Dynamic conformal arc therapy: Transmitted signal in vivo dosimetry
- Istituto di Fisica, Universita Cattolica del S. Cuore, Roma (Italy) and U.O. di Fisica Sanitaria, Centro di Ricerca e Formazione ad Alta Tecnologia nelle Scienze Biomediche dell'Universita Cattolica S. Cuore, Campobasso (Italy)
A method for the determination of the in vivo isocenter dose, D{sub iso}, has been applied to the dynamic conformal arc therapy (DCAT) for thoracic tumors. The method makes use of the transmitted signal, S{sub t,{alpha}}, measured at different gantry angles, {alpha}, by a small ion chamber positioned on the electronic portal imaging device. The in vivo method is implemented by a set of correlation functions obtained by the ratios between the transmitted signal and the midplane dose in a solid phantom, irradiated by static fields. The in vivo dosimetry at the isocenter for the DCAT requires the convolution between the signals , S{sub t,{alpha}}, and the dose reconstruction factors, C{sub {alpha}}, that depend on the patient's anatomy and on its tissue inhomogeneities along the beam central axis in the {alpha} direction. The C{sub {alpha}} factors are obtained by processing the patient's computed tomography scan. The method was tested by taking measurements in a cylindrical phantom and in a Rando Alderson phantom. The results show that the difference between the convolution calculations and the phantom measurements is within {+-}2%. The in vivo dosimetry of the stereotactic DCAT for six lung tumors, irradiated with three or four arcs, is reported. The isocenter dose up to 17 Gy per therapy fraction was delivered on alternating days for three fractions. The agreement obtained in this pilot study between the total in vivo dose D{sub iso} and the planned dose D{sub iso,TPS} at the isocenter is {+-}4%. The method has been applied on the DCAT obtaining a more extensive monitoring of possible systematic errors, the effect of which can invalidate the current therapy which uses a few high-dose fractions.
- OSTI ID:
- 21120687
- Journal Information:
- Medical Physics, Vol. 35, Issue 5; Other Information: DOI: 10.1118/1.2900718; (c) 2008 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-2405
- Country of Publication:
- United States
- Language:
- English
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