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  • Title: In patient dose reconstruction using a cine acquisition for dynamic arc radiation therapy.
    Author: Piermattei A, Fidanzio A, Azario L, Greco F, Mameli A, Cilla S, Grimaldi L, D'Onofrio G, Augelli BG, Stimato G, Gaudino D, Ramella S, D'Angelillo R, Cellini F, Trodella L.
    Journal: Med Biol Eng Comput; 2009 Apr; 47(4):425-33. PubMed ID: 19221822.
    Abstract:
    An amorphous silicon (a-Si) electronic portal imaging device (EPID) was implemented to perform transit in vivo dosimetry for dynamic conformal arc therapy (DCAT). A set of images was acquired for each arc irradiation using the EPID cine acquisition mode, that supplies a frame acquisition rate of one image every 1.66 s, with a monitor unit rate equal to 100 UM/min. In these conditions good signal stability, +/-1% (2SD) evaluated during 3 months, signal reproducibility within +/-0.8% (2SD) and linearity with dose and dose rate within +/-1% (2SD) were obtained. The transit signal, S (t), due to the transmitted radiotherapy beam below a solid phantom, measured by the EPID cine acquisition mode was used to determine, (1) a set of correlation functions, F(w, L), defined as the ratio between S (t) and the dose at half thickness, D (m), measured in solid water phantoms of different thicknesses, w and with square fields of side L, (2) a set of factors, f(d, L), that take into account the different x-ray scatter contribution from the phantom to the S (t) signal as a function of the variation, d, of the air gap between the phantom and the EPID. The reconstruction of the isocenter dose, D (iso), for DCAT was obtained convolving the transit signal values, obtained at different gantry angles, with the respective reconstruction factors determined by a house-made software. The method was applied to a first patient and the results show that the reconstructed D (iso) values can be obtained with an accuracy within +/-5%. In conclusion, it was assessed that an a-Si EPID with the cine acquisition mode is suitable to perform transit in vivo dosimetry for the DCAT therapy.
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