the research that the resolution of the array detector is the most crucial factor when conducting profile measurements using the FFF beam and the depth of detectors placed in each array also played a big role. With the exception of (729, 1500, and 1600) arrays, Starcheck and EPID outcomes were remarkably comparable to those of IEC 60976 and Pinpoint 3D.

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