Dosimetric performance of continuous EPID imaging in stereotactic treatment conditions |
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| Affiliation: | 1. CRCT, UMR 1037, INSERM, Université Toulouse III Paul Sabatier, 2 avenue Hubert Curien, 31037 Toulouse, France;2. Engineering and Medical Physics Department, IUCT-Oncopole, 1 avenue Irène Joliot Curie, 31059 Toulouse Cedex 9, France;3. Université Toulouse III Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex 9, France;1. School of Biomedical Engineering, Southern Medical University, Guangzhou 510515, China;2. Guangdong Provincial Key Laboratory of Medical Image Processing, Southern Medical University, Guangzhou 510515, China;3. The Sixth affiliated Hospital of Sun Yat-sen University, Guangzhou 510655, China;1. Medical Physics Department, Veneto Institute of Oncology IOV – IRCCS, Via Gattamelata 64, 35128 Padova, Italy;2. University of Turin, Department of Oncology, Turin, Italy;3. School of Bioengineering and Medical-surgical Sciences, Politecnico di Torino, Corso Bramante, 88, 10126 Torino, Italy;4. University Hospital “Maggiore della Carità”, Department of Medical Physics, Corso Giuseppe Mazzini, 18, 28100 Novara, Italy;5. Tecnologie Avanzate, Lungo Dora Voghera, 36, 10153 Torino, Italy;1. Physics Department, University of Coimbra, Coimbra, Portugal;2. Medical Physics Department, IPOCFG, E.P.E., Coimbra, Portugal |
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| Abstract: | PurposeThis study aims at investigating the dosimetric characteristics of a Varian aS1000 EPID, focusing on its continuous acquisition mode under the challenging conditions that can be met in stereotactic radiotherapy verification.MethodsAn aS1000 EPID installed on a Varian TrueBeamSTx was irradiated with 6 and 10 MV unflattened and flattened photon beams. In order to avoid detector saturation, the source-to-detector distance (SDD) was set to 150 or 180 cm depending on the dose rate. EPID image sets were acquired in continuous mode (CM) and also in the commonly used integrated mode (IM) for comparison, to evaluate dose linearity (including dose rate dependence), repeatability, reproducibility, stability, ghosting effect and field size dependence.ResultsCM response linearity was found to be within 0.8% of IM and independent of dose rate. Response repeatability was slightly better for IM and FF beams, being in all cases within 0.9%. Reproducibility was within 0.6% for both modes and all beam qualities. Response stability between continuous frames varied within 1% for dynamic and static irradiations and for all the beam qualities, showing its independence from these parameters. Ghosting effect was not significant, being comparable to signal variations between continuous frames (±1%). Field size dependence in both modes agreed within 1%.ConclusionsThe dosimetric response of the aS1000 EPID in CM with FFF beams and high dose rates is comparable to that in IM and for flattened beams provided that the appropriate SDD is used. aS1000 EPID in continuous acquisition mode is therefore suitable for stereotactic applications. |
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| Keywords: | EPID dosimetry EPID response Portal imaging Stereotactic radiotherapy verification |
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