Beschreibung:
<jats:title>Abstract</jats:title><jats:sec>
<jats:title>Background</jats:title>
<jats:p>A simultaneous integrated boost (SIB) may result in increased out-of-field (D<jats:sub>OOF</jats:sub>) and photoneutron (H<jats:sub>PN</jats:sub>) doses in volumetric modulated arc therapy (VMAT) for prostate cancer (PCA). This work therefore aimed to compare D<jats:sub>OOF</jats:sub> and H<jats:sub>PN</jats:sub> in flattened (FLAT) and flattening filter-free (FFF) 6‑MV and 10-MV VMAT treatment plans with and without SIB.</jats:p>
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<jats:title>Methods</jats:title>
<jats:p>Eight groups of 30 VMAT plans for PCA with 6 MV or 10 MV, with or without FF and with uniform (2 Gy) or SIB target dose (2.5/3.0 Gy) prescriptions (CONV, SIB), were generated. All 240 plans were delivered on a slab-phantom and compared with respect to measured D<jats:sub>OOF</jats:sub> and H<jats:sub>PN</jats:sub> in 61.8 cm distance from the isocenter. The 6‑ and 10-MV flattened VMAT plans with conventional fractionation (6- and 10-MV FLAT CONV) served as standard reference groups. Doses were analyzed as a function of delivered monitor units (MU) and weighted equivalent square field size A<jats:sub>eq</jats:sub>. Pearson’s correlation coefficients between the presented quantities were determined.</jats:p>
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<jats:title>Results</jats:title>
<jats:p>The SIB plans resulted in decreased H<jats:sub>PN</jats:sub> over an entire prostate RT treatment course (10-MV SIB vs. CONV −38.2%). Omission of the flattening filter yielded less H<jats:sub>PN</jats:sub> (10-MV CONV −17.2%; 10-MV SIB −22.5%). The SIB decreased D<jats:sub>OOF</jats:sub> likewise by 39% for all given scenarios, while the FFF mode reduced D<jats:sub>OOF</jats:sub> on average by 60%. A strong Pearson correlation was found between MU and H<jats:sub>PN</jats:sub> (<jats:italic>r</jats:italic> > 0.9) as well as D<jats:sub>OOF</jats:sub> (0.7 < <jats:italic>r</jats:italic> < 0.9).</jats:p>
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<jats:title>Conclusion</jats:title>
<jats:p>For a complete treatment, SIB reduces both photoneutron and OOF doses to almost the same extent as FFF deliveries. It is recommended to apply moderately hypofractionated 6‑MV SIB FFF-VMAT when considering photoneutron or OOF doses.</jats:p>
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