Small field characterization of a Nanochamber prototype under flattening filter free photon beams |
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| Institution: | 1. Physics Service of Radiation Oncology Dept., Humanitas Clinical and Research Hospital, Milan-Rozzano, Italy;2. Radiotherapy and Radiosurgery department, Humanitas Clinical and Research Hospital, Milan-Rozzano, Italy;3. Department of Biomedical Sciences, Humanitas University, Rozzano, Milano, Italy;1. Department of Radiation Oncology, Technical University of Munich, Klinikum rechts der Isar, Munich, Germany;2. Physik-Department, Technical University of Munich, Munich, Germany;3. Department of Computer Science, Johns Hopkins University, Baltimore, MD, USA;4. Institute of Innovative Radiotherapy (iRT), Department of Radiation Sciences (DRS), Helmholtz Zentrum München, Munich, Germany;1. Department of Medical Physics, Medical School, University of Crete, P.O. Box 2208, Heraklion 71003, Crete, Greece;2. Department of Radiology, University Hospital of Heraklion, P.O. Box 1352, Heraklion 71110, Crete, Greece;3. Department of Medical Physics, University Hospital of Heraklion, P.O. Box 1352, Heraklion 71110, Crete, Greece;4. Department of Medical Physics, University Hospital of Heraklion, Greece;5. Department of Radiology, Medical School, University of Crete, Greece;1. Medical Physics Department, Azienda USL Toscana Centro, I-50012 Firenze, Italy;2. Department of Medical Physics and Radiation Oncology, IFCA, Radiotherapy, I-50139 Firenze, Italy;3. Department of Radiation Oncology, Ospedale Di Vicenza, I-36100 Vicenza, Italy;4. Medical Physics Unit, Meyer Children’s University Hospital, I-50139 Firenze, Italy;5. Medical Physics Unit, Istituto Besta, Radiotherapy, I-20133 Milano, Italy;6. Radiotherapy Department, Mater Dei Hospital, Città di Bari Hospital spa, I-70125 Bari, Italy;7. Medical Physics Unit, C.D.I., Radiotherapy, I-20147 Milano, Italy;8. Unit of Medical Physics, I. E. O., Radiotherapy, I-20141 Milano, Italy;9. Medical Physics Department, A.O. Ordine Mauriziano, I-10128 Torino, Italy;10. Medical Physics Department, Candiolo Cancer Institute – FPO, IRCCS, I-10060 Torino, Italy;11. Medical Physics Unit of Radiation Oncology Dept, Humanitas Clinical and Research Hospital, I-20089 Rozzano-Milano, Italy;1. Institute of Medical Physics, School of Physics, The University of Sydney, Sydney, New South Wales, Australia;2. School of Medicine, Taif University, Taif, Saudi Arabia;3. Liverpool and Macarthur Cancer Therapy Centers, Liverpool, NSW, Australia;4. Ingham Institute for Applied Medical Research, Sydney, NSW, Australia;5. Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia;6. South Western Sydney Clinical School, University of New South Wales, Sydney, NSW, Australia;1. Radiation Oncology, Sacro Cuore Don Calabria Hospital, Negrar-Verona, Italy;2. Statistic Science Faculty, University of Palermo, Palermo, Italy;3. University of Brescia, Brescia, Italy |
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| Abstract: | IntroductionNanochambers present some advantages in terms of energy independence and absolute dose measurement for small field dosimetry in the SBRT scenario. Characterization of a micro-chamber prototype was carried out both under flattened and flattening-filter-free (FFF) beams with particular focus on stem effect.MethodsThe study included characterization of leakage and stem effects, dose rate and dose per pulse dependence, measurement of profiles, and percentage depth doses (PDDs). Ion collection efficiency and polarity effects were measured and evaluated against field size and dose per pulse. The 6_MV, 6_MV_FFF and 10_MV FFF beams of a Varian EDGE were used. Output factors were measured for field sizes ranging from 0.8 × 0.8 cm2 to 20 × 20 cm2 and were compared with other detectors.ResultsThe 2 mm diameter of this chamber guarantees a high spatial resolution with low penumbra values. In orthogonal configuration a strong stem (and cable) effect was observed for small fields. Dose rate and dose per pulse dependence were <0.3% and 0.6% respectively for the whole range of considered values. The Nanochamber exhibits a field size (FS) dependence of the polarity correction >2%. The OF values were compared with other small field detectors showing a good agreement for field sizes >2 × 2 cm2. The large field over-response was corrected applying kpol(FS).ConclusionsNanochamber is an interesting option for small field measurements. The spherical shape of the active volume is an advantage in terms of reduced angular dependence. An interesting feature of the Nanochamber is its beam quality independence and, as a future development, the possibility to use it for small field absolute dosimetry. |
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