A Simplified Approach for Determination of Inflection Points of Flattening Filter-Free Photon Beam Using In-House Developed Software and Derivation of Reference Levels.

Abstract

This article aimed to present the salient features of the in-house developed Java program for the determination of inflection point and dosimetric parameters of flattening filter-free (FFF) photon beam. Reference levels for the dosimetric parameters of the FFF photon beams were also presented. Beam profiles of 6 MV FFF and 10 MV FFF photon beams for a collimator setting of 20 cm × 20 cm measured at 10 cm depth in an isocentric setup acquired from various institutions were analyzed using an in-house developed Java program and manual method. The values of reference dose value (RDV), field size, penumbra, and degree of un-flatness (defined as the lateral separation between 90% [X90%], 75% [X75%], and 60% [X60%] dose points on the profile) were calculated and compared. The reference values of field size, penumbra, and degree of un-flatness were also determined for Varian and Elekta medical electron linear accelerators (LINACs). The maximum differences for RDV determined using the Java method and manual method are 2.4% and 2.7% for 6 and 10 MV FFF photon beams, respectively. The maximum difference between the values of field size, penumbra, and degree of un-flatness determined using Java and manual methods is within 1.3 mm. The reference values of field size and penumbra for Varian LINACs are 19.94 ± 0.10 cm and 0.83 ± 0.08 cm (6 MV FFF) and 19.95 ± 0.10 cm and 0.83 ± 0.08 cm (10 MV FFF). Similarly, the reference values of field size and penumbra for Elekta LINACs are 20.02 ± 0.09 cm and 0.94 ± 0.12 cm (6 MV FFF) and 20.03 ± 0.11 cm and 0.97 ± 0.16 cm (10 MV FFF). A software program was developed in Java for analyzing the beam profiles of FFF photon beams. The results of Java-derived values of dosimetric parameters of FFF photon beams were found in good agreement with the values determined using the manual method. The reference values of these parameters were also derived and quoted using a large cohort of the data.