Experimental Validation of Small-field Dosimetry in Radiotherapy Using Ionization Chamber and Edge Detector

Introduction:To study the impact of ۶ MV and ۱۰ MV flattened beam (FB) and flattening filter free (FFF) beam in whole brain radiotherapy (WBRT) by using volumetric modulated arc therapy (VMAT). Material and Methods: Twenty WBRTpatients were selected randomly. The dose prescription was ۳۰ Gy, which was delivered in ten fractions. The planning target volume (PTV) and organs at risk (OARs) were contoured. Four VMAT plans, including ۶ MV FB, ۶ MV FFF, ۱۰ MV FB, and ۱۰ MV FFF beam plans, were generated. Results: The ۶MV FB and FFF beam plans were statistically significant (p <۰.۰۵) in terms of the dose received by ۹۸% of the PTV (D۹۸%) (۲۶.۸۶ Gy vs. ۲۷.۳۱ Gy, P=۰.۰۰۶), the dose received by ۹۵% of the PTV (D۹۵%) (۲۸.۲۸ Gy vs. ۲۸.۵۲ Gy, P=۰.۰۳۸), ۱۰۷% isodose (V۱۰۷%) of the PTV (۲.۴۳% vs. ۳.۷۴%, P=۰.۰۰۱), D۱۰۰% of the hippocampus (۹.۳۱ Gy vs. ۹.۱۶ Gy, P=۰.۰۰۹), and the Dmean scalp (۱۶.۷ Gy vs. ۱۶.۸ Gy, p=۰.۰۳۵). The ۱۰ MV FB and FFF beam plans showed significant differences in the conformity index (۰.۹ vs. ۰.۸۵, P=۰.۰۱), V۱۰۷% of the PTV (۱.۶۸% vs. ۴.۵۴%, P=۰.۰۰۱), D۱۰۰% (۱۰.۰۸ Gy vs. ۹.۸۱ Gy, P=۰.۰۳۶), and Dmean of the hippocampus (۱۲.۷۸ Gy vs. ۱۲.۵۷ Gy, P=۰.۰۱۸). The ۶ MV and ۱۰ MV FFF beams showed homogeneous conformal plans, which required ۱۸-۱۹% more MUs, compared to the FB plans. Conclusion: The ۶ MV and ۱۰ MV FB and FFFB spared the hippocampus and the scalp with acceptable target coverage in WBRT cases.

کلیدواژه ها:

Whole brain radiotherapy ، Hippocampus ، scalp sparing ، flattened beam ، flattening filter free beam