Preliminary study about the feasibility of developing novel analysis methods based on visible light absorption for Fricke dosimetry

P. PÉREZ; V. GALVÁN; M. VALENTE

Córdoba

Congreso; 2do Congreso de Radioquimioterapia y Braquiterapia. 5ta Jornada de Física Médica.; 2009

Fundación Marie Curie

<!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } --During the last years, modern radiotherapy technologies and treatment techniques are increasingly characterized by complex field arrangements using conformal as well as intensity modulated irradiation modalities improving significantly radiotherapy treatment quality. The development and clinical implementation of irradiation techniques allows to perform highly conformal irradiations achieving accurately complex dose distributions. However, at the same time, it is necessary to investigate and develop novel and user-friendly dosimetric methods devoted to the quality assurance (QA) procedures. A novel dosimetric system has been introduced by Gore et al. This method is mainly based on ferrous sulphate (Fricke) solution fixed to an aqueous tissue-equivalent gel matrix. The ferrous (Fe2+) ions are oxidized to ferric (Fe3+) ions under radiation exposure and the radiation yield, i.e. the produced amount of Fe3+, is proportionally related to the absorbed dose. Spin-lattice relaxation measurements have been proposed for determining the radiation-induced ferric ion yield, therefore rapidly developing Fricke gel dosimetry into a successful tool for mapping 3D dose distributions when combined with the powerful imaging modality of MRI. Fricke gel dosimeters analyzed by means of magnetic resonance enable accurate and continuous distribution determinations, however the clinical implementation of this technique presents an important drawback due to the difficults found in the access to magnetic resonance scanner facilities. On the other hand, Fricke gel dosimeters in form of spectrophotometric vials or thin layers optically analyzed have shown to be a useful method for dose distribution measurements. The analysis method consists mainly on light transmittance measurements by means of images captured with a CCD camera before and after exposure. In this context, Fricke gel dosimeters optically analyzed have shown enough capabilities and significant good performance regarding accuracy, spatial and dose resolution within a tissue-equivalent material, therefore becoming a promising tool for punctual measurements, 1D, 2D and 3D dose mapping.