Abstract
The purpose of this study is to investigate the potential for reducing dose to the scalp, parotid glands, and external auditory canals using intensity-modulated radiation therapy (IMRT) or volumetrically modulated arc therapy (VMAT) to deliver whole brain radiation therapy (WBRT). Nine patients with brain metastases previously treated with standard opposed lateral (OL) WBRT were studied. Four new plans were created for each patient: (1) four-beam IMRT, (2) seven-beam IMRT, (3) 13-beam IMRT, and (4) VMAT (single arc technique). All plans were optimized to achieve equivalent planning target volume (PTV) coverage while minimizing dose to the scalp, parotid gland, and external ear. Each of the plans was then dosimetrically compared via multiple dose–volume histogram (DVH) parameters. All IMRT and VMAT plans significantly reduced dose to the scalp, ears, and parotid glands without increasing dose to other critical structures. Improved scalp sparing for low, intermediate, and high doses (V5, V10, V20, and V30), was achieved with the 4- and 13-beam IMRT plans. The 7-field plan reduced intermediate and high scalp doses (V10, V20, and V30) while only high doses (V20 and V30) were reduced with the VMAT plan. Depending on the DVH parameter, IMRT/VMAT reduced scalp dose between 10 % and 70 %, parotid gland dose by 3 % and 31 %, and external auditory canal dose by 2 % and 96 %. IMRT or VMAT is able to reduce dose to the scalp, parotid glands, and external auditory canal without sacrificing PTV coverage when compared to a standard OL treatment plan. Such improvement is promising and may decrease non-cognitive WBRT toxicities (e.g., alopecia, xerostomia, otitis), which could improve quality of life for patients receiving WBRT. Future planning will attempt to reduce cochlear dose to avoid hearing loss but will likely require PTV modification.
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