Dosimetric comparison of flattened and unflattened beams for stereotactic body radiation therapy: Impact of the size of the PTV on dynamic conformal arc and volumetric modulated arc therapy |
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| Institution: | 1. Institut Claudius Regaud, Institut Universitaire du Cancer de Toulouse Oncopole, Toulouse, France;2. INSERM, CRCT, équipe n°15, Toulouse, France;3. Université Paul Sabatier, Toulouse, France;4. SCM Oncologie, Montauban, France;1. Department of Medical Physics, University of Wisconsin–Madison, UW Medical Radiation Research Center, Madison, WI;2. Department of Radiation Oncology, Tufts University School of Medicine, Boston, MA;1. College of Sciences, Huazhong Agricultural University, Wuhan 430074, Hubei, PR China;2. School of Mathematics and Computer Science, Yunnan University of Nationalities, Kunming, 650500 Yunnan, PR China;3. The Center for OPTical IMagery Analysis and Learning (OPTIMAL), State Key Laboratory of Transient Optics and Photonics, Xi?an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi?an 710119, Shaanxi, PR China;1. Medical Physics Unit, McGill University and Cedars Cancer Center, Montréal, Canada;2. Department of Radiation Oncology, McGill University Health Centre, Montréal, Canada;3. Department of Radiation Oncology, Centre Hospitalier de l’Université de Montréal, Canada;4. Department of Oncology, McGill University, Montréal, Canada;5. Department of Radiation Oncology, University of Michigan, Ann Arbor, United States;1. Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, Ontario, Canada;2. Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada;3. Department of Biostatistics, Princess Margaret Cancer Centre, Toronto, Ontario, Canada;1. Department of Radiation Oncology, The First Hospital of China Medical University, 155# NanjingBei street, Shenyang, 110001, China;2. Department of Clinical Oncology, Shengjing Hospital of China Medical University, 36# Huaxiang street, Shenyang, 110024, China;1. Department of Radiation Oncology, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada;2. Division of Neurosurgery, St Michaels Hospital, University of Toronto, Toronto, Ontario, Canada;3. Division of Neurosurgery, Sunnybrook Health Sciences Center, University of Toronto, Toronto, Ontario, Canada;4. Department of Medical Physics, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada |
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| Abstract: | PurposeFlattening filter free (FFF) beams are frequently used for stereotactic body radiation therapy with various treatment modalities: conventional static fields, dynamic conformal arc (DCA) or Rapid Arc (RA). The goal of this study was to obtain some criteria to enable a conscious choice of the employment of FFF beams and of the DCA or RA technique, depending on the PTV size.Methods and materials24 PTVs from 1.52 cm3 to 445.24 cm3 were studied in various sites: virtual phantom, lung and liver. For each PTV, DCA and RA plans were prepared using two flattened (FF) and two unflattened photon beams. Parameters such as conformity index, gradient index, healthy-tissue and organs at risk mean doses, number of monitor units (MU), beam on time (BOT) were used to quantify obtained dose distributions. Friedman tests and Spearman’s rank correlation coefficients were also performed.ResultsNo significant differences were found between FF and FFF beams for RA regarding conformity and gradient indices. For DCA, 10FFF is less suitable and forward planning becomes more challenging as PTV volume increases. FFF beams provided a better sparing of healthy-tissues except for 10FFF used with DCA. 6FFF was slightly better than 10FFF in terms of healthy-tissue mean doses. FFF beams generated significantly reduced BOTs and increased MUs. These effects were more pronounced for larger volumes and especially for RA plans.ConclusionsFFF showed better results than FF beams for the considered plans. 10FFF used with DCA should be used with caution for medium and large volumes. |
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| Keywords: | Flattening filter free SBRT Dynamic conformal arc Rapid arc |
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