Two-argument total scatter factor for small fields simultaneously collimated by MLC and jaws: application to stereotactic radiosurgery and radiotherapy.

Two-argument total scatter factor for small fields simultaneously collimated by MLC and jaws: application to stereotactic radiosurgery and radiotherapy. Phys Med Biol. 2017 Nov 06;: Authors: Han Z, Friesen S, Hacker FL, Zygmanski P Abstract Direct use of the total scatter factor (S<sub>tot</sub>) for independent monitor unit (MU) calculations can be a good alternative approach to the traditional separate treatment of head/collimator scatter (S<sub>c</sub>) and phantom scatter (S<sub>p</sub>), especially for stereotactic small fields under the simultaneous collimation of secondary jaws and tertiary multileaf collimators (MLC). We have carried out the measurement of S<sub>tot</sub> in water for field sizes down to 0.5 × 0.5 cm<sup>2</sup> on a Varian TrueBeam STx medical linear accelerator (linac) equipped with high definition (HD) MLCs. Both the jaw field size (c) and MLC field size (s) significantly impact the linac output factors, especially when c >> s and s is small (e.g. s < 5 cm). The combined influence of MLC and jaws gives rise to a two-argument dependence of the total scatter factor, S<sub>tot</sub>(c,s), which is difficult to functionally decouple. The (c,s) dependence can be conceived as a set of s-dependent functions ("branches") define...
Source: Physics in Medicine and Biology - Category: Physics Authors: Tags: Phys Med Biol Source Type: research
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